Cathode materials and batteries

Abstract

This positive electrode material includes a first solid electrolyte, a positive electrode active material, and a coating material that at least partially coats the surface of the positive electrode active material. The first solid electrolyte is represented by composition formula (1): LiaMbXc. In composition formula (1), a, b, and c, are positive real numbers and satisfy the mathematical expression a+b<c, M is at least one selected from the group consisting of metalloid elements and metal elements other than Li, and X is at least one selected from the group consisting of F, Cl, Br, and I. The coating material includes an oxoacid salt using a non-metal or metalloid as a cation.

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a battery that uses, as a solid electrolyte, a compound that contains indium as a cation and a halogen element as an anion.

[0003] Patent Document 2 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-244734 [Patent Document 2] International Publication No. 2007 / 004590 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides a positive electrode material that can reduce the resistance of a battery. [Means for solving the problem]

[0006] The positive electrode material according to one embodiment of the present disclosure comprises: a first solid electrolyte; a positive electrode active material, and 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) In the above compositional formula (1), a, b, and c are positive real numbers and satisfy the mathematical formula: a + b < c, M is at least one selected from the group consisting of metal elements other than Li and metalloid elements, X is at least one selected from the group consisting of F, Cl, Br, and I, The coating material contains an oxoacid salt having a nonmetal or a metalloid as a cation.

Advantages of the Invention

[0007] The present disclosure provides a positive electrode material capable of reducing the resistance of a battery.

Brief Description of the Drawings

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a positive electrode material in Embodiment 1. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery in Embodiment . [Figure 3] FIG. 3 is a diagram showing a Nyquist diagram at 3.7 V of a battery in Comparative Example 1. [Figure 4A] FIG. 4A is a diagram showing an O1s spectrum in X-ray photoelectron spectroscopy of an active material used in Comparative Example 1. [Figure 4B] FIG. 4B is a diagram showing an O1s spectrum in X-ray photoelectron spectroscopy of an active material used in Comparative Example 1 and an O1s spectrum in X-ray photoelectron spectroscopy of an active material whose surface is not coated with a coating material. [Figure 5] FIG. 5 is a diagram showing the correlation between the coating rate and the resistance of the active materials of Comparative Example 4 and Examples 1 to 6.

Modes for Carrying Out the Invention

[0009] (Knowledge on which the present disclosure is based) Patent Document 1 discloses an all-solid-state secondary battery including a solid electrolyte made of a compound containing indium as a cation and a halogen element as an anion. Patent Document 1 mentions that in this all-solid-state secondary battery, it is desirable that the potential of the positive electrode active material against Li is 3.9 V or less on average, which suppresses the formation of a film made of decomposition products due to oxidative decomposition of the solid electrolyte, thereby obtaining good charge-discharge characteristics. Furthermore, as a positive electrode active material having an average potential against Li of 3.9 V or less, LiCoO2 or LiNi 0.8 Co 0.15 Al 0.05 Patent Document 1 discloses a common layered transition metal oxide positive electrode such as O2. However, Patent Document 1 does not clarify the detailed mechanism of oxidative decomposition.

[0010] The present inventors have investigated the resistance of halide solid electrolytes to oxidative decomposition. As a result of extensive research, the present inventors have found that in batteries using a halide solid electrolyte as the solid electrolyte contained in the positive electrode material, the halide solid electrolyte undergoes oxidative decomposition during charging, even when a positive electrode active material with an average potential vs. Li of 3.9 V or less is used. Furthermore, the present inventors have found that the oxidative decomposition of the halide solid electrolyte causes a problem of reduced battery charge / discharge efficiency, and that the cause of this problem is the oxidation reaction of the halogen element contained in the halide solid electrolyte.

[0011] Specifically, in addition to the normal charging reaction in which lithium and electrons are extracted from the positive electrode active material in the positive electrode material, a side reaction occurs in which electrons are extracted from the halide solid electrolyte in contact with the positive electrode active material, and charge is consumed in this side reaction (i.e., the oxidation reaction of the halide solid electrolyte). The oxidation reaction of the halide solid electrolyte results in the formation of an oxide layer with poor lithium ion conductivity between the positive electrode active material and the halide solid electrolyte. It is believed that this oxide layer acts as a large interfacial resistance in the electrode reaction at the positive electrode. To solve this problem, it is necessary to suppress the transfer of electrons to the halide solid electrolyte and to suppress the formation of the oxide layer.

[0012] Patent Document 2 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. In particular, it is known that the use of lithium niobate (i.e., LiNbO3) disclosed in Patent Document 2 as the lithium ion conductive oxide reduces the interfacial resistance of the electrode reaction and significantly improves the output characteristics. For these reasons, lithium niobate is often used as a coating material for positive electrode active material particles in batteries including a lithium ion conductive solid electrolyte mainly composed of sulfide.

[0013] On the other hand, as a result of extensive research, the present inventors have newly discovered that in batteries using a halide solid electrolyte as the solid electrolyte in the positive electrode material, a coating material containing an oxoacid salt such as lithium phosphate can significantly reduce battery resistance compared to a coating material containing lithium niobate. Specifically, they have discovered that the coating material that provides a significant effect varies depending on whether the lithium ion conductive solid electrolyte used as the battery's solid electrolyte is a sulfide or a halide. While the underlying mechanism is unclear, it is believed that a combination of various factors contributes to this reduction, including the voltage resistance of the coating material, the voltage resistance of the lithium ion conductive solid electrolyte used as the battery's solid electrolyte, the reactivity of the coating material with the active material, the reactivity of the coating material with the solid electrolyte, and the coverage of the coating material on the surface of the active material. The present inventors have further discovered that, among these factors, the coverage, in particular, is significantly related to the reduction in battery resistance.

