Cathode Materials and Batteries

Abstract

This positive electrode material 1000 comprises a mixture of a positive electrode active material 110, a solid electrolyte 100 and a conductive material 140. The conductive material 140 contains a first conducive material 150 that has an average major axis diameter of 1 µm or more and a second conductive material 160 that has an average particle diameter of 100 nm or less. The ratio of the volume of the positive electrode active material 110 to the total volume of the positive electrode active material 110 and the solid electrolyte 100 is 60% to 90%.

Description

[Technical Field]

[0001] The present disclosure relates to positive electrode materials and batteries. [Background technology]

[0002] Patent Document 1 discloses a solid-state battery having a positive electrode containing an active material, a fibrous conductive material, a granular conductive material, and a solid electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 130069 Summary of the Invention

[0004] In the prior art, it is desirable to achieve both energy density and electronic conductivity in the positive electrode.

[0005] In one embodiment of the present disclosure, the positive electrode material is a mixture of a positive electrode active material, a solid electrolyte, and a conductive material; the conductive material includes a first conductive material having an average major axis diameter of 1 μm or more and a second conductive material having an average particle size of 100 nm or less; The ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte is 60% or more and 90% or less.

[0006] According to the present disclosure, it is possible to achieve both energy density and electronic conductivity in the positive electrode. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a positive electrode material in Modification 1. As shown in FIG. [Figure 3]FIG. 3 is a cross-sectional view showing a schematic configuration of a battery according to the second embodiment. [Figure 4] FIG. 4 is a diagram illustrating a method for evaluating the electronic conductivity of the positive electrode. [Figure 5] FIG. 5 is a graph showing the correlation between the voltage and the current value in the counter positive electrode of Example 1. [Figure 6] FIG. 6 is a graph showing the electronic conductivities of the positive electrodes of Examples 1 to 9 and Comparative Examples 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0008] (Findings that formed the basis of this disclosure) Patent Document 1 discloses a solid-state battery having a positive electrode containing an active material, a fibrous conductive material, a granular conductive material, and a solid electrolyte. Patent Document 1 describes that the amount of active material in the positive electrode material is approximately 60 parts by mass per 100 parts by mass of the total amount of the active material, the fibrous conductive material, the granular conductive material, and the solid electrolyte. That is, in the positive electrode material of Patent Document 1, the volume ratio of the active material to the total volume of the active material, the fibrous conductive material, the granular conductive material, and the solid electrolyte is approximately 43%. Thus, in the positive electrode material of Patent Document 1, the volume ratio of the solid electrolyte having electronic insulation is greater than the volume ratio of the active material. Therefore, when the positive electrode material of Patent Document 1 is used, it is difficult to ensure sufficient electronic conductivity in the positive electrode. On the other hand, if the ratio of the conductive material is increased to ensure electronic conductivity, the ratio of the active material decreases, resulting in a decrease in the energy density of the positive electrode.

[0009] The present inventors have conducted extensive research into methods for reducing the resistance of all-solid-state lithium-ion batteries. As a result, they have discovered that improving the electronic conductivity of the positive electrode reduces the battery resistance. This is presumably due to the influence of the resistance between the positive electrode and the current collector. The present inventors have further discovered that excessively increasing the proportion of conductive material to improve electronic conductivity not only reduces the battery's energy density, but also inhibits lithium ion conduction between the positive electrode active material and the solid electrolyte. Inhibition of lithium ion conduction increases the reaction resistance of the positive electrode active material. Based on these findings, the present inventors have discovered a positive electrode material that can achieve both high energy density and high electronic conductivity in the positive electrode.

[0010] (Summary of one aspect of the present disclosure) The positive electrode material according to the first aspect of the present disclosure is a mixture of a positive electrode active material, a solid electrolyte, and a conductive material; the conductive material includes a first conductive material having an average major axis diameter of 1 μm or more and a second conductive material having an average particle size of 100 nm or less; The ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte is 60% or more and 90% or less.

[0011] According to the above configuration, the volume ratio of the positive electrode active material is greater than the volume ratio of the solid electrolyte, thereby improving the energy density of the positive electrode. Furthermore, since the first conductive material has an average major axis diameter of 1 μm or more, the first conductive material and the second conductive material are easily connected in the positive electrode. Therefore, an electron conduction network can be efficiently formed in the positive electrode. This allows both energy density and electron conductivity to be achieved in the positive electrode.

[0012] In the second aspect of the present disclosure, for example, in the positive electrode material according to the first aspect, the ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte may be 65% or more and 85% or less. This configuration can further improve the energy density of the positive electrode.

[0013] In a third aspect of the present disclosure, for example, in the positive electrode material according to the first aspect, the ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte may be 67% or more and 75% or less. This configuration can further improve the energy density of the positive electrode.

[0014] In a fourth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to third aspects, when the mass ratio of the positive electrode active material is taken as 100, the mass ratio of the conductive material may be 3 or less. With this configuration, it is possible to prevent the conductive material from interfering with lithium ion conduction between the positive electrode active material and the solid electrolyte.

[0015] In a fifth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to fourth aspects, the ratio of the mass of the second conductive material to the mass of the conductive material may be 80% or less. This configuration can further improve the electronic conductivity of the positive electrode.

[0016] In a sixth aspect of the present disclosure, for example, in the positive electrode material according to the fifth aspect, the ratio of the mass of the second conductive material to the mass of the conductive material may be 5% or more and 50% or less. This configuration can further improve the electronic conductivity of the positive electrode.

[0017] In a seventh aspect of the present disclosure, for example, in the positive electrode material according to the fifth aspect, the ratio of the mass of the second conductive material to the mass of the conductive material may be 6% or more and 25% or less. This configuration can further improve the electronic conductivity of the positive electrode.

[0018] In an eighth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to seventh aspects, the first conductive material may have an average major axis diameter of 4 μm or more. This configuration makes it easier for the first conductive material to form a conductive path that enables long-distance electron conduction in the positive electrode. This can further improve the electron conductivity in the positive electrode.

[0019] In a ninth aspect of the present disclosure, for example, in the positive electrode material according to the eighth aspect, the second conductive material may have an average particle size of 25 nm or less. This configuration allows the second conductive material to adhere more easily to the surface of the positive electrode active material. Therefore, the first conductive material and the second conductive material are connected to each other, which facilitates the formation of an electron conduction network in the positive electrode.

[0020] In a tenth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to ninth aspects, the first conductive material and the second conductive material may contain a carbon material. This configuration can further improve the electronic conductivity of the positive electrode.

[0021] In an eleventh aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to tenth aspects, the first conductive material may include a fibrous carbon material. This configuration can further improve the electronic conductivity of the positive electrode.

[0022] In a twelfth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to eleventh aspects, the second conductive material may contain carbon black. This configuration can further improve the electronic conductivity of the positive electrode.

