Positive electrode material and battery

Abstract

A positive electrode material according to an aspect of the present disclosure includes a first solid electrolyte, a positive electrode active material, and a coating material that coats the surface of the positive electrode active material. The first solid electrolyte is represented by the following composition formula: LiaMbOcXd. In the composition formula, a, b, c, and d are positive real numbers, M is at least one selected from the group consisting of Ta and Nb, and X is at least one selected from the group consisting of Cl, Br, and I.

Description

Technical Field

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

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present disclosure provides a positive electrode material capable of reducing the resistance of a battery and further improving the charge and discharge efficiency.

Means for Solving the Problems

[0007] The positive electrode material of the present disclosure is a first solid electrolyte, a positive electrode active material, and A coating material that coats the surface of the positive electrode active material is included. The first solid electrolyte is represented by the following compositional formula (1). Li a M b O c X d ··· Formula (1) In the compositional formula (1), a, b, c, and d are positive real numbers, M is at least one selected from the group consisting of Ta and Nb, and X is at least one selected from the group consisting of Cl, Br, and I.

Advantages of the Invention

[0008] The present disclosure provides a positive electrode material capable of reducing the resistance of a battery and further improving the charge and discharge efficiency.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Modes for Carrying Out the Invention

[0010] (Findings on which the present disclosure is based) Patent Document 1 discloses an all-solid-state lithium battery including a lithium ion conductive solid electrolyte mainly made of sulfide and an active material whose surface is coated with a lithium ion conductive oxide. Patent Document 1 particularly discloses lithium niobate (i.e., LiNbO 3 It is described that by using the sulfide solid electrolyte as a lithium ion conductive oxide, the generation of a high resistance layer between the sulfide solid electrolyte and the surface of the positive electrode active material is suppressed, and the output characteristics are significantly improved.

[0011] Non-Patent Document 1 describes that the cause of the formation of a high-resistance layer between the sulfide solid electrolyte and the surface of the positive electrode active material is the interdiffusion of metal elements contained in the positive electrode active material and sulfur elements (i.e., S) constituting the solid electrolyte. In other words, the formation of such a high-resistance layer is due to S, which is a constituent element of the solid electrolyte.

[0012] According to the knowledge gained from 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 and polarization increases, 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 not containing S is used as the solid electrolyte contained in the positive electrode material, the surface of the active material is covered with a coating material, thereby reducing the resistance of the battery. The reason for this is not clear, but it is believed that various factors 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 of the coating material with the active material, the reactivity of the coating material with the solid electrolyte, and the physical contact between the active material and the solid electrolyte contribute in a complex manner.

[0014] For example, when a lithium ion conductive solid electrolyte used as a solid electrolyte of a battery is a halide, oxidation of the halogen contained in the solid electrolyte is induced when the potential of the positive electrode becomes high during the charging process of the battery. Due to such oxidation of the halogen, decomposition of the solid electrolyte occurs. Further, when the oxidation reaction of the halogen occurs, halogen gas is generated, so that a gap is generated at the contact interface between the active material and the solid electrolyte, and the effective reaction area is reduced. As a result, the resistance of the battery increases. It is considered that the oxidation of the halogen can be suppressed because the contact between the solid electrolyte and the high-potential active material is suppressed by interposing a coating material that coats the surface of the active material between the active material and the solid electrolyte. For these reasons, it is considered that the resistance of the battery can be reduced.

[0015] Based on the above findings, the inventors of the present invention have arrived at the following positive electrode materials of the present disclosure that can reduce the resistance of the battery.

[0016] (Outline of one aspect according to 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 the surface of the positive electrode active material and includes. Here, the first solid electrolyte is represented by the following compositional formula (1). Li a M b O c X d ··· Formula (1) In the compositional formula (1), a, b, c and d are positive real numbers, M is at least one selected from the group consisting of Ta and Nb, and X is at least one selected from the group consisting of Cl, Br and I.

[0017] 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, even when the potential of the positive electrode becomes high in the charging process of the battery, the transfer of electrons to and from the halide solid electrolyte is suppressed. For this reason, since the oxidation reaction of the halogen in the halide solid electrolyte is suppressed, the decomposition of the first solid electrolyte is suppressed and the generation of halogen gas is also suppressed. As a result, the deterioration of the first solid electrolyte is suppressed and the reduction of 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 aspect can reduce the resistance of the battery. As a further result, the positive electrode material according to the first aspect can also improve the charge-discharge efficiency of the battery.

[0018] 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.

[0019] The positive electrode material according to the second aspect can more effectively reduce the resistance of the battery and further improve the charge-discharge efficiency.

[0020] In the 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 F.

[0021] The positive electrode material according to the third aspect can more effectively reduce the resistance of the battery.

[0022] In the 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 contain at least one selected from the group consisting of B, N, P, S, and Si.

[0023] By including at least one selected from the group consisting of B, N, P, S, and Si in the coating material, a coating with low electron conductivity can be formed on the surface of the positive electrode active material. Therefore, the positive electrode material according to the fourth aspect can further reduce the oxidation reaction of the first solid electrolyte. In addition, elements such as B, N, P, S, and Si form strong covalent bonds with oxygen. Therefore, since the electrons in the coating material are delocalized, the electron conductivity of the coating made of the coating material becomes low. Therefore, even when the thickness of the coating material on the surface of the positive electrode active material is thin, the transfer of electrons between the positive electrode active material and the first solid electrolyte can be blocked, so that the oxidation reaction of the first solid electrolyte can be more effectively suppressed. Therefore, the positive electrode material according to the fourth aspect can more effectively reduce the resistance of the battery and further improve the charge-discharge efficiency.

[0024] 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 coating material may include an oxoacid salt having a non-metal or semi-metal as a cation.

[0025] The positive electrode material according to the fifth aspect can more effectively reduce the resistance of the battery.

[0026] 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 include a glass-forming oxide.

[0027] The positive electrode material according to the sixth aspect can increase the lithium ion conductivity in the coating material. Specifically, by including a lithium compound of an oxide called a glass-forming oxide such as phosphoric acid or silicic acid in the coating material, a part of the coating becomes amorphous and the ion conduction path becomes wider. Therefore, it is considered that the lithium ion conductivity in the coating material can be increased. Thereby, the positive electrode material according to the sixth aspect can more effectively reduce the resistance of the battery.

[0028] 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 coating material may include a mixed oxide.

[0029] The positive electrode material according to the seventh aspect can increase the lithium ion conductivity in the coating material. Specifically, since the coating material contains a lithium compound of an oxide called an intermediate oxide such as niobic acid, a part of the coating becomes amorphous and the ion conduction path becomes wider. For this reason, it is considered that the lithium ion conductivity in the coating material can be increased. Thereby, the positive electrode material according to the sixth aspect can more effectively reduce the resistance of the battery.

[0030] In the eighth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to seventh aspects, the coating material may contain Li.

[0031] The positive electrode material according to the eighth aspect can increase the carrier concentration, that is, the Li concentration, at the interface between the positive electrode active material and the first solid electrolyte. Therefore, the positive electrode material according to the eighth aspect can more effectively reduce the resistance of the battery.

