KR102853401B1 - Preparation method of secondary battery - Google Patents

Abstract

An embodiment of the present invention relates to a method for manufacturing a secondary battery, which includes a process for pre-doping a negative electrode with lithium by a redox reaction, wherein a secondary battery manufactured by the method not only realizes safety, but also significantly improves energy density, further improves cycle characteristics and rate characteristics, and in particular, significantly improves initial discharge capacity and capacity retention rate.

Description

Preparation method of secondary battery

The present invention relates to a method for manufacturing a secondary battery, which includes a process of pre-doping a negative electrode with lithium by a redox reaction.

Recent advancements in the information and communication industry have led to electronic devices becoming smaller, lighter, thinner, and more portable. This has led to a growing demand for higher energy density batteries used as power sources for these devices. Lithium secondary batteries are ideally suited to meet these demands, and research is actively underway on their application not only in small batteries but also in large electronic devices such as automobiles and power storage systems.

Lithium secondary batteries have mainly used lithium-containing transition metal oxides such as LiCoO ₂ and LiMn ₂ O ₄ as positive electrodes and carbon-based materials such as graphite as negative electrodes. However, in order to achieve high capacity of lithium secondary batteries, methods for reducing the film thickness of constituent materials such as separators have been recently used, resulting in problems that adversely affect the safety of lithium secondary batteries due to excessive increase in the charging rate of active materials, thinning of separators, or high charging voltages.

Accordingly, new materials capable of achieving high energy density while realizing the reliability and safety of secondary batteries, such as alloy anode active materials such as silicon, tin, and their oxides, are attracting attention as next-generation high-capacity materials. The oxide alloy anode active materials have the advantage of having less volume change than non-oxide alloy anode active materials and a charge/discharge capacity that is four times higher than that of graphite. However, the oxide alloy anode active materials have the problem of having a large irreversible capacity during the first charge/discharge.

Typically, the negative active material, typically composed of silicon oxide, undergoes an alloying reaction during initial charging, forming a material capable of reversibly absorbing and releasing lithium and a material (irreversible material) that cannot absorb or release lithium. This leads to a problem in that the lithium ions initially present in the positive electrode are reduced.

In this regard, Japanese Patent Application Laid-Open No. 2002-313324 discloses a method for improving initial efficiency by directly adding lithium metal to the negative electrode during its manufacture. However, when lithium metal is directly added to the negative electrode, gelation occurs during the manufacture of the negative electrode active material composition, which can cause processing and performance issues in the secondary battery.

In addition, Japanese Patent Application Laid-Open No. 2008-084842 discloses a method of doping lithium metal by bringing it into contact with a negative electrode during the manufacture of a secondary battery. However, in this case, a reaction with a large amount of heat generation may occur with silicon oxide or tin oxide, which may pose a problem with the safety of the secondary battery.

Meanwhile, a technology for directly doping lithium into silicon oxide (SiOx(0.9≤x≤1.6)) materials is disclosed in Japanese Patent Application Laid-Open No. 2011-222153 and Japanese Patent Registration No. 6274253. However, when following the technology presented in these documents, satisfactory secondary battery characteristics are not obtained, or the reaction speed is slow, making mass production and practical use difficult.

Japanese Patent Publication No. 2002-313324 Japanese Patent Publication No. 2008-084842 Japanese Patent Publication No. 2011-222153 Japanese Patent Publication No. 6274253

The present invention has been designed to solve the problems of the above-mentioned prior art, and the technical problem to be solved by the present invention is to provide a method for manufacturing a secondary battery capable of improving energy density, cycle characteristics, and rate characteristics.

In order to achieve the above object, one embodiment of the present invention comprises (1) a first step of manufacturing a negative electrode by applying a negative electrode active material composition including a silicon-based negative electrode active material to a negative electrode current collector; (2) a second step of placing the negative electrode and a lithium metal plate in a reaction vessel and then performing a redox reaction to predope the negative electrode with lithium; and (3) the negative electrode predoped with lithium. A method for manufacturing a secondary battery is provided, including a third process for manufacturing an electrode by sequentially stacking a separator and a cathode including a metal oxide.

The method for manufacturing a secondary battery according to the above embodiment can not only realize safety, but also significantly improve energy density, further improve cycle characteristics and rate characteristics, and in particular, significantly improve the initial discharge capacity and capacity retention rate of the secondary battery.

FIG. 1 illustrates an example of a process for pre-doping a negative electrode with lithium in a method for manufacturing a secondary battery according to one embodiment of the present invention.

The present invention is not limited to the contents disclosed below, and may be modified in various forms as long as the gist of the invention is not changed.

As used herein, the term “comprising” means that other components may be included unless otherwise stated.

Additionally, all numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification should be understood to be modified by the term “about” in all cases unless otherwise specified.

A method for manufacturing a secondary battery according to one embodiment of the present invention comprises: (1) a first step of manufacturing an anode by applying a negative electrode active material composition including a silicon-based negative electrode active material to a negative electrode current collector; (2) a second step of placing the negative electrode and a lithium metal plate in a reaction vessel and then performing a redox reaction to predope the negative electrode with lithium; and (3) the negative electrode predoped with lithium. A third process for manufacturing an electrode by sequentially stacking a separator and an anode including a metal oxide;

The above first process is a process for manufacturing a negative electrode by applying a negative electrode active material composition including a silicon-based negative electrode active material to a negative electrode current collector. In addition, the above first process may further include a step of rolling and drying after applying the silicon-based negative electrode active material composition to the negative electrode current collector, which may be performed using a method commonly used.

Specifically, the negative electrode is manufactured by applying a negative electrode active material composition comprising a silicon-based negative electrode active material, a conductive agent, and a binder to a negative electrode current collector, and then drying the same. Specifically, the negative electrode can be manufactured by mixing and stirring the silicon-based negative electrode active material with a binder, a solvent, and, if necessary, a conductive agent and a dispersant to manufacture a negative electrode active material composition, and then applying the same to a current collector, rolling, and drying the same.

According to one embodiment of the present invention, the negative electrode includes a silicon-based negative electrode active material, and the silicon-based negative electrode active material may include at least one selected from the group consisting of silicon fine particles, a compound represented by SiOx (0.3≤x≤1.6), silicon dioxide, and a silicate containing magnesium, calcium, aluminum, or a combination thereof.

