Negative electrode composite material containing graphite particles and sulfide solid electrolyte, and all-solid-state battery having the same

Abstract

To provide a negative electrode mixture for an all-solid-state battery capable of achieving a high discharge capacity.SOLUTION: A negative electrode mixture for an all-solid-state battery includes a sulfide solid electrolyte composed of an ion conductive compound composed of lithium, sulfur, and phosphorus, and graphite particles, and the void ratio in a negative electrode mixture layer obtained by powder molding the negative electrode mixture is 5% or less, the graphite particles preferably have an average flatness of 0 or more and less than 0.3, a particle size distribution D50 of 8 μm or more and 13 μm or less, and the BET value of 1 m2 / g or more and 3 m2 / g or less, and the average surface spacing d002 of (002) planes measured by X-ray diffraction method has a crystallinity of 0.336 nm or more and 0.337 nm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a negative electrode composite material containing graphite particles and a sulfide solid electrolyte, and an all-solid-state battery having the same.

Background Art

[0002] In recent years, in electronic devices such as mobile phones, tablet terminals, and notebook personal computers, higher performance and more functions have been increasingly pursued. Along with this, there is an increasing demand for further miniaturization, weight reduction, and higher capacity in secondary batteries mounted on these electronic devices. Under such circumstances, non-aqueous electrolyte (liquid system) secondary batteries typified by lithium secondary batteries have a higher battery voltage and can achieve a higher energy density compared to nickel-cadmium batteries and nickel-metal hydride batteries, and thus have rapidly spread in the field of the above-mentioned electronic devices.

[0003] In addition, non-aqueous electrolyte secondary batteries have also become mainstream in applications such as power sources for motor drives in electric vehicles and hybrid vehicles against the backdrop of current environmental problems. However, since non-aqueous electrolyte secondary batteries generally contain flammable organic solvents, they have safety problems such as ignition when abnormal conditions such as thermal runaway occur in the secondary batteries, and urgent improvement is desired. As one of the technologies for improving such safety problems, research and development of all-solid-state lithium secondary batteries using solid electrolytes instead of electrolytes using organic solvents have been actively promoted.

[0004] The main configuration of the above all-solid-state lithium secondary battery includes a positive electrode composite material (layer) containing a positive electrode active material and a solid electrolyte, a negative electrode material using In metal, Li-In alloy, or carbon, and a negative electrode composite material (layer) containing a solid electrolyte, and a laminated three-layer structure provided between the positive electrode composite material and the negative electrode composite material and composed of a solid electrolyte (layer). The solid electrolyte contained in the above constituent materials can be roughly classified into an oxide-based and a sulfide-based. As a representative example of the former oxide-based, Li 7 La 3 Zr 2 O 12 or Li 5 La 3 Nb2 O 12 can be cited.

[0005] However, since oxide-based solid electrolytes are inferior in crushability, in the powder compacting process of compressing and molding powdery raw materials during the manufacture of all-solid-state lithium secondary batteries, a dense structure may not be obtained. In addition, oxide-based solid electrolytes also had problems such as requiring sintering treatment under high-temperature conditions to exhibit high ionic conductivity. On the other hand, sulfide-based solid electrolytes do not particularly have the problems of the above-mentioned oxide-based solid electrolytes. In particular, as disclosed in Patent Document 1, Li 7 PS 6 phase, Li 4 P 2 S 6 phase, or a typical sulfide-based solid electrolyte having a Li 3 PS 4 phase (hereinafter also referred to as LPS) has the flexibility and adhesiveness peculiar to sulfides, and thus can be easily deformed during the above-mentioned powder compacting. Furthermore, since sulfide-based solid electrolytes also have the advantage of obtaining high ionic conductivity without heat treatment depending on the composition, they are expected as more promising materials than oxide-based ones.

[0006] The above LPS is a compound synthesized using phosphorus pentasulfide and lithium sulfide as raw materials. As its synthesis method, a method of reaction synthesis by heat due to the impact of balls over a long time using a planetary ball mill (mechanical milling device) filled with an inert gas, or a method of precipitating a crystal phase (meta-stable phase) by further heat treatment as necessary is generally used. In addition, Patent Document 2 discloses a technique that is advantageous in terms of cost and allows ions to be inserted and desorbed by an electrochemical action when producing a negative electrode composite material using LPS synthesized by the above method, by blending graphite (graphite) particles that can be used as an active material. This technique mechanically mixes graphite particles and LPS particles, and uses the obtained mixed powder as a negative electrode composite material layer by powder compacting. Note that the LPS contained in the negative electrode composite material layer plays the role of a conduction path for Li ions.

