JP2007234418A - Negative electrode mixture paste for non-aqueous secondary battery, negative electrode and non-aqueous secondary battery using the same, and method for producing negative electrode mixture paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative electrode mixture paste which is superior in dispersion characteristics and dispersion stability for a long period of a negative electrode active material even if a submaterial such as a binder in the mixture is reduced. <P>SOLUTION: This is a manufacturing method of the negative electrode mixture paste for a nonaqueous secondary battery having a mixing process of mixing the negative electrode active material and a dispersion containing swollen styrene butadiene rubber particles dispersed by an organic solvent which makes the styrene butadiene rubber particles swell and which substantially contains no water within the range of styrene butadiene rubber particles 0.5 to 1.5 pts.wt. per the negative electrode active material 100 pts.wt. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a negative electrode mixture paste used for producing a negative electrode of a nonaqueous secondary battery represented by a lithium ion secondary battery, a negative electrode produced using the negative electrode mixture paste, and a nonaqueous secondary battery. And a method for producing the negative electrode mixture paste.

  Lithium ion secondary batteries used as power sources for portable electronic devices are the mainstream of non-aqueous secondary batteries. This type of non-aqueous secondary battery is generally formed by applying a positive electrode active material paste composed of a composite oxide of transition metal and lithium, a positive electrode mixture paste containing a binder and a solvent onto a current collector and drying it. A sheet-like positive electrode in which a mixture is formed, and a sheet in which a negative electrode mixture paste containing a negative electrode active material such as a carbon material, a binder, and a solvent is applied onto a current collector and dried to form a negative electrode mixture An electrode body is configured by facing a negative electrode with a separator interposed therebetween and wound or laminated in a spiral shape, and enclosed in a battery case together with a non-aqueous electrolyte in which a lithium salt or the like is dissolved. Produced.

  In recent years, with the development of mobile devices such as PCs and mobile phones, there is a demand for higher battery capacity in the market. In order to increase the capacity of the battery, it is necessary to fill the battery case with as many power generation elements as possible. As one means for achieving this, the active material ratio in the electrode mixture is increased to increase the density. It can be considered as a mixture.

  However, when the electrode mixture is densified, vacancies in the mixture are reduced and diffusion of lithium ions is hindered, leading to deterioration in rate characteristics, cycle characteristics, and the like. In particular, in the negative electrode, the lithium ion storage capacity of the negative electrode active material is reduced by increasing the density of the negative electrode mixture, so that lithium ions that cannot be stored during charging are deposited as metallic lithium. For this reason, a negative electrode having a high density negative electrode mixture causes a decrease in battery characteristics.

  In order to solve the problem due to the decrease in the pores when the negative electrode mixture is densified as described above, for example, the amount of the active material is reduced by reducing the amount of secondary materials that do not contribute to the battery capacity such as the binder. It is conceivable to secure pores in the mixture by reducing the amount of the auxiliary material.

  Conventionally, a vinylidene fluoride polymer having both a binding effect and a thickening effect has been used as a typical binder for an electrode for a lithium ion secondary battery. However, since the vinylidene fluoride polymer has a weak binding property with the active material and the current collector, when forming a high-density electrode mixture, the problem is that the mixture easily falls off from the current collector during electrode preparation. was there. In such places where the mixture has dropped, lithium ions are not occluded when the battery is charged. Accordingly, the battery capacity is reduced, and the deposition of metallic lithium is easily induced at the location where the battery is dropped.

  Therefore, in order to improve the binding property of the electrode mixture, a proposal to silane-modify the vinylidene fluoride polymer (see Patent Document 1), obtained by copolymerizing vinylidene fluoride and monoester of unsaturated dibasic acid. Proposal using a vinylidene fluoride copolymer (see Patent Document 2), and proposal of adding an acid other than hydrofluoric acid after dehydrofluorination from a vinylidene fluoride polymer (see Patent Document 3) ing.

  However, although any of the above-mentioned vinylidene fluoride-based polymers provides improved binding properties, it still requires a large amount of addition, so that it can be used to increase the battery capacity required in recent years. High density due to weight loss of materials cannot be expected. For example, Patent Document 3 describes that about 11 parts by mass of vinylidene fluoride is added to 100 parts by mass of the negative electrode active material.

  Proposal using an aqueous emulsion type binder in which particles of styrene-butadiene rubber (styrene-butadiene copolymer rubber, hereinafter abbreviated as SBR) with high binding power are dispersed in water instead of vinylidene fluoride polymers (See Patent Document 4). However, when the negative electrode active material is dispersed in water, secondary aggregation occurs and the dispersibility is poor. In addition, SBR particles themselves in a state of being dispersed in water as an emulsion have no thickening effect or dispersing effect, and a thickener such as carboxymethylcellulose must be used in combination. Therefore, although the amount of binder used can be reduced by using SBR particles, it is necessary to use a thickener in combination, and as a result, the amount of secondary materials that do not contribute to battery capacity cannot be greatly reduced. For example, Patent Document 4 describes that a total of about 4.2 parts by mass of a binder and a thickener is added to 100 parts by mass of the negative electrode active material.

