Positive electrode material, positive electrode, and battery

Abstract

A positive electrode material 100 according to the present disclosure includes a positive electrode active material 110, a solid electrolyte 112, and a conduction assistance agent 114, wherein: the positive electrode active material 110 includes a lithium cobalt oxide and a lithium nickel cobalt manganese oxide; and the content ratio of the lithium cobalt oxide in the positive electrode active material 110 is 8-92 mass%. The positive electrode active material 110 may include a mixture of particles of the lithium cobalt oxide and particles of the lithium nickel cobalt manganese oxide.

Description

Positive electrode material, positive electrode, and battery

[0001] This disclosure relates to cathode materials, cathodes, and batteries.

[0002] Lithium cobalt oxide and lithium nickel cobalt manganese oxide are typical positive electrode active materials for lithium secondary batteries. Lithium nickel cobalt manganese oxide is obtained by replacing some of the cobalt atoms in lithium cobalt oxide with nickel and manganese atoms. Lithium nickel cobalt manganese oxide is cheaper than lithium cobalt oxide and has a larger theoretical capacity. Therefore, the demand for lithium nickel cobalt manganese oxide is increasing.

[0003] International Publication No. 2017 / 145894

[0004] This disclosure aims to provide a cathode material suitable for achieving both the output characteristics and capacity of a battery containing a solid electrolyte.

[0005] This disclosure provides a positive electrode material comprising a positive electrode active material, a solid electrolyte, and a conductive additive, wherein the positive electrode active material comprises lithium cobalt oxide and lithium nickel cobalt manganese oxide, and the content of lithium cobalt oxide in the positive electrode active material is 8% by mass or more and 92% by mass or less.

[0006] The cathode material of this disclosure is suitable for achieving both the output characteristics and capacity of a battery containing a solid electrolyte.

[0007] Figure 1 is a cross-sectional view showing the schematic configuration of the positive electrode material according to Embodiment 1. Figure 2 is a cross-sectional view showing the schematic configuration of the positive electrode material according to Modification 1. Figure 3 is a cross-sectional view showing the schematic configuration of the positive electrode material according to Modifications 2 and 3. Figure 4 is a cross-sectional view showing the schematic configuration of the positive electrode according to Embodiment 2. Figure 5 is a cross-sectional view showing the schematic configuration of the battery according to Embodiment 3. Figure 6A is a graph showing the measurement results of the initial discharge capacity at 0.05C for the batteries of Examples 1 to 7, Comparative Example 1 and Comparative Example 2. Figure 6B is a graph showing the ratio of the initial discharge capacity at 1C to the initial discharge capacity at 0.05C (capacity retention rate). Figure 7 is a graph showing the measurement results of the pulse discharge voltage for the batteries of Examples 1 to 7, Comparative Example 1 and Comparative Example 2. Figure 8A is a graph showing the measurement results of the initial discharge capacity at 0.05C for the batteries of Example 3, Example 4, Comparative Example 1 and Comparative Example 3. Figure 8B is a graph showing the ratio of the initial discharge capacity at 1C to the initial discharge capacity at 0.05C (capacity retention rate) for the batteries of Example 3, Example 4, Comparative Example 1 and Comparative Example 3. Figure 9 is a graph showing the measurement results of the pulse discharge voltage of the batteries in Example 3, Example 4, Comparative Example 1, and Comparative Example 3.

[0008] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0009] (Embodiment 1) Figure 1 is a cross-sectional view showing the schematic configuration of a positive electrode material 100 according to Embodiment 1. The positive electrode material 100 includes a positive electrode active material 110, a solid electrolyte 112, and a conductive additive 114. The positive electrode active material 110 includes a first active material 101 and a second active material 102. The first active material 101 is lithium cobalt oxide. The second active material 102 is lithium nickel cobalt manganese oxide. In the positive electrode active material 110, the content of lithium cobalt oxide, which is the first active material 101, is 8% by mass or more.

[0010] In this specification, lithium cobalt oxide may be denoted as "LCO," and lithium nickel cobalt manganese oxide may be denoted as "NCM."

[0011] NCM has a larger capacity than LCO. NCM is also less expensive than LCO. Therefore, when battery capacity and cost are important, NCM is a desirable cathode active material. On the other hand, LCO has superior output characteristics. To achieve a balance between battery output characteristics and battery capacity, a combination of LCO and NCM can be considered.

[0012] By adjusting the content of the first active material 101, LCO, to 8% by mass or more, a sufficient effect of improving the output characteristics of the battery can be obtained. If the content of LCO is too low, the effect of improving the output characteristics will be insufficient. The second active material 102, NCM, is suitable for improving the capacity of the battery. By combining the first active material 101, LCO, and the second active material 102, NCM, a positive electrode material 100 suitable for achieving both the output characteristics and capacity of the battery can be provided.

[0013] LCO has a composition represented by LiCoO2. The content of LCO in the positive electrode active material 110 may be 92% by mass or less. When the content of LCO is 92% by mass or less, the output characteristics can be sufficiently improved while ensuring the initial discharge capacity of the positive electrode active material 110. The content of LCO may be less than 52% by mass.

[0014] The LCO content may be 8% by mass or more and 92% by mass or less, 8% by mass or more and less than 52% by mass, 8% by mass or more and 42% by mass or less, or 8% by mass or more and 22% by mass or less.

[0015] NCM is LiNi x Co y Mn z It has a composition represented by O2(x+y+z=1). In NCM, the ratio of the amount of nickel to the total amount of nickel, cobalt, and manganese may be 82% or less. If the proportion of nickel is high, the proportion of cobalt can be relatively reduced. In this case, the material cost of NCM can be reduced. Furthermore, by adjusting the proportion of nickel to an appropriate range, the effect brought about by the combination of LCO and NCM can be enhanced.

