Positive electrode material for all-solid-state batteries, all-solid-state battery, and method for manufacturing the positive electrode material for all-solid-state batteries

Abstract

Improvement of all-solid-state batteries [Solution] The solution comprises a positive electrode active material and a coating material, wherein the positive electrode active material is of formula (1-1):Li2Co (1-x) P (2-y) M 1 x M 2 y A positive electrode material for an all-solid-state battery, having a composition represented by O7, wherein the coating material has a composition represented by formula (2):Li4P2O7, and the coating material is present in an amount greater than 0.5% by weight and less than 15.0% by weight relative to the positive electrode active material.

Description

[Technical Field]

[0001] This invention relates to a positive electrode material. Specifically, this invention relates to a positive electrode material for an all-solid-state battery, an all-solid-state battery using the same, and a method for manufacturing the positive electrode material for the all-solid-state battery. [Background technology]

[0002] Lithium-ion batteries are widely used in electronic devices and automobiles, and represent a large global market. Various next-generation products are being proposed to improve the performance and safety of lithium-ion batteries. All-solid-state lithium-ion batteries have attracted particular attention in recent years among these next-generation batteries due to their expected high level of safety. While various batteries are known as "solid-state batteries," both theoretically and practically, today the term "all-solid-state battery" narrowly refers to all-solid-state lithium-ion batteries.

[0003] The main body of an all-solid-state battery is formed from a laminate of a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a current collector film. In developing solid-state batteries using NASICON-type solid electrolyte LAGP, the applicant has conducted extensive research from various angles, including materials such as NASICON-type solid electrolyte LAGP and positive electrode material, and manufacturing processes (Patent Documents 1, 2, 3, 4).

[0004] As described in Non-Patent Documents 1, 2, and 3, one of the problems in the practical application of solid-state batteries is the large resistance that occurs at the interface between the electrolyte layer and the electrode layer. To solve this problem, materials that exist between the electrolyte layer and the electrode layer to control the interfacial resistance have been proposed (referred to as "interfacial control material" in Non-Patent Document 1, and as "buffer layer" in Non-Patent Documents 2 and 3).

[0005] As an example of reducing interfacial resistance using such materials, Non-Patent Document 1 describes a layered structure: negative electrode Li / solid electrolyte Li7La3Zr2O 12An example of forming a Li-Nb-O-based material on the interface of the positive electrode active material LiCoO2 is described. In Non-Patent Document 2 and Non-Patent Document 3, an example of forming a buffer layer on the surface of the positive electrode active material LiCoO2 with a nanometer order composed of Li4Ti5O 12 is described.

[0006] On the other hand, the applicant has succeeded in forming a Li4P2O7 layer on the surface of the pyrophosphate-based positive electrode active material in order to suppress the reaction between the positive electrode active material and the solid electrolyte during the heat treatment when manufacturing the electrode layer of the all-solid-state battery (Patent Document 5). The reactivity between this Li4P2O7 layer and the solid electrolyte LAGP is low, and the crystal structures of the positive electrode active material and the solid electrolyte are maintained even after firing. Since the crystal structure of the positive electrode active material having the above Li4P2O7 layer is stable, it can be said that it is difficult to deteriorate during the process of repeatedly charging and discharging the all-solid-state battery. However, the above interface resistance has not been considered here. The relationship between the above Li4P2O7 layer and the above interface resistance is not mentioned at all in Patent Document 5.

Prior Art Documents

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0009] The object of the present invention is to reduce the resistance of all-solid-state batteries. Specifically, the present inventor has sought an effective interface control material (buffer layer) for a pyrophosphate-based positive electrode active material, particularly for the pyrophosphate-based positive electrode active material and the solid electrolyte LAGP. From another perspective of controlling the interfacial resistance between the electrolyte layer and the electrode layer, the present inventor has reexamined the surface treatment of the pyrophosphate-based positive electrode active material.

Means for Solving the Problems

[0010] As a result, the present inventor has succeeded in suppressing an increase in the interfacial resistance value between the positive electrode active material and the solid electrolyte by modifying the pyrophosphate-based positive electrode active material with a specific amount of the film-forming material Li4P2O7. That is, the present invention is as follows.

[0011] (Invention 1) Comprising a positive electrode active material and a film-forming material, the positive electrode active material has a composition represented by the following formula (1-1), ​​​​​​​​​​​​​​​​​​​​This is one or more nonmetallic and / or metallic elements selected from boron (B), aluminum (Al), gallium (Ga), carbon (C), silicon (Si), and germanium (Ge). x and y are numbers that satisfy 0 ≤ x < 1 and 0 ≤ y ≤ 0.07. The above coating material has a composition represented by formula (2):Li4P2O7, The above coating material is present in an amount greater than 0.5% by weight and less than 15.0% by weight relative to the above positive electrode active material. Cathode material for all-solid-state batteries. (Invention 2) The positive electrode material of Invention 1, wherein the positive electrode active material has a composition represented by formula (1-2):Li2CoP2O7. (Invention 3) The positive electrode material of Invention 1, wherein the coating material is present in an amount of 0.7% to 10% by weight relative to the positive electrode active material. (Invention 4) A solid-state battery comprising a positive electrode layer containing the positive electrode material of Invention 1. (Invention 5) This includes the following steps 1, 2, and 3: Step 1: A step in which a water-soluble lithium salt, a water-soluble phosphate, a complexing agent, and water are mixed to prepare an aqueous solution of the film material raw materials. Step 2: A step in which the aqueous solution obtained in Step 1 is brought into contact with the positive electrode active material to prepare the positive electrode material precursor. Step 3: A step in which the cathode material precursor obtained in Step 2 is calcined to obtain a cathode material for an all-solid-state battery, which includes a cathode active material and a coating material. The above positive electrode active material has a composition represented by the following formula (1-1), Li2Co (1-x) P (2-y) M 1 x M 2 y O7···(1-1) (In formula (1), M 1 It is one or more metallic elements selected from titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), and nickel (Ni). M 2This is one or more nonmetallic and / or metallic elements selected from boron (B), aluminum (Al), gallium (Ga), carbon (C), silicon (Si), and germanium (Ge). x and y are numbers that satisfy 0 ≤ x < 1 and 0 ≤ y ≤ 0.07. The above coating material has a composition represented by formula (2):Li4P2O7, In the above positive electrode material, the coating material is present in an amount greater than 0.5% by weight and less than 15.0% by weight relative to the positive electrode active material. A method for manufacturing positive electrode material for all-solid-state batteries. (Invention 6) The method for manufacturing the invention of the present invention, wherein the positive electrode active material has a composition represented by formula (1-2):Li2CoP2O7. (Invention 7) A method for producing the positive electrode material of the invention 5, wherein the coating material is present in a range of 0.7% to 10% by weight relative to the positive electrode active material. [Effects of the Invention]

