JP6975435B2 - Non-aqueous electrolyte secondary battery Negative electrode manufacturing method - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention has a graphite coating suitable as a negative electrode material for a non-aqueous electrolyte secondary battery, which has high capacity and excellent cycle characteristics when used as a negative electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. The present invention relates to a method for producing a silicon composite.

In recent years, with the remarkable development of portable electronic devices, communication devices and the like, there is a strong demand for non-aqueous electrolyte secondary batteries having a high energy density from the viewpoints of economy, miniaturization and weight reduction of the devices. Conventionally, as a measure for increasing the capacity of this type of secondary battery, for example, a method of using an oxide such as V, Si, B, Zr, Sn as a negative electrode material and a composite oxide thereof (Patent Document 1: JP-A-5). -174818, Patent Document 2: JP-A-6-60867, etc.), Method of applying melt-quenched metal oxide as negative electrode material (Patent Document 3: JP-A-10-294112), Oxidation to negative electrode material A method using silicon (Patent Document 4: Patent No. 2997741), a method using Si ₂ N ₂ O and Ge ₂ N ₂ O as the negative electrode material (Patent Document 5: Japanese Patent Application Laid-Open No. 11-102705), as the negative electrode material. A method of using a composite particle in which silicon and a silicon oxide are dispersed in a carbonaceous material and a material having a carbonaceous material coating layer covering the entire surface of the particles (Patent Document 6: Japanese Patent Application Laid-Open No. 2006-92969) and the like. Are known. Further, for the purpose of imparting conductivity to the negative electrode material, a method of carbonizing SiO after mechanical arranging with graphite (Patent Document 7: JP-A-2000-2433396), and a carbon layer on the surface of silicon particles by a chemical vapor deposition method. (Patent Document 8: JP-A-2000-215887), a method of coating a carbon layer on the surface of silicon oxide particles by a chemical vapor deposition method (Patent Document 9: JP-A-2002-42806), and the like can be mentioned. ..

Japanese Unexamined Patent Publication No. 5-174818 Japanese Unexamined Patent Publication No. 6-60867 Japanese Unexamined Patent Publication No. 10-294112 Japanese Patent No. 2997741 Japanese Unexamined Patent Publication No. 11-102705 Japanese Unexamined Patent Publication No. 2006-92969 Japanese Unexamined Patent Publication No. 2000-2433396 Japanese Unexamined Patent Publication No. 2000-2158887 Japanese Unexamined Patent Publication No. 2002-42806

Although the above-mentioned conventional method increases the charge / discharge capacity and the energy density, it is insufficient for the characteristics required by the market, the conductivity imparting process is complicated, the productivity is inferior, and the cost is high. There were problems, and it was not always satisfactory, and further improvement in energy density was desired. In particular, in Japanese Patent No. 2997741, silicon oxide is used as a negative electrode material for a lithium ion secondary battery to obtain a high-capacity electrode. However, since silicon oxide has very low electronic conductivity, a conductive auxiliary agent simply coexists. It is not enough to just make it, and a technique to improve electron conductivity is being studied. Regarding the conventional technique for imparting conductivity to a negative electrode material, Japanese Patent Application Laid-Open No. 2000-243366 states that a uniform carbon film is not formed and the conductivity is insufficient because it is a fusion of solids. There is a problem, and in the method of JP-A-2000-2158887, although a uniform carbon film can be formed, since Si is used as the negative electrode material, expansion / contraction during adsorption / desorption of lithium ions occurs. It is too large to withstand practical use as a result, and the cycleability is deteriorated. Therefore, a limit on the amount of charge must be provided to prevent this, and in the method of JP-A-2002-42806, Although it is confirmed that the cycle performance is improved while maintaining the high capacity, there is a problem that the process is complicated, so that it is not suitable for mass production and the cost is high.

