JP6459700B2 - Negative electrode and secondary battery containing amorphous-containing Si powder, and methods for producing the same - Google Patents

Description

  The present invention relates to a negative electrode and a secondary battery containing amorphous-containing Si powder, and methods for producing them.

  A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. Currently, it is mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future.

  In recent years, silicon-based materials such as silicon and silicon compounds, and tin-based materials such as tin and tin compounds, which have a charge / discharge capacity that greatly exceeds the theoretical capacity of carbon materials, have been studied as negative electrode active materials for lithium ion secondary batteries. . However, it is known that when a silicon-based material or a tin-based material is used as the negative electrode active material, the negative electrode active material expands and contracts with insertion and extraction of lithium (Li) in the charge / discharge cycle.

  As the negative electrode active material expands and contracts, a load is applied to the binder that holds the negative electrode active material on the current collector. As a result, the adhesiveness between the negative electrode active material and the current collector is reduced, and the capacity is reduced due to the increase in resistance of the electrode due to the destruction of the conductive path in the electrode. Further, the negative electrode active material is distorted due to repetition of expansion and contraction, and desorption of the active material from the electrode occurs due to the refinement of the negative electrode active material. Thus, the expansion and contraction of the negative electrode active material affect the cycle characteristics of the battery. Various studies have been conducted in order to suppress the deterioration of the cycle characteristics.

  For example, when crystalline Si has an amorphous structure, stress concentration due to expansion and contraction of Si tends to be relaxed. Therefore, amorphous-containing Si having at least a part of an amorphous structure has been studied.

  For example, Patent Document 1 proposes an electrode in which a thin film containing silicon as a main component is formed on a current collector by a vapor deposition method. It is disclosed that the thin film is an amorphous silicon thin film.

  However, the vapor deposition method has a slow film formation speed, and it takes a lot of time and energy to form a thick thin film.

  Therefore, there is a demand for a new method for manufacturing an electrode including amorphous-containing Si.

JP 2009-231072 A

  This invention is made | formed in view of this situation, and it aims at providing the manufacturing method of the negative electrode containing new amorphous content Si powder.

  The inventor has conceived that an amorphous-containing Si powder is obtained under completely different conditions from the conventional manufacturing method. Specifically, the raw material Si powder is put into a plasma at a temperature of about 10,000 ° C. to 15,000 ° C., the raw material Si powder is made into a gas or liquid state, the outside of the plasma is cooled, and the extreme inside and outside the plasma It was recalled that the product was quenched by using a simple temperature difference to obtain amorphous Si powder. And when this inventor repeated trial and error and earnestly examined, it confirmed that the amorphous-containing Si powder of the arbitrary fine particle sizes by which the amorphousization degree was controlled was obtained with the said manufacturing method. It was also confirmed that the amorphous-containing Si powder could be carbon coated by bringing a carbon source gas into contact with Si during cooling. And based on such knowledge, the present inventor produced a negative electrode comprising an amorphous-containing Si powder or a carbon-coated amorphous-containing Si powder produced by a new production method, and confirmed that this operates normally, The present invention has been completed.

  That is, the negative electrode of the present invention is characterized by comprising an amorphous-containing Si powder having an average particle diameter of 1 nm to 200 nm.

  The negative electrode manufacturing method of the present invention also includes an amorphous process including a step of introducing raw material Si powder into the plasma by an introduction flow, and a cooling step of cooling the flow after the introduction flow passes through the plasma. The manufacturing process of containing Si powder and the process of using amorphous containing Si powder are included.

  The present invention can provide a negative electrode and a secondary battery comprising an amorphous-containing Si powder produced by a new production method.

It is a schematic diagram of a plasma generator. 4 is a particle size distribution diagram of the powder of Production Example 1 and the powder of Production Example 2. FIG. 6 is a transmission electron microscope image of the powder of Production Example 2. 2 is an X-ray diffraction chart of the powder of Comparative Production Example 1 and the powders of Production Examples 1, 2, and 11. It is an analysis result by energy dispersive X-ray spectroscopy (hereinafter referred to as EDX) of the powder of Production Example 14. It is an analysis result by EDX of the powder of manufacture example 14. It is a graph which shows the relationship between the cycle number of a lithium ion secondary battery using the negative electrode of Example 1- Example 4, and the comparative example 1, and a capacity maintenance rate.

  The best mode for carrying out the present invention will be described below. Unless otherwise specified, the numerical range “x to y” described in this specification includes the lower limit x and the upper limit y. The numerical range can be configured by arbitrarily combining these upper limit value and lower limit value and the numerical values listed in the examples. Furthermore, numerical values arbitrarily selected from the numerical value range can be used as upper and lower numerical values.

  Hereinafter, the present invention will be described along the method for producing a negative electrode of the present invention.

  The method for producing a negative electrode of the present invention includes an amorphous-containing Si including a step of introducing raw material Si powder into a plasma by an introduction flow, and a cooling step of cooling the flow after the introduction flow passes through the plasma. It includes a manufacturing process of powder and a process using amorphous-containing Si powder.

  First, a process for producing amorphous-containing Si powder including a step of introducing the raw material Si powder into the plasma by the introduction flow and a cooling step of cooling the passage flow after the introduction flow has passed through the plasma will be described. Hereinafter, the production process of the amorphous-containing Si powder is sometimes simply referred to as “powder production process”, and the amorphous-containing Si powder produced in the production process of the amorphous-containing Si powder is referred to as “powder of the present invention”. In addition, the carbon-coated amorphous-containing Si powder produced in the production process of the amorphous-containing Si powder is sometimes referred to as “carbon-coated powder of the present invention”.

A commercially available Si powder may be used as the raw material Si powder. The structure of the raw material Si powder is not particularly limited. Although the raw material Si average particle diameter _{D 50} of the powder is not particularly limited, but is preferably 1 m to 100 m, more preferably 1Myuemu～40myuemu, more preferably 2Myuemu～10myuemu. When the average particle diameter D ₅₀ of the raw material Si powder is too small, the less likely to move the raw material Si powder by static electricity, when the average particle diameter D ₅₀ of the raw material Si powder is too large, to uniformly move the raw material Si powder It may be difficult, and it may be difficult to vaporize or make the entire amount of the raw material Si powder introduced into the plasma in the plasma.

The average particle diameter D ₅₀ can be measured by particle size distribution measurement method. The average particle diameter D ₅₀ is that the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the average particle diameter D ₅₀ means the median size measured by volume.