Prior Art Documents

[0007] [Patent Document 1] JP 2013-155087 A [Patent Document 2] JP 2014-203545 A Summary of the Invention [Problem to be solved by the invention]

[0008] In the above-mentioned all-solid-state lithium ion battery (hereinafter also referred to as all-solid-state battery), it is considered preferable to increase the content of graphite particles in the negative electrode mixture from the viewpoint of increasing the capacity. The reason is that if the content of graphite particles is high, the negative electrode can accept more Li ions that have migrated from the positive electrode. However, when the negative electrode mixture is prepared so as to contain a large amount of graphite particles, it may be difficult to uniformly mix the graphite particles and the LPS particles depending on the type of graphite particles.

[0009] In particular, when preparing a negative electrode composite by a dry method, the mixture of graphite particles and LPS particles is likely to be insufficient, and the quality of the mixture can affect the superiority or inferiority of the battery characteristics. Therefore, unless the above-mentioned mixture is improved, simply increasing the content of graphite particles cannot fully exert the role of LPS as a conductive path, and the desired discharge capacity cannot be obtained. The present invention has been made in consideration of the above problems, and aims to provide a negative electrode composite for an all-solid-state battery that can achieve a high discharge capacity. [Means for solving the problem]

[0010] In order to achieve the above object, the negative electrode composite for an all-solid-state battery according to the present invention comprises a sulfide solid electrolyte made of an ion-conductive compound composed of lithium, sulfur, and phosphorus, and an average interplanar spacing d of the (002) plane measured by an X-ray diffraction method. 002A negative electrode composite material for an all-solid-state battery containing graphite particles having a crystallinity of 0.336 nm or more and 0.337 nm or less, wherein the porosity in the negative electrode composite material layer obtained by compacting and molding the negative electrode composite material is 5% or less Yes, the graphite particles have an average flatness ratio of 0 or more and less than 0.3, a particle size distribution D50 of 8 μm or more and 13 μm or less, and a BET value of 1 m 2 / g or more and 3 m 2 / g or less, and the ionic conductive compound is passed through a 100-mesh sieve It is characterized by being.

Advantages of the Invention

[0011] According to the present invention, it becomes possible to provide an all-solid-state battery having a high initial charge-discharge capacity.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0013] 1. Negative electrode composite material for all-solid-state battery Hereinafter, a negative electrode composite material for an all-solid-state battery according to an embodiment of the present invention will be described. This negative electrode composite material contains a sulfide solid electrolyte having ion conductivity and graphite particles, and the porosity in the negative electrode composite material layer obtained by compacting and molding this negative electrode composite material is 5% or less. Here, the porosity in the negative electrode composite material layer can be obtained by the following method. That is, the cross section of the compacted and molded negative electrode composite material layer is processed using a CP (Cross Section Polisher) device, and five arbitrarily selected fields of view of the cross section finished to a mirror surface are imaged by SEM. By performing binarization processing on the obtained SEM images of each field of view, the void part and the other parts are distinguished, the ratio of the area occupied by the void part to the total area of the SEM image of each field of view is obtained, and the obtained area ratio is averaged over five fields of view. Thereby, the porosity can be obtained.

[0014] As described above, by suppressing the porosity in the negative electrode composite material to 5% or less, it becomes possible to increase the initial charge-discharge capacity of the all-solid-state battery having the negative electrode composite material layer. That is, during the charge and discharge of the all-solid-state battery, Li ions move while passing through LPS that serves as an ion conduction path in the negative electrode composite material, and are inserted into or detached from the crystal layer of the graphite particles. Therefore, when the contact between the graphite particles and the surrounding LPS particles decreases, the proportion of voids existing at their interface (which may be expressed as the graphite particle / LPS interface) increases. When the porosity in the negative electrode composite material layer exceeds 5%, the contact area between the graphite particles and the LPS particles becomes too small, preventing good movement of Li ions and making it difficult for Li ions to be inserted into and detached from the graphite particles. That is, an excessive amount of graphite particles that do not contribute to charge and discharge will exist in the negative electrode composite material layer, resulting in a significant decrease in the charge-discharge capacity.

[0015] As described above, the reason for the generation of voids at the graphite particle / LPS interface is considered to be due to insufficient mixing of the graphite particles and the LPS particles when preparing the negative electrode composite material, resulting in insufficient filling of the LPS particles around the graphite particles during press molding. That is, generally, since the LPS particles have very poor fluidity, it is difficult to obtain uniform mixing when mixing the graphite particles and the LPS particles to produce the negative electrode composite material.