The present invention has been made in view of the above circumstances, and a graphite-coated silicon composite suitable as a negative electrode material for a non-aqueous electrolyte secondary battery, which has little variation in battery characteristics, has a high capacity and is excellent in cycle characteristics, can be obtained and mass-produced. The purpose is to provide an industrial-scale manufacturing method that is capable of conversion and keeps costs down.

As a result of diligent studies to achieve the above object, the present inventors are expected to have a charge / discharge capacity several times that of the graphite-based one, which is currently the mainstream, but repeatedly. We focused on silicon-based materials, which have a major bottleneck in performance deterioration due to charging and discharging. By coating the surface of the silicon-based substance with a graphite film, significant improvement in battery characteristics was observed. However, the conventional graphite coating treatment is complicated, and it is difficult to produce on an industrial scale. A detailed study was conducted on a graphite coating treatment method that can withstand industrial-scale production. As a result, it was confirmed that mass production is possible by using a polymer material as a graphite source. However, there is a problem that it is difficult to form a uniform film by simple mixing and firing as in the prior art, and the battery characteristics are likely to vary. Therefore, it has been found that uniform coating of the graphite coating is possible by mixing and firing the polymer material a plurality of times, and as a result, the battery characteristics are stabilized, and the present invention has been completed.

Therefore, the present invention provides the following method for producing a graphite-coated silicon complex.
[1]. (I-1) (A) Silicon particles, silicon oxide particles represented by the general formula SiOx (0.5≤x <1.5), particles having a fine structure in which fine particles of silicon are dispersed in a silicon-based compound, And the mixing step of mixing the particles selected from these mixtures with (B) the polymer material to prepare a mixture.
(II-1) The obtained mixture is calcined in an inert atmosphere or a vacuum atmosphere to prepare a calcined product, which further comprises the following (I-2) obtained calcined product and (B). The mixing step of mixing the polymer material to prepare a mixture of the calcined product and the polymer material, and (II-2) the mixture of the obtained calcined product and the polymer material in an inert atmosphere or a vacuum atmosphere. A method for producing a graphite-coated silicon composite, which comprises a firing step of firing in the middle to prepare a fired product, or repeats the above steps (I-2) and (II-2) a plurality of times.
[2]. (A) The method for producing a graphite-coated silicon composite according to [1], wherein the average particle size of the particles is 0.1 to 30 μm and the BET specific surface area is 0.1 to 30 m ^{2 / g.}
[3]. (B) The method for producing a graphite-coated silicon composite according to [1] or [2], wherein the polymer material is a polymer selected from an aromatic group-containing thermoplastic polymer and a polyolefin-based thermoplastic polymer.
[4]. (I) Described in any one of [1] to [3], wherein the mixing step is a mixture of (B) a solution of a polymer material in an organic solvent and (A) particles or a fired product. A method for producing a graphite-coated silicon composite.
[5]. (II) The method for producing a graphite-coated silicon complex according to any one of [1] to [3], wherein the firing temperature in the firing step is 600 to 1,200 ° C.
[6]. Of [1] to [5], the graphite-coated silicon composite has an average particle size of 0.1 to 30 μm, a BET specific surface area of 0.1 to 30 m ² / g, and a graphite coating ratio of 0.5 to 40% by mass. The method for producing a graphite-coated silicon composite according to any one.
[7]. The method for producing a graphite-coated silicon composite according to any one of [1] to [6], wherein the graphite-coated silicon composite is used as a negative electrode material for a non-aqueous electrolyte secondary battery.

According to the manufacturing method of the present invention, as a negative electrode material for a non-aqueous electrolyte secondary battery having a high capacity and excellent cycle characteristics by using it as a negative electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. A suitable graphite-coated silicon composite is obtained. Since this manufacturing method is simple, mass production is possible and cost reduction can be achieved.

Hereinafter, each step of the manufacturing method of the present invention will be described in detail.
In the present invention, the (I) step means the (I-1) step and the (I-2) step, and the (II) step means the (II-1) step and the (II-2) step. ..