[0023] In a thirteenth aspect of the present disclosure, for example, in the positive electrode material according to the twelfth aspect, the carbon black may contain acetylene black. This configuration can further improve the electronic conductivity of the positive electrode.

[0024] In a fourteenth aspect of the present disclosure, for example, in the cathode material according to any one of the first to thirteenth aspects, the solid electrolyte may include at least one selected from the group consisting of a sulfide solid electrolyte and a halide solid electrolyte. This configuration can improve the output characteristics of the battery.

[0025] In a fifteenth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to fourteenth aspects, the positive electrode active material may have a layered rock salt structure. In the layered rock salt structure, transition metals and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Therefore, with the above configuration, the energy density of the battery can be improved.

[0026] In a sixteenth aspect of the present disclosure, for example, the cathode material according to any one of the first to fifteenth aspects may further include a coating layer that covers at least a portion of the surface of the cathode active material. This configuration can further reduce the resistance of the battery.

[0027] A battery according to a seventeenth aspect of the present disclosure comprises: a positive electrode comprising the positive electrode material according to any one of the first to sixteenth aspects; a negative electrode; an electrolyte layer provided between the positive electrode and the negative electrode; Equipped with.

[0028] According to the above configuration, it is possible to achieve both energy density and electronic conductivity in the positive electrode, thereby improving the energy density of the battery and reducing the resistance of the battery.

[0029] In an eighteenth aspect of the present disclosure, for example, in the battery according to the seventeenth aspect, the electrolyte layer may contain a sulfide solid electrolyte. With this configuration, the output characteristics of the battery can be improved.

[0030] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0031] (Embodiment 1) [Cathode material] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 1000 according to the first embodiment.

[0032] The positive electrode material 1000 includes a mixture of a positive electrode active material 110, a solid electrolyte 100, and a conductive material 140. The conductive material 140 includes a first conductive material 150 having an average major axis diameter of 1 μm or more and a second conductive material 160 having an average particle size of 100 nm or less. The ratio of the volume of the positive electrode active material 110 to the total volume of the positive electrode active material 110 and the solid electrolyte 100 is 60% or more and 90% or less.

[0033] According to the above configuration, the volume content of the positive electrode active material 110 is greater than the volume content of the solid electrolyte 100, thereby improving the energy density of the positive electrode. Furthermore, since the first conductive material 150 has an average major axis diameter of 1 μm or more, the first conductive material 150 and the second conductive material 160 are easily connected in the positive electrode. This allows an electron conduction network to be efficiently formed in the positive electrode. This allows both energy density and electron conductivity to be achieved in the positive electrode.

[0034] The average major axis diameter of the first conductive material 150 can be measured, for example, using an SEM image taken with a scanning electron microscope. Specifically, the average major axis diameter is determined by using the SEM image to calculate the average value of the major axis diameters of 20 arbitrarily selected particles of the first conductive material 150. Here, the major axis diameter of the first conductive material 150 is defined as the diameter of the smallest circle that surrounds the particles of the first conductive material 150 in the SEM image of the particles of the first conductive material 150.

[0035] The average particle size of the second conductive material 160 can be measured, for example, using a TEM image obtained by a transmission electron microscope (TEM). Specifically, the average particle size can be determined by using the TEM image to calculate the average value of the equivalent circle diameter of 20 arbitrarily selected particles of the second conductive material 160.

[0036] Here, the average major axis of the first conductive material and the average particle size of the second conductive material contained in the positive electrode material can be measured, for example, as follows. First, the positive electrode material is obtained from a battery by scraping off the positive electrode material, for example, without mixing in the negative electrode material. The obtained positive electrode material is mixed with water to dissolve the solid electrolyte, and then filtered to extract the active material, binder, and conductive material other than the solid electrolyte. Next, the extracted active material, binder, and conductive material are mixed with an organic solvent such as toluene to dissolve the binder, and then filtered to extract the active material and conductive material. Furthermore, the extracted active material and conductive material are mixed with an acid aqueous solution to dissolve the active material, and then filtered to extract the conductive material. The extracted conductive material is then dried. Using the dried conductive material, the average major axis of the first conductive material can be measured based on SEM images, as described above, and the average particle size of the second conductive material can be measured based on TEM images.

[0037] The ratio of the volume of the positive electrode active material 110 to the total volume of the positive electrode active material 110 and the solid electrolyte 100 can be calculated, for example, by the following method. The positive electrode active material 110 contained in the positive electrode material 1000 can be extracted, for example, by dissolving only the solid electrolyte 100 using a solvent. The total mass of the positive electrode active material 110 and the solid electrolyte 100 and the mass of the positive electrode active material 110 can be obtained from the masses before and after the dissolution. The specific gravities of the positive electrode active material 110 and the solid electrolyte 100 can be found from literature, etc. From these values, the ratio of the volume of the positive electrode active material 110 to the total volume of the positive electrode active material 110 and the solid electrolyte 100 can be calculated.

[0038] The ratio of the volume of the positive electrode active material 110 to the total volume of the positive electrode active material 110 and the solid electrolyte 100 may be 65% or more and 85% or less. According to the above configuration, the energy density of the positive electrode can be further improved.

[0039] The ratio of the volume of the positive electrode active material 110 to the total volume of the positive electrode active material 110 and the solid electrolyte 100 may be 67% or more and 75% or less. With the above configuration, the energy density of the positive electrode can be further improved.

[0040] When the mass ratio of the positive electrode active material 110 is taken as 100, the mass ratio of the conductive material 140 may be equal to or less than 3. With the above configuration, it is possible to prevent the conductive material 140 from interfering with lithium ion conduction between the positive electrode active material 110 and the solid electrolyte 100.

[0041] The mass ratio of the conductive material 140 when the mass ratio of the positive electrode active material 110 is taken as 100 can be calculated, for example, by the following method. The mass of the positive electrode active material 110 contained in the positive electrode material 1000 can be obtained by the method described above. The mass of the conductive material 140 contained in the positive electrode material 1000 can be obtained, for example, from the mass reduction due to high-temperature pyrolysis. From these values, the mass ratio of the conductive material 140 when the mass ratio of the positive electrode active material 110 is taken as 100 can be calculated.

[0042] The ratio of the mass of the second conductive material 160 to the mass of the conductive material 140 may be 80% or less. According to the above configuration, the electron conductivity in the positive electrode can be further improved.

[0043] The ratio of the mass of the second conductive material 160 to the mass of the conductive material 140 can be calculated, for example, by the following method. The conductive material 140 extracted by the above-mentioned method can be subjected to particle size distribution measurement or classification to obtain the mass of the second conductive material 160 to the mass of the conductive material 140. In this way, the ratio of the mass of the second conductive material 160 to the mass of the conductive material 140 can be calculated.

[0044] The ratio of the mass of the second conductive material 160 to the mass of the conductive material 140 may be 5% or more and 50% or less. With the above configuration, the electron conductivity in the positive electrode can be further improved.

