Cathode Materials and Batteries

Abstract

A positive pole material 1000 includes a positive pole active material 110, a first solid electrolyte 100, and a covering material which covers at least a portion of the surface of the positive pole active material 110. The first solid electrolyte is represented by formula (1) as follows: LiaMbXc ... formula (1). In composition formula (1), a, b, and c are, independently, positive real numbers, M includes calcium, yttrium, and at least one rare earth element other than yttrium, and X includes at least one element selected from the group consisting of F, Cl, Br, and I.

Description

[Technical Field]

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

[0002] Patent Document 1 discloses an all-solid-state lithium battery including a lithium ion conductive solid electrolyte mainly composed of sulfide and an active material the surface of which is coated with a lithium ion conductive oxide.

[0003] Non-Patent Document 1 describes that in a battery using a sulfide solid electrolyte, an interface layer is formed at the interface between the positive electrode material and the sulfide solid electrolyte after initial charging, causing an increase in the resistance of the battery. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2007 / 004590 [Non-patent literature]

[0005] [Non-Patent Document 1] Am. Chem. Soc. 2010, Vol. 22, 3, 949-956 Summary of the Invention

[0006] The present disclosure provides a positive electrode material that can reduce the resistance of a battery.

[0007] The positive electrode material of the present disclosure comprises: a positive electrode active material; a first solid electrolyte; a coating material that coats at least a portion of the surface of the positive electrode active material; Including, The first solid electrolyte is represented by the following composition formula (1): Li a M b Xc ...Equation (1) where: In the composition formula (1), a, b, and c are each independently a positive real number; M includes calcium, yttrium, and at least one rare earth element other than yttrium; X includes at least one selected from the group consisting of F, Cl, Br and I.

[0008] The present disclosure provides a positive electrode material that can reduce the resistance of a battery. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material 1000 according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the second embodiment. [Figure 3] FIG. 3 is a diagram showing a Nyquist diagram at 3.7 V of the battery in Example 1. [Figure 4] FIG. 4 is a diagram showing an O1s spectrum of the active material used in Example 1 in X-ray photoelectron spectroscopy. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Findings that formed the basis of this disclosure) Patent Document 1 discloses an all-solid-state lithium battery including a lithium ion conductive solid electrolyte mainly composed of sulfide and an active material whose surface is coated with a lithium ion conductive oxide. Patent Document 1 describes that the use of lithium niobate (i.e., LiNbO3) as the lithium ion conductive oxide in particular suppresses the generation of a high resistance layer between the sulfide solid electrolyte and the surface of the positive electrode active material, thereby significantly improving output characteristics.

[0011] Non-Patent Document 1 describes that the formation of a high-resistance layer between a sulfide solid electrolyte and the surface of a positive electrode active material is due to interdiffusion between metal elements contained in the positive electrode active material and elements constituting the solid electrolyte. P and S are cited as constituent elements of the solid electrolyte. That is, the formation of such a high-resistance layer is due to the presence of P or S, which are constituent elements of the solid electrolyte.

[0012] According to the findings of the inventions described in Patent Document 1 and Non-Patent Document 1, in the case of a battery using a sulfide as a solid electrolyte, unless the surface of the active material is coated with a coating material such as a lithium ion conductive oxide to sufficiently suppress contact between the active material and the solid electrolyte, the resistance at the interface between the active material and the solid electrolyte increases, increasing polarization, making it practically difficult to operate as a battery. On the other hand, in the case of a battery using a solid electrolyte that does not contain S, it is possible to operate as a battery even if the surface of the active material is not coated with a lithium ion conductive oxide.

[0013] However, as a result of intensive research, the present inventors have found that even when a solid electrolyte containing neither P nor S is used as the first solid electrolyte contained in the positive electrode material, the resistance of the battery is reduced by coating the surface of the active material with a coating material. The reason for this is not clear, but it is thought that a combination of various factors contributes, such as the voltage resistance of the coating material, the oxidation resistance of the lithium ion conductive solid electrolyte used as the solid electrolyte of the battery, the reactivity between the coating material and the active material, the reactivity between the coating material and the solid electrolyte, and the physical contact between the active material and the solid electrolyte.

[0014] For example, if the lithium ion conductive solid electrolyte used as the solid electrolyte of a battery is a halide, the oxidation of the halogen contained in the solid electrolyte is induced when the potential of the positive electrode increases during the charging process of the battery. This halogen oxidation leads to decomposition of the solid electrolyte. Furthermore, the halogen oxidation reaction generates halogen gas, which creates gaps at the contact interface between the active material and the solid electrolyte, reducing the effective reaction area. This increases the resistance of the battery. The presence of a coating material that coats the surface of the active material between the active material and the solid electrolyte prevents the solid electrolyte from coming into contact with the high-potential active material, which is thought to suppress the oxidation of the halogen. These reasons are thought to contribute to a reduction in battery resistance.

[0015] Halide solid electrolytes are crystals with strong ionic bonds. Therefore, when a solid electrolyte contains a rare earth element with a relatively large ionic radius, particularly Sc and / or lanthanoid elements, the bond distance between the cations (Sc and / or lanthanoid elements) and the anions (halogens) is large. A large bond distance means that the bonding strength between the cations and anions is weak, making the anions (halogens) more likely to be released. Therefore, to reduce the resistance of a battery, it is more effective to suppress the oxidation of the halogens in the solid electrolyte by coating the active material.

[0016] Based on the above findings, the present inventors have arrived at the following positive electrode material of the present disclosure, which is capable of reducing the resistance of a battery.

[0017] (Summary of one aspect of the present disclosure) The positive electrode material according to the first aspect of the present disclosure is a positive electrode active material; a first solid electrolyte; a coating material that coats at least a portion of the surface of the positive electrode active material; Including, The first solid electrolyte is represented by the following composition formula (1): Li a M b X c ...Equation (1) where: In the composition formula (1), a, b, and c are each independently a positive real number; M includes calcium, yttrium, and at least one rare earth element other than yttrium; X includes at least one selected from the group consisting of F, Cl, Br and I.

[0018] In the positive electrode material according to the first embodiment, a coating material is interposed between the positive electrode active material and the first solid electrolyte, which is a halide solid electrolyte. This coating material suppresses electron transfer to and from the halide solid electrolyte, even when the potential of the positive electrode increases during the charging process of the battery. This suppresses the oxidation reaction of halogen in the halide solid electrolyte, thereby suppressing decomposition of the first solid electrolyte and generation of halogen gas. As a result, deterioration of the first solid electrolyte is suppressed, and a decrease in the effective reaction area between the positive electrode active material and the first solid electrolyte is also suppressed. For these reasons, the positive electrode material according to the first embodiment can reduce the resistance of the battery. It can also further improve the ionic conductivity of the first solid electrolyte. This can further improve the charge / discharge efficiency of the battery.