(I-1) Silicon particles, silicon oxide particles represented by the general formula SiOx (0.5≤x <1.5), particles having a fine structure in which silicon fine particles are dispersed in a silicon-based compound, and these. A mixing step of mixing particles selected from the mixture and (B) the polymer material to prepare a mixture.

In the present invention, silicon oxide is a general term for amorphous silicon oxide obtained by cooling and precipitating silicon monoxide gas generated by heating a mixture of silicon dioxide and metallic silicon. In the present invention, the general formula SiOx (0.5 ≦ x <1.5) is used. x is preferably 1.0 ≦ x <1.3, more preferably 1.0 ≦ x ≦ 1.2.

The particles having a fine structure in which silicon fine particles are dispersed in a silicon-based compound are disproportionated by heat treatment using silicon oxide particles represented by the general formula SiOx (0.5 ≦ x <1.5) as a starting material. It can be obtained by reacting. The size of the silicon fine particles is preferably 1 to 500 nm. As for the size of the fine particles, a diffraction peak attributed to Si (111) centered around 2θ = 28.4 ° was observed in X-ray diffraction (Cu-Kα) with copper as the counter cathode. It is the particle size of the silicon crystal obtained by the Scheller's equation based on the spread of the diffraction line. Further, as the silicon-based compound, an inert compound is preferable, and silicon dioxide is preferable in terms of ease of production.

The average particle size of the particles (A) is preferably 0.1 to 30 μm, more preferably 0.3 to 25 μm. Further, BET specific surface area is preferably 0.1~30m ² / g, more preferably 0.1~25m ² / g, more preferably 0.2~20m ² / g. (A) If the average particle size and BET specific surface area of the particles are out of the above ranges, a graphite-coated silicon composite having a desired average particle size and BET specific surface area may not be obtained. The average particle size is the weight average particle size in the particle size distribution measurement by the laser light diffraction method, and the BET specific surface area is the value measured by the BET 1-point method evaluated by the _{N 2 gas adsorption amount.}

(B) Polymer Material The graphite-coated silicon composite is formed by coating the surface of the particles (A) with a graphite film using the polymer material (B) as a carbon source. Examples of the polymer material include aromatic group-containing thermoplastic polymers such as polystyrene, xylene resin, biphenyl resin, naphthylene resin, anthracene resin, poly1-vinylnaphthalin, poly3-vinylpyrene, and polyalkylfluorene-based thermoplastic polymers, polyethylene, and polypropylene. Polyolefin-based thermoplastic polymers such as polybutene, polypentene, polyhexane, polyoctene, polynonene, polydecene, etc., thermoplastic resins such as condensed polynuclear aromatic resin, furan resin, phenol resin, etc., polytriazine resin, polypyridazine resin, polypyridine resin, polypiperidine Examples thereof include nitrogen-containing resins such as resins, polytriazole resins, polypyrazole resins, and polypyrrolidene resins, and these can be used alone or in combination of two or more. Of these, aromatic group-containing thermoplastic polymers and polyolefin-based thermoplastic polymers are preferable from the viewpoint of graphite coating effect. Among them, polystyrene and polyethylene are preferably used because of their cost and availability.

The polymer material (B) can be mixed as a powder, or a solution previously dissolved in an organic solvent such as toluene, acetone, hexane, xylene, or ethanol can be mixed with the particles (A), but more uniformly mixed. It is preferable to mix with a solution from the viewpoint that The mixing method is not particularly limited, and examples thereof include a ball mill, a stirring type mixer, and a mortar, but a ball mill is simple and is more preferably used.

(II-1) Firing step of calcining the obtained mixture in an inert atmosphere or a vacuum atmosphere to prepare a calcined product Argon or nitrogen is generally used as the inert gas, and the gas is aerated or sealed. However, in order to prevent the pressure from rising and to discharge the by-product gas to the outside of the system, it is preferable to perform the firing while the gas is aerated or inflowing. If the flow rate of the inert gas is excessive, the hydrocarbon gas may be discharged to the outside of the system and the graphite coating treatment speed may decrease. Therefore, the minimum necessary amount is preferable.

