All-solid-state battery

Abstract

The present application relates to an all-solid battery having: a positive electrode layer including a positive electrode current collector layer and a positive electrode active material layer; a negative electrode layer including a negative electrode current collector layer and a negative electrode active material layer; and a solid electrolyte layer including a solid electrolyte, the positive electrode active material layer and the negative electrode active material layer each containing carbon particles having an average interlayer spacing d002 of less than 0.342 (nm).

Description

Technical Field

[0001] This invention relates to an all-solid-state battery.

[0002] This application claims priority based on Japanese Patent Application No. 2020-39384, filed in Japan on March 6, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as their power source has increased significantly. In batteries used for such applications, liquid electrolytes (electrolytes) such as organic solvents have traditionally been used as the medium for ion movement. However, batteries using such electrolytes are prone to problems such as electrolyte leakage.

[0004] To address these issues, the development of all-solid-state batteries, which use solid electrolytes instead of liquid electrolytes and consist of all other solid components, is underway. Because the electrolyte in an all-solid-state battery is solid, there are no concerns about leakage, liquid drying out, or corrosion-induced performance degradation. All-solid-state batteries are being actively researched as rechargeable batteries that can easily achieve high charge / discharge capacity and energy density.

[0005] However, compared to batteries using liquid electrolytes, all-solid-state batteries using solid electrolytes generally still suffer from low discharge capacity. Li3V2(PO4)3 (hereinafter referred to as LVP323), a phosphate-based active material of the sodium superionic conductor type (NASICON), has multiple redox potentials (3.8V, 1.8V). Using it in a symmetrical electrode battery with positive and negative electrodes can yield an all-solid-state battery with a capacity in the 2V range. However, compared to using LiCoO2 as the active material, LVP323 suffers from low electronic conductivity, high internal resistance, and low discharge capacity. Therefore, to improve electronic conductivity, multiple conductors oriented approximately perpendicular to the stacking direction are included in the electrode layer or current collector layer, thereby increasing the planar electronic conductivity within the electrode layer or current collector layer. In particular, as a current collector produced during firing, to address concerns about metal oxidation, a method containing carbon can be cited (Patent Document 1).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 5804208 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] However, the internal resistance of all-solid-state batteries needs to be further reduced. Therefore, even with the all-solid-state battery disclosed in Patent Document 1, there is still room for improvement in discharge capacity.

[0011] The present invention addresses the problems of the prior art, and its objective is to provide an all-solid-state battery with further reduced internal resistance.

[0012] Technical solutions for solving technical problems

[0013] In order to achieve the above-mentioned problem, the inventors of this invention conducted in-depth research and found that in an all-solid-state battery with a solid electrolyte layer between a pair of electrodes, by using carbon particles with an average interplanar spacing d002 of less than 0.342 (nm) in the positive electrode active material layer and the negative electrode active material layer, the internal resistance of the battery can be reduced by adding a small amount, thus completing this invention.

[0014] That is, according to the present invention, an all-solid-state battery as shown below is provided.

[0015] One aspect of the present invention relates to an all-solid-state battery, characterized in that it comprises: a positive electrode layer comprising a positive current collector layer and a positive active material layer; a negative electrode layer comprising a negative current collector layer and a negative active material layer; and a solid electrolyte layer comprising a solid electrolyte, wherein the positive and negative active material layers contain carbon particles with an average interplanar spacing d002 of less than 0.342 (nm).

[0016] This structure allows for a reduction in the internal resistance of all-solid-state batteries. Carbon particles with an average interplanar spacing d002 of less than 0.342 nm exhibit good crystallinity and low periodicity disorder as a graphite structure, resulting in high thermal stability. Even with heat treatment processes such as sintering, they can easily remain in the electrode. Therefore, high electronic conductivity can be achieved with a small amount of addition, enabling the realization of high-density electrodes. Furthermore, due to the high crystallinity of these carbon particles, their electronic conductivity is also high. Therefore, by mixing these carbon particles with active materials to form an electrode, the electronic conductivity of the electrode can be improved with a small amount of addition, thereby reducing the internal resistance of the all-solid-state battery.

[0017] In addition, a small number of voids may be formed near the carbon particles due to the evaporation of carbon during heat treatment and other processes.

[0018] In one aspect of the all-solid-state battery of the present invention, regarding carbon particles, when the long side of the carbon particles is set as a and the short side as b, the ratio can be 1.0 < a / b.

[0019] Based on this configuration, by using carbon particles with small anisotropy in shape, they can be tightly packed together with the active material particles, increasing the contact area with the active material and facilitating electron movement. Therefore, the electron conductivity in the electrode can be improved, and the internal resistance of the all-solid-state battery can be reduced.

[0020] In one embodiment of the all-solid-state battery of the present invention, the carbon particles may have a particle size distribution in which D10 is greater than or equal to 0.1 μm and D90 is less than or equal to 5.0 μm.

[0021] With this configuration, carbon particles can contact the active material in a manner that is neither too much nor too little relative to the mass of the active material, and they can contact the material without creating gaps between them and the active material. Therefore, electron exchange can proceed smoothly, reducing the internal resistance of the all-solid-state battery. Furthermore, when containing particles as fine as D10 less than 0.1 μm, the carbon particles will evaporate during processes such as heat treatment, failing to achieve the desired effect.

[0022] In one embodiment of the all-solid-state battery of the present invention, the positive electrode active material layer and the negative electrode active material layer may contain 0.5 (wt%) or more and 15.0 (wt%) or less of the above-mentioned carbon particles, respectively.

[0023] Within this carbon particle content, the carbon particles are in sufficient contact with each other, which can improve the electronic conductivity as an electrode and suppress the reduction of substantial active material. Therefore, it can reduce the internal resistance of the all-solid-state battery while obtaining high capacity.

[0024] The effects of the invention

[0025] According to the present invention, it is possible to provide an all-solid-state battery with reduced internal resistance. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view of the all-solid-state battery of this embodiment. Detailed Implementation

[0027] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, identical or equivalent parts are labeled with the same symbols, and repeated descriptions are omitted. Furthermore, the scale of the drawings is not limited to the illustrated scale. In the drawings used in the following description, for ease of understanding of the features of the present invention, sometimes the parts that are characteristic are enlarged for convenience. Therefore, the scale of the constituent elements shown in the drawings may sometimes differ from the actual scale. The materials, dimensions, shapes, etc., exemplified in the following description are examples, and the present invention is not limited thereto. Appropriate modifications can be made to the implementation without changing its essence and while achieving the desired effect. For example, different combinations of the configurations described in different embodiments or embodiments can be used to implement the invention. In this embodiment, one direction of the stacking direction is sometimes referred to as the upper direction and the lower direction, but the upper and lower directions mentioned here are not necessarily consistent with the direction in which gravity is applied.

[0028] (All-solid-state battery)

[0029] Figure 1 This is a cross-sectional schematic diagram showing the structure of the all-solid-state battery 10 used to illustrate the concept of this embodiment. (As shown...) Figure 1 As shown, the all-solid-state battery 10 of this embodiment has at least one positive electrode layer 1, at least one negative electrode layer 2, and at least a portion of a solid electrolyte layer 3 sandwiched between the positive electrode layer 1 and the negative electrode layer 2. The positive electrode layer 1, the solid electrolyte layer 3, and the negative electrode layer 2 are stacked sequentially to form a laminate 4. The positive electrode layer 1 is connected to a terminal electrode 5 disposed on one end side, and the negative electrode layer 2 is connected to a terminal electrode 6 disposed on the other end side.