In the above negative active material, the content of silicon may be 30 wt% to 80 wt%, specifically 40 wt% to 80 wt%, more specifically 40 wt% to 70 wt%, and especially 40 wt% to 60 wt%, based on the total weight of the negative active material. When the content of silicon is less than 30 wt%, the amount of negative active material that acts upon absorption and release of lithium is small, so that the charge/discharge capacity of the secondary battery may decrease, and conversely, when it exceeds 80 wt%, the charge/discharge capacity of the secondary battery may increase, but the expansion and contraction of the electrode during charge/discharge may become excessively large, so that the cycle characteristics may decrease.

The above silicon particles may be crystalline or amorphous, and specifically, may be amorphous or a similar phase. When the silicon particles are amorphous or a similar phase, expansion or contraction during charging and discharging of a lithium secondary battery is small, and battery performance, such as capacity characteristics, can be further improved.

In addition, the silicon fine particles may be uniformly dispersed in or may be present while surrounding at least one selected from the group consisting of a compound represented by SiOx (0.3≤x≤1.6), silicon dioxide, and a silicate containing magnesium, calcium, aluminum, or a combination thereof, and in this case, expansion or contraction of silicon can be suppressed, thereby improving the performance of the secondary battery. Meanwhile, in the case where the silicon fine particles form a carbon layer containing a carbon film, the structure may likewise be dispersed in a silicon oxide compound or silicate.

In addition, when the silicon-based negative electrode active material includes silicon microparticles, it is preferable because the large specific surface area of the silicon microparticles forms a lithium alloy, thereby suppressing bulk destruction. The silicon microparticles react with lithium during charging to form Li _4.2 Si, and revert to silicon during discharge.

The above silicon particles may have a crystallite size of 2 nm to 10 nm, specifically 2 nm to 9 nm, and more specifically 2 nm to 8 nm, when calculated by the Sherrer equation based on the full width at half maximum (FWHM) of the diffraction peak of Si (220) centered around 2θ = 47.5° during X-ray diffraction (Cu-Kα) analysis using copper as a cathode target. If the crystallite size of the silicon particles exceeds 10 nm, cracks may occur in the cathode active material due to volume expansion or contraction during charge and discharge, which may deteriorate the cycle characteristics. In addition, if the crystallite size of the silicon particles is less than 2 nm, the charge and discharge capacity may decrease, and since the reactivity increases, changes in the physical properties may occur during storage, which may cause processability problems. When the crystallite size of the silicon microparticles is within the above range, there is almost no area that does not contribute to charge and discharge, and the decrease in the Coulomb efficiency, which represents the ratio of charge capacity to discharge capacity, i.e., charge and discharge efficiency, can be suppressed.

When the above-mentioned silicon microparticles are further refined to an amorphous or crystalline size of approximately 2 to 6 nm, the density of the negative active material increases, approaching the theoretical density, and pores can be significantly reduced. This enhances the density and strength of the matrix, thereby preventing cracking, thereby further improving the initial efficiency and cycle life characteristics of the secondary battery.

In addition, the negative active material may include a compound represented by SiOx(0.3≤x≤1.6) or a silicon oxide compound such as silicon dioxide. The compound may be specifically SiOx(0.5≤x≤1.6), silicon dioxide or a mixture thereof, and more specifically, SiOx(0.7≤x≤1.2), silicon dioxide or a mixture thereof. By including such a silicon oxide compound, when applied to a secondary battery, the capacity can be improved and volume expansion can be reduced.

The above silicon oxide compound may be amorphous or may have a structure in which silicon fine particles (amorphous) of several nm to several tens of nm in size are dispersed in the silicon oxide compound as confirmed by energy dispersive X-ray diffraction (EDX) or transmission electron microscopy.

The above silicon oxide compound can be obtained by a method including a step of cooling and precipitating silicon oxide gas generated by heating a mixture of silicon dioxide and sub-micron silicon powder or silicon fine particles of 50 nm or less.

The above silicon oxide compound is amorphous and can undergo an irreversible reaction with lithium ions during discharge to form Li-Si-O or Si+Li ₂ O. Therefore, as the content of silicon dioxide in the silicon oxide compound increases, the initial irreversible reaction increases and the initial efficiency may decrease.

The above silicon oxide compound may be included in an amount of 5 mol% to 20 mol% relative to the entire negative electrode active material. If the content of the silicon oxide compound is less than 5 mol%, the volume expansion and lifespan characteristics of the secondary battery may deteriorate, and if it exceeds 20 mol%, the initial irreversible reaction of the secondary battery may increase.

According to one embodiment of the present invention, the negative active material may not include silicon dioxide. This is because, while the formation of lithium silicate can be suppressed when silicon is inserted, thereby improving initial efficiency, the inclusion of silicon dioxide may cause an irreversible reaction that generates lithium silicate when silicon dioxide reacts with lithium, thereby reducing the initial efficiency.

Additionally, the negative active material may include a silicate containing magnesium, calcium, aluminum, or a combination thereof. The magnesium, calcium, aluminum, or a combination thereof may be included in a doped form. Specifically, the negative active material may include a silicate containing magnesium, and the magnesium may be included in a doped form.

According to one embodiment of the present invention, the silicate containing magnesium may include MgSiO ₃ crystals, Mg ₂ SiO ₄ crystals, or a mixture thereof.

Additionally, according to one embodiment, the silicate containing magnesium comprises MgSiO ₃ crystals and may further comprise Mg ₂ SiO ₄ crystals.

In the case of the silicate containing the above magnesium, when doping with magnesium, for example, when SiO and Mg are reacted in a 1:1 ratio, if the elements are uniformly distributed, thermodynamically, only Si and MgO will exist, but if the element concentration distribution is non-uniform, other substances such as unreacted SiO, metallic Mg, etc. may exist in addition to Si and MgO.

According to one embodiment of the present invention, the negative active material may include Mg ₂ SiO ₄ crystals and MgO, but may include substantially more MgSiO ₃ crystals to improve charge/discharge capacity and initial efficiency.

As used herein, “substantially comprises” or “substantially comprises” means to include as a major component or to include primarily.

Specifically, containing substantially a large amount of MgSiO ₃ means containing a large amount of MgSiO ₃ crystals compared to Mg ₂ SiO ₄ crystals, and for example, it means that the ratio of the intensity (IF) of the X-ray diffraction peak corresponding to Mg ₂ SiO ₄ crystals appearing in the range of 2θ = 22.3° to 23.3° in X-ray diffraction analysis and the intensity (IE) of the X-ray diffraction peak corresponding to MgSiO ₃ crystals appearing in the range of 2θ = 30.5° to 31.5°, IF/IE, is 1 or less.