The firing temperature is preferably 600 to 1,200 ° C, more preferably 700 to 1,100 ° C. If the firing temperature is lower than 600 ° C., the graphite coating treatment takes a long time, and the productivity may decrease. On the contrary, when the treatment temperature exceeds 1,200 ° C., the disproportionation reaction proceeds too much when the silicon oxide represented by the general formula SiOx (0.5 ≦ x <1.5) is coated with graphite. When this graphite-coated silicon composite is used as a negative electrode material for a non-aqueous electrolyte secondary battery, the cycle characteristics are deteriorated. The firing time is appropriately selected, but is preferably 0.2 to 15 hours, more preferably 0.5 to 10 hours.

As the firing device, a reaction device having a heating mechanism may be used in an inert gas atmosphere or a vacuum atmosphere, and the treatment is not particularly limited, and can be processed by a continuous method or a batch method. , A rotary furnace, an annular furnace, a vertical mobile layer reactor, a tunnel furnace, a batch furnace, a rotary kiln, etc. can be appropriately selected according to the purpose.

(I-2) Mixing step of mixing the obtained calcined product and (B) polymer material to prepare a mixture of calcined product and polymer material In the present invention, it is obtained by the above step (I). (B) The polymer material is further mixed with the fired product to prepare a mixture of the fired product and the polymer material. The suitable components of the component (B), the mixing method, etc. are the same as those described in the above step (I-1), and the polymer material (B) can be mixed as a powder, and is a solution previously dissolved in an organic solvent. (A) can be mixed with the particles, and the mixing method is not particularly limited, and examples thereof include a ball mill, a stirring type mixer, and a mortar, but the ball mill is simple and more preferably used. (B) Other conditions such as the polymer material and the mixing method may be the same as or different from the above (I-1).

(II-2) Firing step of calcining the obtained mixture of the calcined product and the polymer material in an inert atmosphere or a vacuum atmosphere to prepare a calcined product. It can be selected in the same manner as in step I-2), but may be the same as or different from (I-2) above. The firing temperature is preferably 600 to 1,200 ° C, more preferably 700 to 1,100 ° C. The firing time is appropriately selected, but is preferably 0.2 to 15 hours, more preferably 0.5 to 10 hours.

In the present invention, the above steps (I-2) and (II-2) may be included, and the steps (I-2) and (II-2) may be repeated a plurality of times. By repeating the mixing and firing of the polymer material a plurality of times in this way, uniform coating of the graphite coating becomes possible. The number of steps (I-2) and (II-2) is not particularly limited and is appropriately selected depending on the mixing ratio of the polymer material and the firing temperature, but 1 to 4 times is preferable (including the step (I)). 2 to 5 times), more preferably once. If the number of steps (I-2) and (II-2) exceeds four, mass production and cost reduction, which are the original purposes, become difficult, so it is preferable to reduce the number as much as possible.

The mixing ratio of the particles (A) and the polymer material (B) is preferably 20 to 500 parts by mass of the polymer material (B) with respect to 100 parts by mass of the particles (A) as the total amount of all steps. It is preferably 30 to 400 parts by mass. The mixing amount of each step (I) with respect to the particles (A) or the fired product is appropriately selected from the number ± 30 parts by mass obtained by dividing the amount of all the steps by the number of steps (I), and each (I). The mixing amount per step is preferably 5 to 300 parts by mass, more preferably 7 to 250 parts by mass, based on 100 parts by mass of the particles or the calcined product (B). (B) If the polymer material is too small, the graphite coating amount may be small, while if it is too large, the graphite coating amount is large, and when used as a negative electrode material for a non-aqueous electrolyte secondary battery, the charge / discharge capacity May decrease.