[0014] By combining the above findings, the inventors arrived at the following positive electrode material of the present disclosure, which is capable of reducing the resistance of a battery.

[0015] (Summary of one aspect of the present disclosure) The positive electrode material according to the first aspect of the present disclosure is a first solid electrolyte; a positive electrode active material, and 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 compositional formula (1): Li a M b X c ··· Formula (1) In the compositional formula (1), a, b, and c are positive real numbers and satisfy the mathematical formula: a + b < c, M is at least one selected from the group consisting of metal elements other than Li and metalloid elements, X is at least one selected from the group consisting of F, Cl, Br, and I, The coating material contains an oxoacid salt having a non-metal or a semi-metal as a cation.

[0016] In the positive electrode material according to the first aspect, a coating material is interposed between the positive electrode active material and the first solid electrolyte which is a halide solid electrolyte. By this coating material, the transfer of electrons to and from the halide solid electrolyte is suppressed. Therefore, side reactions of the halide solid electrolyte are suppressed, formation of an oxide layer is suppressed, and as a result, the interfacial resistance of the electrode reaction is reduced.

[0017] In the positive electrode material according to the first aspect, further, the coating material contains an oxide material. Specifically, it contains an oxoacid salt having a non-metal or a semi-metal as a cation. Thereby, further, the resistance of the battery can be more effectively reduced.

[0018] For the above reasons, the positive electrode material according to the first aspect can reduce the resistance of the battery. As a result, the positive electrode material according to the first aspect can 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, a part of the surface of the positive electrode active material may be exposed.

[0020] A second embodiment of the cathode material includes a halide solid electrolyte. The coating material covering the cathode active material includes the oxide material of the first embodiment, but does not completely cover the entire surface of the cathode active material. That is, a portion of the surface of the cathode active material is exposed. As described above, if the cathode active material and the solid electrolyte come into direct contact, electrons are extracted from the solid electrolyte when the cathode potential increases during battery charging, resulting in the formation of an oxide layer. To prevent this, the inclusion of a layer formed by the coating material is effective. However, the layer formed by the coating material also blocks, for example, electronic contact between the active material and the conductive additive, as well as electronic contact between the active materials themselves. Therefore, if the surface of the cathode active material is completely covered by the coating material, the electronic path from the battery current collector to each active material particle may be cut off, and the isolated active material may no longer contribute to the charge / discharge reaction. In this case, the apparent amount of active material in the electrode decreases, reducing the reaction area and increasing resistance. The positive electrode material according to the second embodiment does not cover the entire surface of the active material with a coating material, but rather exposes part of the surface, thereby making it possible to both suppress side reactions and ensure an electron path.

[0021] In a third aspect of the present disclosure, for example, in the positive electrode material according to the first or second aspect, a coverage rate, which is the ratio of the surface area of ​​the positive electrode active material coated with the coating material to the total surface area of ​​the positive electrode active material, may be 10% or more and 90% or less.

[0022] The positive electrode material according to the third embodiment 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 oxide material may contain at least one selected from the group consisting of B, Si, P, Ge, and Te.

[0024] The positive electrode material according to the fourth embodiment can 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 oxide material may contain at least one selected from the group consisting of P, Si, and B.

[0026] The positive electrode material according to the fifth embodiment can more effectively reduce the resistance of the battery.

[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 oxide material may contain Li.

[0028] The positive electrode material according to the sixth aspect can increase the carrier 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.

[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 oxide material may include at least one selected from the group consisting of lithium phosphate, lithium silicate, lithium borate, and lithium silicophosphate.

[0030] The positive electrode material according to the seventh aspect can increase the lithium ion conductivity in the coating material. Specifically, when the coating material contains a lithium compound of an oxide known as a glass-forming oxide, such as phosphoric acid or silicate, a portion of the coating material becomes amorphous, widening the ion conduction path, which is thought to increase the lithium ion conductivity. As a result, the positive electrode material according to the fourth aspect can more effectively reduce the resistance 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, the mass ratio of the oxide material to the positive electrode active material may be 0.1 mass % or more and 2.3 mass % or less.

[0032] By setting the mass ratio of the oxide material to the cathode active material to 0.1 mass% or more, side reactions between the cathode active material and the first solid electrolyte can be effectively suppressed. Therefore, the cathode material according to the eighth aspect can more effectively reduce the resistance of the battery. Furthermore, by setting the mass ratio of the oxide material to the cathode active material to 2.3 mass% or less, the proportions of the cathode active material and the first solid electrolyte in the cathode can be increased. Therefore, the cathode material according to the eighth aspect can increase the energy density of the battery.

[0033] 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 mass ratio of the oxide material to the positive electrode active material may be 0.1 mass % or more and 2.0 mass % or less.

[0034] By setting the mass ratio of the oxide material to the cathode active material to 0.1 mass% or more, side reactions between the cathode active material and the first solid electrolyte can be effectively suppressed. Therefore, the cathode material according to the ninth aspect can more effectively reduce the resistance of the battery. Furthermore, by setting the mass ratio of the oxide material to the cathode active material to 2.0 mass% or less, the proportions of the cathode active material and the first solid electrolyte in the cathode can be increased. Therefore, the cathode material according to the ninth aspect can increase the energy density of the battery.

[0035] 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 mass ratio of the oxide material to the positive electrode active material may be 0.25 mass % or more and 1.14 mass % or less.

[0036] By setting the mass ratio of the oxide material to the positive electrode active material to 0.25 mass% or more, side reactions between the positive electrode active material and the first solid electrolyte can be effectively suppressed. Therefore, the positive electrode material according to the tenth aspect can more effectively reduce the resistance of the battery. Furthermore, by setting the mass ratio of the oxide material to the positive electrode active material to 1.14 mass% or less, the proportions of the positive electrode active material and the first solid electrolyte in the positive electrode can be increased. Therefore, the positive electrode material according to the tenth aspect can increase the energy density of the battery.