[0045] The ratio of the mass of the second conductive material 160 to the mass of the conductive material 140 may be 6% or more and 25% or less. With the above configuration, the electron conductivity in the positive electrode can be further improved.

[0046] (Conductive materials) The first conductive material 150 and the second conductive material 160 may contain a carbon material. According to the above configuration, the electron conductivity in the positive electrode can be further improved.

[0047] Carbon materials may be used as the first conductive material 150 and the second conductive material 160. According to the above configuration, the electron conductivity in the positive electrode can be further improved.

[0048] The first conductive material 150 may contain a fibrous carbon material. According to the above configuration, the electron conductivity of the positive electrode can be further improved.

[0049] The first conductive material 150 may be a fibrous carbon material. According to the above configuration, the electron conductivity of the positive electrode can be further improved.

[0050] Examples of fibrous carbon materials include fibrous carbon such as vapor-grown carbon fiber, carbon nanotubes, and carbon nanofibers. When the first conductive material 150 includes a fibrous carbon material, the first conductive material 150 may include any one of these materials, or may include two or more of these materials. When the first conductive material 150 is a fibrous carbon material, the first conductive material 150 may be composed of any one of these materials, or may be composed of two or more of these materials.

[0051] The second conductive material 160 may contain carbon black. According to the above configuration, the electron conductivity in the positive electrode can be further improved.

[0052] Carbon black may be used as the second conductive material 160. According to the above configuration, the electron conductivity in the positive electrode can be further improved.

[0053] Examples of carbon black include acetylene black and ketjen black. When the second conductive material 160 contains carbon black, the second conductive material 160 may contain either acetylene black or ketjen black. The second conductive material 160 may contain both acetylene black and ketjen black. When the carbon black contains acetylene black, the electronic conductivity of the positive electrode can be further improved. When the second conductive material 160 is carbon black, the second conductive material 160 may be either acetylene black or ketjen black. The second conductive material 160 may be composed of acetylene black and ketjen black.

[0054] When the first conductive material 150 is a fibrous carbon material, the first conductive material 150 contains the fibrous carbon material as a main component, and may further contain unavoidable impurities, or starting materials, by-products, decomposition products, etc. used in synthesizing the fibrous carbon material. In the present disclosure, the "main component" refers to the component that is contained in the largest amount by mass.

[0055] The first conductive material 150 may contain, for example, 100% fibrous carbon material in terms of mass ratio relative to the entire first conductive material 150, excluding unavoidable impurities.

[0056] In this way, the first conductive material 150 may be made of only the fibrous carbon material.

[0057] When the second conductive material 160 is carbon black, the second conductive material 160 contains carbon black as a main component, and may further contain unavoidable impurities, or starting materials, by-products, decomposition products, etc. used in synthesizing the carbon black.

[0058] The second conductive material 160 may contain, for example, 100% carbon black in terms of mass ratio relative to the entire second conductive material 160, excluding unavoidable impurities.

[0059] Thus, the second conductive material 160 may consist solely of carbon black.

[0060] The first conductive material 150 may have an average major axis diameter of 4 μm or more. According to the above configuration, the first conductive material 150 easily forms a conductive path in the positive electrode that enables long-distance electron conduction. This can further improve the electron conductivity in the positive electrode.

[0061] The second conductive material 160 may have an average particle size of 25 nm or less. With the above configuration, the second conductive material 160 is easily attached to the surface of the positive electrode active material 110. Therefore, the first conductive material 150 and the second conductive material 160 are connected to each other, which makes it easier to form an electron conduction network in the positive electrode.

[0062] The shape of the first conductive material 150 is not particularly limited as long as it has an average major axis diameter of 1 μm or more. The first conductive material 150 may be, for example, fibrous or needle-like. The shape of the first conductive material 150 may be fibrous.

[0063] The shape of the second conductive material 160 is not particularly limited as long as it has an average particle size of 100 nm or less. The second conductive material 160 may be, for example, spherical or oval. The shape of the second conductive material 160 may be spherical.

[0064] The conductive material 140 may include a conductive material different from the first conductive material 150 and the second conductive material 160. Examples of such conductive materials include graphites such as natural graphite or artificial graphite, metal fibers, carbon fluoride, metal powders such as aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. According to the above configuration, the electron conductivity in the positive electrode can be further improved.

[0065] The conductive material 140 may be composed only of the first conductive material 150 and the second conductive material 160. That is, the conductive material 140 may not include a conductive material different from the first conductive material 150 and the second conductive material 160.

[0066] (Positive electrode active material) As the positive electrode active material 110, a material that can be used as the positive electrode active material of an all-solid-state lithium-ion battery can be used. Examples of the positive electrode active material 110 include LiCoO2, LiNi x Me 1-x O2, LiNi x Co 1-x O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMnO2, hetero-element-substituted Li-Mn spinel, lithium titanate, lithium metal phosphate, and transition metal oxides. In LiNi x Me 1-x O2, x satisfies 0.5 ≦ x < 1, and Me includes at least one or more selected from the group consisting of Co, Mn, and Al. In LiNi x Co 1-x O2, x satisfies 0 < x < 0.5. Examples of the hetero-element-substituted Li-Mn spinel include LiMn 1.5 Ni 0.5 O4, LiMn 1.5 Al 0.5 O4, LiMn 1.5 Mg 0.5 O4, LiMn 1.5 Co 0.5 O4, LiMn1.5 Fe 0.5 O4, and LiMn 1.5 Zn 0.5 Lithium titanate includes Li4Ti5O 12 Lithium metal phosphates include LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4. Transition metal oxides include V2O5 and MoO3.

[0067] The positive electrode active material 110 is LiCoO2, LiNi x Me 1-x O2, LiNi x Co 1-x O2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The oxide may be a lithium-containing composite oxide selected from O2, LiMnO2, Li-Mn spinel substituted with a different element, lithium metal phosphate, and the like.

[0068] When the positive electrode active material 110 is a lithium-containing composite oxide, the positive electrode active material 110 may have a layered rock salt structure. In the layered rock salt structure, transition metals and lithium are regularly arranged to form a two-dimensional plane, allowing two-dimensional diffusion of lithium. Therefore, with this configuration, the energy density of the battery can be improved.

[0069] (solid electrolyte) The solid electrolyte 100 may contain at least one selected from the group consisting of sulfide solid electrolytes and halide solid electrolytes. With the above configuration, the output characteristics of the battery can be improved.

[0070] The solid electrolyte 100 may be a mixture of a sulfide solid electrolyte and a halide solid electrolyte.

[0071] Sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10GeP2S 12 In addition, sulfide solid electrolytes with an argyrodite structure, such as Li6PS5Cl, Li6PS5Br, and Li6PS5I, can be used. These sulfide solid electrolytes can be used with LiX, Li2O, MO q , Li p MO q or the like may be added. Here, X is at least one selected from the group consisting of F, Cl, Br, and I. Furthermore, M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. p and q are each a natural number. One or more sulfide solid electrolytes selected from the above materials may be used.

