Coating active material, cathode material, cathode and battery

Abstract

This coating active material 110 is provided with a positive electrode active material 101 and a coating layer 104 that coats as least part of the surface of the positive electrode active material 101, wherein the coating layer 104 includes a first coating layer 102 and a second coating layer 103, the first coating layer 102 is positioned outside of the second coating layer 103, and the rate of change in the specific surface area from the specific surface area of the positive electrode active material 101 covered by the second coating layer 103 to the specific surface area of the coating active material 110 is -62.8% to +3.79%.

Description

Technical Field

[0001] The present disclosure relates to a coating active material, a positive electrode material, a positive electrode, and a battery.

Background Art

[0002] Patent Document 1 describes a method for producing a composite active material by coating a positive electrode active material with an oxide solid electrolyte and further coating it with a sulfide solid electrolyte.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] In the prior art, it has been desired to further reduce the resistance of a battery.

[0005] The present disclosure provides a positive electrode active material, a coating layer that coats at least a part of the surface of the positive electrode active material, and a coated active material comprising the same, where the coating layer includes a first coating layer and a second coating layer, the first coating layer is located outside the second coating layer, and the rate of change of the specific surface area from the specific surface area of the positive electrode active material coated with the second coating layer to the specific surface area of the coated active material is -62.8% or more and +3.79% or less. A coated active material is provided.

[0006] According to the present disclosure, the resistance of a battery can be reduced.

Brief Description of the Drawings

[0007] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a coated active material according to Embodiment 1. [Figure 2] Figure 2 is a cross-sectional view showing the schematic configuration of the cathode material in Embodiment 2. [Figure 3] Figure 3 is a cross-sectional view showing the schematic configuration of the battery in Embodiment 3. [Modes for carrying out the invention]

[0008] (Knowledge that forms the basis of this disclosure) For example, when a positive electrode active material is in contact with a sulfide solid electrolyte, the sulfide solid electrolyte may oxidize and decompose during battery charging. To solve this problem, the surface of the active material is coated with a material that has excellent oxidation stability, such as an oxide solid electrolyte.

[0009] Here, the inventors noticed that even when the coating material for the active material is the same, there are significant differences in the characteristics of the battery, particularly in the interfacial resistance. Furthermore, the inventors discovered that this difference is related to the rate of change in the specific surface area of ​​the active material before and after coating with the coating material, which led to the present disclosure.

[0010] (Summary of one aspect of this disclosure) The coating active material relating to the first aspect of this disclosure is Positive electrode active material and, A coating layer covering at least a portion of the surface of the positive electrode active material, A coating active material comprising, The coating layer includes a first coating layer and a second coating layer, The first coating layer is located outside the second coating layer, The rate of change in specific surface area from the specific surface area of ​​the positive electrode active material covered by the second coating layer to the specific surface area of ​​the coating active material is -62.8% or more and +3.79% or less.

[0011] According to the coating active material of the first embodiment, the resistance of the battery can be reduced.

[0012] In a second aspect of this disclosure, for example, in the coating active material according to the first aspect, the rate of change may be -56.6% or more and 0% or less. Such a configuration further enhances the effect of suppressing the interfacial resistance of the battery.

[0013] In a third aspect of this disclosure, for example, in the coating active material according to the first aspect, the rate of change may be -24.0% or more and -13.0% or less. Such a configuration further enhances the effect of suppressing the interfacial resistance of the battery.

[0014] In a fourth aspect of this disclosure, for example, in a coating active material according to any one of the first to third aspects, the first coating layer may contain a first solid electrolyte, the first solid electrolyte may contain Li, M, and X, where M is at least one selected from the group consisting of metal elements other than Li and metalloid elements, and X is at least one selected from the group consisting of F, Cl, Br, and I. Such materials exhibit excellent ionic conductivity and oxidation resistance.

[0015] In a fifth aspect of this disclosure, for example, in the coating active material according to the fourth aspect, M may contain yttrium. When M contains Y, the first solid electrolyte exhibits high ionic conductivity.

[0016] In a sixth aspect of this disclosure, for example, in a coating active material according to any one of the first to fifth aspects, the first coating layer may contain a first solid electrolyte, the first solid electrolyte may be represented by the following compositional formula (1), where α, β, and γ may each be independently greater than 0. When a halogen solid electrolyte represented by compositional formula (1) is used in a battery, the output characteristics of the battery can be improved. Li α M β X γ ...Equation (1)

[0017] In a seventh aspect of this disclosure, for example, in a coating active material according to any one of the first to sixth aspects, the second coating layer may include a base material, and the base material may include a lithium-containing oxide. By using a lithium-containing oxide as the base material, the charge and discharge efficiency of the battery can be improved.

[0018] In the eighth aspect of this disclosure, for example, in a coating active material according to any one of the first to seventh aspects, the second coating layer may include a base material, and the base material may include an oxide solid electrolyte having lithium ion conductivity. By using an oxide solid electrolyte as the base material, the charge and discharge efficiency of the battery can be improved.

[0019] In the ninth aspect of this disclosure, for example, in the coating active material according to any one of the first to eighth aspects, the second coating layer may include a base material, and the base material may include lithium niobate. Such a configuration can improve the charge and discharge efficiency of the battery.

[0020] The cathode material relating to the tenth aspect of this disclosure is A coating active material relating to any one of the first to ninth embodiments, Second solid electrolyte, It is equipped with.

[0021] According to the positive electrode material of the tenth embodiment, the resistance of the battery can be reduced.

[0022] In the eleventh aspect of this disclosure, for example, in the cathode material according to the tenth aspect, the second solid electrolyte may contain Li and S. Sulfide solid electrolytes have high ionic conductivity and can improve the charge and discharge efficiency of the battery. On the other hand, sulfide solid electrolytes may have poor oxidation resistance. When a sulfide solid electrolyte is included in the battery as the second solid electrolyte, a high effect can be obtained by applying the technology of this disclosure.

[0023] A cathode according to a twelfth aspect of this disclosure comprises a cathode material according to the tenth or eleventh aspect.

[0024] According to the positive electrode of the twelfth embodiment, the resistance of the battery can be reduced.