[Graphite-coated silicon complex]
The graphite-coated silicon composite obtained by the above production method has silicon particles, silicon oxide particles represented by the general formula SiOx (0.5≤x <1.5), and fine particles of silicon dispersed in a silicon-based compound. The particles having such a structure and the surface of the particles selected from the mixture thereof are coated with the above (B) polymer material as a graphite source. The silicon particles, silicon oxide particles, and particles having a fine structure in which silicon fine particles are dispersed in a silicon-based compound are as described in (A) particles. When silicon oxide particles represented by the general formula SiOx (0.5 ≦ x <1.5) are used as the raw material, the disproportionation reaction proceeds by sintering, and the silicon fine particles are dispersed in the silicon-based compound. The surface of the particles having a fine structure may be a graphite-coated silicon-coated silicon composite using (B) a polymer material as a graphite source.

The graphite coverage of the graphite-coated silicon composite (%: ratio to the graphite-coated silicon composite) is preferably 0.5 to 40% by mass, more preferably 2 to 30% by mass. If the graphite coating amount is less than 0.5% by mass, it is insufficient in terms of forming a conductive film, and there is a possibility that sufficient conductivity cannot be maintained. As a result, when it is used as a negative electrode material for a non-aqueous electrolyte secondary battery. Cycleability may decrease. On the other hand, even if the graphite coating amount exceeds 40% by mass, not only the effect is not improved, but also the ratio of graphite in the negative electrode material increases, and the graphite-coated silicon composite is used as the negative electrode material for the non-aqueous electrolyte secondary battery. When used, the charge / discharge capacity decreases. The graphite coating amount in each mixing and firing is not particularly limited, and is uniform by setting the total graphite coating amount to about ± 30% of the graphite coating amount divided by each mixing and firing. Graphite coating treatment becomes possible.

The graphite-coated silicon complex is a particle, and the average particle size thereof is preferably 0.1 to 30 μm, more preferably 0.3 to 25 μm. If the average particle size is smaller than 0.1 μm, the purity will decrease due to the effect of surface oxidation, and when used as a negative electrode material for non-aqueous electrolyte secondary batteries, the charge / discharge capacity will decrease, the bulk density will decrease, and the unit volume will decrease. There is a risk that the charge / discharge capacity per unit will decrease. On the contrary, if it is larger than 30 μm, the amount of graphite deposited in the graphite coating treatment is reduced, and as a result, the cycle performance may be deteriorated when used as a negative electrode material for a non-aqueous electrolyte secondary battery. Further, BET specific surface area is preferably 0.1~30m ² / g, more preferably 0.1~25m ² / g, more preferably 0.2~20m ² / g. If the BET specific surface area is ^{less than 0.1 m 2} / g, the surface activity becomes small, and as a result, the charge / discharge capacity may decrease when the non-aqueous electrolyte secondary battery negative electrode material is used. On the contrary, when the BET specific surface area ^{exceeds 30 m 2} / g, the amount of the binder at the time of manufacturing the electrode increases, and the capacity as the electrode may decrease.

[Non-water electrolyte secondary battery negative electrode material]
The graphite-coated silicon composite is suitable as a negative electrode active material for a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, and is used as a negative electrode material for a non-aqueous electrolyte secondary battery. When a negative electrode is manufactured using the negative electrode material of the non-aqueous electrolyte secondary battery, a conductive agent such as graphite can be added to the negative electrode material of the non-aqueous electrolyte secondary battery. Even in this case, the type of the conductive agent is not particularly limited as long as it is an electron-conducting material that does not decompose or deteriorate in the configured battery, and specifically, Al, Ti, Fe, Ni, Cu, Metal powder or metal fiber such as Zn, Ag, Sn, Si, natural graphite, artificial graphite, various coke powder, mesophase carbon, gas phase growth carbon fiber, pitch carbon fiber, PAN carbon fiber, various resin firing Graphite such as body can be used.

