JP5835141B2 - Negative electrode active material for secondary battery, method for producing the same, negative electrode for secondary battery, secondary battery, and Si-oxide solid electrolyte composite - Google Patents

Description

  The present invention relates to a negative electrode active material for a secondary battery, a method for producing the same, a negative electrode for a secondary battery, a secondary battery, and a Si-oxide solid electrolyte composite.

  Secondary batteries are batteries that can be repeatedly charged and discharged, and lead storage batteries, lithium ion secondary batteries, nickel metal hydride storage batteries, nickel cadmium storage batteries, sodium sulfur batteries, redox flow batteries, and the like are known.

  These secondary batteries have a positive electrode and a negative electrode, and have an electrolyte that connects the electrodes. As the electrolyte, an aqueous electrolyte, a non-aqueous electrolyte, a molten salt electrolyte, a solid electrolyte (for example, a polymer solid electrolyte, β alumina solid electrolyte), an ionic liquid electrolyte, or the like is used. In recent years, lithium ion secondary batteries are well known as secondary batteries. Lithium ion secondary batteries include nonaqueous electrolyte lithium ion secondary batteries that use nonaqueous electrolytes, aqueous lithium ion secondary batteries that use aqueous electrolytes, and all solid lithium ion secondary batteries that use solid electrolytes. An ion secondary battery is a secondary battery that has a high charge / discharge capacity and can achieve high output. Lithium ion secondary batteries are mainly used as power sources for portable electronic devices, and are expected to be used as power sources for electric vehicles that are expected to become popular in the future.

  The lithium ion secondary battery has an active material capable of inserting and extracting Li ions in the positive electrode and the negative electrode, respectively. And these lithium ion secondary batteries operate | move when a lithium ion moves within the electrolyte provided between both electrodes.

  In the lithium ion secondary battery, a lithium-containing metal composite oxide such as lithium cobalt composite oxide is mainly used as a positive electrode active material, and a carbon material is mainly used as a negative electrode active material. The positive and negative electrode plates are prepared by dispersing the active material, binder resin, and conductive additive in a solvent to form a slurry on a metal foil as a current collector. After forming the agent layer, it is produced by compression molding with a roll press.

  In recent years, a material having a charge / discharge capacity that greatly exceeds the theoretical capacity of a carbon material has been developed as a negative electrode active material for a lithium ion secondary battery. For example, silicon-based materials such as silicon, silicon alloys, and silicon oxides having higher capacities than carbon materials are being studied.

  A silicon-based material has a high capacity of 1000 mAh / g or more by being alloyed with lithium. However, it is known that when a silicon-based material is used as a negative electrode active material, the negative electrode active material expands and contracts with insertion and extraction of lithium (Li) in a charge / discharge cycle. When the negative electrode active material expands or contracts, a load is applied to the binder that plays a role of holding the negative electrode active material on the current collector, and the adhesion between the negative electrode active material and the current collector is reduced. The conductive path is destroyed and the capacity is remarkably reduced, or the negative electrode active material is distorted due to repeated expansion and contraction, and is refined and detached from the electrode. Therefore, to use a silicon-based material as the negative electrode active material, due to the expansion and contraction of the negative electrode active material, the charge / discharge efficiency of the battery is lower than originally intended, the capacity of the battery is lower than originally intended, There is a problem that the cycle characteristics of the battery are deteriorated from those which should originally be possessed.

In order to solve this problem, studies have been made to make Si into nanoparticles. For example, Patent Document 1 discloses a negative electrode for a non-aqueous electrolyte secondary battery including particles in which Si is dispersed in SiO ₂ . It is described that the negative electrode material expressed as SiO _x has a structure in which nano-silicon of about several nm to several tens of nm is finely dispersed in silicon oxide according to analysis by X-ray diffraction.

However, in SiO _x , a substance expressed as Li _x SiO _y in which SiO ₂ and SiO ₂ which are matrix components occlude Li has low Li ion conductivity. Therefore, the inherent capacity of SiO _x is not exhibited. Therefore, a negative electrode active material having a sufficient battery capacity and good cycle characteristics using Si is demanded.

  In general, nanomaterials are difficult to synthesize because particle growth proceeds unless the conditions are properly controlled. Nanomaterials may ignite or explode during handling, and may be harmful to the human respiratory system. In addition, nanomaterials are difficult to handle, such as so-called dusting in the air due to static electricity and adhering to containers. Therefore, the nanomaterial synthesis process requires safety equipment such as dust collection, protection, and atmosphere control. For this reason, it is expensive to synthesize nanomaterials. Accordingly, there is a need for a method that can easily produce a composite containing a nanomaterial and that can be produced safely and inexpensively.

JP 2011-60676 A

  The present invention has been made in view of such circumstances. A negative electrode active material for a secondary battery that can have sufficient capacity and good cycle characteristics using Si as a negative electrode active material, and a method for producing the same An object of the present invention is to provide a negative electrode for a secondary battery, a secondary battery, and a Si-oxide solid electrolyte composite.

  As a result of intensive studies by the present inventors, a crystallite size measured by X-ray powder diffraction (XRD) measurement using a matrix made of an oxide solid electrolyte and CuKα rays dispersed in the matrix is 100 nm or less. It has been found that the output characteristics of the secondary battery can be improved by using a negative electrode active material comprising a Si-oxide solid electrolyte composite containing certain Si particles.

  That is, the negative electrode active material for a secondary battery of the present invention includes a matrix composed of an oxide solid electrolyte, and a crystallite size measured by X-ray powder diffraction (XRD) measurement using CuKα rays dispersed in the matrix. It consists of Si-oxide solid electrolyte composite containing Si particle | grains which are 100 nm or less.

  The crystallite size is preferably 65 nm or less.

  The oxide solid electrolyte is preferably amorphous or low crystalline.

  When the Si-oxide solid electrolyte composite is 100% by mass, the Si particle content is preferably 5% by mass or more and 95% by mass or less.

  The Si-oxide solid electrolyte composite is preferably prepared by applying mechanical energy to the Si powder and the oxide solid electrolyte, pulverizing, and compositing.

  The Si powder preferably has an average particle size of 1 μm or more.

  The negative electrode for secondary batteries of this invention contains the said negative electrode active material for secondary batteries.

  The secondary battery of this invention contains the said negative electrode for secondary batteries.