In the above silicate, the content of magnesium relative to SiO _X can affect the initial discharge characteristics or the cycle characteristics during charge and discharge.

Silicon in the above SiO _X can significantly improve the initial discharge characteristics by alloying with lithium atoms. Meanwhile, when the magnesium silicate of the MgSiO ₃ crystal is included in a substantial amount, the refinement of the silicon fine particles is maintained, so that the strength of the matrix can be further strengthened. In addition, the density can be improved, so that a dense matrix can be formed. As a result, the initial efficiency can be improved or the cycle improvement effect can be greatly improved during charge and discharge. However, when the Mg ₂ SiO ₄ crystal is included in an excessive amount, the size of the silicon fine particles can increase, which can cause a decrease in the strength or density of the matrix, and the alloying of silicon atoms and lithium atoms can be reduced, which can cause a deterioration in the initial discharge characteristics of the secondary battery.

When the above-described negative active material comprises a silicate containing magnesium, for example, when manufacturing a negative active material composition using polyimide as a binder, the chemical reaction between the negative active material and the binder can be suppressed compared to when lithium is doped instead of magnesium. Therefore, by using such a negative active material, the safety of the negative active material composition can be improved, and thereby not only the safety of the negative electrode but also the cycle characteristics of the secondary battery can be improved. In addition, since the silicate containing magnesium is difficult to react with lithium ions, when applied to an electrode, it is thought that the cycle characteristics can be improved by reducing the amount of expansion and contraction of the electrode when lithium ions rapidly increase. In addition, it is thought that the strength of the matrix, which is a continuous phase surrounding the silicon fine particles, can be strengthened by the silicate.

When the above-mentioned negative active material comprises a silicate containing magnesium, the doping amount of magnesium, i.e., the content, may be 3 wt% to 15 wt%, specifically 4 wt% to 12 wt%, based on the total weight of the negative active material. When the content of magnesium is 3 wt% or more, an improvement in the first-cycle efficiency of the secondary battery can be achieved, and when it is 15 wt% or less, it may be advantageous in terms of the cycle characteristics and handling safety of the secondary battery.

According to another embodiment of the present invention, when the negative electrode active material is a silicate containing calcium, aluminum or a combination thereof, the doping amount, i.e., content, of the calcium or aluminum may be 3 wt% to 15 wt%, specifically 4 wt% to 12 wt%, based on the total weight of the negative electrode active material.

According to one embodiment of the present invention, the silicate containing magnesium, calcium or aluminum can be represented by the following chemical formula 1:

[Chemical Formula 1]

M _x SiO _y

In the above chemical formula 1,

M is one or more metals selected from the group consisting of Mg, Ca and Al,

x is 0.5≤x≤2,

y is 2.5≤y≤4.

The silicate of the above chemical formula 1 is an oxide having a more negative Gibbs free energy thermodynamically than a silicon oxide compound, and is amorphous and stable to lithium, which can play a role in suppressing the occurrence of an initial irreversible reaction.

In a method for manufacturing a secondary battery according to one embodiment of the present invention, the silicon-based negative electrode active material may be manufactured by a process including the steps of: mixing silicon powder and silicon dioxide powder to obtain a silicon-silicon oxide raw material powder mixture; heating and depositing the raw material powder mixture to obtain a silicon oxide composite; and crushing and classifying the silicon oxide composite to obtain a silicon-based negative electrode active material.

Specifically, in the method for manufacturing the above silicon-based negative electrode active material, the first step may include a step of mixing silicon powder and silicon dioxide powder to obtain a silicon-silicon oxide raw material powder mixture.

When mixing the above silicon powder and silicon dioxide powder, the mixing molar ratio of the silicon dioxide powder to the silicon powder, i.e., the molar ratio of silicon dioxide powder/silicon powder, may be greater than 0.9 and less than 1.1, specifically, 1.01 or more and 1.08 or less.

In the method for manufacturing the above silicon-based negative electrode active material, the second step may include a step of heating and depositing the raw material powder mixture to obtain a silicon oxide composite.

The heating and deposition of the raw material powder mixture in the second step may be performed at a temperature of 800°C to 1600°C, specifically 1200°C to 1500°C. If the heating and deposition temperature is lower than 800°C, the reaction may be difficult to proceed, resulting in reduced productivity. If it exceeds 1600°C, the raw material powder mixture may melt, resulting in reduced reactivity.

In the method for manufacturing the above silicon-based negative electrode active material, the third step may include a step of pulverizing and classifying the silicon oxide complex to obtain the silicon-based negative electrode active material.

The above pulverization can be performed by pulverizing and classifying the silicon-based negative electrode active material so that the average particle size (D ₅₀ ) is 0.5 ㎛ to 15 ㎛, specifically 2 ㎛ to 10 ㎛, and more specifically 4 ㎛ to 8 ㎛. The above pulverization can be performed using a conventionally used pulverizer or sieve.

Additionally, according to one embodiment of the present invention, between the second step and the third step, a step of cooling the silicon oxide complex may be further included.

The above cooling can be performed at room temperature by injecting an inert gas. The inert gas can be at least one selected from carbon dioxide, argon (Ar), water vapor (H ₂ O), helium (He), nitrogen (N ₂ ), and hydrogen (H).

Meanwhile, according to one embodiment of the present invention, after the pulverization and classification in the third step, a step of forming a carbon layer including a carbon film on the surface of the silicon-based negative electrode active material using a chemical pyrolysis deposition method may be further included.

The above carbon layer formation can be achieved by injecting at least one carbon source gas selected from among a compound represented by the following chemical formula 2; a compound represented by the following chemical formula 3; a compound represented by the following chemical formula 4; and at least one hydrocarbon gas selected from among acetylene, benzene, toluene, and xylene, and reacting the carbon source gas in a gaseous state at 600°C to 1200°C, thereby forming a carbon layer including a carbon film on the surface of the negative electrode active material.

[Chemical Formula 2]

C _n H _(2n+2-A) [OH] _A

In the above chemical formula 2,

n is an integer from 1 to 20,

A is 0 or 1,

[Chemical Formula 3]

C _m H _2m

In the above chemical formula 3,

m is an integer from 2 to 6,

[Chemical Formula 4]

C _x H _y O _z

In the above chemical formula 4,

x is an integer from 1 to 20 ,

y is an integer from 0 to 20,

z is 1 or 2.