[0025] Battery relating to the 13th aspect of this disclosure The positive electrode of the 12th embodiment, The negative electrode and, An electrolyte layer disposed between the positive electrode and the negative electrode, It is equipped with.

[0026] According to the 13th aspect, a battery with suppressed interfacial resistance can be provided.

[0027] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0028] (Embodiment 1) Figure 1 is a cross-sectional view showing the schematic configuration of a coated active material according to Embodiment 1. The coated active material 110 includes a positive electrode active material 101 and a coating layer 104. The shape of the coated active material 110 is, for example, particulate. The coating layer 104 covers at least a portion of the surface of the positive electrode active material 101. The coating layer 104 may cover only a portion of the surface of the positive electrode active material 101, or it may uniformly cover the surface of the positive electrode active material 101. The coating layer 104 has a first coating layer 102 and a second coating layer 103. The first coating layer 102 is located outside the second coating layer 103. The rate of change in specific surface area from the specific surface area of ​​the positive electrode active material 101 covered by the second coating layer 103 to the specific surface area of ​​the coated active material 110 is -62.8% or more and +3.79% or less. The coating layer 104 suppresses direct contact between the positive electrode active material 101 and the solid electrolyte at the battery electrodes, thereby suppressing side reactions of the solid electrolyte. As a result, the interfacial resistance of the battery may be reduced. Here, "the rate of change in specific surface area from the specific surface area of ​​the positive electrode active material 101 coated by the second coating layer 103 to the specific surface area of ​​the coating active material 110" refers, for example, to "the rate of change in specific surface area from the specific surface area of ​​the positive electrode active material 101 coated only by the second coating layer 103 to the specific surface area of ​​the coating active material 110." "Coated only by the second coating layer 103" refers to the state in which the positive electrode active material 101 is coated by the second coating layer 103, excluding the first coating layer 102. Also, when the rate of change in specific surface area is 0%, uncoated positive electrode active material 101 is not included. Here, uncoated positive electrode active material 101 refers to positive electrode active material 101 that is not coated by the coating layer 104.

[0029] The fact that the rate of change of the specific surface area falls within the above range means that the positive electrode active material 101 having the second coating layer 103 is uniformly coated by the first coating layer 102. A uniform coating with minimal unevenness is advantageous for reducing the interfacial resistance of the battery. The rate of change of the specific surface area may be between -56.6% and 0%. When the rate of change of the specific surface area falls within this range, the effect of suppressing the interfacial resistance of the battery is further enhanced. Note that the rate of change of the specific surface area may be less than 0%.

[0030] The rate of change of specific surface area may be -56.6% or more and 0% or less, or -24.0% or more and -13.0% or less. When the rate of change of specific surface area falls within this range, the effect of suppressing the interfacial resistance of the battery is further enhanced. The rate of change of specific surface area may also be -56.6% or more and -18.8% or less.

[0031] The rate of change of specific surface area can be calculated based on the specific surface area of ​​the positive electrode active material 101 having the second coating layer 103. That is, the specific surface area of ​​the positive electrode active material 101 having the second coating layer 103 is defined as S0. The specific surface area of ​​the coating active material 110 is defined as S. The rate of change of specific surface area is obtained by the following formula (i). When the rate of change is a negative value, it means that the specific surface area has decreased. When the rate of change is a positive value, it means that the specific surface area has increased.

[0032] (Percentage change in specific surface area) = 100 × (S - S0) / S0 (Unit: %) ... (i)

[0033] In this specification, the specific surface area of ​​the coated active material 110 refers to the specific surface area of ​​the particle group of the coated active material 110. Similarly, the specific surface area of ​​the positive electrode active material 101 coated with the second coating layer 103 refers to the specific surface area of ​​the particle group of the positive electrode active material 101 coated with the second coating layer 103.

[0034] The specific surface area can be measured by the following method. First, the adsorption isotherm is measured using a gas adsorption measuring device. The specific surface area (unit: m²) is then calculated from the adsorption isotherm using the BET (Brunauer-Emmett-Teller) analysis method. 2 Calculate the value (per g).

[0035] The specific surface area of ​​the positive electrode active material 101 coated with the second coating layer 103 can be measured by selectively removing the first coating layer 102 from the coated active material 110 using an inorganic solvent or organic solvent. For example, if the first solid electrolyte contained in the first coating layer 102 is a solid electrolyte containing a halogen, the first coating layer 102 can be selectively removed by washing the coated active material 110 with a solvent such as water or ethanol.

[0036] <Cathode active material> The positive electrode active material 101 includes a material having the property of intercalating and releasing metal ions (e.g., lithium ions). Examples of positive electrode active materials 101 include lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using a lithium-containing transition metal oxide as the positive electrode active material 101 can reduce the manufacturing cost of the battery and increase the average discharge voltage. Examples of lithium-containing transition metal oxides include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2.

[0037] The positive electrode active material 101 has, for example, a particle shape. The particle shape of the positive electrode active material 101 is not particularly limited. The particle shape of the positive electrode active material 101 may be spherical, ellipsoidal, flaky, or fibrous.

[0038] <First coating layer> The first coating layer 102 is a layer containing a first solid electrolyte. In the first coating layer 102, the first solid electrolyte contains Li, M, and X. M is at least one selected from the group consisting of metal elements and metalloid elements other than Li. X is at least one selected from the group consisting of F, Cl, Br, and I. Such materials have excellent ionic conductivity and oxidation resistance. Therefore, the coating active material 110 having the first coating layer 102 containing the first solid electrolyte reduces the interfacial resistance of the battery and improves the charge and discharge efficiency of the battery.

[0039] "Metallic elements" include B, Si, Ge, As, Sb, and Te.

[0040] "Metallic elements" include all elements in groups 1 through 12 of the periodic table except hydrogen, as well as all elements in groups 13 through 16 except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metallic elements are a group of elements that can become cations when forming halogen compounds and inorganic compounds.

[0041] The first solid electrolyte is a halogen-containing solid electrolyte, a so-called halide solid electrolyte. Halide solid electrolytes have excellent oxidation resistance. Therefore, by coating the positive electrode active material 101 with the first solid electrolyte, oxidation of other materials such as the solid electrolyte contained in the positive electrode can be suppressed. This makes it possible to reduce the interfacial resistance of a battery using the coating active material 110.