[0012] The positive electrode material of the present invention results in an all-solid-state battery with low resistance. When the coating material is present in an amount greater than 0.5% by weight and less than 15.0% by weight relative to the positive electrode active material, preferably when the coating material is present in an amount of 0.7% by weight or more and 10% by weight or less relative to the positive electrode active material, the increase in the resistance value of the all-solid-state battery body is significantly suppressed. [Brief explanation of the drawing]

[0013] [Figure 1] Figures 1A to 1C are schematic diagrams showing the configuration of the solid-state battery according to this embodiment. [Figure 2] A schematic diagram showing the particles of the positive electrode material of the present invention. [Figure 3] Figures 3A to 3E are schematic diagrams illustrating an example of the manufacturing process for positive electrode composite layer parts. [Figure 4] Figures 4A to 4C are schematic diagrams showing examples of fabricated positive electrode mixture layer parts. [Figure 5]Figures 5A to 5C are schematic diagrams showing an example of a fabricated negative electrode mixture layer part. [Figure 6] Figures 6A to 6C are schematic diagrams illustrating an example of the process for manufacturing a solid-state battery. [Figure 7] Figures 7A to 7C are schematic diagrams illustrating an example of the process for manufacturing a solid-state battery. [Figure 8] A graph showing the results of the cycle tests performed in the examples and comparative examples. [Modes for carrying out the invention]

[0014] [Cathode material for all-solid-state batteries] The positive electrode material for all-solid-state batteries of the present invention comprises a positive electrode active material and a coating material. The coating material is generally present in a range of more than 0.5% by weight and less than 15.0% by weight relative to the positive electrode active material, and preferably in a range of 0.7% by weight and more and 10% by weight or less. Figure 2 schematically shows the particles of the positive electrode material of the present invention.

[0015] The increase in resistance of the all-solid-state battery body is significantly suppressed only when the ratio of the coating material to the positive electrode active material is limited to the above range. In this case, the mechanism by which the coating material controls charge transfer inside and / or on the surface of the electrode and electrolyte is not clear. However, it is clear from the examples described later that in this case the coating material functions as a so-called interface control material or buffer layer.

[0016] [Cathode active material] The positive electrode active material constituting the positive electrode material for the all-solid-state battery of the present invention has a composition represented by the following formula (1-1).

[0017] Formula (1-1): Li2Co (1-x) P (2-y) M 1 x M 2 y O7 M in equation (1) above 1M is one or more metallic elements selected from titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), and nickel (Ni). 2 x is one or more nonmetallic and / or metallic elements selected from boron (B), aluminum (Al), gallium (Ga), carbon (C), silicon (Si), and germanium (Ge). In equation (1) above, x and y are numbers that satisfy 0 ≤ x < 1 and 0 ≤ y ≤ 0.07.

[0018] The positive electrode active material (1-1) used in the present invention may be a so-called LCPO, which is typical as a pyrophosphate-based positive electrode active material. That is, the positive electrode active material (1-1) typically has a composition represented by the following formula (1-2).

[0019] Formula (1-2): Li2CoP2O7

[0020] [Coating material] The coating material constituting the positive electrode material for the all-solid-state battery of the present invention has a composition represented by the following formula (2).

[0021] Formula (2): Li4P2O7

[0022] [Manufacturing method for cathode material] The method for manufacturing the cathode material of the present invention includes steps 1, 2, and 3 described below. [Process 1] Step 1 is a process of preparing an aqueous solution of the coating material raw materials by mixing a water-soluble lithium salt, a water-soluble phosphate, a complexing agent, and water.

[0023] The above water-soluble lithium salt is not particularly limited, but lithium carbonate (Li2CO3) is generally used due to its price and availability. The above water-soluble phosphate is specifically ammonium phosphate, specifically ammonium dihydrogen phosphate (NH4H2PO4) or diammonium hydrogen phosphate ((NH4)2HPO4). As the above complexing agent, any commonly used compound can be used without limitation, for example, carboxylic acids such as acetic acid and succinic acid, or hydroxycarboxylic acids such as lactic acid, citric acid, and malic acid.

[0024] The amounts of the above-mentioned water-soluble lithium salt and water-soluble phosphate used (amounts added) are adjusted in a ratio such that Li4P2O7 is produced during calcination in the subsequent step 3.

[0025] [Process 2] Step 2 is a step in which the aqueous solution obtained in Step 1 is brought into contact with the positive electrode active material to prepare a positive electrode material precursor. However, the positive electrode active material has a composition represented by the following formula (1-1).