Therefore, the negative electrode active material is dispersed in advance using only an organic solvent, water is added to the dispersion, and then an aqueous emulsion type dispersion in which SBR particles are emulsion-dispersed is added to the aqueous solvent. A method for preventing secondary aggregation and improving dispersibility without using a thickener has been previously proposed by the present applicants (see Patent Document 5).
JP-A-6-93025 Japanese Patent Laid-Open No. 6-172452 JP-A-10-255808 JP-A-4-342966 JP 2003-142082 A

  However, the aqueous emulsion type dispersion containing the SBR particles has the particles covered with a surfactant in order to prevent aggregation in an aqueous solvent. For this reason, when mixed with an organic solvent during the production of the negative electrode mixture paste, it tends to be preferentially present in water rather than in an organic solvent, and a sufficient thickening effect as expected without a thickener cannot be obtained. . Specifically, the negative electrode mixture paste produced by the method according to Patent Document 5 is highly dispersible immediately after the preparation of the mixture paste, but it is clear that the mixture settles in a relatively short time if left untreated. became. In particular, in order to industrially mass-produce negative electrodes for non-aqueous secondary batteries, it is necessary to prepare a large amount of negative electrode mixture paste and continuously supply and apply the mixture paste to the application process. The current situation is that it takes a long time from the preparation to the completion of coating. Therefore, when a mixture paste having a large change over time and inferior in dispersion stability is applied onto the current collector, the mixture weight varies greatly, and the mixture is frequently dropped due to segregation of the binder. Therefore, in a battery made using such a negative electrode, lithium ions cannot be fully occluded during charging at locations where the negative electrode mixture is low or where the negative electrode mixture is removed, and lithium ions are deposited as metallic lithium, and charge / discharge cycles The capacity was reduced.

  In view of the above-mentioned problems, the present invention has a negative electrode active material dispersibility and long-term dispersion stability even if the amount of a secondary material such as a binder in the mixture is reduced in order to obtain a negative electrode having a high-density negative electrode mixture. A negative electrode mixture paste with excellent dispersion, and thereby producing a negative electrode with less variation in the mixture weight and less dropping of the mixture, thus efficiently producing a non-aqueous secondary battery with little capacity deterioration in the charge / discharge cycle. With the goal.

  The present invention that has solved the above problems includes a negative electrode active material, swollen SBR particles, and an organic solvent that swells the SBR particles as a solvent component, and the content of SBR particles is 0.5 per 100 parts by mass of the negative electrode active material. This is a negative electrode mixture paste for a non-aqueous secondary battery that is ˜1.5 parts by mass and does not substantially contain water.

  According to the above configuration, the SBR particles swollen in the organic solvent have a high binding force and high adhesiveness, so that the dispersibility of the negative electrode active material is excellent and a high thickening effect is obtained with a small amount of use. For this reason, not only the usage-amount of a binder but the usage-amount of a thickener can also be reduced. In addition, since the organic solvent that swells the SBR particles is used as the solvent component of the negative electrode mixture paste, and the water is not substantially contained in the negative electrode mixture paste, the SBR particles dispersed in a highly sticky swelling state Aggregation is also suppressed. Furthermore, since the negative electrode mixture paste is dispersed in a solvent consisting of an organic solvent compared to a binder consisting of an aqueous emulsion dispersed in an aqueous solvent, the occurrence of secondary aggregation of the negative electrode active material is also suppressed, A high thickening effect can be maintained over a long period of time.

  In this invention, it is preferable that the said negative mix paste contains 1.0 mass part or less of thickeners which can be melt | dissolved in the said organic solvent per 100 mass parts of negative electrode active materials.

  According to the above configuration, since the thickening effect of the SBR particles can be sufficiently obtained, even if a thickener is used, excellent binding and dispersion with a small amount of the thickener relative to the negative electrode active material. Sex is obtained. For this reason, the usage-amount of submaterial can be reduced and a negative electrode mixture density can be made high.

  In the present invention, the thickener is preferably polyvinylidene difluoride (hereinafter abbreviated as PVDF) or a modified product thereof.

  Since PVDF or a modified product thereof is excellent in solubility in an organic solvent, according to the above configuration, an excellent thickening effect can be obtained by using a small amount.

In the present invention, the organic solvent is preferably an organic solvent having an SP value (solubility coefficient) of 12 (cal · cm ⁻³ ) ^1/2 or less.

  According to the said structure, since it is SBR particle | grains with large swelling and high adhesiveness in a paste, the paste excellent in dispersion stability is obtained.

  Moreover, this invention is the negative electrode for non-aqueous secondary batteries which apply | coated said negative electrode mixture paste for non-aqueous secondary batteries on the electrical power collector, and dried and formed the negative electrode mixture.

  Since the negative electrode mixture paste is excellent in the dispersibility of the negative electrode active material and the dispersion stability of the negative electrode mixture paste, even with a negative electrode having a high mixture density, a negative electrode with less variation in the mixture weight and less dropping of the mixture can be obtained.

  And this invention is a non-aqueous secondary battery which has said negative electrode, a positive electrode, and a non-aqueous electrolyte.

  The negative electrode produced using the negative electrode mixture paste can improve the productivity because the dispersion of the mixture weight is suppressed and a negative electrode with less dropping of the mixture is obtained even when the mixture density is increased. Thus, stable charge / discharge is possible, and a non-aqueous secondary battery with little capacity deterioration can be obtained.

  The present invention also provides a negative electrode active material and a SBR particle-containing dispersion containing a swollen SBR particle dispersed in a first organic solvent substantially free of water that swells SBR particles per 100 parts by mass of the negative electrode active material. It is a manufacturing method of the negative mix paste for non-aqueous secondary batteries which has the mixing process mixed in the range of 0.5-1.5 mass parts.

  According to the above configuration, since the dispersion composed of an organic solvent in which SBR particles are dispersed in a swollen state and the negative electrode active material are mixed, the swollen SBR particles have high binding properties and high adhesiveness. When used in a small amount, the negative electrode active material is excellent in dispersibility, and a high thickening effect is obtained. For this reason, not only the usage-amount of a binder but the usage-amount of a thickener can also be reduced. Moreover, since the organic solvent which does not contain water substantially is used as a solvent at the time of preparation of negative mix paste, aggregation of the SBR particle | grains disperse | distributed in the swelling state is also suppressed. Furthermore, compared to a binder composed of an aqueous emulsion dispersed in an aqueous solvent, the occurrence of secondary aggregation of the negative electrode active material can be suppressed, and a high thickening effect can be maintained over a long period of time.

  In the mixing step of the present invention, the negative electrode active material is the same as or different from the first organic solvent, and the swollen SBR particles are used as a negative electrode active material dispersion liquid dispersed in a second organic solvent that does not substantially contain water. It is preferable to mix with the containing dispersion.