  The manufacturing method of the negative electrode active material for secondary batteries of this invention adds mechanical energy to Si powder and oxide solid electrolyte, and X-ray powder diffraction (XRD) measurement using Si K powder for Si powder is performed. It has the compounding process which grind | pulverizes until the measured crystallite size is set to 100 nm or less, and combines the grinded Si powder and the oxide solid electrolyte.

  In the composite step, the oxide solid electrolyte is preferably pulverized until it becomes amorphous or low crystalline.

  The compounding step is preferably performed in a sealed space.

  The Si powder preferably has an average particle size of 1 μm or more.

  The Si-oxide solid electrolyte composite of the present invention has a crystallite size measured by X-ray powder diffraction (XRD) measurement using a matrix made of an oxide solid electrolyte and CuKα rays dispersed in the matrix. Si particles that are 100 nm or less.

  The negative electrode active material for a secondary battery according to the present invention is an Si particle having a crystallite size of 100 nm or less measured by X-ray powder diffraction (XRD) measurement using a solid oxide electrolyte as a matrix and CuKα rays in the matrix. The output characteristics of the secondary battery can be improved by comprising the Si-oxide solid electrolyte composite in which is dispersed.

  Since the secondary battery of the present invention has a secondary battery negative electrode having the secondary battery negative electrode active material, a battery having sufficient capacity and good cycle characteristics can be obtained.

  According to the method for producing a negative electrode active material for a secondary battery of the present invention, a Si-oxide solid electrolyte composite can be easily produced. Further, if Si powder having an average particle diameter of 1 μm or more is used, Si nano-composition and composite treatment can be performed simultaneously. In addition, special equipment for handling nanoparticles is not required, and the equipment cost is excellent.

  When the Si-oxide solid electrolyte composite of the present invention is used as a negative electrode active material for a secondary battery, the output characteristics of the secondary battery can be improved.

It is explanatory drawing explaining a particle size and a crystallite. It is a schematic cross section explaining the negative electrode active material for secondary battery of this embodiment. It is a powder X-ray-diffraction result of the Si-oxide solid electrolyte complex of Example 1 and Example 2. 2 is a SEM photograph of a cross section of the Si-oxide solid electrolyte composite of Example 1. FIG. The SEM photograph of the surface of the Si-oxide solid electrolyte complex of Example 1 is compared with the SEM photograph of the surface of the Si-oxide solid electrolyte complex of Example 3. The SEM photograph of the surface of the Si-oxide solid electrolyte composite of Example 2 and the SEM photograph of the surface of the Si-oxide solid electrolyte composite of Example 4 are compared. It is a graph which shows the capacity | capacitance maintenance factor for every cycle of the model battery of Examples 1-4 and the model battery of the comparative example 1. FIG.

<Negative electrode active material for secondary battery>
The negative electrode active material for a secondary battery of the present invention comprises a Si-oxide solid electrolyte composite containing a matrix made of an oxide solid electrolyte and Si particles dispersed in the matrix.

In general, an electrolyte is a substance through which ions move. As a well-known electrolyte, sodium chloride (NaCl) can be mentioned. Sodium chloride does not move ions until it becomes a solution. A substance in which ions move in a solid state is generally called a “solid electrolyte”. That is, the solid electrolyte is an electrolyte that can move ions (charged substances) in a solid state by an electric field applied from the outside. The solid electrolyte generally refers to one having a Li ion conductivity of 1.0 × 10 ⁻⁶ S / cm or more near room temperature. Solid electrolytes are generally composed of oxides, organic polymers, and sulfides. The Young's modulus of organic polymer solid electrolytes and sulfide solid electrolytes is less than 1 GPa. The Young's modulus of the solid electrolyte is 50 GPa to 400 GPa.

  The negative electrode active material for a secondary battery of the present invention comprises a Si-oxide solid electrolyte composite. The Si-oxide solid electrolyte composite is a composite in which Si particles are dispersed in a matrix. In addition to the matrix and the Si particles, the Si-oxide solid electrolyte composite may include additives such as a conductive additive and other Si alloy particles.

  The matrix consists of an oxide solid electrolyte. Since the matrix in the present invention is an ionic conductor, the matrix does not hinder the conduction of ions as they pass through the matrix. Further, since the matrix does not occlude ions during charge and discharge, for example, the irreversible capacity of Li due to the occlusion of Li by the matrix does not occur. Moreover, since the matrix in this invention has a large Young's modulus, the expansion | swelling and shrinkage | contraction accompanying Li occlusion and discharge | release of Si particle | grains disperse | distributed to a matrix can be suppressed effectively.

  The oxide solid electrolyte is preferably amorphous or low crystalline. Amorphous refers to a solid state having no long-range regularity such as a crystal structure in the arrangement of constituent atoms. Low crystallinity is located between the amorphous and the crystal, and consists of single crystal grains with different orientations, "crystal grains". The regularity of the crystal structure is relatively short (for example, less than 100 nm) The state that is. The low crystallinity can be recognized by the peak of the X-ray diffraction result being lowered or widened. Here, when the peak is lowered or widened, for example, Scherrer's equation D = (Kλ) / (βcosθ), (λ: measured X-ray wavelength (Å), β: half-value width (rad), θ : Bragg angle of diffraction line, K: Atomic form factor (here 0.9), D is 1000 Å (100 nm) or less.

  When the oxide solid electrolyte is amorphous or has low crystallinity, growth of grain boundaries of the oxide solid electrolyte is suppressed. As a result, the interface resistance at the grain boundary, which is the main cause of the resistance of the solid electrolyte material, is reduced, so that the oxide solid electrolyte that is amorphous or has low crystallinity has high ionic conductivity.

As the oxide solid electrolyte, a Li ion conductive oxide solid electrolyte is preferable. Examples of the Li ion conductive oxide solid electrolyte include Li ₂ O—SiO ₂ —P ₂ O ₅ -based multicomponent glass, Li _4-x Si _x P _1-x O ₄ (0 ≦ x ≦ 1), and Li _x. La _{2−x / 3} TiO ₃ (x = 0.1 to 0.5), Li _{7 + x} La ₃ Zr ₂ O _{12+ (x / 2)} (−5 ≦ x ≦ 3, preferably −2 ≦ x ≦ 2) Li _{1 + x + y} (Al, Ga) _x (Ti, Ge, Zr) _2-x Si _y P _3-y O ₁₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), Li ₂ O-5Al ₂ O ₃ , Li ₂ O-11Al ₂ O ₃ , Li ₅ La ₃ (Nb, Ta) ₂ O ₁₂ , Li ₁₄ ZnGe ₄ O ₁₆ , Li ₉ SiAlO ₈ is Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ). ₃ is mentioned. The composition of the oxide solid electrolyte is not limited to the above, and may be, for example, an oxide solid electrolyte in which part or all of the above composition is replaced with other components within a range not impairing Li ion conductivity.