[0026] Formula (1-1): Li2Co (1-x) P (2-y) M 1 x M 2 y O7 M in equation (1) above 1 M is one or more metallic elements selected from titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), and nickel (Ni). 2 x is one or more nonmetallic and / or metallic elements selected from boron (B), aluminum (Al), gallium (Ga), carbon (C), silicon (Si), and germanium (Ge). In equation (1) above, x and y are numbers that satisfy 0 ≤ x < 1 and 0 ≤ y ≤ 0.07.

[0027] The positive electrode active material used in step 2 may be a typical pyrophosphate-based positive electrode active material, such as a so-called LCPO. That is, the positive electrode active material used in step 2 may have a composition represented by formula (1-2):Li2CoP2O7.

[0028] Such positive electrode active materials are generally manufactured according to standard methods as pyrophosphate-based positive electrode active materials LCPO or pyrophosphate-based positive electrode active materials in which some of the cobalt (Co) elements are substituted. The positive electrode active material used in step 2 is usually in powder form. Generally, in step 2, the powdered positive electrode active material is first mixed with the aqueous solution obtained in step 1. At this time, the weight of the positive electrode active material powder and the weight of the coating material raw materials (the water-soluble lithium salt and the water-soluble phosphate) contained in the aqueous solution are set so that the amount of the coating material Li4P2O7 synthesized from the coating material raw materials relative to the positive electrode active material is in the range of more than 0.5% by weight and less than 15.0% by weight, preferably in the range of 0.7% by weight and 10% by weight or less. In this way, a dispersion containing the positive electrode active material powder and the aqueous solution is first obtained.

[0029] In step 2, the resulting dispersion is dried. The drying method is not particularly limited. Conventional methods such as vacuum drying, air drying at a temperature of approximately 50°C to 95°C, and natural drying at room temperature can be used without restriction. The drying equipment is also not particularly limited and can be those used in the ceramics, pottery, and battery fields.

[0030] Thus, a cathode material precursor is obtained in step 2.

[0031] [Process 3] Step 3 is a process of firing the cathode material precursor obtained in Step 2 to obtain a cathode material for an all-solid-state battery that includes a cathode active material and a coating material.

[0032] Generally, in step 3, the cathode material precursor obtained in the above step is first calcined at a temperature of 200°C to 300°C for several hours, preferably 3 to 10 hours. In this way, a calcined product of the cathode material precursor is obtained.

[0033] After the above calcination, the calcined material is subjected to final calcination. The final calcination temperature is generally 500°C to 700°C, preferably 550°C to 650°C. The final calcination time is generally several hours, preferably 1 to 3 hours. During the final calcination process, the composite oxide Li4P2O7 derived from the coating material raw materials is synthesized on the surface of the positive electrode active material particles. It is believed that the composition and crystal structure of the positive electrode active material are maintained during the final calcination process.

[0034] Thus, the main calcined product of the positive electrode material precursor is obtained. The main calcined product is crushed and / or pulverized as necessary to obtain the desired positive electrode material for an all-solid-state battery.

[0035] The above-mentioned positive electrode material for all-solid-state batteries comprises a positive electrode active material having a composition represented by formula (1-1) or formula (1-2) and a coating material having a composition represented by formula (2):Li4P2O7.

[0036] In the above-described positive electrode material for all-solid-state batteries, the coating material is present in a range of more than 0.5% by weight and less than 15.0% by weight relative to the positive electrode active material, preferably in a range of 0.7% by weight and more and 10% by weight or less. The presence of such a specific amount of coating material suppresses the increase in resistance during charging and discharging of the all-solid-state battery using the above-described positive electrode active material.

[0037] [All-solid battery] Hereinafter, a solid-state battery 1, which is an example of the all-solid-state battery of the present invention, will be described with reference to Figures 1, 3 to 7. Figure 1A is a schematic perspective view of the main part of the solid-state battery, Figure 1B is a schematic cross-sectional view along line 1B in Figure 1A, and Figure 1C is a schematic cross-sectional view along line 1C in Figure 1A. The solid-state battery 1 includes a solid-state battery body 10, a protective layer 20, an external electrode 31, and an external electrode 32.

[0038] (Solid-state battery unit 10) The solid-state battery body 10 has a positive electrode layer 11, a negative electrode layer 12, and a solid electrolyte layer 13 disposed between them. In this embodiment, multiple positive electrode layers 11, multiple negative electrode layers 12, and multiple solid electrolyte layers 13 are stacked such that a solid electrolyte layer 13 is interposed between a pair of positive electrode layers 11 and negative electrode layers 12. That is, the solid-state battery body 10 of this embodiment has a structure in which, from bottom to top, a negative electrode layer 12, a solid electrolyte layer 13, a positive electrode layer 11, a solid electrolyte layer 13, a negative electrode layer 12, a solid electrolyte layer 13, and a positive electrode layer 11 are stacked.

[0039] (Positive electrode layer 11) The positive electrode layer 11 is located on a portion of one surface 13a of the solid electrolyte layer 13. The positive electrode layer 11 contains a positive electrode material for an all-solid-state battery. The positive electrode layer 11 may further contain a solid electrolyte and a conductive additive as needed. Examples of the solid electrolyte in the positive electrode layer 11 include materials similar to those used in the solid electrolyte layer 13 described later, and preferably oxide solid electrolytes such as LAGP described later are used. Examples of conductive additives include carbon materials such as carbon fiber, carbon black, graphite, graphene, and carbon nanotubes.

[0040] The thickness of the positive electrode layer 11 is not particularly limited, but is, for example, 5 to 30 μm, preferably 10 to 20 μm. If the thickness of the positive electrode layer 11 is above the lower limit, the discharge capacity can be further increased, and if it is below the upper limit, the increase in resistance due to the diffusion of Li ions in the thickness direction of the positive electrode layer 11 can be further suppressed.

