JP6215804B2 - Negative electrode active material for nonaqueous electrolyte secondary battery, negative electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery, and method for producing negative electrode active material particles - Google Patents

Description

  The present invention relates to a negative electrode active material for a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery, and a method for producing negative electrode active material particles.

  In recent years, small electronic devices typified by mobile terminals have been widely used, and further downsizing, weight reduction, and long life have been strongly demanded. In response to such market demands, development of secondary batteries capable of obtaining a high energy density, in particular, being small and light is underway. This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.

  Among them, lithium ion secondary batteries are highly expected because they are small and easy to increase in capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.

  A lithium ion secondary battery includes an electrolyte solution together with a positive electrode, a negative electrode, and a separator. This negative electrode contains a negative electrode active material involved in the charge / discharge reaction.

  As a negative electrode active material, while carbon materials are widely used, further improvement in battery capacity is required due to recent market demand. As an element for improving battery capacity, the use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected. The development of a siliceous material as a negative electrode active material has been examined not only for silicon itself but also for compounds represented by alloys and oxides. The shape of the active material is studied from a standard coating type of carbon material to an integrated type directly deposited on a current collector.

  However, when silicon is used as the negative electrode active material as the main raw material, the negative electrode active material particles expand and contract during charge / discharge, and therefore, they tend to break mainly in the vicinity of the surface layer of the negative electrode active material particles. Further, an ionic material is generated inside the active material, and the negative electrode active material particles are easily broken. When the negative electrode active material surface layer is cracked, a new surface is generated and the reaction area of the active material is increased. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating film that is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.

  To date, various studies have been made on negative electrode materials and electrode configurations for lithium ion secondary batteries mainly composed of a siliceous material in order to improve battery initial efficiency and cycle characteristics.

  Specifically, for the purpose of obtaining good cycle characteristics and high safety, silicon and amorphous silicon dioxide are deposited simultaneously using a vapor phase method (see, for example, Patent Document 1). Further, in order to obtain a high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of the silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed (for example, (See Patent Document 3). Further, in order to improve the cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, see Patent Document 4).

Further, Si phase, (for example, see Patent Document 5) by using a nanocomposite containing SiO 2, _M y _O metal oxide in order to improve the initial charge and discharge efficiency. In order to improve the initial charge / discharge efficiency, a Li-containing material is added to the negative electrode, and pre-doping is performed to decompose Li and return Li to the positive electrode when the negative electrode potential is high (see, for example, Patent Document 6).

  Further, in order to improve cycle characteristics, SiOx (0.8 ≦ x ≦ 1.5, particle size range = 1 μm to 50 μm) and a carbon material are mixed and fired at a high temperature (for example, see Patent Document 7). Further, in order to improve cycle characteristics, the molar ratio of oxygen to silicon in the negative electrode active material is 0.1 to 1.2, and the molar ratio of oxygen amount to silicon amount in the vicinity of the interface between the active material and the current collector The active material is controlled in a range where the difference between the maximum value and the minimum value is 0.4 or less (see, for example, Patent Document 8). Further, in order to improve battery load characteristics, a metal oxide containing lithium is used (see, for example, Patent Document 9). In addition, in order to improve cycle characteristics, a hydrophobic layer such as a silane compound is formed on the surface of the siliceous material (see, for example, Patent Document 10).

In order to improve cycle characteristics, silicon oxide is used and conductivity is imparted by forming a graphite film on the surface layer (see, for example, Patent Document 11). In this case, in Patent Document 11, with respect to the shift value obtained from the Raman spectra for graphite coating, with broad peaks appearing at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio _I 1330 _{/ I 1580} is 1.5 <I ₁₃₃₀ / I ₁₅₈₀ <3.

  Moreover, in order to improve high battery capacity and cycle characteristics, particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 12). Further, in order to improve overcharge and overdischarge characteristics, silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 <y <2) is used (for example, see Patent Document 13). .

JP 2001-185127 A JP 2002-042806 A JP 2006-164955 A JP 2006-114454 A JP 2009-070825 A Special table 2013-513206 gazette JP 2008-282819 A JP 2008-251369 A JP 2008-177346 A JP 2007-234255 A JP 2009-212074 A JP 2009-205950 A Japanese Patent No. 2999741

  As described above, in recent years, small mobile devices represented by electronic devices have been improved in performance and functionality, and non-aqueous electrolyte secondary batteries, particularly lithium ion secondary batteries, which are the main power source, There is a need for increased battery capacity. As one method for solving this problem, development of a non-aqueous electrolyte secondary battery including a negative electrode using a siliceous material as a main material is desired. In addition, non-aqueous electrolyte secondary batteries using a siliceous material are desired to have cycle characteristics close to those of a non-aqueous electrolyte secondary battery using a carbon material.

  The present invention has been made in view of such problems, and its purpose is to increase the battery capacity, and to improve the cycle characteristics, the initial battery efficiency, and the slurry stability during the production of the negative electrode. It is to provide a negative electrode active material for a battery. Another object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery using the negative electrode active material, and a non-aqueous electrolyte secondary battery using the negative electrode. Another object of the present invention is to provide a method for producing negative electrode active material particles for a non-aqueous electrolyte secondary battery that can be used for such a negative electrode.

In order to achieve the above object, the present invention includes negative electrode active material particles, and the negative electrode active material particles include a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) containing a Li compound. A negative electrode active material for a water electrolyte secondary battery, wherein the negative electrode active material particles have a 1% dispersion having a pH at 25 ° C of 9 or less. provide.

  The negative electrode active material particles contained in such a negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention have moderate conductivity. Further, since this negative electrode active material particle partially deactivates the alkali component at the time of preparation of the aqueous slurry for preparing the negative electrode, the binder added to the aqueous slurry in which the negative electrode active material of the present invention is dispersed is used. The viscosity can be set to an appropriate value. As a result, the negative electrode made from this aqueous slurry exhibits excellent capacity retention and initial efficiency. Further, since the negative electrode active material is mainly composed of a silicon compound, the battery capacity can be increased.

  At this time, the negative electrode active material particles preferably contain an acid and a Li salt thereof.

  When the negative electrode active material particles contain an acid and a Li salt thereof, the pH in the 1% dispersion of the negative electrode active material particles can be easily adjusted to pH 9 or less.

  At this time, the acid and its Li salt preferably include a weak acid and its Li salt.

  Since the weak acid causes little damage to the active material at the time of neutralization, it exhibits a better capacity retention ratio and initial efficiency. The weak acid Li salt is formed during neutralization.

  At this time, it is preferable that the said acid and its Li salt contain the polymeric acid which has a carboxy group, and its Li salt.

  The polymer acid having a carboxy group clings to the active material at the time of neutralization, and suppresses the elution of the Li compound in the active material, so that a more excellent capacity retention rate and initial efficiency are exhibited.

  At this time, the acid and its Li salt preferably include an organic acid and its Li salt.

  Since the Li compound produced at the time of neutralization is easily compatible with water and an excellent slurry is obtained, the organic acid exhibits a more excellent capacity retention ratio and initial efficiency.

  At this time, it is preferable that the said acid and its Li salt are contained in the ratio of 2 to 25 mass% with respect to the said silicon compound.

  If the said ratio is 2 mass% or more, the effect which improves a capacity | capacitance maintenance factor and initial efficiency is fully acquired. If the said ratio is 25 mass% or less, the energy density of a negative electrode can be kept high, performing sufficient neutralization.