  The powder production process is performed using a plasma generator. The plasma may be generated by arc discharge, high frequency electromagnetic induction, microwave heating discharge, or the like.

  In the case of a high-frequency electromagnetic induction type plasma generator, the frequency may be, for example, in the range of 0.5 MHz to 400 MHz, preferably in the range of 1 MHz to 80 MHz.

  The plasma output may be, for example, in the range of 3 kW to 300 kW, preferably in the range of 5 kW to 50 kW. By increasing the plasma output, the degree of amorphization of the powder of the present invention can be increased. Further, if the plasma output is increased, the supply amount of the raw material Si powder can be increased.

  What is necessary is just to set the pressure in a plasma generator suitably, for example, the inside of the range of 10 kPa-atmospheric pressure can be illustrated. By varying the plasma output and the pressure in the plasma generator, the degree of amorphization and the average particle diameter of the powder of the present invention can be changed. For example, the average particle diameter of the powder of the present invention can be reduced by bringing the pressure in the plasma generator close to atmospheric pressure.

  As the introduction flow, in consideration of the stability of the plasma, a gas that can be used under the plasma is preferably used as the main flow. As the gas, a rare gas such as helium or argon or hydrogen is preferable. As an introduction gas flow rate, 20 L / min. -120 L / min. Can be illustrated.

  Depending on the type of plasma generator, in the powder production process, the carrier gas that carries the raw Si powder, the inner gas that is introduced into the coil separately from the carrier gas, and the plasma generation site are inert atmosphere It is preferable to employ a process gas for lowering.

  The flow rate of the carrier gas is 1 L / min. -10 L / min. Can be illustrated. The higher the flow rate of the carrier gas, the higher the degree of amorphization of the powder of the present invention. This is presumably because the time from the nucleation of Si to the low temperature portion is shortened by increasing the carrier gas flow rate.

  The flow rate of the inner gas is 1 L / min. -10 L / min. Can be illustrated.

  The flow rate of the process gas is 15 L / min. ~ 100 L / min. Can be illustrated. As the flow rate of the process gas, 30 L / min. ~ 100 L / min. Is preferred. Further, it is preferable to use a mixed gas of argon and helium as the process gas. When a mixed gas of argon and helium is used as the process gas, the temperature in the plasma can be increased as compared with the case where only argon is used as the process gas. Although depending on the ratio of helium and argon, when the apparatus of the embodiment is used, the temperature in the plasma when only argon is used as the process gas is about 10,000 ° C., and a mixed gas of argon and helium When using as a process gas, the temperature in the plasma is about 15,000 ° C. When the temperature in the plasma is increased, the cooling rate in the cooling step is increased, and the degree of amorphization of the powder of the present invention can be increased.

  The supply rate of the raw material Si powder is preferably 50 mg / min to 1000 mg / min. If the supply speed of the raw material Si powder becomes too fast, the heat of the plasma may be taken away due to the vaporization of many Si particles, and the temperature in the plasma may decrease.

  The temperature in the plasma is about 8,000 ° C. to 20,000 ° C. Si is vaporized in the plasma, and the passing flow containing the vaporized Si is cooled, and Si nuclei are generated at about 2,000 ° C. to 2,300 ° C. The nucleated Si is further rapidly cooled to about room temperature. Since it is rapidly cooled from a high temperature state to near room temperature, Si has almost no period of crystal growth, and amorphous-containing Si powder is produced.

  In the cooling step, the through flow after the introduction flow passes through the plasma is cooled. Since the inside of the plasma is in a high temperature state and the ambient temperature outside the plasma is room temperature, the passing flow is rapidly cooled only by the passing flow coming out of the plasma to the outside of the plasma. In addition, by cooling the entire plasma generator with cooling water or the like, the ambient temperature outside the plasma can be further lowered and the cooling rate can be further increased.

  Further, the cooling rate of the passing flow can be further increased by bringing the cooling gas into contact with the passing flow. In order to further increase the cooling rate, it is preferable to inject a cooling gas flow facing the passing flow toward the passing flow. By injecting the cooling gas flow facing the through flow toward the through flow, the cooling gas flow and the through flow are in good contact with each other, and the through flow is evenly cooled, thereby cooling the through flow more rapidly. it can.

  In the powder production process, if the cooling rate of the passing flow is increased, the powder of the present invention that is finer and has a high degree of amorphization can be obtained.

  As the cooling gas, a rare gas such as helium or argon is preferable. The temperature of the cooling gas may be room temperature or lower than room temperature. The flow rate of the cooling gas may be a flow rate smaller than that of the introduction flow, for example, 1 L / min. -30 L / min. This can be illustrated as an example. The larger the flow rate of the cooling gas, the higher the degree of amorphization of the powder of the present invention.

  In the powder production process, the average particle diameter of the powder can be arbitrarily adjusted. According to the powder production process, the powder of the present invention having an average particle size of nanosize can be easily produced. The average particle size of the powder of the present invention is preferably in the range of 1 nm to 200 nm, more preferably in the range of 10 nm to 50 nm. The average particle diameter here means an arithmetic average value of the longest diameter of the particles when the powder of the present invention is observed with an electron microscope such as a scanning electron microscope or a transmission electron microscope.

  When the average particle size of the amorphous-containing Si powder is small, when the amorphous-containing Si powder is used as a negative electrode active material of a battery, for example, stress concentration due to expansion and contraction of Si during battery charging / discharging can be alleviated, and the electrode and battery The effect of improving the lifetime of the film is exhibited.

  The powder of the present invention preferably has an amorphous degree of 50% or more. When amorphous-containing Si powder having a high degree of amorphization is used as the negative electrode active material of the battery, effects such as a reduction in the degree of expansion and contraction of Si and an improvement in the life of the electrode and the battery are exhibited.

  Here, the degree of amorphization refers to the content of the amorphous structure in the powder of the present invention. In the present invention, the degree of amorphization is obtained by performing the following calculation method 1 and calculation method 2 using measurement data of a powder X-ray diffraction method (hereinafter referred to as XRD).

  The degree of amorphization in the present invention is determined from the following formula: degree of amorphization = Si (a) / (Si (c) + Si (a)).

(Calculation method 1: Internal standard method)
Zinc oxide (hereinafter referred to as ZnO) is used as an internal standard substance.