The compound represented by the above chemical formula 2 may include, for example, at least one selected from methane (CH ₄ ), ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH), and propanol (C ₃ H ₈ O), and the compound represented by the above chemical formula 3 may include at least one selected from methylene (CH ₂ ), ethylene (C ₂ H ₄ ), and propylene (C ₃ H ₆ ). Meanwhile, the compound represented by the above chemical formula 4 may include, as an oxygen-containing gas, at least one selected from carbon monoxide (CO) and carbon dioxide (CO ₂ ).

In addition, when forming the carbon layer, an inert gas including at least one selected from carbon dioxide, argon (Ar), water vapor (H ₂ O), helium (He), nitrogen (N ₂ ), and hydrogen (H) may be injected. According to one embodiment, when water vapor is included when forming the carbon layer, the negative electrode active material may exhibit higher electrical conductivity. Specifically, when water vapor is included when forming the carbon layer, the negative electrode active material may include a highly crystalline carbon film on its surface by reaction with the gas mixture, and may exhibit high electrical conductivity even when a smaller amount of carbon is coated. The content of water vapor in the gas mixture is not particularly limited, and may be, for example, 0.01% by volume to 10% by volume based on 100% by volume of the total carbon source gas.

According to one embodiment, a mixture of CH ₄ and CO ₂ gas, or a mixture of CH ₄ , CO ₂ and H ₂ O gas, may be used as a carbon source gas when forming the carbon layer. When a mixture of CH ₄ and CO ₂ gas is used, the molar ratio of CH ₄ : CO ₂ may be about 1:0.20 to 0.50, specifically about 1:0.25 to 0.45, and more specifically about 1:0.30 to 0.40. When using a mixture of CH ₄ , CO ₂ and H ₂ O, the molar ratio of CH ₄ : CO ₂ : H ₂ O may be about 1 : 0.20 to 0.50 : 0.01 to 1.45, specifically about 1 : 0.25 to 0.45 : 0.10 to 1.35, and more specifically about 1 : 0.30 to 0.40 : 0.50 to 1.0.

According to another embodiment, C0, _CO2 or a combination thereof may be used as a carbon source gas when forming the carbon layer.

According to another embodiment, when forming the carbon layer, CH ₄ may be included as a carbon source gas, and N ₂ may be used as an inert gas. The mixing ratio of the CH ₄ and N ₂ mixed gases may be about 1:0.20 to 0.50 molar ratio, specifically about 1:0.25 to 0.45 molar ratio, and more specifically about 1:0.30 to 0.40 molar ratio.

In some embodiments, the inert gas may not be included.

In addition, the heat treatment temperature, the composition of the gas mixture, etc. during the above reaction can be selected by considering the amount of the desired carbon film, etc.

The heat treatment temperature when forming the above carbon layer may be 600°C to 1200°C, specifically 700°C to 1100°C, and more specifically 700°C to 1000°C.

Additionally, the pressure during the heat treatment can be controlled by adjusting the amount of the introduced gas mixture. For example, the pressure during the heat treatment can be 1 atm or more, for example, 1 to 5 atm, but is not limited thereto.

In addition, the heat treatment time is not limited, but can be appropriately adjusted depending on the heat treatment temperature, the pressure during the heat treatment, the composition of the gas mixture, and the desired amount of carbon coating. For example, the heat treatment time may be 10 minutes to 100 hours, specifically 30 minutes to 90 hours, and more specifically 50 minutes to 40 hours. According to one embodiment, as the heat treatment time increases, the thickness of the carbon film formed may become thicker, and when adjusted to an appropriate thickness, the electrical properties of the negative electrode active material may be improved.

According to an embodiment of the present invention, a carbon film can be formed uniformly and thinly over the entire surface of the negative electrode active material, and it is preferable that the carbon film forms a substantial amount of carbon nanofibers, graphene, graphene oxide, and reduced graphene oxide.

Furthermore, by inducing a vapor phase reaction of a carbon source gas, a carbon layer comprising a uniform carbon film can be formed on the surface of the negative electrode active material even at relatively low temperatures. The negative electrode active material thus produced is resistant to carbon film desorption. Furthermore, by inducing a vapor phase reaction, a carbon film with high crystallinity can be formed. Therefore, when used as a negative electrode active material, its electrical conductivity can be improved without structural changes.

The above carbon layer may include at least one selected from the group consisting of carbon nanofibers, graphene, graphene oxide, and reduced graphene oxide.

The structure of the above carbon layer may be a layer, a nano sheet type, or a structure in which several flakes are mixed.

The above film may mean a film in which graphene is continuously and uniformly formed on the surface of one or more selected from silicon microparticles, silicon oxide compounds, magnesium silicate, and reduction products thereof.

In addition, the above nanosheet may mean a case where carbon nanofibers or graphene-containing materials are irregularly formed on the surface of at least one selected from the group consisting of silicon microparticles, compounds represented by SiOx (0.3≤x≤1.6), silicon dioxide, and silicates including magnesium, calcium, aluminum, or combinations thereof.

Additionally, the above flake may mean a case where a part of the nanosheet or film is broken or deformed.

After forming the carbon layer, a step of crushing and classifying the silicon-based negative electrode active material may be further included.

The average particle size (D ₅₀ ) of the negative electrode active material forming the above carbon layer can be formed by pulverization as described above. In addition, classification can be performed to refine the particle size distribution after pulverization, and dry classification, wet classification, or dividing classification can be used. The above dry classification mainly uses air current to sequentially or simultaneously perform the processes of dispersion, separation (separation of fine particles and defective particles), capture (separation of solid and gas), and discharge, so that the classification efficiency is not lowered due to interference between particles, particle shape, confusion in the flow of air current, velocity distribution, or the influence of static electricity, so that the moisture or oxygen concentration of the air current used can be adjusted by performing pre-treatment (adjustment of moisture, dispersibility, humidity, etc.). In addition, by performing pulverization and classification at once, a desired particle size distribution can be obtained.

By using a negative electrode active material having the above average particle size through the above pulverization and classification treatment, the initial efficiency or cycle characteristics can be improved by about 10% to 20% compared to before classification. The negative electrode active material after the above pulverization and classification has a Dmax of about 10 μm or less, in which case the specific surface area of the negative electrode active material can be reduced, which can reduce the lithium supplemented to the SEI layer.