[0016] The lower limit of the ratio of nickel to the total amount of nickel, cobalt, and manganese is, for example, 28%. The lower limit of the ratio of nickel may also be 38%. From the viewpoint of NCM capacity and NCM material cost, it is desirable for the ratio of nickel to be moderately high in NCM.

[0017] The ratio of the amount of nickel to the total amount of nickel, cobalt, and manganese is, for example, 28% to 82%, preferably 38% to 82%, and more preferably 45% to 72%.

[0018] The first active material 101 may be LCO particles. The second active material 102 may be NCM particles. In other words, the positive electrode active material 110 may contain a mixture of LCO particles and NCM particles. With this configuration, the positive electrode material 100 can be easily prepared.

[0019] The LCO particles and NCM particles may be primary or secondary particles. The LCO particles and NCM particles have, for example, an average particle size of 1 μm to 10 μm. The average particle size refers to the particle diameter (median diameter) when the cumulative volume in the volume-based particle size distribution is 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction particle size analyzer.

[0020] The solid electrolyte 112 has lithium ion conductivity. Examples of solid electrolytes 112 include halide solid electrolytes, sulfide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes. Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12Examples include the following. As the polymer solid electrolyte, compounds such as a compound of a polymer compound having an ethylene oxide structure and a lithium salt can be mentioned. The lithium salt can be, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. Examples of the complex hydride solid electrolyte include LiBH4-LiI and LiBH4-P2S5. The halide solid electrolyte may be a material represented by the following formula (1).

[0021] Li α M3 β X’ γ ・・・Formula (1)

[0022] In formula (1), α, β, and γ are each independently values greater than 0, M3 is at least one selected from the group consisting of metal elements and semi-metal elements other than Li, and X’ is at least one selected from the group consisting of F, Cl, Br, and I.

[0023] The "semi-metal elements" include B, Si, Ge, As, Sb, and Te.

[0024] The "metal elements" include all elements contained in Groups 1 to 12 of the periodic table excluding hydrogen, and all elements contained in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. That is, the metal elements are a group of elements that can become cations when forming an inorganic compound with a halogen element.

[0025] The solid electrolyte 112 may contain at least one selected from the group consisting of a sulfide solid electrolyte and a halide solid electrolyte. In this case, the positive electrode material 100 has excellent lithium ion conductivity. The solid electrolyte 112 may be a sulfide solid electrolyte.

[0026] The conductive additive 114 is used to reduce the resistance of a battery using the positive electrode material 100. Examples of conductive additives include carbon materials and conductive polymer compounds. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. At least one of these conductive additives can be used.

[0027] The positive electrode material 100 may contain a binder.

[0028] A binder is used to improve the bonding properties of the materials constituting the positive electrode material 100. Examples of binders include polymer materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one of these binders can be used.

[0029] The positive electrode material 100 can be manufactured by mixing a first active material 101, a second active material 102, a solid electrolyte 112, and a conductive additive 114 in a desired ratio.

[0030] (Modification 1) Figure 2 is a cross-sectional view showing the schematic configuration of the positive electrode material 100a according to Modification 1. In the positive electrode material 100a according to Modification 1, at least a portion of the surface of the positive electrode active material 110 is covered by a coating layer 120. More specifically, at least a portion of the surface of the first active material 101 and / or at least a portion of the surface of the second active material 102 is covered by the coating layer 120.

[0031] When the positive electrode active material 110 is covered by the coating layer 120, direct contact between the positive electrode active material 110 and the solid electrolyte 112 is prevented. This suppresses the decomposition of the solid electrolyte 112 by the positive electrode active material 110. For example, if the solid electrolyte 112 contains sulfur, the positive electrode active material 110 and the solid electrolyte 112 may come into direct contact. When the positive electrode active material 110 and the solid electrolyte 112 come into direct contact, the solid electrolyte 112 may decompose and generate hydrogen sulfide gas. The coating layer 120 can suppress the generation of such hydrogen sulfide gas.

[0032] The coating layer 120 may be a layer containing a solid electrolyte that has lithium ion conductivity. With such a configuration, the coating layer 120 is less likely to hinder the conduction of lithium ions.

[0033] In this modified example 1, the solid electrolyte contained in the coating layer 120 may be referred to as the "first solid electrolyte."

[0034] The coating layer 120 may contain Li, Ti, M1, and F. M1 can be at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb. In other words, the first solid electrolyte contained in the coating layer 120 can be a fluoride solid electrolyte. In this case, the coating layer 120 has excellent oxidation resistance due to the high electronegativity of fluorine.

[0035] The coating layer 120 may consist substantially of the first solid electrolyte, or it may consist solely of the first solid electrolyte. Here, "the coating layer 120 consists substantially of the first solid electrolyte" means that the content of the first solid electrolyte in the coating layer 120 is 90% by mass or more. As an example, this content may be 95% by mass or more.

[0036] The first solid electrolyte contained in the coating layer 120 may consist substantially of Li, Ti, M1, and F, or it may consist only of Li, Ti, M1, and F. Here, "the first solid electrolyte consists substantially of Li, Ti, M1, and F" means that the molar ratio of the total amount of substance of Li, Ti, M1, and F to the total amount of substance of all elements constituting the first solid electrolyte is 90% or more. As an example, this molar ratio may be 95% or more.

[0037] In the first solid electrolyte, the ratio of the amount of Li to the sum of the amounts of Ti and M1 is, for example, 0.5 or more and 4.5 or less. When this ratio falls within this range, the first solid electrolyte has excellent lithium ion conductivity.