[0041] (Negative electrode layer 12) The negative electrode layer 12 is provided on a portion of the other surface 13b of the solid electrolyte layer 13. As shown in Figure 1B, the paired positive electrode layer 11 and negative electrode layer 12 are arranged to partially overlap each other via the solid electrolyte layer 13. The negative electrode layer 12 contains a negative electrode active material.

[0042] Various types of titanium oxide can be used as the negative electrode active material. The titanium oxide is not limited as long as it provides the necessary function as a negative electrode active material.

[0043] The negative electrode layer 12 may further contain other negative electrode active materials as long as the effects of the present invention are not impaired. Examples of other negative electrode active materials include LATP, LVP, niobium oxide (Nb2O5), metal silicides such as nickel (Ni), etc. The negative electrode layer 12 may further contain a solid electrolyte and a conductive additive as needed. The solid electrolyte and conductive additive used in the negative electrode layer 12 can be the same as those used in the positive electrode layer 11.

[0044] The thickness of the negative electrode layer 12 is not particularly limited, but for example, it is 5 to 30 μm, preferably 10 to 20 μm. When the thickness of the negative electrode layer 12 is at least the lower limit value, it is easier to further increase the discharge capacity. When the thickness of the negative electrode layer 12 is at most the upper limit value, an increase in resistance due to diffusion of Li ions in the thickness direction of the negative electrode layer 12 is further suppressed.

[0045] (Solid electrolyte layer 13) The solid electrolyte layer 13 contains a solid electrolyte. Examples of the solid electrolyte include an oxide solid electrolyte, a sulfide solid electrolyte, a nitride solid electrolyte, a halide solid electrolyte, etc., but an oxide solid electrolyte is preferred. As the oxide solid electrolyte, the general formula is Li 1+y Al y M 2-y (PO4)3, and a NASICON type (Na super ionic conductor type, also referred to as "NASICON type") oxide solid electrolyte is suitable. Here, the composition ratio y satisfies 0 < y ≤ 1, and M is one or both of germanium (Ge) and titanium (Ti). Among them, LAGP is used. LAGP is an oxide solid electrolyte represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 < x ≤ 1), and is also referred to as lithium germanium aluminum phosphate, etc. For example, as the LAGP of the solid electrolyte layer 13, Li 1.5 Al 0.5 Ge 1.5 (PO4)3 with a composition ratio x = 0.5 is preferably used. Also, as LAGP, it is not limited to the composition of Li 1.5 Al 0.5 Ge 1.5 (PO4)3, and NASICON type LAGP with other compositions such as Li 1.4 Al 0.4 Ge 1.6 (PO4)3 may also be used. LAGP may be amorphous LAGP, crystalline LAGP, or a combination thereof.

[0046] The thickness of the solid electrolyte layer 13 is not particularly limited, but is, for example, 2 to 10 μm, preferably 3 to 6 μm. If the thickness of the solid electrolyte layer 13 is above the lower limit, the insulating properties between the positive electrode layer 11 and the negative electrode layer 12 are more easily improved. If the thickness of the solid electrolyte layer 13 is below the upper limit, the increase in resistance due to the diffusion of Li ions in the thickness direction of the solid electrolyte layer 13 can be further suppressed.

[0047] During charging of the solid-state battery body 10, lithium ions are conducted from the positive electrode layer 11 through the solid electrolyte layer 13 to the negative electrode layer 12 and absorbed. During discharging of the solid-state battery body 10, lithium ions are conducted from the negative electrode layer 12 through the solid electrolyte layer 13 to the positive electrode layer 11 and absorbed. This lithium ion conduction enables the charging and discharging operation.

[0048] (Protective layer 20) The protective layer 20 covers the solid battery body 10 such that the end face 11a of the positive electrode layer 11 and the end face 12a of the negative electrode layer 12 of the solid battery body 10 are exposed (see Figure 1B). The side of the solid battery body 10 where the end face 11a of the positive electrode layer 11 is exposed from the protective layer 20 becomes the positive electrode lead surface 1a, and the side where the end face 12a of the negative electrode layer 12 is exposed from the protective layer 20 becomes the negative electrode lead surface 1b. In this way, by covering the periphery of the solid battery body 10 with the protective layer 20, the solid battery body 10 can be protected from external forces and the external environment.

[0049] The material of the protective layer 20 is not limited as long as it has insulating properties. A preferred protective layer 20 has low permeability to moisture and gases and good sealing properties. In particular, it is preferable that it has a coefficient of thermal expansion similar to that of each layer constituting the solid battery body 10, and that it has good adhesion to each layer. The material constituting the protective layer 20 is typically the solid electrolyte used in the solid electrolyte layer 13, or glass or ceramics.

[0050] (External electrodes 31 and 32) The external electrode 31 is provided on the positive electrode lead-out surface 1a of the solid-state battery 1 and is connected to the end face 11a of the positive electrode layer 11 that is exposed from the positive electrode lead-out surface 1a (see Figure 1B). The external electrode 32 is provided on the negative electrode lead-out surface 1b of the solid-state battery 1 and is connected to the end face 12a of the negative electrode layer 12 that is exposed from the negative electrode lead-out surface 1b (see Figure 1B).

[0051] Various conductive materials can be used for the external electrodes 31 and 32. For example, the external electrodes 31 and 32 can be made from a conductive paste containing metal particles such as silver (Ag) or conductive particles such as carbon particles, which has been dried and hardened, or from materials formed by depositing various metals using sputtering or plating methods.

[0052] [Manufacturing method for all-solid-state batteries] The solid-state battery of the present invention is typically manufactured by a step of obtaining a negative electrode paste (negative electrode mixture), a step of forming a laminate containing a negative electrode mixture layer, a positive electrode mixture layer, and an electrolyte mixture layer obtained from the negative electrode paste, and a step of firing the laminate. The manufacturing method of the solid-state battery 1 will be described below with reference to Figures 1, 3 to 7.