At this time, the silicon compound is coated with a carbon film containing carbon at least in part, the carbon coating is in the Raman spectrum analysis, have a scattering peak at 1330 cm ^-1 and 1580 cm ^-1, their It is preferable that the intensity ratio I ₁₃₃₀ / I ₁₅₈₀ satisfies 0.7 <I ₁₃₃₀ / I ₁₅₈₀ <2.0.

If the silicon compound has a carbon film, the conductivity between the negative electrode active material particles can be improved, and thus the battery characteristics can be improved. Further, as long as it has such an intensity ratio I _{1330 /} I _1580, it is possible to optimize the ratio between the carbon material having contained in the carbon film, a carbon material and a graphite structure having a diamond structure, capacity Battery characteristics such as maintenance rate and initial efficiency can be improved.

  At this time, it is preferable that the content rate of the said carbon film is 5 to 20 mass% with respect to the sum total of the said silicon compound and the said carbon film.

  If it has a carbon film in such a ratio, a high capacity | capacitance silicon compound can be included in a suitable ratio, and sufficient battery capacity can be ensured.

  At this time, it is preferable that the negative electrode active material particles include an acid and a Li salt thereof, and the acid and the Li salt are detected from the outer peripheral surface of the carbon coating.

  It is desirable that the acid and its Li salt contained in the negative electrode active material exist mainly in the vicinity of the silicon compound in the negative electrode. If it exists in a position closer to the silicon compound, the effect of improving battery characteristics is further improved.

At this time, it is preferable that the silicon compound contains at least one Li compound among Li ₂ SiO ₃ , Li ₆ Si ₂ O ₇ , and Li ₄ SiO ₄ therein.

If the negative electrode active material contains a silicon compound in which the SiO ₂ component part that is destabilized when lithium is inserted or desorbed is modified in advance to such a Li compound, the irreversible capacity generated during charging is reduced. be able to.

  Moreover, it is preferable at this time that the said negative electrode active material particle is produced by the process including an electrochemical method.

  As described above, when the silicon compound containing the Li compound is produced by a process including an electrochemical method, a stable Li compound can be obtained, and the battery characteristics can be further improved.

  At this time, the half width (2θ) of the diffraction peak due to the (111) crystal plane obtained by X-ray diffraction of the silicon compound is 1.2 ° or more, and the crystallite size due to the crystal plane Is preferably 7.5 nm or less.

  A silicon compound having such a half width and crystallite size has low crystallinity. By using a silicon compound having low crystallinity and a small amount of Si crystals, battery characteristics can be improved.

  At this time, the median diameter of the silicon compound is preferably 0.5 μm or more and 20 μm or less.

  If it is a negative electrode active material containing the silicon compound of such a median diameter, a capacity | capacitance maintenance factor can be improved.

  The present invention also provides a negative electrode for a non-aqueous electrolyte secondary battery comprising any one of the above negative electrode active materials for a non-aqueous electrolyte secondary battery and a carbon-based active material.

  With such a negative electrode for a non-aqueous electrolyte secondary battery, the initial efficiency and capacity maintenance rate can be improved while increasing the capacity of the negative electrode.

  At this time, the ratio of the silicon compound to the total amount of the carbon-based active material and the silicon compound is preferably 5% by mass or more.

  With such a negative electrode, the volume energy density of the battery can be improved.

  The present invention also provides a nonaqueous electrolyte secondary battery using any one of the above negative electrodes for nonaqueous electrolyte secondary batteries.

  The non-aqueous electrolyte secondary battery using the negative electrode of the present invention has a high capacity and good cycle characteristics and initial efficiency.

The present invention also relates to a method for producing negative electrode active material particles contained in a negative electrode material for a non-aqueous electrolyte secondary battery, wherein a silicon compound represented by SiO _x (0.5 ≦ x ≦ 1.6) is produced. A step of modifying the silicon compound by inserting Li into the silicon compound to form a Li compound on the surface or inside of the silicon compound or both, and a silicon compound after the modification. There is provided a method for producing negative electrode active material particles, wherein the negative electrode active material particles are produced by a treatment with an acid, and a step of controlling the pH of a 1% dispersion at 25 ° C. to 9 or less.

  Included in the negative electrode active material for non-aqueous electrolyte secondary battery of the present invention, which can increase the battery capacity and improve the cycle characteristics and the initial efficiency of the battery by the method for producing negative electrode active material particles having such steps. The negative electrode active material particles to be obtained can be obtained stably.

  The step of modifying the silicon compound is preferably performed by an electrochemical method.

  If an electrochemical method is used for the modification of the silicon compound, a more stable Li compound can be obtained, and the battery characteristics can be further improved.

  In the negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention, the negative electrode active material particles have moderate conductivity. Furthermore, since the alkali component at the time of preparation of the aqueous slurry for preparing the negative electrode is partially deactivated, the binder added to the aqueous slurry in which the negative electrode active material for the non-aqueous electrolyte secondary battery of the present invention is dispersed The viscosity can be set to an appropriate value. Therefore, the negative electrode produced from this aqueous slurry exhibits an excellent capacity retention rate and initial efficiency. Furthermore, since the negative electrode active material is mainly composed of a silicon compound, the battery capacity can be increased. Moreover, the same characteristic can be acquired also in the negative electrode using the negative electrode active material for nonaqueous electrolyte secondary batteries of this invention, and the secondary battery using the negative electrode. Moreover, the same effect can be acquired also in the electronic device, electric tool, electric vehicle, electric power storage system, etc. which used the secondary battery of this invention.

  Moreover, said negative electrode active material particle can be stably obtained by the manufacturing method of the negative electrode active material particle of this invention.

It is sectional drawing showing an example of a structure of the negative electrode for nonaqueous electrolyte secondary batteries of this invention. It is a simplified diagram of the bulk reformer used when manufacturing the silicon compound contained in the negative electrode for nonaqueous electrolyte secondary batteries of the present invention. It is an exploded view showing an example of the structure of the secondary battery (laminate film type) using the negative electrode for nonaqueous electrolyte secondary batteries of this invention.

  Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.

  As described above, as one method for increasing the battery capacity of a non-aqueous electrolyte secondary battery, it has been studied to use a negative electrode using a siliceous material as a main material as a negative electrode of a non-aqueous electrolyte secondary battery.

  The non-aqueous electrolyte secondary battery using this siliceous material is expected to have cycle characteristics similar to those of the non-aqueous electrolyte secondary battery using the carbon material, but the non-aqueous electrolyte secondary battery using the carbon material and A negative electrode material exhibiting equivalent cycle stability has not been proposed. In particular, the silicon compound containing oxygen has a lower initial efficiency than the carbon material, so that the battery capacity has been limited to that extent.

  Thus, the inventors have conducted extensive studies on a negative electrode active material that can provide good cycle characteristics and initial efficiency when used in a negative electrode of a nonaqueous electrolyte secondary battery, and have reached the present invention.

The negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention has negative electrode active material particles, and the negative electrode active material particles include a silicon compound containing a Li compound (SiO _x : 0.5 ≦ x ≦ 1.6). Have Furthermore, the negative electrode active material particles have a 1% dispersion having a pH of 9 or less at 25 ° C. The negative electrode active material particles contained in the active material of the present invention have moderate conductivity and partially deactivate the alkali component in the aqueous slurry for producing the negative electrode. Therefore, the viscosity of the binder added to the aqueous slurry in which the negative electrode active material of the present invention is dispersed can be set to an appropriate value, and the negative electrode made from this aqueous slurry exhibits an excellent capacity maintenance ratio and initial efficiency. It becomes. Further, since the negative electrode active material is mainly composed of a silicon compound, the battery capacity can be increased.