[0037] 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 M may include Y (ie, yttrium).

[0038] The positive electrode material according to the eleventh aspect can further improve the ionic conductivity of the first solid electrolyte, thereby further improving the charge / discharge efficiency of the battery.

[0039] In a twelfth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to eleventh aspects, the X may include at least one selected from the group consisting of F, Cl, and Br.

[0040] The positive electrode material according to the twelfth aspect can further improve the ionic conductivity of the first solid electrolyte, thereby further improving the charge / discharge efficiency of the battery.

[0041] In a thirteenth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to twelfth aspects, the X may include at least two selected from the group consisting of F, Cl, and Br.

[0042] In the positive electrode material according to the thirteenth aspect, the ionic conductivity of the first solid electrolyte can be further improved, thereby further improving the charge / discharge efficiency of the battery.

[0043] In a fourteenth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to thirteenth aspects, the X may include Cl and Br.

[0044] In the positive electrode material according to the fourteenth aspect, the ionic conductivity of the first solid electrolyte can be further improved, thereby further improving the charge / discharge efficiency of the battery.

[0045] In a fifteenth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to fourteenth aspects, the positive electrode active material may contain a lithium-containing transition metal oxide.

[0046] The positive electrode material according to the fifteenth aspect can improve the energy density of a battery.

[0047] A battery according to a sixteenth aspect of the present disclosure comprises: a positive electrode comprising the positive electrode material according to any one of the first to fifteenth aspects; a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode; Equipped with.

[0048] In the battery according to the sixteenth aspect, the charge / discharge efficiency can be improved.

[0049] In a seventeenth aspect of the present disclosure, for example, in the battery according to the sixteenth aspect, the electrolyte layer may include a sulfide solid electrolyte.

[0050] In the battery according to the seventeenth aspect, the charge / discharge efficiency can be improved.

[0051] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0052] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of the positive electrode material 1000 in Embodiment 1. The positive electrode material 1000 in Embodiment 1 includes a first solid electrolyte 100, a positive electrode active material 110, and a coating material 111 that coats the surface of the positive electrode active material 110. As shown in FIG. 1, the first solid electrolyte 100 and the positive electrode active material 110 may be in a particulate form. A part of the surface of the positive electrode active material 110 is not coated with the coating material 111 and is exposed. That is, the positive electrode active material 110 and the first solid electrolyte 100 are separated by the coating material 111, and there are a contacting part and a non-contacting part. The coating material 111 includes an oxide material.

[0053] The first solid electrolyte 100 is represented by the following compositional formula (1). Li a M b X c ···Formula (1)

[0054] In the above compositional formula (1), a, b, and c are positive real numbers and satisfy the mathematical formula: a + b < c. 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.

[0055] Regarding M in the compositional formula (1) of the first solid electrolyte 100, the "metalloid element" means B, Si, Ge, As, Sb, and Te. The "metal element" means all elements included in Groups 1 to 12 of the periodic table excluding hydrogen, and elements included in Groups 13 to 16 excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. That is, it is a group of elements that can become cations when forming a halogen compound and an inorganic compound.

[0056] 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. This suppresses side reactions in the halide solid electrolyte, thereby suppressing the formation of an oxide layer and, as a result, reducing the interfacial resistance of the electrode reaction. Furthermore, the cathode material 1000 of this embodiment contains a halide solid electrolyte. The coating material 111 that coats the cathode active material 110 contains an oxide material and does not completely coat the entire surface of the cathode active material 110. That is, a portion of the surface of the cathode active material 110 is exposed. Therefore, the cathode material 1000 of this embodiment can simultaneously suppress side reactions in the cathode during charging and ensure an electron path. For these reasons, the cathode material 1000 of this embodiment can reduce the resistance of the battery. As a result, the charge / discharge efficiency of the battery can be improved.

[0057] In order to further suppress side reactions in the battery and more effectively reduce the battery resistance, the coverage, which is the ratio of the surface area of ​​the positive electrode active material covered with the coating material 111 to the total surface area of ​​the positive electrode active material 110, may be 10% or more and 90% or less. In order to more effectively reduce the battery resistance, the coverage may be 18% or more and 87% or less. In order to more effectively reduce the battery resistance, the coverage may be 30% or more and 70% or less, or 40% or more and 60% or less.

[0058] 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.

[0059] 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 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.

[0060] The oxide material contained in the coating material 111 may include an oxoacid salt. When the coating material 111 includes 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" include B, Si, Ge, As, Sb, and Te. "Nonmetal elements" include N, P, S, Cl, Br, and I. In other words, these elements are a group of elements that combine with oxygen to form oxoacids.

[0061] The oxide material contained in the coating material 111 may include at least one selected from the group consisting of B, Si, P, Ge, and Te. This configuration allows the coating material 111 to have low electron conductivity on the surface of the active material 110, thereby further reducing side reactions in the battery. Elements such as B, Si, P, Ge, and Te form strong covalent bonds with oxygen. Therefore, electrons in the material forming the coating material 111 are delocalized, resulting in low electron conductivity. Therefore, even if the thickness of the coating layer formed from the coating material 111 is reduced, the exchange of electrons between the active material 110 and the first solid electrolyte 100 can be blocked, thereby more effectively suppressing side reactions.

[0062] The oxide material contained in the coating material 111 may contain at least one selected from the group consisting of P, Si, and B. This configuration allows the coating material 111 to be formed on the surface of the active material 110 with lower electronic conductivity, thereby further reducing side reactions in the battery. Elements such as P, Si, and B form stronger covalent bonds with oxygen. As a result, electrons in the material forming the coating material 111 are delocalized, resulting in lower electronic conductivity. Therefore, even if the thickness of the coating layer formed from the coating material 111 is reduced, the exchange of electrons between the active material 110 and the first solid electrolyte 100 can be blocked, thereby more effectively suppressing side reactions.