  Each mixture is prepared by mixing crystalline Si powder and ZnO at several mass ratios. The X-ray diffraction pattern of each mixture is measured. The ratio between the maximum intensity peak of crystalline Si and the maximum intensity peak of ZnO is determined from the X-ray diffraction pattern of each mixture. A calibration curve is prepared by taking the mass ratio of crystalline Si mass / ZnO mass on the horizontal axis and the peak intensity ratio of crystalline Si peak intensity / ZnO peak intensity on the vertical axis.

  A sample whose degree of amorphization is to be measured and ZnO are mixed at a predetermined mass ratio X to produce a mixture, and the X-ray diffraction pattern of the mixture is measured. The ratio of the maximum peak intensity of the sample to the maximum peak intensity of ZnO is determined from the X-ray diffraction pattern. The obtained peak ratio is applied to the calibration curve to determine the mass ratio X ′ on the calibration curve.

(Calculation method 2: Elimination of influence due to the mass of SiO ₂ contained in the sample)
The amorphous-containing Si powder of the present invention may have an oxide film, that is, a SiO ₂ layer on the surface. Since the average particle diameter of the amorphous-containing Si powder of the present invention is nano-sized, an error may occur in the degree of amorphization depending on the content ratio of the SiO ₂ layer. In order to obtain a more accurate numerical value, the mass of SiO ₂ is obtained as follows, and the mass is corrected to be deleted as a factor that affects the degree of amorphization. The procedure is as follows.

  1. The sample is observed with a transmission electron microscope (hereinafter referred to as TEM) to determine the average particle size of the sample. The average particle diameter of the sample is an arithmetic average value for 200 particles.

2. The sample is observed with a scanning transmission electron microscope (hereinafter referred to as STEM), O element mapping is performed, and the thickness of the SiO ₂ layer is calculated. The thickness value is an arithmetic average value for 200 particles.

3. The volume ratio of Si: SiO ₂ is determined from the average particle diameter of the sample and the thickness of the SiO ₂ layer.

4). The mass ratio of Si: SiO ₂ is determined from the Si density of 2.33 g / cm ³ and the SiO ₂ density of 2.21 g / cm ³ and the above volume ratio.

5. The mass of SiO ₂ is determined from the mass ratio and the mass of the sample.

6). When the mass of crystalline Si is Si (c), the mass of amorphous Si is Si (a), and the mass of SiO ₂ is SiO ₂ , the mass of the sample = Si (c) + Si (a) + SiO ₂ . Therefore, Si (c) + Si (a) = (mass of sample) − (mass of SiO ₂ ).

Actually, X = (Si (c) + Si (a) + SiO ₂ ) / (Si (c) + Si (a) + SiO ₂ + ZnO), and X ′ = Si (c) / (Si (c) + Si ( a) + SiO ₂ + ZnO), (X−X ′) / X = (Si (a) + SiO ₂ ) / (Si (c) + Si (a) + SiO ₂ ) Si (a) / (Si (c) + Si (a)) is calculated by substituting the value of X, the value of X ′, the mass of SiO ₂ , and the mass of the sample into this equation.

  Since the powder of the present invention has a preferable degree of amorphization and an average particle size, a synergistic effect can be expected.

The powder of the present invention has a high sphericity. In the present invention, the sphericity is calculated by the following formula 1 or formula 2 from the result of observing the powder of the present invention with an electron microscope such as a scanning electron microscope or a transmission electron microscope. The number of particles to be observed is 200, and the sphericity is an average value of the 200 particles.
Sphericality = (Smallest particle diameter) / (Longest particle diameter) (Formula 1)
Sphericality = 4πS / l ² (S: area of particle, l: circumference of particle) (Equation 2)
Regardless of whether the sphericity is obtained by using either Equation 1 or Equation 2, the value of sphericity is almost the same.

  The sphericity is preferably 0.8 or more and 1 or less. The sphericity closer to 1 is closer to a true sphere. If the sphericity is within this range, when amorphous-containing Si powder is used as the negative electrode active material of the battery, for example, fluctuation of the filling rate of amorphous-containing Si powder for each electrode is suppressed, and the quality of the electrode is stabilized. Effects such as are produced. The powder produced by the rotating disk method described in the prior art is subjected to centrifugal force during production. For this reason, the produced powder may have a biased shape, and it is difficult to easily produce a uniform shaped powder with the conventional technology.

Preferably the specific surface area of the powder of the present invention is ^{10m 2} / ^g~300m 2 / ^g, more preferably 40m ² / g~200m 2 / ^g, is 60m ² / g~160m 2 / g More preferably. The specific surface area is measured by the BET method using nitrogen adsorption.

  If the specific surface area is too large, the oxide film formed on the surface of the powder of the present invention may increase. When the specific surface area is too small, when the powder of the present invention is used as a negative electrode active material for a battery, the charge / discharge capacity of the battery may be reduced.

(Carbon coat amorphous Si powder)
In the cooling step described above, Si in the passing flow can be brought into contact with the carbon source gas to carbon-coat Si. In order to bring Si in the flow through into contact with the carbon source gas, it can be simply performed by including the carbon source gas in the cooling gas. It is preferable to inject a carbon source gas flow facing the through flow toward the through flow.

  When the carbon source gas flow is injected toward the passing flow, it is preferable that the carbon source gas is not mixed in the plasma. If the carbon source gas is mixed in the plasma, Si and C may react to generate SiC.

  In order to coat Si with carbon, only a carbon source gas may be used as a cooling gas, or a carbon source gas and a rare gas may be used in combination. The ratio of the carbon source gas in the cooling gas is preferably noble gas: carbon source gas = 0: 100 to 99: 1, more preferably noble gas: carbon source gas = 80: 20 to 98: 2, and noble gas: carbon source. Gas = 90: 10 to 97: 3 is more preferable.

  Examples of the carbon source gas include alkanes such as methane, ethane, propane, butane, pentane, hexane, heptane, and octane, alkynes such as acetylene, methylacetylene, butyne, pentyne, hexyne, heptine, and octyne, ethylene, Alkenes such as propylene, butene, pentene, hexene, heptene, octene, ethers such as dimethyl ether, ethyl methyl ether, diethyl ether, ethyl propyl ether, dipropyl ether, propyl butyl ether, dibutyl ether, ethylene glycol, propylene glycol, glycerin Glycols such as methyl formate, ethyl formate, ethyl acetate, methyl acetate, methyl butyrate, ethyl butyrate, diethyl ether, ethyl methyl ether, tetrahydrofuran, etc. Ethers, benzene, toluene, xylene, pyridine, aromatic such as furan and the like. These may be used alone or in combination of two or more. As the carbon source gas, alkanes, alkynes, and alkenes are preferable.