[0032] In the ninth aspect of the present disclosure, for example, in the positive electrode material according to any one of the first to eighth aspects, the coating material may contain at least one selected from the group consisting of lithium phosphate, lithium niobate, lithium fluorosulfonate, and lithium bis(fluorosulfonyl)imide.

[0033] Lithium phosphate and lithium niobate can increase the lithium ion conductivity of the coating material. Further, lithium fluorosulfonate and lithium bis(fluorosulfonyl)imide can form a good interface between the positive electrode active material and the first solid electrolyte, that is, an interface with low resistance. Thereby, the positive electrode material according to the ninth aspect can more effectively reduce the resistance of the battery.

[0034] In the 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 contain Cl.

[0035] In the positive electrode material according to the 10th aspect, the ionic conductivity of the first solid electrolyte can be further improved. As a result, the positive electrode material according to the 10th aspect can further improve the charge-discharge efficiency of the battery.

[0036] In the 11th aspect of the present disclosure, for example, in the positive electrode material according to any one of the 1st to 10th aspects, the positive electrode active material may contain a lithium-containing transition metal oxide.

[0037] The positive electrode material according to the 11th aspect can improve the energy density of the battery.

[0038] The battery according to the 12th aspect of the present disclosure a positive electrode including a positive electrode material according to any one of the 1st to 11th aspects, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, and includes.

[0039] The battery according to the 12th aspect can reduce resistance and further improve the charge-discharge efficiency.

[0040] In the 13th aspect of the present disclosure, for example, in the battery according to the 12th aspect, the electrolyte layer may contain a sulfide solid electrolyte.

[0041] In the battery according to the 13th aspect, resistance can be reduced and the charge-discharge efficiency can be further improved.

[0042] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0043] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a 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. Note that the coating material 111 may coat the entire surface of the positive electrode active material 110 or may partially coat the surface of the positive electrode active material 110. That is, the coating material 111 only needs to coat at least a part of the surface of the positive electrode active material 110. In other words, the positive electrode active material 110 and the first solid electrolyte 100 are separated by the coating material 111, and there are portions that do not contact each other. The positive electrode active material 110 and the first solid electrolyte 100 may have portions that contact each other.

[0044] The first solid electrolyte 100 is represented by the following compositional formula (1). Li a M b O c X d ··· Formula (1)

[0045] In the above compositional formula (1), a, b, c, and d are positive real numbers. M is at least one selected from the group consisting of Ta and Nb. X is at least one selected from the group consisting of Cl, Br, and I.

[0046] In the positive electrode material 1000 in this embodiment, a coating material 111 is interposed between the positive electrode active material 110 and the first solid electrolyte 100 which is a halide solid electrolyte. Even when the potential of the positive electrode becomes high during the charging process of the battery, the transfer of electrons to and from the halide solid electrolyte is suppressed by this coating material 111. For this reason, since the oxidation reaction of the halogen in the first solid electrolyte 100 is suppressed, the decomposition of the first solid electrolyte 100 is suppressed, and the generation of halogen gas due to the oxidation reaction is also suppressed. As a result, the deterioration of the first solid electrolyte 100 is suppressed, and a decrease in the effective reaction area between the positive electrode active material 110 and the first solid electrolyte 100 is also suppressed. For these reasons, the positive electrode material 1000 in this embodiment can reduce the resistance of the battery. As a further result, the positive electrode material 1000 according to the first aspect can also improve the charge and 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. Thereby, direct contact between the positive electrode active material 110 and the first solid electrolyte 100 is suppressed, and the oxidation reaction of the first solid electrolyte 100 can be more reliably suppressed. For this reason, the charge and discharge characteristics of the battery can be further enhanced, and an increase in the reaction overvoltage of the battery can be suppressed.

[0048] Alternatively, the coating material 111 may coat a part of the surface of the positive electrode active material 110. By the particles of the plurality of positive electrode active materials 110 coming into direct contact with each other through the portion not covered by the coating material 111, the electron conductivity between the particles of the positive electrode active material 110 is improved. For this reason, the battery can operate at high output.

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

[0050] The oxide material that can be used for the coating material 111 is, for example, SiO 2 、Al 2 O 3 、TiO2 , B 2 O 3 , Nb 2 O 5 , WO 3 or ZrO 2 etc. The oxide solid electrolyte that can be used for the coating material 111 is, for example, Li 3 PO 4 etc. Li-P-O compounds such as LiNbO 3 etc. Li-Nb-O compounds such as LiBO 2 , Li 3 BO 3 etc. Li-B-O compounds such as LiAlO 2 etc. Li-Al-O compounds such as Li 4 SiO 4 etc. Li-Si-O compounds such as Li 2 SO 4 , Li 4 Ti 5 O 12 etc. Li-Ti-O compounds such as Li 2 ZrO 3 etc. Li-Zr-O compounds such as Li 2 MoO 3 etc. Li-Mo-O compounds such as LiV 2 O 5 etc. Li-V-O compounds or Li 2 WO 4 etc. Li-W-O compounds etc.

[0051] The coating material 111 may contain an oxide solid electrolyte. The oxide solid electrolyte has high ionic conductivity and high 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. By including an oxoacid salt in the coating material 111, the resistance of the battery can be more effectively reduced. The oxoacid salt may be an oxoacid salt having a non-metal or a semi-metal as a cation. As described above, the "semi-metal elements" are B, Si, Ge, As, Sb, and Te. The "non-metal elements" are N, P, S, Cl, Br, and I. That is, these elements are a group of elements that combine with oxygen to form an oxoacid.

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

[0054] By including at least one selected from the group consisting of B, N, P, S, and Si in the coating material 111, a coating with low electron conductivity can be formed on the surface of the positive electrode active material 110. Therefore, the positive electrode material 1000 in Embodiment 1 can further reduce the oxidation reaction of the first solid electrolyte 100. In addition, elements such as B, N, P, S, and Si form strong covalent bonds with oxygen. Therefore, since the electrons in the coating material 111 are delocalized, the electron conductivity of the coating made of the coating material 111 is lowered. Therefore, even when the thickness of the coating material 111 on the surface of the positive electrode active material 110 becomes thin, the transfer of electrons between the positive electrode active material 111 and the first solid electrolyte 100 can be blocked, so that the oxidation reaction of the first solid electrolyte 100 can be more effectively suppressed. Therefore, by including at least one selected from the group consisting of B, N, P, S, and Si in the coating material 111, the positive electrode material 1000 can more effectively reduce the resistance of the battery and further improve the charge-discharge efficiency.

[0055] The coating material 111 may contain Li. According to this configuration, the carrier concentration at the interface between the positive electrode active material 110 and the first solid electrolyte 100 can be increased, so that the resistance of the battery can be more effectively reduced.

[0056] When the coating material 111 contains Li, the molar ratio Li / (other cations) of lithium and other cations in the coating material 111 may be 0.2 or more and 3.6 or less, and may also be 0.2 or more and 3.0 or less. By the molar ratio Li / (other cations) being 0.2 or more and 3.6 or less, the lithium ion conductivity in the coating material 111 can be increased. Thereby, the resistance of the battery can be more effectively reduced.