[0063] The oxide material contained in 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.

[0064] The coating material 111 may contain at least one selected from the group consisting of lithium phosphate, lithium silicate, lithium borate, and lithium silicophosphate. This configuration can increase the lithium ion conductivity in the coating material 111. This can more effectively reduce the resistance of the battery.

[0065] It is believed that the coating material 111 contains a lithium compound of an oxide known as a glass-forming oxide, such as phosphate, silicate, or borate, which makes a portion of the coating material 111 amorphous, widening the ion conduction path and thereby increasing lithium ion conductivity. This allows the cathode material 1000 to more effectively reduce the resistance of the battery.

[0066] The mass ratio of the oxide material contained in the coating material 111 to the positive electrode active material 110 may be 2.0 mass % or less, or may be 1.14 mass % or less. This configuration allows the proportion of the active material 110 or the first solid electrolyte 100 in the positive electrode to be increased, thereby increasing the energy density of the battery.

[0067] The mass ratio of the oxide material contained in coating material 111 to positive electrode active material 110 may be 0.1 mass % or more, or may be 0.25 mass % or more. This configuration can effectively suppress side reactions between active material 110 and first solid electrolyte 100, thereby more effectively reducing the resistance of the battery.

[0068] The mass ratio of the oxide material contained in the coating material 111 to the positive electrode active material 110 can be determined, for example, by dissolving the positive electrode in acid or the like to prepare an aqueous solution, and then quantifying the elements contained therein using inductively coupled plasma (ICP) atomic emission spectroscopy to determine the mass ratio. In this case, the mass ratio can be determined from the quantitative values ​​of elements contained in only one of the active material 110 or the coating material 111, assuming a stoichiometric composition. For example, if LiNiO2 is coated with Li3PO4, the mass ratio of the coating material can be determined from the quantitative values ​​of Ni and P, assuming that LiNiO2 and Li3PO4 exist in a stoichiometric composition.

[0069] In the above composition formula (1), M may contain Y (=yttrium). That is, the first solid electrolyte 100 may contain Y as a metal element. This configuration can further improve the ionic conductivity of the first solid electrolyte 100. This can further improve the charge / discharge efficiency of the battery.

[0070] In the above composition formula (1), 2.5≦a≦3, 1≦b≦1.1, 5.4≦c≦6.6, may be satisfied.

[0071] 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.

[0072] In the above composition formula (1), X may contain at least one element selected from the group consisting of F, Cl, and Br. This configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0073] The X (=anion) contained in the first solid electrolyte 100 may further contain oxygen in addition to at least one element selected from the group consisting of F, Cl, Br, and I. This configuration can further improve the ionic conductivity of the first solid electrolyte 100, thereby further improving the charge / discharge efficiency of the battery.

[0074] X in the above composition formula (1) may contain Cl and Br. This configuration can further improve the ionic conductivity of the first solid electrolyte 100. This can further improve the charge / discharge efficiency of the battery.

[0075] The positive electrode active material 110 may be a lithium-containing transition metal oxide. This configuration can improve the energy density of the battery.

[0076] For example, Li3YX6, Li2MgX4, Li2FeX4, Li(Al, Ga, In)X4, or Li3(Al, Ga, In)X6 may be used as the first solid electrolyte 100.

[0077] 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(Ni, Co, Al)O2, Li(Ni, Co, Mn)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.

[0078] To increase the energy density of the battery, the active cathode material 110 may be lithium nickel-cobalt-manganese oxide, for example, Li(Ni,Co,Mn)O2.

[0079] According to the above configuration, the energy density and charge / discharge efficiency of the battery can be further increased.

[0080] The coating material 111 may contain lithium phosphate or lithium silicate as a main component, and may further contain unavoidable impurities, or starting materials, by-products, decomposition products, etc. used in forming the coating material. That is, the coating material 111 may contain, for example, a total of 50% or more (50 mass% or more) of lithium phosphate and lithium silicate in mass relative to the entire coating material 111. The coating material 111 may contain, for example, 100% (100 mass%) of the total of lithium phosphate and lithium silicate in mass relative to the entire coating material 111, excluding unavoidable impurities.

[0081] The thickness of the coating material 111 may be 1 nm or more and 100 nm or less.

[0082] 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 can be suppressed, thereby improving the charge / discharge efficiency.

[0083] 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.

[0084] The thickness of the coating material 111 may be 2 nm or more and 40 nm or less.

[0085] 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.

[0086] 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.

[0087] The method for measuring the thickness of the coating material 111 is not particularly limited, but for example, it can be determined by directly observing the thickness of the coating material 111 using a transmission electron microscope or the like. Alternatively, it can be determined from the change in the spectrum derived from the active material by measuring XPS while scraping off the coating layer by Ar sputtering.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] In the first embodiment, the median diameter of first solid electrolyte 100 may be smaller than that of positive electrode active material 110 .

[0092] 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.

[0093] The median diameter of the positive electrode active material 110 may be 0.1 μm or more and 100 μm or less.

[0094] If the median diameter of the positive electrode active material 110 is smaller than 0.1 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 results in a deterioration in the charge / discharge characteristics of the battery. Furthermore, if the median diameter of the positive electrode active material 110 is larger than 100 μm, lithium diffusion within the positive electrode active material 110 slows down. This may make it difficult for the battery to operate at high power.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] <Method for producing the first solid electrolyte> The first solid electrolyte in the first embodiment can be produced, for example, by the following method.

[0100] Prepare raw material powders of binary halides with a blend ratio of the desired composition. For example, to produce Li3YBr3Cl3, prepare LiBr and YCl3 in a molar ratio of 3:1.