[0072] According to the above configuration, the ionic conductivity of the sulfide solid electrolyte can be further improved, thereby further improving the charge / discharge efficiency of the battery.

[0073] The halide solid electrolyte is represented by, for example, the following composition formula (1).

[0074] Li α M β X γ ...Equation (1)

[0075] where α, β, and γ are each independently a value greater than 0. M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li. X includes at least one element selected from the group consisting of F, Cl, Br, and I.

[0076] In this disclosure, "metalloid elements" refer to B, Si, Ge, As, Sb, and Te. "Metal elements" refer to all elements in Groups 1 to 12 of the periodic table excluding hydrogen, and all elements in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, "metalloid elements" or "metal elements" refer to a group of elements that can become cations when forming inorganic compounds with halogen elements.

[0077] The halide solid electrolyte represented by composition formula (1) has higher ionic conductivity than halide solid electrolytes such as LiI, which are composed of Li and a halogen element. Therefore, the halide solid electrolyte represented by composition formula (1) can further improve the ionic conductivity of the halide solid electrolyte.

[0078] In composition formula (1), M may be at least one element selected from the group consisting of metal elements and metalloid elements other than Li.

[0079] In the composition formula (1), X may be at least one selected from the group consisting of F, Cl, Br, and I.

[0080] The composition formula (2) may satisfy 2.5≦α≦3, 1≦β≦1.1, and γ=6. According to the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved.

[0081] In the composition formula (1), M may contain Y (=yttrium). That is, the halide solid electrolyte may contain Y as a metal element. According to the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved.

[0082] The halide solid electrolyte containing Y is, for example, Li a Me b Y c The compound may be a compound represented by the formula X6, where a+mb+3c=6 and c>0 are satisfied. Me is at least one element selected from the group consisting of metal elements and metalloid elements excluding Li and Y. m is the valence of the element Me. X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0083] Me may be at least one selected from the group consisting of, for example, Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0084] According to the above configuration, the ionic conductivity of the halide solid electrolyte can be further improved.

[0085] As the halide solid electrolyte, for example, the following materials can be used. According to the following configuration, the ionic conductivity of the halide solid electrolyte can be further improved.

[0086] The halide solid electrolyte may be a material represented by the following composition formula (A1).

[0087] Li 6-3d Y d X6 ··· Formula (A1)

[0088] In the composition formula (A1), X is at least one selected from the group consisting of F, Cl, Br, and I. Also, 0 < d < 2 is satisfied.

[0089] The halide solid electrolyte may be a material represented by the following composition formula (A2).

[0090] Li3YX6 ··· Formula (A2)

[0091] In the composition formula (A2), X is at least one selected from the group consisting of F, Cl, Br, and I.

[0092] The halide solid electrolyte may be a material represented by the following composition formula (A3). ​​​​​​​​​​​​

[0095] The halide solid electrolyte may be a material represented by the following compositional formula (A4).

[0096] Li 3-3δ Y 1+δ Br6 ··· Formula (A4)

[0097] In the compositional formula (A4), 0 < δ ≦ 0.25 is satisfied.

[0098] The halide solid electrolyte may be a material represented by the following compositional formula (A5).

[0099] Li 3-3δ+a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A5)

[0100] In the compositional formula (A5), Me includes at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn.

[0101] In the compositional formula (A5), -1 < δ < 2, 0 < a < 3, 0 < (3 - 3δ + a), 0 < (1 + δ - a), 0 ≦ x ≦ 6, 且 0 ≦ y ≦ 6, 以及 (x + y) ≦ 6 are satisfied.

[0102] The halide solid electrolyte may be a material represented by the following compositional formula (A6).

[0103] Li 3-3δ Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A6)

[0104] In the compositional formula (A6), Me contains at least one selected from the group consisting of Al, Sc, Ga, and Bi. Me may be at least one selected from the group consisting of Al, Sc, Ga, and Bi.

[0105] In the compositional formula (A6), -1 < δ < 1, 0 < a < 2, 0 < (1 + δ - a), 0 ≤ x ≤ 6, 0 ≤ y ≤ 6, and (x + y) ≤ 6 are satisfied.

[0106] The halide solid electrolyte may be a material represented by the following compositional formula (A7).

[0107] Li 3-3δ-a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A7)

[0108] In the compositional formula (A7), Me contains at least one selected from the group consisting of Zr, Hf, and Ti. Me may be at least one selected from the group consisting of Zr, Hf, and Ti.

[0109] In the compositional formula (A7), -1 < δ < 1, 0 < a < 1.5, 0 < (3 - 3δ - a), 0 < (1 + δ - a), 0 ≤ x ≤ 6, 0 ≤ y ≤ 6, and (x + y) ≤ 6 are satisfied.

[0110] [[ID=�6]]The halide solid electrolyte may be a material represented by the following compositional formula (A8).

[0111] Li 3-3δ-2a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A8)

[0112] In the compositional formula (A8), Me contains at least one selected from the group consisting of Ta and Nb. Me may be at least one selected from the group consisting of Ta and Nb.

[0113] In compositional formula (A8), -1 < δ < 1, 0 < a < 1.2, 0 < (3 - 3δ - 2a), 0 < (1 + δ - a), 0 ≤ x ≤ 6, 0 ≤ y ≤ 6, and (x + y) ≤ 6 are satisfied.

[0114] As the halide solid electrolyte, more specifically, for example, Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li3(Al,Ga,In)X6, etc. can be used. Here, X is at least one selected from the group consisting of F, Cl, Br, and I.

[0115] In the present disclosure, the notation “(A,B,C)” in the chemical formula means “at least one selected from the group consisting of A, B, and C”. For example, “(Al,Ga,In)” is synonymous with “at least one selected from the group consisting of Al, Ga, and In”. The same applies to other elements.

[0116] The halide solid electrolyte may not contain sulfur. According to the above configuration, the generation of hydrogen sulfide gas can be suppressed. Therefore, it is possible to realize a battery with improved safety.

[0117] The shape of the solid electrolyte 100 is not particularly limited. The shape of the solid electrolyte 100 may be, for example, needle-like, spherical, ellipsoidal, etc. For example, the shape of the solid electrolyte 100 may be particulate.

[0118] For example, when the shape of the solid electrolyte 100 is particulate (e.g., spherical), the median diameter of the solid electrolyte 100 may be 100 μm or less. When the median diameter of the solid electrolyte 100 is 100 μm or less, the positive electrode active material 110 and the solid electrolyte 100 in the positive electrode material 1000 can form a good dispersion state. Thereby, the charge and discharge characteristics of the battery are improved.

[0119] The median diameter of the solid electrolyte 100 may be 10 μm or less. According to the above configuration, the positive electrode active material 110 and the solid electrolyte 100 in the positive electrode material 1000 can be well dispersed.