[0016] Under the above circumstances, intensive research was carried out to suppress the porosity in the negative electrode composite material layer to 5% or less so that voids are not generated at the graphite particle / LPS interface as much as possible. As a result, it was found that the porosity can be reduced by defining the characteristics of the graphite particles that affect the miscibility of the graphite particles and the LPS particles. Specifically, the average flatness of the graphite particles constituting the negative electrode composite material is 0 or more and less than 0.3, the particle size distribution D50 is 8 μm or more and 13 μm or less, and the BET value is 1 m 2 / g or more and 3 m 2 / g or less, the porosity can be reduced to 5% or less.

[0017] Thus, by using graphite particles whose characteristics of average flatness ratio, particle size distribution D50, and specific surface area based on BET value are respectively defined within a predetermined range, when pressure-compacted, the contact state between the graphite particles and the LPS particles becomes good, and voids are less likely to occur at the graphite particle / LPS interface, so that the porosity in the negative electrode composite layer can be made 5% or less. As a result, a sufficient contact area of the interface between the graphite particles and the solid electrolyte particles constituting the negative electrode composite layer is ensured, so that innumerable ion conduction paths are formed in the negative electrode composite layer, and the utilization rate of the graphite particles can be increased. Consequently, the charge-discharge capacity of the all-solid-state battery can be increased, and the discharge capacity retention rate during the cycle test can also be improved.

[0018] When the above-mentioned average flatness ratio, which is a characteristic related to the shape of the graphite particles, is 0.3 or more, a large number of irregularly shaped graphite particles are included. Therefore, when forming the negative electrode composite layer by pressure-compaction, the smooth flow of the LPS particles is hindered, and voids where the LPS particles are not partially filled around the graphite particles are likely to occur. Conversely, as the average flatness ratio of the graphite particles approaches zero, the shape changes from an irregular shape to a true spherical shape. Therefore, even if the fluidity of the LPS particles is poor, the filling property of the LPS particles around the graphite particles is improved.

[0019] Note that the average flatness ratio of the graphite particles can be obtained by the following formula 1. Here, f is the average flatness ratio, a is the major axis radius of a single particle, and b is the minor axis radius of a single particle. These radii are obtained by imaging five arbitrarily selected fields of view of the cross-section or surface of the graphite particle group with SEM, and measuring and averaging the major axis radius and minor axis radius of five arbitrarily selected graphite particles from each SEM image. [Formula 1] f = 1 - b / a

[0020] When the above-mentioned particle size distribution D50, which is a characteristic related to the average particle size of graphite particles, is less than 8 μm, the dispersibility decreases when the graphite particles are mixed with LPS particles because the graphite particles are too fine, and voids are likely to occur around the graphite particles. That is, when the graphite particles are excessively fine, the graphite particles are likely to aggregate with each other, so the contact area with the LPS particles is insufficient, and the number of LPS particles that do not conduct ions and graphite particles that do not insert and detach Li ions increases. Conversely, when the particle size distribution D50 exceeds 13 μm, the number of graphite particles per unit thickness of the negative electrode composite material layer decreases, so the charge and discharge capacity decreases. The particle size distribution D50 of the graphite particles was determined by using the laser diffraction method, which irradiates the graphite particles dispersed in a liquid with a laser to obtain refracted and scattered light.

[0021] When the BET value, which is a characteristic related to the specific surface area of graphite particles, is less than 1 m 2 / g, the chance of contact between the graphite particles and the LPS particles during mixing for the production of the negative electrode composite material decreases, so the mixing property deteriorates, and it becomes difficult for the LPS particles to adhere to the surface of the graphite particles, so voids are likely to occur at the graphite particle / LPS interface during pressure molding. Conversely, when the BET value exceeds 3 m 2 / g, gas components and moisture are excessively adsorbed on the surface of the graphite particles, which is likely to cause factors that make the battery characteristics unstable, and there is a possibility that a high capacity cannot be obtained. The BET value is obtained by using the BET equation by the gas adsorption method (nitrogen adsorption method).

[0022] Furthermore, the graphite particles are preferably a carbon material having a crystallinity with an average interplanar spacing d of the (002) plane measured by the X-ray diffraction method of 0.336 nm or more and 0.337 nm or less. Thereby, lithium ions can be inserted and detached well. 002

[0023] 1. Method for manufacturing negative electrode composite material layer Next, an embodiment of the method for manufacturing a negative electrode composite material layer according to the present invention will be described by taking the case where lithium sulfide and diphosphorus pentasulfide are used as raw materials for LPS particles as an example.