[0030] Positive electrode layer 1 is an example of the first electrode layer, and negative electrode layer 2 is an example of the second electrode layer. Either the first electrode layer or the second electrode layer functions as the positive electrode, and the other functions as the negative electrode. The positive or negative polarity of the electrode layer varies depending on which polarity is connected to terminal electrodes 5 and 6.

[0031] The positive electrode layer 1 has a positive current collector layer 1A and a positive active material layer 1B formed on one or both sides of the positive current collector layer 1A. On the side of the positive current collector layer 1A where there is no opposing negative electrode layer 2, the positive active material layer 1B may be absent. The negative electrode layer 2 has a negative current collector layer 2A and a negative active material layer 2B formed on one or both sides of the negative current collector layer 2A. On the side of the negative current collector layer 2A where there is no opposing positive electrode layer 1, the negative active material layer 2B may be absent. For example, the uppermost or lowermost positive electrode layer 1 or negative electrode layer 2 of the laminate 4 may not have a positive active material layer 1B or a negative active material layer 2B on one side.

[0032] The all-solid-state battery 10 of this embodiment is an all-solid-state battery having a solid electrolyte layer 3 between a pair of electrode layers. The positive electrode active material layer 1B and the negative electrode active material layer 2B contained in the pair of electrode layers contain carbon particles with an average interplanar spacing d002 of less than 0.342 (nm).

[0033] Carbon particles with an average interplanar spacing d002 of less than 0.342 nm exhibit good crystallinity and low periodicity disorder as a graphite structure, resulting in high electronic conductivity. By mixing these carbon particles with active materials to form electrodes, high thermal stability can be achieved, and they are easily retained in the electrode even after heat treatment processes such as sintering. Therefore, high electronic conductivity can be obtained with a small amount of addition, enabling the realization of high-density electrodes. Furthermore, due to the high crystallinity of these carbon particles, their electronic conductivity is also high. Therefore, by mixing these carbon particles with active materials to form electrodes, the electronic conductivity of the electrode can be improved with a small amount of addition, reducing the internal resistance of all-solid-state batteries.

[0034] In addition, small amounts of voids may form near each carbon particle due to the evaporation of carbon during heat treatment and other processes.

[0035] Furthermore, the interplanar spacing d002 of the carbon particles in this embodiment can be calculated, for example, using an X-ray diffraction apparatus (apparatus name: Xpert-N, manufactured by Malvem-Panalytical) based on the peak angle of the crystal plane index (002) using 2d·sinθ=n·λ (where d is the interplanar spacing, θ is the measurement angle, n is an arbitrary integer, and λ is the wavelength of the X-rays used).

[0036] The positive electrode active material layer 1B and the negative electrode active material layer 2B of the all-solid-state battery 10 of this embodiment are further preferably carbon particles in which the ratio of the long side of the particles to the short side to the short side is 1.0 < a / b.

[0037] Based on this configuration, by using carbon particles with small anisotropy in shape, they can be tightly packed together with the active material particles, increasing the contact area with the active material and facilitating electron movement. Therefore, the electron conductivity in the electrode can be improved, and the internal resistance of the all-solid-state battery 10 can be reduced.

[0038] The positive electrode active material layer 1B and the negative electrode active material layer 2B of the all-solid-state battery 10 of this embodiment preferably contain carbon particles with a D10 of 0.1 μm or more and a D90 of 5.0 μm or less in the particle size distribution. D10 is the diameter of particles whose cumulative volume is 10% of capacity in the particle size distribution curve obtained by particle size distribution measurement based on the equivalent circle diameter calculated from the area data of the carbon particles. Furthermore, D90 is the diameter of particles whose cumulative volume is 90% of capacity in the particle size distribution curve obtained by particle size distribution measurement.

[0039] This configuration allows carbon particles to contact the active material in a manner that is neither too much nor too little, and to contact it in a way that does not create gaps between them. Therefore, electron exchange can proceed smoothly, reducing the internal resistance of the all-solid-state battery. Furthermore, by eliminating particles with a D10 of less than 0.1 μm, carbon particle evaporation during processes such as heat treatment can be suppressed, ensuring optimal performance.

[0040] The positive electrode active material layer 1B and the negative electrode active material layer 2B of the all-solid-state battery 10 of this embodiment preferably contain 0.5 (wt%) or more and 15.0 (wt%) or less carbon particles, respectively.

[0041] Based on the carbon particle content of this structure, the carbon particles are in sufficient contact with each other, which can improve the electronic conductivity as an electrode and suppress the reduction of substantial active material. Therefore, the internal resistance of the all-solid-state battery 10 can be reduced while obtaining high capacity.

[0042] (Carbon particles)

[0043] In this embodiment, the carbon particles can be carbon particles with an average interplanar spacing d002 of less than 0.342 (nm), and can be artificial synthetic materials or natural minerals.

[0044] (Solid electrolyte)

[0045] At least a portion of the solid electrolyte layer 3 is sandwiched between the positive electrode layer 1 and the negative electrode layer 2. For example... Figure 1 As shown, at least a portion of the solid electrolyte layer 3 may also be located in the in-plane direction of the positive electrode layer 1 and the negative electrode layer 2. For the solid electrolyte in the aforementioned solid electrolyte layer 3, a material with ionic conductivity and negligible electronic conductivity is used, for example. Examples of solid electrolytes include lithium halides, lithium nitrides, lithium oxyacids, and their derivatives. Furthermore, examples include Li-P-O compounds such as lithium phosphate (Li3PO4), and LIPON (LiPO4), which is a mixture of nitrogen and lithium phosphate. 4－x N xLi-Si-O compounds such as Li4SiO4, Li-P-Si-O compounds, Li-VSi-O compounds, and La with perovskite structure 0.51 Li 0.35 TiO 2.94 La 0.55 Li 0.35 TiO3, Li 3x La 2 / 3－x Perovskite compounds such as TiO3, compounds with garnet structures containing Li, La, and Zr, and especially compounds containing sodium superionic conductor structures are preferred. The composition of compounds with sodium superionic conductor structures consists of Li... x M y (PO4)3 (x = 1–2, y = 1–2, M = containing at least one of Ti, Ge, Al, Ga, Zr) is represented, and a portion of P can also be replaced by B, Si, etc. Examples of compounds having a sodium superionic conductor structure include, for example, Li. 1.3 Al 0.3 Ti 1.7 (PO4)3 or Li 1.5 Al 0.5 Ge 1.5 (PO4)3.

[0046] (Negative electrode active material)

[0047] The negative electrode active material layer 2B contains a negative electrode active material. The negative electrode active material can be selected from Li4Ti5O4. 12 Oxides of at least one of the elements selected from Ti, Nb, W, Si, Sn, Cr, Fe, and Mo, as well as phosphorus-containing compounds such as Li3V2(PO4)3 and LiFePO4.

[0048] (Positive electrode active material)

[0049] The positive electrode active material layer 1B contains a positive electrode active material. The positive electrode active material can be LiCoO2, LiCo... 1 / 3Ni 1 / 3 Mn 1 / 3 Layered compounds such as O2, LiMn2O4, LiNi 0.5 Mn 1.5 Spinel materials such as O4, phosphorus-containing compounds such as Li3V2(PO4)3 and LiFePO4, etc. The effects of this invention can be achieved as long as at least one of the positive and negative electrode active materials contains the carbon material of this invention.