[0053] (Preparation of negative electrode paste) First, prepare the negative electrode paste. The negative electrode paste contains a negative electrode active material and may further contain a solid electrolyte, conductive additive, binder, dispersant, plasticizer, diluent, etc., as needed. For example, the negative electrode paste contains commercially available titanium oxide particles as the negative electrode active material, an oxide solid electrolyte (preferably LAGP) as the solid electrolyte, a conductive additive, a binder, a dispersant, and a diluent (organic solvent).

[0054] (Preparing the positive electrode paste) The positive electrode paste comprises the positive electrode material for the all-solid-state battery of the present invention and may further contain, as necessary, a solid electrolyte, a conductive additive, a binder, a dispersant, a plasticizer, a diluent, etc. For example, the positive electrode paste may contain a positive electrode active material such as LCPO, an oxide solid electrolyte such as LAGP, a conductive additive such as carbon nanofiber, a binder, and a diluent.

[0055] (Electrolyte paste) The electrolyte paste contains a solid electrolyte and, if necessary, further contains a solid electrolyte, conductive additive, binder, dispersant, plasticizer, diluent, etc. For example, the electrolyte paste may contain a solid electrolyte such as LAGP and a diluent.

[0056] (Protective paste) As a protective paste, an electrolyte paste may be used, or a paste containing glass components or ceramic components such as Al2O3 may be used.

[0057] (Manufacturing of laminates) In the manufacture of the all-solid-state battery 1, a laminate 44 is typically formed using the various pastes described above, and includes a positive electrode mixture layer 41, a negative electrode mixture layer 42, an electrolyte mixture layer 43, a protective material layer 21, and a protective sheet 22. In this case, positive electrode mixture layer parts and negative electrode mixture layer parts are manufactured and laminated to form the laminate 44.

[0058] (Fabrication of positive electrode composite layer parts) Figures 3A to 3E are schematic diagrams showing an example of the manufacturing process for a positive electrode mixture layer part. Figures 4A to 4C are schematic diagrams showing an example of a manufactured positive electrode mixture layer part. Of these, Figure 4A is a schematic perspective view of the positive electrode mixture layer part, Figure 4B is a schematic cross-sectional view along line 4B in Figure 4A, and Figure 4C is a schematic cross-sectional view along line 4C in Figure 4A.

[0059] First, a positive electrode paste is applied to a portion of the support 40, for example by screen printing, and then dried to form a positive electrode mixture layer 41 (Figures 3A and 3B). Next, a protective paste is applied around the positive electrode mixture layer 41 formed on a portion of the support 40, for example by screen printing, and then dried to form a protective material layer 21 (embedded layer) (see Figure 3C).

[0060] The coating of the positive electrode paste and the surrounding protective paste may be performed alternately multiple times to adjust the thickness of the positive electrode mixture layer 41 and the amount of active material. In this case, the drying of the positive electrode paste and protective paste may be performed each time after coating, or it may be performed all at once after multiple coatings of the positive electrode paste and protective paste.

[0061] Next, an electrolyte paste is applied to the positive electrode mixture layer 41 and a portion of the protective material layer 21 formed around it, for example by screen printing, and dried to form an electrolyte mixture layer 43 (see Figure 3D). After the formation of the electrolyte mixture layer 43, a protective paste is applied to the portion of the protective material layer 21 not covered by the electrolyte mixture layer 43, for example by screen printing, and dried to form a protective material layer 21 (embedded layer) (see Figure 3E). This yields the positive electrode mixture layer part (see Figure 4A).

[0062] The application of the electrolyte paste and the protective paste on its outer surface may be repeated alternately multiple times to adjust the thickness of the electrolyte mixture layer 43, etc. In this case, the drying of the electrolyte paste and protective paste may be performed each time after application, or it may be performed all at once after multiple applications of the electrolyte paste and protective paste.

[0063] Furthermore, a part obtained by peeling the support 40 off a positive electrode mixture layer part, as shown in Figures 4A to 4C, can also be used as a positive electrode mixture layer part. In addition, a part as shown in Figure 3C, before the formation of the electrolyte mixture layer 43, or a part obtained by peeling the support 40 off said part, can also be used as a positive electrode mixture layer part.

[0064] Furthermore, although an example was shown in which the positive electrode mixture layer 41 and the surrounding protective material layer 21 are formed on the support 40, followed by the formation of the electrolyte mixture layer 43 and the outer protective material layer 21, this order can also be reversed. That is, the electrolyte mixture layer 43 and the outer protective material layer 21 may be formed on the support 40 first, followed by the formation of the positive electrode mixture layer 41 and the surrounding protective material layer 21.

[0065] Furthermore, each layer may be applied directly onto the support 40, or it may be applied onto another release film (e.g., PET film) and then transferred onto the support 40 to form the layer.

[0066] (Fabrication of negative electrode composite layer parts) Figures 5A to 5C are schematic diagrams showing examples of fabricated negative electrode mixture layer parts. Of these, Figure 5A is a schematic perspective view of the negative electrode mixture layer part, Figure 5B is a schematic cross-sectional view along line 5B in Figure 5A, and Figure 5C is a schematic cross-sectional view along line 5C in Figure 5A.

[0067] The negative electrode mixture layer part can be manufactured in the same manner as the positive electrode mixture layer part. This allows for the production of a negative electrode mixture layer part in which the support 40, the negative electrode mixture layer 42 and its surrounding protective material layer 21, and the electrolyte mixture layer 43 and its outer protective material layer 21 are laminated in this order (Figures 5A to 5C).