[0038] M1 may be at least one selected from the group consisting of Ca, Mg, and Al. In this case, the first solid electrolyte has excellent lithium ion conductivity.

[0039] M1 may be Al. In this case, the first solid electrolyte has excellent lithium ion conductivity.

[0040] The first solid electrolyte may have a composition represented by the following formula (2).

[0041] Li6-(4-4x+m1x)b(Ti 1-x M1 x ) b F6...Formula (2)

[0042] In equation (2) above, the conditions 0 < x < 1 and 0 < b ≤ 2 are satisfied. Note that m1 is the valence of M1.

[0043] When the first solid electrolyte has the composition represented by formula (2) above, the first solid electrolyte has excellent lithium ion conductivity.

[0044] The first solid electrolyte does not need to contain sulfur. With this configuration, the generation of hydrogen sulfide gas can be prevented. Therefore, it becomes possible to realize a battery with improved safety.

[0045] In the example shown in Figure 2, the first active material 101 and the second active material 102 are each covered by a coating layer 120.

[0046] The coating layer 120 can be formed by depositing the first solid electrolyte onto the surface of the particles of the first active material 101 and / or the surface of the particles of the second active material 102.

[0047] The method for attaching the first solid electrolyte to the surface of the particles of the first active material 101 and / or the surface of the particles of the second active material 102 is not particularly limited. For example, the first active material 101, the second active material 102 and the first solid electrolyte are mixed in an appropriate ratio to obtain a mixture. The mixture is then milled to impart mechanical energy to it. A mixing device such as a ball mill can be used for the milling process. To suppress oxidation of the material, the milling process may be carried out in a dry and inert atmosphere.

[0048] The coating layer 120 may be manufactured by a dry particle compounding method. The dry particle compounding method involves applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the first active material 101, the second active material 102, and the first solid electrolyte.

[0049] Examples of devices capable of imparting mechanical energy to a mixture of the first active material 101, the second active material 102, and the first solid electrolyte include ball mills, processing devices (particle compounding devices) such as "Mechanofusion" (manufactured by Hosokawa Micron Corporation), and "Nobilta" (manufactured by Hosokawa Micron Corporation).

[0050] In any of the apparatuses, the thickness of the coating layer 120 can be controlled by adjusting conditions such as rotation speed, processing time, and input amount. However, processing using the above apparatus is not mandatory. The coating layer 120 may also be formed by mixing the first active material 101, the second active material 102, and the first solid electrolyte using a mortar and pestle, a mixer, or the like. The first solid electrolyte may be deposited on the surface of the particles of the first active material 101 and / or the surface of the particles of the second active material 102 by various methods such as spraying, spray dry coating, electrodeposition, immersion, or mechanical mixing using a disperser.

[0051] (Modification 2) Figure 3 is a cross-sectional view showing the schematic configuration of the positive electrode material 100b according to Modification 2. In Modification 2, the solid electrolyte 112 contained in the positive electrode material 100b may be referred to as the "third solid electrolyte 112".

[0052] In the positive electrode material 100b according to the second modification, at least a portion of the surface of the positive electrode active material 110 is covered by a coating layer 120. More specifically, at least a portion of the surface of the first active material 101 and / or the second active material 102 is covered by a coating layer 120.

[0053] In this modified example 2, the coating layer 120 comprises a first layer 121 containing a first solid electrolyte and a second layer 122 containing a second solid electrolyte. The first layer 121 is located between the second layer 122 and the first active material 101. The first layer 121 is located between the second layer 122 and the second active material 102.

[0054] The first solid electrolyte may be the solid electrolyte contained in the coating layer 120 described in Modification 1. The second solid electrolyte may be a solid electrolyte having a different composition from the first solid electrolyte.

[0055] By providing such a second layer 122 on the positive electrode active material 110, the interfacial resistance between the positive electrode active material 110 and other materials such as the third solid electrolyte 112 is reduced. As a result, the discharge capacity and pulse discharge characteristics of the battery can be improved. In the positive electrode material 100b according to the modified example 2, the effects of the first layer 121 and the second layer 122 are obtained in combination. The effect of the first layer 121 is to suppress the decomposition of the third solid electrolyte 112. The effect of the second layer 122 is to reduce interfacial resistance.

[0056] In this modified example, the second layer 122 may be a layer that includes the outermost surface of the first active material 101 and / or the second active material 102. That is, the second layer 122 forms at least a portion of the outermost surface of the first active material 101 and / or the second active material 102. With this configuration, the interfacial resistance between the positive electrode active material 110 and other materials such as the third solid electrolyte 112 is more reliably reduced. As a result, the characteristics of the battery can be improved. The positive electrode material 100b according to Modified Example 2 can improve the discharge capacity of the battery and improve the output characteristics of the battery.

[0057] The first layer 121 is in contact with, for example, the first active material 101 and the second active material 102, respectively. With this configuration, the interfacial resistance between the positive electrode active material 110 and the third solid electrolyte 112 is more reliably reduced.

[0058] In the coating layer 120, the first layer 121 and the second layer 122 may be provided in contact with each other as shown in Figure 3, or other layers may be included. That is, the coating layer 120 may further have other layers provided between the first layer 121 and the second layer 122. The other layers may include, for example, another solid electrolyte having a different composition from the first and second solid electrolytes.

[0059] The first layer 121 of the coating layer 120 may consist substantially of a first solid electrolyte, or it may consist solely of a first solid electrolyte. Here, "the first layer 121 consists substantially of a first solid electrolyte" means that the content of the first solid electrolyte in the first layer 121 is 90% by mass or more. As an example, this content may be 95% by mass or more.