<1. Negative electrode for non-aqueous electrolyte secondary battery>
The negative electrode for nonaqueous electrolyte secondary batteries using the negative electrode active material for nonaqueous electrolyte secondary batteries of the present invention will be described. FIG. 1 shows a cross-sectional configuration of a negative electrode for a nonaqueous electrolyte secondary battery (hereinafter sometimes simply referred to as “negative electrode”) according to an embodiment of the present invention.

[Configuration of negative electrode]
As shown in FIG. 1, the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. The negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. Furthermore, the negative electrode current collector 11 may be omitted as long as the negative electrode active material of the present invention is used.

[Negative electrode current collector]
The negative electrode current collector 11 is an excellent conductive material and is made of a material that is excellent in mechanical strength. Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).

  The negative electrode current collector 11 preferably contains carbon (C) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved. In particular, in the case of having an active material layer that expands during charging, if the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector. Although content of said content element is not specifically limited, Especially, it is preferable that it is 100 ppm or less. This is because a higher deformation suppressing effect can be obtained.

  The surface of the negative electrode current collector 11 may be roughened or not roughened. The roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching. The non-roughened negative electrode current collector is, for example, a rolled metal foil.

[Negative electrode active material layer]
The negative electrode active material layer 12 includes a plurality of negative electrode active material particles capable of occluding and releasing lithium ions, and may further include other materials such as a negative electrode binder and a conductive additive in terms of battery design. . The negative electrode active material for a nonaqueous electrolyte secondary battery of the present invention is a material constituting the negative electrode active material layer 12.

As described above, the negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention includes negative electrode active material particles having a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) containing a Li compound. Furthermore, the negative electrode active material particles of the negative electrode active material of the present invention have a pH of 9 or less at 25 ° C. of a 1% dispersion. In the present invention, the pH of the 1% dispersion of negative electrode active material particles at 25 ° C. is preferably 3 or more and 9 or less, and more preferably 8 or more and 9 or less. When the pH is higher than 9, the viscosity of the binder contained in the slurry for producing the negative electrode is deviated from an appropriate value, the coating property of the slurry is deteriorated, and the cycle characteristics of the negative electrode using this slurry are deteriorated. Moreover, if pH is 3 or more, since the detachment | desorption of Li content in a silicon compound can be suppressed, initial efficiency can be improved.

  As described above, the negative electrode active material particles in the present invention contain a silicon compound that can occlude and release lithium ions. The Li compound contained in the silicon compound may be contained on the surface, inside, or both of the silicon compound.

The negative electrode active material particles of the negative electrode active material of the present invention have a silicon oxide material containing a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6), and x is 1 as the composition of the silicon compound. It is preferable to be close to. This is because high cycle characteristics can be obtained. The siliceous material composition in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements.

The silicon compound containing the Li compound contained in the negative electrode active material particles of the present invention can be obtained by selectively changing a part of the SiO ₂ component generated inside the silicon compound to the Li compound. Such a selective compound preparation method, that is, modification of the silicon compound is preferably performed by an electrochemical method.

  It is possible to reduce or avoid the formation of Li compounds in the Si region by producing negative electrode active material particles using an electrochemical modification (in-bulk modification) method. In the atmosphere or an aqueous slurry Medium, stable material in solvent slurry. Further, by performing modification by an electrochemical method, it is possible to produce a more stable material than thermal modification (thermal dope method) in which compounds are randomly formed.

In the present invention, silicon compounds, of _{Li 2 SiO 3, Li 6 Si} 2 O 7, Li 4 SiO 4 therein, it is preferable that at least one or more of Li compounds. The presence of at least one of Li ₄ SiO ₄ , Li ₆ Si ₂ O ₇ , and Li ₂ SiO ₃ generated in the bulk of the silicon compound improves the characteristics. However, two or more kinds of characteristics are improved more. Coexistence state.

In the present invention, it is preferable that at least one Li compound of LiF, Li ₂ CO ₃ , Li ₂ O, and LiOH exists on the surface of the silicon compound.

These selective compounds can be produced by changing the conditions by regulating the potential or current of the lithium counter electrode in an electrochemical manner. Li compounds can be quantified by NMR (nuclear magnetic resonance) and XPS (X-ray photoelectron spectroscopy). The XPS and NMR measurements can be performed, for example, under the following conditions.
XPS
・ Device: X-ray photoelectron spectrometer,
・ X-ray source: Monochromatic Al Kα ray,
・ X-ray spot diameter: 100 μm,
Ar ion gun sputtering conditions: 0.5 kV 2 mm × 2 mm.
²⁹ Si MAS NMR (magic angle rotating nuclear magnetic resonance)
Apparatus: 700 NMR spectrometer manufactured by Bruker,
Probe: 4 mm HR-MAS rotor 50 μL,
Sample rotation speed: 10 kHz,
-Measurement environment temperature: 25 ° C.

  In the present invention, the negative electrode active material particles preferably include an acid and a Li salt thereof. In the aqueous slurry for producing the negative electrode, the alkali component can be partially deactivated by the acid contained in the negative electrode active material. Therefore, the viscosity of the binder added to the aqueous slurry in which the negative electrode active material of the present invention is dispersed can be set to an appropriate value. The Li salt of an acid may be referred to as an acid Li conjugate salt.

  The acid and its Li salt preferably include a weak acid and its Li salt. This is because the weak acid causes less damage to the active material during neutralization when neutralizing the alkali component. The weak acid here refers to an acid that does not partially dissociate in an aqueous solution, and has a pKa in water of pKa> 0. Specifically, phosphoric acid, acetic acid, polyacrylic acid and the like. The strong acid is an acid that dissociates substantially completely in an aqueous solution to give hydrogen ions, and specifically, hydrochloric acid or the like.

  Furthermore, it is preferable that an acid and its Li salt contain an organic acid and its Li salt. This is because the Li compound produced at the time of neutralization is easily adapted to water and a good slurry is obtained.

  Further, the acid and its Li salt preferably include a polymer acid having a carboxy group and its Li salt. This is because the polymer acid clings to the active material during neutralization, and elution of the Li compound in the negative electrode active material can be suppressed.

  In the present invention, by including an acid and a Li salt thereof in a silicon compound containing a Li compound on the surface or inside or both as described above, the alkaline component is partially deactivated when creating an aqueous slurry. When used as a negative electrode, it exhibits excellent capacity retention and initial efficiency.

  When the negative electrode active material particles include an acid and a Li salt thereof, the acid and the Li salt are preferably included in a proportion of 2% by mass to 25% by mass with respect to the silicon compound. If this ratio is 2% by mass or more, the effect of improving the capacity retention rate and the initial efficiency is sufficiently obtained. If the said ratio is 25 mass% or less, the energy density of a negative electrode can be kept high, performing sufficient neutralization.

  Examples of the method of adding an acid to the negative electrode active material particles include a method in which a silicon compound is dispersed in a protic solvent such as water or ethanol, and an acid or an aqueous solution thereof is added thereto, or a powder of a silicon compound and an acid. Or the method of mixing a liquid physically etc. are mentioned.