  According to the said structure, since a negative electrode active material is excellent in the dispersibility to an organic solvent, the negative mix paste which was further excellent in the dispersibility is obtained. In addition, since the second organic solvent does not contain water, when mixed with the swollen SBR resin-containing dispersion, aggregation of SBR particles is also suppressed.

  Moreover, in this invention, it is preferable that the said negative mix paste contains 1.0 mass part or less of thickeners which can be melt | dissolved in a said 1st organic solvent per 100 mass parts of negative electrode active materials.

  According to the said structure, since the thickening effect of SBR particle | grains is fully acquired, the binding property and the dispersibility which were excellent with a small amount of thickeners with respect to the negative electrode active material are obtained. For this reason, the usage-amount of submaterial can be reduced and a negative electrode mixture density can be made high.

  In the present invention, the thickener is preferably PVDF or a modified product thereof.

  Since PVDF or a modified product thereof is excellent in solubility in an organic solvent, according to the above configuration, an excellent thickening effect can be obtained by using a small amount.

In the present invention, the first organic solvent is preferably an organic solvent having an SP value (solubility coefficient) of 12 (cal · cm ⁻³ ) ^1/2 or less.

  According to the above configuration, a swollen SBR particle-containing dispersion liquid having large swelling and high adhesiveness can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, while being excellent in the dispersibility of a negative electrode active material, the negative mix paste used for preparation of the negative electrode for non-aqueous secondary batteries which is excellent in long-term dispersion stability can be produced. And the negative electrode produced using this negative electrode mixture paste can obtain a negative electrode with little variation in the mixture weight and less dropping of the mixture. Therefore, even when a negative electrode having a high density negative electrode mixture in which secondary materials such as a binder and a thickener are reduced, a non-aqueous secondary battery with good productivity and little capacity deterioration in a charge / discharge cycle is obtained. It is done.

  First, SBR particles made of a copolymer of styrene and butadiene, which are used as a binder for negative electrodes for non-aqueous secondary batteries, will be described. Since SBR particles themselves have high adhesiveness, they are bonded. Even if the amount of the adhesive is reduced, it is possible to suppress the dropping of the mixture. However, SBR particles are generally produced in an aqueous system by emulsion polymerization, and the particles exist as an emulsion covered with a surfactant to impart dispersibility in this aqueous solvent. This emulsion itself has no thickening effect, and the resulting mixture paste is inferior in dispersion stability. Therefore, it is essential to use a thickener together, and a secondary material that does not contribute to battery capacity is added, resulting in high density. The negative electrode mixture cannot be obtained. In the aqueous solvent, the surfactant has a structure in which a hydrophilic group is arranged outside the micelle structure, whereas the surface of the carbon material or the like as the negative electrode active material is hydrophobic. Therefore, it was considered that in the conventional aqueous emulsion dispersion, the binding of the binder to the active material was inhibited by the surfactant, and a sufficient binding effect could not be obtained.

  For this reason, the negative electrode mixture paste for a non-aqueous secondary battery of the present invention is a dispersion containing swollen SBR particles dispersed in a negative electrode active material and a first organic solvent substantially free of water that swells SBR particles. It is produced through a mixing step of mixing the liquid.

  In the present invention, by mixing the swollen SBR particles with the negative electrode active material in an organic solvent substantially free of water, the dispersibility of the negative electrode active material is excellent even when the amount of the secondary material is greatly reduced, and long-term The reason why a negative electrode mixture paste excellent in dispersion stability is obtained is considered to be mainly as follows.

  First, SBR particles swollen in an organic solvent not containing water exhibit a thickening effect. Therefore, unlike an aqueous emulsion type dispersion, a large amount of thickener is not required, so that the amount of thickener can be reduced. In addition, since the SBR particles swollen in the organic solvent do not have a micelle structure covered with a surfactant, the binding of the SBR particles to the negative electrode active material is not suppressed. In order to improve the binding property to the negative electrode active material, a certain degree of thickening is required. From this point, the swollen SBR particles exhibit adhesiveness in an organic solvent in which the negative electrode active material is easily dispersed. The binding property is also improved. As a result, the binding effect of the SBR particles is sufficiently exerted, and the amount of the binder can be reduced. Furthermore, if it is in the solution which uses an organic solvent as a solvent component, the negative electrode active material which is hydrophobic can be disperse | distributed easily. That is, it is difficult to disperse the negative electrode active material in an aqueous solvent, and aggregation occurs to accelerate the precipitation of the mixture. A negative electrode mixture paste that is suppressed and excellent in dispersion stability can be obtained, and thereby the weight of the thickener can be further reduced. Furthermore, since the swollen SBR particles have high tackiness, they tend to aggregate in the presence of water, but the aggregation is also suppressed in an organic solvent that does not contain water, so that a uniform and stable negative electrode mixture paste can be obtained. can get.

  Therefore, according to the negative electrode mixture paste of the present invention, there is little weight variation of the negative electrode mixture and dropping of the mixture as a high-density negative electrode mixture in which the auxiliary material that does not contribute to the battery capacity is reduced. Even if the proportion of the negative electrode active material is increased by the above, since the voids in the negative electrode mixture are secured, the productivity of the negative electrode can be improved and a negative electrode having good capacity characteristics can be obtained.

  Although the content ratio of styrene and butadiene in the SBR particles used in the present invention is not particularly limited, from the viewpoints of binding properties in organic solvents, adhesiveness, and battery characteristics, it is −30 ° C. to + 60 ° C. It is preferable to use one synthesized at a ratio that provides rubber particles having a glass transition temperature. A part of the copolymer of styrene and butadiene may be modified with a substituent or the like.