[0024] 1.1 Graphite particles For the graphite particles constituting the negative electrode composite material, natural graphite or artificial graphite can be used. However, artificial graphite is preferred because it can easily satisfy the above-described characteristics of the average flatness ratio, particle size distribution D50, and BET value. MCMB (Meso-Carbon MicroBeads: spherical carbon material particles) is particularly preferred. On the other hand, generally, natural graphite has a non-spherical shape, so it is inferior in flatness ratio, has a wide particle size distribution D50, and a high BET value, so its miscibility with LPS particles is often not improved. In addition, amorphous carbon may be provided on the surface of the graphite particles to increase the insertion and extraction of Li ions during charge and discharge. As a result, LPS particles are likely to adhere to the surface of the graphite particles during mixing of the negative electrode composite material, and it becomes possible to obtain a higher charge and discharge capacity.

[0025] 1.2 LPS Particles (1) Lithium Sulfide (Li 2 S) There are no particular restrictions on the lithium sulfide (Li 2 S) that is one of the raw materials for the LPS particles constituting the negative electrode composite material, but it is preferably a commercially available product manufactured industrially, and particularly preferably one with a purity of 99% or more. Lithium sulfide can be produced, for example, by the method described in Japanese Patent No. 3528866. This production method involves blowing hydrogen sulfide into a charge liquid composed of lithium hydroxide and an aprotic organic solvent charged into a reaction vessel to react the lithium hydroxide with the hydrogen sulfide to produce lithium hydrosulfide, and then subjecting the reaction liquid containing the obtained lithium hydrosulfide to a desulfurization treatment to produce lithium sulfide.

[0026] (2) Phosphorus Pentasulfide (P 2 S 5 ) There are no particular restrictions on the phosphorus sulfide that is the other raw material for the LPS particles constituting the negative electrode composite material, but it is preferably commercially available phosphorus pentasulfide (P 2 S 5 ) manufactured industrially. This phosphorus pentasulfide preferably has a purity of 99% or more.

[0027] (3) Mixing Ratio When producing a general high-ion-conductivity sulfide, it is preferable to adjust the mixing ratio of lithium sulfide to the total of the above-mentioned lithium sulfide and phosphorus pentasulfide used as starting materials to be within the range of 30 to 95 mol%. The specific mixing ratio is appropriately determined according to its use. For example, 70Li 2 S-30P 2 S 5 When the mixing ratio of lithium sulfide is 70 mol% or less, such as in a solid electrolyte, the high-ion-conductivity sulfide becomes glassy, and heat treatment is required during the production of the high-ion-conductivity sulfide. Also, since it is unstable in an air atmosphere, it becomes difficult to handle during synthesis, storage, etc. Therefore, the mixing ratio of lithium sulfide in the starting material of LPS, which is the high-ion-conductivity sulfide, is preferably within the range of 75 to 80 mol%.

[0028] (4) LPS synthesis LPS can be obtained by synthesizing lithium sulfide and phosphorus pentasulfide as starting materials mixed in the above mixing ratio. It is preferable to use the mechanical milling method for this synthesis. The mechanical milling method involves charging a large number of metal or ceramic balls, which are media that physically act on the powder, into the milling container of the mixing device together with the powder to be treated, and applying physical forces such as mixing, stirring, and impact to the powder by the media that move with the rotation or vibration of this milling container to perform the treatment.

[0029] The mixing device used in this mechanical milling method is not particularly limited as long as it can charge the media that exerts actions such as uniform mixing and stirring on the powder to be processed into the milling container for mixing. General powder mixing devices such as planetary ball mills, rotating ball mills, and attritors can be used. Among these, the planetary ball mill is particularly preferred. This is because the random movement of the balls due to the planetary motion promotes the uniform mixing of the powder to be processed and gives a large reaction energy to the powder, so that the driving force for promoting the synthesis reaction can be imparted extremely efficiently.

[0030] Thus, different from the two-step processing method of first mixing a plurality of starting material powders and then performing heat treatment on the obtained mixed powder, the mechanical milling method generates heat by the impact of rapidly moving balls, and thereby can simultaneously and parallelly perform uniform mixing and a locally rapidly occurring chemical reaction on the plurality of starting material powders. Therefore, it is suitable for generating special high ion conductors.

[0031] In the above mechanical milling method, it is preferable to control the atmosphere in the milling container. For example, when filling the starting materials into a milling container having a structure in which the inner surface of a SUS container is covered with ZrO 2 it is desirable to make the inside of the milling container an inert gas atmosphere. For this reason, it is desirable to perform the filling operation into the milling container in a glove box filled with an inert gas such as Ar gas, N 2 gas, or He gas. However, since the mechanical milling device main body usually cannot be placed in this glove box, after filling, the milling container is taken out of the glove box and milling such as mixing is performed in an environment exposed to the outside air atmosphere. Therefore, the lid portion of the milling container preferably has a structure that can hermetically seal the inside of the milling container with a silicone packing.