[0050] There is no clear distinction between the active materials constituting the positive electrode active material layer 1B and the negative electrode active material layer 2B. By comparing the potentials of the compounds in the positive electrode active material layer 1B and the negative electrode active material layer 2B, the compound exhibiting the higher potential can be used as the positive electrode active material, and the compound exhibiting the lower potential can be used as the negative electrode active material. Furthermore, if the compound possesses both lithium-ion release and lithium-ion retention functions, the same material can be used for the active materials constituting the positive electrode active material layer 1B and the negative electrode active material layer 2B. By using the same material for the active materials constituting the positive electrode active material layer 1B and the negative electrode active material layer 2B, a non-polar all-solid-state battery is created. Therefore, no orientation needs to be specified when mounting it onto a circuit board, thus facilitating installation.

[0051] (Current collector)

[0052] The materials constituting the positive electrode current collector layer 1A and the negative electrode current collector layer 2A are preferably materials with high conductivity, such as silver, palladium, gold, platinum, aluminum, copper, and nickel. Copper is particularly preferred because it does not readily react with lithium titanium aluminum phosphate and is effective in reducing the internal resistance of the all-solid-state battery. The materials constituting the current collector layers can be the same or different in the positive and negative electrode layers.

[0053] Furthermore, the positive electrode current collector layer 1A and the negative electrode current collector layer 2A of the all-solid-state battery in this embodiment preferably contain positive electrode active material and negative electrode active material, respectively.

[0054] The positive electrode current collector layer 1A and the negative electrode current collector layer 2A contain positive electrode active material 1B and negative electrode active material 2B respectively, which improves the adhesion between the positive electrode current collector layer 1A and the positive electrode active material layer 1B, as well as between the negative electrode current collector layer 2A and the negative electrode active material layer 2B, and is therefore preferred.

[0055] (Terminal electrode)

[0056] Terminal electrodes 5 and 6 are formed by contacting the side of the sintered body. Terminal electrodes 5 and 6 are connected to external terminals and are responsible for supplying and receiving electrons to the sintered body.

[0057] Terminal electrodes 5 and 6 are preferably made of materials with high conductivity. For example, silver, gold, platinum, aluminum, copper, tin, nickel, gallium, indium, and their alloys can be used.

[0058] (Manufacturing method of all-solid-state batteries)

[0059] In the manufacturing method of the all-solid-state battery of this embodiment, firstly, the materials of the positive electrode current collector layer, positive electrode active material layer, solid electrolyte layer, negative electrode active material layer, and negative electrode current collector layer are pasted, coated, and dried to produce a green sheet (first step). Next, the green sheet is stacked to produce a laminate (second step). Then, the laminate is simultaneously fired to manufacture the battery (third step).

[0060] (First process)

[0061] First, prepare the positive electrode active material, the negative electrode active material, and the carbon material. If the active material contains compounds of two or more elements, prepare a mixed material by mixing the compounds of each element. Alternatively, if the active material contains a solid electrolyte, prepare a mixed material as well.

[0062] There are no particular limitations on the manufacturing methods of the pastes for the positive electrode active material layer and the negative electrode active material layer. For example, the above-mentioned positive electrode active material, negative electrode active material, and carbon material can be mixed in a carrier to obtain the paste. Here, the carrier refers to the general term for the medium in the liquid phase. The carrier contains a solvent and a binder. By this method, pastes for the positive electrode current collector layer, pastes for the positive electrode active material layer, pastes for the solid electrolyte layer, pastes for the negative electrode active material layer, and pastes for the negative electrode current collector layer can be produced.

[0063] The prepared paste is applied to a substrate such as PET in the desired order. After drying as needed, the substrate is peeled off to produce raw sheets. There are no particular restrictions on the application method of the paste; known methods such as screen printing, coating, transfer printing, and doctor blade application can be used.

[0064] (Second process)

[0065] The prepared green sheets are stacked in the desired order and number of layers, and aligned and cut as needed to create a laminate. When manufacturing parallel or series-parallel connected batteries, it is preferable to align and stack them with the end faces of the positive electrode layer not being the same as those of the negative electrode layer.

[0066] When making a laminate, you can also prepare the active material layer units as described below to make the laminate.

[0067] In this method, firstly, a solid electrolyte layer paste is formed into a sheet on a PET film using a doctor blade method, resulting in a solid electrolyte sheet. Then, a positive electrode active material layer paste is screen-printed onto this solid electrolyte sheet and allowed to dry. Next, a positive electrode current collector layer paste is screen-printed onto it and allowed to dry. Further, a positive electrode active material layer paste is screen-printed again and allowed to dry. Finally, the PET film is peeled off, thus obtaining a positive electrode active material layer unit. This yields a positive electrode active material layer unit with a positive electrode active material layer paste, a positive electrode current collector layer paste, and a positive electrode active material layer paste sequentially formed on the solid electrolyte sheet. The same steps are used to fabricate a negative electrode active material layer unit, resulting in a negative electrode active material layer unit with a negative electrode active material layer paste, a negative electrode current collector layer paste, and a negative electrode active material layer paste sequentially formed on the solid electrolyte sheet.

[0068] One positive electrode active material layer unit and one negative electrode active material layer unit are overlapped with a solid electrolyte sheet in between. At this point, the units are staggered so that the positive current collector layer paste of the first positive electrode active material layer unit extends only from one end face, and the negative current collector layer paste of the second negative electrode active material layer unit extends only from the other side. A solid electrolyte sheet of a specified thickness is then further overlapped on both sides of the overlapped units to create a laminate.

[0069] The fabricated laminates are pressed together. Pressing is performed while heating is in progress, for example, at a temperature of 40–95°C.

[0070] (Third process)

[0071] For example, the laminated material is heated to 600℃~1100℃ under a nitrogen atmosphere and fired. The firing time is set to, for example, 0.1~3 hours. Through this firing process, the laminate is completed.

[0072] Furthermore, terminal electrodes can be provided to efficiently extract current from the sintered body. The terminal electrodes are connected to one end of a positive electrode layer extending from one side of the sintered body and one end of a negative electrode layer extending from one side of the sintered body, respectively. Thus, a pair of terminal electrodes are formed by clamping one side of the sintered body. Methods for forming the terminal electrodes include sputtering, screen printing, and dip coating. In screen printing and dip coating, a terminal electrode paste containing metal powder, resin, and solvent is prepared and formed into a terminal electrode. Next, a baking process to remove the solvent and a protective and mounting plating treatment are performed on the surface of the terminal electrode. On the other hand, in sputtering, because a protective layer or a mounting layer can be formed on the terminal electrode, the baking and plating processes are unnecessary.

[0073] Through the processes described above, it is possible to manufacture all-solid-state batteries.

[0074] Furthermore, the present invention is not necessarily limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. That is, each component and combination thereof in the above embodiments is only one example, and additions, omissions, substitutions, and other modifications to the components can be made without departing from the spirit of the invention.

[0075] Example

[0076] [Examples 1-4]

[0077] The present invention will be described in more detail with reference to the embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0078] (Preparation of positive electrode active material)

[0079] To verify the effectiveness of this embodiment, Li3V2(PO4)3 was used as the active material. LiPO3 and V2O3 were used as starting materials. After weighing the starting materials, they were mixed and pulverized in ethanol using a ball mill (120 rpm / zirconia balls) for 16 hours. The mixed powder of the starting materials was separated from the balls and ethanol and dried, then pre-calcined using a magnesium oxide crucible. Pre-calcination was carried out at 950°C for 2 hours in a reducing atmosphere. Afterwards, to pulverize the pre-calcined powder, it was treated in ethanol using a ball mill (120 rpm / zirconia balls) for 16 hours. The pulverized powder was separated from the balls and ethanol and dried to obtain Li3V2(PO4)3 powder.