In particular, Li _x La _{2−x / 3} TiO ₃ (x = 0.1 to 0.5), Li _{7 + x} La ₃ Zr ₂ O _{12+ (x / 2)} (−5 ≦ x ≦ 3, preferably −2 ≦ x ≦ 2), Li _{1 + x + y} (Al, Ga) _x (Ti, Ge, Zr) _2−x Si _y P _3−y O ₁₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1), Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (LAGP) is preferable because of its high Li ion conductivity. In particular, Li _{7 + x} La ₃ Zr ₂ O _{12+ (x / 2)} (−5 ≦ x ≦ 3, preferably −2 ≦ x ≦ 2) is preferable because of high electrochemical durability.

It is preferable to use a lithium ion conductive oxide solid electrolyte having a Li ion conductivity at room temperature of 1.0 × 10 ⁻⁴ S / cm or more. The higher the ion conductivity, the more uniform and efficient the alloying reaction between Si and Li can be, so that the capacity of Si particles can be efficiently extracted.

  The Si particles have a crystallite size of 100 nm or less as measured by X-ray powder diffraction (XRD) measurement using CuKα rays. The crystallite size measured by X-ray powder diffraction (XRD) measurement using CuKα rays indicates the average of individual crystallite sizes.

  FIG. 1 is an explanatory diagram for explaining the grain size and crystallites. A crystallite is the smallest microcrystalline unit that forms a crystal. As seen in FIG. 1, in the case of single crystal particles, the particle size and crystallite size are the same, but in the case of polycrystalline particles, the crystallite size is small because the polycrystalline particles are aggregates of crystals smaller than the particles. And the particle size is different. In the composite, it is considered that there are places where individual crystals are polycrystalline or single crystals.

  In the present invention, the crystallite size is measured by X-ray powder diffraction (XRD) measurement using CuKα rays. The crystallite size measured by X-ray powder diffraction (XRD) measurement using CuKα rays is the average of the individual crystallite sizes.

  The crystallite size is determined from the half width of the XRD peak of Si obtained by X-ray powder diffraction (XRD) measurement. The full width at half maximum is the width at a location corresponding to half the height of the peak intensity. As the full width at half maximum increases, the crystallite size decreases.

  FIG. 2 shows a schematic cross-sectional view of the negative electrode active material for a secondary battery of the present embodiment. As shown in FIG. 2, the Si particles 1 are dispersed in a matrix 2 made of an oxide solid electrolyte. Moreover, as shown in FIG. 2, the range of the particle size of the Si particles 1 is large. In the present embodiment, the Si particles are defined to have a crystallite size of 100 nm or less measured by X-ray powder diffraction (XRD) measurement using CuKα rays. Therefore, the particle size of each Si particle is It is a town.

  The crystallite size of the Si particles is 100 nm or less. The crystallite size is preferably 65 nm or less, more preferably 53 nm or less, and further preferably 1 nm or more and 40 nm or less. The volume of Si expands and contracts due to insertion and extraction of Li. Therefore, by setting the crystallite size to nano-size, the expansion and contraction of Si is also performed in the nano-size, so that the expansion and contraction of Si particles can be easily suppressed by the matrix. Since the effect of suppressing the expansion and contraction of the Si particles by the matrix is high, it is more preferable that the crystallite size of the Si particles is small.

  Si particles are dispersed in the matrix. Here, that the Si particles are dispersed in the matrix means that at least a part of the outer surface of the Si particles is in contact with the matrix. Desirably, the entire outer surface of the Si particles is in contact with the matrix. A part of the outer surface of the Si particle may be in contact with a part of the outer surface of another adjacent Si particle.

  If the Si particles are in a non-contact state, the matrix around the Si particles suppresses the individual expansion and contraction of the Si particles, so that the Si particles are in contact with each other in a lump state. The expansion and contraction of the whole negative electrode active material can be suppressed.

  When the Si-oxide solid electrolyte composite is 100% by mass, the Si particle content is preferably 5% by mass or more and 95% by mass or less. If the content of Si particles is less than 5% by mass, the desired battery capacity cannot be obtained. If the content is more than 95% by mass, the expansion and contraction of Si particles can be efficiently suppressed by the oxide solid electrolyte. Absent. When the Si-oxide solid electrolyte composite is 100% by mass, the Si particle content is more preferably 20% by mass to 80% by mass.

  The Si-oxide solid electrolyte composite preferably has a median diameter of 200 nm to 20 μm. The median diameter of the Si-oxide solid electrolyte composite is more preferably 2 μm or more and 10 μm or less. If the median diameter of the Si-oxide solid electrolyte composite is smaller than 200 nm, the handleability is poor and difficult to handle. If the median diameter of the Si-oxide solid electrolyte composite is larger than 20 μm, it is difficult to apply to the current collector during electrode preparation. The median diameter is a 50% diameter of the powder particles. For example, the median diameter can be measured by a laser diffraction method (Microtruc 3300 MTII) using a 0.2 mass% sodium hexametaphosphate aqueous solution as a dispersion medium.

  The method for synthesizing the Si-oxide solid electrolyte composite is not particularly limited, but it may be produced by adding mechanical energy to the Si powder and the oxide solid electrolyte, pulverizing, and compositing. preferable.

  The Si-oxide solid electrolyte composite produced in this way can be produced with a reduced specific surface area. When the specific surface area is small, the amount of a surface film called SEI (Solid Electrolyte Interface) formed on the active material surface can be reduced. Since SEI is a resistance, it is desirable that SEI is small.

  The Si powder preferably has an average particle size of 1 μm or more. The average particle diameter used at this time indicates a median diameter of 50%. By using micron-sized Si as a raw material and simultaneously performing nano-ization and composite treatment, Si can be easily made into a nano-state to produce a Si-oxide solid electrolyte composite.

<Method for producing negative electrode active material for secondary battery>
The above-described negative electrode active material for a secondary battery can be suitably manufactured by the following manufacturing method.

  The manufacturing method of the negative electrode active material for secondary batteries of this invention adds mechanical energy to Si powder and oxide solid electrolyte, and X-ray powder diffraction (XRD) measurement using Si K powder for Si powder is performed. It has the compounding process which grind | pulverizes until the measured crystallite size is set to 100 nm or less, and combines the grinded Si powder and the oxide solid electrolyte.