[0019] In the second aspect of the present disclosure, for example, in the positive electrode material according to the first aspect, the coating material may contain O.

[0020] The positive electrode material according to the second embodiment can more effectively reduce the resistance of the battery.

[0021] In a third aspect of the present disclosure, for example, in the positive electrode material according to the first or second aspect, the coating material may contain Li.

[0022] The positive electrode material according to the third aspect can increase the carrier concentration, i.e., the Li concentration, at the interface between the positive electrode active material and the first solid electrolyte, and therefore can more effectively reduce the resistance of the battery.

[0023] 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, the coating material may include at least one selected from the group consisting of lithium phosphate and lithium niobate.

[0024] Lithium phosphate and lithium niobate can increase the lithium ion conductivity of the coating material, which allows the positive electrode material according to the fourth aspect to more effectively reduce the resistance of the battery.

[0025] 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 mass ratio of the coating material to the positive electrode active material 110 may be 0.5 mass % or more and 2.0 mass % or less.

[0026] When the coating amount is adjusted to fall within the above range, lithium ions are smoothly exchanged between the active material and the solid electrolyte, and the resistance of the battery can be reduced more effectively.

[0027] In a sixth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to fifth aspects, the coating material may have a thickness of 2 nm or more and 20 nm or less.

[0028] When the thickness of the coating material is adjusted to fall within the above range, the energy density of the battery can be improved, and the resistance of the battery can be more effectively reduced.

[0029] In a seventh aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to sixth aspects, the M may contain at least one element selected from the group consisting of Gd and Sm.

[0030] The positive electrode material according to the seventh aspect can further improve the ionic conductivity of the first solid electrolyte, thereby further improving the charge / discharge efficiency of the battery.

[0031] 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, X may contain at least one element selected from the group consisting of F, Cl, and Br.

[0032] In a ninth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to eighth aspects, the X may contain at least two elements selected from the group consisting of F, Cl, and Br.

[0033] 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 X may include Cl and Br.

[0034] The above configuration can further improve the ionic conductivity of the first solid electrolyte, thereby enabling the positive electrode material to further improve the charge / discharge efficiency of the battery.

[0035] 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 positive electrode active material may contain a lithium-containing transition metal oxide.

[0036] The positive electrode material according to the eleventh embodiment can improve the energy density of a battery.

[0037] A battery according to a twelfth aspect of the present disclosure comprises: a positive electrode comprising the positive electrode material according to any one of the first to eleventh embodiments; a negative electrode; an electrolyte layer provided between the positive electrode and the negative electrode; Equipped with.

[0038] The battery according to the twelfth aspect can reduce resistance and further improve charge / discharge efficiency.

[0039] In a thirteenth aspect of the present disclosure, for example, in the battery according to the twelfth aspect, the electrolyte layer may include a sulfide solid electrolyte.

[0040] In the battery according to the thirteenth aspect, the resistance can be reduced and the charge / discharge efficiency can be improved.

[0041] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0042] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a cathode material 1000 according to the first embodiment. The cathode material 1000 according to the first embodiment includes a first solid electrolyte 100, a cathode active material 110, and a coating material 111 that coats at least a portion of the surface of the cathode active material 110. The first solid electrolyte 100 and the cathode active material 110 may be particulate. The coating material 111 may coat the entire surface of the cathode active material 110, or may coat only a portion of the surface of the cathode active material 110. That is, it is sufficient that the coating material 111 coats at least a portion of the surface of the cathode active material 110. In other words, the cathode active material 110 and the first solid electrolyte 100 are separated by the coating material 111, and there are portions where they are not in contact with each other. The cathode active material 110 and the first solid electrolyte 100 may also be in contact with each other.

[0043] The first solid electrolyte 100 is represented by the following composition formula (1).

[0044] Li a M b X c ...Equation (1)

[0045] In composition formula (1), a, b, and c are each independently a positive real number. M includes calcium, yttrium, and at least one rare earth element other than yttrium. X includes at least one element selected from the group consisting of F, Cl, Br, and I.

[0046] In the cathode material 1000 of this embodiment, a coating material 111 is interposed between the cathode active material 110 and the first solid electrolyte 100, which is a halide solid electrolyte. This coating material 111 suppresses electron transfer to and from the halide solid electrolyte, even when the cathode potential increases during battery charging. This suppresses the oxidation reaction of halogen in the first solid electrolyte 100, thereby suppressing decomposition of the first solid electrolyte 100 and the generation of halogen gas resulting from the oxidation reaction. As a result, deterioration of the first solid electrolyte 100 is suppressed, and a decrease in the effective reaction area between the cathode active material 110 and the first solid electrolyte 100 is also suppressed. For these reasons, the cathode material 1000 of this embodiment can reduce the resistance of the battery. Furthermore, as a result, the cathode material 1000 of the first aspect can also improve the charge / discharge efficiency of the battery.

[0047] As described above, the coating material 111 may uniformly coat the entire surface of the positive electrode active material 110. This prevents direct contact between the positive electrode active material 110 and the first solid electrolyte 100, and more reliably suppresses the oxidation reaction of the first solid electrolyte 100. This further improves the charge / discharge characteristics of the battery and suppresses an increase in the reaction overvoltage of the battery.

[0048] The coating material 111 may cover only a portion of the surface of the positive electrode active material 110. Particles of the positive electrode active material 110 come into direct contact with each other through the portions not covered with the coating material 111, thereby improving the electronic conductivity between the particles of the positive electrode active material 110. This enables the battery to operate at high power output.

[0049] For example, a material with low electron conductivity can be used for the coating material 111. For example, a material containing O can be used for the coating material 111. Examples of the material containing O include an oxide material or an oxide solid electrolyte.

[0050] Examples of oxide materials that can be used for the coating material 111 include SiO2, Al2O3, TiO2, B2O3, Nb2O5, WO3, and ZrO2. Examples of oxide solid electrolytes that can be used for the coating material 111 include Li-PO compounds such as Li3PO4, 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, and Li4Ti5O. 12 Li-Ti-O compounds such as Li2ZrO3, Li-Zr-O compounds such as Li2MoO3, Li-VO compounds such as LiV2O5, Li-WO compounds such as Li2WO4, and Li2SO4.

[0051] The coating material 111 may contain an oxide solid electrolyte. The oxide solid electrolyte has high ionic conductivity and high potential stability. Therefore, by using the oxide solid electrolyte, the charge / discharge efficiency can be further improved.