[0120] The median diameter of the solid electrolyte 100 may be smaller than the median diameter of the positive electrode active material 110. According to the above configuration, the positive electrode active material 110 and the solid electrolyte 100 can be dispersed in the positive electrode material 1000 in a better state.

[0121] There are no particular limitations on the shape of the positive electrode active material 110. The shape of the positive electrode active material 110 may be, for example, needle-like, spherical, oval-spherical, etc. For example, the shape of the positive electrode active material 110 may be particulate.

[0122] The median diameter of the positive electrode active material 110 may be 0.1 μm or more and 100 μm or less. When the median diameter of the positive electrode active material 110 is 0.1 μm or more, the positive electrode active material 110 and the solid electrolyte 100 can form a well-dispersed state in the positive electrode material 1000. This improves the charge / discharge characteristics of the battery. When the median diameter of the positive electrode active material 110 is 100 μm or less, the diffusion rate of lithium in the positive electrode active material 110 is sufficiently ensured. This allows the battery to operate at high power.

[0123] The median diameter of the positive electrode active material 110 may be larger than the median diameter of the solid electrolyte 100. This allows the positive electrode active material 110 and the solid electrolyte 100 to form a good dispersed state.

[0124] In the present disclosure, the median diameter refers to the particle size (d50) when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measurement device or an image analysis device.

[0125] In the positive electrode material 1000, the solid electrolyte 100 and the positive electrode active material 110 may be in contact with each other.

[0126] The cathode material 1000 may include a plurality of particles of the solid electrolyte 100 and a plurality of particles of the cathode active material 110 .

[0127] In the positive electrode material 1000, the content of the solid electrolyte 100 and the content of the positive electrode active material 110 may be the same as or different from each other.

[0128] The cathode material 1000 may include a plurality of conductive materials 140 .

[0129] The cathode material 1000 may include a plurality of first conductive materials 150 and a plurality of second conductive materials 160 .

[0130] <Method of manufacturing positive electrode material> The positive electrode material 1000 can be produced, for example, by the following method.

[0131] A mixture of the positive electrode active material 110, the solid electrolyte 100, and the conductive material 140 is prepared. The conductive material 140 includes a first conductive material 150 and a second conductive material 160. For example, a solvent and the conductive material 140 may be prepared, the conductive material 140 may be mixed with the solvent, and then the positive electrode active material 110 and the solid electrolyte 100 may be added to and mixed with the resulting mixture. This results in a positive electrode material 1000 containing a mixture of the positive electrode active material 110, the solid electrolyte 100, and the conductive material 140.

[0132] The method for mixing the positive electrode active material 110, the solid electrolyte 100, and the conductive material 140 is not particularly limited. For example, these materials may be mixed using a machine such as a homogenizer. Using a homogenizer can achieve uniform mixing. The mixing ratio of the positive electrode active material 110 and the solid electrolyte 100 is not particularly limited.

[0133] (Variation 1) FIG. 2 is a cross-sectional view showing a schematic configuration of a positive electrode material 1001 in Modification 1. The positive electrode material 1001 further includes a coating layer 120 that coats at least a portion of the surface of the positive electrode active material 110. The positive electrode active material 110 having at least a portion of its surface coated with the coating layer 120 is referred to as a "coated positive electrode active material 130." In this way, the positive electrode material 1001 may further include the coating layer 120 that coats at least a portion of the surface of the positive electrode active material 110. This configuration can further reduce the resistance of the battery.

[0134] The coating layer 120 is in direct contact with the positive electrode active material 110 .

[0135] Hereinafter, the material that constitutes coating layer 120 will be referred to as the "coating material." Coated positive electrode active material 130 in the second embodiment includes positive electrode active material 110 and a coating material. The coating material is present on at least a portion of the surface of positive electrode active material 110, thereby forming coating layer 120.

[0136] The coating layer 120 may uniformly coat the positive electrode active material 110. According to the above configuration, the positive electrode active material 110 and the coating layer 120 are in close contact with each other, which can further reduce the resistance of the battery.

[0137] The coating layer 120 may cover only a portion of the surface of the positive electrode active material 110. The particles of the positive electrode active material 110 come into direct contact with each other through the portion not covered by the coating layer 120, thereby improving the electronic conductivity between the particles of the positive electrode active material 110. As a result, the battery can operate at high power output.

[0138] The coating layer 120 on the positive electrode active material 110 suppresses the formation of an oxide film due to oxidative decomposition of the other solid electrolyte during charging of the battery. As a result, the charge / discharge efficiency of the battery is improved. An example of the other solid electrolyte is the solid electrolyte 100.

[0139] The coating material may contain Li and at least one selected from the group consisting of O, F and Cl.

[0140] The coating material may include at least one selected from the group consisting of lithium niobate, lithium phosphate, lithium titanate, lithium tungstate, lithium fluorozirconate, lithium fluoroaluminate, lithium fluorotitanate, and lithium fluoromagnesium oxide.

[0141] The coating material may be lithium niobate (LiNbO3).

[0142] <Method of manufacturing positive electrode material> The positive electrode material 1001 can be produced by replacing the positive electrode active material 110 with the coated positive electrode active material 130 in the method for producing the positive electrode material 1000 described in the first embodiment.

[0143] Here, the coated positive electrode active material 130 can be produced, for example, by the following method. First, the coating layer 120 is formed on the surface of the particles of the positive electrode active material 110. The method for forming the coating layer 120 is not particularly limited. Methods for forming the coating layer 120 include a liquid-phase coating method and a vapor-phase coating method.

[0144] For example, in the liquid-phase coating method, a precursor solution of an ion-conductive material is applied to the surface of the positive electrode active material 110. When forming a coating layer 120 containing LiNbO3, the precursor solution can be a mixed solution (sol solution) of a solvent, lithium alkoxide, and niobium alkoxide. Examples of lithium alkoxide include lithium ethoxide. Examples of niobium alkoxide include niobium ethoxide. The solvent is, for example, an alcohol such as ethanol. The amounts of lithium alkoxide and niobium alkoxide are adjusted depending on the target composition of the coating layer 120. Water may be added to the precursor solution if necessary. The precursor solution may be acidic or alkaline.

[0145] The method for applying the precursor solution to the surface of the positive electrode active material 110 is not particularly limited. For example, the precursor solution can be applied to the surface of the positive electrode active material 110 using a tumbling fluidized granulation coating device. With the tumbling fluidized granulation coating device, the precursor solution can be sprayed onto the positive electrode active material 110 while tumbling and fluidizing the positive electrode active material 110, thereby applying the precursor solution to the surface of the positive electrode active material 110. As a result, a precursor coating is formed on the surface of the positive electrode active material 110. The positive electrode active material 110 coated with the precursor coating is then heat-treated. The heat treatment promotes gelation of the precursor coating, forming a coating layer 120. As a result, a coated positive electrode active material 130 is obtained. At this point, the coating layer 120 covers substantially the entire surface of the positive electrode active material 110. The thickness of the coating layer 120 is generally uniform.