Moreover, it is preferable that a silicon compound has a carbon film formed at least partially. In particular, the carbon coating is in the Raman spectrum analysis, have a scattering peak at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio _I 1330 _{/ I 1580} is _{0.7 <I 1330 / I 1580 <} 2.0 It is preferable to satisfy. If the silicon compound has a carbon film, the conductivity between the negative electrode active material particles can be improved, and thus the battery characteristics can be improved. If the carbon film has an intensity ratio of I ₁₃₃₀ / I ₁₅₈₀ , the ratio of the carbon material having a diamond structure and the carbon material having a graphite structure contained in the carbon film can be optimized, and the capacity retention rate And battery characteristics such as initial efficiency can be improved.

  Examples of the method for forming the carbon film include a method of coating a silicon compound with a carbon material (carbon compound) such as graphite.

  Furthermore, it is preferable that the content rate of a carbon film is 5 mass% or more and 20 mass% or less with respect to the sum total of a silicon compound and the said carbon film.

  Thus, if content rate is 5 mass% or more, it is possible to improve electrical conductivity reliably. Moreover, if a content rate is 20 mass% or less, battery characteristics will improve and battery capacity will become large. Although the coating method of these carbon compounds is not particularly limited, a sugar carbonization method and a thermal decomposition method of hydrocarbon gas are preferable. This is because these methods can improve the coverage of the carbon film on the surface of the silicon compound.

Here, the details of the Raman spectrum analysis are shown below. The ratio of the carbon material having a diamond structure (carbon film or carbon-based material) and the carbon material having a graphite structure can be obtained from a Raman spectrum obtained by microscopic Raman analysis (that is, Raman spectrum analysis). That is, diamond shows a sharp peak with a Raman shift of 1330 cm ⁻¹ and graphite with a Raman shift of 1580 cm ⁻¹ , and the ratio of the carbon material having a diamond structure and the carbon material having a graphite structure is simply obtained from the intensity ratio. Can do.

  Diamond has high strength, high density, and high insulation, and graphite has excellent electrical conductivity. Therefore, a silicon compound having a carbon material satisfying the above strength ratio on the surface is optimized for each of the above characteristics, and as a result, it is possible to prevent electrode breakdown due to expansion / contraction of the electrode material during charge / discharge, and a conductive network The negative electrode active material having

  In the present invention, it is desirable that the acid and its Li salt contained in the negative electrode active material are present around the silicon compound in the negative electrode. In particular, when the silicon compound has a carbon coating as described above, the acid and its Li salt are preferably detected from the outer peripheral surface of the carbon coating. If it exists in a position closer to the silicon compound, the effect of improving battery characteristics is further improved.

  The detection method of the location of the acid and its Li salt includes SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy), TOF-SIMS (time-of-flight secondary ion mass spectrometry), micro Raman / IR Measurement and so on.

  In the present invention, the lower the crystallinity of the silicon compound, the better. Specifically, the half width (2θ) of the diffraction peak attributed to the (111) crystal plane obtained by X-ray diffraction of the silicon compound is 1.2 ° or more, and the crystallite size attributed to the crystal plane is It is desirable that it is 7.5 nm or less. The presence of a silicon compound having low crystallinity can improve battery characteristics. In addition, a stable Li compound can be generated inside or on the surface of the silicon compound or both.

  The median diameter of the silicon compound is not particularly limited, but is preferably 0.5 μm or more and 20 μm or less. This is because, within this range, lithium ions are easily occluded and released during charging and discharging, and the particles are difficult to break. If the median diameter is 0.5 μm or more, the surface area does not increase, so that the battery irreversible capacity can be reduced. On the other hand, if the median diameter is 20 μm or less, it is preferable because the particles are difficult to break and a new surface is difficult to appear. In addition, the temperature of the measurement environment in the median diameter measurement is 25 ° C.

  The negative electrode active material layer may contain a negative electrode conductive additive in addition to the negative electrode active material. Examples of the negative electrode conductive assistant include one or more of graphite such as carbon black, acetylene black, and scaly graphite, ketjen black, carbon nanotube, and carbon nanofiber. These conductive assistants are preferably in the form of particles having a median diameter smaller than that of the silicon compound.

  In the present invention, the negative electrode active material layer 12 as shown in FIG. 1 may further contain a carbon material (carbon-based active material) in addition to the negative electrode active material of the present invention. As a result, the electrical resistance of the negative electrode active material layer 12 can be reduced, and the expansion stress associated with charging can be reduced. Examples of the carbon-based active material include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, and carbon blacks.

  In this case, the negative electrode of the present invention preferably has a silicon compound ratio of 5% by mass or more based on the total amount of the carbon-based active material and the silicon compound. With such a negative electrode for a non-aqueous electrolyte secondary battery, the initial efficiency and capacity retention rate do not decrease. Moreover, it is preferable that the upper limit of this content is less than 90 mass%.

  The negative electrode active material layer 12 is formed by, for example, a coating method. The coating method is a method in which a negative electrode active material particle and the above-described binder, and the like, and a conductive additive and a carbon material are mixed as necessary, and then dispersed and coated in an organic solvent or water.

[Production method of negative electrode]
A method for producing the negative electrode of the present invention will be described. First, the manufacturing method of the negative electrode active material particle contained in the negative electrode material used for a negative electrode is demonstrated. First, a silicon compound represented by SiO _x (0.5 ≦ x ≦ 1.6) is produced. Next, by inserting Li into the silicon compound, the Li compound is generated on the surface or inside of the silicon compound or both, thereby modifying the silicon compound. Thereafter, by treating the silicon compound with an acid, negative electrode active material particles in which the pH at 25 ° C. of the 1% dispersion is controlled to 9 or less are obtained. Thus, after manufacturing negative electrode active material particle, negative electrode active material particle is mixed with a conductive support agent, a binder, and a solvent, and a slurry is obtained. Next, the slurry is applied to the surface of the negative electrode current collector and dried to form a negative electrode active material layer.

  More specifically, the negative electrode is manufactured, for example, by the following procedure.

  First, a raw material that generates silicon oxide gas is heated in a temperature range of 900 ° C. to 1600 ° C. in the presence of an inert gas or under reduced pressure to generate silicon oxide gas. In this case, the raw material is a mixture of metal silicon powder and silicon dioxide powder, and considering the surface oxygen of the metal silicon powder and the presence of trace amounts of oxygen in the reactor, the mixing molar ratio is 0.8 <metal silicon powder / It is desirable that the silicon dioxide powder is in the range of <1.3. The Si crystallites in the particles are controlled by changing the preparation range and vaporization temperature, and by heat treatment after generation. The generated gas is deposited on the adsorption plate. The deposit is taken out with the temperature in the reactor lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like.

  Next, a carbon film can be formed on the surface layer of the obtained powder material, but this step is not essential.

  Pyrolysis CVD is desirable as a method for generating a carbon film on the surface layer of the obtained powder material. Thermal decomposition CVD fills the silicon oxide powder set in the furnace and the hydrocarbon gas into the furnace to raise the temperature in the furnace. The decomposition temperature is not particularly limited, but is particularly preferably 1200 ° C. or lower, and more preferably 950 ° C. or lower. This is because it is possible to suppress disproportionation of the active material particles.

When producing a carbon film by pyrolytic CVD, for example, by adjusting the pressure and temperature in the furnace, a carbon film satisfying a desired peak intensity ratio I ₁₃₃₀ / I ₁₅₈₀ in the Raman spectrum is formed on the surface layer of the powder material. be able to.