  The average particle diameter of the carbon coat powder of the present invention is preferably in the range of 1 nm to 200 nm, and more preferably in the range of 10 nm to 60 nm. The average particle diameter here means an arithmetic average value of the longest diameter of the particles when the powder of the present invention is observed with an electron microscope such as a scanning electron microscope or a transmission electron microscope.

  The carbon-coated powder of the present invention is carbon-coated on the above-described powder of the present invention. Since Si is low in conductivity, conductivity can be improved by carbon coating. In addition, when the carbon coat powder of the present invention is used as a negative electrode active material of a battery, for example, an effect of reducing the reaction resistance of the battery is exhibited, and an effect of exhibiting a sufficient capacity even at high speed charge / discharge is achieved. The effect of improving the life of the battery and the battery is exhibited.

  The carbon coat powder of the present invention has a carbon layer formed on the surface of the powder of the present invention. The carbon in the carbon layer may be crystalline carbon, amorphous carbon, or a mixture of both. In the carbon coat powder of the present invention, it is preferable that at least a part of carbon is amorphous. Since the carbon of the carbon layer has an amorphous structure, even if Si expands or contracts, the carbon layer is difficult to peel off from the surface of the Si particles, and the effect of the carbon coat can be easily maintained.

  The thickness of the carbon layer is not particularly limited. The thickness of the carbon layer is preferably 20 nm or less.

  Further, in the cooling step, Si in the passing flow can be brought into contact with the carbon source gas so that Si is coated with carbon, so that Si is coated with carbon without being exposed to oxygen in the atmosphere. Therefore, the surface of Si in the carbon coat amorphous-containing Si powder is not easily oxidized. Accordingly, the carbon-coated amorphous Si powder produced in this way has a low oxygen content.

  The oxygen content of the carbon-coated amorphous-containing Si powder is preferably 10% or less, and more preferably 5% or less. When the oxygen content of the carbon-coated amorphous-containing Si powder is small, an effect of reducing the irreversible capacity of the battery is exhibited when used as a negative electrode active material of the battery.

The specific surface area of the carbon coating powder of the present invention is preferably from ^{1m 2} / ^g~200m 2 / ^g, more preferably ^{30m 2 / g~150m 2 / g,} 50m 2 / g~100m 2 / g More preferably. The specific surface area is measured by the BET method using nitrogen adsorption.

  Next, the process using the powder of the present invention will be described. Specifically, the step is a step of mixing the amorphous-containing Si powder functioning as the negative electrode active material with a solvent to obtain a negative electrode active material layer composition.

  Examples of the solvent include N-methyl-2-pyrrolidone, methanol, and methyl isobutyl ketone. The amount of the solvent used is preferably such that the composition for the negative electrode active material layer becomes a slurry.

  In addition to the amorphous-containing Si powder and the solvent, other known negative electrode active materials, binders, and conductive assistants may be added to the negative electrode active material layer composition.

  The binder plays a role of securing the active material to the surface of the current collector and maintaining a conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, poly ( Examples thereof include acrylic resins such as (meth) acrylic acid, styrene-butadiene rubber, and carboxymethyl cellulose. These binders may be used singly or in plural.

  Examples of the other negative electrode active material include a carbon-based material capable of inserting and extracting lithium, an element that can be alloyed with lithium, a compound having an element that can be alloyed with lithium, a polymer material, and the like.

  Examples of the carbon-based material include non-graphitizable carbon, graphite, cokes, graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon, and carbon blacks. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Specifically, elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si. , Ge, Sn, Pb, Sb, Bi can be exemplified, and Si or Sn is particularly preferable.

Specific examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , _{CaSi 2, CrSi 2, Cu 5} Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO can be exemplified, especially SiO _x (0.3 ≦ x ≦ 1.6 or 0.5 ≦ x ≦ 1.5) Is preferred.

  The mixing ratio of the binder in the composition for the negative electrode active material layer is preferably a mass ratio in the range of negative electrode active material: binder = 1: 0.001 to 1: 0.3. More preferably, it is within the range of 0.005 to 1: 0.2, and even more preferably within the range of 1: 0.01 to 1: 0.15. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density of the electrode is lowered.

  The conductive assistant is added to increase the conductivity of the electrode. Therefore, the conductive auxiliary agent may be added arbitrarily when the electrode conductivity is insufficient, and may not be added when the electrode conductivity is sufficiently excellent. The conductive auxiliary agent may be any chemically inert electronic high conductor, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), vapor grown carbon fiber (Vapor Grown Carbon). Fiber: VGCF) and various metal particles are exemplified. These conductive assistants can be added to the negative electrode active material layer alone or in combination of two or more.

  The blending ratio of the conductive assistant in the negative electrode active material layer composition is, by mass ratio, preferably negative electrode active material: conductive assistant = 1: 0.005 to 1: 0.5, A range of 0.01 to 1: 0.2 is more preferable, and a range of 1: 0.02 to 1: 0.1 is even more preferable. This is because if the amount of the conductive aid is too small, an efficient conductive path cannot be formed, and if the amount of the conductive aid is too large, the formability of the negative electrode active material layer is deteriorated and the energy density of the electrode is lowered.

  The negative electrode of the present invention is produced through a step of applying the negative electrode active material layer composition to the current collector, a drying step, and a compression step as necessary.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel, etc. Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  In order to apply the negative electrode active material layer composition to the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used. .

  The negative electrode of the present invention can be used as a negative electrode for a secondary battery. Hereinafter, the secondary battery provided with the negative electrode of the present invention is referred to as the secondary battery of the present invention. One embodiment of the secondary battery of the present invention includes the negative electrode, the positive electrode, the electrolytic solution, and the separator of the present invention. The case where the secondary battery of the present invention is a lithium ion secondary battery will be described as an example.

  The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and may further include a conductive additive and other additives. A positive electrode active material, a conductive support agent, and a binder are not particularly limited.