[0080] (Preparation of negative electrode active material)

[0081] The same powder as the positive electrode active material is used as the negative electrode active material.

[0082] (Preparation of solid electrolytes)

[0083] Using Li produced by the following method 1.3 Al 0.3 Ti 1.7 (PO4)3 was used as the solid electrolyte. Li2CO3, Al2O3, TiO2, and NH4H2PO4 were used as starting materials and wet-mixed in ethanol as a solvent using a ball mill for 16 hours. The mixed powder of the starting materials was separated from the balls and ethanol and dried, then pre-calcined in an alumina crucible at 850°C under atmospheric conditions for 2 hours. Subsequently, to pulverize the pre-calcined powder, it was treated in ethanol using a ball mill (120 rpm / zirconia balls) for 16 hours. The pulverized powder was separated from the balls and ethanol and dried to obtain a powder.

[0084] (A mixture of active materials and carbon materials)

[0085] To verify the effectiveness of this embodiment, as Examples 1-4, the following carbon materials were used: D10 of 0.25 μm and D90 of 4.5 μm, a / b ratio of 3, and average interplanar spacing d002 of 0.3354, 0.3365, 0.3380, and 0.3410 (nm), respectively. Furthermore, the active material used was Li3V2(PO4)3 as described above. First, carbon materials having each average interplanar spacing were weighed in proportions of 10.7, 11.3, 12.6, and 13.5 (wt%) relative to Li3V2(PO4)3, and mixed in an organic solvent using a ball mill. The powder was separated from the balls and the organic solvent and dried to obtain a mixed powder of carbon material and Li3V2(PO4)3. The amount of carbon material added to Li3V2(PO4)3 is recorded in the table as the amount added as feed.

[0086] (Preparation of paste for positive electrode active material layer and paste for negative electrode active material layer)

[0087] Regarding the paste for the positive and negative electrode active material layers, 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent are added to 100 parts of the above-mentioned carbon material and Li3V2(PO4)3 mixed powder, and the mixture is kneaded and dispersed using three rollers to produce the paste for the positive and negative electrode active material layers.

[0088] (Preparation of a paste for a solid electrolyte layer)

[0089] Using the above-mentioned Li 1.3 Al 0.3 Ti 1.7 (PO4)3 powder was used as a solid electrolyte. 100 parts of ethanol and 200 parts of toluene were added to 100 parts of the powder as solvents, and the mixture was wet-mixed using a ball mill. Then, 16 parts of polyvinyl butyral binder and 4.8 parts of butyl benzyl phthalate were added and mixed to prepare a paste for the solid electrolyte layer.

[0090] (Fabrication of solid electrolyte layer sheets)

[0091] Using PET film as a substrate, the solid electrolyte layer is sheet-formed with paste using a doctor blade method to obtain a solid electrolyte layer sheet with a thickness of 15μm.

[0092] (Preparation of paste for positive electrode current collector layer and paste for negative electrode current collector layer)

[0093] After mixing Cu powder and Li3V2(PO4)3 powder at a weight ratio of 100:9, 10 parts of ethyl cellulose as a binder and 50 parts of dihydroterpineol as a solvent are added. The mixture is then mixed and dispersed using three rollers to prepare pastes for the positive electrode current collector layer and the negative electrode current collector layer.

[0094] (Preparation of terminal electrode paste)

[0095] Silver powder, epoxy resin, and solvent are mixed and dispersed to prepare a thermosetting terminal electrode paste.

[0096] (Fabrication of active material layer units)

[0097] Electrode current collector layer paste was screen-printed to a thickness of 5 μm on the aforementioned solid electrolyte layer sheet and dried at 80°C for 10 minutes. Positive electrode active material layer paste was then screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a positive electrode layer unit. Conversely, negative electrode active material layer paste was screen-printed to a thickness of 5 μm on the solid electrolyte layer sheet and dried at 80°C for 10 minutes. Electrode current collector layer paste was then screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a negative electrode layer unit. The PET film was then peeled off.

[0098] (Creating a layered body)

[0099] A laminate is obtained by stacking positive electrode layer units, negative electrode layer units, and solid electrolyte layer sheets in the following order: solid electrolyte layer, positive current collector layer, positive active material layer, solid electrolyte layer, negative active material layer, negative current collector layer, and solid electrolyte layer. The units are staggered so that the positive current collector layer of the positive electrode layer unit extends only from one end face, and the negative current collector layer of the negative active material layer unit extends only from the other end face. The laminate is then formed by thermoforming and cut to create the laminate.

[0100] (Preparation of sintered bodies)

[0101] After debinding the obtained laminate, it was simultaneously fired to obtain a sintered body. For debinding, the temperature was increased to the firing temperature of 700°C in nitrogen at a rate of 50°C / hour and held at that temperature for 10 hours. For simultaneous firing, the temperature was increased to the firing temperature of 850°C in nitrogen at a rate of 200°C / hour and held at that temperature for 1 hour. After firing, it was allowed to cool naturally.

[0102] Furthermore, it was confirmed that the residual carbon content in the electrode active material layer region of the obtained sintered body was approximately 10 (wt%).

[0103] (Fabrication of terminal electrodes)

[0104] Terminal electrode paste is applied to the end face of the sintered body and then thermosetting at 150°C for 30 minutes to form a pair of terminal electrodes. This completes the all-solid-state battery.

[0105] (Evaluation of the average interplanar spacing d002 of carbon particles in the electrode active material layer)

[0106] The electrode active material layer region of the sintered body is exposed and smoothed by grinding or other means. For example, it can be calculated using an X-ray diffraction device (device name: Xpert-N, manufactured by Malvem-Panalytical) based on the peak angle of the crystal plane index (002) by 2d·sinθ=n·λ (where d is the interplanar spacing, θ is the measurement angle, n is an arbitrary integer, and λ is the wavelength of the X-ray used).

[0107] (Evaluation of the long side a and short side b of the carbon particles in the electrode active material)

[0108] The electrode active material layer of the sintered body is exposed and smoothed through grinding and other processes. Scanning electron microscopy (SEM) is used to observe more than 100 carbon particles in the field of view. The length of the longest axis of each carbon particle is defined as 'a', and the length of the shortest axis as 'b'. Their ratio is then calculated as a / b. For the SEM magnification, an appropriate value is selected based on the particle size of the carbon particles, choosing a magnification that allows for the observation of more than 100 particles but less than 300 in the field of view. The a / b ratio of all carbon particles in the field of view is calculated, and the average is determined.

[0109] (Evaluation of the particle size distribution of carbon particles in electrode active materials)

[0110] The electrode active material layer of the sintered body was exposed and smoothed by grinding and other processes. The area of ​​each of the more than 200 particles in the field of view was measured by scanning electron microscopy (SEM) using image processing. The equivalent circle diameter was calculated based on these area data. The particle size with a cumulative volume of 10% capacity was set as D10, and the particle size with a cumulative volume of 90% capacity was set as D90.