[0057] The coating material 111 may contain a glass-forming oxide such as phosphoric acid or silicic acid. Here, the glass-forming oxide means a network-forming oxide that can form a glass alone. Elements that can be cations forming the glass-forming oxide, that is, elements called network formers, are, for example, Si, P, B, Ge, and V. By the coating material 111 containing 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 called a glass-forming oxide such as phosphoric acid or silicic acid, a part of the coating becomes amorphous and the ion conduction path becomes wider. For this reason, the lithium ion conductivity in the coating material 111 can be increased, and the resistance of the battery can be more effectively reduced.

[0058] The coating material 111 may contain an intermediate oxide such as niobic acid. Here, the intermediate oxide means an oxide that cannot form a glass alone (that is, cannot form a glass network alone), but can form a glass or enter the glass network depending on the composition. Elements that can be cations forming the intermediate oxide are, for example, Nb, Ti, Zn, Al, and Zr. By the coating material 111 containing 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 part of the coating becomes amorphous and the ion conduction path becomes wider. For this reason, the lithium ion conductivity in the coating material 111 can be increased, and the resistance of the battery can be more effectively reduced.

[0059] The coating material 111 may contain at least one selected from the group consisting of lithium phosphate, lithium niobate, lithium fluorosulfonate, and lithium bis(fluorosulfonyl)imide.

[0060] Lithium phosphate and lithium niobate can increase the lithium ion conductivity of the coating material 111. Further, lithium fluorosulfonate and lithium bis(fluorosulfonyl)imide can form a good interface between the positive electrode active material 110 and the first solid electrolyte 100, that is, an interface with low resistance. Thereby, the positive electrode material 1000 of the present embodiment can more effectively reduce the resistance of the battery.

[0061] The coating material 111 may contain at least one selected from the group consisting of lithium phosphate, lithium niobate, lithium fluorosulfonate, and lithium bis(fluorosulfonyl)imide as a main component, and further contain inevitable impurities, or starting materials, by-products, decomposition products, etc. used when forming the coating material 111. That is, the coating material 111 may contain the total of lithium phosphate, lithium niobate, lithium fluorosulfonate, and lithium bis(fluorosulfonyl)imide, for example, at 50% or more (50 mass% or more) in terms of the mass ratio to the whole of the coating material 111. The coating material 111 may contain the total of lithium phosphate, lithium niobate, lithium fluorosulfonate, and lithium bis(fluorosulfonyl)imide at 100% (100 mass%) in terms of the mass ratio to the whole of the coating material 111 excluding inevitable impurities due to mixing.

[0062] In Embodiment 1, the coating material 111 may be LiNbO 3 . LiNbO 3 has higher ion conductivity and higher high-potential stability. Therefore, by using LiNbO 3 , the charge and 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 and the battery is charged to increase the potential of the positive electrode, electrons are drawn from the first solid electrolyte 100, causing 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 the electronic contact between the positive electrode active material 110 - conductive assistant or between the positive electrode active materials 110 themselves. In that case, the electronic path from the current collector of the battery to the particles of each positive electrode active material 110 is cut off, and the isolated positive electrode active material 110 may cease to contribute to the charge - discharge reaction. That is, the apparent amount of the active material decreases, and the reaction area decreases, making it difficult to sufficiently reduce the resistance. On the other hand, by exposing a part of the surface of the positive electrode active material 110 without covering it with the coating material 111, it is possible to achieve both suppression of the oxidation reaction of the first solid electrolyte 100 and ensuring of the electronic path. Therefore, a part of the surface of the positive electrode active material 110 may be exposed without being covered by the coating material 111.

[0064] In order to more effectively suppress the oxidation reaction of the first solid electrolyte 100 and more effectively reduce the resistance of the battery, the coating rate, which is the ratio of the coated surface area of the positive electrode active material 111 coated by the coating material 111 to the total surface area of the positive electrode active material 110, may be 47% or more. In order to more effectively reduce the resistance of the battery, the above - mentioned coating rate may be 60% or more, or may be 100%.

[0065] The above - mentioned coating rate can be obtained by separating the peak of O1s in X - ray photoelectron spectroscopy (XPS). For example, when Li(Ni,Co,Mn)O 2 is used as the positive electrode active material 110 and lithium phosphate is used as the coating material 111, the coating ratio may be obtained by dividing the area of the O1s peak derived from the positive electrode active material with the peak top at around 529 eV by the area obtained by subtracting the O1s peak derived from carbonate appearing at around 531 eV from the O1s peak appearing at around 532 eV.

[0066] When it is difficult to accurately determine the coating ratio by the above method, as an alternative method, 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 may be determined by XPS measurement, and the coating rate may be determined from their ratio.

[0067] The coating material 111 may contain an oxoacid salt. By including an oxoacid salt in the coating material 111, the resistance of the battery can be more effectively reduced. The oxoacid salt may be an oxoacid salt having a non-metal or a semi-metal as a cation. As described above, the "semi-metal element" is B, Si, Ge, As, Sb, and Te. The "non-metal element" is N, P, S, Cl, Br, and I. That is, these elements are a group of elements that combine with oxygen to form an oxoacid.

[0068] The mass ratio of the coating material 111 to the positive electrode active material 110 may be 2.0 mass% or less, or may be 1.1 mass% or less. According to this configuration, since the ratio of the active material 110 or the first solid electrolyte 100 in the positive electrode can be increased, the energy density of the battery can be increased.

[0069] The mass ratio of the coating material 111 to the positive electrode active material 110 may be 0.1 mass% or more, or may be 0.2 mass% or more. According to this configuration, since the side reaction between the active material 110 and the first solid electrolyte 100 can be effectively suppressed, the resistance of the battery can be more effectively reduced.

[0070] The method for determining the mass ratio of the coating material 111 to the positive electrode active material 110 is, for example, after dissolving the positive electrode in an acid or the like to form an aqueous solution, the contained elements may be quantified by inductively coupled plasma (ICP) emission spectroscopic analysis, and the mass ratio may be determined. At this time, it may be determined assuming a stoichiometric composition from the quantification value of an element contained only in either the positive electrode active material 110 or the coating material 111. For example, when LiNiO 2 is coated with Li 3 PO 4 , from the quantification values of Ni and P, LiNiO 2and Li 3 PO 4 Assuming that it exists in a stoichiometric composition, the mass ratio of the coating material 111 may be obtained.

[0071] In the above composition formula (1), X may contain Cl. According to this configuration, the ionic conductivity of the first solid electrolyte 100 can be further improved. Thereby, the charge and discharge efficiency of the battery can be further improved.

[0072] The positive electrode active material 110 is, for example, a material having the property of occluding and releasing metal ions (for example, 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, or transition metal oxynitrides. Examples of the lithium-containing transition metal oxide are Li(Ni, Co, Al)O 2 , Li(Ni, Co, Mn)O 2 , or LiCoO 2 and the like. When, for example, 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.

[0073] In order to increase the energy density of the battery, the positive electrode active material 110 may be lithium nickel cobalt manganate. For example, the positive electrode active material 110 may be Li(Ni,Co,Mn)O 2 .

[0074] According to the above configuration, the energy density and charge and discharge efficiency of the battery can be further increased.

[0075] The thickness of the coating material 111 may be 1 nm or more and 100 nm or less.

[0076] Since the thickness of the coating material 111 is 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. Therefore, the charge and discharge efficiency can be improved.