As the positive electrode active material, a material capable of occluding and releasing charge carriers such as Li may be used. As the positive electrode active material, the layered compound Li _a Ni _b Co _c Mn _{d De} O _f (0.2 ≦ a ≦ 2, b + c + d + e = 1, 0 ≦ e <1, D is Li, Fe, Cr, Cu, At least one element selected from Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 3 ), Li ₂ MnO ₃ . Further, as a positive electrode active material, a solid solution composed of a spinel such as LiMn ₂ O ₄ and Li ₂ Mn ₂ O ₄ and a mixture of a spinel and a layered compound, LiMPO ₄ , LiMVO _4, or Li ₂ MSiO ₄ (M in the formula) Are selected from at least one of Co, Ni, Mn, and Fe). Furthermore, as the positive electrode active material, tavorite compound (the M a transition metal) LiMPO ₄ F, such as LiFePO ₄ F represented by, Limbo ₃ such LiFeBO ₃ (M is a transition metal) include borate-based compound represented by be able to. Any metal oxide used as the positive electrode active material may have the above composition formula as a basic composition, and a metal element contained in the basic composition may be substituted with another metal element. Further, as a positive electrode active material, a positive electrode active material that does not contain lithium ions that contribute to charge / discharge, for example, sulfur alone (S), a compound in which sulfur and carbon are combined, a metal sulfide such as TiS ₂ , V ₂ O, etc. ₅ , oxides such as MnO ₂ , polyaniline and anthraquinone, compounds containing these aromatics in the chemical structure, conjugated materials such as conjugated diacetic acid organic materials, and other known materials can also be used. Further, a compound having a stable radical such as nitroxide, nitronyl nitroxide, galvinoxyl, phenoxyl, etc. may be adopted as the positive electrode active material. When using a positive electrode active material that does not contain lithium, it is necessary to add ions to the positive electrode and / or the negative electrode in advance by a known method. Here, in order to add the ion, a metal or a compound containing the ion may be used.

  The current collector used for the positive electrode is not limited as long as it is generally used for the positive electrode of a lithium ion secondary battery, such as aluminum, nickel, and stainless steel. .

  What is necessary is just to employ | adopt suitably suitably what was demonstrated with the negative electrode about the conductive support agent used for a positive electrode with the same compounding ratio.

  What is necessary is just to employ | adopt suitably suitably about the binder used for a positive electrode by the same mixture ratio as what was demonstrated with the negative electrode.

  The electrolytic solution includes a nonaqueous solvent and an electrolyte dissolved in the nonaqueous solvent.

  As the non-aqueous solvent, cyclic esters, chain esters, ethers and the like can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, ethyl methyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane. As the non-aqueous solvent, a compound in which part or all of hydrogen in the chemical structure of the specific solvent is substituted with fluorine may be employed.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / L to 1.7 mol of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 in} a nonaqueous solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and diethyl carbonate. A solution dissolved at a concentration of about / L can be exemplified.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass while preventing a short circuit of current due to contact between the two electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile, and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin, suberin, etc. Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

  Next, a method for producing a secondary battery of the present invention will be described taking a lithium ion secondary battery as an example. The manufacturing method of the secondary battery of this invention includes the process of arrange | positioning the negative electrode obtained by the manufacturing method of the negative electrode of this invention. Specifically, it is as follows.

  A separator is sandwiched between the positive electrode and the negative electrode as necessary to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. It is good to do. Moreover, the secondary battery of this invention should just be charged / discharged in the voltage range suitable for the kind of active material contained in an electrode.

  The shape of the secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from the secondary battery for all or part of its power source, and may be, for example, an electric vehicle, a hybrid vehicle, or the like. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with lithium ion secondary batteries include various home appliances driven by batteries such as personal computers and portable communication devices, office devices, and industrial devices in addition to vehicles. Furthermore, the lithium ion secondary battery of the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power supplies for ships and / or auxiliary power supply sources, aircraft, Power supply for spacecraft and / or auxiliary equipment, auxiliary power supply for vehicles that do not use electricity as a power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charging station for electric vehicles.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described more specifically with reference to production examples, examples and comparative examples. In addition, this invention is not limited by these Examples.

(Production Example 1)
The powder of Production Example 1 was produced using the plasma generator shown in FIG. In the plasma generator in FIG. 1, the raw material powder is supplied from the powder supplier 1, and the raw material powder is introduced into the plasma generator through the carrier gas path 6. The carrier gas is introduced into the plasma generator through the carrier gas path 6, the process gas is introduced into the plasma generator through the process gas path 7, and the inner gas is introduced into the plasma generator through the inner gas path 8. Power is supplied by the power supply device 2, and plasma is generated in the plasma generator. The cooling gas carried through the cooling gas path 9 is injected in a direction opposite to the passing flow after passing through the plasma. Each gas is exhausted outside the apparatus through the exhaust unit 3. The product falls by its own weight and is stored in the lower part of the internal chamber 5. In the plasma generator shown in FIG. 1, white arrows represent cooling water.

As a raw material Si powder, measured values of the average particle diameter _{D 50} was prepared 3 [mu] m Si powder (produced by Kojundo Chemical Laboratory Co., Ltd., product number SIE23PB).

  The raw material Si powder was placed in a powder feeder.

  In the plasma generator, argon gas as a process gas was added at 60 L / min. At 5 L / min. As an inner gas. At a flow rate of 3 L / min. Supplied with. Electric power was supplied from the power supply device, and a magnetic field with a frequency of 4 MHz was applied to the coil to generate plasma with an output of 20 kW. The pressure in the plasma generator was atmospheric pressure.

  After the plasma was stabilized, the powder feeder was operated, and the raw material Si powder was added at 100 mg / min. Was introduced into the plasma together with the carrier gas at a rate of The powder discharged together with the flow after passing through the plasma was collected and used as the powder of Production Example 1. The powder of Production Example 1 was ocher. In Production Example 1, no cooling gas was used.

(Production Example 2)
Argon gas was used as a cooling gas at 20 L / min. The powder of Production Example 2 was produced in the same manner as in Production Example 1, except that it was supplied in the above. The powder of Production Example 2 was ocher.

(Production Example 3)
Argon gas as a process gas was 55 L / min. In the plasma generator. Helium gas at 5 L / min. And a 27 kW output plasma is generated, and the raw material supply rate is 600 mg / min. A powder of Production Example 3 was produced in the same manner as Production Example 1 except that. The powder of Production Example 3 was ocher.