  In the compounding step, the Si powder and the oxide solid electrolyte are pulverized simultaneously, the Si powder becomes Si particles, and the Si particles and the oxide solid electrolyte are compounded using mechanical energy applied in the pulverization process, A Si-oxide solid electrolyte composite is synthesized. Such a composite method is called a mechanochemical method or mechanical milling.

As the Si powder, a powder having an average particle size of 1 nm to 100 μm can be used. A commercially available product can be used as the Si powder. If the Si powder is 1 μm or more, it is difficult to scatter during operations such as weighing, which is preferable in terms of handling and safety and hygiene. On the other hand, a powder of less than 1 μm is preferable from the viewpoint of improving cycle characteristics because a uniform composite is easily obtained.
Further, powders exceeding 100 μm can be preliminarily pulverized to 100 μm or less using a mortar, pestle, various milling devices, or the like.

The oxide solid electrolyte is prepared by a method such as a solid phase method, a coprecipitation method, a hydrothermal method, a sol-gel method, or a glass crystallization method. A commercial item can also be used for an oxide solid electrolyte. As a commercially available product, a LATP-based oxide solid electrolyte sheet (manufactured by OHARA, composition formula Li _{1 + x + y} (Al, Ga) _x (Ti, Ge) _2-x Si _y P _3-y O ₁₂ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1)), Li _1.3 Al _0.35 Ti _1.7 (PO ₄ ) ₃ (LATP, manufactured by Toshima Seisakusho), aluminum-substituted germanium lithium phosphate (Li _1.5 Al _0.5 Ge _{1 .5} (PO ₄ ) ₃ (LAGP, made by Toshima Seisakusho)), Li _0.33 La _0.55 TiO ₃ (LLT, made by Toshima Seisakusho), Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ, made by Toshima Seisakusho), Li ₅ La ₃ Ta ₂ O ₁₂ (manufactured by Toshima Seisakusho), Li ₃ PO ₄ (manufactured by Wako Pure Chemical, Kanto Chemical, high-purity chemical, Aldrich, etc.) can be used.

  The prepared oxide solid electrolyte may be preliminarily pulverized with a mortar, ball mill, bead mill or the like.

  Moreover, you may use an oxide solid electrolyte raw material for a mechanochemical method as it is. The oxide solid electrolyte raw material is not particularly limited, and for example, oxides, hydroxides, carbonates, nitrates, sulfates, acetates, phosphates, complex oxides, metal alkoxides, and the like can be used.

  Compounding may be performed using a mortar and pestle, or using a pulverizing and mixing device such as a ball milling device.

  When a mortar and pestle are used, the mechanochemical reaction is small, and thus the Si-oxide solid electrolyte composite is synthesized by mixing and grinding for 10 hours or more. In addition to hand mixing, an automatic mortar or stamp mill can be used for the synthesis. As the mortar and pestle, mullite, alumina, zirconia, agate, glass, porcelain, iron, stainless steel and the like can be used. Further, the mechanochemical effect can be enhanced by providing irregularities such as slits (for example, width 0.1 mm, depth 0.2 mm) inside the mortar.

  As the pulverizing and mixing apparatus, for example, a planetary ball mill apparatus and a mechano-fusion system can be used.

  For example, a planetary ball mill device can be used as the ball milling device. If a ball milling apparatus is used, nano-processing and composite processing can be performed in a sealed container. Therefore, it is not necessary to handle nano-sized Si particles directly, and there is little danger. In addition, since equipment for handling nano-sized Si particles is not required, equipment costs can be reduced.

  The atmosphere in the pulverization container of the ball mill device may be filled with an inert gas such as nitrogen, argon, carbon dioxide in addition to air or dry air.

  Crushing 1/10 to 1/2 volume of oxide solid electrolyte or oxide solid electrolyte raw material and Si powder of grinding ball of planetary ball mill apparatus together with 1/5 to 2/3 volume of grinding balls of grinding container Put into the container. Next, the Si-oxide solid electrolyte composite can be synthesized by grinding under the following grinding conditions.

  The grinding conditions are preferably 300 rpm to 2000 rpm, more preferably 450 rpm to 1100 rpm. By pulverizing at a higher speed than the pulverization conditions (for example, 60 rpm) used in the synthesis of a general inorganic material, mechanical energy can be applied to the material, and the Si particles and the oxide solid electrolyte can be combined. If the pulverization is slow, the mechanochemical reaction hardly occurs. If the pulverization exceeds 2000 rpm, the heat generated during the pulverization becomes too large, and it becomes difficult to control the mechanochemical reaction. The grinding time is preferably 10 minutes to 72 hours, particularly preferably 15 minutes to 24 hours. If the heat generated during pulverization is too large, the pulverization time may be divided and a cooling time may be provided.

  There is no limitation on the pulverization container, and pots such as zirconia, alumina, stainless steel, agate, glass, and resin can be used, but because the pulverization energy is high in the mechanochemical method, the pulverization container is made of zirconia, A pot made of alumina or stainless steel is particularly preferable.

  There is no restriction on the balls for grinding, and balls made of zirconia, alumina, stainless steel, agate, glass, resin, etc. can be used. However, the mechanochemical method has high grinding energy, so the grinding balls are zirconia. Particularly preferred are balls made of aluminum, alumina and stainless steel. The size of the grinding ball is, for example, 0.1 mm to 20 mm in diameter, but the size of the grinding ball can be freely selected depending on the desired composite size.

  In either case of using a mortar and pestle, or in the case of using a pulverizing and mixing device, the compounding can be carried out either dry or wet, but it is desirable to carry out by a dry method having a strong mechanochemical reaction. In the case where the heat generation during the composite synthesis is large, wet may be used. In the case of wet, a solvent having low solubility of the oxide solid electrolyte or the oxide solid electrolyte raw material can be used. As the solvent, for example, water, alcohols such as ethanol and isopropanol, ketones such as acetone, hexane and the like can be used.

  In the composite step, the oxide solid electrolyte is preferably pulverized until it becomes amorphous or low crystalline. In order to make the oxide solid electrolyte amorphous or low crystalline, in the case of a mortar, it may be pulverized and mixed for 10 hours or more, preferably 24 hours or more. In the case of a pulverizing and mixing device, the mechanochemical reaction is facilitated by increasing the pulverizing speed. Therefore, in the case of a planetary ball mill, the number of rotations may be increased.