[0077] Further, when the thickness of the coating material 111 is 100 nm or less, the thickness of the coating material 111 does not become too large. Therefore, the internal resistance of the battery can be made sufficiently small. As a result, the energy density of the battery can be increased.

[0078] The thickness of the coating material 111 may be 2 nm or more and 40 nm or less.

[0079] 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 better suppressed, and side reactions of the first solid electrolyte 100 can be suppressed. Therefore, the charge-discharge efficiency can be better improved.

[0080] Further, when the thickness of the coating material 111 is 40 nm or less, the internal resistance of the battery can be made smaller. As a result, the energy density of the battery can be increased.

[0081] The method for measuring the thickness of the coating material 111 is not particularly limited. For example, it can be obtained by directly observing the thickness of the coating material 111 using a transmission electron microscope or the like. Also, it can be obtained from the change in the spectrum derived from the active material by measuring XPS while etching the coating layer by Ar sputtering.

[0082] The shape of the first solid electrolyte 100 in Embodiment 1 is not particularly limited, and may be, for example, needle-shaped, spherical, ellipsoidal, or the like. For example, the shape of the first solid electrolyte 100 may be particulate.

[0083] For example, when the shape of the first solid electrolyte 100 in Embodiment 1 is particulate (for example, spherical), the median diameter may be 100 μm or less. When the median diameter is 100 μm or less, the positive electrode active material 110 and the first solid electrolyte 100 are in a good dispersion state in the positive electrode material 1000, so the charge-discharge characteristics are improved. Also, in Embodiment 1, the median diameter may be 10 μm or less.

[0084] According to the above configuration, in the positive electrode material 1000, the positive electrode active material 110 and the first solid electrolyte 100 can form a good dispersion state.

[0085] Further, in Embodiment 1, the first solid electrolyte 100 may be smaller than the median diameter of the positive electrode active material 110.

[0086] According to the above configuration, in the electrode, the first solid electrolyte 100 and the positive electrode active material 110 can form a better dispersion state.

[0087] The median diameter of the positive electrode active material 110 may be 0.1 μm or more and 100 μm or less.

[0088] When the median diameter of the positive electrode active material 110 is 0.1 μm or more, in the positive electrode material 1000, the positive electrode active material 110 and the first solid electrolyte 100 form a good dispersion state in the positive electrode material 1000, so that the charge-discharge characteristics of the battery are improved. Further, when the median diameter of the positive electrode active material 110 is 100 μm or less, the diffusion of lithium in the positive electrode active material 110 is fast, so that the operation of the battery at high output becomes easier.

[0089] The median diameter of the positive electrode active material 110 may be larger than the median diameter of the first solid electrolyte 100. Thereby, the positive electrode active material 110 and the first solid electrolyte 100 can form a good dispersion state.

[0090] The median diameter means the particle diameter when the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured by, for example, a laser diffraction type measuring device or an image analysis device.

[0091] In addition, in the positive electrode material 1000 in Embodiment 1, the first solid electrolyte 100 and the coating material 111 may be in contact with each other as shown in FIG. 1.

[0092] The positive electrode material 1000 in Embodiment 1 may include a plurality of particulate first solid electrolytes 100 and a plurality of particulate positive electrode active materials 110.

[0093] Also, in the positive electrode material 1000 in Embodiment 1, 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.

[0094] <Manufacturing method of the first solid electrolyte> The first solid electrolyte in Embodiment 1 can be manufactured, for example, by the following method.

[0095] Raw material powders having a blending ratio of the target composition are prepared and mixed. Examples of the raw material powders are oxides, hydroxides, halides, or acid halides. For example, when producing a solid electrolyte composed of Li, Ta, O, and Cl, LiOH and TaCl 5 are prepared in a molar ratio of 1:1.

[0096] At this time, by selecting the type of the raw material powder, "M" in the above composition formula (1) can be determined. Further, by adjusting the raw materials, the blending ratio, and the synthesis process, the above values "a", "b", "c", and "d" can be adjusted.

[0097] After thoroughly mixing the raw material powders, the raw material powders are mixed, pulverized, and reacted with each other using the method of mechanochemical milling. Alternatively, after thoroughly mixing the raw material powders, they may be sintered in a vacuum.

[0098] Thereby, the first solid electrolyte is obtained.

[0099] <Manufacturing method of the positive electrode active material coated with the coating material> The positive electrode active material 110 coated with the coating material 111 can be manufactured by the following method.

[0100] First, prepare the powder of the positive electrode active material 110. The powder of the positive electrode active material 110 is produced, for example, by a coprecipitation method. In the coprecipitation method, a precursor composed of a metal oxide is produced, and the positive electrode active material 110 can be produced by firing the precursor together with a lithium source. Also, powders of positive electrode active materials 110 with various compositions are commercially available and can be easily obtained.

[0101] Next, form the coating material 111 on the surface of the particles of the positive electrode active material 110. The method for forming the coating material 111 is not particularly limited. Examples of the method for forming the coating material 111 include a liquid phase coating method and a gas phase coating method.

[0102] 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.

[0103] Note that the raw materials are not limited in any way as long as they are dissolved or dispersed in a solvent. Examples of the lithium source include alkyllithiums such as tert-butyllithium, lithium alkoxides such as lithium methoxide, lithium ethoxide, lithium isopropoxide, lithium-tert-butoxide, lithium iodide, lithium bromide, lithium chloride, lithium carbonate, lithium nitrate, lithium sulfate, or metallic lithium. Examples of the phosphate source include trimethyl phosphate, tripropyl phosphate, tributyl phosphate, phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, or ammonium phosphate. Raw materials containing phosphate and lithium may also be used.

[0104] The solvent is, for example, an alcohol such as ethanol. However, the solvent is not limited at all as long as it can dissolve or disperse the raw material, and various solvents can be selected depending on the raw material. Examples of the solvent are methanol, propanol, isopropanol, butanol, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl sulfoxide, tetrahydrofuran, hexane, benzene, toluene, methylene chloride, acetone, or acetonitrile.

[0105] According to the target composition of the coating material 111, the amounts of lithium hydroxide and triethyl phosphate are adjusted. If necessary, water may be added to the precursor solution. The precursor solution may be acidic or alkaline.

[0106] (Embodiment 2) Hereinafter, Embodiment 2 will be described. Descriptions overlapping with Embodiment 1 will be omitted as appropriate.

[0107] FIG. 2 is a cross-sectional view showing a schematic configuration of the battery 2000 in Embodiment 2.

[0108] The battery 2000 in Embodiment 2 includes a positive electrode 201, an electrolyte layer 202, and a negative electrode 203.

[0109] The positive electrode 201 includes the positive electrode material 1000 in Embodiment 1.

[0110] The electrolyte layer 202 is disposed between the positive electrode 201 and the negative electrode 203.

[0111] According to the above configuration, the charge and discharge efficiency of the battery 2000 can be improved.

[0112] Regarding the volume ratio "v1:100 - v1" of the positive electrode active material 110 and the first solid electrolyte 100 contained in the positive electrode 201, 30 ≤ v1 ≤ 95 may be satisfied. 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 set to 100. When 30 ≤ v1 is satisfied, it is easy to ensure a sufficient energy density of the battery 2000. When v1 ≤ 95 is satisfied, the operation of the battery 2000 at high power becomes easier.