In addition, the specific surface area of the negative active material may be 2 m2/g to 20 m2/g. When the specific surface area of the negative active material is less than 2 m2/g, the rate characteristics of the secondary battery may deteriorate, and when it exceeds 20 m2/g, the contact area with the electrolyte may increase, which may promote the decomposition reaction of the electrolyte or cause a battery side reaction. The specific surface area of the negative active material may be specifically 3 m2/g to 15 m2/g, and more specifically 3 m2/g to 10 m2/g. The specific surface area can be measured by the BET method using nitrogen adsorption, and for example, a specific surface area measuring device generally used in the art (such as Macsorb HM (model 1210) of MOUNTECH or Belsorp-mini Ⅱ of MicrotracBEL) can be used.

The specific gravity of the above-mentioned negative active material may be 1.8 g/cm3 to 3.2 g/cm3, specifically 2.5 g/cm3 to 3.2 g/cm3. The higher the specific gravity, the fewer pores there are in the negative active material, so the conductivity can be improved, and the strength of the matrix can be strengthened, thereby improving the initial efficiency or cycle life characteristics. In this specification, the specific gravity can be expressed in the same meaning as true specific gravity, density, or true density. For the measurement of the specific gravity, for example, the measurement of the specific gravity by a dry density meter can use Accupick II1340 manufactured by Shimadzu Corporation as a dry density meter. The purge gas used can be helium gas, and after repeating the purge 200 times in a sample holder set to a temperature of 23°C, the measurement can be performed.

According to one embodiment of the present invention, the negative electrode active material including the carbon layer can suppress volume expansion and reduce the phenomenon of silicon particles, silicon oxide compounds, or silicates being compressed and shrunk by directly growing a carbon layer, particularly a material containing carbon nanofibers or graphene, which has excellent conductivity and is flexible in volume expansion, on its surface. In addition, since the silicon contained in the negative electrode active material can be controlled to directly react with the electrolyte by the carbon nanofibers or graphene, the formation of an SEI layer on the electrode can be reduced.

The carbon content of the above carbon layer may be 2 wt% to 10 wt%, specifically 4 wt% to 8 wt%, based on the total weight of the silicon-based negative electrode active material. When the carbon content is less than 2 wt%, the conductivity of the negative electrode may be reduced, and when it exceeds 10 wt%, the carbon content may become excessively large, thereby reducing the capacity of the negative electrode, and thus it may be difficult to achieve the energy density improvement effect desired in the present invention. Examples of the method for forming the carbon layer include a method of chemical vapor deposition (CVD) in an organic gas and/or vapor, or a method of introducing an organic gas and/or vapor into a reactor during heat treatment.

In addition, the cumulative 50% average particle diameter (D ₅₀ ) of the particle distribution of the silicon-based negative electrode active material on which the carbon layer is formed may be 0.5 ㎛ to 15 ㎛, specifically 2 ㎛ to 10 ㎛, more specifically 3 ㎛ to 10 ㎛ or 4 ㎛ to 8 ㎛. If the D ₅₀ is too small, the bulk density may become excessively small, which may lower the charge/discharge capacity per unit volume, and conversely, if the D ₅₀ is too large, it may become difficult to manufacture the electrode film of the secondary battery, and there is a risk of peeling off from the current collector. Meanwhile, the D ₅₀ is a value measured as a weight average value D ₅₀ (i.e., the particle diameter or median diameter when the cumulative weight becomes 50%) in particle size distribution measurement according to a laser diffraction method.

According to one embodiment of the present invention, the average thickness of the carbon layer may be 10 nm to 200 nm, specifically 20 nm to 200 nm.

If the average thickness of the carbon layer is 10 nm or more, conductivity can be improved, and if it is 200 nm or less, capacity reduction of the secondary battery can be suppressed. The average thickness of the carbon layer can be calculated, for example, by the following procedure.

First, the negative active material is observed using a transmission electron microscope (TEM) at an arbitrary magnification. The magnification is preferably sufficient for visual inspection. Next, the thickness of the carbon layer is measured at 15 arbitrary points. In this case, it is preferable to measure the measurement locations randomly, rather than focusing on a specific location as much as possible. Finally, the average thickness of the carbon layer at the 15 points is calculated.

In addition, when using a silicon-based negative electrode active material according to one embodiment of the present invention, the battery capacity per unit weight of the negative electrode active material can be 1500 to 3000 mAh/g, so that a secondary battery having high conductivity, relatively small volume expansion, and improved cycle characteristics can be provided. In addition, when used in combination with a carbon-based negative electrode active material, the coulombic efficiency and cycle characteristics can be improved.

In this way, when using a negative electrode active material including a carbon layer, structural collapse due to volume expansion of silicon particles, silicon oxide compounds, and silicates can be suppressed without a binder during the manufacture of a negative electrode active material composition, and by minimizing an increase in resistance, it can be usefully used in the manufacture of electrodes and lithium secondary batteries having excellent electrical conductivity and capacity characteristics.

In addition, according to one embodiment of the present invention, the negative electrode active material may further include a carbon-based negative electrode material.

Specifically, the negative electrode active material may be a mixture of the silicon-based negative electrode active material and the carbon-based negative electrode material. In this case, the electrical resistance of the negative electrode active material can be reduced, and at the same time, expansion stress accompanying charging can be alleviated. The carbon-based negative electrode material may include, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon, carbon fiber, carbon nanotube, pyrolytic carbon, coke, glassy carbon fiber, organic polymer compound sintered body, and carbon black.

The content of the carbon-based negative electrode material may be 30 wt% to 95 wt%, specifically 30 wt% to 90 wt%, and more specifically 50 wt% to 80 wt%, based on the total weight of the negative electrode active material. In particular, when the negative electrode active material includes silicon particles, since the silicon particles do not cause volume expansion, a secondary battery having excellent cycle characteristics can be obtained when mixed with the carbon-based negative electrode material.

The binder is not particularly limited, but may include, for example, one or more selected from the group consisting of fluorine-based resins such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, and polytetrafluoroethylene; rubber-based materials such as fluororubber and styrene butylene rubber (SBR); polyolefins such as polyethylene and polypropylene; acrylic resins; and polyimide-based resins. However, since the silicon-based negative electrode active material has a large volume change during charge and discharge, a material having excellent adhesiveness may be more preferable, and for example, the binder may include a polyimide-based resin including polyimide, polyamideimide, or a mixture thereof. In addition, when manufacturing a negative electrode, the mixing amount with the binder can be used in consideration of the type, particle size, shape, mixing composition amount, etc. of the negative electrode active material of the present invention, and by mixing appropriately in consideration of the strength and adhesiveness of the negative electrode, etc., good cycle characteristics of the secondary battery can be obtained.