In the present invention, as the first organic solvent for imparting binding properties and tackiness to the SBR particles used for preparing the dispersion containing the swollen SBR particles, the solubility of the SBR particles is low and the SBR particles are swollen. Although it will not specifically limit if it is an organic solvent which has a property, Specifically, the organic solvent whose SP value (solubility coefficient) is 12 (cal * cm < ^-3 >) < ^1/2 > [25 degreeC] or less is preferable. . Examples of such an organic solvent include N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) (SP value: 11.9), toluene (8.9), and n-pentane (7.0). , N-heptane (same as 7.2), n-hexane (same as 7.4), n-octane (same as 7.6), n-decane (same as 7.7), diethyl ether (same as 7.7), Methylcyclohexane (same as 7.8), isobutyl-n-butyrate (same as 7.8), n-dodecane (same as 7.8), n-hexadecane (same as 7.9), cyclohexane (same as 8.2), ethyl -N-butyrate (8.3), n-butyl acetate (8.5), 1,1,1-trichloroethane (8.5), carbon tetrachloride (8.6), n-propyl acetate (8.7), n-propylformate (8.9), ethyl propio Over preparative (the 9.0), methyl ethyl ketone (the 9.0), and the like. These may be used alone or in combination of two or more. However, when a plurality of organic solvents having different solubility of SBR particles are mixed, SBR particles are likely to aggregate. It is preferable to use it.

  In the present invention, an organic solvent substantially free of water is used as the first organic solvent. The SBR particles in a dispersed state are likely to agglomerate when water is contained in the organic solvent, and the agglomeration of the negative electrode active material also occurs during the preparation of the negative electrode mixture paste, so that dispersibility and dispersion stability are reduced. In the present invention, the organic solvent substantially free of water means an organic solvent containing an amount of water in which the SBR particles swollen in the negative electrode mixture paste do not aggregate, and the water content is Although it is determined by the organic solvent used, the type of SBR particles, etc., it is preferably 100 ppm or less. The water content is determined by measuring the sample using the coulometric method with the Karl Fischer method.

  The method for preparing the dispersion containing the swollen SBR particles of the present invention is not particularly limited. However, in the case of preparing using conventionally known SBR particles, the aqueous solvent of the aqueous emulsion-type dispersion is dissolved in the first organic solvent. The method of substitution is mentioned. When preparing a dispersion containing swollen SBR particles by solvent substitution, for example, after adding an organic solvent to be substituted and a third solvent such as benzene or ethanol, water is finally added to the first organic solvent by an azeotropic mixing process. By replacing the solvent, a dispersion in which SBR particles are dispersed in a swollen state can be obtained. As for the swelling state of the SBR particles in the dispersion liquid, the whole particle may be swollen, but if the particle has a non-swelled part at the center and the periphery is swollen, the non-swelled part becomes the nucleus. It is considered that the deformation of the particle shape is small, whereby the binding portion between the SBR particles and the negative electrode active material is considered to be close to a point, and the covering area of the negative electrode active material by the binder is reduced, which is preferable.

  The content of SBR particles in the swollen SBR particle-containing dispersion is not particularly limited, but is preferably 8 to 80% by mass. Further, the viscosity of the dispersion is not particularly limited, but 4.5 to 10 poise (8% by mass, 8% by mass, when measured with a BM viscometer in order to obtain sufficiently swollen SBR particles. The value at 25 ° C.) is preferable.

  In the present invention, the SBR particles in the negative electrode mixture paste are 0.5 to 1.5 parts by mass, preferably 0.5 to 100 parts by mass per 100 parts by mass of the negative electrode active material in order to increase the mixture density of the obtained negative electrode mixture. The negative electrode active material is mixed in the range of 1.0 part by mass. Even in such a small amount of binder, the present invention uses swollen SBR particles having high binding and adhesive properties, so that it is excellent in dispersibility of the negative electrode active material and is also stable in dispersion due to the thickening effect. Is obtained. When the content is less than 0.5 parts by mass, sufficient dispersibility and binding properties cannot be ensured, and variations in the mixture weight and dropping of the mixture are easily induced. On the other hand, when the content is more than 1.5 parts by mass, the ratio of the negative electrode active material decreases, and in the high density negative electrode mixture, sufficient pores cannot be secured, and the capacity characteristics are deteriorated.

  As a negative electrode active material of this invention, a conventionally well-known thing is used without being specifically limited. Specifically, for example, carbon materials such as various natural graphites, artificial graphite, fibrous carbon, carbon nanotubes, and carbon nanofibers, as well as silicon-based composite materials such as silicide, various alloy materials, etc. are mixed with these carbon materials. Can be used.

  As the ratio of the negative electrode active material in the solid mixture, the higher the negative electrode, the higher the capacity of the negative electrode, and the more preferable it is 88.0 to 99.5% by mass in the entire negative electrode mixture. 99.5 mass% is more preferable, and 98.0-99.5 mass% is the most preferable.

  In the present invention, the negative electrode active material may be mixed with a swollen SBR particle-containing dispersion as a negative electrode active material dispersion in which the negative electrode active material is dispersed in a second organic solvent. It is preferable to disperse the negative electrode active material in advance in an organic solvent because the dispersibility of the hydrophobic negative electrode active material in the paste is improved. The second organic solvent is not particularly limited as long as it is an organic solvent in which the negative electrode active material is dispersed, and may be the same organic solvent as the first organic solvent or a different organic solvent. . However, if the solubility of the SBR particles is too different between the first organic solvent and the second organic solvent, aggregation of the SBR particles is likely to occur. Therefore, it is preferable to use the same organic solvent as the first organic solvent.

  In the present invention, as the second organic solvent used when the negative electrode active material dispersion is prepared, an organic solvent substantially free of water is used as in the first organic solvent. When the second organic solvent contains water, the hydrophobic negative electrode active material is likely to cause secondary aggregation, and the SBR particles are likely to aggregate during mixing. For this reason, when a negative electrode active material dispersion liquid is used, it is necessary for the second organic solvent to have a water content comparable to that of the first organic solvent.