[0113] The thickness of the positive electrode 201 may be 10 μm or more and 500 μm or less. In addition, when the thickness of the positive electrode 201 is 10 μm or more, it is easy to ensure a sufficient energy density of the battery 2000. In addition, when the thickness of the positive electrode 201 is 500 μm or less, the operation of the battery 2000 at high power becomes easier.

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

[0115] The electrolyte layer 202 is a layer containing an electrolyte material. The electrolyte material is, for example, a solid electrolyte (that is, a second solid electrolyte). That is, the electrolyte layer 202 may be a solid electrolyte layer.

[0116] Examples of the second solid electrolyte contained in the electrolyte layer 202 include the first solid electrolyte described in the above-described Embodiment 1. That is, the electrolyte layer 202 may contain the first solid electrolyte described in the above-described Embodiment 1.

[0117] According to the above configuration, the charge and discharge efficiency of the battery 2000 can be further improved.

[0118] Examples of the second solid electrolyte contained in the electrolyte layer 202 may be a halide solid electrolyte different from the first solid electrolyte described in the above-described Embodiment 1. That is, the electrolyte layer 202 may contain a halide solid electrolyte different from the first solid electrolyte described in the above-described Embodiment 1.

[0119] According to the above configuration, the output density and charge-discharge efficiency of the battery 2000 can be improved.

[0120] The halide solid electrolyte contained in the electrolyte layer 202 may contain Y as a metal element.

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

[0122] As the second solid electrolyte contained in the electrolyte layer 202, a sulfide solid electrolyte may be used. That is, the electrolyte layer 202 may contain a sulfide solid electrolyte.

[0123] According to the above configuration, since a sulfide solid electrolyte excellent in 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.

[0124] Examples of the sulfide solid electrolyte are Li 2 S-P 2 S 5 、Li 2 S-SiS 2 、Li 2 S-B 2 S 3 、Li 2 S-GeS 2 、Li 3.25 Ge 0.25 P 0.75 S 4 、or Li 10 GeP 2 S 12 、etc. Also, LiX2, Li 2 O, M2O q 、Li p M2O q etc. may be added. Here, X2 is one or more elements selected from the group consisting of F, Cl, Br, and I. Also, M2 is any one of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. Also, p and q are each independently natural numbers.

[0125] As the second solid electrolyte contained in the electrolyte layer 202, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte may be used.

[0126] Examples of the oxide solid electrolyte include NASICON-type solid electrolytes typified by LiTi 2 (PO 4 ) 3 and its element substitution products, perovskite-type solid electrolytes of the (LaLi)TiO 3 system, LISICON-type solid electrolytes typified by Li 14 ZnGe 4 O 16 、Li 4 SiO 4 、LiGeO 4 and its element substitution products, garnet-type solid electrolytes typified by Li 7 La 3 Zr 2 O 12 and its element substitution products, Li 3 N and its H substitution products, Li 3 PO 4 and its N substitution products, LiBO 2 、Li 3 BO 3 etc. Based on Li-B-O compounds such as Li 2 SO 4 、Li 2 CO 3 etc. added glass, glass ceramics, etc. may be used.

[0127] Examples of the polymer solid electrolyte include compounds of a polymer compound and a lithium salt. 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 the ionic conductivity can be further increased. Examples of the lithium salt include LiPF 6 、LiBF 4 、LiSbF 6 、LiAsF 6 、LiSO 3 CF 3 、LiN(SO 2 CF 3) 2 、 LiN(SO 2 C 2 F 5 ) 2 、 LiN(SO 2 CF 3 )(SO 2 C 4 F 9 )、 LiC(SO 2 CF 3 ) 3 、 etc., can be used. As the lithium salt, one lithium salt selected from these can be used alone. Or, as the lithium salt, a mixture of two or more lithium salts selected from these can be used.

[0128] As the complex hydride solid electrolyte, for example, LiBH 4 -LiI, LiBH 4 -P 2 S 5 etc., can be used.

[0129] Note that the electrolyte layer 202 may contain a second solid electrolyte as a main component. That is, the electrolyte layer 202 may contain the second solid electrolyte, for example, at 50% or more (50 mass% or more) by mass ratio with respect to the whole electrolyte layer 202.

[0130] According to the above configuration, the charge and discharge characteristics of the battery 2000 can be further improved.

[0131] Also, the electrolyte layer 202 may contain the second solid electrolyte, for example, at 70% or more (70 mass% or more) by mass ratio with respect to the whole electrolyte layer 202.

[0132] According to the above configuration, the charge and discharge characteristics of the battery 2000 can be further improved.

[0133] Note that the electrolyte layer 202 may contain, while containing the second solid electrolyte as a main component, further inevitable impurities, or starting materials, by-products, decomposition products, etc. used when synthesizing the second solid electrolyte.

[0134] Further, the electrolyte layer 202 may contain a second solid electrolyte at a mass ratio of 100% (100% by mass) with respect to the entire electrolyte layer 202, for example, excluding inevitably mixed impurities.

[0135] According to the above configuration, the charge-discharge characteristics of the battery 2000 can be further improved.

[0136] As described above, the electrolyte layer 202 may be composed only of the second solid electrolyte.

[0137] Note that 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.

[0138] 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 circuit between the positive electrode 201 and the negative electrode 203 is reduced. Further, when the thickness of the electrolyte layer 202 is 300 μm or less, operation at high output becomes easy. That is, when 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 output.

[0139] The negative electrode 203 contains a material having the property of occluding and releasing metal ions (for example, lithium ions). The negative electrode 203 contains, for example, a negative electrode active material.

[0140] As the negative electrode active material, a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound, etc., can be used. The metal material may be a single metal. Or, the metal material may be an alloy. Examples of the metal material include lithium metal or a lithium alloy. Examples of the carbon material include natural graphite, coke, carbon in the process of graphitization, carbon fiber, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), a silicon compound, or a tin compound can be used as the negative electrode active material.

[0141] The negative electrode 203 may contain a third solid electrolyte. According to the above configuration, the lithium ion conductivity inside the negative electrode is enhanced, enabling operation at high output. As the third solid electrolyte contained in the negative electrode 203, the materials exemplified as the second solid electrolyte of the electrolyte layer 202 can be used.

[0142] 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, in the negative electrode 203, the negative electrode active material particles and the third solid electrolyte are in a good dispersion state, improving the charge and discharge characteristics of the battery 2000. Further, when the median diameter of the negative electrode active material particles is 100 μm or less, since the diffusion of lithium within the negative electrode active material particles is fast, operation of the battery at high output becomes easier.

[0143] The median diameter of the negative electrode active material particles may be larger than the median diameter of the third solid electrolyte. Thereby, a good dispersion state between the negative electrode active material particles and the solid electrolyte can be formed.

[0144] Regarding the volume ratio "v2:100 - v2" of the negative electrode active material particles and the solid electrolyte contained in the negative electrode 203, 30 ≤ v2 ≤ 95 may be satisfied. When 30 ≤ v2 is satisfied, it is easy to ensure a sufficient energy density of the battery 2000. When v2 ≤ 95 is satisfied, operation of the battery 2000 at high output becomes easier.