The hydrocarbon gas used in the thermal decomposition CVD is not particularly limited, but 3 ≧ n is desirable in the C _n H _m composition. This is because the manufacturing cost can be lowered and the physical properties of the decomposition product are good.

  Next, modification in the bulk of the powder material is performed. It is desirable that in-bulk modification can electrochemically insert and desorb Li. Although the apparatus structure is not particularly limited, for example, the bulk reforming can be performed using the bulk reforming apparatus 20 shown in FIG. The in-bulk reformer 20 includes a bathtub 27 filled with an organic solvent 23, a positive electrode (lithium source, reforming source) 21 disposed in the bathtub 27 and connected to one of the power sources 26, And a separator 24 provided between the positive electrode 21 and the powder storage container 25. The powder storage container 25 is connected to the other side of the power source 26. The powder storage container 25 stores silicon oxide powder 22. At this time, smooth modification can be obtained by adhering the carbon particles to the silicon oxide powder 22 via polyacrylic acid.

  As described above, the obtained modified particles may not contain a carbon coating. However, when more uniform control is required in the reforming process in the bulk, it is necessary to reduce the potential distribution and the like, and it is desirable that a carbon coating exists.

As the organic solvent 23 in the bathtub 27, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, or the like can be used. As the electrolyte salt contained in the organic solvent 23, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), or the like can be used.

  The positive electrode 21 may use a Li foil or a Li-containing compound. Examples of the Li-containing compound include lithium carbonate, lithium oxide, lithium cobaltate, lithium olivine, lithium nickelate, and lithium vanadium phosphate.

  As a method for treating the modified silicon compound with an acid, for example, a method in which the silicon compound is dispersed in a protic solvent such as water or ethanol and an acid or an aqueous solution thereof is added thereto, or the silicon compound and the acid are added. And a method of physically mixing the powder or liquid.

  Moreover, when adding the carbonaceous material whose median diameter is smaller than a silicon compound as a conductive support agent, acetylene black can be selected and added, for example.

  Moreover, if the negative electrode current collector contains 90 ppm or less of carbon and sulfur, higher battery characteristics can be improved.

<2. Lithium ion secondary battery>
Next, a lithium ion secondary battery using the above-described negative electrode for a lithium ion secondary battery will be described.

[Configuration of laminated film type secondary battery]
A laminated film type secondary battery 30 shown in FIG. 3 is one in which a wound electrode body 31 is accommodated mainly in a sheet-like exterior member 35. This wound body has a separator between a positive electrode and a negative electrode and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated. In both electrode bodies, the positive electrode lead 32 is attached to the positive electrode, and the negative electrode lead 33 is attached to the negative electrode. The outermost peripheral part of the electrode body is protected by a protective tape.

  The positive and negative electrode leads are led out in one direction from the inside of the exterior member 35 to the outside, for example. The positive electrode lead 32 is formed of a conductive material such as aluminum, and the negative electrode lead 33 is formed of a conductive material such as nickel or copper.

  The exterior member 35 is a laminate film in which, for example, a fusion layer, a metal layer, and a surface protective layer are laminated in this order. The laminate film is formed by fusing two films so that the fusion layer faces the electrode body 31. The outer peripheral edge portions in the adhesion layer are bonded together with an adhesive or the like. The fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like. The protective layer is, for example, nylon.

  An adhesion film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent intrusion of outside air. This material is, for example, polyethylene, polypropylene, or polyolefin resin.

[Positive electrode]
The positive electrode has, for example, a positive electrode active material layer on both sides or one side of the positive electrode current collector, similarly to the negative electrode 10 of FIG.

  The positive electrode current collector is formed of, for example, a conductive material such as aluminum.

  The positive electrode active material layer includes one or more positive electrode materials capable of occluding and releasing lithium ions, and includes other materials such as a binder, a conductive additive, and a dispersant depending on the design. You can leave. In this case, details regarding the binder and the conductive additive are the same as, for example, the negative electrode binder and the negative electrode conductive additive already described.

As the positive electrode material, a lithium-containing compound is desirable. Examples of the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element. Among these described positive electrode materials, compounds having at least one of nickel, iron, manganese, and cobalt are preferable. These chemical formulas are represented by, for example, Li _x M ₁ O ₂ or Li _y M ₂ PO ₄ . In the formula, M ₁ and M ₂ represent at least one transition metal element. The values of x and y vary depending on the battery charge / discharge state, but are generally expressed as 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and phosphoric acid having lithium and a transition metal element. Examples of the compound include a lithium iron phosphate compound (LiFePO ₄ ) and a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (0 <u <1)). This is because, when these positive electrode materials are used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.

[Negative electrode]
The negative electrode has the same configuration as the above-described negative electrode 10 for a lithium ion secondary battery in FIG. 1. For example, the negative electrode has negative electrode active material layers 12 on both surfaces of the current collector 11. The negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. This is because the deposition of lithium metal on the negative electrode can be suppressed.

  The positive electrode active material layer is provided on part of both surfaces of the positive electrode current collector, and the negative electrode active material layer is also provided on part of both surfaces of the negative electrode current collector. In this case, for example, the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is for a stable battery design.

  In the non-opposing region, that is, the region where the negative electrode active material layer and the positive electrode active material layer do not face each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation. This makes it possible to accurately examine the composition with good reproducibility without depending on the presence or absence of charge / discharge, such as the composition of the negative electrode active material.

[Separator]
The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing a short circuit due to contact between the two electrodes. This separator is formed of, for example, a porous film made of synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated. Examples of the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.

[Electrolyte]
At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution). This electrolytic solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.

  For example, a non-aqueous solvent can be used as the solvent. Examples of the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran.

  Among these, it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. This is because better characteristics can be obtained. In this case, more advantageous characteristics can be obtained by combining a high viscosity solvent such as ethylene carbonate or propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.

  The solvent additive preferably contains an unsaturated carbon bond cyclic carbonate. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed. Examples of the unsaturated carbon bond cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.

  The solvent additive preferably contains sultone (cyclic sulfonic acid ester). This is because the chemical stability of the battery is improved. Examples of sultone include propane sultone and propene sultone.

  Furthermore, it is preferable that the solvent contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved. Examples of the acid anhydride include propanedisulfonic acid anhydride.

The electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts. Examples of the lithium salt include the following materials. Examples thereof include lithium hexafluorophosphate (LiPF ₆ ) and lithium tetrafluoroborate (LiBF ₄ ).

  The content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent. This is because high ionic conductivity is obtained.

[Production method of laminated film type secondary battery]
First, a positive electrode is manufactured using the positive electrode material described above. First, a positive electrode active material and, if necessary, a binder, a conductive additive and the like are mixed to form a positive electrode mixture, and then dispersed in an organic solvent to form a positive electrode mixture slurry. Subsequently, the mixture slurry is applied to the positive electrode current collector with a coating apparatus such as a die coater having a knife roll or a die head, and dried with hot air to obtain a positive electrode active material layer. Finally, the positive electrode active material layer is compression molded with a roll press or the like. At this time, heating may be performed. Further, compression and heating may be repeated a plurality of times.

  Next, a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector, using the same operation procedure as the production of the negative electrode 10 for a lithium ion secondary battery described above.