[0052] The coating material 111 may contain an oxoacid salt. When the coating material 111 contains an oxoacid salt, the resistance of the battery can be reduced more effectively. The oxoacid salt may be an oxoacid salt having a nonmetal or a metalloid as the cation. As described above, "metalloid elements" are B, Si, Ge, As, Sb, and Te. "Nonmetal elements" are N, P, S, Cl, Br, and I. In other words, these elements are a group of elements that combine with oxygen to form oxoacids.

[0053] The coating material 111 may contain at least one selected from the group consisting of B, N, P, S, and Si.

[0054] The coating material 111 contains at least one element selected from the group consisting of B, N, P, S, and Si, which allows the formation of a coating with low electronic conductivity on the surface of the positive electrode active material 110. Therefore, the positive electrode material 1000 of the first embodiment can further reduce the oxidation reaction of the first solid electrolyte 100. Furthermore, elements such as B, N, P, S, and Si form strong covalent bonds with oxygen. Therefore, electrons in the coating material 111 are delocalized, resulting in low electronic conductivity of the coating made of the coating material 111. Therefore, even if the thickness of the coating material 111 on the surface of the positive electrode active material 110 is reduced, the exchange of electrons between the positive electrode active material 110 and the first solid electrolyte 100 can be blocked, thereby more effectively suppressing the oxidation reaction of the first solid electrolyte 100. Therefore, the coating material 111 contains at least one element selected from the group consisting of B, N, P, S, and Si, which allows the positive electrode material 1000 to more effectively reduce the resistance of the battery and further improve the charge / discharge efficiency.

[0055] Coating material 111 may contain Li. This configuration increases the carrier concentration at the interface between positive electrode active material 110 and first solid electrolyte 100, thereby more effectively reducing the resistance of the battery.

[0056] When the coating material 111 contains Li, the molar ratio of lithium to other cations in the coating material 111, Li / (other cations), may be 0.8 or more and 3.6 or less, or 1.0 or more and 3.0 or less. When the molar ratio Li / (other cations) is 0.8 or more and 3.6 or less, the lithium ion conductivity in the coating material 111 can be increased. This makes it possible to more effectively reduce the resistance of the battery.

[0057] The coating material 111 may contain a glass-forming oxide such as phosphate or silicate. Here, glass-forming oxide refers to a network-forming oxide that can form glass by itself. Elements that become cations that can form glass-forming oxides, i.e., elements known as network formers, include, for example, Si, P, B, Ge, and V. When the coating material 111 contains a glass-forming oxide, the lithium ion conductivity in the coating material 111 can be increased. Specifically, when the coating material 111 contains a lithium compound of an oxide known as a glass-forming oxide, such as phosphate or silicate, a portion of the coating becomes amorphous, widening the ion conduction path. This increases the lithium ion conductivity in the coating material 111, thereby more effectively reducing the battery resistance.

[0058] The coating material 111 may contain an intermediate oxide such as niobic acid. Here, the intermediate oxide refers to an oxide that cannot form glass by itself (i.e., cannot form a glass network by itself) but can form glass or enter the glass network depending on the composition. Elements that can become cations that can form intermediate oxides include, for example, Nb, Ti, Zn, Al, and Zr. When the coating material 111 contains an intermediate oxide, the lithium ion conductivity in the coating material 111 can be increased. Specifically, when the coating material 111 contains a lithium compound of an oxide called an intermediate oxide such as niobic acid, a portion of the coating becomes amorphous, widening the ion conduction path. This increases the lithium ion conductivity in the coating material 111, and can more effectively reduce the battery resistance.

[0059] The coating material 111 may contain at least one selected from the group consisting of lithium phosphate and lithium niobate.

[0060] Lithium phosphate and lithium niobate can increase the lithium ion conductivity of the coating material 111. This allows the positive electrode material 1000 of this embodiment to more effectively reduce the resistance of the battery.

[0061] The coating material 111 contains at least one selected from the group consisting of lithium phosphate and lithium niobate as a main component, and may further contain unavoidable impurities, or starting materials, by-products, decomposition products, and the like used in forming the coating material 111. That is, the coating material 111 may contain, for example, a total of 50% or more (50 mass% or more) of the lithium phosphate and lithium niobate in terms of mass ratio relative to the entire coating material 111. The coating material 111 may contain, for example, 100% (100 mass%) of the lithium phosphate and lithium niobate in terms of mass ratio relative to the entire coating material 111, excluding unavoidable impurities.

[0062] In the first embodiment, the coating material 111 may be LiNbO3. LiNbO3 has higher ionic conductivity and higher high potential stability. Therefore, by using LiNbO3, the charge / discharge efficiency of the battery can be further improved.

[0063] When the positive electrode active material 110 and the first solid electrolyte 100 are in direct contact with each other, if the battery is charged and the potential of the positive electrode increases, electrons are extracted from the first solid electrolyte 100, resulting in oxidation of the first solid electrolyte 100. To prevent this, it is effective to interpose a coating material 111 between the positive electrode active material 110 and the first solid electrolyte 100. However, the coating material 111 may also block electronic contact between the positive electrode active material 110 and the conductive additive, or between the positive electrode active materials 110 themselves. In this case, the electronic path from the battery's current collector to each particle of the positive electrode active material 110 is cut off, and the isolated positive electrode active material 110 may no longer contribute to the charge / discharge reaction. In other words, the apparent amount of active material decreases, reducing the reaction area and making it difficult to sufficiently reduce resistance. In contrast, by leaving a portion of the surface of the positive electrode active material 110 exposed without being covered with the coating material 111, it is possible to both suppress the oxidation reaction of the first solid electrolyte 100 and ensure an electron path. Therefore, a portion of the surface of the positive electrode active material 110 may be exposed without being covered with the coating material 111.

[0064] In order to further suppress the oxidation reaction of the first solid electrolyte 100 and more effectively reduce the resistance of the battery, the coverage, which is the ratio of the surface area of ​​the positive electrode active material 110 covered with the coating material 111 to the total surface area of ​​the positive electrode active material 110, may be 18% or more. In order to more effectively reduce the resistance of the battery, the coverage may be 47% or more, 90%, or 100%.

[0065] The coverage can be determined by separating the O1s peak in X-ray photoelectron spectroscopy (XPS). For example, when Li(Ni,Co,Mn)O2 is used as the positive electrode active material 110 and lithium phosphate is used as the coating material 111, the coverage may be determined by dividing the area of ​​the O1s peak derived from the positive electrode active material, which has a peak top at around 529 eV, by the area obtained by subtracting the O1s peak derived from carbon dioxide, which appears around 531 eV, from the O1s peak appearing around 532 eV.