(Production Example 4)
The powder of Production Example 4 was produced in the same manner as in Production Example 3, except that plasma with an output of 30 kW was generated. The powder of Production Example 4 was ocher.

(Production Example 5)
The powder of Production Example 5 was produced in the same manner as Production Example 3, except that plasma with an output of 33 kW was generated. The powder of Production Example 5 was ocher.

(Production Example 6)
Argon as a carrier gas is 4.5 L / min. The powder of Production Example 6 was produced in the same manner as in Production Example 4 except that the powder was supplied in the above. The powder of Production Example 6 was ocher.

(Production Example 7)
Argon as a carrier gas is 6.0 L / min. The powder of Production Example 7 was produced in the same manner as in Production Example 4 except that the powder was supplied in the above. The powder of Production Example 7 was ocher.

(Production Example 8)
The raw material supply rate was 350 mg / min. A powder of Production Example 8 was produced in the same manner as Production Example 4 except that. The powder of Production Example 8 was ocher.

(Production Example 9)
Argon gas was used as a cooling gas at 10 L / min. The powder of Production Example 9 was produced in the same manner as in Production Example 4 except that the powder was supplied in the above. The powder of Production Example 9 was ocher.

(Production Example 10)
Argon gas was used as a cooling gas at 20 L / min. The powder of Production Example 10 was produced in the same manner as in Production Example 4 except that the powder was supplied in the above. The powder of Production Example 10 was ocher.

(Production Example 11)
Argon gas was used as a cooling gas at 10 L / min. The powder of Production Example 11 was produced in the same manner as in Production Example 1 except that the powder was supplied in the above. The powder of Production Example 11 was ocher.

(Comparative Production Example 1)
The raw material Si powder was used as the powder of Comparative Production Example 1.

<Measurement of average particle size and amorphization degree>
The amorphization degree and average particle diameter of the powders of Production Examples 1 to 11 were measured.

As described above, the degree of amorphization was obtained from the formula: degree of amorphization = Si (a) / (Si (c) + Si (a)). XRD was measured using a powder X-ray diffractometer (biaxial X-ray diffractometer (product name: RINT2550V, manufactured by Rigaku Denki Co., Ltd.). A raw material Si powder was used as the crystalline Si powder, and a calibration curve was obtained using the raw material Si powder and ZnO. The thickness of the SiO ₂ layer of each powder observed with STEM was 1 nm to ₄ nm.

  The average particle diameter was measured using TEM. From the obtained TEM images, the longest diameter of each particle was measured for 200 particles, and the average particle diameter which was an arithmetic average value of the longest diameter was calculated.

  For example, the average particle size of the powder of Production Example 1 was 30 nm, and the average particle size of the powder of Production Example 2 was 22 nm. A particle size distribution diagram of the powder of Production Example 1 and the powder of Production Example 2 is shown in FIG. Moreover, the TEM image of the powder of the manufacture example 2 is shown in FIG.

  From this result, it was found that nano-sized amorphous-containing Si powder can be produced in the powder production process.

Table 1 shows the production conditions, the degree of amorphization, and the average particle size of the powders of Production Examples 1 to 11 and Comparative Production Example 1. However, the average particle diameter of the powder Comparative Preparation Example 1 is the value of the average particle diameter D _50, the amorphous degree of powder Comparative Preparation Example 1 was 0%.

<Measurement of sphericity>
The sphericity is the sphericity when the powder of the present invention is observed with an electron microscope such as a scanning electron microscope or a transmission electron microscope. (Sphericity = shortest particle diameter) / (longest particle diameter) It was calculated by equation 1). The number of particles to be observed was 200, and the sphericity was an average value of the 200 particles. Table 1 shows the sphericity of the powders of Production Examples 2 to 5 and Production Example 10. The sphericity of each powder was in the range of 0.8 to 1, and it was confirmed that the powder of the present invention was close to a sphere.

Further, the sphericity of each powder was also determined by using the sphericity = 4πS / l ² (S: particle area, l: particle circumference) (Equation 2). Since it was almost the same as the value obtained in 1), Table 1 shows only the value of the sphericity obtained in Expression (1).

<Measurement of specific surface area>
The specific surface areas of the powders of Production Examples 1, 2, and 11 and Comparative Production Example 1 were measured by the BET method using nitrogen adsorption. The results are shown in Table 1. The specific surface areas of the powders of Production Examples 1, 2, and 11 were extremely larger than the specific surface area of the powder of Comparative Production Example 1. The specific surface area of the powder of Production Example 1, 2 and 11 were confirmed to be ^{40m 2} / ^g~160m 2 / g.

<Examination of average particle size>
(Influence of cooling gas)
Comparing the average particle sizes of the powders of Production Examples 1 and 2, it was found that the average particle size can be reduced by injecting a cooling gas flow facing the through flow toward the through flow.

(Examination of plasma output)
When the average particle diameters of the powders of Production Examples 3 to 5 were compared, it was found that the average particle diameter decreased as the plasma output increased.

(Examination of carrier gas flow rate)
When the average particle sizes of the powders of Production Examples 4 and 7 were compared, it was found that the average particle size decreased as the carrier gas flow rate increased.

<Examination of degree of amorphization>
(Examination of plasma output)
When the degree of amorphization of the powders of Production Examples 3 to 5 was compared, it was found that the degree of amorphization increased as the plasma output increased.

  It is considered that when the plasma output is increased, the maximum temperature in the plasma is increased and the cooling rate is further increased. For this reason, it is considered that the time from the evaporation of the raw material to the low temperature part is also shortened. This also increases the cooling rate. It is presumed that the degree of amorphization increased as the cooling rate increased.

(Examination of carrier gas flow rate)
Comparing the amorphization degree of the powders of Production Examples 4, 6, and 7, it was found that the amorphization degree increased as the carrier gas flow rate increased.

  As the carrier gas flow rate increases, the flow rate of the raw material powder increases. Therefore, it is estimated that the time from the nucleation of particles to the low temperature part is shortened. Increasing the carrier gas flow rate increases the cooling rate. It is presumed that the degree of amorphization increased as the cooling rate increased.

(Examination of raw material supply speed)
When the degree of amorphization of the powders of Production Examples 4 and 8 was compared, it was found that the degree of amorphization increased with decreasing raw material supply rate.

  It is considered that when the supply speed of the raw material Si powder is increased, the heat of the plasma is taken away by the vaporization of many Si particles and the temperature in the plasma is lowered. It is considered that the degree of amorphization decreases as the temperature in the plasma decreases.