  The positive electrode and the negative electrode are manufactured by the same manufacturing procedure as described above. In this case, each active material layer can be formed on both surfaces of the positive electrode and the negative electrode current collector. At this time, the active material application length of both surface portions may be shifted in either electrode (see FIG. 1).

  Subsequently, the electrolytic solution is adjusted. Subsequently, the positive electrode lead 32 is attached to the positive electrode current collector and the negative electrode lead 33 is attached to the negative electrode current collector by ultrasonic welding or the like. Then, a positive electrode and a negative electrode are laminated | stacked or wound through a separator, a wound electrode body is created, and a protective tape is adhere | attached on the outermost periphery part. Next, the wound body is molded so as to have a flat shape. Subsequently, after sandwiching the wound electrode body between the folded film-shaped exterior member 35, the insulating portions of the exterior member are bonded to each other by a thermal fusion method, and the wound electrode body is released in only one direction. Enclose. The adhesion film 34 is inserted between the positive electrode lead 32 and the negative electrode lead 33 and the exterior member 35. A predetermined amount of the adjusted electrolytic solution is introduced from the release portion, and vacuum impregnation is performed. After impregnation, the release part is bonded by a vacuum heat fusion method.

  The laminated film type secondary battery 30 can be manufactured as described above.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.

(Example 1-1)
The laminate film type secondary battery 30 shown in FIG. 3 was produced by the following procedure.

First, a positive electrode was produced. The positive electrode active material is a mixture of 95 parts by mass of LiCoO ₂ which is a lithium cobalt composite oxide, 2.5 parts by mass of a positive electrode conductive additive, and 2.5 parts by mass of a positive electrode binder (polyvinylidene fluoride: Pvdf). A positive electrode mixture was obtained. Subsequently, the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste slurry. Subsequently, the slurry was applied to both surfaces of the positive electrode current collector with a coating apparatus having a die head, and dried with a hot air drying apparatus. At this time, the positive electrode current collector had a thickness of 15 μm. Finally, compression molding was performed with a roll press.

Next, a negative electrode was prepared. In order to produce a negative electrode active material, first, a raw material (also referred to as a vaporization starting material) mixed with metallic silicon and silicon dioxide is placed in a reaction furnace, deposited in a vacuum of 10 Pa, sufficiently cooled, and then the deposit is taken out and ball milled Crushed with. After adjusting the particle diameter, pyrolytic CVD was performed to obtain a carbon coating. The prepared powder was subjected to bulk modification using an electrochemical method in a 1: 1 mixed solvent of propylene carbonate and ethylene carbonate (containing 1.3 mol / kg of lithium hexafluorophosphate: LiPF ₆ ). Subsequently, the modified silicon compound was immersed in a polyacrylic acid slurry and acid-treated. Next, the acid-treated silicon compound was dried under reduced pressure.

The silicon compound after acid treatment and drying contained Li ₄ SiO ₄ and Li ₂ SiO ₃ inside, and lithium carbonate (Li ₂ CO ₃ ) was contained in the surface layer thereof. The value _x of the silicon compound SiO _x was 0.5, and the median diameter D ₅₀ of the silicon compound was 5 μm. The silicon compound has a half-value width (2θ) of a diffraction peak due to the (111) crystal plane obtained by X-ray diffraction of 1.85 °, and the crystallite size due to the crystal plane (111) is 4 .62 nm. Moreover, the content rate of the carbon film was 5 mass% with respect to the sum total of a silicon compound and a carbon film, the film thickness of the carbon film was 100 nm, and the coverage of the silicon film surface of the carbon film was 80%. The pH at 25 ° C. of a 1% dispersion of negative electrode active material particles having a silicon compound coated with a carbon coating was 8.5. The acid and its Li salt contained in the negative electrode active material particles were polyacrylic acid containing a Li conjugate salt, and the concentration thereof was contained at a ratio of 10% by mass with respect to the silicon compound.

  A 1% dispersion of negative electrode active material particles used for pH measurement was prepared by mixing a part of silicon compound powder after acid treatment with polyacrylic acid and drying into purified water and shaking for 2 minutes. did. And after preparation, after leaving still for 10 minutes, pH measurement was performed. The pH measuring device was F-71 manufactured by Horiba, Ltd., and calibration was performed with a standard solution before pH measurement.

  Subsequently, negative electrode active material particles (powder of silicon compound after acid treatment with polyacrylic acid and dried), negative electrode binder 1 (polyacrylic acid (hereinafter also referred to as PAA)), negative electrode binder 2 ( Sodium salt of carboxymethyl cellulose (hereinafter also referred to as CMC-Na), negative electrode binder 3 (styrene butadiene rubber (hereinafter also referred to as SBR)), conductive auxiliary agent 1 (scalar graphite), conductive auxiliary agent 2 (acetylene) Black) and conductive additive 3 (carbon nanotubes) at a dry mass ratio of 91: 1: 2.5: 2.5: 1: 0.5: 1.5, and then diluted with water to form a paste Negative electrode mixture slurry. Water was used as a solvent for polyacrylic acid used as the negative electrode binder. Subsequently, the negative electrode mixture slurry was applied to both surfaces of the negative electrode current collector with a coating apparatus and then dried. As this negative electrode current collector, an electrolytic copper foil (thickness = 15 μm) was used. Finally, it was baked at 90 ° C. for 1 hour in a vacuum atmosphere. Thereby, a negative electrode active material layer is formed.

Next, after mixing a solvent (4-fluoro-1,3-dioxolan-2-one (FEC), ethylene carbonate (EC) and dimethyl carbonate (DMC)), an electrolyte salt (lithium hexafluorophosphate: LiPF) ₆ ) was dissolved to prepare an electrolytic solution. In this case, the composition of the solvent was FEC: EC: DMC = 10: 20: 70 by volume ratio, and the content of the electrolyte salt was 1.0 mol / kg with respect to the solvent.

  Next, a secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to the negative electrode current collector. Subsequently, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order and wound in the longitudinal direction to obtain a wound electrode body. The end portion was fixed with a PET protective tape. As the separator, a laminated film of 12 μm sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used. Subsequently, after sandwiching the electrode body between the exterior members, the outer peripheral edges except for one side were heat-sealed, and the electrode body was housed inside. As the exterior member, a nylon film, an aluminum foil, and an aluminum laminate film in which a polypropylene film was laminated were used. Subsequently, the prepared electrolyte was injected from the opening, impregnated in a vacuum atmosphere, and then heat-sealed and sealed.

(Examples 1-2 to 1-5, Comparative Example 1-1, Comparative Example 1-2)
A secondary battery was manufactured in the same manner as Example 1-1 except that the amount of oxygen in the bulk of the silicon compound was adjusted. In this case, the amount of oxygen was adjusted by changing the ratio and temperature of the vaporized starting material. The values of x of the silicon compounds represented by SiO _x in Examples 1-1 to 1-5 and Comparative Examples 1-1 and 1-2 are shown in Table 1.

  When the cycle characteristics (maintenance rate%) and the initial charge / discharge characteristics (initial efficiency%) of the secondary batteries of Examples 1-1 to 1-5 and Comparative Examples 1-1 and 1-2 were examined, Table 1 shows The results shown are obtained.