[0066] If it is difficult to accurately determine the coverage ratio using the above method, an alternative method is to use XPS measurement to determine the elemental amounts of metals, such as Ni, Co, and Mn, in the positive electrode active material 110 and the elemental amounts of cation species, such as P or Si, in the coating material 111, and then determine the coverage ratio from the ratio between them.

[0067] The coverage may be determined from the difference in contrast due to the difference in composition between the active material and the coating material using a backscattered electron image of a scanning electron microscope (SEM).

[0068] The coverage may be determined by mapping the constituent elements of the active material and the coating material using energy dispersive X-ray analysis (EDX).

[0069] The mass ratio of coating material 111 to positive electrode active material 110 may be 2.0 mass % or less, or may be 1.5 mass % or less. This configuration allows the proportion of positive electrode active material 110 or first solid electrolyte 100 in the positive electrode to be increased, thereby increasing the energy density of the battery.

[0070] The mass ratio of coating material 111 to positive electrode active material 110 may be 0.1 mass % or more, or 0.5 mass % or more. This configuration allows the proportion of positive electrode active material 110 or first solid electrolyte 100 in the positive electrode to be increased, thereby increasing the energy density of the battery.

[0071] The mass ratio of coating material 111 to positive electrode active material 110 may be 0.5 mass % or more and 2.0 mass % or less. This configuration increases the proportion of positive electrode active material 110 or first solid electrolyte 100 in the positive electrode, thereby increasing the energy density of the battery.

[0072] The mass ratio of the coating material 111 to the positive electrode active material 110 may be 0.5 mass % or more and 1.5 mass % or less.

[0073] The mass ratio of the coating material 111 to the positive electrode active material 110 may be determined, for example, by dissolving the positive electrode in an acid or the like to prepare an aqueous solution, and then quantifying the elements contained therein by inductively coupled plasma (ICP) atomic emission spectroscopy to determine the mass ratio. In this case, the mass ratio may be determined from the quantitative values ​​of elements contained in only one of the positive electrode active material 110 or the coating material 111, assuming a stoichiometric composition. For example, when LiNiO2 is coated with Li3PO4, the mass ratio of the coating material 111 may be determined from the quantitative values ​​of Ni and P, assuming that LiNiO2 and Li3PO4 exist in a stoichiometric composition.

[0074] In the composition formula (1), the at least one rare earth element other than yttrium contained in M ​​may include Sc and a lanthanoid element. Examples of the lanthanoid element include La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Since the chemical properties of rare earth elements are similar to each other, any of them can be used as a constituent element of the halide solid electrolyte of the present embodiment.

[0075] In the above compositional formula (1), M may contain calcium, yttrium, and one rare earth element other than yttrium. M may contain at least one rare earth element other than yttrium, and may contain only one rare earth element other than yttrium.

[0076] In the above compositional formula (1), M may contain at least one selected from the group consisting of Gd and Sm.

[0077] In the above compositional formula (1), M may contain only one selected from the group consisting of Gd and Sm.

[0078] According to the above configuration, the ionic conductivity of the first solid electrolyte 100 can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0079] In the above compositional formula (1), X may contain at least one element selected from the group consisting of F, Cl, and Br. In the above compositional formula (1), X may contain at least two elements selected from the group consisting of F, Cl, and Br. In the above compositional formula (1), X may contain Cl and Br. According to this configuration, the ionic conductivity of the first solid electrolyte 100 can be further improved. Thereby, the charge-discharge efficiency of the battery can be further improved.

[0080] The first solid electrolyte 100 may be represented by the following compositional formula (2).

[0081] Li 6-2a-3d Ca a (Y 1-b Gd b ) d Br 6-c Cl c ··· Formula (2)

[0082] The compositional formula (2) satisfies 0 < a, 0 < b < 1, 0 < c < 6, and 0 < d < 1.5.

[0083] The above configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0084] The composition formula (2) may satisfy 0.01≦a≦0.3.

[0085] The above configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0086] The composition formula (2) may satisfy a≦0.2.

[0087] The above configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0088] The composition formula (2) may satisfy 0.1≦b≦0.9.

[0089] The above configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0090] The composition formula (2) may satisfy 0.8≦b<1.

[0091] The above configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0092] The composition formula (2) may satisfy 1.0≦c≦1.2.

[0093] The above configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0094] It should be noted that first solid electrolyte 100 and the halide solid electrolyte do not necessarily need to contain sulfur.

[0095] The positive electrode active material 110 is, for example, a material that has the property of absorbing and releasing metal ions (e.g., lithium ions). Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Examples of lithium-containing transition metal oxides include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2. When a lithium-containing transition metal oxide is used as the positive electrode active material, the manufacturing cost of the positive electrode can be reduced and the average discharge voltage can be increased.

[0096] To increase the energy density of the battery, the active cathode material 110 may be lithium nickel-cobalt-manganese oxide, for example, Li(NiCoMn)O2.

[0097] According to the above configuration, the energy density and charge / discharge efficiency of the battery can be further increased.

[0098] The thickness of the coating material 111 may be 1 nm or more and 100 nm or less.

[0099] By making the thickness of the coating material 111 1 nm or more, direct contact between the positive electrode active material 110 and the first solid electrolyte 100 can be suppressed, and side reactions of the first solid electrolyte 100 can be suppressed, thereby improving the charge / discharge efficiency.

[0100] Furthermore, by setting the thickness of the coating material 111 to 100 nm or less, the thickness of the coating material 111 does not become too thick. This allows the internal resistance of the battery to be sufficiently small. As a result, the energy density of the battery can be increased.

[0101] The thickness of the coating material 111 may be 2 nm or more and 20 nm or less.

[0102] When the thickness of the coating material 111 is 2 nm or more, direct contact between the positive electrode active material 110 and the first solid electrolyte 100 can be effectively suppressed, and side reactions of the first solid electrolyte 100 can be suppressed. As a result, the charge / discharge efficiency can be improved.

[0103] Furthermore, by making the thickness of the coating material 111 40 nm or less, the internal resistance of the battery can be further reduced, and as a result, the energy density of the battery can be increased. The thickness of the coating material 111 may be 20 nm or less.

[0104] The method for measuring the thickness of the coating material 111 is not particularly limited, but for example, the thickness can be determined by directly observing the thickness of the coating material 111 using a transmission electron microscope or the like. Alternatively, the thickness can be determined from changes in the spectrum derived from the active material by measuring XPS while scraping off the coating layer by Ar sputtering.

[0105] The shape of first solid electrolyte 100 in embodiment 1 is not particularly limited and may be, for example, needle-like, spherical, oval-spherical, etc. For example, first solid electrolyte 100 may be in the form of particles.