[Negative electrode]
Examples of the method for preparing the negative electrode (molded body) include the following methods. A graphite-coated silicon composite, a conductive agent if necessary, and another additive such as a binder are kneaded with a solvent such as N-methylpyrrolidone or water to form a paste-like mixture. Is applied to the sheet of the current collector. In this case, as the current collector, any material such as copper foil or nickel foil, which is usually used as a current collector for the negative electrode, can be used without particular limitation on the thickness and surface treatment. The molding method for molding the mixture into a sheet is not particularly limited, and a known method can be used.

[Non-water electrolyte secondary battery]
A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery is characterized in that the above-mentioned graphite-coated silicon composite is used, and other materials such as a positive electrode, a negative electrode, an electrolyte, a separator, and a battery shape are known. Can be used and is not particularly limited. For example, as the positive electrode active material _{, oxides of transition metals such as LiCoO 2} , LiNiO ₂ , LiMn ₂ O ₄ , V ₂ O ₅ , MnO ₂ , TiS ₂ , MoS ₂ , lithium, and chalcogen compounds are used. As the electrolyte, for example, a non-aqueous solution containing a lithium salt such as lithium hexafluorophosphate and lithium perchlorate is used, and as the non-aqueous solvent, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, γ-butyrolactone, etc. It is used by one kind or a combination of two or more kinds such as 2-methyltetraethane. In addition, various other non-aqueous electrolytes and solid electrolytes can also be used.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Example 1]
_{50 g of silicon oxide particles represented by the general formula SiO x} (x = 1.02) having an average particle diameter of 5 μm are placed in a solution in which 25 g of polystyrene is dissolved in 25 g of toluene, mixed for 1 hour with a ball mill, and silicon oxide / A polystyrene mixture was made. Next, the entire amount of the mixture was charged into the annular furnace of φ120, and firing was carried out at 1,000 ° C. for 1 hour while inflowing 0.2 L / min of argon (Ar) gas. After the completion of firing, the temperature was lowered to obtain a black powder. The obtained black powder had a graphite coverage of 2.5% by mass. The resulting black powder was then mixed with polystyrene in the same manner as above. That is, the obtained black powder was put into a solution in which 25 g of polystyrene was dissolved in 25 g of toluene and mixed with a ball mill for 1 hour to prepare a black powder / polystyrene mixture. After that, the same firing treatment as described above was carried out. The finally obtained black powder was a graphite-coated silicon composite having an average particle size of 5.0 μm, a BET specific surface area of 4.7 m ² / g, and a graphite coverage of 4.5% by mass.

○ Battery evaluation Next, a battery evaluation was performed using the obtained graphite-coated silicon complex as a negative electrode active material by the following method.
First, 10% by mass of polyimide was added to the obtained graphite-coated silicon composite, and N-methylpyrrolidone was further added to form a slurry. This slurry was applied to a copper foil having a thickness of 20 μm, dried at 80 ° C. for 1 hour, and then dried. The electrode was pressure-molded by a roller press, vacuum dried at 350 ° C. for 1 hour, ^{and then punched to 2 cm 2} to obtain a negative electrode.

Here, in order to evaluate the charge / discharge characteristics of the obtained negative electrode, a lithium foil was used as the counter electrode, and lithium hexafluoride was mixed as a non-aqueous electrolyte with 1/1 (volume ratio) of ethylene carbonate and diethyl carbonate. A lithium ion secondary battery for evaluation was prepared by using a non-aqueous electrolyte solution dissolved in a liquid at a concentration of 1 mol / L and using a microporous polyethylene film having a thickness of 30 μm as a separator.

The produced lithium-ion secondary battery was left at room temperature overnight, and then used with a secondary battery charge / discharge test device (manufactured by Nagano Co., Ltd.) at 0.5 mA / cm ^{2 until the voltage of the test cell reached 0 V.} Charging was performed with a constant current, and after reaching 0 V, charging was performed by reducing the current so as to keep the cell voltage at 0 V. Then, charging was terminated when the current value fell below 40 μA / cm ^2. The discharge was performed at a constant current of 0.5 mA / cm ² , and when the cell voltage exceeded 2.0 V, the discharge was terminated and the discharge capacity was determined.