(Examination of cooling gas flow rate)
When the degree of amorphization of the powders of Production Example 1, Production Example 2, Production Example 4 and Production Examples 9 to 11 is compared, the degree of amorphization is increased by using a cooling gas and increasing the flow rate of the cooling gas. I understood. It was also found that the amorphization degree can be further increased by reducing the raw material supply rate.

  From the results of the degree of amorphization of the powders of Production Example 2 and Production Example 11, it was found that an amorphous-containing Si powder having an amorphization degree close to 100% was obtained.

  When the cooling gas flow rate is increased, the flow passing through the plasma is cooled more rapidly outside the plasma. It is presumed that the degree of amorphization increased with an increase in the cooling rate.

(Comparison of XRD chart and degree of amorphization)
An XRD chart of the powders of Production Example 1, Production Example 2, Production Example 11 and Comparative Production Example 1 is shown in FIG. The amorphization degree of the powder of Comparative Production Example 1 is 0%, the amorphization degree of the powder of Production Example 1 is 18%, the amorphization degree of the powder of Production Example 11 is 94%, and the powder of Production Example 2 The degree of amorphous formation was 93%. As can be seen in FIG. 4, it was clearly understood that each peak of XRD becomes smaller as the degree of amorphization increases.

<Examination of carbon coat>
(Production Example 12)
The raw material Si powder was placed in a powder feeder.

  In the plasma generator, argon gas as process gas is supplied at 60 L / min, and argon gas as inner gas is supplied at 5 L / min. At a flow rate of 3 L / min. Supplied with. Electric power was supplied from the power supply device, and a magnetic field with a frequency of 4 MHz was applied to the coil to generate plasma with an output of 20 kW. The pressure in the plasma generator was atmospheric pressure.

  After the plasma was stabilized, the powder feeder was operated, and the raw material Si powder was reduced to 600 mg / min. Was introduced into the plasma together with the carrier gas at a rate of As the cooling gas, methane gas is used at 1 L / min. The powder discharged together with the flow after passing through the plasma was collected and used as the powder of Production Example 12. The powder of Production Example 12 was black. The powder of Production Example 12 is presumed that the color of the powder became black by coating with carbon.

(Production Example 13)
The raw material Si powder was 600 mg / min. The argon gas was supplied at a rate of 9 L / min. Methane gas at 1 L / min. The powder of Production Example 13 was produced in the same manner as in Production Example 12, except that it was supplied in the above. The powder of Production Example 13 was black.

(Production Example 14)
The raw material Si powder was 600 mg / min. The argon gas was supplied at a rate of 19 L / min. Methane gas at 1 L / min. The powder of Production Example 14 was produced in the same manner as in Production Example 12, except that the powder was supplied in the above. The powder of Production Example 14 was black.

<Observation of carbon coat>
(TEM observation)
The powders of Production Examples 12 to 14 were dispersed on a Mo mesh and observed with a TEM. According to the TEM images of the powders of Production Examples 12 to 14, it was found that the surface of the Si particles was coated with carbon with a thickness of 1 nm to 5 nm.

(Composition analysis by EDX)
The composition analysis of each powder in the TEM image was performed by EDX. The EDX measurement result of the powder of the manufacture example 14 is shown in FIGS. 5 shows the EDX measurement result of (I) the central portion of one particle of the powder of Production Example 14, and FIG. 6 shows the EDX measurement result of the (II) peripheral portion of the particle shown in FIG.

  As shown in FIG. 5, the intensity of the peak derived from Si was detected to be high in the center of the particle, and a peak derived from C was observed less than the peak derived from Si. Further, as shown in FIG. 6, the intensity of the peak derived from C was detected at the periphery of the particle, and the intensity of the peak derived from Si was detected very low. 5 and 6, the Si peak of the Si particle and the C peak of the carbon layer on the surface of the Si particle are observed at the center of the particle, and the peripheral edge of the particle is the C peak of the carbon layer. Can be said to be observed. The peak of Mo shown in FIGS. 5 to 6 is derived from the Mo mesh for supporting the sample powder.

(Raman spectroscopy measurement)
The Raman spectra of the powders of Production Examples 12 to 14 were measured using a Raman spectroscope (Horiba, Ltd. LabRAM ARAMIS). The measurement conditions were a wavelength of 532 nm, a measurement range of 450 cm ^{−1 to} 1700 cm ⁻¹ , a measurement time of 30 seconds, and an integration count of 50 times. In the Raman spectra of the obtained powders of Production Examples 12 to 14, peaks of both G band and D band were observed. From this, it was confirmed that the carbon layer contains amorphous carbon.

(Measurement of average particle size)
The average particle diameter of the powders of Production Examples 12 to 14 was measured using TEM. From the obtained TEM images, the longest diameter of each particle was measured for 200 particles, and the average particle diameter which was an arithmetic average value of the longest diameter was calculated.

(Measurement of oxygen content)
The oxygen content of the powders of Production Examples 12 to 14, Production Example 2, Production Example 3 and Production Example 5 was measured using Horiba, Ltd. and an oxygen analyzer EMGA-820.

  The measurement results are shown in Table 2.

<Measurement of specific surface area>
The specific surface areas of the powders of Production Examples 12, 13, and 14 were measured by the BET method using nitrogen adsorption. The results of specific surface area are shown in Table 2. The specific surface area of the powder of Production Example 12, 13 and 14 were confirmed to be ^{50m 2} / ^g~100m 2 / g.

  The surface of the amorphous-containing Si particles is oxidized when taken out from the production apparatus into the atmosphere. Therefore, it is considered that the oxygen content of the amorphous-containing Si powder refers to the surface oxidized amount of the amorphous-containing Si particles. From the amorphization degree and oxygen content of the powders of Production Example 2, Production Example 3 and Production Example 5 in Table 2, it was found that the higher the amorphization degree, the higher the oxygen content. If the degree of amorphization is high, the surface area of the particles increases, and it is assumed that the surface is easily oxidized.

  The oxygen content of the powders of Production Examples 12 to 14 with carbon coating was significantly smaller than the oxygen content of the powders of Production Example 2, Production Example 3 and Production Example 5 without carbon coating. From this, it is speculated that the surface-oxidation of the Si particles in the atmosphere was suppressed because the carbon-coated amorphous-containing Si particles were already carbon-coated on the surface when taken out from the production equipment to the atmosphere. Is done.