[0111] (Evaluation of carbon content in electrode active materials)

[0112] The electrode active material layer region of the obtained sintered body was separated and pulverized. A carbon / sulfur analysis device (manufactured by LECO Corporation, Japan, device name: CS-844) was used as the analysis device, and the determination was performed using combustion-infrared absorption method in an oxygen gas flow.

[0113] (Relative density measurement)

[0114] The external dimensions of the obtained sintered body are measured and its volume is calculated. The density of the sintered body is obtained by dividing its weight by its volume. On the other hand, the theoretical density for this shape and size is obtained using the shape, size, and specific gravity of each component of the sintered body. Specifically, to obtain the theoretical density, firstly, the dimensions of each component of the sintered body are calculated. Here, each component of the sintered body refers to the solid electrolyte layer, the positive electrode active material layer, the positive electrode current collector layer, the negative electrode active material layer, and the negative electrode current collector layer. Next, the volume of each component is calculated based on its shape and size. Then, the specific gravity of each component of the solid electrolyte layer is multiplied by the calculated volume. The specific gravity of each component is a known specific gravity. Next, the weight of the sintered body is calculated by adding them together. Furthermore, the ratio of the positive electrode active material and the negative electrode active material, which contain active material and carbon, is considered in the calculation. Finally, the theoretical density is calculated by dividing the calculated weight of the sintered body by its volume. Then, the relative density is obtained by calculating the ratio of the obtained sintered body density to the theoretical density. The relative density is obtained by (sintered body density / theoretical density).

[0115] (Impedance evaluation)

[0116] The internal resistance was measured using an impedance / gain-phase analyzer (Solartron Analytical, device name: 1260A), mounted on a fixture secured with spring-loaded pins. The measurement was performed at a frequency of 0.005 Hz and an applied AC voltage of 0.05 V. The obtained internal resistance values ​​are shown in Table 1. Values ​​with an internal resistance less than 1 × 10⁻⁶ are considered acceptable. 7 (Ω) is set to good.

[0117] (Evaluation of charge and discharge characteristics)

[0118] Then, using a charge-discharge testing machine, the obtained laminate was mounted on a fixture secured with spring-loaded pins, and the charge-discharge capacity was measured. As test conditions, the charge-discharge current was 2 μA, and the voltage was 0 V to 1.6 V. The measured discharge capacity is shown in Table 1. A discharge characteristic value greater than 1.5 μAh was considered good.

[0119] [Comparative Example 1]

[0120] In this comparative example, the following carbon material was used: D10 of 0.25 μm and D90 of 4.5 μm, a / b ratio of 3, and average interplanar spacing d002 of 0.3425 nm. Furthermore, the aforementioned Li3V2(PO4)3 powder was used as the active material.

[0121] The carbon material was weighed at 10 wt% relative to Li3V2(PO4)3 and mixed in an organic solvent using a ball mill. The powder was separated from the balls and the organic solvent and dried to obtain a mixed powder of carbon material and Li3V2(PO4)3. Furthermore, after fabricating the laminate using the same method as in Example 1, it was debonded and sintered using the same method. The discharge characteristics of the laminate were evaluated using the same method as in Example 1. The measured internal resistance and discharge capacity are shown in Table 1.

[0122] As can be seen from Table 1, by using carbon materials and active substances within the scope of this invention in the active material layer, even a small amount can be added to achieve an effective residual amount, thereby enabling a dense electrode region and exhibiting significantly low internal resistance as an all-solid-state battery. It is also evident that a high discharge capacity is obtained.

[0123] [Table 1]

[0124]

[0125] [Examples 5-12]

[0126] (A mixture of active materials and carbon materials)

[0127] To verify the effectiveness of this embodiment, as Examples 5-12, the following carbon materials were used: D10 of 0.25 μm and D90 of 4.5 μm, average interplanar spacing d002 of 0.3365 and 0.3380 (nm), and a / b ratios of 1.0, 1.1, 1.5, 5.0, 10.0, 50.0, 100.0, and 200.0, respectively. Furthermore, the active material used was the aforementioned Li3V2(PO4)3 powder. These carbon materials were weighed at 11.3 wt% relative to Li3V2(PO4)3 and mixed in an organic solvent using a ball mill. The powder was separated from the balls and the organic solvent and dried to obtain a mixed powder of carbon material and Li3V2(PO4)3.

[0128] (Preparation of paste for positive electrode active material layer and paste for negative electrode active material layer)

[0129] Regarding the paste for the positive and negative electrode active material layers, 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent are added to 100 parts of the above-mentioned carbon material and Li3V2(PO4)3 mixed powder, and the mixture is kneaded and dispersed using three rollers to produce the paste for the positive and negative electrode active material layers.

[0130] (Preparation of a paste for a solid electrolyte layer)

[0131] Using the above-mentioned Li 1.3 Al 0.3 Ti1.7 (PO4)3 powder was used as a solid electrolyte. 100 parts of ethanol and 200 parts of toluene were added to 100 parts of the powder as solvents, and the mixture was wet-mixed using a ball mill. Then, 16 parts of polyvinyl butyral binder and 4.8 parts of butyl benzyl phthalate were added and mixed to prepare a paste for the solid electrolyte layer.

[0132] (Fabrication of solid electrolyte layer sheets)

[0133] Using PET film as a substrate, the solid electrolyte layer is sheet-formed with paste using a doctor blade method to obtain a solid electrolyte layer sheet with a thickness of 15μm.

[0134] (Preparation of paste for positive electrode current collector layer and paste for negative electrode current collector layer)

[0135] Cu powder and Li3V2(PO4)3 powder were mixed at a weight ratio of 100:9. Then, 10 parts of ethyl cellulose as a binder and 50 parts of dihydroterpineol as a solvent were added. The mixture was then mixed and dispersed using three rollers to prepare pastes for the positive electrode current collector layer and the negative electrode current collector layer.

[0136] (Preparation of terminal electrode paste)

[0137] Silver powder, epoxy resin, and solvent are mixed and dispersed to prepare a thermosetting terminal electrode paste.

[0138] (Fabrication of active material layer units)

[0139] A positive electrode current collector layer paste was screen-printed to a thickness of 5 μm on the aforementioned solid electrolyte layer sheet and dried at 80°C for 10 minutes. A positive electrode active material layer paste was then screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a positive electrode layer unit. Conversely, a negative electrode active material layer paste was screen-printed to a thickness of 5 μm on the solid electrolyte layer sheet and dried at 80°C for 10 minutes. Then, a negative electrode current collector layer paste was screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a negative electrode layer unit. The PET film was then peeled off.

[0140] (Creating a layered body)

[0141] Using positive electrode layer units, negative electrode layer units, and solid electrolyte layer sheets, a single-layer product is obtained by overlapping them in the following order: solid electrolyte layer, positive current collector layer, positive active material layer, solid electrolyte layer, negative active material layer, negative current collector layer, and solid electrolyte layer. At this point, the units are staggered and overlapped such that the positive current collector layer of the positive electrode layer unit extends only from one end face, and the negative current collector layer of the negative electrode layer unit extends only from the other end face. Afterward, they are formed by hot pressing and then cut to create a laminate.

[0142] (Preparation of sintered bodies)

[0143] After debinding the obtained laminate, it was simultaneously fired to obtain a sintered body. For debinding, the temperature was increased to the firing temperature of 700°C in nitrogen at a rate of 50°C / hour and held at that temperature for 10 hours. For simultaneous firing, the temperature was increased to the firing temperature of 850°C in nitrogen at a rate of 200°C / hour and held at that temperature for 1 hour. After firing, it was allowed to cool naturally.