[0042] The first solid electrolyte has ionic conductivity. This ionic conductivity is typically lithium ion conductivity. The first coating layer 102 may contain the first solid electrolyte as its main component, or it may contain only the first solid electrolyte. "Main component" means the component that is present in the largest amount by mass. "Containing only the first solid electrolyte" means that, excluding unavoidable impurities, no materials other than the first solid electrolyte have been intentionally added. For example, raw materials for the first solid electrolyte and by-products generated during the production of the first solid electrolyte are included in unavoidable impurities. The ratio of the mass of unavoidable impurities to the total mass of the first coating layer 102 may be 5% or less, 3% or less, 1% or less, or 0.5% or less.

[0043] A halide solid electrolyte as the first solid electrolyte can be represented, for example, by the following compositional formula (1). In compositional formula (1), α, β, and γ are each independently a value greater than 0. γ may be 4 or 6.

[0044] Li α M β X γ ...Equation (1)

[0045] The halide solid electrolyte represented by compositional formula (1) has higher ionic conductivity compared to halide solid electrolytes such as LiI, which consists only of Li and halogen elements. Therefore, when the halide solid electrolyte represented by compositional formula (1) is used in a battery, the charge and discharge efficiency of the battery can be improved.

[0046] M may contain Y (= yttrium). That is, the halide solid electrolyte may contain Y as a metal element. When M contains Y, the halide solid electrolyte exhibits high ionic conductivity.

[0047] The halide solid electrolyte containing Y is represented, for example, by the following composition formula (2).

[0048] Li a Me b Y c X6 ··· Formula (2)

[0049] The composition formula (2) satisfies a + mb + 3c = 6 and c > 0. In the composition formula (2), Me contains at least one selected from the group consisting of metal elements and metalloid elements other than Li and Y. m is the valence of Me. When Me contains a plurality of elements, mb is equal to the sum of the values obtained by multiplying the composition ratio of each element by the valence of the element. For example, when Me contains element Me1 and element Me2, the composition ratio of element Me1 is b1, the valence of element Me1 is m1, the composition ratio of element Me2 is b2, and the valence of element Me2 is m2, mb = m1b1 + m2b2 holds. In the composition formula (2), X is at least one selected from the group consisting of F, Cl, Br, and I.

[0050] Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, Gd, and Nb.

[0051] The halide solid electrolyte may be the following material. The following halide solid electrolyte exhibits high ionic conductivity. Therefore, the ionic conductivity of the positive electrode material 10 is also improved. Thereby, the charge-discharge efficiency of the battery using the positive electrode material 10 is also improved.

[0052] The halide solid electrolyte may be a material represented by the following compositional formula (A1). Here, in the compositional formula (A1), X is at least one selected from the group consisting of Cl, Br, and I. In the compositional formula (A1), 0 < d < 2 is satisfied.

[0053] Li 6-3d Y d X6 ··· Formula (A1)

[0054] The halide solid electrolyte may be a material represented by the following compositional formula (A2). Here, in the compositional formula (A2), X is at least one selected from the group consisting of Cl, Br, and I.

[0055] Li3YX6 ··· Formula (A2)

[0056] The halide solid electrolyte may be a material represented by the following compositional formula (A3). Here, in the compositional formula (A3), 0 < δ ≤ 0.15 is satisfied.

[0057] Li 3-3δ Y 1+δ Cl6 ··· Formula (A3)

[0058] The halide solid electrolyte may be a material represented by the following compositional formula (A4). Here, in the compositional formula (A4), 0 < δ ≤ 0.25 is satisfied.

[0059] Li 3-3δ Y 1+δ Br6 ··· Formula (A4)

[0060] The halide solid electrolyte may be a material represented by the following compositional formula (A5). Here, in the compositional formula (A5), Me is at least one selected from the group consisting of Mg, Ca, Sr, Ba, and Zn. In the compositional formula (A5), -1 < δ < 2, 0 < a < 3, 0 < (3 - 3δ + a), 0 < (1 + δ - a), 0 ≤ x ≤ 6, 0 ≤ y ≤ 6, and (x + y) ≤ 6 are satisfied.

[0061] Li 3-3δ+a Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A5)

[0062] The halide solid electrolyte may be a material represented by the following compositional formula (A6). Here, in compositional formula (A6), Me is at least one selected from the group consisting of Al, Sc, Ga, and Bi. In 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.

[0063] Li 3-3δ Y 1+δ-a Me a Cl 6-x-y Br x I y ··· Formula (A6)

[0064] The halide solid electrolyte may be a material represented by the following compositional formula (A7). Here, in compositional formula (A7), Me is at least one selected from the group consisting of Zr, Hf, and Ti. In 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.

[0065] Li 3-3δ-a Y 1+δ-a Me a Cl 6-x-y Br x I<00OO034>··· Formula (A7)

[0066] The halide solid electrolyte may be a material represented by the following compositional formula (A8). Here, in compositional formula (A8), Me is at least one selected from the group consisting of Ta and Nb. In compositional formula (A8), -1 < δ < 1, 0 < a < 1.2, 0 < (3 - 3δ - 2a), 0 < (1 + δ - a), 0 ≦ x ≦ 6,

[0067] Li 3-3δ-2a Y 1+δ-a Me a Cl 6-x-y Br x I y ...Formula (A8)

[0068] Specifically, the following can be used as the halide solid electrolyte: Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, Li3(Al,Ga,In)X6, etc. Here, X is at least one selected from the group consisting of F, Cl, Br, and I.

[0069] In this disclosure, when an element in a formula is represented as "(Al,Ga,In)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(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.

[0070] A typical composition of Li3YX6 is, for example, Li3YBr2Cl4. The halide solid electrolyte may also be Li3YBr2Cl4.

[0071] Halide solid electrolytes include Li 2.7 Y 1.1 Cl6, Li3YBr6, or Li 2.5 Y 0.5 Zr 0.5 Cl6 is also possible.