[0060] The second layer 122 may consist substantially of a second solid electrolyte, or it may consist solely of a second solid electrolyte. Here, "the second layer 122 consists substantially of a second solid electrolyte" means that the content of the second solid electrolyte in the second layer 122 is 90% by mass or more. As an example, this content may be 95% by mass or more.

[0061] The second solid electrolyte may contain, for example, a halide solid electrolyte. In this case, the second layer 122 has excellent lithium-ion conductivity and can effectively reduce the interfacial resistance between the positive electrode active material 110 and other materials such as the third solid electrolyte 112.

[0062] The second solid electrolyte includes, for example, Li, M2, Y, and X. M2 is at least one element selected from the group consisting of group 3 to group 13 elements. M2 may be at least one selected from the group consisting of Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Sc, Ti, Zr, Hf, Nb, Ta, W, Zn, Al, Ga, In, Si, Ge, Sn, Sb, and Bi. Preferably, M2 is at least one selected from the group consisting of Ti, Hf, Zr, and In, and M2 may be Zr. X is at least one selected from the group consisting of F, Cl, Br, and I. In this case, the second layer 122 containing the second solid electrolyte has excellent lithium ion conductivity and can effectively reduce the interfacial resistance between the positive electrode active material 110 and other materials such as the third solid electrolyte 112.

[0063] X may be Cl. In this case, the positive electrode material 100b can further improve the output characteristics of the battery.

[0064] The second solid electrolyte may have a composition represented by the following formula (3).

[0065] Li d M2 e Y f X6...Formula (3)

[0066] Here, M2 and X in equation (3) are as described above. Furthermore, in equation (3), the conditions 5.7 < d + m2e + 3f < 6.3, d > 0, e > 0, and f ≥ 0 are satisfied. Note that m2 is the valence of M2.

[0067] When the second solid electrolyte has the composition represented by formula (3) above, the second layer 122 containing the second solid electrolyte has excellent lithium ion conductivity and can effectively reduce the interfacial resistance between the positive electrode active material 110 and other materials such as the third solid electrolyte 112.

[0068] The second solid electrolyte does not need to contain sulfur. With this configuration, the generation of hydrogen sulfide gas can be prevented. Therefore, it becomes possible to realize a battery with improved safety.

[0069] The average thickness of the first layer 121 is, for example, 1 nm or more and 150 nm or less. Preferably, the average thickness of the first layer 121 is 100 nm or less, and more preferably 50 nm or less. By appropriately adjusting the average thickness of the first layer 121, the effect of improving the output characteristics of the battery can be enhanced. The average thickness of the first layer 121 can be calculated from a STEM image obtained by a scanning transmission electron microscope (STEM). The average thickness may be the average value of the thickness at any multiple points (for example, 5 points).

[0070] The average thickness of the second layer 122 is, for example, 1 nm or more and 150 nm or less. The average thickness of the first layer 121 is preferably 100 nm or less. By appropriately adjusting the average thickness of the second layer 122, the effect of improving the output characteristics of the battery can be enhanced. The average thickness of the second layer 122 can be calculated from a STEM image obtained by STEM, similar to the first layer 121. The average thickness can be the average value of the thickness at any multiple points (for example, five points).

[0071] In Modification 2, the coating layer 120 can be formed by attaching the first solid electrolyte and the second solid electrolyte to the surface of the particles of the first active material 101 and / or the surface of the particles of the second active material 102 in that order. The method for attaching the first solid electrolyte to the surface of the particles of the first active material 101 and / or the surface of the particles of the second active material 102 is as described in Modification 1. After attaching the first solid electrolyte to the surface of the particles of the first active material 101 and / or the surface of the particles of the second active material 102, the second solid electrolyte can be further attached by the method described in Modification 1.

[0072] (Modification 3) In the positive electrode material 100b shown in Figure 3, the first solid electrolyte contained in the first layer 121 may be an oxide. In this case, the second solid electrolyte contained in the second layer 122 may be a fluoride solid electrolyte containing Li, Ti, M1, and F. Here, M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb. In other words, the first solid electrolyte described in Modification 1 and Modification 2 can be used as the second solid electrolyte in Modification 3.

[0073] According to this modified example, it is possible to suppress the decomposition of the solid electrolyte 112 by the positive electrode active material 110 while suppressing the increase in battery resistance.

[0074] Examples of oxides used as the first solid electrolyte include lithium niobium oxide, lithium phosphate, lithium nitride phosphate, and Li7La3Zr2O. 12 (LLZO), Li 1.5 Al 0.5 Ge 1.5 P3O 12 (LAGO), Li 1.3 Al 0.3 Ti 1.7 P3O 12 Examples include (LATP), LiAlO4, and Li2SiO4.

[0075] In this modified example, the second solid electrolyte contained in the second layer 122 may be the second solid electrolyte described in Modified Example 2. That is, the second solid electrolyte may contain Li, M2, Y, and X. M2 is at least one element selected from the group consisting of group 3 elements to group 13 elements. X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0076] Methods for forming the first layer 121 containing lithium niobium oxide include liquid-phase coating and gas-phase coating.

[0077] For example, in the liquid-phase coating method, a precursor solution of the oxide solid electrolyte is applied to the surface of the positive electrode active material 110. For example, when coating with LiNbO3 as the oxide solid electrolyte, the precursor solution may be a mixture of a solvent, lithium alkoxide, and niobalkoxide. An example of lithium alkoxide is lithium ethoxide. An example of niobalkoxide is niobethoxide. The solvent is, for example, an alcohol such as ethanol. The amounts of lithium alkoxide and niobalkoxide are adjusted to obtain the desired oxide solid electrolyte composition. The precursor solution may be acidic or alkaline.