  The compounding step is preferably performed in a sealed space. By being performed in the sealed space, the raw material powder can be prevented from scattering into the atmosphere. For example, the compounding step may be performed in a closed container of a pulverizing and mixing apparatus.

  A heat treatment can be applied after the compounding step. The heat treatment strengthens the skeleton structure of the matrix made of the oxide solid electrolyte and strengthens the bond between the Si particles and the oxide solid electrolyte. Therefore, the strength of the Si-oxide solid electrolyte composite is increased. However, when heat treatment is performed, the crystallite size of the Si particles increases. When the crystallite size of the Si particles increases, the matrix cannot suppress the expansion and contraction of Si, and the cycle characteristics of the secondary battery deteriorate.

  If heat treatment is performed, the obtained composite is heat treated at 100 ° C to 800 ° C. By the heat treatment, excess organic substances are decomposed and evaporated. The heat treatment strengthens the skeletal structure of the matrix made of the oxide solid electrolyte and strengthens the bond between the Si particles and the oxide solid electrolyte. Therefore, the strength of the Si-oxide solid electrolyte composite is increased, and the negative electrode active material using the Si-oxide solid electrolyte composite improves the charge / discharge cycle characteristics of the secondary battery. In addition, as the density of the Si-oxide solid electrolyte composite increases, the capacity per unit volume of the negative electrode active material using the Si-oxide solid electrolyte composite increases.

  When heat treatment is performed at a temperature higher than 800 ° C., the Si particles and the oxide solid electrolyte matrix react with each other, and the initial capacity of the secondary battery is reduced. Since the problem that a characteristic deteriorates arises, it is not preferable. If the heat treatment is performed at a temperature lower than 100 ° C. in the heat treatment step, the effect of removing excess moisture and organic matter is small, and the influence of oxidizing the surface of the Si particles and lowering the capacity is not preferable.

  The atmosphere during the heat treatment can be air or an inert gas, and can be pressurized or reduced as necessary. An inert atmosphere is preferable because it can prevent oxidation of Si particles.

  In particular, when the mechanochemical method is used with the oxide solid electrolyte raw material, heat treatment is better.

<Anode for secondary battery>
The negative electrode for a secondary battery according to the present invention includes the above-described negative electrode active material for a secondary battery. If it is set as the negative electrode which has the said negative electrode active material for secondary batteries, a secondary battery will have sufficient capacity | capacitance and favorable cycling characteristics.

  The negative electrode is formed by attaching a negative electrode active material layer formed by binding the negative electrode active material with a binder to a current collector.

  A current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a secondary battery. Examples of the material used for the current collector include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. The current collector can take the form of a foil, a sheet, a film, or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector.

  The current collector preferably has a thickness of 5 μm to 200 μm.

  The negative electrode active material layer may further contain a conductive additive. The negative electrode is prepared by preparing a composition for forming a negative electrode active material layer containing a negative electrode active material, a binder, and, if necessary, a conductive additive, and adding a suitable solvent to the above composition to make a paste. After coating on the surface of the electric body, it can be dried and compressed to increase the electrode density as necessary.

  As a method for applying the composition for forming a negative electrode active material layer, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used.

  As the solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.

  The binder plays a role of connecting the negative electrode active material and the conductive additive to the current collector, and includes a fluorine-containing resin such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, and a thermoplastic resin such as polypropylene and polyethylene. Imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, styrene-butadiene rubber (SBR), and the like can be used.

  The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination as a conductive additive. Can be added. The amount of the conductive aid used is not particularly limited, but for example, it can be about 1 part by mass to 95 parts by mass with respect to 100 parts by mass of the active material contained in the negative electrode.

<Secondary battery>
The secondary battery of the present invention uses a positive electrode and an electrolyte in addition to the above-described negative electrode for a secondary battery as battery components. A separator may be used as necessary.

  The positive electrode has a current collector and a positive electrode active material layer bound to the surface of the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and includes a conductive additive as necessary. The current collector, binder, and conductive additive are the same as those described for the negative electrode.

  A lithium-containing compound is suitable as the positive electrode active material. For example, lithium-containing metal composite oxides such as lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, and lithium iron phosphate composite oxide can be used. Other metal compounds or polymer materials can also be used as the positive electrode active material. Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide and manganese dioxide, and sulfides such as titanium sulfide and molybdenum sulfide. Examples of the polymer material include conductive polymers such as polyaniline and polythiophene. When a metal compound or a polymer material not containing lithium is used for the positive electrode, the positive electrode and / or the negative electrode and / or the battery structure are doped with Li ions. Although the doping method is not particularly defined, there are Li sputtering on the electrode, preliminary charge / discharge with the counter electrode Li, and the like.

As the positive electrode active material, a composite metal oxide represented by the general formula: LiCo _p Ni _q Mn _r O ₂ (p + q + r = 1, 0 <p <1, 0 ≦ q <1, 0 ≦ r <1) is used. There are many cases. As the composite metal oxide, for example, LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , Li ₂ MnO ₂ , LiFePO ₄ , LiMnPO ₄ , Li ₂ FeP ₂ O ₇ , Li ₂ FeSiO ₄ , LiMnSiO ₄ , LiNi _0.8 Co _0.2 O ₂ , and the foregoing An oxide solid solution containing any of these oxides can be used. As the positive electrode active material, a non-metallic positive electrode active material such as sulfur or a sulfur-containing organic substance, oxygen, or an organic polymer can also be used.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator, for example, a porous film or a nonwoven fabric made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a natural polymer such as cellulose, or a porous film made of ceramics can be used.

  The electrolyte contains movable Li ions. As the electrolyte, a non-aqueous electrolyte, an aqueous electrolyte, a solid electrolyte, or the like can be used. In the case of a solid electrolyte, a separator is not necessarily required.

  The non-aqueous electrolyte contains an organic solvent and an electrolyte salt dissolved in the organic solvent.

  As the organic solvent, for example, cyclic esters, chain esters and ethers 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 that can be used include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. As ethers, for example, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane can be used.

As the electrolyte salt to be dissolved in the organic solvent, for _{example, LiClO 4, LiAsF 6, LiPF} 6, LiBF 4, LiCF 3 SO 3, LiN (CF 3 SO 2) can be used a lithium salt of _2, and the like.

As the non-aqueous electrolyte, for example, an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate is mixed with a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiCF ₃ SO _{3 in} an amount of 0.5 mol / l to 2 mol / l. A solution dissolved at a concentration of about 1 can be used.