[0032] The reason why it is preferable to airtightly seal the inside of the milling vessel as described above is that sulfides begin to deteriorate immediately when exposed to air, and are particularly vulnerable to moisture. If the gas in the milling vessel contains even a small amount of moisture, it will decompose and become H. 2 This is because S gas is generated. Therefore, it is preferable that the inert gas filling the milling container is sealed in the milling container in a dry state and hermetically sealed with a packing as described above so as not to leak to the outside. The state in which the gas leaks to the outside can also be said to be a state in which the air containing moisture from the outside air penetrates into the milling container. In order to seal the dry inert gas in the milling container as described above, it is preferable to control the dew point in the glove box in which the above filling work is performed to be preferably -70°C dp or less, more preferably -80°C dp (moisture content 0.5 ppm) or less.

[0033] 1.3 Powder compaction Next, the graphite particles and LPS particles prepared above are weighed out and mixed in a predetermined mixing ratio, and the obtained negative electrode composite is compacted to produce a negative electrode composite layer for an all-solid-state battery. In the compaction of the negative electrode composite, it is preferable to stack the positive electrode composite, the solid electrolyte, and the negative electrode composite in this order into three layers, and pressurize them in the stacking direction to simultaneously form a three-layered compact. It is desirable for the compaction of the negative electrode composite to have good moldability, but since the negative electrode composite of the embodiment of the present invention does not contain a resin binder, the moldability depends on the adhesiveness of the LPS particles.

[0034] In order to fully utilize the adhesive properties of the LPS particles, it is preferable to mix the graphite particles with the LPS particles in a ratio of 50 to 70 parts by mass per 100 parts by mass of the graphite particles and the LPS particles combined, which makes it possible to form a green compact with excellent shape retention and no defects or cracks when the graphite particles and the LPS particles are compressed together.

[0035] On the one hand, if the amount of graphite particles exceeds 70 parts by mass with respect to a total of 100 parts by mass of graphite particles and LPS particles, the above-mentioned shape retention property may deteriorate and cracks or the like may occur. When cracks occur in the compacted powder in this way, it may cause an increase in resistance and thus there is a risk of a decrease in charge-discharge capacity. Conversely, if the blending ratio of graphite particles is less than 50 parts by mass with respect to a total of 100 parts by mass of graphite particles and LPS particles, the content of carbon derived from graphite particles in the negative electrode composite material layer obtained after pressure molding is too small, so that Li ions sent from the positive electrode active material cannot be sufficiently received, and in this case too, there is a risk of a decrease in charge-discharge capacity. As a countermeasure in this case, it is conceivable to supplement the amount of carbon by increasing the thickness of the negative electrode composite material layer, but increasing the thickness of the negative electrode composite material layer increases the resistance accordingly, so it is not a preferable countermeasure.

[0036] A negative electrode composite material is produced by mixing graphite particles and LPS particles blended at the above-mentioned predetermined blending ratio. It is preferable to adopt a dry mixing method for this mixing. The reason is that in the wet mixing method, there is a risk that the solvent used for mixing and LPS react violently and deteriorate, whereas such a problem does not particularly occur in the dry mixing method. In addition, the synthesized LPS particles are vulnerable to friction and impact generated during mixing, and MCMB may also be pulverized or distorted when force is applied, resulting in a deterioration of battery characteristics. Therefore, a mixing method that does not damage these LPS particles and graphite particles as much as possible is preferable. For this reason, hand mixing using a mortar described later is preferable, but when mixing by a mechanical milling method such as a planetary ball mill in the same manner as when producing LPS particles, it is desirable to mix at the minimum rotation speed for as short a time as possible.

[0037] A more preferable mixing method in terms of being less likely to cause the above damage is the mixing method using a mortar. By appropriately adjusting the force applied to the powder and the mixing time during mixing, it is possible to mix with almost no damage. When LPS particles are damaged, the adhesiveness peculiar to sulfides originally possessed by LPS decreases, and it becomes difficult to exhibit the function as a binder. Therefore, when forming the negative electrode composite material layer, there is a risk that many voids will occur at the interface between the graphite particles and the LPS particles. Furthermore, since the ionic conductivity of LPS itself decreases, the resistance of the negative electrode composite material layer may increase.

[0038] The above mixing using a mortar can be carried out by the following procedure. First, LPS particles and graphite particles are weighed with an electronic balance so as to be within the above mixing ratio range and put into the mortar. For both particles put into this mortar, gentle mixing is carried out at a speed of about 30 to 120 rotations per minute for about 5 to 10 minutes using a pestle, and the LPS particles and the graphite particles are mixed in a dispersed state. By mixing almost uniformly in this way, a negative electrode composite material can be obtained.