[0072] Halide solid electrolytes may also be solid electrolytes that do not contain sulfur. In this case, the generation of sulfur-containing gases such as hydrogen sulfide gas from the solid electrolyte can be avoided. A sulfur-free solid electrolyte means a solid electrolyte represented by a composition formula that does not contain the element sulfur. Therefore, solid electrolytes that contain a very small amount of sulfur, for example, solid electrolytes with a sulfur content of 0.1% by mass or less, belong to the category of sulfur-free solid electrolytes. Halide solid electrolytes may also contain oxygen as anion other than the halogen element.

[0073] The shape of the halide solid electrolyte is not particularly limited and may be, for example, needle-shaped, spherical, or ellipsoidal. For example, the shape of the halide solid electrolyte may be particulate.

[0074] Halide solid electrolytes can be manufactured by the following methods. Here, we will illustrate a method for manufacturing a halide solid electrolyte represented by composition formula (1).

[0075] Depending on the desired composition, raw material powders for the halide are prepared. The halide may be a compound consisting of two elements, including a halogen element. For example, to produce Li3YCl6, LiCl and YCl3 are prepared as raw material powders in a molar ratio of 3:1. By appropriately selecting the type of raw material powder, the elemental species of "M" and "X" in compositional formula (1) can be determined. By adjusting the type of raw material powder, the mixing ratio of the raw material powders, and the synthesis process, the values ​​of "α", "β", and "γ" in compositional formula (1) can be adjusted.

[0076] After mixing and grinding the raw material powders, the powders are reacted with each other using a mechanochemical milling method. Alternatively, after mixing and grinding the raw material powders, they may be calcined in a vacuum or an inert atmosphere. Calcination is carried out, for example, at a temperature of 100°C to 550°C for one hour or more. Through these steps, a halogenated solid electrolyte is obtained.

[0077] The composition of the crystalline phase (i.e., the crystalline structure) of a halide solid electrolyte can be adjusted and determined by the reaction method and conditions of the raw material powders.

[0078] <Second coating layer> The second coating layer 104 is a layer containing a base material. The second coating layer 103 is located between the first coating layer 102 and the positive electrode active material 101. In the coated active material 110, the second coating layer 103 is in direct contact with the positive electrode active material 101. The second coating layer 103 may contain a material with low electronic conductivity as a base material, such as an oxide material or an oxide solid electrolyte.

[0079] Examples of oxide materials include SiO2, Al2O3, TiO2, B2O3, Nb2O5, WO3, and ZrO2. Examples of oxide solid electrolytes include Li-Nb-O compounds such as LiNbO3, Li-BO compounds such as LiBO2 and Li3BO3, Li-Al-O compounds such as LiAlO2, Li-Si-O compounds such as Li4SiO4, Li2SO4, and Li4Ti5O 12 Examples include Li-Ti-O compounds such as Li2ZrO3, Li-ZrO compounds such as Li2MoO3, Li-Mo-O compounds such as LiV2O5, and Li-WO compounds such as Li2WO4. The substrate material may be one of these selected materials, or a mixture of two or more.

[0080] The base material may be a lithium-containing oxide. Lithium-containing oxides have excellent high potential stability. By using a lithium-containing oxide as the base material, the charge and discharge efficiency of the battery can be improved.

[0081] The base material may be a solid electrolyte having lithium-ion conductivity. Typically, the base material is an oxide solid electrolyte having lithium-ion conductivity. Oxide solid electrolytes have high ionic conductivity and excellent high potential stability. By using an oxide solid electrolyte as the base material, the charge and discharge efficiency of the battery can be improved.

[0082] The base material may be a material containing Nb. Typically, the base material contains lithium niobate (LiNbO3). With such a configuration, the charge and discharge efficiency of the battery can be improved. It is also possible to use the materials described above as the oxide solid electrolyte, which is the base material.

[0083] In one example, the ionic conductivity of the halide solid electrolyte contained in the first coating layer 102 is higher than that of the base material contained in the second coating layer 103. With such a configuration, oxidation of other materials used in the positive electrode of the battery can be further suppressed without sacrificing ionic conductivity.

[0084] The thickness of the first coating layer 102 is, for example, 1 nm or more and 500 nm or less. The thickness of the second coating layer 103 is, for example, 1 nm or more and 100 nm or less. If the thicknesses of the first coating layer 102 and the second coating layer 103 are appropriately adjusted, contact between the positive electrode active material 101 and the second solid electrolyte can be sufficiently suppressed. The thickness of each layer can be determined by thinning the coating active material 110 using a method such as ion milling and observing the cross-section of the coating active material 110 with a transmission electron microscope. The average value of the thickness measured at any multiple locations (e.g., 5 points) can be considered as the thickness of each layer.

[0085] <Method for producing coated active material> The coated active material 110 can be manufactured by the following method.

[0086] First, a second coating layer 103 is formed on the surface of the positive electrode active material 101. The method for forming the second coating layer 103 is not particularly limited. Examples of methods for forming the second coating layer 103 include liquid-phase coating and gas-phase coating.

[0087] For example, in the liquid-phase coating method, a precursor solution of the substrate material is applied to the surface of the positive electrode active material 101. When forming a second coating layer 103 containing LiNbO3, the precursor solution may be a mixed solution (sol solution) of a solvent, lithium alkoxide, and niobalkoxide. Examples of lithium alkoxides include lithium ethoxide. Examples of niobalkoxides include niobethoxide. The solvent is, for example, an alcohol such as ethanol. The amounts of lithium alkoxide and niobalkoxide are adjusted according to the target composition of the second coating layer 103. Water may be added to the precursor solution as needed. The precursor solution may be acidic or alkaline.

[0088] The method for applying the precursor solution to the surface of the positive electrode active material 101 is not particularly limited. For example, the precursor solution can be applied to the surface of the positive electrode active material 101 using a rolling fluid granulation coating apparatus. With the rolling fluid granulation coating apparatus, the precursor solution can be sprayed onto the positive electrode active material 101 while rolling and flowing the positive electrode active material 101, thereby applying the precursor solution to the surface of the positive electrode active material 101. This forms a precursor film on the surface of the positive electrode active material 101. Subsequently, the positive electrode active material 101 coated with the precursor film is heat-treated. The heat treatment promotes gelation of the precursor film, forming a second coating layer 103.