[0146] Vapor-phase coating methods include pulsed laser deposition (PLD), vacuum evaporation, sputtering, thermal chemical vapor deposition (CVD), and plasma chemical vapor deposition. For example, in the PLD method, a target made of an ion-conductive material is irradiated with a high-energy pulse laser (e.g., a KrF excimer laser, wavelength: 248 nm), and the sublimated ion-conductive material is deposited on the surface of the positive electrode active material 110. When forming the LiNbO3 coating layer 120, highly sintered LiNbO3 is used as the target.

[0147] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0148] FIG. 3 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the second embodiment.

[0149] Battery 2000 in Embodiment 2 includes positive electrode 201, electrolyte layer 202, and negative electrode 203. Positive electrode 201 includes the positive electrode material in Embodiment 1 or Modification 1. Electrolyte layer 202 is disposed between positive electrode 201 and negative electrode 203. FIG. 3 shows positive electrode material 1000 as an example of the positive electrode material included in positive electrode 201.

[0150] The above configuration makes it possible to achieve both energy density and electronic conductivity in the positive electrode 201. This makes it possible to improve the energy density of the battery 2000 and reduce the resistance of the battery 2000.

[0151] When the positive electrode material is the positive electrode material 1000, the volume ratio "v1:100-v1" of the positive electrode active material 110 to the solid electrolyte 100 contained in the positive electrode 201 may satisfy 30≦v1≦95. Here, v1 represents the volume ratio of the positive electrode active material 110 when the total volume of the positive electrode active material 110 and the solid electrolyte 100 contained in the positive electrode 201 is taken as 100. When 30≦v1 is satisfied, a sufficient energy density of the battery 2000 can be ensured. When v1≦95 is satisfied, the battery 2000 can operate at high output.

[0152] When the positive electrode material is the positive electrode material 1001, the volume ratio "v11:100-v11" of the coated positive electrode active material 130 to the solid electrolyte 100 contained in the positive electrode 201 may satisfy 30≦v11≦95. Here, v11 represents the volume ratio of the coated positive electrode active material 130 when the total volume of the coated positive electrode active material 130 and the solid electrolyte 100 contained in the positive electrode 201 is taken as 100. When 30≦v11 is satisfied, a sufficient energy density of the battery 2000 can be ensured. When v11≦95 is satisfied, the battery 2000 can operate at high output.

[0153] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 201 is 10 μm or more, a sufficient energy density of the battery 2000 can be ensured. When the thickness of the positive electrode 201 is 500 μm or less, the battery 2000 can operate at high output.

[0154] The electrolyte layer 202 is a layer containing an electrolyte. The electrolyte is, for example, a solid electrolyte. That is, the electrolyte layer 202 may be a solid electrolyte layer. The material exemplified as the solid electrolyte 100 in the first embodiment may be used as the solid electrolyte contained in the electrolyte layer 202. That is, the electrolyte layer 202 may contain a solid electrolyte having the same composition as the solid electrolyte 100. With the above configuration, the charge / discharge efficiency of the battery 2000 can be further improved.

[0155] The electrolyte layer 202 may include a halide solid electrolyte having a composition different from that of the solid electrolyte 100 .

[0156] The electrolyte layer 202 may include a sulfide solid electrolyte.

[0157] The electrolyte layer 202 may include only one solid electrolyte selected from the materials listed as solid electrolytes.

[0158] The electrolyte layer 202 may include two or more solid electrolytes selected from the materials listed as solid electrolytes. In this case, the multiple solid electrolytes have different compositions. For example, the electrolyte layer 202 may include a halide solid electrolyte and a sulfide solid electrolyte.

[0159] The thickness of the electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 202 is 1 μm or more, the cathode 201 and the anode 203 are less likely to short-circuit. When the thickness of the electrolyte layer 202 is 300 μm or less, the battery 2000 can operate at high power.

[0160] The negative electrode 203 includes a material having the property of absorbing and releasing metal ions (for example, lithium ions). The negative electrode 203 includes, for example, a negative electrode active material.

[0161] The negative electrode active material may be a metal material, a carbon material, an oxide, a nitride, a tin compound, a silicon compound, or the like. The metal material may be a simple metal. The metal material may be an alloy. Examples of metal materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. The capacity density can be improved by using silicon (Si), tin (Sn), a silicon compound, a tin compound, or the like.

[0162] The negative electrode 203 may contain a solid electrolyte. According to the above configuration, the lithium ion conductivity inside the negative electrode 203 is increased, and the battery 2000 can operate at high output. The material exemplified as the solid electrolyte 100 in the first embodiment may be used as the solid electrolyte contained in the negative electrode 203. That is, the negative electrode 203 may contain a solid electrolyte having the same composition as the solid electrolyte 100.

[0163] The shape of the solid electrolyte contained in the negative electrode 203 in the second embodiment is not particularly limited. The shape of the solid electrolyte contained in the negative electrode 203 may be, for example, needle-like, spherical, or oval-spherical. For example, the shape of the solid electrolyte contained in the negative electrode 203 may be particulate.

[0164] When the solid electrolyte contained in the negative electrode 203 is particulate (e.g., spherical), the median diameter of the solid electrolyte may be 100 μm or less. When the median diameter of the solid electrolyte is 100 μm or less, the negative electrode active material and the solid electrolyte can be well dispersed in the negative electrode 203. This improves the charge / discharge characteristics of the battery 2000.

[0165] The median diameter of the solid electrolyte contained in the negative electrode 203 may be 10 μm or less, or may be 1 μm or less. According to the above configuration, the negative electrode active material and the solid electrolyte can be well dispersed in the negative electrode 203.

[0166] The median diameter of the solid electrolyte contained in the negative electrode 203 may be smaller than the median diameter of the negative electrode active material. According to the above configuration, the negative electrode active material and the solid electrolyte can be better dispersed in the negative electrode 203.

[0167] The shape of the negative electrode active material in Embodiment 2 is not particularly limited. The shape of the negative electrode active material may be, for example, needle-like, spherical, oval-spherical, etc. For example, the shape of the negative electrode active material may be particulate.

[0168] The median diameter of the negative electrode active material may be 0.1 μm or more and 100 μm or less. When the median diameter of the negative electrode active material is 0.1 μm or more, the negative electrode active material and the solid electrolyte can be well dispersed in the negative electrode 203. This improves the charge / discharge characteristics of the battery 2000. When the median diameter of the negative electrode active material is 100 μm or less, the lithium diffusion rate within the negative electrode active material is sufficiently ensured. This allows the battery 2000 to operate at high power.

[0169] The median diameter of the negative electrode active material may be larger than the median diameter of the solid electrolyte contained in the negative electrode 203. This allows the negative electrode active material and the solid electrolyte to form a well-dispersed state.