[0039] When forming a negative electrode composite material layer from this negative electrode composite material, for example, the above negative electrode composite material is filled into a mold with an inner diameter of 10 mm, and after performing temporary powder compacting by applying pressure in the thickness direction at a pressure of about 2 to 4 kN, powder compacting is performed at high pressure. During this high-pressure powder compacting, the positive electrode composite material, the solid electrolyte, and the negative electrode composite material are laminated in this order from the bottom, and powder compacting can be performed on the three layers simultaneously by applying pressure at 40 kN in this lamination direction. Thereby, a powder compact with a three-layer integrated structure can be obtained. By putting the powder compact with the three-layer integrated structure formed in this way into a commercially available battery cell case (sealed type: non-exposed to the atmosphere) and incorporating it, a all-solid-state battery can be manufactured. Next, the present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited to these examples.

Examples

[0040] [Example 1] (Synthesis of LPS) The milling container (capacity 45 ml: inner wall ZrO 2 manufactured) attached to the mechanical milling device (PL-7) manufactured by Fritsch was filled with a total of 80 g of ZrO 2 balls (ball diameter 4 mm) and vacuum dried at 100 °C. This dried milling container was placed in a glove box (-80 °C dp) under an Ar atmosphere and further dried over a period of one day and one night.

[0041] Into the milling container in this glove box, 0.3828 g of lithium sulfide (Li 2 S) manufactured by Junsei Chemical Co., Ltd. and 0.6172 g of phosphorus pentasulfide (P 2 S 5 ) manufactured by Sigma-Aldrich were charged and sealed. In this case, the molar ratio of lithium sulfide to phosphorus pentasulfide is Li 2 S:P 2 S 5 = 75:25. After sealing, the milling container was taken out of the glove box and attached to the above-mentioned mechanical milling device (PL-7) manufactured by Fritsch installed in a dry room (atmospheric temperature 22 °C: -45 °C dp), and then mechanical milling was performed at 510 rpm for 20 hours.

[0042] After completion of this mechanical milling, the milling container was returned to the above glove box, the lid of the milling container was opened, and LPS in the form of powder particles generated by synthesis was taken out, and coarse materials on the sieve were removed by passing through a 100-mesh sieve. The obtained LPS particles under the sieve were placed in a measurement cell for non-exposure to the atmosphere in the glove box and analyzed by a non-atmospheric exposure Raman spectroscopic analyzer (micro laser Raman spectroscopic analyzer LabRAM HR-800, light source: Ar + laser (514 nm excitation), excitation high power: 0.2 mW, measurement range: 100 - 4000 cm -1 ) manufactured by Horiba, Ltd. As a result, since a peak derived from PS -1 was detected in the vicinity of 420 cm 4 3- , it was confirmed that the Li 3 PS 4 phase was included.

[0043] (Fabrication of the negative electrode composite material) 80 mg of the above sifted LPS particles and 80 mg of graphite particles (PG11A) manufactured by Eira Carbon Electronics Co., Ltd. with an average flatness ratio of the particles of 0.03, a particle size distribution D50 of 10.2 μm, and a BET value of 1.2 m 2 / g were placed in a mortar in a glove box (-80°C dp) under an Ar atmosphere, and gently mixed for 10 minutes at a rotational speed of 60 times per minute while paying attention not to press the particles, using a pestle. Thus, a powdery negative electrode composite material as an intermediate product was fabricated. In addition, the average interplanar spacing d 002 of the (002) plane of the above graphite particles was measured separately by X-ray diffraction method, and it was found to be a carbon material having a crystallinity of 0.3364 nm.

[0044] (Fabrication of the positive electrode composite material) Lithium nickel composite oxide powder prepared by a known technique in advance was used as the positive electrode active material. That is, nickel oxide powder mainly composed of Ni and lithium hydroxide were mixed and fired to obtain Li 1.090 Ni 0.76 Co 0.14 Al 0.10 O 2 powdery particles of a lithium nickel composite oxide serving as a positive electrode active material (hereinafter referred to as NCA particles) were fabricated. When the average particle size of the obtained NCA particles was measured by a laser diffraction particle size distribution analyzer, it was 10.6 μm. Also, when the specific surface area was measured by the BET method, it was 0.16 m 2 / g. 120 mg of these NCA particles and 80 mg of the above sifted LPS particles were placed in a mortar in a glove box (-80°C dp) under an Ar atmosphere, and gently mixed for 10 minutes at a rotational speed of 60 times per minute while paying attention not to press the particles, using a pestle.