[0068] (Formation of a laminate) Figures 6A to 6C and 7A to 7C are schematic diagrams showing an example of the process for manufacturing the solid-state battery body 10.

[0069] The positive electrode mixture layer part and the negative electrode mixture layer part prepared as described above are laminated. For example, on the negative electrode mixture layer part with the support 40 attached shown in Figure 5B, the support 40 removed from the positive electrode mixture layer part shown in Figure 4B is laminated, on top of that, the support 40 removed from the negative electrode mixture layer part shown in Figure 5B is laminated, and on top of that, the support 40 removed from the positive electrode mixture layer part shown in Figure 3C is laminated (see Figure 6A). Then, the support 40 is removed from the resulting laminate, protective sheets 22 are laminated on the lower and upper sides, and these are heat-pressed together under predetermined pressure and temperature conditions to form a laminate 44 (see Figure 6B).

[0070] The positive electrode mixture layer and the negative electrode mixture layer are laminated such that the opposing negative electrode mixture layer 42 and positive electrode mixture layer 41 partially overlap via the electrolyte mixture layer 43. The number of layers can be set according to the required performance (capacity, etc.).

[0071] This forms a laminate 44 including a positive electrode mixture layer 41, a negative electrode mixture layer 42, an electrolyte mixture layer 43 interposed between them, a protective material layer 21, and a protective sheet 22 (see Figure 6B).

[0072] (The process of firing the laminated structure) Next, the resulting laminate 44 is cut at predetermined positions C1 and C2 as needed (see Figure 6B). Then, the resulting laminate 44 is fired at a predetermined temperature (see Figures 7A and 7B).

[0073] (Degreasing and firing) The laminate 44 is heat-treated under predetermined conditions of atmosphere, temperature, and time. The heat treatment can be carried out, for example, in a heat treatment furnace 45. Specifically, the heat treatment mainly involves degreasing to burn off organic components such as binders, and firing to sinter solid electrolytes and protective materials.

[0074] The heat treatment for degreasing can be carried out, for example, by holding the material at 300-600°C for 5-30 hours, preferably at 500°C for 10 hours, in an atmosphere containing oxygen. The heat treatment for firing can be carried out, for example, by holding the material at 400-650°C for 1-10 hours, preferably at 600°C for 2 hours, in an atmosphere containing nitrogen or oxygen.

[0075] Through heat treatment for firing, the solid electrolyte in the electrolyte mixture layer 43, the positive electrode mixture layer 41, and the negative electrode mixture layer 42 contained in the laminate 44 are sintered. In addition, the protective material layer 21 and protective sheet 22 contained in the laminate 44 are sintered through the heat treatment for firing, and they are integrated with each other. As a result, a sintered laminate 44 having a positive electrode layer 11, a negative electrode layer 12, a solid electrolyte layer 13, and a protective layer 20 is formed (see Figure 7B).

[0076] The cross-section of the sintered laminate 44 at position C1 becomes the positive electrode extraction surface 1a, and the end face 11a of the positive electrode layer 11 exposed from the positive electrode extraction surface 1a is connected to the external electrode 31. The cross-section of the sintered laminate 44 at position C2 becomes the negative electrode extraction surface 1b, and the end face 12a of the negative electrode layer 12 exposed from the negative electrode extraction surface 1b is connected to the external electrode 32. This allows the solid-state battery body 10 to be obtained (see Figure 7B).

[0077] (Formation of external electrodes) An external electrode 31 is formed on the positive electrode extraction surface 1a of the sintered laminate 44, and an external electrode 32 is formed on the negative electrode extraction surface 1b. The external electrodes 31 and 32 are formed, for example, by coating, drying, and curing a conductive paste, or by depositing metal using methods such as sputtering or plating. This yields a solid-state battery 1 (see Figure 7C). [Examples]

[0078] [Manufacturing of cathode materials] Two positive electrode materials of the present invention (Examples 1 and 2) and three comparative positive electrode materials (Comparative Examples 1, 2, and 3) were manufactured by performing the following steps 1, 2, and 3.

[0079] (Process 1) Aqueous solutions of the film material raw materials were prepared by mixing lithium carbonate (Li2CO3) as a water-soluble lithium salt, diammonium hydrogen phosphate ((NH4)2HPO4) as a water-soluble phosphate, citric acid ((HOOCCH2)2C(OH)COOH) as a complexing agent, and water in the amounts shown in Table 1.

[0080] [Table 1]

[0081] (Process 2) The entire volume of the aqueous solution obtained in step 1 was mixed with the weight of the positive electrode active material (composition: Li2CoP2O7) shown in Table 1 to prepare a dispersion. The resulting dispersion was air-dried in a constant temperature bath at 85°C to obtain a positive electrode material precursor.

[0082] (Step 3) The cathode material precursor obtained in step 2 was calcined at 250°C for 7 hours. The resulting calcined material was crushed in an agate mortar. Next, the calcined powder was transferred to a crucible and fully calcined at 600°C in an air atmosphere for 2 hours. The fully calcined material was cooled and crushed in an agate mortar. In this way, a powdered cathode material was obtained. Table 1 shows the ratio of the coating material to the cathode active material in the cathode material.

[0083] [Manufacturing of all-solid-state batteries] (Preparation of positive electrode paste) Using two positive electrode materials of the present invention (Examples 1 and 2) and three comparative positive electrode materials (Comparative Examples 1, 2, and 3), a positive electrode paste was prepared in which the positive electrode active material, solid electrolyte, and conductive additive were contained in a mass ratio of positive electrode active material:solid electrolyte:conductive additive = 40:60:9 by following the procedure below.