[0170] The volume ratio "v2:100-v2" of the negative electrode active material to the solid electrolyte contained in the negative electrode 203 may satisfy 30≦v2≦95. Here, v2 represents the volume ratio of the negative electrode active material when the total volume of the negative electrode active material and the solid electrolyte contained in the negative electrode 203 is taken as 100. When 30≦v2 is satisfied, a sufficient energy density of the battery 2000 can be ensured. When v2≦95 is satisfied, the battery 2000 can operate at high output.

[0171] The thickness of the negative electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 203 is 10 μm or more, a sufficient energy density of the battery 2000 can be ensured. When the thickness of the negative electrode 203 is 500 μm or less, the battery 2000 can operate at high output.

[0172] At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder to improve adhesion between particles. The binder is used to improve the binding of the materials that make up the electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl ester of acrylic acid, polyethyl ester of acrylic acid, polyhexyl ester of acrylic acid, polymethacrylic acid, polymethyl ester of methacrylic acid, polyethyl ester of methacrylic acid, polyhexyl ester of methacrylic acid, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, and carboxymethyl cellulose. Copolymers of two or more materials selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene can also be used as binders. Mixtures of two or more of the above materials can also be used as binders.

[0173] The negative electrode 203 may contain a conductive additive to improve electronic conductivity. Examples of the conductive additive include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0174] The shape of the battery 2000 in the second embodiment may be, for example, a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type. [Example]

[0175] Hereinafter, the present disclosure will be described in detail using Examples 1 to 9 and Comparative Examples 1 to 5.

[0176] Example 1 [Preparation of sulfide solid electrolyte] In an argon glove box with a dew point below -60°C, the raw material powders Li2S and P2S5 were weighed out to a molar ratio of Li2S:P2S5 = 75:25. The raw material powders were crushed and mixed in a mortar to obtain a mixture. The mixture was then milled for 10 hours at 510 rpm using a planetary ball mill (Fritsch, Model P-7). This resulted in a glassy solid electrolyte. The resulting solid electrolyte was heat-treated in an inert atmosphere at 270°C for 2 hours. This resulted in the production of a sulfide solid electrolyte, a glass-ceramic Li2S-P2S5 (hereinafter referred to as LPS).

[0177] [Preparation of coated positive electrode active material] As the positive electrode active material, LiNi 0.8 (Co,Mn) 0.2 O2 (hereafter referred to as NCM) was used. LiNbO3 was used as the coating material. A coating layer containing LiNbO3 was formed by a liquid-phase coating method. Specifically, a precursor solution of an ion-conducting material was first applied to the surface of the NCM. This formed a precursor coating on the surface of the NCM. The NCM coated with the precursor coating was then heat-treated. The heat treatment promoted gelation of the precursor coating, forming a coating layer made of LiNbO3. Using this method, a coated positive electrode active material (hereafter referred to as Nb-NCM) was produced.

[0178] [Preparation of cathode material] Carbon fiber (VGCF-H, manufactured by Showa Denko K.K.) was used as the first conductive material. The average major axis diameter of the VGCF-H was 6 μm. Acetylene black with an average particle size of 23 nm was used as the second conductive material. The binder, solvent, VGCF-H, and acetylene black were mixed in an argon glove box with a dew point of -60°C or less and dispersed using a homogenizer. This resulted in a mixture of the binder, solvent, VGCF-H, and acetylene black. The mass ratio of VGCF-H to acetylene black was 2:0.125. The coated active material Nb-NCM and the solid electrolyte LPS were added to the mixture, mixed, and dispersed using a homogenizer to produce a slurry containing the positive electrode material. The volume ratio of Nb-NCM to LPS was 70:30. Note that "VGCF" is a registered trademark of Showa Denko K.K.

[0179] [Preparation of positive electrode] The prepared slurry was applied onto a current collector and dried on a hot plate to prepare a positive electrode.

[0180] Example 2 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 2:0.3 by mass, and the other steps were the same as in Example 1 to obtain the positive electrode of Example 2.

[0181] Example 3 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 2:0.4 by mass, and the other steps were the same as in Example 1 to obtain the positive electrode of Example 3.

[0182] Example 4 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 2:0.475 by mass, and the remaining steps were the same as in Example 1 to obtain the positive electrode of Example 4.

[0183] Example 5 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 1.6:0.475 by mass, except for this, the process was the same as in Example 1, and the positive electrode of Example 5 was obtained.

[0184] Example 6 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 2:0.65 by mass, except for this, the process was the same as in Example 1, and the positive electrode of Example 6 was obtained.

[0185] Example 7 In the positive electrode material preparation process, the mixing ratio of VGCF-H and acetylene black was 1.5:0.475 by mass, and the mixing ratio of Nb-NCM and LPS was 67:33 by volume. The other steps were the same as in Example 1, and the positive electrode of Example 7 was obtained.

[0186] Example 8 In the positive electrode material preparation process, the mixing ratio of VGCF-H and acetylene black was 2:0.3 by mass, and the mixing ratio of Nb-NCM and LPS was 72:28 by volume. The other steps were the same as in Example 1, and the positive electrode of Example 8 was obtained.

[0187] Example 9 In the positive electrode material preparation process, the mixing ratio of VGCF-H and acetylene black was 2:0.3 by mass, and the mixing ratio of Nb-NCM and LPS was 75:25 by volume. The other steps were the same as in Example 1, and the positive electrode of Example 9 was obtained.

[0188] Comparative Example 1 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 2.4:0 by mass. That is, the conductive material of Comparative Example 1 was VGCF-H alone. The remaining steps were the same as those of Example 1, and the positive electrode of Comparative Example 1 was obtained.

[0189] Comparative Example 2 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 2:0 by mass. That is, the conductive material of Comparative Example 2 was VGCF-H alone. The remaining steps were the same as those of Example 1, and the positive electrode of Comparative Example 2 was obtained.

[0190] Comparative Example 3 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 1.6:0 by mass. That is, the conductive material of Comparative Example 3 was VGCF-H alone. The remaining steps were the same as those of Example 1, and the positive electrode of Comparative Example 3 was obtained.

[0191] Comparative Example 4 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 0.8:0 by mass. That is, the conductive material of Comparative Example 4 was VGCF-H alone. The remaining steps were the same as those of Example 1, and the positive electrode of Comparative Example 4 was obtained.

[0192] Comparative Example 5 In the process for preparing the positive electrode material, the mixing ratio of VGCF-H and acetylene black was 0:0.65 by mass. That is, the conductive material of Comparative Example 5 was acetylene black alone. The remaining steps were the same as those of Example 1, and the positive electrode of Comparative Example 5 was obtained.

[0193] (Evaluation of electronic conductivity) Using the positive electrodes of Examples 1 to 9 and Comparative Examples 1 to 5, the electronic conductivity was evaluated under the following conditions.