[0145] 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, operation of the battery 2000 at high output becomes easier.

[0146] 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 for the purpose of improving the adhesion between particles. The binder is used to improve the binding property of the materials constituting the electrode and the electrolyte layer. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, methyl polyacrylate ester, ethyl polyacrylate ester, hexyl polyacrylate ester, polymethacrylic acid, methyl polymethacrylate ester, ethyl polymethacrylate ester, hexyl polymethacrylate ester, polyvinyl acetate, polyvinyl pyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene butadiene rubber, carboxymethyl cellulose, and the like. Further, as the binder, 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 can be used. Also, two or more selected from these may be mixed and used as the binder.

[0147] At least one of the positive electrode 201 and the negative electrode 203 may contain a conductive aid for the purpose of enhancing the electron conductivity. Examples of the conductive aid 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, carbon fluoride, metal powders such as 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. When a carbon conductive aid is used, cost reduction can be achieved.

[0148] Note that the battery 2000 in Embodiment 2 can be configured as batteries of various shapes, such as coin type, cylindrical type, square type, sheet type, button type, flat type, laminated type, etc.

[0149] The battery 2000 in Embodiment 2 may be manufactured, for example, by preparing the cathode material 1000, the material for forming the electrolyte layer, and the material for forming the anode in Embodiment 1 respectively, and producing a laminate in which the cathode, the electrolyte layer, and the anode are arranged in this order by a known method.

Example

[0150] Hereinafter, the present disclosure will be described in more detail with reference to Examples and Comparative Examples.

[0151] <<Example 1>> [Preparation of Cathode Active Material Coated with Coating Material] In an argon glove box with an argon atmosphere having a dew point of -60°C or lower, 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.

[0152] On an agate mortar, 2 g of Li(Ni,Co,Mn)O 2 (hereinafter referred to as NCM) was prepared, and then the prepared coating material solution was gradually added thereto while stirring.

[0153] After all the coating material solution was added, stirring was performed until dryness could be visually confirmed.

[0154] The dried powder was placed in an alumina crucible and heat-treated at 400°C for 3 hours in an oxygen atmosphere.

[0155] The powder obtained after the heat treatment was re-ground in an agate mortar to obtain the cathode active material of Example 1 whose surface was coated with the coating material. The coating material is lithium phosphate (Li 3 PO4 ) was obtained.

[0156] [Fabrication of the First Solid Electrolyte] In a dry atmosphere with a dew point of -30°C or lower, LiOH and TaCl were used as raw material powders. 5 were weighed at a molar ratio of LiOH:TaCl 5 = 1:1. These raw material powders were pulverized and mixed in a mortar to obtain a mixed powder. The obtained mixed powder was milled using a planetary ball mill (manufactured by Fritsch, P-7 type) at 600 rpm for 24 hours. Subsequently, the mixed powder was fired at 200°C for 6 hours. Thus, a powder of the solid electrolyte of Example 1 composed of Li, Ta, O, and Cl was obtained.

[0157] Thus, a powder of the first solid electrolyte of Example 1 composed of Li, Ta, O, and Cl was obtained. The solid electrolyte of Example 1 composed of Li, Ta, O, and Cl is hereinafter referred to as "LTOC". The composition of the obtained first solid electrolyte of Example 1 was measured for Li and Ta by inductively coupled plasma optical emission spectrometry, for Cl by ion chromatography, and for O by inert gas fusion-infrared absorption method, respectively. The apparatuses used for the measurement of the composition were an inductively coupled plasma optical emission spectrometer ("iCAP7400" (manufactured by Thermo Fisher Scientific)), an ion chromatograph ("ICS-3000" (manufactured by Thermo Fisher Scientific)), and an oxygen analyzer ("EMGA-920" (manufactured by Horiba, Ltd.)). In the first solid electrolyte of Example 1, the molar ratio of Li / Ta was 1.20, and the molar ratio of O / Cl was 0.35.

[0158] [Fabrication of the Second Solid Electrolyte] In an argon atmosphere with a dew point of -60°C or lower, LiCl, YCl 3 and YBr 3 were used as raw material powders at a molar ratio of LiCl:LYCl 3 :YBr 3It was prepared at a molar ratio of 3.000:0.333:0.666. These were pulverized and mixed in a mortar. Next, the obtained mixture of raw material powders was fired at 500 °C for 3 hours using an electric furnace in an argon atmosphere. The obtained material was pulverized using a pestle and mortar. Thus, a powder of the second solid electrolyte containing Li, Y, Br, and Cl was obtained. The second solid electrolyte of Example 1 is hereinafter referred to as "LYBC".

[0159] [Fabrication of Battery] In an argon atmosphere with a dew point of -60 °C or lower, a cathode active material coated with lithium phosphate as a coating material, LTOC as the first solid electrolyte, and vapor-grown carbon fiber (VGCF) as a conductive assistant were prepared at a mass ratio of cathode active material:LTOC:VGCF = 77:21:2. By mixing these in an agate mortar, a cathode composite material was fabricated.

[0160] In an insulating outer cylinder, the sulfide solid electrolyte Li 6 PS 5 Cl (80 mg), LYBC powder (20 mg), and the above-mentioned cathode composite material (18.2 mg) were laminated in order. A pressure of 720 MPa was applied thereto to obtain a cathode and an electrolyte layer.

[0161] Next, a Li foil was laminated on the side of the electrolyte layer opposite to the side in contact with the cathode. A pressure of 80 MPa was applied thereto to fabricate a laminate of a cathode, an electrolyte layer, and an anode. The anode was formed by the Li foil.

[0162] Next, current collectors made of stainless steel were disposed above and below the laminate, and current collection leads were provided on the current collectors. Finally, using an insulating ferrule, the inside of the insulating outer cylinder was blocked from the outside air atmosphere and sealed.

[0163] Thus, the battery of Example 1 was fabricated.

[0164] [Charge and Discharge Test] The battery of Example 1 was placed in a thermostatic bath at 25°C. The battery was charged at a constant current with a current value of 0.140 mA, and the charging was terminated at a voltage of 4.3 V. Next, it was discharged at a constant current with the same current value of 0.140 mA, and the discharging was terminated at a voltage of 2.5 V. The ratio of the discharge capacity to the charge capacity at this time was defined as the charge-discharge efficiency. The charge-discharge efficiency of the battery in Example 1 was 96%.

[0165] [Resistance measurement] Figure 3 is a diagram showing the Nyquist diagram of the battery in Example 1 at 3.7 V. The battery of Example 1 was placed in a thermostatic bath at 25°C. Then, it was connected to a potentiostat equipped with a frequency response analyzer. After that, the battery was charged at a constant current with a current value of 0.140 mA, and the charging was terminated after reaching a voltage of 3.7 V. Then, the frequency dependence of the resistance component was evaluated by the alternating current impedance method. At this time, the resistance component appearing around 10 5 -10 2 Hz was separated by curve fitting and regarded as the resistance derived from the active material-solid electrolyte interface. From this measurement, the resistance of the battery in Example 1 was estimated to be 7 ohm.

[0166] [Measurement of coating rate] Figure 4A is a diagram showing the O1s spectrum in the XPS method of the active material used in Example 1. By the XPS method, the O1s spectrum of the surface of the positive electrode active material coated with lithium phosphate was obtained. As the XPS light source, Al-Kα rays were used.