The above charge / discharge test was repeated, and the charge / discharge test was performed after 50 cycles of the lithium ion secondary battery for evaluation. As a result, the initial charge capacity is 1,850 mAh / g, the initial discharge capacity is 1,500 mAh / g, the initial charge / discharge efficiency is 81.1%, the discharge capacity at the 50th cycle is 1,350 mAh / g, and the cycle retention rate after 50 cycles is 90. It was confirmed that the lithium ion secondary battery has a high capacity of 0.0% and is excellent in initial charge / discharge efficiency and cycle performance.

[Example 2]
The graphite coating treatment was performed under the same conditions as in Example 1 except that the firing temperature was 650 ° C. and the firing time was 5 hours.
The graphite coating amount of the black powder obtained in the first mixing / firing treatment (I) was 2.3% by mass. The finally obtained black powder was a graphite-coated silicon composite having an average particle size of 5.1 μm, a BET specific surface area of 9.8 m ² / g, and a graphite coverage of 4.1% by mass.

As a result of battery evaluation of this graphite-coated silicon composite by the same method as in Example 1, the initial charge capacity was 1,920 mAh / g, the initial discharge capacity was 1,520 mAh / g, the initial charge / discharge efficiency was 79.2%, and 50. It was confirmed that the lithium-ion secondary battery has a discharge capacity of 1,350 mAh / g at the first cycle, a high capacity of 88.8% of the cycle retention after 50 cycles, and excellent initial charge / discharge efficiency and cycle performance. rice field.

[Example 3]
Graphite coating treatment was performed under the same conditions as in Example 1 except that a solution in which 80 g of polystyrene was dissolved in 80 g of toluene was used.

The graphite coating amount of the black powder obtained in the first mixing / firing treatment (I) was 3.5%. The finally obtained black powder was a graphite-coated silicon composite having an average particle diameter of 5.1 μm, a BET specific surface area of 7.3 m ² / g, and a graphite coverage of 6.2% by mass.

As a result of battery evaluation of this graphite-coated silicon composite by the same method as in Example 1, the initial charge capacity was 1,830 mAh / g, the initial discharge capacity was 1,480 mAh / g, the initial charge / discharge efficiency was 80.9%, and 50. It was confirmed that the lithium-ion secondary battery has a discharge capacity of 1,330 mAh / g at the first cycle, a high capacity of 89.9% with a cycle retention rate after 50 cycles, and excellent initial charge / discharge efficiency and cycle performance. rice field.

[Example 4]
Using a solution in which 5 g of polystyrene was dissolved in 25 g of toluene, the graphite coating treatment was performed under the same conditions as in Example 1 except that the mixing and firing treatments were repeated 5 times (I: 1 time, II: 4 times).
The graphite coating amount of the black powder obtained by the mixing and firing treatment in the first (I) was 1.2% by mass, the second (II) was 2.1% by mass, and the third (II) was 3. 1% by mass, 4.0% by mass in the 4th time (II), and the finally obtained black powder in the 5th time (II) had an average particle diameter of 5.2 μm and a BET specific surface area of 5.3 m ² / g. , It was a graphite-coated silicon composite having a graphite coverage of 4.8% by mass.

As a result of battery evaluation of this graphite-coated silicon composite by the same method as in Example 1, the initial charge capacity was 1,850 mAh / g, the initial discharge capacity was 1,500 mAh / g, and the initial charge / discharge efficiency was 81.1%, 50. It was confirmed that the lithium-ion secondary battery has a discharge capacity of 1,370 mAh / g at the first cycle, a high capacity with a cycle retention rate of 91.3% after 50 cycles, and excellent initial charge / discharge efficiency and cycle performance. rice field.