[0089] Examples of vapor phase coating methods include pulsed laser deposition (PLD), vacuum deposition, sputtering, thermochemical vapor deposition (CVD), and plasma chemical vapor deposition. For example, in the PLD method, a high-energy pulsed laser (e.g., a KrF excimer laser, wavelength: 248 nm) is irradiated onto an ion-conducting material target, and the sublimated ion-conducting material is deposited on the surface of the positive electrode active material 101. When forming a second coating layer 103 of LiNbO3, high-density sintered LiNbO3 is used as the target.

[0090] However, the method for forming the second coating layer 103 is not limited to the above. The second coating layer 103 may be formed by various methods such as spraying, spray dry coating, electrodeposition, immersion, and mechanical mixing using a disperser.

[0091] After the formation of the second coating layer 103, the first coating layer 102 is formed by the following method.

[0092] A mixture is obtained by mixing the powder of the positive electrode active material 101 having a second coating layer 103 and the powder of the first solid electrolyte in an appropriate ratio. The mixture is then milled to impart mechanical energy to it. A mixing device such as a ball mill can be used for the milling process. To suppress oxidation of the materials, the milling process may be carried out in a dry and inert atmosphere.

[0093] The coating active material 110 may be manufactured by a dry particle compounding method. The dry particle compounding method involves applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the positive electrode active material 101 and the first solid electrolyte. The positive electrode active material 101 having the second coating layer 103 and the first solid electrolyte are mixed in an appropriate ratio.

[0094] The apparatus used in the production of the coated active material 110 is not particularly limited and may be any apparatus capable of applying impact, compression, and shear mechanical energy to a mixture of the positive electrode active material 101 having a second coating layer 103 and the first solid electrolyte. Examples of apparatus capable of applying mechanical energy include ball mills, compression and shear processing apparatuses (particle compounding apparatuses) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation) and "Nobilta" (manufactured by Hosokawa Micron Corporation).

[0095] "Mechanofusion" is a particle compounding device that uses a dry mechanical compounding technology, which involves applying strong mechanical energy to multiple different raw material powders. In mechanofusion, mechanical energy in the form of compression, shear, and friction is applied to the raw material powders fed between a rotating container and a press head. This causes the compounding of particles.

[0096] "Nobilta" is a particle compounding device that uses dry mechanical compounding technology, an advanced particle compounding technology, to compound nanoparticles as raw materials. Nobilta manufactures composite particles by applying mechanical energy such as impact, compression, and shear to multiple types of raw material powders.

[0097] In "Nobilta," a rotor positioned within a horizontal cylindrical mixing container, with a predetermined gap between it and the inner wall of the container, rotates at high speed, forcing the raw material powder through the gap multiple times. This applies impact, compression, and shear forces to the mixture, enabling the creation of composite particles of a positive electrode active material 101 having a second coating layer 103 and a first solid electrolyte. By adjusting conditions such as the rotor's rotation speed, processing time, and input amount, the thickness of the first coating layer 102, the coverage rate of the positive electrode active material 101 by the first solid electrolyte, and the specific surface area of ​​the coating active material 110 can be controlled.

[0098] However, processing using the above-mentioned apparatus is not mandatory. The coating active material 110 may be manufactured by mixing the positive electrode active material 101 having the second coating layer 103 with the first solid electrolyte using a mortar and pestle, mixer, or the like. The first solid electrolyte may also be deposited on the surface of the positive electrode active material 101 having the second coating layer 103 by various methods such as spraying, spray dry coating, electrodeposition, immersion, or mechanical mixing using a disperser.

[0099] (Embodiment 2) Figure 2 is a cross-sectional view showing the schematic configuration of the positive electrode material according to Embodiment 2. The positive electrode material 10 has a coating active material 110 and a second solid electrolyte 105. The second solid electrolyte 105 is in contact with the positive electrode active material 101 via a coating layer 104. The configuration of the coating active material 110 is as described in Embodiment 1. The positive electrode material 10 can reduce the interfacial resistance of the battery.

[0100] In the positive electrode material 10, the second solid electrolyte 105 and the coating active material 110 may be in contact with each other. In this case, the first solid electrolyte and the second solid electrolyte 105 are in contact with each other. The positive electrode material 10 may contain a plurality of particles of the second solid electrolyte 105 and a plurality of particles of the coating active material 110.

[0101] In the positive electrode material 10, the ratio "v1:100-v1" of the volume of the positive electrode active material 101 to the volume of the solid electrolyte may satisfy 30 ≤ v1 ≤ 95. If 30 ≤ v1 is satisfied, the energy density of the battery is sufficiently ensured. If v1 ≤ 95 is satisfied, the battery can operate at high power. "Volume of solid electrolyte" is the total volume of the first solid electrolyte and the second solid electrolyte 105.

[0102] The volume ratio can be calculated from the amount of material used, or it can be calculated using the method described below. Specifically, a cross-section of the positive electrode using the positive electrode material 10 is observed with a scanning electron microscope (SEM-EDX) to obtain a two-dimensional mapping image of the elements. The measurement conditions for the scanning electron microscope to obtain the two-dimensional mapping image are, for example, a magnification of 1000x to 3000x and an acceleration voltage of 5kV. The two-dimensional mapping image is obtained with a resolution of 1280 × 960. By analyzing the two-dimensional mapping image of the elements, the volume of the positive electrode active material 101, the volume of the first solid electrolyte, and the volume of the second solid electrolyte 105 can be determined from the number of pixels of the elements contained in the positive electrode active material 101, the first coating layer 102, and the second solid electrolyte 105, respectively.

[0103] The median diameter of the coating active material 110 may be 0.1 μm or more and 100 μm or less. When the median diameter of the coating active material 110 is 0.1 μm or more, the coating active material 110 and the second solid electrolyte 105 can form a good dispersion state in the positive electrode material 10. As a result, the charge and discharge characteristics of the battery are improved. When the median diameter of the coating active material 110 is 100 μm or less, the diffusion rate of lithium inside the coating active material 110 is sufficiently ensured. Therefore, the battery can operate at high power. Preferably, the median diameter of the coating active material 110 may be 2 μm or more and 8 μm or less.