[0101] In this case, "M" and "X" in the above composition formula can be determined by selecting the type of raw material powder. Also, by adjusting the raw materials, compounding ratio, and synthesis process, the above values ​​"a," "b," and "c" can be adjusted.

[0102] After thoroughly mixing the raw material powders, the raw material powders are mixed, pulverized, and reacted with each other using a mechanochemical milling method. Alternatively, after thoroughly mixing the raw material powders, they may be sintered in a vacuum.

[0103] <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.

[0104] 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.

[0105] Next, coating material 111 is formed on the surfaces of the particles of positive electrode active material 110. There are no particular limitations on the method for forming coating material 111. Methods for forming coating material 111 include a liquid phase coating method and a vapor phase coating method.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0111] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the second embodiment.

[0112] The battery 2000 in the second embodiment includes a positive electrode 201 , an electrolyte layer 202 , and a negative electrode 203 .

[0113] The positive electrode 201 includes the positive electrode material 1000 in the first embodiment.

[0114] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0115] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be improved.

[0116] 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 30≦v1 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.

[0117] 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.

[0118] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203 .

[0119] 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.

[0120] The second solid electrolyte contained in the electrolyte layer 202 may be the first solid electrolyte described in the above embodiment 1. That is, the electrolyte layer 202 may contain the first solid electrolyte described in the above embodiment 1.

[0121] According to the above configuration, the charge / discharge efficiency of the battery 2000 can be further improved.

[0122] The second solid electrolyte contained in electrolyte layer 202 may be a halide solid electrolyte different from the first solid electrolyte described above in embodiment 1. That is, electrolyte layer 202 may include a halide solid electrolyte different from the first solid electrolyte described above in embodiment 1.

[0123] According to the above configuration, the output density and charge / discharge efficiency of the battery 2000 can be improved.

[0124] The halide solid electrolyte contained in the electrolyte layer 202 may contain Y as a metal element.

[0125] According to the above configuration, the output density and charge / discharge efficiency of the battery 2000 can be further improved.

[0126] 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.

[0127] 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.

[0128] Examples of sulfide solid electrolytes are Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, or Li 10 GeP2S 12 , etc. In addition to these, LiX2 (X2: F, Cl, Br, I), Li2O, MO q , Li p M2O q (M2: any of P, Si, Ge, B, Al, Ga, In, Fe, and Zn) (p and q: natural numbers), etc. may be added.

[0129] The second solid electrolyte included in the electrolyte layer 202 may be an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte.

[0130] 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.

[0131] 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.

[0132] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0133] 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 a mass ratio of 50% or more (50 mass % or more) relative to the entire electrolyte layer 202.

[0134] According to the above configuration, the charge / discharge characteristics of the battery 2000 can be further improved.

[0135] Furthermore, the electrolyte layer 202 may contain the second solid electrolyte in a mass ratio relative to the entire electrolyte layer 202 of 70% or more (70 mass % or more).

[0136] According to the above configuration, the charge / discharge characteristics of the battery 2000 can be further improved.

[0137] 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.

[0138] Furthermore, the electrolyte layer 202 may contain the second solid electrolyte in a mass ratio of 100% (100 mass %) relative to the entire electrolyte layer 202, excluding unavoidable impurities, for example.

[0139] According to the above configuration, the charge / discharge characteristics of the battery 2000 can be further improved.

[0140] As described above, the electrolyte layer 202 may be composed of only the second solid electrolyte.

[0141] The electrolyte layer 202 may contain two or more of the materials listed as the second solid electrolyte. For example, the solid electrolyte layer may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0142] 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.

[0143] 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.

[0144] 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 simple 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.

[0145] The negative electrode 203 may contain a third solid electrolyte. This configuration improves the lithium ion conductivity inside the negative electrode, enabling high-power operation. The third solid electrolyte contained in the negative electrode 203 can be any of the materials listed as examples of the second solid electrolyte of the electrolyte layer 202.

[0146] The median diameter of the negative electrode active material particles may be 0.1 μm or more and 100 μm or less. If the median diameter of the negative electrode active material particles is smaller than 0.1 μm, there is a possibility that the negative electrode active material particles and the third solid electrolyte may not be well dispersed in the negative electrode 203. This may result in a deterioration in the charge / discharge characteristics of the battery 2000. Furthermore, if the median diameter of the negative electrode active material particles is larger than 100 μm, lithium diffusion within the negative electrode active material particles may be slow. This may result in difficulty in high-power operation of the battery.

[0147] 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.

[0148] 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. When v2≦95 is satisfied, it is easier for the battery 2000 to operate at high output.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] The shape of the battery 2000 in the second embodiment may be, for example, a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type.

[0154] 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]

[0155] Hereinafter, the present disclosure will be described in more detail with reference to examples and comparative examples.

[0156] <<Comparative Example 1>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon glove box with an Ar atmosphere at a dew point of -60°C or less (hereinafter referred to as "argon atmosphere"), 9.5 mg of lithium hydroxide and 24.0 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. In the coating material solution, the molar ratio of lithium to phosphorus was 3:1.

[0157] 2 g of Li(Ni,Co,Mn)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 to it while stirring.

[0158] After the entire coating material solution was added, stirring was continued until the solution was visually confirmed to be dry.

[0159] The dried powder was placed in an alumina crucible and heat-treated at 400°C for 3 hours in an oxygen atmosphere.

[0160] The powder obtained after the heat treatment was re-pulverized in an agate mortar to obtain the positive electrode active material of Comparative Example 1, the surface of which was coated with a coating material. The coating material was lithium phosphate.