[0144] Furthermore, it was confirmed that the residual carbon content in the electrode active material layer region of the obtained sintered body was approximately 10 (wt%).

[0145] (Fabrication of terminal electrodes)

[0146] Terminal electrode paste is applied to the end face of the sintered body and then thermosetting at 150°C for 30 minutes to form a pair of terminal electrodes. This completes the all-solid-state battery.

[0147] (Evaluation of the average interplanar spacing d002 of carbon particles in the electrode active material layer)

[0148] The electrode active material layer region of the sintered body is exposed by grinding and smoothing. The electrode active material layer region is then exposed by grinding and smoothing. The electrode active material layer region is then exposed by X-ray diffraction equipment (Xpert-N, manufactured by Malvem-Panalytical) and the peak angle of the crystal plane index (002) is calculated by 2d·sinθ=n·λ (where d is the interplanar spacing, θ is the measurement angle, n is an arbitrary integer, and λ is the wavelength of the X-rays used).

[0149] (Evaluation of the long side a and short side b of the carbon particles in the electrode active material)

[0150] The electrode active material layer of the sintered body can be exposed and smoothed through grinding and other processes. Based on scanning electron microscopy (SEM) observation, for more than 100 particles in the field of view, the length along the longest axis is defined as 'a', and the length along the shortest axis as 'b', and their ratio is calculated as a / b. Regarding the SEM magnification, an appropriate value is selected based on the particle size of the carbon particles, choosing a magnification that allows for the observation of more than 100 and less than 300 particles in the field of view. Furthermore, the a / b ratio of the carbon particles is calculated as the average of the a / b ratios of all carbon particles in the field of view.

[0151] (Evaluation of the particle size distribution of carbon particles in electrode active materials)

[0152] The electrode active material layer of the sintered body was exposed and smoothed by grinding and other processes. The area of ​​each of the more than 200 particles in the field of view was measured by scanning electron microscopy (SEM) using image processing. The equivalent circle diameter was calculated based on these area data. The particle size with a cumulative volume of 10% capacity was set as D10, and the particle size with a cumulative volume of 90% capacity was set as D90.

[0153] (Evaluation of carbon content in electrode active materials)

[0154] The electrode active material layer region of the obtained sintered body was separated and pulverized. A carbon / sulfur analysis device (manufactured by LECO Corporation, Japan, device name: CS-844) was used as the analysis device, and the determination was performed using combustion-infrared absorption method in an oxygen gas flow.

[0155] (Relative density measurement)

[0156] The external dimensions of the obtained sintered body are measured and its volume is calculated. The density of the sintered body is obtained by dividing its weight by its volume. On the other hand, after calculating the theoretical density for this shape and size, the relative density is obtained by calculating the ratio of the obtained sintered body density to the theoretical density.

[0157] (Impedance evaluation)

[0158] The internal resistance was measured using an impedance / gain-phase analyzer, mounted on a fixture secured with spring-loaded pins. The measurement was performed at a frequency of 0.005 Hz and an applied AC voltage of 0.05 V. The obtained internal resistance values ​​are shown in Table 2. Values ​​with an internal resistance less than 1 × 10⁻⁶ are considered acceptable. 7 (Ω) is set to good.

[0159] (Evaluation of charge and discharge characteristics)

[0160] Then, using a charge-discharge testing machine, the obtained laminate was mounted on a fixture secured with spring-loaded pins, and the charge-discharge capacity was measured. As test conditions, the charge-discharge current was 2 μA, and the voltage was 0 V to 1.6 V. The measured discharge capacity is shown in Table 2.

[0161] As can be seen from Table 2, all-solid-state batteries using carbon materials with a / b ratios within the scope of this invention for both the positive and negative electrode active material layers exhibit significantly low internal resistance. Furthermore, when the a / b value is in the range of 1.1 to 100.0, even lower internal resistance is observed, and good discharge capacity is achieved. Additionally, when the a / b value is in the range of 1.5 to 5.0, even lower internal resistance is observed, and even better discharge capacity is achieved.

[0162] [Table 2]

[0163]

[0164] [Examples 13-15]

[0165] (A mixture of active materials and carbon materials)

[0166] To verify the effectiveness of this embodiment, as Examples 13-15, the following carbon materials were used: average interplanar spacing d002 of 0.3365 nm, a / b ratio of 3.0, D10 of 0.1 μm and D90 of 5 μm (Example 13), D10 of 0.2 μm and D90 of 5.5 μm (Example 14), and D10 of 0.08 μm and D90 of 4.0 μm (Example 15). Furthermore, the active material used was the aforementioned Li3V2(PO4)3 powder. These carbon materials were weighed at 11.3 wt% relative to Li3V2(PO4)3 and mixed in an organic solvent using a ball mill. The powder was separated from the balls and the organic solvent and dried to obtain a mixed powder of carbon material and Li3V2(PO4)3.

[0167] (Preparation of paste for positive electrode active material layer and paste for negative electrode active material layer)

[0168] Regarding the paste for the positive and negative electrode active material layers, 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent are added to 100 parts of the above-mentioned carbon material and Li3V2(PO4)3 mixed powder, and the mixture is kneaded and dispersed using three rollers to produce the paste for the positive and negative electrode active material layers.

[0169] (Preparation of a paste for a solid electrolyte layer)

[0170] Using the above-mentioned Li 1.3 Al 0.3 Ti 1.7 (PO4)3 powder was used as a solid electrolyte. 100 parts of ethanol and 200 parts of toluene were added to 100 parts of the powder as solvents, and the mixture was wet-mixed using a ball mill. Then, 16 parts of polyvinyl butyral binder and 4.8 parts of butyl benzyl phthalate were added and mixed to prepare a paste for the solid electrolyte layer.

[0171] (Fabrication of solid electrolyte layer sheets)

[0172] Using PET film as a substrate, the solid electrolyte layer paste was sheet-formed using a doctor blade method to obtain a solid electrolyte layer sheet with a thickness of 15μm.

[0173] (Preparation of paste for positive electrode current collector layer and paste for negative electrode current collector layer)

[0174] Cu powder and Li3V2(PO4)3 powder were mixed at a weight ratio of 100:9. Then, 10 parts of ethyl cellulose as a binder and 50 parts of dihydroterpineol as a solvent were added. The mixture was then mixed and dispersed using three rollers to prepare pastes for the positive electrode current collector layer and the negative electrode current collector layer.

[0175] (Preparation of terminal electrode paste)

[0176] Silver powder, epoxy resin, and solvent are mixed and dispersed to prepare a thermosetting terminal electrode paste.

[0177] (Fabrication of active material layer units)

[0178] A positive electrode current collector layer paste was screen-printed to a thickness of 5 μm on the aforementioned solid electrolyte layer sheet and dried at 80°C for 10 minutes. A positive electrode active material layer paste was then screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a positive electrode layer unit. Conversely, a negative electrode active material layer paste was screen-printed to a thickness of 5 μm on the solid electrolyte layer sheet and dried at 80°C for 10 minutes. Then, a negative electrode current collector layer paste was screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a negative electrode layer unit. The PET film was then peeled off.