[0078] The method for applying the precursor solution to the surface of the positive electrode active material 110 is not particularly limited. For example, the precursor solution can be applied to the surface of the positive electrode active material 110 using a rolling fluid coating apparatus. With the rolling fluid coating apparatus, the precursor solution can be sprayed onto the positive electrode active material 110 while the positive electrode active material 110 is rolling and flowing, thereby applying the precursor solution to the surface of the positive electrode active material 110. This forms a precursor film on the surface of the positive electrode active material 110. Subsequently, the positive electrode active material 110 coated with the precursor film is heat-treated. The heat treatment promotes gelation of the precursor film, and an oxide solid electrolyte is coated on at least a portion of the surface of the positive electrode active material 110, forming the first layer 121.

[0079] Examples of vapor deposition methods include pulsed laser deposition, vacuum deposition, sputtering, thermochemical vapor deposition, and plasma chemical vapor deposition. For example, in pulsed laser deposition, a high-energy pulsed laser (e.g., KrF excimer laser, wavelength: 248 nm) is irradiated onto an oxide solid electrolyte target, and the sublimated oxide solid electrolyte is deposited on the surface of the positive electrode active material. When LiNbO3 is used as the oxide solid electrolyte, high-density sintered LiNbO3 is used as the target.

[0080] After forming the first layer 121, the second layer 122 can be formed by the method described in Modification 1.

[0081] (Embodiment 2) Figure 4 is a cross-sectional view showing the schematic configuration of the positive electrode according to Embodiment 2. The positive electrode 200 according to this embodiment includes the positive electrode material 100, 100a, or 100b according to Embodiment 1. Since the positive electrode 200 of this embodiment includes the positive electrode material 100, 100a, or 100b, it is suitable for achieving both the output characteristics of the battery and the capacity of the battery.

[0082] The positive electrode 200 may include a positive electrode current collector 210 and a positive electrode active material layer 220. The positive electrode active material layer 220 is supported by the positive electrode current collector 210. The positive electrode active material layer 220 includes the positive electrode material 100, 100a, or 100b according to Embodiment 1.

[0083] The positive electrode current collector 210 is a sheet or film made of a metallic material such as aluminum, aluminum alloy, stainless steel, titanium, or titanium alloy. The sheet or film may be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. A carbon material may be coated on the surface of the positive electrode current collector 210 as a conductive auxiliary material.

[0084] The positive electrode 200 according to Embodiment 2 can be manufactured, for example, by mixing the positive electrode material 100 with a solvent to prepare a positive electrode slurry, applying the positive electrode slurry onto the positive electrode current collector 210 to form a coating film, and then drying the coating film.

[0085] (Embodiment 3) Figure 5 is a cross-sectional view showing the schematic configuration of a battery according to Embodiment 3. The battery 300 comprises a positive electrode 200, an electrolyte layer 320, and a negative electrode 330. The positive electrode 200 includes the positive electrode material 100, 100a, or 100b described in Embodiment 1. Since the battery 300 of this embodiment includes the positive electrode material 100, 100a, or 100b, it has an excellent balance between output and capacity.

[0086] The positive electrode 200 may have the structure described in Embodiment 2.

[0087] The electrolyte layer 320 may be a layer containing a solid electrolyte. Examples of solid electrolytes contained in the electrolyte layer 320 include halide solid electrolytes, sulfide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes. The specific compositions of these solid electrolytes are as described in Embodiment 1.

[0088] The negative electrode 330 contains a negative electrode active material. The negative electrode active material is a material capable of intercalating and deintercalating lithium. Examples of negative electrode active materials capable of intercalating and deintercalating lithium include lithium titanium oxide, graphite, silicon, silicon-containing oxides, zinc alloys, lithium metal, and lithium alloys. At least one of these negative electrode active materials can be used.

[0089] The negative electrode 330 may contain lithium titanium oxide as the negative electrode active material. Since lithium titanium oxide undergoes little volume change during charging and discharging, it can improve the battery's cycle characteristics.

[0090] The negative electrode 330 may contain other materials such as conductive additives and binders. Materials usable for the positive electrode material 100 can also be used for the negative electrode 330 as conductive additives and binders.

[0091] The negative electrode 330 may include a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is supported by the negative electrode current collector.

[0092] Battery 300 may be a solid-state battery.

[0093] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0094] (Technical 1) A positive electrode material comprising a positive electrode active material, a solid electrolyte, and a conductive additive, wherein the positive electrode active material comprises lithium cobalt oxide and lithium nickel cobalt manganese oxide, and the content ratio of lithium cobalt oxide in the positive electrode active material is 8% by mass or more and 92% by mass or less.

[0095] The cathode material of this disclosure is suitable for achieving both the output characteristics and capacity of a battery.

[0096] (Technology 2) The cathode material according to Technology 1, wherein the ratio of the amount of nickel to the total amount of nickel, cobalt, and manganese in the lithium nickel cobalt manganese oxide is 28% or more and 82% or less. By adjusting the ratio of the amount of nickel to an appropriate range, the effect brought about by the combination of LCO and NCM is enhanced.

[0097] (Technical 3) The positive electrode active material is a mixture of lithium cobalt oxide particles and lithium nickel cobalt manganese oxide particles, as described in Technical 1 or 2. With such a configuration, the positive electrode material can be easily prepared.

[0098] (Technical 4) A positive electrode material according to any one of Technical 1 to 3, further comprising a coating layer that covers at least a portion of the surface of the positive electrode active material. With such a configuration, the decomposition of the solid electrolyte by the positive electrode active material is suppressed.

[0099] (Technical 5) The positive electrode material according to Technical 4, wherein the coating layer comprises Li, Ti, M1, and F, and M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb. In this case, the coating layer has excellent oxidation resistance due to the high electronegativity of fluorine.