[0167] Peaks centered at 528 eV and 528 eV were observed. The peak at 528 eV is a peak derived from M-O (Ni-O, Mn-O, Co-O) in the positive electrode active material. The 532 eV peak is a superposition of the C-O peak in lithium carbonate, which is a surface impurity, and the P-O peak in lithium phosphate. By subtracting from the peak area near 532 eV of the coated active material the peak area near 532 eV detected from the active material not coated with the coating material, which was calcined at 400 °C in an oxygen atmosphere, the influence derived from lithium carbonate was removed, and the peak area derived from the coating material was calculated. Fig. 4B is a diagram showing the O1s spectrum in the XPS method of the active material used in Example 1 and the O1s spectrum in the XPS method of the active material whose surface was not coated with the coating material. The O1s spectrum in the XPS method of the active material whose surface was not coated with the coating material shown in Fig. 4B is also a diagram showing the O1s spectrum in the XPS method of the active material used in Comparative Example 1. Therefore, in Fig. 4B, the O1s spectrum in the XPS method of the active material whose surface was not coated with the coating material is shown as the spectrum of the active material used in Comparative Example 1.

[0168] From these peaks, the ratio of M-O to P-O in O1s was determined to estimate the coating rate. The coating rate of lithium phosphate on the active material used in Example 1 was estimated to be 47%.

[0169] <<Example 2>> [Preparation of Positive Electrode Active Material Coated on the Surface with Coating Material] In an argon atmosphere, 5.95 g of lithium ethoxide (manufactured by Kanto Chemical Co., Inc., high purity chemical) and 36.43 g of pentaethoxynbium (manufactured by Kanto Chemical Co., Inc., high purity chemical) were dissolved in 500 mL of ultra-dehydrated ethanol (manufactured by Wako Pure Chemical Industries, Ltd.) to prepare a coating material solution.

[0170] For the formation of the coating material on the positive electrode active material NCM, a rolling fluidized granulation coating apparatus (manufactured by Powrex, FD-MP-01E) was used. The input amount of the positive electrode active material, the stirring rotation speed, and the liquid feeding rate of the coating material solution were set to 1 kg, 400 rpm, and 6.59 g / min, respectively.

[0171] The processed powder was placed in an alumina crucible and taken out in an air atmosphere.

[0172] Subsequently, heat treatment was performed at 300 °C for 1 hour in an air atmosphere.

[0173] The powder after heat treatment was re - pulverized in an agate mortar to obtain the positive electrode active material of Example 2 whose surface was coated with a coating material. The coating material was lithium niobate (LiNbO 3 )

[0174] [Fabrication of Battery] A battery was fabricated in the same manner as in Example 1, except that the positive electrode active material of Example 2 was used.

[0175] [Charge - Discharge Test] The charge - discharge test of the battery was carried out in the same manner as in Example 1.

[0176] [Resistance Measurement] The resistance of the battery was measured in the same manner as in Example 1.

[0177] [Measurement of Coating Rate] The O1s peak of Nb - O derived from lithium niobate appears around 530 eV. The coating rate was determined in the same manner as in Example 1 from this value. The coating rate of the active material used in Example 2 was approximately 100%.

[0178] [[Example 3]] [Fabrication of Positive Electrode Active Material Coated with Coating Material] In an argon glove box with an argon atmosphere having a dew point of - 50 °C or lower, 0.2 g of lithium bis(fluorosulfonyl)imide (LiN(SO 2 F) 2 ) powder was dissolved in 19.80 g of dimethyl carbonate to prepare a 1.0 mass% coating material solution. Lithium bis(fluorosulfonyl)imide is hereinafter referred to as "LiFSI".

[0179] After that, 2 g of NCM, which is a positive electrode active material, was prepared on a polyolefin container, and then 0.5 g of the prepared coating material solution was gradually dropped while stirring. Then, vacuum drying was performed at 100 °C to obtain the positive electrode active material of Example 3 whose surface was coated with the coating material. The coating material was lithium fluorosulfonate.

[0180] [Fabrication of Battery] A battery was fabricated in the same manner as in Example 1, except that the positive electrode active material of Example 3 was used.

[0181] [Charge and Discharge Test] The charge and discharge test of the battery was carried out in the same manner as in Example 1.

[0182] [Resistance Measurement] The resistance of the battery was measured in the same manner as in Example 1.

[0183] [Example 4] [Fabrication of Positive Electrode Active Material Coated with Coating Material] In an argon glove box with an argon atmosphere having a dew point of -50 °C or lower, 0.25 g of lithium fluorosulfonate (LiSO 3 F) powder was dissolved in 19.75 g of dimethyl carbonate to prepare a 1.25 mass% coating material solution.

[0184] After that, 2 g of NCM, which is a positive electrode active material, was prepared on a polyolefin container, and then 1.3 g of the prepared coating material solution was gradually dropped while stirring. Then, vacuum drying was performed at 100 °C to obtain the positive electrode active material of Example 4 whose surface was coated with the coating material. The coating material was LiFSI.

[0185] [Fabrication of Battery] A battery was fabricated in the same manner as in Example 1, except that the positive electrode active material of Example 4 was used.

[0186] [Charge and Discharge Test] The charge and discharge test of the battery was carried out in the same manner as in Example 1.

[0187] [Measurement of Resistance] The resistance of the battery was measured in the same manner as in Example 1.

[0188] <<Comparative Example 1>> [Preparation of Cathode Active Material] The NCM used as the cathode active material in Examples 1 to 4 was used as the cathode active material in Comparative Example 1 without coating the surface with the coating material.

[0189] [Fabrication of Battery] A battery was fabricated in the same manner as in Example 1, except that the cathode active material of Comparative Example 1 was used.

[0190] [Charge-Discharge Test] The charge-discharge test of the battery was carried out in the same manner as in Example 1.

[0191] [Measurement of Resistance] The resistance of the battery was measured in the same manner as in Example 1.

[0192] <<Comparative Example 2>> [Preparation of Cathode Active Material Coated with Coating Material] A cathode active material coated with a coating material was prepared in the same manner as in Example 1. That is, NCM coated with lithium phosphate (Li 3 PO 4 ) was used as the cathode active material in Comparative Example 2.

[0193] [Preparation of Sulfide Solid Electrolyte] In an argon glove box in an argon atmosphere with a dew point of -60°C or lower, Li 2 S and P 2 S 5 were used in a molar ratio of Li 2 S:P 2 S 5Weighed so that the ratio became 75:25. These were pulverized and mixed in a mortar. Then, using a planetary ball mill (manufactured by Fritsch, P-7 type), milling was performed at 510 rpm for 10 hours to obtain a glassy solid electrolyte. The glassy solid electrolyte was heat-treated at 270 °C for 2 hours in an inert atmosphere. As a result, a glass-ceramic solid electrolyte, Li 2 S-P 2 S 5 was obtained. Li 2 S-P 2 S 5 is hereinafter referred to as "LPS".