[0106] For example, when the first solid electrolyte 100 in the first embodiment is particulate (e.g., spherical), the median diameter may be 100 μm or less. If the median diameter is greater than 100 μm, the positive electrode active material 110 and the first solid electrolyte 100 may not be well dispersed in the positive electrode material 1000. This may result in poor charge-discharge characteristics. In the first embodiment, the median diameter may be 10 μm or less.

[0107] According to the above configuration, in the positive electrode material 1000, the positive electrode active material 110 and the first solid electrolyte 100 can be well dispersed.

[0108] In the first embodiment, the median diameter of first solid electrolyte 100 may be smaller than that of positive electrode active material 110 .

[0109] According to the above configuration, the first solid electrolyte 100 and the positive electrode active material 110 can be dispersed in a better state in the electrode.

[0110] The median diameter of the positive electrode active material 110 may be 0.1 μm or more and 100 μm or less.

[0111] 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 first solid electrolyte 100 can be well dispersed in the positive electrode material 1000. As a result, the charge / discharge characteristics of the battery are improved. Furthermore, 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.

[0112] The median diameter of the positive electrode active material 110 may be larger than the median diameter of the first solid electrolyte 100. This allows the positive electrode active material 110 and the first solid electrolyte 100 to form a good dispersed state.

[0113] The median diameter means the particle size 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 measuring device or an image analyzer.

[0114] In the positive electrode material 1000 according to the first embodiment, the first solid electrolyte 100 and the coating material 111 may be in contact with each other as shown in FIG.

[0115] The positive electrode material 1000 in the first embodiment may include a plurality of particles of the first solid electrolyte 100 and a plurality of particles of the positive electrode active material 110.

[0116] Furthermore, in the positive electrode material 1000 of the first embodiment, the content of the first solid electrolyte 100 and the content of the positive electrode active material 110 may be the same as or different from each other.

[0117] <Method for producing the first solid electrolyte> The first solid electrolyte in the first embodiment can be produced, for example, by the following method.

[0118] Raw material powders are prepared and mixed to achieve the desired composition. Examples of raw material powders include oxides, hydroxides, halides, and oxyhalides. For example, to produce Li3YBr3Cl3, LiBr and YCl3 are prepared in a molar ratio of 3:1.

[0119] At this time, by selecting the type of raw material powder, it is possible to determine "M" and "X" in the above composition formula (1). In addition, by adjusting the raw materials, compounding ratio, and synthesis process, it is possible to adjust the above values ​​"a," "b," and "c."

[0120] After the raw material powders are thoroughly mixed, they are mixed, pulverized, and reacted with each other using a mechanochemical milling method, or alternatively, the raw material powders may be thoroughly mixed and then sintered in a vacuum.

[0121] This results in the first solid electrolyte.

[0122] The constitution of the crystalline phase in the solid electrolyte (that is, the crystalline structure) can be determined by adjusting the reaction method and reaction conditions of the raw material powders.

[0123] <Method for producing a positive electrode active material coated with a coating material> The positive electrode active material 110 coated with the coating material 111 can be produced by the following method.

[0124] First, a powder of the positive electrode active material 110 is prepared. The powder of the positive electrode active material 110 is produced, for example, by a coprecipitation method. In the coprecipitation method, a precursor made of a metal oxide is produced and then calcined together with a lithium source, thereby producing the positive electrode active material 110. In addition, powders of the positive electrode active material 110 with various compositions are commercially available and can be easily obtained.

[0125] Next, the surfaces of the particles of the positive electrode active material 110 are coated with a coating material 111. There are no particular limitations on the method for forming the coating material 111. Methods for forming the coating material 111 include a liquid-phase coating method and a vapor-phase coating method.

[0126] For example, in the liquid phase coating method, a precursor solution of the coating material 111 is applied to the surface of the positive electrode active material 110. When forming the coating material 111 containing lithium phosphate, the precursor solution can be a mixed solution of a solvent, lithium hydroxide, and triethyl phosphate.

[0127] The raw material is not limited as long as it can be dissolved or dispersed in a solvent. Examples of the lithium source include alkyllithium such as tert-butyllithium, lithium alkoxides such as lithium methoxide, lithium ethoxide, lithium isopropoxide, and lithium tert-butoxide, lithium iodide, lithium bromide, lithium chloride, lithium carbonate, lithium nitrate, lithium sulfate, and metallic lithium. Examples of the phosphate source include trimethyl phosphate, tripropyl phosphate, tributyl phosphate, phosphoric acid, monoammonium dihydrogen phosphate, diammonium monohydrogen phosphate, and triammonium phosphate. A raw material containing phosphoric acid and lithium may also be used.

[0128] The solvent is, for example, an alcohol such as ethanol. However, the solvent is not limited as long as it can dissolve or disperse the raw materials, and various solvents can be selected depending on the raw materials. Examples of the solvent include methanol, propanol, isopropanol, butanol, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfoxide, tetrahydrofuran, hexane, benzene, toluene, methylene chloride, acetone, and acetonitrile.

[0129] The amounts of lithium hydroxide and triethyl phosphate are adjusted depending on the target composition of the coating material 111. Water may be added to the precursor solution if necessary. The precursor solution may be acidic or alkaline.

[0130] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0131] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the second embodiment.

[0132] The battery 2000 in the second embodiment includes a positive electrode 201 , an electrolyte layer 202 , and a negative electrode 203 .

[0133] The positive electrode 201 includes the positive electrode material 1000 in the first embodiment.

[0134] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0135] According to the above configuration, the resistance of the battery 2000 can be reduced.

[0136] The volume ratio "v1:100-v1" of the positive electrode active material 110 to the first 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 first solid electrolyte 100 contained in the positive electrode 201 is taken as 100. When v1≦30 is satisfied, it is easy to ensure a sufficient energy density of the battery 2000. When v1≦95 is satisfied, it is easier for the battery 2000 to operate at high output.

[0137] 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, high-power operation of the battery 2000 can be achieved.

[0138] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0139] The electrolyte layer 202 is a layer containing an electrolyte material. The electrolyte material is, for example, a solid electrolyte (i.e., a second solid electrolyte). That is, the electrolyte layer 202 may be a solid electrolyte layer.

[0140] The second solid electrolyte contained in the electrolyte layer 202 may be the first solid electrolyte described above in Embodiment 1. That is, the electrolyte layer 202 may include the first solid electrolyte described above in Embodiment 1.

[0141] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be further improved.

[0142] The second solid electrolyte contained in electrolyte layer 202 may be a halide solid electrolyte different from the first solid electrolyte in the above-described embodiment 1. That is, electrolyte layer 202 may include a halide solid electrolyte different from the first solid electrolyte in the above-described embodiment 1.

[0143] According to the above configuration, the output density and charge / discharge efficiency of the battery 2000 can be improved.

[0144] The halide solid electrolyte contained in the electrolyte layer 202 may contain Y as a metal element.