[Comparative Example 1]
_{50 g of silicon oxide powder represented by the general formula SiO x} (x = 1.02) having an average particle diameter of 5 μm was placed in a solution in which 120 g of polystyrene was dissolved in 120 g of toluene, and the mixture was mixed for a time in a ball mill to form a silicon oxide / polystyrene mixture. Was produced. Next, the entire amount of the mixture was charged into a φ120 annular furnace, and firing was carried out at 1,000 ° C. for 1 hour while inflowing 0.2 L / min of Ar gas. The obtained black powder was a graphite-coated silicon composite having an average particle diameter of 5.1 μm, a BET specific surface area of 5.3 m ² / g, and a graphite coverage of 4.7% by mass.

As a result of battery evaluation of this graphite-coated silicon composite by the same method as in Example 1, the initial charge capacity was 1,840 mAh / g, the initial discharge capacity was 1,480 mAh / g, the initial charge / discharge efficiency was 80.4%, and 50. It was confirmed that the lithium ion secondary battery had a discharge capacity of 1,280 mAh / g at the first cycle and a cycle retention rate of 86.5% after 50 cycles, and was inferior in cycleability to the examples.

The conditions and results of Examples and Comparative Examples are shown in the table below.

Claims (6)

(I-1) (A) Silicon particles, silicon oxide particles represented by the general formula SiOx (0.5≤x <1.5), particles having a fine structure in which fine particles of silicon are dispersed in a silicon-based compound, And a mixing step of mixing particles selected from these mixtures with a solution prepared by dissolving (B) a material selected from an aromatic group-containing thermoplastic polymer and a polyolefin-based thermoplastic polymer in an organic solvent to prepare a mixture. ,
(II-1) A firing step of calcining the obtained mixture in an inert atmosphere or a vacuum atmosphere to prepare a calcined product.
(I-2) The obtained calcined product and (B) a material selected from the aromatic group-containing thermoplastic polymer and the polyolefin-based thermoplastic polymer are mixed with a solution in which a solution is dissolved in an organic solvent, and the calcined product and the high-grade product are mixed. Mixing process to make a mixture with a molecular material,
The (II-2) (I- 2) mixed-product obtained in step, and fired at or in a vacuum atmosphere in an inert atmosphere, the baking step of preparing a baked product, or the (I-2) and ( II-2) Repeat the process multiple times,
(B) A step of manufacturing a coated silicon complex coated with a film using the material as a carbon source.
(III) and the object to be covered silicon composite obtained, a conductive agent and a binder, step by kneading a solvent to prepare a paste-like mixture, and the mixture obtained (IV) condensing A method for manufacturing a non-aqueous electrolyte secondary battery negative electrode, which comprises a step of applying to an electric body and forming it into a sheet. (A) The method for manufacturing a non-aqueous electrolyte secondary battery negative electrode according to claim 1, wherein the average particle size of the particles is 0.1 to 30 μm and the BET specific surface area is 0.1 to 30 m ^{2 / g.} The average particle size of the coated silicon complex is 0.1 to 30 μm, and the BET specific surface area is 0.1 to 30 m. ² The method for manufacturing a non-aqueous electrolyte secondary battery negative electrode according to claim 1 or 2, wherein / g. The production of the non-aqueous electrolyte secondary battery negative electrode according to any one of claims 1 to 3, wherein the coating ratio of the coating film (B) using the material as a carbon source is 0.5 to 40% by mass with respect to the coated silicon composite. Method. The method for manufacturing a non-aqueous electrolyte secondary battery negative electrode according to claim 4, wherein the coverage of the coating film (B) using the material as a carbon source with respect to the coated silicon composite is 0.5 to 6.2% by mass. (II) The method for manufacturing a non-aqueous electrolyte secondary battery negative electrode according to any one of claims 1 to 5 , wherein the firing temperature in the firing step is 600 to 1,200 ° C.