[0104] The median diameter of the coating active material 110 may be larger than the median diameter of the second solid electrolyte 105. This allows the coating active material 110 and the second solid electrolyte 105 to form a good dispersion state.

[0105] In this specification, “median diameter” means the particle size at which 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 analyzer or an image analyzer.

[0106] <Second solid electrolyte> The second solid electrolyte 105 may contain at least one selected from the group consisting of halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes.

[0107] Examples of the halide solid electrolyte include the materials previously described as the first solid electrolyte. That is, the composition of the second solid electrolyte 105 may be the same as or different from that of the first solid electrolyte.

[0108] Oxide solid electrolytes are solid electrolytes containing oxygen. Oxide solid electrolytes may further contain anions other than oxygen, such as sulfur and halogen elements.

[0109] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitutions, and (LaLi)TiO3-based perovskite-type solid electrolytes, Li 14 ZnGe4O 16 , LISICON-type solid electrolytes represented by Li4SiO4, LiGeO4 and their elemental substitutions, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those represented by their elemental substitutions, Li3PO4 and its N-substituted derivatives, and Li-BO compounds such as LiBO2 and Li3BO3, can be used as base materials to which materials such as Li2SO4 and Li2CO3 are added, such as glass or glass ceramics.

[0110] As a polymeric solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may have an ethylene oxide structure. Polymeric compounds having an ethylene oxide structure can contain a large amount of lithium salt. Therefore, the ionic conductivity can be further increased. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used.

[0111] Examples of complex hydride solid electrolytes that can be used include LiBH4-LiI and LiBH4-P2S5.

[0112] The second solid electrolyte 105 may contain Li and S. In other words, the second solid electrolyte 105 may contain a sulfide solid electrolyte. Sulfide solid electrolytes have high ionic conductivity and can improve the charge and discharge efficiency of the battery. On the other hand, sulfide solid electrolytes may have poor oxidation resistance. When a sulfide solid electrolyte is included in the battery as the second solid electrolyte 105, a high level of effectiveness can be obtained by applying the technology of this disclosure.

[0113] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These can be used. These include LiX, Li2O, and MO q Li p MO q The following may be added. Here, X in "LiX" is at least one selected from the group consisting of F, Cl, Br, and I.q " and "Li p MO q In ", element M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q In this example, p and q are independent natural numbers.

[0114] The second solid electrolyte 105 may contain two or more of the materials listed as solid electrolytes. For example, the second solid electrolyte 105 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0115] The second solid electrolyte 105 may have a lithium ion conductivity higher than that of the first solid electrolyte.

[0116] The second solid electrolyte 105 may contain unavoidable impurities such as starting materials, by-products, and decomposition products used in the synthesis of the solid electrolyte. This also applies to the first solid electrolyte.

[0117] <Other materials> The positive electrode material 10 may contain a binder for the purpose of improving the adhesion between particles. The binder is used to improve the bonding properties of the materials constituting the positive electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polycarbonate, polyethersulfone, polyetherketone, polyetheretherketone, polyphenylene sulfide, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethylcellulose, and ethylcellulose. Furthermore, copolymers of two or more monomers selected from the group consisting of tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, butadiene, styrene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid ester, acrylic acid, and hexadiene may also be used. One of these may be used alone, or two or more may be used in combination.

[0118] For the reason of excellent binding properties, the binder may be an elastomer. An elastomer is a polymer with rubber elasticity. The elastomer used as a binder may be a thermoplastic elastomer or a thermosetting elastomer. The binder may contain a thermoplastic elastomer. Examples of thermoplastic elastomers include styrene-ethylene-butylene-styrene (SEBS), styrene-ethylene-propylene-styrene (SEPS), styrene-ethylene-ethylene-propylene-styrene (SEEPS), butylene rubber (BR), isoprene rubber (IR), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), styrene-butylene rubber (SBR), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), hydrogenated isoprene rubber (HIR), hydrogenated butyl rubber (HIIR), hydrogenated nitrile rubber (HNBR), hydrogenated styrene-butylene rubber (HSBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). One of these may be used alone, or two or more may be used in combination.

[0119] The coating layer 104 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives include graphites such as natural or artificial graphite, carbon blacks such as acetylene black and Ketjenblack, conductive fibers such as carbon fibers or metal fibers, 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.

[0120] The positive electrode material 10 may contain the above-mentioned conductive additive for the purpose of enhancing electronic conductivity.

[0121] <Manufacturing method for positive electrode material> The positive electrode material 10 is obtained by mixing the coating active material 110 and the second solid electrolyte 105. The method of mixing the coating active material 110 and the second solid electrolyte 105 is not particularly limited. The coating active material 110 and the second solid electrolyte 105 may be mixed using an instrument such as a mortar and pestle, or they may be mixed using a mixing device such as a ball mill.

[0122] (Embodiment 3) Figure 3 is a cross-sectional view showing the schematic configuration of a battery according to Embodiment 3. The battery 200 includes a positive electrode 201, a separator layer 202, and a negative electrode 203. The separator layer 202 is disposed between the positive electrode 201 and the negative electrode 203. The positive electrode 201 includes the positive electrode material 10 described in Embodiment 2. With this configuration, the interfacial resistance of the battery 200 can be reduced.

[0123] The thickness of the positive electrode 201 and the negative electrode 203 may be 10 μm or more and 500 μm or less. If the thickness of the positive electrode 201 and the negative electrode 203 is 10 μm or more, a sufficient energy density of the battery can be ensured. If the thickness of the positive electrode 201 and the negative electrode 203 is 500 μm or less, high-power operation of the battery 200 can be achieved.

[0124] The separator layer 202 is a layer containing an electrolyte material. The separator layer 202 may contain at least one solid electrolyte selected from the group consisting of sulfide solid electrolytes, oxide solid electrolytes, halide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes. Details of each solid electrolyte are as described in Embodiment 1.

[0125] The negative electrode 203 includes a material as the negative electrode active material that has the property of intercalating and releasing metal ions (e.g., lithium ions).