The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, and the like; conductive fibers such as carbon fiber or metal fiber; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

The above dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The above-mentioned negative current collector is not particularly limited, and examples thereof include copper foil, stainless steel foil, or titanium foil. In addition, a collector with an embossed surface or a porous collector, such as expanded metal, mesh, or punched metal, may be used.

In addition, the second process is a process of predoping the negative electrode with lithium by placing the negative electrode and lithium metal plate in a reaction tank and then performing an oxidation-reduction reaction.

Specifically, referring to FIG. 1, after the negative electrode (10) and the lithium metal plate (30) obtained in the first process are placed in a reaction tank, a redox reaction can be performed, and at this time, the redox reaction can be performed in an electrolyte (20). The electrolyte (20) can include a non-aqueous electrolyte, a polymer electrolyte, or a polymer gel electrolyte. The redox reaction can be performed, for example, by doping the negative electrode with lithium through a reduction reaction at 0.0003 to 0.001 V with the lithium metal plate in a non-aqueous electrolyte, and then dedoping by performing an oxidation reaction until the voltage reaches 1.0 to 2.0 V, thereby obtaining a negative electrode electrochemically pre-doped with lithium.

The thickness of the lithium metal plate may be 10 μm to 30 μm, specifically 15 μm to 25 μm. Considering the pre-doping speed, a lithium metal plate with a large surface area is preferable, and considering the handleability, productivity, and pre-doping process atmosphere of the lithium metal plate, a lithium metal plate with a small surface area may be good. If the thickness of the lithium metal plate satisfies the above range, it may be good in terms of lithium residue suppression, pre-doping speed, and productivity. In addition, the density of the lithium metal plate may be 0.3 g/cm ³ to 0.8 g/cm ³ .

The negative electrode can be predoped with lithium by the above redox reaction. In this specification, predoping means doping lithium by absorbing and supporting lithium in the negative electrode active material prior to normal charge and discharge between the positive and negative electrodes. Accordingly, the predoping may include a process of doping the negative electrode with an amount of lithium equivalent to the initial irreversible capacity of the negative electrode by causing absorption and desorption of lithium while electrochemically contacting the negative electrode with a lithium metal plate.

In general, silicon-based negative electrode active materials exhibit high capacity, but as the cycle progresses, the volume expansion rate exceeds 300%, which can lead to increased resistance and increased electrolyte side reactions, and problems due to the formation of a solid electrolyte interface (SEI) layer, such as damage to the electrode structure, can be aggravated. In addition, silicon oxide-based negative electrode active materials have a lower volume expansion rate than silicon-based negative electrode active materials, but the initial irreversible capacity increases due to _Li2O caused by oxygen in the negative electrode active material, which lowers the energy density and causes problems of deterioration in cycle characteristics and rate characteristics.

According to one embodiment of the present invention, in order to obtain a secondary battery having a high energy density, it is important to reduce the irreversible capacity of the negative electrode active material as much as possible. Accordingly, the present invention can reduce the initial irreversible capacity of the negative electrode by pre-doping the negative electrode including the silicon-based negative electrode active material with lithium, prevent the penetration of metal ions into the SEI on the surface of the negative electrode, and improve the high energy density. The pre-doping can compensate for the irreversible capacity or, even when an active material that does not include lithium is used in the positive electrode, include lithium necessary for charge and discharge in the negative electrode, thereby improving the performance of the secondary battery.

An example of a pre-doping method according to one embodiment of the present invention includes a method of doping the negative electrode with an amount of lithium equivalent to the irreversible capacity by performing a redox reaction using a lithium metal plate as a counter electrode in an electrolyte used in a secondary battery.

As described above, by positioning the negative electrode (10) and the lithium metal plate (30) in the electrolyte (20) and then performing a redox reaction, the safety of the secondary battery can be secured compared to the method of directly attaching or depositing the lithium metal plate onto the negative electrode. The method of directly attaching or depositing the lithium metal plate onto the negative electrode can have a safety problem because the lithium metal plate can have a negative effect on the separator due to needle-like crystals (dendrites) by directly attaching the lithium metal plate onto the negative electrode.

In addition, according to another embodiment of the present invention, a pre-doping method may include a method of removing excess lithium (leaving the irreversible capacity in the negative electrode) by de-doping lithium after the doping. The pre-doping may include doping the negative electrode with lithium through a reduction reaction, leaving the lithium for the initial irreversible capacity of the negative electrode, and then releasing (dedoping) the remaining amount of lithium through an oxidation reaction. For example, a redox reaction may be performed in a non-aqueous electrolyte to pre-dope the negative electrode with an amount of lithium corresponding to the initial irreversible capacity, and then releasing (dedoping) the remaining amount of lithium, leaving the lithium for the initial irreversible capacity of the negative electrode. The pre-doping method, particularly when pre-doping the negative electrode with an amount of lithium corresponding to the irreversible capacity through de-doping, can achieve an initial efficiency of close to 100%. As a result, the cathode/anode capacity ratio (N/P ratio) can approach 1.0, which can ultimately improve the capacity of the secondary battery itself. Furthermore, while pre-doping with lithium can entail a large exothermic reaction, controlling the current during lithium doping allows for control of the rate of this reaction, which can offer significant safety advantages.

Therefore, according to the present invention, by doping the negative electrode with lithium through a redox reaction using the pre-doping method, or by dedoping after doping, the negative electrode can be pre-doped with lithium in an amount equivalent to the irreversible capacity of lithium. This allows the negative electrode to reduce volume expansion caused by the absorption and release of lithium. In addition, since the doping speed can be controlled by controlling the current, the safety of doping, such as preventing large heat generation, can be ensured. In particular, when doping is performed in large quantities, the method can be advantageous for mass production because the temperature can be controlled.

Additionally, in the second process, after pre-doping, the redox reaction may be performed one or more more times to remove lithium doped in excess on the negative electrode.

Lithium salts that can be included as electrolytes used in the present invention can be used without limitation those commonly used in electrolytes for lithium secondary batteries, and for example, as anions of the lithium salts, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF _{3 CF 2 (} CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- .