  The oxygen content of the powders of Production Examples 12 to 14 was as small as 2% to 4% by mass. From this, it was found that the powders of Production Examples 12 to 14 are amorphous-containing Si powders that are carbon-coated and have an oxygen content of 5% or less.

<Manufacture of lithium ion secondary batteries>
Example 1
The negative electrode and lithium ion secondary battery of Example 1 were manufactured as follows.

40 parts by mass of the powder of Production Example 1 as an anode active material, 40 parts by mass of natural graphite having an average particle diameter D ₅₀ of 10 μm, 5 parts by mass of acetylene black as a conductive additive, and 15 parts by mass of polyamideimide resin as a binder were mixed. . This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone to prepare a slurry-like composition for a negative electrode active material layer.

  A copper foil having a thickness of 20 μm was prepared as a current collector. The composition for negative electrode active material layers was placed on the surface of the copper foil, and the composition for negative electrode active material layers was applied into a film using a doctor blade. The copper foil coated with the negative electrode active material layer composition was dried at 80 ° C. for 20 minutes to remove N-methyl-2-pyrrolidone by volatilization, thereby forming a negative electrode active material layer on the copper foil surface. The copper foil having the negative electrode active material layer formed on the surface thereof was compressed using a roll press machine, and the copper foil and the negative electrode active material layer were firmly bonded. The joined product was heated in a vacuum dryer at 200 ° C. for 2 hours and cut into a predetermined shape to obtain a negative electrode of Example 1.

  A lithium ion secondary battery (half cell) was produced using the negative electrode of Example 1 produced by the above procedure as a working electrode. The counter electrode was a metal lithium foil.

A working electrode and a counter electrode, and a separator (Hoechst Celanese glass filter and Celgard “Celgard 2400”) interposed between the two electrodes were disposed to form an electrode body. This electrode body was accommodated in a battery case (CR2032-type coin battery member, manufactured by Hosen Co., Ltd.). Into the battery case, a nonaqueous electrolyte solution in which LiPF ₆ was dissolved at a concentration of 1M was poured into a mixed solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1, the battery case was sealed, and A lithium ion secondary battery was obtained.

(Example 2)
A negative electrode and a lithium ion secondary battery of Example 2 were obtained in the same manner as in Example 1, except that the powder of Production Example 2 was used as the negative electrode active material.

(Example 3)
A negative electrode and a lithium ion secondary battery of Example 3 were obtained in the same manner as in Example 1 except that the powder of Production Example 12 was used as the negative electrode active material.

(Example 4)
A negative electrode and a lithium ion secondary battery of Example 4 were obtained in the same manner as in Example 1, except that the powder of Production Example 13 was used as the negative electrode active material.

(Comparative Example 1)
The negative electrode of Comparative Example 1 was prepared in the same manner as in Example 1 except that crystalline Si powder (average particle size D ₅₀ 5 μm (value of D ₅₀ in laser diffraction particle size distribution measurement)) was used as the negative electrode active material. A lithium ion secondary battery was obtained.

(Evaluation example A)
Each lithium ion secondary battery was subjected to a charge / discharge cycle test in which charging from 0.01 V to 1.0 V and discharging from 1.0 V to 0.01 V were performed 50 times at 0.5 mA at room temperature. The discharge capacity at the first time was used as the initial capacity, the discharge capacity for each cycle was measured, and the capacity retention rate was calculated from the following formula.
Capacity maintenance rate (%) = (discharge capacity after each cycle / initial capacity) × 100
FIG. 7 shows a graph showing the relationship between the number of cycles and the capacity retention rate of lithium ion secondary batteries using the negative electrodes of Examples 1 to 4 and Comparative Example 1. Table 3 shows the capacity retention ratio after 50 cycles of each lithium ion secondary battery.

  As can be seen from Table 3, the capacity retention rates of the lithium ion secondary batteries of Examples 1 to 4 using the amorphous-containing Si powder were the capacity maintenance of the lithium ion secondary battery of Comparative Example 1 using the crystalline Si powder. Higher than the rate.

  Comparing the capacity retention rates of Example 1 and Example 2, the capacity retention rate of Example 2 using amorphous-containing Si powder having a high degree of amorphization was higher. From the comparison of capacity retention rates of Example 1 and Example 2, Example 3 and Example 4, it was found that the amorphous content Si powder had a higher capacity retention rate when carbon coated.

As also seen in FIG. 7, the lithium ion secondary battery having an average particle compared diameter D ₅₀ using crystalline Si powder of 5μm Example 1 sharply capacity retention rate decreased Beyond 10 cycles. On the other hand, the lithium ion secondary batteries of Examples 1 to 4 using the nano-sized amorphous-containing Si powder did not rapidly decrease the capacity maintenance rate during the 50-cycle cycle test, and even after 50 cycles, 80%. A high capacity retention rate of more than%

  1: powder feeder, 2: power supply device, 3: exhaust unit, 4: filter, 5: internal chamber, 6: carrier gas path, 7: process gas path, 8: inner gas path, 9: cooling gas path .

Claims (6)

A step of introducing raw material Si powder into the plasma by an introduction flow;
A cooling step for cooling the flow after the introduced flow has passed through the plasma;
Manufacturing process of amorphous-containing Si powder containing
Using the amorphous-containing Si powder;
Only including,
The method for producing a negative electrode, wherein, in the cooling step, the passing flow is cooled with a cooling gas flow facing the passing flow . The method for producing a negative electrode according to claim 1, wherein the amorphous-containing Si powder has an average particle diameter of 1 nm to 200 nm. Method of manufacturing an anode according to the amorphous-containing Si powder according to claim 1 or 2 amorphization degree is 50% or more. The step of using the amorphous-containing Si powder comprises
Mixing the amorphous-containing Si powder and a solvent to form a negative electrode active material layer composition;
Applying the negative electrode active material layer composition to a negative electrode current collector;
The manufacturing method of the negative electrode as described in any one of Claims 1-3 containing this. The method for producing a negative electrode according to any one of claims 1 to 4 , wherein, in the cooling step, Si in the through-flow is brought into contact with a carbon source gas and carbon is coated on Si. The manufacturing method of a secondary battery including the process of arrange | positioning the negative electrode obtained by the manufacturing method as described in any one of Claims 1-5 .