[0126] As the negative electrode active material, metal materials, carbon materials, oxides, nitrides, tin compounds, silicon compounds, etc., can be used. The metal material may be a pure metal, or it may be an alloy. Examples of metal materials include lithium metal and lithium alloys. Examples of carbon materials include natural graphite, coke, carbon in the process of graphitization, carbon fibers, spheroidal carbon, artificial graphite, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds can be suitably used.

[0127] The median diameter of the negative electrode active material particles may be 0.1 μm or more and 100 μm or less.

[0128] The negative electrode 203 may contain other materials such as a solid electrolyte. The materials described in Embodiment 1 can be used as the solid electrolyte. [Examples]

[0129] The details of this disclosure will be explained below using examples and comparative examples. However, the electrodes and batteries of this disclosure are not limited to the following examples.

[0130] <Example 1> [Preparation of the first solid electrolyte] In an argon glove box with a dew point of -60°C or lower, the raw material powders YCl3, LiCl, and LiBr were weighed in a molar ratio of YCl3:LiCl:LiBr = 1:1:2. These were ground in a mortar and mixed to obtain a mixture. The mixture was calcined in an electric furnace at 520°C for 2 hours. This yielded the halide solid electrolyte Li3YBr2Cl4 (hereinafter referred to as "LYBC"). p-chlorotoluene was added to the LYBC, and the LYBC was ground using a wet pulverizer and disperser, and then dried. This yielded LYBC powder (median diameter D50 = 0.4 μm) as the first solid electrolyte.

[0131] [Preparation of coated active material] A coating solution was prepared by dissolving 5.95 g of ethoxylithium (manufactured by Kojun Chemical Co., Ltd.) and 36.43 g of pentaethoxyniobium (manufactured by Kojun Chemical Co., Ltd.) in 500 mL of super-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) in an argon glove box.

[0132] As the positive electrode active material, Li(NiCoAl)O2 (hereinafter referred to as NCA) powder was prepared. A rolling fluid granulation coating apparatus (Powrec Co., Ltd., FD-MP-01E) was used to form a LiNbO3 coating layer on the surface of the NCA. The input amount of NCA, the stirring speed, and the flow rate of the coating solution were 1 kg, 400 rpm, and 6.59 g / min, respectively. The input amount of the coating solution was adjusted so that the LiNbO3 film thickness was 10 nm. The input amount of the coating solution was calculated using the specific surface area of ​​the active material and the density of LiNbO3. The series of processes using the rolling fluid granulation coating apparatus were carried out in a dry atmosphere with a dew point of -30°C or lower. After the completion of the process to form the LiNbO3 coating layer, the obtained powder was placed in an alumina crucible and heat-treated under conditions of air atmosphere, 300°C, and 1 hour. The powder after heat treatment was re-ground in an agate mortar. This resulted in obtaining an NCA with a LiNbO3 coating layer. The coating layer was made of lithium niobate (LiNbO3). Hereafter, an NCA with a LiNbO3 coating layer will be referred to as "Nb-NCA".

[0133] Next, a first coating layer made of LYBC was formed on the surface of Nb-NCA. The first coating layer was formed by compression shearing using a particle composite device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, Nb-NCA and LYBC were weighed in a volume ratio of 90:10 and processed under the following conditions: blade clearance: 2 mm, rotation speed: 2800 rpm, and processing time: 60 min. This yielded the coating active material of Example 1.

[0134] [Measurement of specific surface area] The specific surface area of ​​the coated active material was measured under the following conditions. 3 g of the coated active material was placed in a test tube and connected to a specific surface area and pore distribution analyzer (Microtrac-Bel, BELSORP MAX). Pretreatment was performed at 80°C under vacuum for 1 hour. Subsequently, a nitrogen gas adsorption test was conducted at an adsorption temperature of 77 K and an upper limit of 0.99 (P / P0) relative adsorption pressure. Using the analysis software Belmaster 7, the specific surface area was calculated by performing an analysis using the BET method in the linear region of the adsorption isotherm.

[0135] The specific surface area of ​​the coating active material in Example 1 is 0.849 m². 2 The result was / g. The specific surface area of ​​Nb-NCA was also measured using the same method. The specific surface area of ​​Nb-NCA was 0.818 m². 2 The value was / g. In Example 1, the rate of change of specific surface area, which can be obtained from formula (i) explained earlier, was +3.79%.

[0136] <Example 2> The coated active material of Example 2 was obtained in the same manner as in Example 1, except that the rotation speed of the particle compounding apparatus was changed to 4000 rpm. The specific surface area of ​​the coated active material of Example 2 was 0.664 m². 2 The value was / g. In Example 2, the rate of change of specific surface area, which can be obtained from formula (i) explained earlier, was -18.8%.

[0137] <Example 3> The coated active material of Example 3 was obtained in the same manner as in Example 1, except that the rotation speed of the particle compounding apparatus was changed to 5500 rpm and the processing time was changed to 30 minutes. The specific surface area of ​​the coated active material of Example 3 was 0.355 m². 2 The value was / g. In Example 2, the rate of change of specific surface area, which can be obtained from formula (i) explained earlier, was -56.6%.

[0138] <Example 4> The coated active material of Example 4 was obtained in the same manner as in Example 1, except that the rotation speed of the particle compounding apparatus was changed to 7000 rpm and the processing time was changed to 20 minutes. The specific surface area of ​​the coated active material of Example 4 was 0.304 m². 2The value was / g. In Example 4, the rate of change of specific surface area, which can be obtained from formula (i) explained earlier, was -62.8%.

[0139] <Comparative Example 1> Nb-NCA was prepared as the coating active material for Comparative Example 1. No first coating layer was formed.

[0140] [Preparation of sulfide solid electrolytes] In an argon glove box with a dew point of -60°C or lower, the raw material powders, Li2S and P2S5, were weighed in a molar ratio of Li2S:P2S5 = 75:25. These were ground and mixed in a mortar to obtain a mixture. The mixture was then milled using a planetary ball mill (Fritsch, P-7 type) at 510 rpm for 10 hours. This yielded a glassy solid electrolyte. The glassy solid electrolyte was heat-treated in an inert atmosphere at 270°C for 2 hours. This yielded a glass-ceramic solid electrolyte, Li2S-P2S5 (hereinafter referred to as "LPS").