[0045] (Fabrication of the compacted powder) 60 mg of the above-mentioned sifted LPS powder was charged into a cylindrical mold with an inner diameter of 10 mm and temporarily molded at 2 kN to produce a solid electrolyte layer. 15 mg of the granular negative electrode composite material produced above was laminated on this solid electrolyte layer and temporarily molded again at 2 kN. The obtained two-layered green compact was turned over, and after depositing 20 mg of the granular positive electrode composite material produced above on the side opposite to the side of the negative electrode composite material layer temporarily molded above on both sides of the solid electrolyte layer, it was finally molded at 40 kN. Thus, a green compact having a three-layer integrated structure composed of a positive electrode composite material layer / solid electrolyte layer (SE layer) / negative electrode composite material layer was produced. This green compact was housed in a sealed battery evaluation cell (KP-solidCell) manufactured by Hozen Co., Ltd. as shown in FIGS. 1 and 2, and the evaluation cell was assembled by restraining it with a torque of 7 Nm. As shown in FIG. 3, this evaluation cell is configured such that a green compact 10 having an integrated structure composed of a negative electrode composite material layer 11, a solid electrolyte layer (SE layer) 12, and a positive electrode composite material layer 13 can be pressed in the stacking direction with a predetermined restraining force by an upper electrode 21 and a lower electrode 22 in a cylindrical insulating tube 20.

[0046] (Evaluation of Battery Characteristics and Measurement of Porosity of Negative Electrode Composite Material Layer) The terminals of the obtained evaluation cell were connected to a charge-discharge device (HJ-SD8) manufactured by Hokuto Denko Corporation, and when the initial discharge capacity was determined with a voltage range of 2.37 to 4.17 V_CC (0.1C = 19 mAh / g), it was 118 mAh / g. Also, as the discharge capacity retention rate by the cycle test, charge and discharge were repeated 20 times under the same conditions as in the initial charge and discharge, and when the change in capacity between after the initial discharge and after 20 repetitions was examined, it was 90%. After evaluating the battery characteristics, the porosity of the negative electrode composite material layer was determined by the average of SEM images of 5 fields of view in the manner described above, and it was 3.8%.

[0047] [Example 2] The average flatness ratio is 0.24, the particle size distribution D50 is 8.7 μm, and the BET value is 1.2 m 2A negative electrode composite material as an intermediate product was prepared in the same manner as in Example 1, except that graphite particles (PW8A) manufactured by Eika Electronics Materials Co., Ltd. with a specific surface area of / g were used. Further, a compact powder having a three-layer integrated structure composed of a positive electrode composite material layer / solid electrolyte layer (SE layer) / negative electrode composite material layer was prepared in the same manner as in Example 1. The above graphite particles had a carbon material with a crystallinity having an average interplanar spacing d 002 of 0.3363 nm. Further, after this compact powder was housed in a sealed battery cell in the same manner as in Example 1 to assemble an evaluation cell, the battery characteristics were evaluated and the porosity of the negative electrode composite material layer was measured in the same manner as in Example 1. As a result, the initial discharge capacity was 121 mAh / g, the discharge capacity retention rate was 87%, and the porosity of the negative electrode composite material layer was 4.4%.

[0048] [Example 3] A negative electrode composite material as an intermediate product was prepared in the same manner as in Example 1, except that graphite particles (PG11) manufactured by Eika Electronics Materials Co., Ltd. with an average flatness of 0.04, a particle size distribution D50 of 12.1 μm, and a BET value of 2.2 m 2 / g were used. Further, a compact powder having a three-layer integrated structure composed of a positive electrode composite material layer / solid electrolyte layer (SE layer) / negative electrode composite material layer was prepared in the same manner as in Example 1. The above graphite particles had a carbon material with a crystallinity having an average interplanar spacing d 002 of 0.3361 nm. Further, after this compact powder was housed in a sealed battery cell in the same manner as in Example 1 to assemble an evaluation cell, the battery characteristics were evaluated and the porosity of the negative electrode composite material layer was measured in the same manner as in Example 1. As a result, the initial discharge capacity was 116 mAh / g, the discharge capacity retention rate was 88%, and the porosity of the negative electrode composite material layer was 4.1%.