  In the negative electrode mixture paste of the present invention, only the swollen SBR particles suppress the precipitation of the mixture, but a thickener may be added to further suppress the precipitation. As the thickener, those capable of being dissolved in the first organic solvent are preferable from the viewpoint of thickening. Specifically, a polyvinylidene fluoride-based thickener is preferred, and examples thereof include PVDF or a modified product thereof.

  The addition amount of the thickener is 1.0 part by mass or less, more preferably 0.5 part by mass or less, and most preferably 0 part by mass with respect to 100 parts by mass of the negative electrode active material. In the present invention, since a high thickening effect is obtained by the SBR particles as the binder, a stable negative electrode mixture paste can be prepared even with a small amount of a thickener of 1.0 part by mass or less, and a high density negative electrode mixture In this case, it is possible to secure holes.

  In the present invention, any additive such as carbon black may be used in addition to the above-described thickener, but the negative electrode active material in the negative electrode mixture is reduced. The additive is preferably 10 parts by mass or less per 100 parts by mass of the negative electrode active material.

  In the present invention, the above-described negative electrode active material, swollen SBR particle-containing dispersion, and, if necessary, a thickener and additives are mixed in an organic solvent by a conventionally known method so that substantially no water is contained. A negative electrode mixture paste for a non-aqueous secondary battery is produced. At this time, an additional organic solvent may be further mixed from the viewpoint of viscosity adjustment, drying property at the time of application, etc., but the additional organic solvent is the same as the first organic solvent in order to suppress aggregation of SBR particles. Organic solvents are preferred. In addition, in order to prevent aggregation of the SBR particles and the negative electrode active material, the negative electrode mixture paste finally obtained needs to be a paste that does not substantially contain water, similar to the first organic solvent described above. Preferably, the content of water in the negative electrode mixture paste is 100 ppm or less.

  In the production of the negative electrode mixture paste of the present invention, conventionally known mixing dispersers such as various dispersers and mixers are used. The solid content in the negative electrode mixture paste is preferably 40 to 60% by mass, and the viscosity is a BM viscometer, preferably 10 to 100 poise (25 ° C.).

In the production of the negative electrode of the present invention, the negative electrode mixture paste produced through the above mixing step is used, and this is applied onto a current collector such as a copper foil, dried and rolled to obtain a current on the current collector. A negative electrode in which a negative electrode mixture is formed is obtained. The mixture density of the negative electrode mixture, preferably higher for higher capacity, more preferably 1.65 g / cm ³ or more, further preferably 1.70 g / cm ³ or more. Since the negative electrode mixture obtained by the negative electrode mixture paste of the present invention is excellent in the binding property between the mixture and the binding property between the current collector and the mixture, even as such a negative electrode having a high mixture density. In addition, the mixture is prevented from falling off, and a small amount of secondary material ensures a void. Meanwhile, since not keep up the effect by the binder and too high mixture density is preferably 1.85 g / cm ³ or less, 1.80 g / cm ³ or less is more preferable. The mixture density of the negative electrode mixture is obtained by measuring the weight and thickness of the mixture having a certain area and then dividing the mixture weight by the mixture volume. Note that when the density of the negative electrode mixture is increased, the number of vacancies in the negative electrode mixture is reduced and the diffusion of lithium ions is hindered, leading to a decrease in rate characteristics and cycle characteristics. The rate is preferably 19 to 45 vol%, more preferably 20 to 40 vol%. The porosity in the mixture is obtained by measuring the thickness of the mixture in a certain area to determine the volume (V1) of the entire mixture, and calculating the total solid volume (V2) in the mixture from the true specific gravity and composition of each constituent material. ) And the difference (V1-V2) divided by the total volume (V1) of the mixture.

  In the positive electrode of the present invention, a positive electrode mixture paste in which a positive electrode active material, a binder, and, if necessary, a thickener, a conductive agent and the like are mixed in a solvent is applied onto a current collector such as an aluminum foil, dried, rolled It is produced by doing.

  As the positive electrode active material, conventionally reported various lithium composite oxides are used. Specifically, for example, lithium cobalt oxide such as lithium cobalt oxide, eutectic oxide obtained by replacing a part of cobalt of lithium cobalt oxide with aluminum, magnesium, etc., lithium nickel oxide such as lithium nickel oxide, lithium Examples thereof include eutectic oxides in which part of nickel in nickel oxide is replaced with cobalt, lithium manganese oxide, eutectic oxides in which part of manganese in lithium manganese oxide is replaced with nickel, cobalt, and the like. These lithium composite oxides may be used alone or in combination of two or more.

  As a binder used for a positive electrode, a conventionally well-known binder is used without being specifically limited. Specifically, for example, polytetrafluoroethylene (PTFE), PVDF, a modified product of PVDF, a copolymer of tetrafluoroethylene and hexafluoropropylene (HFP) (PTFE-HFP), and a binder having an acrylonitrile unit. Etc.

  Specific examples of the conductive agent used for the positive electrode include carbon blacks such as acetylene black (AB), ketjen black, channel black, furnace black, lamp black and thermal black, and carbon materials such as various graphites. Can be mentioned. These carbon materials may be used individually by 1 type, and may be used in combination of multiple types. In addition, although the mixture of the above carbon materials and materials other than a carbon material can also be used for a electrically conductive agent, it is preferable that 90-100 mass% of a electrically conductive agent is a carbon material.

  As an organic solvent used for manufacture of positive mix paste, the organic solvent similar to the organic solvent used for manufacture of negative mix pastes, such as NMP, is used.

  The non-aqueous secondary battery of the present invention has a negative electrode and a positive electrode manufactured as described above facing each other via a separator to produce an electrode body obtained by winding or laminating the negative electrode and the positive electrode. At the same time, it is manufactured by enclosing it in a battery case.

  Although it does not specifically limit as a separator, The microporous film which consists of polyolefin resins, such as polyethylene and a polypropylene, is used. The microporous film is generally a single layer film made of one kind of polyolefin or a composite film made of two or more kinds of polyolefin. Although the thickness of a separator is not specifically limited, It is preferable that it is 10-25 micrometers.