[0145] According to the above configuration, the output density and charge / discharge efficiency of the battery can be further improved.

[0146] As the halide solid electrolyte contained in the electrolyte layer 202, the material shown as the first solid electrolyte in the first embodiment can be used.

[0147] A sulfide solid electrolyte may be used as the second solid electrolyte contained in the electrolyte layer 202. That is, the electrolyte layer 202 may include a sulfide solid electrolyte.

[0148] According to the above configuration, since the sulfide solid electrolyte having excellent reduction stability is included, a low potential negative electrode material such as graphite or metallic lithium can be used, and the energy density of the battery 2000 can be improved.

[0149] Sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 , etc. can be used. In addition to these, LiX (X: F, Cl, Br, I), Li2O, MO q , Li p MO q (M: any of P, Si, Ge, B, Al, Ga, In, Fe, and Zn) (p and q: natural numbers), etc. may be added.

[0150] The second solid electrolyte contained in the electrolyte layer 202 may be an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte.

[0151] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element-substituted LISICON-type solid electrolytes, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those typified by LiN and its element substitution products, LiN and its H-substituted products, LiPO4 and its N-substituted products, and glasses and glass ceramics based on Li-BO compounds such as LiBO2 and LiBO3 to which LiSO4, LiCO3, etc. are added, can be used.

[0152] As the polymer 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. By having an ethylene oxide structure, a large amount of lithium salt can be contained, and ionic conductivity can be further increased. As the lithium salt, LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc. can be used. As the lithium salt, one type of lithium salt selected from these can be used alone. Alternatively, as the lithium salt, a mixture of two or more types of lithium salts selected from these can be used.

[0153] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0154] The electrolyte layer 202 may contain the second solid electrolyte as a main component. That is, the electrolyte layer 202 may contain the second solid electrolyte in an amount of, for example, 50% or more by weight (50% by weight or more) relative to the entire electrolyte layer 202.

[0155] According to the above configuration, the charge / discharge characteristics of the battery 2000 can be further improved.

[0156] Furthermore, the electrolyte layer 202 may contain the second solid electrolyte in an amount of, for example, 70% or more by weight (70% by weight or more) relative to the entire electrolyte layer 202.

[0157] According to the above configuration, the charge / discharge characteristics of the battery 2000 can be further improved.

[0158] The electrolyte layer 202 contains the second solid electrolyte as a main component, and may further contain unavoidable impurities, or starting materials, by-products, and decomposition products used in synthesizing the second solid electrolyte.

[0159] Furthermore, the electrolyte layer 202 may contain the second solid electrolyte in a weight ratio of 100% (100 wt %) relative to the entire electrolyte layer 202, excluding unavoidable impurities, for example.

[0160] According to the above configuration, the charge / discharge characteristics of the battery can be further improved.

[0161] As described above, the electrolyte layer 202 may be composed of only the second solid electrolyte.

[0162] The electrolyte layer 202 may contain two or more of the materials listed as the second solid electrolyte. For example, the electrolyte layer 202 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0163] 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 possibility of short-circuiting between the positive electrode 201 and the negative electrode 203 is reduced. Furthermore, when the thickness of the electrolyte layer 202 is 300 μm or less, high-power operation is facilitated. In other words, if the thickness of the electrolyte layer 202 is appropriately adjusted, sufficient safety of the battery 2000 can be ensured, and the battery 2000 can be operated at high power.

[0164] 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.

[0165] The negative electrode active material may be a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound. The metal material may be a single metal. Alternatively, 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. From the viewpoint of capacity density, silicon (Si), tin (Sn), a silicon compound, or a tin compound can be preferably used.

[0166] The negative electrode 203 may contain a third solid electrolyte. The above configuration improves the lithium ion conductivity inside the negative electrode 203, enabling high-power operation. The materials listed as examples of the second solid electrolyte of the electrolyte layer 202 can be used as the third solid electrolyte contained in the negative electrode 203.

[0167] The median diameter of the negative electrode active material particles may be 0.1 μm or more and 100 μm or less. When the median diameter of the negative electrode active material particles is 0.1 μm or more, the negative electrode active material particles and the solid electrolyte can be more favorably dispersed in the negative electrode. This improves the charge / discharge characteristics of the battery. Furthermore, when the median diameter of the negative electrode active material particles is 100 μm or less, the diffusion rate of lithium within the negative electrode active material is sufficiently ensured. This allows the battery to operate at high power.

[0168] The median diameter of the negative electrode active material particles may be larger than the median diameter of the third solid electrolyte, thereby achieving a good dispersion state between the negative electrode active material particles and the solid electrolyte.

[0169] The volume ratio "v2:100-v2" of the negative electrode active material particles to the solid electrolyte contained in the negative electrode 203 may satisfy 30≦v2≦95. When 30≦v2 is satisfied, it is easy to ensure a sufficient energy density of the battery 2000. Furthermore, when v2≦95 is satisfied, it is easier for the battery 2000 to operate at high output.

[0170] 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, it is easy to ensure a sufficient energy density of the battery 2000. When the thickness of the negative electrode 203 is 500 μm or less, it is easier for the battery 2000 to operate at high power.

[0171] 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 constituting 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. The binder may be a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. Alternatively, a mixture of two or more materials selected from these may be used as the binder.

[0172] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives that can be used include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black or ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride or 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, or polythiophene. Using a carbon conductive additive can reduce costs.

[0173] The battery 2000 in the second embodiment can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type.

[0174] The battery 2000 in the second embodiment may be manufactured, for example, by preparing the positive electrode material 1000 in the first embodiment, a material for forming the electrolyte layer, and a material for forming the negative electrode, and by using a known method to fabricate a laminate in which the positive electrode, the electrolyte layer, and the negative electrode are arranged in this order. [Example]

[0175] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0176] Example 1 [Preparation of a positive electrode active material whose surface is coated with a coating material] A coating material solution was prepared by dissolving 6.3 mg of lithium hydroxide and 16.0 mg of triethyl phosphate in an appropriate amount of ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) in an argon glove box with a dew point of -60°C or less. The molar ratio of lithium to phosphorus in the coating material solution was 3:1.

[0177] 2 g of Li(NiCoMn)O2 (hereinafter referred to as NCM), which is a positive electrode active material, was prepared on an agate mortar, and the prepared coating material solution was gradually added thereto while stirring.

[0178] After the entire coating material solution was added, stirring was continued until the solution was visually confirmed to be dry.

[0179] The dried powder was placed in an alumina crucible and heat-treated at 400°C for 3 hours in an oxygen atmosphere.