[0194] FIG. 4 is a diagram illustrating a method for evaluating the electronic conductivity of a positive electrode. The electronic conductivity of the positive electrode was evaluated at 25° C. using a counter positive electrode 3000 as shown in FIG. 4. The counter positive electrode 3000 was fabricated by stacking a current collector 204 on each outer surface of a laminate of two opposing positive electrodes 201, and then pressing the laminate under high pressure. An Al foil was used as the current collector 204. A potentiostat 400 was connected to the counter positive electrode 3000 thus obtained, and the electronic resistance was measured according to the following procedure.

[0195] Using the potentiostat 400, voltages of 0.3 V, 0.2 V, −0.2 V, and −0.3 V were applied for one minute each, and the current value was measured for each voltage. FIG. 5 is a graph showing the correlation between voltage and current value for the counter positive electrode 3000 of Example 1. The current value was linearly approximated according to Ohm's law. The slope of the approximated line indicates the DC resistance.

[0196] Using the value of DC resistance obtained from the slope of the approximation line, the electronic conductivity σ of the positive electrode of Example 1 was calculated using the following formula (2). The calculated electronic conductivity is shown in Table 1.

[0197] σ={R×S / (2t)} -1 ···(2)

[0198] In equation (2), S is the surface area of ​​the positive electrode. R is the DC resistance value obtained from the slope of the approximation line. t is the thickness of the positive electrode. "Thickness of the positive electrode" refers to the thickness of the positive electrode 201 in FIG. 4.

[0199] The electronic conductivities of the positive electrodes of Examples 2 to 9 and Comparative Examples 1 to 5 were calculated using the same method as above. The calculated electronic conductivities are shown in Table 1. In Table 1, VGCF-H (mass%) represents the mass ratio of VGCF-H when the mass of the positive electrode active material is taken as 100%. Acetylene black (mass%) represents the mass ratio of acetylene black when the mass of the positive electrode active material is taken as 100%. Total conductive material (mass%) represents the mass ratio of the total mass of VGCF-H and acetylene black when the mass of the positive electrode active material is taken as 100%. Also in Table 1, VGCF-H (mass%) represents the mass ratio of VGCF-H to the total mass of VGCF-H and acetylene black. Acetylene black (mass%) represents the mass ratio of acetylene black to the total mass of VGCF-H and acetylene black.

[0200] [Table 1]

[0201] ≪Consideration≫ Examples 1 to 9, which contained VGCF-H and acetylene black as conductive materials, showed a tendency for the electron conductivity of the positive electrode to be increased compared to Comparative Examples 1 to 5, which contained only one of VGCF-H and acetylene black.

[0202] Fig. 6 is a graph showing the electronic conductivity of the positive electrodes of Examples 1 to 9 and Comparative Examples 1 to 5. In Fig. 6, the vertical axis represents the calculated electronic conductivity, and the horizontal axis represents the mass ratio of the conductive material when the mass of the coated positive electrode active material is taken as 100%.

[0203] The mass ratio of the conductive material was the same in Example 3 and Comparative Example 1. However, the electronic conductivity of Example 3 was more than twice that of Comparative Example 1. In other words, when the mass ratio of the conductive material was approximately the same, the electronic conductivity could be significantly improved.

[0204] The electronic conductivities of Example 7 and Comparative Example 1 were comparable. However, the mass ratio of the conductive material in Example 7 was smaller than that of Comparative Example 1. In other words, when the electronic conductivities were comparable, the mass ratio of the conductive material could be reduced. This is thought to be because the inclusion of VGCF-H and acetylene black as conductive materials made it easier for the VGCF-H and acetylene black to bond together, efficiently forming an electronic conduction network in the positive electrode.

[0205] The mass ratio of the conductive material was the same in Examples 2, 8, and 9. The volume ratio and electronic conductivity of the coated positive electrode active material increased in the order of Examples 2, 8, and 9. That is, the electronic conductivity could be improved as the volume ratio of the positive electrode active material increased.

[0206] As shown in Examples 2 to 6, the electronic conductivity could be improved as the mass ratio of acetylene black to the entire conductive material increased. [Industrial Applicability]

[0207] The battery of the present disclosure can be used, for example, as an all-solid-state lithium secondary battery. [Explanation of symbols]

[0208] 1000,1001 Cathode material 100 solid electrolyte 110 Cathode active material 120 Covering layer 130 Coated positive electrode active material 140 Conductive Materials 150 First conductive material 160 Second conductive material 2000 batteries 201 Positive electrode 202 Electrolyte layer 203 Negative electrode 204 Current collector 3000 opposing positive electrodes 400 Potentiostat

Claims

1. a mixture of a positive electrode active material, a solid electrolyte, and a conductive material; the conductive material includes a first conductive material having an average major axis diameter of 1 μm or more and a second conductive material having an average particle diameter of 100 nm or less; a ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte is 60% or more and 90% or less; Positive electrode material.

2. a ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte is 65% or more and 85% or less; The positive electrode material according to claim 1 .

3. a ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte is 67% or more and 75% or less; The positive electrode material according to claim 1 .

4. When the mass ratio of the positive electrode active material is 100, the mass ratio of the conductive material is 3 or less. The positive electrode material according to claim 1 .

5. a ratio of the mass of the second conductive material to the mass of the conductive material is 80% or less; The positive electrode material according to claim 1 .

6. a ratio of the mass of the second conductive material to the mass of the conductive material is 5% or more and 50% or less; The positive electrode material according to claim 5 .

7. a ratio of the mass of the second conductive material to the mass of the conductive material is 6% or more and 25% or less; The positive electrode material according to claim 5 .

8. The first conductive material has an average major axis diameter of 4 μm or more. The positive electrode material according to any one of claims 1 to 7.

9. the second conductive material has an average particle size of 25 nm or less; The positive electrode material according to claim 8.

10. the first conductive material and the second conductive material include a carbon material; The positive electrode material according to any one of claims 1 to 9.

11. the first conductive material includes a fibrous carbon material; The positive electrode material according to any one of claims 1 to 10.

12. the second conductive material includes carbon black; The cathode material according to any one of claims 1 to 11.

13. The carbon black includes acetylene black. The positive electrode material according to claim 12.

14. The solid electrolyte includes at least one selected from the group consisting of a sulfide solid electrolyte and a halide solid electrolyte. The cathode material according to any one of claims 1 to 13.

15. The positive electrode active material has a layered rock salt structure. The cathode material according to any one of claims 1 to 14.

16. Further provided with a coating layer that covers at least a part of the surface of the positive electrode active material. The cathode material according to any one of claims 1 to 15.

17. A positive electrode comprising the positive electrode material of any one of claims 1 to 16; a negative electrode; an electrolyte layer disposed between the positive electrode and the negative electrode; Equipped with battery.

18. The electrolyte layer includes a sulfide solid electrolyte.

18. The battery of claim 17.

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