In the electrolyte used in the present invention, the organic solvent contained in the electrolyte can be used without limitation those commonly used in electrolytes for lithium secondary batteries, and representative examples thereof include any one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfuroxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, methyl acetate, methyl formate, and tetrahydrofuran, or a mixture of two or more thereof. The concentration of the electrolyte is not particularly limited, but may be, for example, 0.5 to 2 mol/L. It is preferable to use the above electrolyte having a moisture content of 100 ppm or less. Meanwhile, the term "non-aqueous electrolyte" used in this specification not only refers to a concept including non-aqueous electrolyte and organic electrolyte, but may also refer to a concept including gel-like and solid electrolyte.

According to one embodiment of the present invention, a secondary battery including a negative electrode including a silicon-based negative electrode active material pre-doped with lithium not only has a significantly improved energy density, but also can further improve cycle characteristics and rate characteristics.

The third process is a cathode pre-doped with lithium, This is a process for manufacturing an electrode by sequentially stacking a separator and a cathode containing a metal oxide active material.

When manufacturing the secondary battery, the positive electrode active material included in the positive electrode is not particularly limited as long as it is a material that can electrochemically absorb and release lithium. For example, it may include a metal oxide active material that includes electrochemically releasable lithium, and the metal oxide active material may specifically include an oxide having a spinel structure including lithium cobalt oxide, lithium manganese oxide, or a mixture thereof. Alternatively, the positive electrode active material may include at least one selected from the group consisting of lithium composite cobalt oxide, lithium composite nickel oxide, lithium composite manganese oxide, and lithium composite titanium oxide, and an active material obtained by adding at least one heterometal element to the composite oxide may be used. In addition, as long as it does not include electrochemically releasable lithium, at least one metal oxide selected from the group consisting of manganese, vanadium, and iron, a disulfide-based compound, a polyacene-based compound, and activated carbon, and the like may be used.

In addition, the separator may include a conventional porous polymer film used as a conventional separator, for example, porous propylene. In addition, the separator may use a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, alone or in a laminated manner. In addition, an insulating thin film having high ion permeability and mechanical strength may be used. The separator may include a safety reinforced separator (SRS) in which a ceramic material is thinly coated on the surface of the separator.

In addition, conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc., may be used, but are not limited thereto. The separator may have a thickness of 10 μm to 30 μm, specifically 15 μm to 25 μm.

There is no particular limitation on the external shape, size, etc. of the secondary battery of the present invention, but it may include a cylindrical shape, a square shape, a pouch shape, a film shape, or a coin shape, etc., depending on each use.

The method for manufacturing a secondary battery according to the above embodiment includes a negative electrode including a silicon-based negative electrode active material pre-doped with lithium, thereby not only realizing the safety of the secondary battery, but also significantly improving the energy density and further improving the cycle characteristics and rate characteristics.

[Example]

The above contents are explained in more detail with the following examples. However, the following examples are only intended to illustrate the present invention, and the scope of the examples is not limited to these examples.

Example 1

<Manufacturing of the cathode>

A silicon-based negative electrode active material (manufactured by DAEJOO) having a carbon layer having the following properties was used, and a negative electrode active material composition was prepared by mixing Super-P (TIMCAL) as a conductive agent and polyacrylic acid (PAA, Poly Acrylic acid, Sigma-Aldrich) as a binder in a weight ratio of 80:10:10.

SiOx: x = 1.0

Carbon content: 5.1 wt%

Average particle size of negative active material (D ₅₀ ): 5.3 ㎛

The above negative active material composition was applied to a copper foil having a thickness of 18 μm, dried, and rolled to produce a negative electrode having a thickness of 40 μm and a density of 1.35 g/cm3.

The above negative electrode was doped with lithium through a reduction reaction at 0.0005 V with a 20 μm lithium metal plate in a lithium non-aqueous electrolyte containing 1 M LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and diethylene carbonate (DEC) at a volume ratio of 1:1, and then dedoped by performing an oxidation reaction until the voltage reached 1.5 V, followed by drying, thereby obtaining an electrochemically pre-doped negative electrode with lithium.

<Manufacturing of the positive electrode>

LiNi _0.8 Co _0.2 O ₂ was used as a positive electrode active material, Super-P was used as a conductive material, and polyvinylidene fluoride (PVdF, Solvay) was used as a binder to prepare a positive electrode active material composition (slurry). The positive electrode active material composition was applied onto a 15 μm aluminum foil, and then dried and rolled to obtain a positive electrode.

<Manufacturing of secondary batteries>

A porous polypropylene sheet (25 μm) separator was interposed between the lithium-predoped negative electrode and the positive electrode, and then wound to produce a jelly roll. After this, it was stored and sealed in a cylindrical can, and an electrolyte containing 1 M LiPF ₆ in a mixed solvent of ethylene carbonate (EC) and diethylene carbonate (DEC) at a volume ratio of 1:1 was injected to produce a 1 Ah-class secondary battery.

Example 2

A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that polyimide resin was used as a binder.

Example 3

A negative electrode (thickness 37 ㎛, density 1.10 g/cm3) and a secondary battery were manufactured in the same manner as in Example 2, except that the same silicon-based negative electrode active material as in Example 2 and the carbon-based negative electrode material of natural graphite (average particle size: 7.5 ㎛) were mixed in a weight ratio of 50:50.

Comparative Example 1

A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that the negative electrode was not pre-doped with lithium.

Comparative Example 2

A negative electrode and a secondary battery were manufactured in the same manner as in Example 2, except that the negative electrode was not pre-doped with lithium.

Comparative Example 3

A negative electrode and a secondary battery were manufactured in the same manner as in Example 3, except that the negative electrode was not pre-doped with lithium.

Capacity characteristics and efficiency evaluation of secondary batteries

The lithium secondary batteries obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were aged for 12 hours, and then charged to 4.2 V at a constant current of 0.1 C using a charge/discharge test device (Won-A Tech), and then discharged at a constant current of 0.1 C until the voltage reached 2.5 V. The results are shown in Table 1 below.

As can be seen in Table 1 above, the secondary batteries of Examples 1 to 3 using negative electrodes pre-doped with lithium had superior secondary battery characteristics compared to the secondary batteries of Comparative Examples 1 to 3 using negative electrodes not pre-doped with lithium.

In particular, the efficiency of the secondary batteries of Examples 1 to 3 was 86% or more, whereas the efficiency of Comparative Examples 1 to 3 was all less than 69%. The secondary battery of Example 1 had an efficiency of 86.4%, which was an increase of more than 20% compared to the secondary battery of Comparative Example 1, which had an efficiency of 68.7%.