[0180] The heat-treated powder was re-pulverized in an agate mortar to obtain the positive electrode active material of Example 1, the surface of which was coated with a coating material. The coating material was lithium phosphate (Li3PO4).

[0181] [Preparation of the first solid electrolyte] In an argon atmosphere with a dew point of -60°C or less, raw material powders of LiCl, LiBr, CaBr2, YCl3, and GdCl3 were prepared in a molar ratio of LiCl:LiBr:CaBr2:YCl3:GdCl3 = 1.0:1.8:0.1:0.6:0.4. These were ground and mixed in a mortar. The resulting raw material powder mixture was then fired in an argon atmosphere using an electric furnace at 500°C for 3 hours. The resulting material was ground using a pestle and mortar. As a result, a powder of a first solid electrolyte was obtained. The first solid electrolyte of Example 1 is hereinafter referred to as "HSE."

[0182] [Battery construction] In an argon atmosphere with a dew point below -60°C, NCM (a cathode active material coated with lithium phosphate), HSE (a first solid electrolyte), and vapor-grown carbon fiber (VGCF) (a conductive additive) were prepared. The mass ratio of NCM, HSE, and VGCF was NCM:HSE:VGCF = 80:18:2. These were mixed in an agate mortar to produce a cathode composite.

[0183] The sulfide solid electrolyte Li6PS5Cl (80 mg), HSE powder (20 mg), and the above-mentioned positive electrode composite (18.2 mg) were layered in this order in an insulating outer cylinder, and a pressure of 720 MPa was applied to the stack to obtain a positive electrode and a solid electrolyte layer.

[0184] Next, Li foil was laminated on the side of the electrolyte layer opposite the side that contacted the positive electrode. A pressure of 80 MPa was applied to this, creating a laminate consisting of a positive electrode, a solid electrolyte layer, and a negative electrode. The Li foil formed the negative electrode.

[0185] Next, stainless steel current collectors were placed on the top and bottom of the laminate, and current collecting leads were attached to the current collectors. Finally, an insulating ferrule was used to isolate and seal the inside of the insulating outer cylinder from the outside atmosphere.

[0186] In this way, the battery of Example 1 was produced.

[0187] [Charge / discharge test] The battery of Example 1 was placed in a thermostatic chamber at 25° C. The battery was charged at a constant current of 0.140 mA, and charging was terminated at a voltage of 4.3 V. Next, the battery was discharged at the same current of 0.140 mA, and discharging was terminated at a voltage of 2.5 V.

[0188] [Resistance measurement] FIG. 3 shows the Nyquist diagram of the battery in Example 1 at 3.7 V. The battery in Example 1 was placed in a thermostatic chamber at 25°C. It was then connected to a potentiostat equipped with a frequency response analyzer. Thereafter, the battery was subjected to constant current charging at a current value of 0.140 mA, and after the voltage reached 3.7 V, constant voltage charging was performed and terminated. Thereafter, the frequency dependence of the resistance component was evaluated by the AC impedance method. At this time, 10 5 -10 2 The resistance component appearing near Hz was separated by curve fitting and determined to be the resistance due to the active material-solid electrolyte interface. From this measurement, the resistance of Example 1 was estimated to be 140 ohms.

[0189] [Coverage measurement] 4 shows the O1s spectrum of the active material used in Example 1, measured by the XPS method. The O1s spectrum of the surface of the positive electrode active material coated with lithium phosphate was obtained by the XPS method. Al-Kα radiation was used as the XPS radiation source.

[0190] Two peaks were observed: one centered at 528 eV and the other at 532 eV. The 528 eV peak is due to MO (Ni-O, Mn-O, Co-O) in the positive electrode active material. The 532 eV peak is due to the overlap of the CO peak from lithium carbonate, a surface impurity, and the PO peak from lithium phosphate. The influence of lithium carbonate was removed by subtracting the peak area around 532 eV detected from the uncoated active material calcined at 400°C in an oxygen atmosphere from the peak area around 532 eV of the coated active material, and the peak area due to the coating was calculated.

[0191] From these peaks, the ratio of MO to PO in O1s was calculated to estimate the coverage. The coverage of the lithium phosphate active material used in Example 1 was estimated to be 18%.

[0192] Example 2 [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon glove box with an argon atmosphere having a dew point of −60° C. or less, 14.2 mg of lithium hydroxide and 36.0 mg of triethyl phosphate were dissolved in an appropriate amount of ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating material solution.

[0193] [Battery construction] A battery was fabricated in the same manner as in Example 1, except that the coating amount of the active material was changed.

[0194] [Resistance measurement] The resistance of the battery was evaluated in the same manner as in Example 1.

[0195] Example 3 [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon glove box with an argon atmosphere having a dew point of −60°C or less, 5.95 g of ethoxylithium (manufactured by Kojundo Chemical Co., Ltd.) and 36.43 g of pentaethoxyniobium (manufactured by Kojundo Chemical Co., Ltd.) were dissolved in 500 mL of ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating material solution.

[0196] The coating material was formed on the positive electrode active material (NCM) using a rolling fluidized bed granulation coating machine (Powrex, FD-MP-01E). The amount of positive electrode active material added, the stirring speed, and the coating material solution delivery rate were 1 kg, 400 rpm, and 6.59 g / min, respectively.

[0197] The treated powder was placed in an alumina crucible and taken out into the air.

[0198] Next, a heat treatment was carried out in an air atmosphere at 300° C. for 1 hour.

[0199] The heat-treated powder was re-pulverized in an agate mortar to obtain the positive electrode active material of Example 3, the surface of which was coated with a coating material. The coating material was lithium niobate (LiNbO3).

[0200] [Battery construction] A battery was fabricated in the same manner as in Example 1, except that the coating material for the active material was changed.

[0201] [Charge / discharge test] The battery was subjected to a charge / discharge test in the same manner as in Example 1.

[0202] [Resistance measurement] The resistance of the battery was evaluated in the same manner as in Example 1.

[0203] [Coverage measurement] The O1s peak of Nb—O derived from lithium niobate appears near 530 eV. From this value, the coverage was calculated in the same manner as in Example 1. The coverage of the active materials used in Examples 2 and 3 was approximately 100%.

[0204] Example 4 [Preparation of the first solid electrolyte] In an argon atmosphere with a dew point of -60°C or less, raw material powders of LiCl, LiBr, CaBr2, YCl3, and GdCl3 were prepared in a molar ratio of LiCl:LiBr:CaBr2:YCl3:GdCl3 = 1.0:1.8:0.1:0.9:0.1. These were ground and mixed in a mortar. Next, the resulting raw material powder mixture was fired in an argon atmosphere using an electric furnace at 500°C for 3 hours. The resulting material was ground using a pestle and mortar. As a result, a powder of the first solid electrolyte of Example 4 was obtained.