The cycle characteristics were examined as follows. First, in order to stabilize the battery, charge / discharge was performed for 2 cycles in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 100, and the discharge capacity was measured each time. Finally, the discharge capacity at the 100th cycle was divided by the discharge capacity at the 2nd cycle and multiplied by 100 for% display, and the capacity maintenance rate (hereinafter, sometimes simply referred to as the maintenance rate) was calculated. As cycling conditions, a constant current density until reaching 4.3V, and charged at 2.5 mA / cm ^2, current density 4.3V constant voltage at the stage of reaching the voltage of 4.3V is to 0.25 mA / cm ² Charged until it reached. During discharging, discharging was performed at a constant current density of ^2.5 mA / cm ² until the voltage reached 3.0V.

When examining the initial charge / discharge characteristics, the initial efficiency (hereinafter sometimes referred to as initial efficiency) was calculated. The initial efficiency was calculated from an equation represented by initial efficiency (%) = (initial discharge capacity / initial charge capacity) × 100. The ambient temperature was the same as when the cycle characteristics were examined. The charge / discharge conditions were 0.2 times the cycle characteristics. That is, a constant current density until reaching 4.3V, and charged at 0.5 mA / cm ^2, at 4.3V constant voltage at the stage where the voltage reaches 4.3V until the current density reached 0.05 mA / cm ² The battery was charged and discharged at a constant current density of 0.5 mA / cm ² until the voltage reached 3.0V.

  The maintenance rates and initial efficiency shown in Tables 1 to 7 below do not contain a carbon-based active material such as natural graphite (for example, an average particle size of 20 μm), and only a silicon compound having a carbon coating was used as the negative electrode active material. The maintenance rate and initial efficiency in the case, that is, the maintenance rate and initial efficiency of the silicon-based compound are shown. As a result, the maintenance rate depends only on the change in the silicon-based compound (oxygen content, the included Li compound, the included acid and its Li salt, pH, crystallinity, median diameter change) or the change in the carbon film content. The change in the initial efficiency could be measured.

  As shown in Table 1, in the silicon compound represented by SiOx, when the value of x was outside the range of 0.5 ≦ x ≦ 1.6, the battery characteristics deteriorated. For example, as shown in Comparative Example 1-1, when there is not enough oxygen (x = 0.3), the initial efficiency is improved, but the capacity retention rate is significantly deteriorated. On the other hand, as shown in Comparative Example 1-2, when the amount of oxygen was large (x = 1.8), the conductivity decreased, and both the maintenance rate and the initial efficiency decreased.

(Example 2-1 to Example 2-6, Comparative Example 2-1)
A secondary battery was manufactured basically in the same manner as in Example 1-3. However, in the silicon compound represented by SiOx, the condition of Li doping treatment (in-bulk modification), that is, the treatment method of Li doping was changed. And the contained Li compound species were changed. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Example 2-1 to Example 2-6 and Comparative Example 2-1 were examined, the results shown in Table 2 were obtained.

As shown in Table 2, the silicon compound containing the Li compounds of Examples 2-1 to 2-6 has a better capacity retention ratio and the initial efficiency than the silicon compound not containing the Li compound of Comparative Example 2-1. Have In addition, it is desirable to include Li ₂ CO ₃ , Li ₂ SiO ₃ , Li ₄ SiO _{4 and the} like as the Li compound. Inclusion of more types of these Li compounds improves cycle characteristics and capacity retention. Therefore it is desirable.

(Example 3-1 to Example 3-5, Comparative Example 3-1, Comparative Example 3-2)
A secondary battery was manufactured in the same manner as in Example 1-3 except that the acid and Li salt contained in the silicon compound were changed as shown in Table 3. The acid and Li salt contained in the silicon compound were changed by changing the acid component that acts on the silicon compound. In Comparative Example 3-1, acid treatment of the silicon compound was not performed, and the acid and its Li salt were not included in the silicon compound. When the cycle characteristics and initial charge / discharge characteristics of the secondary batteries of Example 3-1 to Example 3-5, Comparative Example 3-1, and Comparative Example 3-2 were examined, the results shown in Table 3 were obtained. .

  As can be seen from Table 3, in Comparative Example 2-1, in which the silicon compound does not contain a Li compound, the silicon compound is a Li compound even if the 1% dispersion of negative electrode active material particles has a pH of 9 or less at 25 ° C. The battery characteristics will be worse than those containing. Moreover, in Comparative Example 3-1, in which the pH is greater than 9, the capacity retention rate deteriorated. When the acid contained in the silicon compound and its Li conjugate salt are changed, it is preferable to add an acid compared to the acid-free one, and the capacity retention rate in the order of weak acid, organic acid, and polymer acid having a carboxy group. And the amount of increase in the initial efficiency increased. This can prevent the active material from being altered by treatment with a weak acid, and the use of an organic acid further improves the familiarity with the aqueous slurry, and the use of a polymer acid having a carboxy group improves the surface of the silicon compound. This is because a protective action can be provided.

(Example 4-1 to Example 4-8)
A secondary battery was manufactured in the same manner as in Example 1-3 except that the crystallinity of the silicon compound was changed. The change in crystallinity can be controlled by heat treatment in a non-atmospheric atmosphere after Li insertion and desorption. Table 4 shows the half widths of the silicon-based active materials of Examples 4-1 to 4-8. In Example 4-8, the half-value width is calculated to be 20.221 °, but this is a result of fitting using analysis software, and a peak is not substantially obtained. Therefore, it can be said that the silicon-based active material of Example 4-8 is substantially amorphous. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Example 4-1 to Example 4-8 were examined, the results shown in Table 4 were obtained.

  As can be seen from Table 4, when the crystallinity of the silicon compound was changed, the capacity retention ratio and the initial efficiency changed according to the crystallinity. In particular, a high capacity retention ratio is obtained with a low crystalline material having a crystallite size of 7.5 nm or less due to the Si (111) plane. In particular, the best capacity retention ratio can be obtained in the amorphous region.

(Example 5-1 to Example 5-4)
A secondary battery was manufactured in the same manner as in Example 1-3 except that the median diameter of the silicon compound was adjusted. The median diameter was adjusted by changing the grinding time and classification conditions in the silicon compound production process. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 5-1 to 5-4 were examined, the results shown in Table 5 were obtained.

  As can be seen from Table 5, when the median diameter of the silicon compound was changed, the maintenance ratio and the initial efficiency changed accordingly. As shown in Examples 5-1 to 5-3, when the median diameter of the silicon compound particles was 0.5 μm to 20 μm, the capacity retention rate and the initial efficiency were higher. In particular, when the median diameter was 4 μm to 10 μm (Examples 1-3 and 4-3), the capacity retention rate was greatly improved.

(Example 6-1 to Example 6-5)
The secondary battery was manufactured in the same manner as in Example 1-3, except that the content of the carbon coating on the surface of the silicon compound (ratio to the total of the silicon compound and the carbon coating), thickness (film thickness), and coverage were changed. went. Changes in the content, thickness, and coverage of the carbon coating can be controlled by adjusting the CVD time and the fluidity of the silicon compound powder during CVD. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 6-1 to 6-5 were examined, the results shown in Table 6 were obtained.

  As can be seen from Table 6, when the content of the carbon coating is between 5% by mass and 20% by mass, both the maintenance rate and the initial efficiency become better characteristics. If the content of the carbon coating is 5% by mass or more, the electronic conductivity of the silicon compound will be good. Moreover, if the content rate of a carbon film is 20 mass% or less, ionic conductivity will become favorable. Therefore, when the content rate of the carbon coating is within the above range, the capacity retention rate and the initial efficiency are good values.