[0084] 11.8% by mass of the positive electrode material obtained in Example 1, and amorphous Li as the solid electrolyte. 1.5 Al 0.5 Ge 1.5 17.7% by mass of (PO4)3 powder (amorphous LAGP powder), 2.7% by mass of vapor-phase carbon nanofiber powder (VGCF) as a conductive additive, 7.9% by mass of polyvinyl butyral (PVB) as a binder, 0.3% by mass of a commercially available plasticizer, 0.6% by mass of a commercially available dispersant, and 59.0% by mass of terpineol as a diluent were mixed in a ball mill for 72 hours. After this, the mixture was mixed and dispersed in a three-roll mill until the material aggregate size measured with a particle gauge was 1 μm or less to obtain a cathode paste. Cathode pastes were obtained for the other cathode materials (Example 2 and Comparative Examples 1, 2, and 3) using the same procedure.

[0085] (Preparation of electrolyte paste) An electrolyte paste containing amorphous LAGP and crystalline LAGP as a solid electrolyte in a mass ratio of amorphous LAGP:crystalline LAGP = 90:10 was prepared using the following procedure.

[0086] Amorphous LAGP powder (29.0% by mass), crystalline LAGP powder (3.0% by mass), PVB binder (6.5% by mass), commercially available plasticizer (2.0% by mass) used in the preparation of the cathode paste, commercially available dispersant (0.3% by mass) used in the preparation of the cathode paste, commercially available diluent (16.0% by mass), and ethanol (43.2% by mass) were mixed in a ball mill for 48 hours. After this, the mixture was mixed and dispersed in a three-roll mill until the material aggregate size, measured with a particle gauge, was 1 μm or less, to obtain an electrolyte paste.

[0087] (Preparation of negative electrode paste) A negative electrode paste containing a negative electrode active material, solid electrolyte, and conductive additive in a mass ratio of negative electrode active material:solid electrolyte:conductive additive = 30:60:9 was prepared using the following procedure.

[0088] 8.85% by mass of commercially available anatase-type titanium dioxide as the negative electrode active material, 20.65% by mass of amorphous LAGP powder as the solid electrolyte, 2.7% by mass of conductive additive VGCF, 7.9% by mass of binder PVB, 0.3% by mass of commercially available plasticizer used in the preparation of the positive electrode paste, 0.6% by mass of commercially available dispersant used in the preparation of the positive electrode paste, and 59.0% by mass of diluent terpineol were mixed in a ball mill for 72 hours. After this, the mixture was mixed and dispersed in a three-roll mill until the material aggregate size, measured with a particle gauge, was 1 μm or less, to obtain the negative electrode paste.

[0089] (Fabrication of positive electrode composite layer parts) The electrolyte paste was pattern-printed onto a PET film using screen printing and dried at 90°C for 5 minutes. The positive electrode paste was then pattern-printed on top of it using screen printing and dried at 90°C for 5 minutes. Next, the electrolyte paste (embedded paste) was printed around the pattern-printed positive electrode paste using screen printing and dried at 90°C for 5 minutes. These operations were repeated until a predetermined thickness was achieved. In this way, a positive electrode mixture layer part having a laminated structure of PET film / electrolyte mixture layer / positive electrode mixture layer and surrounding electrolyte mixture layer was obtained.

[0090] (Fabrication of negative electrode composite layer parts) The negative electrode mixture layer part was fabricated in the same manner as the positive electrode mixture layer part, except that the negative electrode paste was used instead of the positive electrode paste. In this way, a negative electrode mixture layer part having a laminated structure of PET film / electrolyte mixture layer / negative electrode mixture layer and the surrounding electrolyte mixture layer was obtained.

[0091] (Manufacturing of the upper and lower covers) The electrolyte paste was printed onto a PET film in a solid layer (full-surface printing) and then dried. An upper cover having a laminated structure of PET film / electrolyte mixture layer and a lower cover having a laminated structure of PET film / electrolyte mixture layer were obtained.

[0092] (Fabrication of laminates) A laminate was obtained by following the steps in (1), (2), and (3). (Step 1) The positive electrode mixture layer part prepared above was laminated onto the electrolyte mixture layer of the lower cover prepared in the above procedure, so that the positive electrode mixture layer was in contact with the electrolyte mixture layer of the lower cover, and then heat-pressed to transfer the positive electrode mixture layer / electrolyte mixture layer. (Step 2) Next, the negative electrode mixture layer part was laminated onto the transferred electrolyte mixture layer, so that the negative electrode mixture layer was in contact with the electrolyte mixture layer, and then heat-pressed to transfer the negative electrode mixture layer / electrolyte mixture layer. (Step 3) The transfer of the positive electrode mixture layer part in (1) and the transfer of the negative electrode mixture layer part in (2) were repeated until a predetermined number of layers (10 layers) were reached. The heat-pressure bonding conditions were 20 MPa and 70°C in all cases. In this way, a laminate having the laminated structure shown in Figures 1B and 1C was obtained.

[0093] (Degreasing and firing) After cutting the laminate to a planar dimension of 4.5 mm x 3.2 mm, it was sandwiched between two porous ceramic plates and heated at 500°C for 1 hour in an air atmosphere to degrease the binder components. Subsequently, it was heated at 600°C for 2 hours in a nitrogen atmosphere. In this way, a fired laminate with the desired total thickness was obtained.

[0094] (Formation of external electrodes) External electrodes were formed to cover the extracted portion of the resulting laminated firing. The external electrodes were formed by coating a silver-containing main material, followed by nickel plating and tin plating on their surface. In this way, the all-solid-state battery schematically shown in Figure 1 was completed.

[0095] [Cycle test at 105°C] The obtained all-solid-state batteries were placed in a constant-temperature chamber maintained at 105°C and subjected to cycle testing. Charging and discharging were repeated at voltages from 0V to 3.3V. Each charge-discharge cycle was counted as one cycle, and the DC resistance of the all-solid-state battery at the start of discharge was calculated for each of the 10 cycles. The results are shown in Table 2. The graph in Figure 8 shows the change in resistance values ​​listed in Table 2.