[0194] [Fabrication of Battery] In an argon atmosphere with a dew point of -60 °C or lower, a cathode active material coated with lithium phosphate as a coating material and LPS as a sulfide solid electrolyte were prepared at a mass ratio of cathode active material:LPS = 85:15. By mixing these in an agate mortar, a cathode composite material was fabricated. Thereafter, a battery was fabricated in the same manner as in Example 1.

[0195] [Charge-Discharge Test] The charge-discharge test of the battery was conducted in the same manner as in Example 1.

[0196] [Resistance Measurement] The resistance of the battery was measured in the same manner as in Example 1.

[0197] [Discussion 1] Table 1 shows the coating materials of the cathode active materials used in Examples 1 to 4, Comparative Example 1, and Comparative Example 2, the solid electrolytes used in the cathode materials, the resistance of the batteries, and the charge-discharge efficiency of the batteries.

[0198] When comparing the resistance and charge-discharge efficiency of the batteries of Examples 1 to 4 with those of the battery of Comparative Example 1, it can be seen that when LTOC is used as the solid electrolyte contained in the positive electrode material, and the surface of the positive electrode active material is coated with a coating material such as lithium phosphate, lithium niobate, lithium bis(fluorosulfonyl)imide, and lithium fluorosulfonate, the resistance of the battery can be reduced, and further the charge-discharge efficiency can be improved.

[0199] When comparing the resistance and charge-discharge efficiency of the battery of Example 1 with those of the battery of Comparative Example 2, it can be seen that even if the positive electrode active material coated with the same lithium phosphate is used, the battery of Example 1 using LTOC as the solid electrolyte contained in the positive electrode material is superior in terms of resistance and charge-discharge efficiency.

[0200] <<Example 5>> [Preparation of Positive Electrode Active Material Coated on the Surface with Coating Material] In the same manner as in Example 1, a positive electrode active material coated on the surface with a coating material was prepared. That is, NCM coated on the surface with lithium phosphate (Li 3 PO 4 ) was used as the positive electrode active material of Example 5.

[0201] [Preparation of First Solid Electrolyte] In a dry atmosphere with a dew point of -30°C or lower, Li 2 O 2 and NbCl 5 were used as raw material powders, with Li 2 O 2 :NbCl 5They were weighed in a molar ratio of 1:2. These were pulverized and mixed in a mortar to obtain a mixed powder. The obtained mixed powder was milled for 24 hours at 600 rpm using a planetary ball mill (manufactured by Fritsch, P-7 type). Subsequently, the mixed powder was calcined at 200 °C for 6 hours. Thereby, a powder of a solid electrolyte composed of Li, Nb, O, and Cl was obtained. The first solid electrolyte of Example 5, which consists of the obtained Li, Nb, O, and Cl, is hereinafter referred to as "LNOC". In the obtained LNCO, the molar ratio of Li / Nb was 1.2, and the molar ratio of O / Cl was 0.35. The composition of the first solid electrolyte of Example 5 was measured by ICP emission spectrometry for Li and Nb, ion chromatography for Cl, and inert gas fusion-infrared absorption method for O, respectively. The apparatuses used for the measurement of the composition were an ICP emission spectrometer ("iCAP7400" (manufactured by Thermo Fisher Scientific)), an ion chromatograph ("ICS-3000" (manufactured by Thermo Fisher Scientific)), and an oxygen analyzer ("EMGA-920" (manufactured by Horiba, Ltd.)).

[0202] [Fabrication of Battery] A battery was fabricated in the same manner as in Example 1, except that the cathode active material and the first solid electrolyte of Example 5 were used.

[0203] [Charge and Discharge Test] The charge and discharge test of the battery was conducted in the same manner as in Example 1. However, the cut-off voltage of the discharge, that is, the voltage at which the discharge ends, was set to 3V.

[0204] [Resistance Measurement] The resistance of the battery was measured in the same manner as in Example 1.

[0205] [Measurement of Coating Rate] The resistance measurement of the coating rate was conducted in the same manner as in Example 1. The coating rate of lithium phosphate of the active material used in Example 5 was estimated to be 47%.

[0206] [[Comparative Example 3]] [Preparation of Cathode Active Material] The NCM used as the positive electrode active material in Example 5 was used as the positive electrode active material in Comparative Example 3 without coating the surface with a coating material.

[0207] [Fabrication of Battery] A battery was fabricated in the same manner as in Example 5, except that the positive electrode active material of Comparative Example 3 was used.

[0208] [Charge and Discharge Test] The charge and discharge test of the battery was conducted in the same manner as in Example 5.

[0209] [Resistance Measurement] The resistance of the battery was measured in the same manner as in Example 5.

[0210] [Discussion 2] Table 1 shows the coating material of the positive electrode active material used in Example 5 and Comparative Example 3, the solid electrolyte used in the positive electrode material, the resistance of the battery, and the charge and discharge efficiency of the battery.

[0211] In the batteries of Example 5 and Comparative Example 3, the same LNOC was used as the solid electrolyte contained in the positive electrode material. As a result, even when LNOC was used as the solid electrolyte, it was confirmed that by coating the positive electrode active material with a coating material, the resistance of the battery was reduced and the charge and discharge efficiency of the battery was further improved. From this result, it can be seen that regardless of the difference in the metal species constituting the solid electrolyte, by coating the surface of the positive electrode active material with a coating material, the effect of reducing the resistance of the battery and further improving the charge and discharge efficiency can be obtained.

[0212]

Table 1

Industrial Applicability

[0213] The battery of the present disclosure can be used, for example, as an all-solid-state lithium secondary battery or the like.

Explanation of Reference Signs

[0214] 1000 Positive Electrode Material 100 First solid electrolyte 110 Positive electrode active material 111 Coating material 2000 Battery 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 the surface of the positive electrode active material are included, the first solid electrolyte is represented by the following compositional formula, Li a M b O c X d in the compositional formula, a, b, c, and d are positive real numbers, M is at least one selected from the group consisting of Ta and Nb, and X is at least one selected from the group consisting of Cl, Br, and I, a positive electrode material.

2. The coating material contains O, the positive electrode material according to Claim 1.

3. The coating material contains F, the positive electrode material according to Claim 1 or 2.

4. The coating material contains at least one selected from the group consisting of B, N, P, S, and Si, the positive electrode material according to any one of Claims 1 to 3.

5. The coating material contains an oxoacid salt having a non-metal or semi-metal as a cation, the positive electrode material according to any one of Claims 1 to 4.

6. The coating material contains a glass-forming oxide, the positive electrode material according to any one of Claims 1 to 5.

7. The coating material contains an intermediate oxide, the positive electrode material according to any one of Claims 1 to 6.

8. The coating material contains Li, the positive electrode material according to any one of Claims 1 to 7.

9. The coating material contains at least one selected from the group consisting of lithium phosphate, lithium niobate, lithium fluorosulfonate, and lithium bis(fluorosulfonyl)imide, the positive electrode material according to any one of Claims 1 to 8.

10. The X contains Cl, the positive electrode material according to any one of Claims 1 to 9.

11. The positive electrode active material contains a lithium-containing transition metal oxide, the positive electrode material according to any one of Claims 1 to 10.

12. A positive electrode containing the positive electrode material according to any one of Claims 1 to 11, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, are provided, a battery.

13. The electrolyte layer contains a sulfide solid electrolyte, the battery according to Claim 12.

Images