Meanwhile, the secondary batteries of the above examples and comparative examples were left at room temperature overnight, and then charged at a constant current of 0.5 mA/cm2 using a charge/discharge test device (manufactured by Nagano Co., Ltd.) until the voltage of the test cell reached 4.2 V. Discharging was performed at a constant current of 0.5 mA/cm2, and when the cell voltage reached 2.5 V, discharging was terminated, and then the discharge capacity was measured. The charge/discharge test was repeated 50 times, and the capacity retention rate was measured.

The discharge capacity and capacity retention rate after the cycle were calculated as follows, and the results are shown in Table 2.

Initial discharge capacity: discharge capacity at 1 ^st cycle

Capacity retention: 100Ⅹ(discharge capacity at ^50th cycle) / (discharge capacity at ^1st cycle)

As can be seen in Table 2 above, the secondary batteries of Examples 1 to 3 using negative electrodes pre-doped with lithium have initial discharge capacities of 11 mAh to 13.2 mAh, respectively, whereas the secondary batteries of Comparative Examples 1 to 3 using negative electrodes not pre-doped with lithium have initial discharge capacities of 8.5 mAh or less, which is a decrease of 20% to 50% compared to Examples 1 and 2.

10: Cathode
20: Electrolyte
30: Lithium metal plate

Claims (22)

(1) A first process for manufacturing a negative electrode by applying a negative electrode active material composition including a silicon-based negative electrode active material to a negative electrode current collector;
(2) A second process of placing the cathode and lithium metal plate in a reaction tank and then performing a redox reaction to predope the cathode with lithium; and
(3) The above lithium-predoped negative electrode, A third process for manufacturing an electrode by sequentially stacking a separator and an anode including a metal oxide;
Includes,
A method for manufacturing a secondary battery, wherein the silicon-based negative electrode active material includes MgSiO ₃ crystals and Mg ₂ SiO ₄ crystals, and the ratio of the intensity (IF) of an X-ray diffraction peak corresponding to Mg ₂ SiO ₄ crystals appearing in the range of 2θ=22.3° to 23.3° in X-ray diffraction analysis and the intensity (IE) of an X-ray diffraction peak corresponding to MgSiO ₃ crystals appearing in the range of 2θ=30.5° to 31.5°, IF/IE, is 1 or less.
In the first paragraph,
A method for manufacturing a secondary battery, wherein, in the second process above, after pre-doping, an oxidation-reduction reaction is performed one or more more times to remove lithium doped in excess on the negative electrode.
In the first paragraph,
A method for manufacturing a secondary battery, comprising, in the second process, electrochemically contacting the negative electrode and the lithium metal plate to cause absorption and desorption of lithium, thereby pre-doping the negative electrode with an amount of lithium equivalent to the initial irreversible capacity of the negative electrode.
In the first paragraph,
A method for manufacturing a secondary battery, wherein the metal oxide comprises an oxide having a spinel structure including lithium cobalt oxide, lithium manganese oxide, or a mixture thereof.
In the first paragraph,
A method for manufacturing a secondary battery, wherein the silicon-based negative electrode active material comprises at least one selected from the group consisting of silicon fine particles, a compound represented by SiOx (0.3≤x≤1.6), silicon dioxide, and a silicate containing magnesium, calcium, aluminum, or a combination thereof.
In paragraph 5,
A method for manufacturing a secondary battery, wherein the silicon particles have a crystallite size of 2 nm to 10 nm.
delete In the first paragraph,
A method for manufacturing a secondary battery, wherein the silicon-based negative electrode active material includes a carbon layer including a carbon film on its surface.
In paragraph 8,
A method for manufacturing a secondary battery, wherein the carbon content of the carbon layer is 2 wt% to 10 wt% based on the total weight of the silicon-based negative electrode active material.
In paragraph 8,
A method for manufacturing a secondary battery, wherein the carbon layer comprises at least one selected from the group consisting of carbon nanofibers, graphene, graphene oxide, and reduced graphene oxide.
In paragraph 8,
A method for manufacturing a secondary battery, wherein the cumulative 50% average particle diameter (D ₅₀ ) of the particle distribution of the above silicon-based negative electrode active material is 0.5 ㎛ to 15 ㎛.
In the first paragraph,
A method for manufacturing a secondary battery, wherein the silicon-based negative electrode active material has a specific gravity of 1.8 g/cm3 to 3.2 g/cm3 and a specific surface area (Brunauer-Emmett-Teller; BET) of 2 m ² /g to 20 m ² /g.
In the first paragraph,
A method for manufacturing a secondary battery, further comprising, in the first process, a step of rolling and drying after application.
In paragraph 1,
A method for manufacturing a secondary battery, wherein the separator comprises porous propylene and has a thickness of 10 μm to 30 μm.
　 In paragraph 1,
The above pre-doping is performed in an electrolyte,
A method for manufacturing a secondary battery, wherein the electrolyte comprises a non-aqueous electrolyte, a polymer electrolyte or a polymer gel electrolyte.
In the first paragraph,
A method for manufacturing a secondary battery, wherein the negative active material composition further comprises a binder.
In paragraph 16,
A method for manufacturing a secondary battery, wherein the binder comprises at least one selected from the group consisting of a fluorine-based resin, a rubber-based material, a polyolefin, an acrylic resin, and a polyimide-based resin.
In the first paragraph,
The above silicon-based negative electrode active material,
A step of mixing silicon powder and silicon dioxide powder to obtain a silicon-silicon oxide raw material powder mixture;
A step of heating and depositing the above raw material powder mixture to obtain a silicon oxide composite; and
A step of crushing and classifying the above silicon oxide complex to obtain a silicon-based negative electrode active material;
A method for manufacturing a secondary battery, the secondary battery being manufactured by a process including:
In paragraph 18,
A method for manufacturing a secondary battery, wherein the above heating is performed in a range of 800°C to 1600°C.
In paragraph 18,
A method for manufacturing a secondary battery, wherein the above-mentioned grinding is performed so that the average particle diameter of the silicon-based negative electrode active material is 0.5 ㎛ to 15 ㎛.
In paragraph 18,
A method for manufacturing a secondary battery, further comprising a step of forming a carbon layer including a carbon film on the surface of the silicon-based negative electrode active material using a chemical pyrolysis deposition method after the above-mentioned crushing and classification.
In paragraph 21,
A method for manufacturing a secondary battery, further comprising the step of crushing and classifying the silicon-based negative electrode active material after forming the carbon layer.