As the aqueous electrolyte, various water-soluble lithium salt aqueous solutions can be used. Preferred water-soluble lithium salts include Li ₂ SO ₄ , LiNO ₃ , LiCl, CH ₃ COOLi, or LiOH, or combinations thereof.

As the solid electrolyte, for example, a gel electrolyte containing a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used.

Examples of the solid electrolyte include lithium sulfide, silicon sulfide, phosphorus sulfide and a composite thereof, lithium nitride, lithium iodide, LiPON (Li ₃ PO _4−x N _x ), Li _4−x Si _x P _1−x O. ₄ (0 ≦ x ≦ 1), Li _x La _{2−x / 3} TiO ₃ (x = 0.1 to 0.5), Li _{7 + x} La ₃ Zr ₂ O _{12+ (x / 2)} (−5 ≦ x ≦ 3, preferably −2 ≦ x ≦ 2), Li _{1 + x + y} (Al, Ga) _x (Ti, Ge, Zr) _2−x Si _y P _3−y O ₁₂ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1) ), Li ₂ O-5Al ₂ O ₃ , Li ₂ O-11Al ₂ O ₃ , Li ₅ La ₃ (Nb, Ta) ₂ O ₁₂ , Li ₁₄ ZnGe ₄ O ₁₆ , Li ₉ SiAlO _8, or the like can be used. .

  Since it has the said negative electrode for secondary batteries, the secondary battery of this invention has sufficient capacity | capacitance and favorable cycling characteristics.

  The secondary battery of the present invention can be mounted on a vehicle. Since the secondary battery has a sufficient capacity and good cycle characteristics, a vehicle equipped with the secondary battery can be a high-performance vehicle.

  The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.

<Si-oxide solid electrolyte composite>
The Si-oxide solid electrolyte composite of the present invention has a crystallite size measured by X-ray powder diffraction (XRD) measurement using a matrix made of an oxide solid electrolyte and CuKα rays dispersed in the matrix. Si particles that are 100 nm or less.
When the Si-oxide solid electrolyte composite is used as a negative electrode active material for a secondary battery, the output characteristics of the secondary battery can be improved.

  As described above, the embodiments of the negative electrode active material for secondary battery, the manufacturing method thereof, the negative electrode for secondary battery, the secondary battery, and the Si-oxide solid electrolyte composite according to the present invention have been described. The form is not limited. 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 in more detail with reference to examples.

<Preparation of materials>
As Si, a Si powder having a median diameter of 50% of 5 μm (manufactured by High-Purity Chemical Co., Ltd., 3N) and a Si nanopowder having a D ₅₀ of 50 nm (manufactured by Nanostructured & Amorphous Materials Inc.) were prepared.

As an oxide solid electrolyte, a LATP-based oxide solid electrolyte sheet (manufactured by OHARA, composition formula Li _{1 + x + y} (Al, Ga) _x (Ti, Ge) _2−x Si _y P _3−y O ₁₂ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1)) and aluminum-substituted lithium germanium phosphate (Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ (hereinafter referred to as LAGP) crystal powder (manufactured by Toshima Seisakusho) Got ready.

<Preparation of Si-oxide solid electrolyte composite>
Example 1
Put the LATP oxide solid electrolyte sheet into a planetary ball mill in which the powder obtained by pre-grinding the LATP oxide solid electrolyte sheet with a mortar and pestle and Si powder having an average particle diameter of 5 μm is 1: 1 (mass ratio) and the ball for grinding is a 5 mm ball made of zirconia. The Si-oxide solid electrolyte composite of Example 1 was obtained by mixing and pulverizing at 600 rpm for 30 minutes. The ratio of the oxide solid electrolyte in the Si-oxide solid electrolyte composite of Example 1 was 50% by mass.

(Example 2)
A Si-oxide solid electrolyte composite of Example 2 was obtained in the same manner as in Example 1 except that the mixture was pulverized at 300 rpm for 30 minutes.

(Example 3)
The Si-oxide solid electrolyte composite of Example 1 was heat-treated in an Ar atmosphere at 500 ° C. for 5 hours to obtain the Si-oxide solid electrolyte composite of Example 3.

Example 4
The Si-oxide solid electrolyte composite of Example 2 was heat-treated at 500 ° C. for 5 hours in an Ar atmosphere to obtain the Si-oxide solid electrolyte composite of Example 4.

(Example 5)
The Si-oxide solid electrolyte composite of Example 5 was used in the same manner as in Example 1 except that LAGP was used instead of the powder obtained by pre-grinding the LATP-based oxide solid electrolyte sheet of Example 1 with an agate mortar and pestle. Got the body.

(Example 6)
The Si-oxide solid electrolyte composite of Example 5 was heat-treated in an Ar atmosphere at 500 ° C. for 5 hours to obtain the Si-oxide solid electrolyte composite of Example 6.

(Example 7)
A Si-oxide solid electrolyte composite of Example 7 was obtained in the same manner as in Example 1 except that Si nanopowder having a D ₅₀ of 50 nm was used instead of the Si powder having an average particle diameter of 5 μm. .

(Example 8)
A Si-oxide solid electrolyte composite of Example 8 was obtained in the same manner as in Example 7 except that the mixture was pulverized at 300 rpm for 30 minutes.

Example 9
The Si-oxide solid electrolyte composite of Example 7 was heat-treated in an Ar atmosphere at 500 ° C. for 5 hours to obtain the Si-oxide solid electrolyte composite of Example 9.

(Example 10)
The Si-oxide solid electrolyte composite of Example 8 was heat-treated at 500 ° C. for 5 hours in an Ar atmosphere to obtain the Si-oxide solid electrolyte composite of Example 10.

(Example 11)
A Si-oxide solid electrolyte composite of Example 11 was obtained in the same manner as in Example 7 except that LAGP was used instead of the LATP-based oxide solid electrolyte sheet of Example 7.

(Example 12)
The Si-oxide solid electrolyte composite of Example 11 was heat-treated at 500 ° C. for 5 hours in an Ar atmosphere to obtain the Si-oxide solid electrolyte composite of Example 12.

<Powder X-ray diffraction (XRD) measurement result>
The Si-oxide solid electrolyte composites of Example 1 and Example 2 were analyzed by powder X-ray diffraction (XRD) (SmartLab, manufactured by Rigaku). The analysis results are shown in FIG. 3 together with the LATP analysis results. In the Si-oxide solid electrolyte of Example 1, the LATP crystal phase disappeared, and it was confirmed that the oxide solid electrolyte was amorphous. The oxide solid electrolyte of Example 2 was able to confirm the peaks of LATP and Si and confirmed that the crystals of LATP remained.