[0141] [Fabrication of cathode materials] In an argon glove box, the coating active material and LPS of Example 1 were weighed so that the volume ratio of Nb-NCA to solid electrolyte was 75:25. These were mixed in an agate mortar to prepare the cathode material of Example 1. In the volume ratio of Nb-NCA to solid electrolyte, "solid electrolyte" refers to the total volume of LYBC and LPS.

[0142] The cathode materials for Examples 2 to 4 and Comparative Example 1 were prepared using the same method as in Example 1.

[0143] [Fabrication of negative electrode materials] In an argon glove box, graphite and LPS were weighed out so that the volume ratio of graphite to LPS was 65:35. These were then mixed in an agate mortar to prepare a negative electrode material common to both the examples and comparative examples.

[0144] [Battery construction] The positive electrode material was weighed to contain 14 mg of Nb-NCA. The negative electrode material, LPS, and positive electrode material were layered in this order inside an insulating outer cylinder. The resulting laminate was pressure-molded at a pressure of 720 MPa. This produced a laminate consisting of a negative electrode, a solid electrolyte layer, and a positive electrode. Next, stainless steel current collectors were placed above and below the laminate. Current collector leads were attached to each current collector. Then, the inside of the outer cylinder was sealed with an insulating ferrule to isolate it from the outside atmosphere. Through these steps, the batteries of the example and comparative example were fabricated. A surface pressure of 150 MPa was applied to the battery by restraining it from above and below with four bolts.

[0145] [Charge / Discharge Test] The battery was placed in a constant temperature bath at 25°C. The battery was charged with a constant current of 147 μA, which corresponds to a rate of 0.05 C (20-hour rate) relative to the battery's theoretical capacity, until the voltage reached 3.7 V. After the current was cut off, the open-circuit voltage was maintained for 30 minutes. Subsequently, the resistance at 3.7 V was measured using the AC impedance method. Next, the battery was charged again at a rate of 0.05 C to 4.2 V, and after the current was cut off, the open-circuit voltage was maintained for 30 minutes. Subsequently, the resistance at 4.2 V was measured using the AC impedance method. The interaxial resistance was read from the value between the high-frequency and low-frequency real-axis intercepts of the Nyquist plot obtained by the AC impedance measurement. The ratio of the interaxial resistance value at 4.2 V to the interaxial resistance value at 3.7 V was calculated as a percentage. The calculated value was considered as the rate of increase in interaxial resistance. The results are shown in Table 1.

[0146] [Table 1]

[0147] <Consideration> As can be seen from the results of the examples and comparative examples, the presence of the first coating layer significantly suppressed the increase in interfacial resistance. As can be seen by comparing the results of Example 1 and Example 2, the specific surface area decreased by uniformly forming the first coating layer, thereby suppressing the increase in interfacial resistance. As can be seen from the results of Examples 2 to 4, when the specific surface area decreased further, the interfacial resistance increased. This is thought to be because, as indicated by the decrease in specific surface area, the surface shape of the coating active material particles approached a perfect sphere, making it difficult to form an interfacial bond between the coating active material and the solid electrolyte within the cathode material.

[0148] In Example 2, the rate of increase in interfacial resistance was the lowest. The rate of change in specific surface area in Example 2 was 18.8%. Therefore, it is reasonable to consider that the desirable range for the rate of change in specific surface area is around 18.8%, for example, in the range of -24.0% or more and -13.0% or less.

[0149] The average particle size of the positive electrode active material used in this embodiment was 5 μm. The specific surface area of ​​a 5 μm perfect sphere is 0.259 m². 2 Given the value per gram, it is unlikely that the rate of change in specific surface area will be less than -68.3%. [Industrial applicability]

[0150] The technology disclosed herein is useful, for example, in all-solid-state lithium secondary batteries. [Explanation of Symbols]

[0151] 10. Positive electrode material 110 Coated active material 101 Cathode active material 102 1st coating layer 103 Second coating layer 104 Covering layer 105 Second solid electrolyte 200 batteries 201 Positive electrode 202 Separator layer 203 Negative electrode

Claims

1. Positive electrode active material and, A coating layer covering at least a portion of the surface of the positive electrode active material, A coating active material comprising, The coating layer includes a first coating layer and a second coating layer, The first coating layer is located outside the second coating layer, The rate of change in specific surface area from the specific surface area of ​​the positive electrode active material coated by the second coating layer to the specific surface area of ​​the coating active material is -62.8% or more and +3.79% or less. The first coating layer contains a first solid electrolyte, The first solid electrolyte comprises Li, M, and X. M is at least one selected from the group consisting of metallic elements and metalloid elements other than Li. X is at least one selected from the group consisting of F, Cl, Br, and I. The aforementioned second coating layer includes a base material, The aforementioned substrate material contains a lithium-containing oxide, Coated active material.

2. The aforementioned rate of change is -56.6% or more and 0% or less. The coated active material according to claim 1.

3. The aforementioned rate of change is -24.0% or more and -13.0% or less. The coated active material according to claim 1.

4. M is a metallic element other than Li. The coated active material according to claim 1.

5. X is at least one selected from the group consisting of F, Cl, and Br. The coated active material according to claim 1.

6. M contains yttrium. The coated active material according to claim 1.

7. The first solid electrolyte is represented by the following compositional formula (1): Li α M β X γ ... Equation (1) Here, α, β, and γ are each independently greater than 0. The coated active material according to claim 1.

8. The lithium-containing oxide includes an oxide solid electrolyte having lithium ion conductivity. The coated active material according to claim 1.

9. The lithium-containing oxide includes lithium niobate. The coated active material according to claim 1.

10. The coating active material according to claim 1, Second solid electrolyte, A positive electrode material possessing the following characteristics.

11. The second solid electrolyte comprises Li and S. The positive electrode material according to claim 10.

12. A positive electrode comprising the positive electrode material according to claim 10 or 11.

13. The positive electrode according to claim 12, The negative electrode and, An electrolyte layer disposed between the positive electrode and the negative electrode, A battery equipped with a battery.

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