[0161] [Preparation of sulfide solid electrolyte] In an argon atmosphere, Li2S and P2S5 were weighed out so that the molar ratio of Li2S:P2S5 was 75:25. These were then pulverized and mixed in a mortar. Then, a planetary ball mill (Fritsch, P-7) was used to mill the mixture at 510 rpm for 10 hours to obtain a glassy solid electrolyte. The glassy solid electrolyte was then heat-treated at 270°C for 2 hours in an inert atmosphere. This resulted in a glass-ceramic solid electrolyte, Li2S-P2S5.

[0162] [Battery construction] In an argon atmosphere, a positive electrode active material coated with lithium phosphate and a sulfide solid electrolyte, Li2S-P2S5, were prepared in a mass ratio of 85:15. These were mixed in an agate mortar to produce a positive electrode composite.

[0163] The sulfide solid electrolyte Li6PS5Cl (80 mg), LYBC powder (20 mg), and the above-mentioned positive electrode composite (19.5 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 an electrolyte layer.

[0164] 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 of the positive electrode, electrolyte layer, and negative electrode. The Li foil formed the negative electrode.

[0165] 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.

[0166] In this way, the battery of Comparative Example 1 was fabricated.

[0167] [Charge / discharge test] The battery of Comparative 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.

[0168] [Resistance measurement] FIG. 3 shows the Nyquist diagram of the battery of Comparative Example 1 at 3.7 V. The battery of Comparative 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 charged at a constant current of 0.140 mA, and charging was terminated at a voltage of 3.7 V. 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 around 100 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 the battery of Comparative Example 1 was estimated to be 53 ohms.

[0169] [Resistance change rate] A battery was fabricated in the same manner as the battery of Comparative Example 1, except that the positive electrode active material used in Comparative Example 1 was used without coating its surface with a coating material. This battery was used as a reference battery. The resistance of the reference battery was measured in the same manner as the resistance of the battery of Comparative Example 1. The resistance of the reference battery was estimated to be 2300 ohms. The resistance change rate of the battery of Comparative Example 1 was calculated by dividing the resistance of the battery of Comparative Example 1 by the resistance of the reference battery, multiplying the result by 100, and then subtracting 100 from the result. In other words, this value indicates the degree to which the resistance of the battery changed by coating the positive electrode active material with a coating material.

[0170] [Coverage measurement] FIG. 4A shows the O1s spectrum of the active material used in Comparative 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. In Example 1, described below, the same active material as that used in Comparative Example 1 was used. That is, the O1s spectrum of the active material measured by the XPS method shown in FIG. 4A is also a diagram showing the O1s spectrum of the active material used in Example 1, measured by the XPS method. Therefore, the O1s spectrum in FIG. 4A is shown as the spectrum of the active material used in Example 1.

[0171] Two peaks were observed, one centered at 528 eV and the other at 532 eV. The 528 eV peak is a peak derived from MO (Ni-O, Mn-O, Co-O) in the positive electrode active material. The 532 eV peak is a peak derived from CO in lithium carbonate, a surface impurity, and the other from PO in lithium phosphate. The peak area derived from the coating material was calculated by subtracting the peak area derived from the non-coated active material calcined at 400 °C in an oxygen atmosphere from the peak area derived from the non-coated active material at 532 eV. Figure 4B shows the O1s spectrum of the active material used in Comparative Example 1, measured by XPS, and the O1s spectrum of the active material not coated with a coating material, measured by XPS. In Comparative Example 4, described below, the same positive electrode active material NCM used in Comparative Example 1, but without a coating material, was used. That is, the O1s spectrum of the active material not coated with a coating material, as shown in FIG. 4B, obtained by the XPS method, is also a diagram showing the O1s spectrum of the active material used in Comparative Example 4. Therefore, in FIG. 4B, the two O1s spectra are shown as the spectra of the active materials used in Example 1 and Comparative Example 4, respectively.

[0172] 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 Comparative Example 1 was estimated to be 47%.

[0173] <<Comparative Example 2>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon atmosphere, 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.

[0174] 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.

[0175] The treated powder was placed in an alumina crucible and taken out into the air.

[0176] Next, a heat treatment was carried out in an air atmosphere at 300° C. for 1 hour.

[0177] The heat-treated powder was re-pulverized in an agate mortar to obtain a positive electrode active material of Comparative Example 2, the surface of which was coated with a coating material. The coating material was lithium niobate (LiNbO3).

[0178] [Battery construction] A battery was fabricated in the same manner as in Comparative Example 1, except that the positive electrode active material of Comparative Example 2 was used.

[0179] [Charge / discharge test] A charge-discharge test of the battery was carried out in the same manner as in Comparative Example 1.

[0180] [Resistance measurement] The resistance of the battery was measured in the same manner as in Comparative Example 1.

[0181] [Resistance change rate] The resistance change rate of Comparative Example 2 was determined in the same manner as in Comparative Example 1, using the reference battery used in Comparative Example 1 as the reference battery.

[0182] [Coverage measurement] The O1s peak of Nb—O derived from lithium niobate appears near 530 eV. The coverage was calculated from this value in the same manner as in Comparative Example 1. The coverage of the active material used in Comparative Example 2 was approximately 100%.

[0183] [Consideration 1] Table 1 shows the coverage of the active materials used in Comparative Examples 1 and 2, and the resistance change rate when a sulfide solid electrolyte was used as the first solid electrolyte.

[0184] Comparing the resistance change rates of Comparative Example 1 and Comparative Example 2, it can be seen that Comparative Example 2 has a larger resistance change rate in the negative direction, resulting in a greater reduction in resistance. It is known that direct contact between an active material and a sulfide solid electrolyte results in the formation of a highly resistive layer on the surface. Therefore, this result is thought to be due to the fact that the high coverage of lithium niobate prevents contact between the active material and the sulfide solid electrolyte, thereby suppressing the formation of a resistive layer. It can be seen that when sulfide is used as the solid electrolyte, a high coverage of lithium niobate is more effective.