[0179] (Creating a layered body)

[0180] Using positive electrode layer units, negative electrode layer units, and solid electrolyte layer sheets, a single-layer product is obtained by overlapping them in the following order: solid electrolyte layer, positive current collector layer, positive active material layer, solid electrolyte layer, negative active material layer, negative current collector layer, and solid electrolyte layer. At this point, the units are staggered and overlapped such that the positive current collector layer of the positive electrode layer unit extends only from one end face, and the negative current collector layer of the negative electrode layer unit extends only from the other end face. Afterward, they are formed by hot pressing and then cut to create a laminate.

[0181] (Preparation of sintered bodies)

[0182] After debinding the obtained laminate, it was simultaneously fired to obtain a sintered body. For debinding, the temperature was increased to the firing temperature of 700°C in nitrogen at a rate of 50°C / hour and held at that temperature for 10 hours. For simultaneous firing, the temperature was increased to the firing temperature of 850°C in nitrogen at a rate of 200°C / hour and held at that temperature for 1 hour. After firing, it was allowed to cool naturally.

[0183] Furthermore, it was confirmed that the residual carbon content in the electrode active material layer region of the obtained sintered body was approximately 10 (wt%).

[0184] (Fabrication of terminal electrodes)

[0185] Terminal electrode paste is applied to the end face of the sintered body and then thermosetting at 150°C for 30 minutes to form a pair of terminal electrodes. This completes the all-solid-state battery.

[0186] (Evaluation of the average interplanar spacing d002 of carbon particles in the electrode active material layer)

[0187] The electrode active material layer region of the sintered body is exposed by grinding and smoothing. The electrode active material layer region is then exposed by grinding and smoothing. The electrode active material layer region is then exposed by X-ray diffraction equipment (Xpert-N, manufactured by Malvem-Panalytical) and the peak angle of the crystal plane index (002) is calculated by 2d·sinθ=n·λ (where d is the interplanar spacing, θ is the measurement angle, n is an arbitrary integer, and λ is the wavelength of the X-rays used).

[0188] (Evaluation of the long side a and short side b of the carbon particles in the electrode active material)

[0189] The electrode active material layer of the sintered body is exposed and smoothed through grinding and other processes. Scanning electron microscopy (SEM) is used to observe more than 100 particles in the field of view. The length along the longest axis is defined as 'a', and the length along the shortest axis as 'b'. The ratio of these lengths is calculated as a / b. Regarding the SEM magnification, an appropriate value is selected based on the carbon particle size, choosing a magnification that observes more than 100 but less than 300 particles in the field of view. Furthermore, the a / b ratio of the carbon particles is calculated as the average of the a / b ratios of all carbon particles in the field of view. (Evaluation of the particle size distribution of carbon particles in the electrode active material)

[0190] The electrode active material layer of the sintered body was exposed and smoothed by grinding and other processes. The area of ​​each of the more than 200 particles in the field of view was measured by scanning electron microscopy (SEM) using image processing. The equivalent circle diameter was calculated based on these area data. The particle size with a cumulative volume of 10% capacity was set as D10, and the particle size with a cumulative volume of 90% capacity was set as D90.

[0191] (Evaluation of carbon content in electrode active materials)

[0192] The electrode active material layer region of the obtained sintered body was separated and pulverized. A carbon / sulfur analysis device (manufactured by LECO Corporation, Japan, device name: CS-844) was used as the analysis device, and the determination was performed using combustion-infrared absorption method in an oxygen gas flow.

[0193] (Relative density measurement)

[0194] The external dimensions of the obtained sintered body are measured and its volume is calculated. The density of the sintered body is obtained by dividing its weight by its volume. On the other hand, after calculating the theoretical density for this shape and size, the relative density is obtained by calculating the ratio of the obtained sintered body density to the theoretical density.

[0195] (Impedance evaluation)

[0196] The internal resistance was measured using an impedance / gain-phase analyzer, mounted on a fixture secured with spring-loaded pins. The measurement was performed at a frequency of 0.005 Hz and an applied AC voltage of 0.05 V. The obtained internal resistance values ​​are shown in Table 3. Values ​​with an internal resistance less than 1 × 10⁻⁶ are considered acceptable. 7 (Ω) is set to good.

[0197] (Evaluation of charge and discharge characteristics)

[0198] Then, using a charge-discharge testing machine, the obtained laminate was mounted on a fixture secured with spring-loaded pins, and the charge-discharge capacity was measured. As test conditions, the charge-discharge current was 2 μA, and the voltage was 0 V to 1.6 V. The measured discharge capacity is shown in Table 3. A discharge characteristic value greater than 1.5 μAh was considered good.

[0199] As can be seen from Table 3, all-solid-state batteries using carbon materials with D10 and D90, which fall within the scope of this invention, for the positive and negative electrode active material layers, respectively, exhibit significantly low internal resistance. It is also evident that when D10 is above 0.1 μm and D90 is below 5.0 μm, even lower internal resistance is observed, and good discharge capacity is achieved.

[0200] [Table 3]

[0201]

[0202] [Examples 16-21]

[0203] (A mixture of active materials and carbon materials)

[0204] To verify the effectiveness of this embodiment, as Examples 16-21, carbon materials with the following characteristics were used: an average interplanar spacing d002 of 0.3380 nm, an a / b ratio of 3, a D10 of 0.25 μm, and a D90 of 4.5 μm. Furthermore, the active material used was the aforementioned Li3V2(PO4)3 powder. These carbon materials were weighed at amounts of 0.49 wt%, 0.58 wt%, 1.13 wt%, 7.12 wt%, 11.30 wt%, and 16.95 wt% relative to Li3V2(PO4)3, and mixed in an organic solvent using a ball mill. The powder was separated from the balls and the organic solvent and dried to obtain a mixed powder of carbon material and Li3V2(PO4)3.

[0205] (Preparation of paste for positive electrode active material layer and paste for negative electrode active material layer)

[0206] Regarding the paste for the positive and negative electrode active material layers, 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent are added to 100 parts of the above-mentioned carbon material and Li3V2(PO4)3 mixed powder, and the mixture is kneaded and dispersed using three rollers to produce the paste for the positive and negative electrode active material layers.

[0207] (Preparation of a paste for a solid electrolyte layer)

[0208] Using the above-mentioned Li 1.3 Al 0.3 Ti 1.7 (PO4)3 powder was used as a solid electrolyte. 100 parts of ethanol and 200 parts of toluene were added to 100 parts of the powder as solvents, and the mixture was wet-mixed using a ball mill. Then, 16 parts of polyvinyl butyral binder and 4.8 parts of butyl benzyl phthalate were added and mixed to prepare a paste for the solid electrolyte layer.

[0209] (Fabrication of solid electrolyte layer sheets)

[0210] Using PET film as a substrate, the solid electrolyte layer is sheet-formed with paste using a doctor blade method to obtain a solid electrolyte layer sheet with a thickness of 15μm.

[0211] (Preparation of paste for positive electrode current collector layer and paste for negative electrode current collector layer)

[0212] Cu powder and Li3V2(PO4)3 powder were mixed at a weight ratio of 100:9. Then, 10 parts of ethyl cellulose as a binder and 50 parts of dihydroterpineol as a solvent were added. The mixture was then mixed and dispersed using three rollers to prepare pastes for the positive electrode current collector layer and the negative electrode current collector layer.

[0213] (Preparation of terminal electrode paste)

[0214] Silver powder, epoxy resin, and solvent are mixed and dispersed to prepare a thermosetting terminal electrode paste.