(Example 7-1 to Example 7-3)
A secondary battery was manufactured in the same manner as in Example 1-3, except that the ratio of polyacrylic acid and its Li salt contained in the silicon compound to the silicon compound was changed. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Example 7-1 to Example 7-3 were examined, the results shown in Table 7 were obtained.

  As can be seen from Table 7, when the concentration of polyacrylic acid and its Li salt contained in the silicon compound was increased, the maintenance ratio and the initial efficiency changed accordingly. As shown in Examples 7-1 to 7-3 of Table 7, when the ratio of polyacrylic acid and its Li salt is 2% by mass or more and 25% by mass or less with respect to the silicon compound, good battery characteristics are obtained. can get. If this ratio is 2% by mass or more, a sufficient effect of improving battery characteristics can be obtained, and if it is 25% by mass or less, the amount of acid does not increase excessively through neutralization, and the energy density of the negative electrode Will improve.

(Example 8-1 to Example 8-5)
In Example 8-1 to Example 8-5, a secondary battery was manufactured basically in the same manner as in Example 1-3. However, a carbon-based active material (graphite) was further added as a negative electrode active material. It was. Here, the ratio between the content of the carbon-based active material in the negative electrode and the content of the silicon compound was fixed at 90:10 (mass ratio). That is, the ratio of the silicon compound to the total amount of the carbon-based active material and the silicon compound was 10% by mass. Moreover, the distribution part of an acid and Li salt was changed by changing the timing which acid-treats negative electrode active material particle. When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 8-1 to 8-5 were examined, the results shown in Table 8 were obtained. Table 8 shows the center of the distribution of the acid and its Li salt.

  As can be seen from Table 8, the capacity retention ratio and the initial efficiency are improved when the acid and its Li conjugated salt contained in the negative electrode active material are present around the silicon compound having a carbon coating in the negative electrode. The closer the acid and its Li conjugated salt are to the silicon compound having the carbon coating, the greater the effect of improving capacity retention and initial efficiency. In particular, it can be seen that the acid and its Li salt are preferably detected from the outer peripheral surface of the carbon coating.

(Examples 9-1 to 9-4)
The state of the carbon coating on the surface of the silicon compound is changed, in the Raman spectrum analysis, except that changing the intensity ratio _I 1330 _{/ I 1580} of the scattering peak of 1330 cm ^-1 and 1580 cm ^-1, as in Example 8-1 In addition, a secondary battery was manufactured. The results are shown in Table 9. The intensity ratio of the scattering peak was determined by changing the temperature and gas pressure during CVD.

  When the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries of Examples 9-1 to 9-4 were examined, the results shown in Table 9 were obtained.

As shown in Table 9, when I ₁₃₃₀ / I ₁₅₈₀ in the Raman spectrum analysis is less than 2.0, the surface does not have too many carbon components having a messy bonding mode derived from I ₁₃₃₀ , and the electron conductivity is low. Since it becomes good, the maintenance rate and the initial efficiency can be improved. Further, when the value of I ₁₃₃₀ / I ₁₅₈₀ is larger than 0.7, carbon components such as graphite derived from I ₁₅₈₀ on the surface do not increase excessively, and accompanying ion insertion and Li insertion of the silicon compound of the carbon coating. The followability to expansion is improved, and the capacity maintenance rate can be improved.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

10 ... negative electrode, 11 ... negative electrode current collector, 12 ... negative electrode active material layer,
20 ... reformer in bulk, 21 ... positive electrode (lithium source, reforming source),
22 ... Silicon compound powder, 23 ... Organic solvent, 24 ... Separator,
25 ... Powder storage container, 26 ... Power supply, 27 ... Bathtub,
30 ... Lithium secondary battery (laminate film type), 31 ... Electrode body,
32 ... Positive electrode lead (positive electrode aluminum lead),
33 ... negative electrode lead (negative electrode nickel lead), 34 ... adhesion film,
35 ... exterior member.

Claims (13)

The negative electrode active material particles have negative electrode active material particles, and the negative electrode active material particles have a silicon compound (SiO _x : 0.5 ≦ x ≦ 1.6) containing a Li compound. ,
The negative active material particles state, and are pH 7.8 to 9 at 25 ° C. 1% dispersion,
An acid and a Li salt thereof on the surface;
The acid and its Li salt include a polymer acid having a carboxy group and its Li salt,
As the polymer acid having a carboxy group and its Li salt, any one or more of polyacrylic acid and polyacrylic acid Li salt, carboxymethylcellulose and carboxymethylcellulose Li salt, and polymaleic acid and polymaleic acid Li salt Including
The negative active material for a non-aqueous electrolyte secondary battery , wherein the silicon compound contains Li ₂ SiO ₃ therein . The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the acid and its Li salt include acetic acid and a Li salt of acetic acid . The acid and Li salts, the silicon compound to the non-aqueous electrolyte secondary battery negative electrode according to claim 1 or claim 2, characterized in that in a ratio of 25 mass% or more than 2 mass% Active material. The silicon compound is coated with a carbon film containing carbon at least in part, the carbon coating is in the Raman spectrum analysis, have a scattering peak at 1330 cm ^-1 and 1580 cm ^-1, their intensity ratio _{I 1330} / _{I 1580 0.7} <negative active material for a non-aqueous electrolyte secondary battery as claimed in any one of claims 3 to satisfy the _{I 1330 / I} 1580 <2.0. 5. The negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 4 , wherein the content of the carbon coating is 5% by mass or more and 20% by mass or less with respect to the total of the silicon compound and the carbon coating. . The negative active material particles, the acid and its Li salt, a negative electrode active material for a nonaqueous electrolyte secondary battery according to claim 4 or claim 5, characterized in that it is detected from the outer peripheral surface of said carbon film . The silicon compound is, among the _{L i 6 Si 2 O 7,} Li 4 SiO 4 therein, claim 1, characterized in that contains at least one or more of Li compound in any one of claims 6 The negative electrode active material for nonaqueous electrolyte secondary batteries as described. Negative active material for a non-aqueous electrolyte secondary battery as claimed in any one of claims 7, wherein the median diameter of the silicon compound is 0.5μm or more 20μm or less. A negative electrode for a nonaqueous electrolyte secondary battery comprising the negative electrode active material for a nonaqueous electrolyte secondary battery according to any one of claims 1 to 8 , and a carbon-based active material. The negative electrode for a non-aqueous electrolyte secondary battery according to claim 9 , wherein a ratio of the silicon compound to a total amount of the carbon-based active material and the silicon compound is 5% by mass or more. Non-aqueous non-aqueous electrolyte secondary battery, wherein the electrolyte is obtained using the negative electrode for secondary battery according to claim 9 or claim 10. A method for producing negative electrode active material particles contained in a negative electrode material for a nonaqueous electrolyte secondary battery,
Producing a silicon compound represented by SiO _x (0.5 ≦ x ≦ 1.6);
Modifying the silicon compound by inserting Li into the silicon compound to generate Li ₂ SiO ₃ as a Li compound on the surface or inside of the silicon compound or both;
By treating the modified silicon compound with a polymer acid having at least one carboxy group of polyacrylic acid, carboxymethylcellulose and polymaleic acid, the pH at 25 ° C. of the 1% dispersion is 7 A method for producing negative electrode active material particles, wherein the negative electrode active material particles are produced by a step of controlling to 8 or more and 9 or less. The method for producing negative electrode active material particles according to claim 12 , wherein the step of modifying the silicon compound is performed by an electrochemical method.

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