[0100] (Technical 6) The positive electrode material according to Technical 4, wherein the solid electrolyte includes a third solid electrolyte, the coating layer comprises a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte, the first layer is located between the second layer and the positive electrode active material, the first solid electrolyte includes Li, Ti, M1, and F, M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb, and the second solid electrolyte has a different composition from the first solid electrolyte. With such a configuration, the effects of the first layer and the effects of the second layer are obtained in a superposition.

[0101] (Technical 7) The positive electrode material according to Technical 6, wherein the second solid electrolyte comprises Li, M2, Y, and X, where M2 is at least one element selected from the group consisting of group 3 to group 13 elements, and X is at least one selected from the group consisting of F, Cl, Br, and I. In this case, the second layer containing the second solid electrolyte has excellent lithium ion conductivity and can effectively reduce the interfacial resistance between the positive electrode active material and other materials.

[0102] (Technical 8) The positive electrode material according to Technical 6, wherein the third solid electrolyte is a sulfide solid electrolyte. In this case, the positive electrode material has excellent lithium ion conductivity.

[0103] (Technical 9) The positive electrode material according to Technical 4, wherein the solid electrolyte includes a third solid electrolyte, the coating layer comprises a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte, the first layer is located between the second layer and the positive electrode active material, the first solid electrolyte includes an oxide, the second solid electrolyte includes Li, Ti, M1, and F, and M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb. With such a configuration, it is possible to suppress the decomposition of the solid electrolyte by the positive electrode active material while suppressing an increase in the resistance of the battery.

[0104] (Technical 10) The positive electrode material according to Technical 9, wherein the third solid electrolyte is a sulfide solid electrolyte. In this case, the positive electrode material has excellent lithium ion conductivity.

[0105] (Technical 11) A positive electrode comprising the positive electrode material described in any one of Technical 1 to 10. The positive electrode of this disclosure is suitable for achieving both the output characteristics of a battery and the capacity of a battery because it comprises the positive electrode material of this disclosure.

[0106] (Technical 12) A battery having the positive electrode described in Technical 11. The battery of this disclosure has an excellent balance between output characteristics and capacity because it includes the positive electrode material of this disclosure.

[0107] (Technology 13) The battery described in Technology 12, further comprising a negative electrode containing lithium titanium oxide. Since lithium titanium oxide undergoes little volume change during charging and discharging, it can improve the battery's cycle characteristics.

[0108] (Examples 1 to 7) [Preparation of the first solid electrolyte] Under an argon atmosphere with a dew point of -60°C or lower, the raw material powders LiF, TiF4, and AlF3 were weighed in a molar ratio of LiF:TiF4:AlF3 = 2.7:0.3:0.7. These were crushed and mixed in a mortar to obtain a mixture. The mixture was then milled using φ5 mm zirconia balls and a planetary ball mill (Fritsch, P-7 type) for 12 hours at 500 rpm. As a result, Li 2.7 Ti 0.3 Al 0.7 A powdered first solid electrolyte having the composition of F6 was obtained. Hereinafter, Li 2.7 Ti 0.3 Al 0.7 F6 is denoted as "LTAF".

[0109] [Preparation of positive electrode active material] Lithium cobalt oxide (LCO) powder (average particle size 5 μm) and lithium nickel cobalt manganese oxide powder (average particle size 5 μm) were prepared. Lithium nickel cobalt manganese oxide is LiNi 0.6 Co 0.2 Mn 0.2 It had the composition of O2. Hereinafter, LiNi 0.6 Co 0.2 Mn 0.2 Lithium nickel cobalt manganese oxide having an O2 composition is sometimes referred to as "NCM622".

[0110] The positive electrode active material was prepared by mixing LCO and NCM622 in the mass ratios shown in Table 1.

[0111]

[0112] [Formation of Coating Layer] A coating layer was formed by attaching LTAF to the surface of the positive electrode active material particles. The coating layer was formed by compression shearing treatment using a particle compounding device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, the positive electrode active material and LTAF were mixed in a mass ratio of 100:3, and the mixture was treated at a rotation speed of 6000 rpm for a processing time of 30 minutes. This resulted in obtaining a positive electrode active material with a coating layer formed on its surface.

[0113] [Preparation of Cathode Composition Material] A cathode composition material was prepared by mixing a coated cathode active material, a sulfide solid electrolyte, and a conductive additive in an agate mortar. The mass ratio of the coated cathode active material, sulfide solid electrolyte, and conductive additive was coated cathode active material:sulfide solid electrolyte:conductive additive = 64:34:2. Li2S-P2S5 was used as the sulfide solid electrolyte. Carbon nanofiber (manufactured by Resonaq Corporation) was used as the conductive additive.

[0114] [Preparation of Negative Electrode Mixture] Under a dry argon atmosphere, Li2S-P2S5 is used as the solid electrolyte and Li4Ti5O is used as the negative electrode active material. 12 A negative electrode composite was prepared by mixing a conductive additive (average particle size 2.5 μm) in an agate mortar. The mass ratio of the negative electrode active material, solid electrolyte, and conductive additive was 71:28:1. Carbon nanofiber (manufactured by Resonaq) was used as the conductive additive.

[0115] [Battery Fabrication] 59.2 mg of positive electrode material, 28.3 mg of solid electrolyte (Li2S-P2S5), and 89.0 mg of negative electrode material were layered in this order inside an insulating outer cylinder having an inner diameter of 9.4 mm. The positive electrode material, solid electrolyte, and negative electrode material were pressure-molded at a pressure of 720 MPa. This created a laminate having a positive electrode, an electrolyte layer, and a negative electrode. Next, stainless steel current collectors were placed above and below the laminate, and current collector leads were attached to the current collectors. Finally, the insulating outer cylinder was sealed using an insulating ferrule so that the inside of the insulating outer cylinder was isolated from the outside atmosphere. This obtained the solid batteries of Examples 1 to 7.