[0185] [Table 1]

[0186] <<Example 1>> [Preparation of halide solid electrolytes] In an argon atmosphere, raw material powders of LiCl, YCl3, and YBr3 were prepared in a molar ratio of LiCl:LYCl3:YBr3 = 3.000:0.333:0.666. 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 then ground using a pestle and mortar. This resulted in a powder of the first solid electrolyte, hereinafter referred to as LYBC.

[0187] [Preparation of a positive electrode active material whose surface is coated with a coating material] In the same manner as in Comparative Example 1, a positive electrode active material whose surface was coated with lithium phosphate as a coating material was produced.

[0188] [Battery construction] In an argon atmosphere, a positive electrode active material whose surface was coated with lithium phosphate, a first solid electrolyte (LYBC), and a conductive additive (vapor grown carbon fiber (VGCF; manufactured by Showa Denko K.K.)) were prepared in a mass ratio of positive electrode active material:LYBC:VGCF = 80:18:2. These were mixed in an agate mortar to prepare a positive electrode composite. Thereafter, the battery of Example 1 was fabricated in the same manner as in Comparative Example 1.

[0189] [Charge / discharge test] A charge-discharge test of the battery was carried out in the same manner as in Comparative Example 1.

[0190] [Resistance measurement] The resistance of the battery was measured in the same manner as in Comparative Example 1.

[0191] [Resistance change rate] A battery was fabricated in the same manner as the battery of Example 1, except that the positive electrode active material used in Example 1 was used without coating its surface with a coating material. This battery was used as a reference battery. The resistance of the reference battery was measured in the same manner as the resistance of the battery of Comparative Example 1. The resistance of the reference battery was estimated to be 73 ohms. The resistance change rate of the battery of Example 1 was calculated by dividing the resistance of the battery of Example 1 by the resistance of the reference battery, multiplying the result by 100, and then subtracting 100 from the result. In other words, this value indicates the degree to which the resistance of the battery changed by coating the positive electrode active material with a coating material.

[0192] [Coverage measurement] The coverage of Example 1 was determined in the same manner as in Comparative Example 1. The coverage of the active material used in Example 1 was estimated to be 47%.

[0193] <<Comparative Example 3>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In the same manner as in Comparative Example 2, a positive electrode active material whose surface was coated with lithium phosphate as a coating material was produced.

[0194] [Secondary battery production] In an argon atmosphere, an active material coated with lithium niobate, a first solid electrolyte (LYBC), and a conductive additive (vapor grown carbon fiber (VGCF; manufactured by Showa Denko)) were prepared in a mass ratio of 80:18:2 (positive electrode active material:LYBC:VGCF). These were mixed in an agate mortar to prepare a positive electrode composite. The battery of Comparative Example 3 was fabricated in the same manner as in Comparative Example 1.

[0195] [Coverage measurement] The coverage of Comparative Example 3 was determined in the same manner as in Comparative Example 2. The coverage of the active material used in Comparative Example 3 was estimated to be approximately 100%.

[0196] [Consideration 2] Table 3 shows the coverage of the active materials used in Example 1 and Comparative Example 3, and the resistance change rate when a halide solid electrolyte was used as the first solid electrolyte.

[0197] Comparing the resistance change rates of Example 1 and Comparative Example 3, it can be seen that the resistance change rate of Example 1 is significantly negative, demonstrating a greater reduction in resistance than Comparative Example 3. Direct contact between a halide solid electrolyte and an active material oxidizes the halogen elements in the electrolyte. Therefore, as with the use of a sulfide solid electrolyte, coating the active material to prevent direct contact is effective in suppressing an increase in battery resistance. However, when a halide solid electrolyte is used as the first solid electrolyte, using lithium niobate with a high coverage rate can similarly result in loss of contact between the active materials and between the active material and the conductive additive, resulting in insufficient electronic conductivity in the positive electrode composite. On the other hand, in Example 1, in which lithium phosphate was used, only the highly reactive crystal faces of the active material are coated, suppressing reaction while leaving a portion of the active material exposed, presumably ensuring electronic connectivity. Thus, comparing Example 1 and Comparative Example 3 confirmed that a portion of the active material is preferably exposed when a halide solid electrolyte is used.

[0198] [Table 2]

[0199] <<Comparative Example 4>> [Battery construction] In an argon atmosphere, a positive electrode active material (NCM) not coated with a coating material, LYBC as a first solid electrolyte, and vapor-grown carbon fiber (VGCF; manufactured by Showa Denko) as a conductive additive were prepared in a mass ratio of NCM:LYBC:VGCF of 80:18:2. These were mixed in an agate mortar to prepare a positive electrode composite. A battery was fabricated in the same manner as in Comparative Example 1, except that this positive electrode composite was used. The resistance of the obtained battery was evaluated in the same manner as in Comparative Example 1.

[0200] <<Example 2>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon glove box, 3.2 mg of lithium hydroxide and 8.0 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. A positive electrode active material whose surface was coated with the coating material was prepared in the same manner as in Example 1.

[0201] [Battery construction] A battery was produced in the same manner as in Example 1, except that a positive electrode composite was produced using a positive electrode active material whose surface was coated with the coating material of Example 2. The resistance of the obtained battery was evaluated in the same manner as in Comparative Example 1.

[0202] [Coverage measurement] The coverage of Example 2 was determined in the same manner as in Comparative Example 1.

[0203] <<Example 3>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon atmosphere, 6.3 mg of lithium hydroxide and 16.0 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. A positive electrode active material whose surface was coated with the coating material was prepared in the same manner as in Example 1.