[0049] [Comparative Example 1] A negative electrode composite material as an intermediate product was prepared in the same manner as in Example 1, except that graphite particles (AC1) manufactured by Eika Electronics Materials Co., Ltd. with an average flatness of 0.42, a particle size distribution D50 of 5.3 μm, and a BET value of 2.4 m 2 / g were used. Further, a compact powder having a three-layer integrated structure composed of a positive electrode composite material layer / solid electrolyte layer (SE layer) / negative electrode composite material layer was prepared in the same manner as in Example 1. The above graphite particles had an average interplanar spacing d 002It was a carbon material having a crystallinity with an interplanar spacing d of 0.3372 nm. Further, after enclosing this compacted powder in a sealed battery cell in the same manner as in Example 1 to assemble an evaluation cell, the battery characteristics were evaluated and the porosity of the negative electrode composite material layer was measured in the same manner as in Example 1. As a result, the initial discharge capacity was 104 mAh / g, the discharge capacity retention rate was 79%, and the porosity of the negative electrode composite material layer was 6.7%.

[0050] [Comparative Example 2] Graphite particles (OMAC-R) manufactured by Osaka Gas Chemical Co., Ltd. with an average flatness ratio of 0.37, a particle size distribution D50 of 11.8 μm, and a BET value of 4.4 m 2 / g were used to produce a negative electrode composite material as an intermediate product in the same manner as in Example 1, and further, a compacted powder having a three-layer integrated structure composed of a positive electrode composite material layer / solid electrolyte layer (SE layer) / negative electrode composite material layer was produced in the same manner as in Example 1. The above graphite particles were carbon materials having a crystallinity with an average interplanar spacing d 002 of 0.3358 nm. Further, after enclosing this compacted powder in a sealed battery cell in the same manner as in Example 1 to assemble an evaluation cell, the battery characteristics were evaluated and the porosity of the negative electrode composite material layer was measured in the same manner as in Example 1. As a result, the initial discharge capacity was 105 mAh / g, the discharge capacity retention rate was 80%, and the porosity of the negative electrode composite material layer was 5.3%.

[0051] [Comparative Example 3] Graphite particles (PG13) manufactured by Eika Electronics Materials Co., Ltd. with an average flatness ratio of 0.21, a particle size distribution D50 of 16.7 μm, and a BET value of 1.3 m 2 / g were used to produce a negative electrode composite material as an intermediate product in the same manner as in Example 1, and further, a compacted powder having a three-layer integrated structure composed of a positive electrode composite material layer / solid electrolyte layer (SE layer) / negative electrode composite material layer was produced in the same manner as in Example 1. The above graphite particles were carbon materials having an average interplanar spacing d 002It was a carbon material having a crystallinity of 0.3359 nm. Further, after this compacted powder was housed in a sealed battery cell in the same manner as in Example 1 to assemble an evaluation cell, the battery characteristics were evaluated and the porosity of the negative electrode composite material layer was measured in the same manner as in Example 1. As a result, the initial discharge capacity was 102 mAh / g, the discharge capacity retention rate was 77%, and the porosity of the negative electrode composite material layer was 5.6%. The measurement results of the above Examples 1 to 3 and Comparative Examples 1 to 3 are summarized in Table 1 below.

[0052]

Table 1

Explanation of Symbols

[0053] 10 Compacted powder 11 Negative electrode composite material layer 12 Solid electrolyte layer (SE layer) 13 Positive electrode composite material layer 20 Insulating tube 21 Upper electrode 22 Lower electrode

Claims

1. A negative electrode composite material for an all-solid-state battery including a sulfide solid electrolyte composed of an ion-conductive compound composed of lithium, sulfur, and phosphorus, and the average interplanar spacing d of the (002) plane measured by X-ray diffraction method ００２ is a graphite particle having crystallinity with a value of 0.336 nm or more and 0.337 nm or less, and the porosity in the negative electrode composite material layer obtained by compacting the negative electrode composite material is 5% or less. The graphite particle has an average flatness of 0 or more and less than 0.3, a particle size distribution D50 of 8 μm or more and 13 μm or less, and a BET value of 1 m2 / g or more and 3 m2 / g or less. The ion-conductive compound passes through a 100-mesh sieve. The negative electrode composite material for an all-solid-state battery is characterized by the above.

2. wherein the ionic conductive compound contains Li ３ PS ４ The negative electrode composite material for all-solid-state batteries according to claim 1, characterized by including a phase.

3. The negative electrode composite material contains 50 parts by mass or more and 70 parts by mass or less of the graphite particles with respect to a total of 100 parts by mass of the graphite particles and the ion conductive compound, and is the negative electrode composite material for an all-solid-state battery according to Claim 1 or 2.

4. An all-solid-state battery having a three-layer structure in which a positive electrode composite material layer containing a positive electrode active material composed of lithium, nickel, cobalt, aluminum, and oxygen and the ion conductive compound, a solid electrolyte layer composed of the ion conductive compound, and a negative electrode composite material layer according to any one of Claims 1 to 3 are laminated.

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