The nonaqueous electrolyte may be not only a liquid electrolyte used for a lithium ion secondary battery but also a gel or solid electrolyte used for a lithium polymer secondary battery. As the liquid electrolyte, a solution in which a solute is dissolved in a non-aqueous solvent is used. Lithium salts such as LiPF ₆ and LiBF ₄ are preferably used as the solute, but are not limited thereto. As the non-aqueous solvent, carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (MEC) are preferably used, but are not limited thereto. . The non-aqueous solvent is preferably used in combination of two or more. Moreover, it is preferable to add the additive which forms a membrane | film | coat on a positive electrode or a negative electrode to a liquid electrolyte. Examples of additives that can be used include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), cyclohexylbenzene (CHB), and modified products of VC and CHB. The film formed by such an additive can improve the safety of the battery during overcharge. Examples of the gel or solid electrolyte include polyethylene oxide containing a lithium salt.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these.

Example 1
[Production of negative electrode]
SBR particles obtained by replacing the aqueous solvent of an aqueous emulsion dispersion containing SBR particles (manufactured by JSR Corporation, 0696) with NMP (SP value: 11.9, water content: 100 ppm or less) as a binder. A dispersion containing swollen SBR particles having a content of 8% by mass was used. The viscosity of the dispersion was 5.7 poise (25 ° C.).

  Artificial graphite (“MAG-D” manufactured by Hitachi Chemical Co., Ltd.) is used as the negative electrode active material, and artificial graphite and the above-described swollen SBR so that the SBR particles are 1.0 part by mass with respect to 100 parts by mass of the artificial graphite. The particle-containing dispersion is added to a double-arm kneader together with a predetermined amount of NMP (water content: 100 ppm or less), stirred, and a negative electrode mixture paste (water content: 50% by mass). Content: 100 ppm or less) was prepared.

The obtained negative electrode mixture paste was continuously applied on both sides of a current collector made of a copper foil having a thickness of 10 μm so that the total dry thickness with the copper foil was 300 μm, and dried. Next, the dried coating film was pressed so that the total thickness was 175 μm. Thereafter, the current collector carrying the negative electrode mixture on both sides was slit into a width of 59 mm to produce 20 negative electrodes. The average mixture density of the negative electrode was 1.77 g / cm ³ , and the average porosity was 20.1 vol%.

[Production of positive electrode]
100 parts by mass of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, 3 parts by mass of AB as a conductive agent, and 3 parts by mass of PVDF as a binder are added to a double-arm kneader together with a predetermined amount of NMP and stirred. A positive electrode mixture paste having a solid content of 70% by mass was prepared. The obtained positive electrode mixture paste was applied to both sides of a current collector made of aluminum foil having a thickness of 15 μm and dried, and dried so that the total thickness of the positive electrode mixture and current collector on both sides was about 300 μm. A film was formed. Next, the dried coating film was pressed so that the total thickness was 180 μm. Thereafter, the current collector carrying the positive electrode mixture on both sides was slit into a width of 56 mm to produce a positive electrode.

[Preparation of non-aqueous electrolyte]
After adding 3 parts by mass of VC to 100 parts by mass of a 3: 3: 2 volume ratio of EC, DMC and MEC, LiPF ₆ was dissolved at a concentration of 1 mol / L to obtain a nonaqueous electrolyte.

[Battery assembly]
The positive electrode and the negative electrode manufactured as described above were wound through a separator (# 2320 manufactured by Celgard Co., Ltd.) made of a polyethylene microporous film having a thickness of 20 μm, and an electrode body was manufactured. The obtained electrode body was inserted into an iron battery case having an inner surface plated with Ni, and 5.0 g of nonaqueous electrolyte was injected, and then the battery case was sealed. As described above, a cylindrical type 18650 lithium ion secondary battery having a nominal capacity of 2400 mAh was manufactured.

(Example 2)
In the production of the negative electrode of Example 1, a negative electrode was produced in the same manner as in Example 1, except that a swollen SBR particle-containing dispersion liquid having an amount of 0.5 parts by mass of SBR particles was used. The content of water in the negative electrode mixture paste was 100 ppm or less, the average mixture density of the negative electrode was 1.76 g / cm ³ , and the average porosity was 21.0 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Example 3)
In the production of the negative electrode of Example 1, a negative electrode was produced in the same manner as in Example 1, except that a swollen SBR particle-containing dispersion liquid having an amount of 1.5 parts by mass of SBR particles was used. The content of water in the negative electrode mixture paste was 100 ppm or less, the average mixture density of the negative electrode was 1.78 g / cm ³ , and the average porosity was 19.2 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