[0116] (Comparative Example 1) A solid-state battery of Comparative Example 1 was prepared in the same manner as in Example 1, except that only NCM622 was used as the positive electrode active material.

[0117] (Comparative Example 2) A solid-state battery of Comparative Example 2 was prepared in the same manner as in Example 1, except that only LCO was used as the positive electrode active material.

[0118] [Battery Evaluation] (Measurement of Initial Discharge Capacity at 0.05C) The initial discharge capacity of the batteries in the examples and comparative examples at 0.05C was measured by the following method. Constant current charging was performed with a current of 0.05C until the voltage reached 2.6V, and then constant voltage charging was performed with a voltage of 2.6V until the current reached 0.01C. After a rest period of 60 minutes, constant current discharge was performed with a current of 0.05C until the voltage reached 1.5V. The discharge capacity measured at this time was considered as the initial discharge capacity. Charging and discharging were performed under temperature conditions of 25°C (ambient temperature). The results are shown in Figure 6A.

[0119] (Measurement of initial discharge capacity at 1C) After measuring the initial discharge capacity of the batteries of the example and comparative example at 0.05C, the initial discharge capacity at 1C was measured by the following method. Constant current charging was performed with a current of 0.05C until the voltage reached 2.6V, and then constant voltage charging was performed with a voltage of 2.6V until the current reached 0.01C. After a rest period of 60 minutes, constant current discharge was performed with a current of 1C until the voltage reached 1.5V. The discharge capacity measured at this time was considered as the initial discharge capacity. Charging and discharging were performed under temperature conditions of 25°C (ambient temperature). The capacity retention rate was calculated by dividing the initial discharge capacity at 1C by the initial discharge capacity at 0.05C. The results are shown in Figure 6B.

[0120] Figure 6A is a graph showing the measurement results of the initial discharge capacity at 0.05C for the batteries of Examples 1 to 7, Comparative Example 1, and Comparative Example 2. The values ​​on the vertical axis of Figure 6A are relative to the initial discharge capacity (=100) of Comparative Example 1, where NCM622 is 100% by mass. Figure 6B is a graph showing the ratio of the initial discharge capacity at 1C to the initial discharge capacity at 0.05C (capacity retention rate). A high capacity retention rate means that the battery has excellent output characteristics.

[0121] As shown in Figure 6A, the initial discharge capacity at 0.05C was improved in Examples 1 to 7 compared to Comparative Example 2, and in Examples 1 and 2, it was comparable to or improved compared to Comparative Example 1. As shown in Figure 6B, the ratio of the initial discharge capacity at 1C to the initial discharge capacity at 0.05C (capacity retention rate) improved sharply as the LCO ratio was increased from 0% by mass (Comparative Example 1) to 10% (Example 1).

[0122] [Measurement of Pulse Discharge Voltage] After measuring the initial discharge capacity at 1C, the pulse discharge voltage of the batteries in the example and comparative example at 25°C (ambient temperature) was measured using the following method. Constant current charging was performed with a current of 0.05C until the voltage reached 2.75V, and then constant voltage charging was performed with a voltage of 2.75V until the current reached 0.01C. After a rest period of 2 hours, the batteries were discharged with a current of 5C, and the voltage was measured after 1 second. The results are shown in Figure 7.

[0123] Figure 7 is a graph showing the measured pulse discharge voltage of the batteries in Examples 1 to 7, Comparative Example 1, and Comparative Example 2. A high pulse discharge voltage indicates that the battery has excellent output characteristics.

[0124] As shown in Figure 7, the pulse discharge voltage of the battery in Comparative Example 1, where the LCO ratio was 0 mass%, was low. In contrast, the batteries of Examples 1 to 7, where the LCO ratio was in the range of 10 mass% to 90 mass%, showed pulse discharge voltages of 1.8V to 2.3V.

[0125] As can be seen from the measurement results of initial discharge capacity shown in Figures 6A and 6B, and the measurement results of pulse discharge voltage shown in Figure 7, the batteries of Examples 1 to 7 exhibited an excellent balance between capacity and output characteristics. In particular, the batteries of Examples 1 and 2, in which the LCO ratio was in the range of 8 mass% to 22 mass%, showed a high initial discharge capacity at 1C despite the low LCO ratio. Furthermore, considering the composition of NCM, when the ratio of nickel to the total amount of nickel, cobalt, and manganese was between 45% and 72%, the batteries of Examples 1 and 2, in which the LCO ratio was in the range of 8 mass% to 22 mass%, showed a high initial discharge capacity at 1C despite the low LCO ratio. Also, as can be seen from the results in Figure 7, there was a tendency for the pulse discharge voltage to increase sharply as the LCO ratio changed from 0 mass% to 10 mass%.

[0126] (Example 8) In Example 8, instead of NCM622, LiNi 0.8 Co 0.1 Mn 0.1 Lithium nickel cobalt manganese oxide having an O2 composition was used. Hereinafter, LiNi 0.8 Co 0.1Mn 0.1 Lithium nickel cobalt manganese oxide having an O2 composition is sometimes referred to as "NCM811". The solid-state battery of Example 8 was prepared by the same method as in Examples 1 to 7, except that the positive electrode active material was prepared by mixing LCO and NCM811 in a mass ratio of LCO:NCM811 = 25:75.

[0127] (Example 9) A solid-state battery of Example 9 was prepared in the same manner as in Example 8, except that the positive electrode active material was prepared by mixing LCO and NCM811 in a mass ratio of LCO:NCM811 = 65:35.