[0205] [Battery construction] A battery was fabricated in the same manner as in Example 2, except that the solid electrolyte was changed.

[0206] [Resistance measurement] The resistance was evaluated in the same manner as in Example 1.

[0207] Comparative Example 1 [Preparation of positive electrode active material] The NCM used as the positive electrode active material in Examples 1 to 4 was used as the positive electrode active material in Comparative Example 1 without coating the surface with a coating material.

[0208] [Charge / discharge test] The battery was subjected to a charge / discharge test in the same manner as in Example 1.

[0209] [Resistance measurement] The resistance of the battery was measured in the same manner as in Example 1.

[0210] [Consideration 1] Table 1 shows the coating material, thickness of the coating material, mass ratio, first solid electrolyte, and resistance of Examples 1 to 4 and Comparative Example 1. The mass ratio means the ratio of the mass of the coating material to the mass of the positive electrode active material.

[0211] In the batteries of Example 1 and Comparative Example 1, the same HSE was used as the first solid electrolyte contained in the positive electrode material. As a result, it was confirmed that even when HSE was used as the first solid electrolyte, the resistance of the battery was reduced by coating the positive electrode active material with a coating material. This result shows that the effect of reducing the resistance of the battery can be obtained by coating the surface of the positive electrode active material with a coating material, regardless of the type of metal that constitutes the solid electrolyte.

[0212] In the batteries of Examples 1 and 2, the same HSE was used as the first solid electrolyte contained in the positive electrode material. In the batteries of Examples 1 and 2, the same lithium phosphate was used as the coating material that coated the positive electrode active material contained in the positive electrode material. As a result, it was confirmed that the resistance of the battery was further reduced as the mass ratio of the coating material in the positive electrode active material increased. It is believed that the coverage rate of the positive electrode active material increased as the mass ratio of the coating material in the positive electrode active material increased, thereby reducing the direct contact area between the positive electrode active material and the solid electrolyte. In other words, it is believed that the battery resistance was reduced by suppressing the formation of a resistance layer between the active material and the solid electrolyte.

[0213] As shown by the results of Example 3 and Comparative Example 1, the battery resistance was reduced even when lithium niobate was used as the coating material. When lithium-containing oxides, particularly the glass-forming oxide phosphoric acid and the intermediate oxide lithium niobate, were used as the coating material, the thickness of the coating material was likely to be thin. In this case, firing at low temperatures formed a highly amorphous coating. Therefore, it is believed that the lithium exchange between the active material and the solid electrolyte was not inhibited, and the formation of a resistance layer between the active material and the solid electrolyte was suppressed.

[0214] Comparing Example 2 and Example 4, which use the same coating material but different compositions of the first solid electrolyte, it is clear from the results that the battery resistance could be reduced regardless of the ratio of elements constituting the first solid electrolyte.

[0215] [Table 1]

[0216] Example 5 [Preparation of the first solid electrolyte] In an argon atmosphere with a dew point of -60°C or less, raw material powders of LiCl, LiBr, CaBr2, YCl3, and SmCl3 were prepared in a molar ratio of LiCl:LiBr:CaBr2:YCl3:SmCl3 = 1.0:1.8:0.1:0.8:0.2. These were ground and mixed in a mortar. Next, the resulting raw material powder mixture was fired in an argon atmosphere using an electric furnace at 500°C for 3 hours. The resulting material was ground using a pestle and mortar. As a result, a powder of the first solid electrolyte of Example 5 was obtained.

[0217] [Battery construction] A battery was fabricated in the same manner as in Example 2, except that the first solid electrolyte was changed.

[0218] [Resistance measurement] The resistance of the battery was measured in the same manner as in Example 1.

[0219] Comparative Example 2 [Battery construction] A battery was fabricated in the same manner as in Example 5, except that the surface of the NCM used as the positive electrode active material in Examples 1 to 5 was not coated with a coating material.

[0220] [Charge / discharge test] The battery was subjected to a charge / discharge test in the same manner as in Example 1.

[0221] [Resistance measurement] The resistance of the battery was evaluated in the same manner as in Example 1.

[0222] [Consideration 2] Table 2 shows the coating material, thickness of the coating material, mass ratio, first solid electrolyte, and resistance of Example 5 and Comparative Example 2.

[0223] In the batteries of Example 5 and Comparative Example 2, a material containing Sm was used as a constituent element of the first solid electrolyte contained in the positive electrode material. As a result, it was found that the resistance of the battery can be significantly reduced by coating the active material with lithium phosphate. The effects of the present disclosure are not limited to the case where the first solid electrolyte contains Y and Gd as constituent elements, but can be said to be effective when it contains Y as well as a rare earth element other than Y.

[0224] [Table 2] [Industrial Applicability]

[0225] The battery of the present disclosure can be used, for example, as an all-solid-state lithium secondary battery. [Explanation of symbols]

[0226] 1000 cathode materials 100 1st solid electrolyte 110 Cathode active material 111 Coating materials 2000 batteries 201 Positive electrode 202 Electrolyte Layer 203 Negative electrode

Claims

1. a positive electrode active material; a first solid electrolyte; a coating material that coats at least a portion of the surface of the positive electrode active material; Including, The first solid electrolyte is represented by the following composition formula (1): Li a M b X c ... Equation (1) where: In the composition formula (1), a, b, and c are each independently a positive real number; M includes calcium, yttrium, and at least one rare earth element other than yttrium; X comprises at least one selected from the group consisting of F, Cl, Br, and I; The coating material includes at least one selected from the group consisting of lithium phosphate and lithium niobate. Positive electrode material.

2. The mass ratio of the coating material to the positive electrode active material is 0.5 mass% or more and 2.0 mass% or less. The positive electrode material according to claim 1 .

3. The thickness of the coating material is 2 nm or more and 20 nm or less. The positive electrode material according to claim 1 or 2.

4. The M includes at least one selected from the group consisting of Gd and Sm. The positive electrode material according to any one of claims 1 to 3.

5. X includes at least one selected from the group consisting of F, Cl, and Br. The positive electrode material according to any one of claims 1 to 4.

6. The X includes at least two selected from the group consisting of F, Cl, and Br. The positive electrode material according to any one of claims 1 to 5.

7. X includes Cl and Br. The positive electrode material according to any one of claims 1 to 6.

8. The positive electrode active material includes a lithium-containing transition metal oxide. The positive electrode material according to any one of claims 1 to 7.

9. A positive electrode comprising the positive electrode material according to any one of claims 1 to 8; a negative electrode; an electrolyte layer provided between the positive electrode and the negative electrode; A battery.

10. The electrolyte layer includes a sulfide solid electrolyte.

10. The battery of claim 9.

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