Example 4
In the production of the negative electrode of Example 1, 8% by mass of swollen SBR particle-containing dispersion (water content: 100 ppm or less, viscosity [25] dispersed with toluene (SP value: 8.9) as the swollen SBR particle-containing dispersion. [° C.]: 6.0 poise) was used, and a negative electrode was produced in the same manner as in Example 1 except that toluene (water content: 100 ppm or less) was also used as the organic solvent at the time of mixing. The content of water in the negative electrode mixture paste was 100 ppm or less, the average mixture density of the negative electrode was 1.77 g / cm ³ , and the average porosity was 20.1 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Example 5)
In the preparation of the negative electrode of Example 1, as a swollen SBR particle-containing dispersion, an 8% by weight swollen SBR particle-containing dispersion dispersed in butyl acetate (SP value: 8.5) (water content: 100 ppm or less, viscosity [ 25 ° C.]: 6.1 poise) was used, and a negative electrode was produced in the same manner as in Example 1 except that butyl acetate (water content: 100 ppm or less) was also used as the organic solvent during mixing. . The content of water in the negative electrode mixture paste was 100 ppm or less, the average mixture density of the negative electrode was 1.77 g / cm ³ , and the average porosity was 20.1 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Example 6)
In the production of the negative electrode of Example 1, a negative electrode was produced in the same manner as in Example 1, except that 0.5 parts by mass of PVDF was further added to 100 parts by mass of artificial graphite during mixing. The content of water in the negative electrode mixture paste was 100 ppm or less, the average mixture density of the negative electrode was 1.78 g / cm ³ , and the average porosity was 19.6 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Example 7)
In the production of the negative electrode of Example 1, a negative electrode was produced in the same manner as in Example 1, except that 1.0 part by mass of PVDF was further added to 100 parts by mass of artificial graphite during mixing. The content of water in the negative electrode mixture paste was 100 ppm or less, the average mixture density of the negative electrode was 1.79 g / cm ³ , and the average porosity was 19.1 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Example 8)
In the production of the negative electrode of Example 1, first, 100 parts by mass of artificial graphite and 89.5 parts by mass of NMP (water content: 100 ppm or less) were added to a double-arm kneader, stirred, and negative electrode active A substance dispersion was prepared. A negative electrode was produced in the same manner as in Example 1 except that this negative electrode active material dispersion was used and NMP was not added during mixing. The content of water in the negative electrode mixture paste was 100 ppm or less, the average mixture density of the negative electrode was 1.77 g / cm ³ , and the average porosity was 20.1 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Comparative Example 1)
In the production of the negative electrode of Example 1, 1.0 part by mass of an aqueous emulsion type dispersion (JSR Co., Ltd., 0696) having a SBR particle content of 40% by mass was used instead of the swollen SBR particle-containing dispersion. A negative electrode was produced in the same manner as in Example 1 except that a predetermined amount of water was used as a solvent during mixing. The content of water in the negative electrode mixture paste was 40 mass%, the average mixture density of the negative electrode was 1.77 g / cm ³ , and the average porosity was 20.1 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Comparative Example 2)
In the production of the negative electrode of Example 1, 1.0 part by mass of an aqueous emulsion type dispersion (JSR Co., Ltd., 0696) having a SBR particle content of 40% by mass was used instead of the swollen SBR particle-containing dispersion. A negative electrode was produced in the same manner as in Example 1, except that 1 part by mass of carboxymethylcellulose (Dellogen 4H, Cellogen 4H) was further added as a thickener. The content of water in the negative electrode mixture paste was 50 mass%, the average mixture density of the negative electrode was 1.79 g / cm ³ , and the average porosity was 18.9 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Comparative Example 3)
In the production of the negative electrode of Example 1, the same procedure as in Example 1 was conducted except that 5.0 parts by mass of PVDF (manufactured by Kureha Chemical Co., Ltd., KF polymer 1320) was used instead of the dispersion containing swollen SBR particles. Thus, a negative electrode was produced. The content of water in the negative electrode mixture paste was 100 ppm, the average mixture density of the negative electrode was 1.84 g / cm ³ , and the average porosity was 16.9 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Comparative Example 4)
In producing the negative electrode of Example 1, a negative electrode was produced except that 1.0 part by mass of PVDF (manufactured by Kureha Chemical Co., Ltd., KF polymer 1320) was used instead of the swollen SBR particle-containing dispersion. The content of water in the negative electrode mixture paste was 100 ppm, the average mixture density of the negative electrode was 1.77 g / cm ³ , and the average porosity was 20.9 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Comparative Example 5)
In the production of the negative electrode of Example 1, a negative electrode was produced in the same manner as in Example 1, except that a swollen SBR particle-containing dispersion liquid having an amount of 0.3 parts by mass of SBR particles was used. The content of water in the negative electrode mixture paste was 100 ppm, the average mixture density of the negative electrode was 1.76 g / cm ³ , and the average porosity was 21.3 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Comparative Example 6)
In the production of the negative electrode of Example 1, a negative electrode was produced in the same manner as in Example 1, except that a swollen SBR particle-containing dispersion liquid having an amount of 2.0 parts by mass of SBR particles was used. The content of water in the negative electrode mixture paste was 100 ppm, the average mixture density of the negative electrode was 1.79 g / cm ³ , and the average porosity was 18.3 vol%. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode obtained as described above was used.

(Comparative Example 7)
In preparation of the negative electrode of Example 1, first, 100 parts by mass of artificial graphite and 40 parts by mass of NMP were added to a double-arm kneader and stirred to prepare a negative electrode active material dispersion. Next, 60 parts by mass of water was added to the obtained negative electrode active material dispersion, and the mixture was stirred again to prepare a negative electrode active material dispersion containing an organic solvent and water. To this dispersion, 40% by mass of an aqueous emulsion dispersion (manufactured by JSR Co., Ltd., 0696) is added so that the amount of SBR particles is 1.0 part by mass, and the mixture is stirred until finally solid. A negative electrode mixture paste (water content: 30% by mass) with a content of 50% by mass was prepared. A lithium ion secondary battery was produced in the same manner as in Example 1 except that this negative electrode mixture paste was used. The negative electrode thus prepared had an average mixture density of 1.77 g / cm ³ and an average porosity of 20.1 vol%.

  The following evaluation was performed about each negative electrode and lithium ion secondary battery which were produced as mentioned above. These evaluation results are shown in Table 1.

[Diffusion of mixture weight]
When each negative electrode mixture paste is applied to a current collector and dried, a negative electrode mixture applied on the current collector over a longitudinal direction of 2000 m by a β-ray gravimetric meter that simply measures the weight by β-ray reflection. The weight was measured, and the variation with respect to the intended set weight was measured.

[Displacement of negative electrode mixture]
After each electrode body was produced, the winding was temporarily loosened, and the state of the negative electrode mixture near the core was visually observed. The state of the negative electrode mixture of 20 electrode bodies was observed, and the number of electrode bodies in which the negative electrode mixture was dropped or cracks were observed in the mixture was determined.

[Capacity maintenance rate]
After each lithium ion secondary battery is stored in a 45 ° C. environment for 7 days, the charge / discharge cycle is repeated 200 times under the following charge / discharge conditions, and the ratio of the discharge capacity at the 200th cycle to the first cycle is the capacity maintenance rate. As sought.