  In Example 1, Example 3, Example 5, and Example 6 that were pulverized under the pulverization condition of 600 rpm, it was found by XRD measurement that the oxide solid electrolyte was amorphous or low crystalline.

<Measurement of crystallite size>
The crystallite size was determined from the half width of the XRD peak of Si. The crystallite size of the Si powder used as a raw material was similarly determined from the XRD peak. The crystallite size of the Si powder having an average particle diameter of 5 μm as the raw material was 107 nm, and the crystallite size of the Si nanopowder having a D50 of ₅₀ nm as the raw material was 38 nm.

  The crystallite sizes of Si in Examples 1 to 12 are shown in Table 1. From the measurement result of the Si crystallite size, the Si crystallite size is 8 nm to 53 nm by rotating the Si powder and the oxide solid electrolyte at a high speed of 600 rpm using a planetary ball mill. Nevertheless, it has been found that the crystallite size of Si can be made very small.

  Example 3 was obtained by heat treating Example 1, Example 4 was obtained by heat treating Example 2, and Example 9 was obtained by heat treating Example 7. Example 10 was obtained by heat-treating Example 8, and Example 12 was obtained by heat-treating Example 11. Comparing these results, it was found that the crystallite size of Si increases with heat treatment.

<Scanning electron microscope (SEM) observation>
The Si-oxide solid electrolyte composites of Example 1 and Example 2 were observed with SEM (S-4800 manufactured by Hitachi High-Tech).

  FIG. 4 shows a cross-sectional SEM photograph of the Si-oxide solid electrolyte composite of Example 1. From the cross-sectional SEM photograph of FIG. 4, a plurality of dark color irregularities having a size of about several tens of nm to 1 μm were observed in the cross section of the Si-oxide solid electrolyte composite of Example 1. This dark color unevenness is Si particles. From FIG. 4, it was observed that the Si particles were dispersed in the matrix, and the Si particles and the oxide solid electrolyte were integrated.

  FIG. 5 shows a comparison between the SEM photograph of the surface of the Si-oxide solid electrolyte composite of Example 1 and the SEM photograph of the surface of the Si-oxide solid electrolyte composite of Example 3. From FIG. 5, it was found that the surface grain could not be clearly observed in the SEM photograph of Example 1, but the surface grain was observed in the SEM photograph of Example 3, and the grain was grown by the heat treatment.

  FIG. 6 shows a comparison between the SEM photograph of the surface of the Si-oxide solid electrolyte composite of Example 2 and the SEM photograph of the surface of the Si-oxide solid electrolyte composite of Example 4. From FIG. 6, it was found that the surface grain could not be clearly observed in the SEM photograph of Example 2, but the surface grain was observed in the SEM photograph of Example 4, and the grain was grown by the heat treatment. Further, large Si particles having a diameter of about 3 μm were observed on the surface of the Si-oxide solid electrolyte composite of Example 4.

  From FIG. 5 and FIG. 6, when comparing the SEM photographs of Example 3 and Example 4, in Example 4 where the grinding condition of the planetary ball mill is 300 rpm and 30 minutes, micron-sized Si remains in part, It was found that the particles were not sufficiently nanosized. On the other hand, in Example 3 where the pulverization conditions of the planetary ball mill were 600 rpm and 30 minutes, no large Si particles were confirmed, and it was found that nano-ization was sufficiently advanced.

<Production of coin-type lithium ion secondary battery>
(Example 1 to Example 12)
Coin-type lithium ion secondary batteries were produced as follows using the Si-oxide solid electrolyte composites of Examples 1 to 12 as the negative electrode active material.

  Each Si-oxide solid electrolyte composite was pulverized in a mortar and then Si-oxide solid electrolyte composite / natural graphite (SMG) / acetylene black (conductive aid) / polyamideimide resin (binder) = 45/40. The mixture was mixed at / 5/10 (mass ratio), and the mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry.

The slurry was placed on a copper foil having a thickness of 20 μm, and a film was formed on the copper foil using a doctor blade. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then the current collector made of electrolytic copper foil and the negative electrode layer made of the above mixture were firmly adhered and bonded by a roll press machine. . This was extracted with a 0.95 cm ² circular punch and vacuum dried at 200 ° C. for 2 hours to obtain each electrode. The coating amount was adjusted so that the basis weight was about 2 mg (1.5 mg to 2.5 mg).

The above-mentioned electrode was used as an evaluation electrode, and metal lithium was used as a counter electrode. 1 mol LiPF ₆ / ethylene carbonate (EC) + diethyl carbonate (DEC) (EC: DEC = 1: 1 (volume ratio)) as an electrolyte and a coin-type model battery (CR 2032 type) in a dry room ) Was produced. In the coin-type model battery, a spacer, a 500 μm-thick Li foil as a counter electrode, a separator (trade name Celgard # 2400, manufactured by Celgard), and an evaluation electrode are sequentially stacked and caulked to obtain a model of Example 1 to Example 12. A battery was produced.

(Comparative Example 1)
A model battery of Comparative Example 1 was produced in the same manner as the model battery of the example except that Si powder was used instead of the Si-oxide solid electrolyte composite.

<Charge / discharge characteristics measurement>
The charge / discharge test of the coin type model batteries of Examples 1 to 12 and Comparative Example 1 was performed. The charge / discharge test was performed by discharging to 1 mg of electrode material at a constant current of 0.1 mA until reaching 0.01 V and charging at a constant current of 0.1 mA until reaching 2.0 V. This charging / discharging was repeated up to 50 cycles as one cycle. The initial charge capacity was measured, and the initial capacity per electrode mixture was calculated. The 50th cycle capacity per electrode mixture was calculated in the same manner from the 50th cycle charge capacity. The capacity maintenance rate was obtained by the following formula. Capacity retention rate (%) = (50th capacity / initial capacity) × 100.

  Si utilization efficiency was obtained from the following equation. Si utilization efficiency (%) = ((initial charge capacity) − (capacity derived from SMG)) / ((Si theoretical capacity) × (Si mass ratio) × (negative electrode active material mass)) × 100. In addition, Si mass ratio was calculated by 1- (matrix ratio).

<Rate characteristics measurement>
The initial charge capacity was measured in the same manner as the charge / discharge characteristic measurement except that the charge was changed to 0.5C and 10C. The charge rate at this time calculated | required each electric current value from the initial charge capacity | capacitance in charge / discharge characteristic measurement. Therefore, the charge for the charge / discharge characteristic measurement corresponds to 1C.