[0128] (Comparative Example 3) A solid-state battery of Comparative Example 3 was prepared in the same manner as in Example 8, except that only NCM811 was used as the positive electrode active material.

[0129] [Battery Evaluation] (Measurement of Initial Discharge Capacity) The initial discharge capacity at 0.05C and 1C of Example 8, Example 9, and Comparative Example 3 was measured using the method described above.

[0130] Figure 8A is a graph showing the measurement results of the initial discharge capacity at 0.05C for the batteries of Example 3, Example 4, Comparative Example 1, and Comparative Example 3. Figure 8B is a graph showing the ratio of the initial discharge capacity at 1C to the initial discharge capacity at 0.05C (capacity retention rate) for the batteries of Example 3, Example 4, Comparative Example 1, and Comparative Example 3. The measurement results for the battery of Comparative Example 1 shown in Figures 8A and 8B are the same as the measurement results for the battery of Comparative Example 1 shown in Figures 6A and 6B. A high capacity retention rate means that the battery has excellent output characteristics.

[0131] As shown in Figure 8A, the initial discharge capacity at 0.05C decreased with increasing LCO percentage. As shown in Figure 8B, the capacity retention rate of the battery in Example 3, where the LCO percentage was 25% by mass, was approximately equal to that of the battery in Example 4, where the LCO percentage was 65% by mass.

[0132] [Measurement of pulse discharge voltage] The pulse discharge voltages of Example 3, Example 4, Comparative Example 1, and Comparative Example 3 were measured using the method described above. The results are shown in Figure 9.

[0133] Figure 9 is a graph showing the measurement results of the pulse discharge voltage of the batteries in Example 3, Example 4, Comparative Example 1, and Comparative Example 3. The measurement results for the battery in Comparative Example 1 shown in Figure 9 are the same as the measurement results for the battery in Comparative Example 1 shown in Figure 7. A high pulse discharge voltage indicates that the battery has excellent output characteristics.

[0134] As shown in Figure 9, the pulse discharge voltage increased as the proportion of LCO increased.

[0135] As can be seen from the measurement results of the initial discharge capacity shown in Figures 8A and 8B, and the measurement results of the pulse discharge voltage shown in Figure 9, the batteries of Examples 3 and 4 had an excellent balance between capacity and output characteristics.

[0136] On the other hand, as can be seen by comparing Figure 6B and Figure 8B, the batteries of Examples 1 to 7 were superior to the batteries of Examples 3 and 4 in terms of the ratio of the initial discharge capacity at 1C to the initial discharge capacity at 0.05C (capacity retention rate). As can be seen by comparing Figure 7 and Figure 9, the batteries of Examples 1 to 7 were also superior to the batteries of Examples 3 and 4 in terms of pulse discharge voltage. In other words, the combination of LCO and NCM622 was more suitable for achieving both battery capacity and battery output characteristics compared to the combination of LCO and NCM811.

[0137] Based on the above results, it can be said that in lithium nickel cobalt manganese oxide, the ratio of nickel to the total amount of nickel, cobalt, and manganese is preferably less than 82%. Considering the discharge capacity at low discharge rates and the cost of the battery, the lower limit of the nickel ratio is preferably 28% or more. Considering that the highest effect is obtained with NCM622, it is even more preferable that the nickel ratio be between 45% and 72%.

[0138] The technology disclosed herein is useful, for example, in solid-state batteries.

Claims

1. A positive electrode material comprising a positive electrode active material, a solid electrolyte, and a conductive additive, wherein the positive electrode active material comprises lithium cobalt oxide and lithium nickel cobalt manganese oxide, and the content ratio of lithium cobalt oxide in the positive electrode active material is 8% by mass or more and 92% by mass or less.

2. The positive electrode material according to claim 1, wherein in the lithium nickel cobalt manganese oxide, the ratio of the amount of nickel to the total amount of nickel, cobalt, and manganese is 28% or more and 82% or less.

3. The positive electrode material according to claim 1, wherein the positive electrode active material comprises a mixture of lithium cobalt oxide particles and lithium nickel cobalt manganese oxide particles.

4. The positive electrode material according to claim 1, further comprising a coating layer that covers at least a portion of the surface of the positive electrode active material.

5. The positive electrode material according to claim 4, wherein the coating layer comprises Li, Ti, M1, and F, and M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb.

6. The positive electrode material according to claim 4, wherein the solid electrolyte comprises a third solid electrolyte, the coating layer comprises a first layer comprising a first solid electrolyte and a second layer comprising a second solid electrolyte, the first layer is located between the second layer and the positive electrode active material, the first solid electrolyte comprises Li, Ti, M1, and F, M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb, and the second solid electrolyte has a different composition from the first solid electrolyte.

7. The positive electrode material according to claim 6, wherein the second solid electrolyte comprises Li, M2, Y, and X, wherein M2 is at least one element selected from the group consisting of group 3 to group 13 elements, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

8. The positive electrode material according to claim 6, wherein the third solid electrolyte is a sulfide solid electrolyte.

9. The positive electrode material according to claim 4, wherein the solid electrolyte comprises a third solid electrolyte, the coating layer comprises a first layer comprising a first solid electrolyte and a second layer comprising a second solid electrolyte, the first layer is located between the second layer and the positive electrode active material, the first solid electrolyte comprises an oxide, the second solid electrolyte comprises Li, Ti, M1, and F, and M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb.

10. The positive electrode material according to claim 9, wherein the third solid electrolyte is a sulfide solid electrolyte.

11. A positive electrode comprising the positive electrode material described in claim 1.

12. A battery comprising the positive electrode described in claim 11.

13. The battery according to claim 12, further comprising a negative electrode containing lithium titanium oxide.

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