[0215] (Fabrication of active material layer units)

[0216] A positive electrode current collector layer paste was screen-printed to a thickness of 5 μm on the aforementioned solid electrolyte layer sheet and dried at 80°C for 10 minutes. A positive electrode active material layer paste was then screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a positive electrode layer unit. Conversely, a negative electrode active material layer paste was screen-printed to a thickness of 5 μm on the solid electrolyte layer sheet and dried at 80°C for 10 minutes. Then, a negative electrode current collector layer paste was screen-printed to a thickness of 5 μm on the same sheet and dried at 80°C for 10 minutes to form a negative electrode layer unit. The PET film was then peeled off.

[0217] (Creating a layered body)

[0218] Using positive electrode layer units, negative electrode layer units, and solid electrolyte layer sheets, a single-layer product is obtained by overlapping them in the following order: solid electrolyte layer, positive current collector layer, positive active material layer, solid electrolyte layer, negative active material layer, negative current collector layer, and solid electrolyte layer. At this point, the units are staggered and overlapped such that the positive current collector layer of the positive electrode layer unit extends only from one end face, and the negative current collector layer of the negative electrode layer unit extends only from the other end face. Afterward, they are formed by hot pressing and then cut to create a laminate.

[0219] (Preparation of sintered bodies)

[0220] After debinding the obtained laminate, it was simultaneously fired to obtain a sintered body. For debinding, the temperature was increased to the firing temperature of 700°C in nitrogen at a rate of 50°C / hour and held at that temperature for 10 hours. For simultaneous firing, the temperature was increased to the firing temperature of 850°C in nitrogen at a rate of 200°C / hour and held at that temperature for 1 hour. After firing, it was allowed to cool naturally.

[0221] Furthermore, the residual carbon content in the electrode active material layer region of the obtained sintered body was confirmed to be 0.43, 0.51, 1.00, 6.30, 15.00, and 16.00 (wt%), respectively.

[0222] (Fabrication of terminal electrodes)

[0223] Terminal electrode paste is applied to the end face of the sintered body and then thermosetting at 150°C for 30 minutes to form a pair of terminal electrodes. This completes the all-solid-state battery.

[0224] (Evaluation of the average interplanar spacing d002 of carbon particles in the electrode active material layer)

[0225] The electrode active material layer region of the sintered body is exposed by grinding and smoothing. The electrode active material layer region is then exposed by grinding and smoothing. The electrode active material layer region is then exposed by X-ray diffraction equipment (Xpert-N, manufactured by Malvem-Panalytical) based on the peak angle of the crystal plane index (002) and the Bragg equation 2d·sinθ=n·λ (where d is the interplanar spacing, θ is the measurement angle, n is an arbitrary integer, and λ is the wavelength of the X-rays used).

[0226] (Evaluation of the long side a and short side b of the carbon particles in the electrode active material)

[0227] The electrode active material layer of the sintered body can be exposed and smoothed through grinding and other processes. Based on scanning electron microscopy (SEM) observation, for more than 100 particles in the field of view, the length along the longest axis is defined as 'a', and the length along the shortest axis as 'b', and their ratio is calculated as a / b. Regarding the SEM magnification, an appropriate value is selected based on the particle size of the carbon particles, choosing a magnification that allows for the observation of more than 100 and less than 300 particles in the field of view. Furthermore, the a / b ratio of the carbon particles is calculated as the average of the a / b ratios of all carbon particles in the field of view.

[0228] (Evaluation of the particle size distribution of carbon particles in electrode active materials)

[0229] The electrode active material layer of the sintered body was exposed and smoothed by grinding and other processes. The area of ​​each of the more than 200 particles in the field of view was measured by scanning electron microscopy (SEM) using image processing. The equivalent circle diameter was calculated based on these area data. The particle size with a cumulative volume of 10% capacity was set as D10, and the particle size with a cumulative volume of 90% capacity was set as D90.

[0230] (Evaluation of carbon content in electrode active materials)

[0231] The electrode active material layer region of the obtained sintered body was separated and pulverized. A carbon / sulfur analysis device (manufactured by LECO Corporation, Japan, device name: CS-844) was used as the analysis device, and the determination was performed using combustion-infrared absorption method in an oxygen gas flow.

[0232] (Relative density measurement)

[0233] The external dimensions of the obtained sintered body are measured and its volume is calculated. The density of the sintered body is obtained by dividing its weight by its volume. On the other hand, after calculating the theoretical density for this shape and size, the relative density is obtained by calculating the ratio of the obtained sintered body density to the theoretical density. The relative density is obtained by (sintered body density / theoretical density).

[0234] (Impedance evaluation)

[0235] The internal resistance was measured using an impedance / gain-phase analyzer, mounted on a fixture secured with spring-loaded pins. The measurement was performed at a frequency of 0.005 Hz and an applied AC voltage of 0.05 V. The obtained internal resistance values ​​are shown in Table 4. Values ​​with an internal resistance less than 1 × 10⁻⁶ are considered acceptable. 7 (Ω) is set to good.

[0236] (Evaluation of charge and discharge characteristics)

[0237] Then, using a charge-discharge testing machine, the obtained laminate was mounted on a fixture secured with spring-loaded pins, and the charge-discharge capacity was measured. As test conditions, the charge-discharge current was 2 μA, and the voltage was 0 V to 1.6 V. The measured discharge capacity is shown in Table 4. A discharge characteristic value greater than 1.5 μAh was considered good.

[0238] As can be seen from Table 4, using carbon materials within the scope of this invention for both the positive and negative electrode active material layers in an all-solid-state battery results in a significantly denser sintered body, exhibiting low internal resistance. Furthermore, when the carbon particle content is 0.5 wt% or more and 15.0 wt% or less, even lower internal resistance is observed, along with good discharge capacity. Moreover, when the carbon particle content is 1.00 wt% or more and 15.0 wt% or less, even lower internal resistance is observed, along with better discharge capacity.

[0239] [Table 4]

[0240]

[0241] As described above, the all-solid-state battery of the present invention is effective in reducing internal resistance.

[0242] Symbol Explanation

[0243] 1: Positive electrode layer; 2: Negative electrode layer; 3: Solid electrolyte layer; 4: Laminated structure; 5, 6: Terminal electrodes; 10: All-solid-state battery.

Claims

1. An all-solid-state battery, characterized in that, have: The positive electrode layer comprises a positive current collector layer and a positive active material layer; The negative electrode layer comprises a negative electrode current collector layer and a negative electrode active material layer; and A solid electrolyte layer, which contains a solid electrolyte. The positive electrode active material layer and the negative electrode active material layer each contain carbon particles with an average interplanar spacing d002 of less than 0.342 nm. In the particle size distribution of the carbon particles, D10 is greater than or equal to 0.1 μm, and D90 is less than or equal to 5.0 μm. The ratio a / b of the long side to the short side of the carbon particle satisfies 1.5 ≤ a / b ≤ 5.

0. The positive electrode active material layer and the negative electrode active material layer respectively contain more than 1.0 wt% and less than 15.0 wt% of the carbon particles. The positive electrode active material layer is composed of the positive electrode active material, the carbon particles, and a binder. The negative electrode active material layer is composed of the negative electrode active material, the carbon particles, and the binder.

2. The all-solid-state battery as described in claim 1, characterized in that: In the particle size distribution of the carbon particles, D10 is less than 0.25 μm.

3. The all-solid-state battery as described in claim 1, characterized in that: In the particle size distribution of the carbon particles, D90 is greater than 4.0 μm.

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