  The rate characteristic was evaluated as (10C charge capacity) / (0.5C charge capacity) × 100.

  Table 1 shows Si crystallite size, charge / discharge characteristic measurement results, and rate characteristic measurement results.

  From the results of Table 1, since Comparative Example 1 did not use a matrix, the initial capacity of Comparative Example 1 was reduced to 1/2 (1704/2 = 852) for comparison, and compared with Examples. Each of the model batteries of Examples 1 to 4 has an initial capacity higher than or slightly different from that of Comparative Example 1 as compared to the model battery of Comparative Example 1 using Si powder instead of the Si-oxide solid electrolyte. It was also found that the capacity retention rate at the 50th cycle was improved. Regarding the cycle characteristics, in particular, the capacity retention rate at the 50th cycle of the model battery of Comparative Example 1 was 10%, whereas the capacity retention rate at the 50th cycle of the model batteries of Example 1 and Example 3 was 36%. The cycle characteristics were greatly improved.

  Further, as shown in FIG. 7, when comparing the Si crystallite size of the model batteries of Examples 1 to 4 and Comparative Example 1 with the capacity retention ratio at the 50th cycle, the smaller crystallite size is at the 50th cycle. The capacity maintenance rate was high. In particular, when the Si crystallite size was 65 nm or less, the capacity retention ratio at the 50th cycle was greatly improved.

  In Examples 1, 3 and 5, it is known from the XRD results that the oxide solid electrolyte is amorphous or low crystalline. Since the oxide solid electrolyte is amorphous or low crystalline, it is assumed that the grain boundary resistance of the oxide solid electrolyte is reduced and the initial capacity is improved.

In all of Examples 7 to 12, the raw material Si powder is Si nanopowder having a D50 of ₅₀ nm. The initial capacities of Examples 7 to 12 were all lower than those of Comparative Example 1. A surface oxide film (silicon oxide layer) is originally formed on the surface of Si nanopowder. It is considered that the silicon oxide layer is a resistance component in the electrode. Therefore, when Si nanopowder is used as a raw material, it is presumed that the original capacity did not come out even if it became a composite.

  When the Si utilization efficiency was compared, all of the examples using the Si nanopowder had lower Si utilization efficiency than the examples using the Si powder.

  However, the capacity retention ratio at the 50th cycle in Examples 7 to 12 was significantly improved as compared with Comparative Example 1. Note that silicon oxide on the surface of the Si nanopowder is repeatedly charged and discharged to change to a lithium silicate amorphous phase, and the conductivity in the electrode is improved. Therefore, the reason why the capacity retention ratio at the 50th cycle in Example 11 and Example 12 is larger than 100 is considered to be because the apparent capacity has increased.

  From this, it was found that if a material having a high initial capacity is desired, the Si-oxide solid electrolyte composite should be compounded using a micron-sized Si powder as the raw material.

  In Example 5, Example 6, Example 11 and Example 12 in which the oxide solid electrolyte is LAGP, the cycle characteristics were improved as compared with Comparative Example 1 as in Example 1 in which the oxide solid electrolyte was LATP. .

  In the case of Example 5, the same method as in Example 1 was used, but unlike the crystallite size of 8 nm in Example 1, the crystallite size of Si in Example 5 was 32 nm. In the examples, LAGP used a raw material with high crystallinity as compared with LATP which was synthesized by a glass crystallization method and used a raw material having an impurity phase and low crystallinity. Therefore, in the case of Example 5, since LAGP having high crystallinity was used as the oxide solid electrolyte, a part of the pulverization energy was consumed for pulverization of LAGP. Presumed to have been.

  Example 6 is obtained by heat-treating Example 5. When heat treatment was performed, the crystallite size of Si increased to 39 nm, but it did not increase significantly. Although the initial capacity of the model battery of Example 6 was lower than that of the model battery of Example 5, the capacity retention rate at the 50th cycle was improved. From this, it can be inferred that the heat treatment strengthens the skeleton structure of the matrix made of the oxide solid electrolyte and also strengthens the bond between the Si particles and the oxide solid electrolyte, thereby improving the cycle characteristics.

  The initial capacity of Example 6 was lower than that of Example 5. The pulverization conditions of Example 5 and Example 6 were nano-composition and compounding of Si by ball milling at 600 rpm for 30 minutes. In Example 5 and Example 6, since the crystallinity of the raw material Si particles and LAGP particles is large, the reaction is not sufficient in part, and it is considered that there was a portion where the surface of the Si particles was exposed on the composite surface. In Example 6, the heat treatment of Example 5 is further performed. It is considered that the Si particles were oxidized at the site exposed on the surface of the complex on the surface of the Si particles by the heat treatment. Therefore, it is estimated that the initial capacity of Example 6 was lower than that of Example 5.

  When LAGP is used, it is presumed that sufficient complexation can be achieved by increasing the mixing / pulverization rate and / or lengthening the mixing / pulverization time than when LATP is used.

  Examples 1, 3, 7, and 9 are composites using solid electrolyte LATP at a mixing and grinding speed of 600 rpm. The capacity retention rate at the 50th cycle was improved from those obtained by combining Examples 2, 4, 8, and 10 at a mixing / pulverization rate of 300 rpm. From this, it was found that it is better to increase the mixing and grinding speed in the composite treatment.

  From the rate characteristic measurement results shown in Table 1, it was found that Examples 1 to 12 showed higher rate characteristics than Comparative Example 1. It was found that a battery having a higher output than that of uncomposited Si can be provided by compounding with an oxide solid electrolyte.

  1: Si particles, 2: Matrix.

Claims (4)

Add mechanical energy to Si powder and oxide solid electrolyte,
The Si powder is pulverized until the crystallite size measured by X-ray powder diffraction (XRD) measurement using CuKα rays becomes 100 nm or less, and the pulverized Si powder and the oxide solid electrolyte are combined. The manufacturing method of the negative electrode active material for secondary batteries which has the composite process to perform. 2. The method for producing a negative electrode active material for a secondary battery according to claim 1 , wherein in the complexing step, the oxide solid electrolyte is pulverized until it becomes amorphous or has low crystallinity. Said composite step method of preparing a negative active material for a secondary battery according to claim 1 or 2 carried out in the closed space. The said Si powder is an average particle diameter of 1 micrometer or more, The manufacturing method of the negative electrode active material for secondary batteries as described in any one of Claims 1-3 .