[0204] [Battery construction] A battery was produced in the same manner as in Example 1, except that a positive electrode composite was produced using a positive electrode active material whose surface was coated with the coating material of Example 3. The resistance of the obtained battery was evaluated in the same manner as in Comparative Example 1.

[0205] [Coverage measurement] The coverage of Example 3 was determined in the same manner as in Comparative Example 1.

[0206] <<Example 4>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon atmosphere, 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. A positive electrode active material whose surface was coated with the coating material was prepared in the same manner as in Example 1.

[0207] [Battery construction] A battery was produced in the same manner as in Example 1, except that a positive electrode composite was produced using a positive electrode active material whose surface was coated with the coating material of Example 4. The resistance of the obtained battery was evaluated in the same manner as in Comparative Example 1.

[0208] [Coverage measurement] In the same manner as in Comparative Example 1, the coverage of Example 4 was determined.

[0209] <<Example 5>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon atmosphere, 10.5 mg of lithium hydroxide, 11.4 mg of triethyl phosphate, and 13.1 mg of tetraethyl orthosilicate were dissolved in an appropriate amount of ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating material solution. A positive electrode active material whose surface was coated with the coating material was prepared in the same manner as in Example 1.

[0210] [Battery construction] A battery was produced in the same manner as in Example 1, except that a positive electrode composite was produced using a positive electrode active material whose surface was coated with the coating material of Example 5. The resistance of the obtained battery was evaluated in the same manner as in Comparative Example 1.

[0211] [Coverage measurement] In the same manner as in Comparative Example 1, the coverage of Example 5 was determined.

[0212] <<Example 6>> [Preparation of a positive electrode active material whose surface is coated with a coating material] In an argon atmosphere, 11.5 mg of lithium hydroxide and 25.0 mg of tetraethyl orthosilicate were dissolved in an appropriate amount of ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating material solution. A positive electrode active material whose surface was coated with the coating material was prepared in the same manner as in Example 1.

[0213] [Battery construction] A battery was produced in the same manner as in Example 1, except that a positive electrode composite was produced using a positive electrode active material whose surface was coated with the coating material of Example 6. The resistance of the obtained battery was evaluated in the same manner as in Comparative Example 1.

[0214] [Coverage measurement] In the same manner as in Comparative Example 1, the coverage of Example 6 was determined.

[0215] [Consideration 3] Table 3 shows the coating materials, assumed thicknesses, coating amounts, coating rates, and resistances at 3.7 V for Comparative Example 4 and Examples 1 to 6. FIG. 5 is a graph showing the correlation between the coating rates and resistances for the active materials of Comparative Example 4 and Examples 1 to 3 and 5 and 6.

[0216] The assumed thickness was calculated from the BET specific surface area of ​​the active material and the density of the coating material, assuming that the entire surface area that can be measured by the BET specific surface area is coated. Here, the BET specific surface area of ​​the active material is 0.5 m 2 g -1 , the density of lithium phosphate is 2.54 gcm -3 , the density of lithium silicophosphate is 2.47 gcm -3 , and the density of lithium silicate is 2.39 g cm -3 It was decided.

[0217] The coating amount is the mass ratio of the oxide material used as the coating material to the positive electrode active material. The mass ratio of the coating to the amount of active material was calculated assuming that the target coating material, for example, lithium phosphate, remained when all volatile components such as water and carbon dioxide had evaporated from the added coating raw material. The assumed reaction formula is shown in Equation (3) below. 3LiOH+(C2H5)3PO4+15 / 2O2→Li3PO4+9H2O↑+6CO2↑ …Formula (3)

[0218] Comparing the resistance of Comparative Example 4 with the resistance of Examples 1 to 6, it can be seen that the resistance of the battery can be reduced by coating the surface of the positive electrode active material with lithium phosphate, lithium silicophosphate, or lithium silicate.

[0219] As shown in Figure 5, the relationship between the coverage and the resistance shows that the resistance decreased as the coverage increased from 10% to 47%. On the other hand, the resistance increased as the coverage increased from 47% to 90%. This indicates that the resistance reduction effect is more pronounced when the exposed proportion of the active material is within a certain range. In the present invention, it was revealed that the resistance of the battery can be significantly reduced when the coverage is in the range of 10% to 90% compared to an uncoated battery.

[0220] [Table 3] [Industrial Applicability]

[0221] The battery of the present disclosure can be used, for example, as an all-solid-state lithium secondary battery. [Explanation of symbols]

[0222] 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 first solid electrolyte; a positive electrode active material, and 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 ... Formula (1) In the composition formula (1), a, b, and c are positive real numbers that satisfy the mathematical formula: a+b<c; M is at least one selected from the group consisting of metal elements and metalloid elements other than Li, and X is at least one selected from the group consisting of F, Cl, Br, and I; the coating material is made of at least one oxoacid salt selected from the group consisting of lithium phosphate and lithium silicophosphate; a coverage rate, which is a ratio of the surface area of ​​the positive electrode active material coated with the coating material to the total surface area of ​​the positive electrode active material, is 10% or more and 90% or less; Positive electrode material.

2. a mass ratio of the oxoacid salt to the positive electrode active material is 0.1 mass% or more and 2.3 mass% or less; The positive electrode material according to claim 1 .

3. a mass ratio of the oxoacid salt to the positive electrode active material is 0.1 mass% or more and 2.0 mass% or less; The positive electrode material according to claim 2 .

4. a mass ratio of the oxoacid salt to the positive electrode active material is 0.25 mass% or more and 1.14 mass% or less; The positive electrode material according to claim 1 .

5. The M includes Y. The positive electrode material according to claim 1 .

6. 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 5.

7. 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 6.

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

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

10. A positive electrode comprising the positive electrode material according to any one of claims 1 to 9. a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode; Equipped with battery.

11. The electrolyte layer includes a sulfide solid electrolyte. The battery of claim 10.

Images