[0096] [Table 2]

[0097] [evaluation] In Example 1, a positive electrode material was used in which the coating material was present at 1% by weight relative to the positive electrode active material. In Example 2, a positive electrode material was used in which the coating material was present at 7% by weight relative to the positive electrode active material. In solid-state batteries using the positive electrode materials of Examples 1 and 2, the DC resistance of the battery increased only slightly even after 10 charge-discharge cycles at 105°C.

[0098] In contrast, Comparative Examples 1, 2, and 3 used positive electrode materials in which the coating material was present in an amount of 0.1% by weight, 0.5% by weight, and 15% by weight relative to the positive electrode active material. In the solid-state batteries using the positive electrode materials of Comparative Examples 1, 2, and 3, the DC resistance of the battery increased significantly after 10 charge-discharge cycles at 105°C.

[0099] From the results of the examples and comparative examples, it is understood that the positive electrode material of the present invention, in which the coating material is present in a limited range of more than 0.5% by weight and less than 15.0% by weight relative to the positive electrode active material, suppresses the increase in battery resistance when charged and discharged at a high temperature of 105°C.

[0100] Prior art, including Patent Document 5 mentioned above, does not mention the increase in interfacial resistance in high-temperature environments. In particular, Patent Document 5 does not mention the amount ratio of the coating layer (corresponding to the coating material of the present invention) in the positive electrode active material, nor does it describe the relationship between the coating layer formed on the positive electrode active material and the interfacial resistance at high temperatures. The effect of the positive electrode material of the present invention and the all-solid-state battery using it in suppressing the increase in battery resistance at high temperatures is a surprising improvement that was neither considered nor expected in the prior art. [Industrial applicability]

[0101] This invention provides a cathode material useful for extending the lifespan of all-solid-state batteries at high temperatures. This invention contributes to improving the performance of all-solid-state batteries. This invention makes it possible to provide more practical all-solid-state batteries to the market. [Explanation of symbols]

[0102] 1 solid state battery 1a Positive electrode extraction surface 1b Negative electrode extraction surface 10 Solid-state battery unit 11 Positive electrode layer 12 Negative electrode layer 13 Solid electrolyte layer 11a,12a end face 13a One side 13b The other side 20 protective layer 21 Protective material layer 22 protective sheets 31,32 External electrode 40 Support 41. Cathode mixture layer 42 Negative electrode mixture layer 43 Electrolyte mixture layer 44-layer structure 45 Heat treatment furnace 100 Cathode materials for all-solid-state batteries 200 Cathode active material 300 Coating material

Claims

1. It comprises a positive electrode active material and a coating material, The above positive electrode active material has a composition represented by the following formula (1-1), Li ２ Co （１－ｘ） P （２－ｙ） M １ ｘ M ２ ｙ O ７ ・・・(1-1) (In formula (1), M １ is one or more metal elements selected from titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), and nickel (Ni), M ２ This is one or more nonmetallic elements and / or metallic elements selected from boron (B), aluminum (Al), gallium (Ga), carbon (C), silicon (Si), and germanium (Ge). x and y are numbers that satisfy 0 ≤ x < 1 and 0 ≤ y ≤ 0.

07. The above coating material is formula (2): Li ４ P ２ O ７ Having a composition represented by, The above coating material is present in an amount greater than 0.5% by weight and less than 15.0% by weight relative to the above positive electrode active material. Cathode material for all-solid-state batteries.

2. The above positive electrode active material is given by formula (1-2): Li ２ CoP ２ O ７ The positive electrode material according to claim 1, having a composition represented by .

3. The positive electrode material according to claim 1, wherein the coating material is present in an amount of 0.7% by weight or more and 10% by weight or less relative to the positive electrode active material.

4. A solid-state battery comprising a positive electrode layer containing the positive electrode material described in claim 1.

5. The following steps 1, 2, and 3 are included: Step 1: A step in which a water-soluble lithium salt, a water-soluble phosphate, a complexing agent, and water are mixed to prepare an aqueous solution of the raw materials for the coating material. Step 2: A step in which the aqueous solution obtained in Step 1 is brought into contact with the positive electrode active material to prepare the positive electrode material precursor. Step 3: A step in which the cathode material precursor obtained in Step 2 is calcined to obtain a cathode material for an all-solid-state battery that includes a cathode active material and a coating material. The above positive electrode active material has a composition represented by the following formula (1-1), Li ２ Co （１－ｘ） P （２－ｙ） M １ ｘ M ２ ｙ O ７ ・・・(1-1) (In formula (1), M １ This is one or more metallic elements selected from titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), and nickel (Ni). M ２ This is one or more nonmetallic elements and / or metallic elements selected from boron (B), aluminum (Al), gallium (Ga), carbon (C), silicon (Si), and germanium (Ge). x and y are numbers that satisfy 0 ≤ x < 1 and 0 ≤ y ≤ 0.

07. The above coating material is formula (2): Li ４ P ２ O ７ Having a composition represented by, In the above positive electrode material, the coating material is present in an amount greater than 0.5% by weight and less than 15.0% by weight relative to the positive electrode active material. A method for manufacturing positive electrode material for all-solid-state batteries.

6. The above positive electrode active material is given by formula (1-2): Li ２ CoP ２ O ７ The manufacturing method according to claim 5, having a composition represented by [the specified composition].

7. The manufacturing method according to claim 5, wherein the positive electrode material is obtained in which the coating material is present in a range of 0.7% by weight or more and 10% by weight or less relative to the positive electrode active material.

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