<Charging / discharging conditions>
Constant current charging: 1700 mA
End-of-charge voltage: 4.2V
Constant voltage charging: 4.2V
End-of-charge current: 50 mA
Constant current discharge: 2400 mA
End-of-discharge voltage: 3V

  From Table 1, in the organic solvent which does not contain water substantially, a negative electrode active material and a swelling SBR particle containing dispersion liquid are 0.5-1.5 mass with respect to 100 mass parts of negative electrode active materials. The negative electrode obtained by using the negative electrode mixture paste prepared by mixing in the range of parts is a small amount of binder, but the negative electrode mixture has little weight variation, excellent dispersibility, and long time It can be seen that the dispersion stability is maintained even in mass production. Moreover, since the obtained negative electrode does not drop off the negative electrode mixture, it is excellent in the binding property of the mixture. Furthermore, the lithium ion secondary battery produced using this negative electrode has a good capacity retention rate after 200 cycles, and a lithium ion secondary battery with little capacity deterioration can be obtained even with a negative electrode having a high mixture density. I understand that. In particular, even when no thickener is added, the variation in the mixture weight is the same as when the thickener is added, and the capacity retention rate is also improved (Examples 1 to 8).

  On the other hand, even when SBR particles are used as a binder, a paste to which a conventional aqueous emulsion type dispersion is added has a large dispersion in the mixture weight because the mixture settles in the paste. Dropping of the mixture has also occurred (Comparative Example 1). In order to suppress sedimentation of the mixture, the addition of a thickener improves the dispersion of the mixture weight, but the capacity retention rate of 200 cycles is reduced. This is because the number of vacancies in the mixture decreased and the diffusion of lithium ions was inhibited (Comparative Example 2). Also, a negative electrode mixture paste prepared by mixing a negative electrode active material in advance with an organic solvent to prepare a negative electrode active material dispersion, adding water to the dispersion, and then adding an aqueous emulsion dispersion However, even if the dispersibility is improved immediately after the paste is produced, the coexistence of water in the paste reduces the effect of thickening, and the settling of the mixture increases due to agglomeration. It can be seen that the drop-out of the agent is still improved although it is improved as compared with Comparative Example 1, and the capacity is also reduced (Comparative Example 7).

  Further, even when a swelled SBR particle-containing dispersion is used, if the amount of SBR particles added is small, the adhesion of the mixture cannot be ensured, resulting in significant variations in the mixture and dropping of the mixture ( Comparative Example 5). On the other hand, when the amount of SBR particles added is too large, the number of vacancies in the electrode plate is reduced and the diffusion of lithium ions is inhibited, so that the capacity retention rate of 200 cycles decreases (Comparative Example 6). In the case of using 1 part by mass of PVDF as the binder, the dispersion is insufficient and the thickening effect is low, so the mixture weight varies greatly, and the mixture drops off, resulting in only a low capacity retention rate. It can be seen (Comparative Example 4). Moreover, when 5 parts by mass of PVDF is added, the dropping of the negative electrode mixture can be suppressed, but the capacity retention rate is further lowered because the vacancies in the mixture are reduced and the diffusion of lithium ions is inhibited (comparison) Example 3).

Claims (11)

  Negative electrode active material, swollen styrene butadiene rubber particles, and a non-aqueous secondary battery negative electrode mixture paste containing an organic solvent that swells styrene butadiene rubber particles as a solvent component, wherein the content of styrene butadiene rubber particles is a negative electrode A negative electrode mixture paste for a non-aqueous secondary battery that is 0.5 to 1.5 parts by mass per 100 parts by mass of the active material and substantially does not contain water.   2. The negative electrode mixture paste for a non-aqueous secondary battery according to claim 1, wherein the negative electrode mixture paste contains 1.0 part by mass or less of a thickener soluble in the organic solvent per 100 parts by mass of the negative electrode active material. .   The negative electrode mixture paste for a non-aqueous secondary battery according to claim 2, wherein the thickener is polyvinylidene difluoride or a modified product thereof. 4. The negative electrode mixture paste for a non-aqueous secondary battery according to claim 1, wherein the organic solvent has an SP value (solubility coefficient) of 12 (cal · cm ⁻³ ) ^1/2 or less.   The negative electrode for non-aqueous secondary batteries which apply | coated the negative mix paste of any one of Claims 1-4 on the electrical power collector, and dried and formed the negative mix.   A nonaqueous secondary battery comprising the negative electrode according to claim 5, a positive electrode, and a nonaqueous electrolyte.   Styrene butadiene rubber particles per 100 parts by mass of the negative electrode active material, the negative electrode active material and a dispersion containing swollen styrene butadiene rubber particles dispersed in a first organic solvent substantially free of water that swells the styrene butadiene rubber particles The manufacturing method of the negative mix paste for non-aqueous secondary batteries which has a mixing process mixed in the range of 0.5-1.5 mass parts.   In the mixing step, the negative electrode active material is the same as or different from the first organic solvent, and contains the swollen styrene butadiene rubber particles as a negative electrode active material dispersion dispersed in a second organic solvent that does not substantially contain water. The manufacturing method of the negative mix paste for non-aqueous secondary batteries of Claim 7 mixed with a dispersion liquid.   The non-aqueous secondary battery according to claim 7 or 8, wherein the negative electrode mixture paste contains 1.0 part by mass or less of a thickener that is soluble in the first organic solvent per 100 parts by mass of the negative electrode active material. For producing negative electrode material mixture paste.   The method for producing a negative electrode mixture paste for a non-aqueous secondary battery according to claim 9, wherein the thickener is polyvinylidene difluoride or a modified product thereof. 11. The negative electrode composition for a non-aqueous secondary battery according to claim 7, wherein the first organic solvent has an SP value (solubility coefficient) of 12 (cal · cm ⁻³ ) ^1/2 or less. A method for producing a paste.