Coated active material, positive electrode, and battery

Abstract

The coated active material (100) of the present disclosure includes a positive electrode active material (110) and a coating layer (120) that coats at least a portion of the surface of the positive electrode active material (110). The coating layer (120) includes a first layer (111) containing a first solid electrolyte and a second layer (112) containing a second solid electrolyte. The first layer (111) is positioned between the second layer (112) and the positive electrode active material. The first solid electrolyte contains Li, Ti, M1, and F, where M1 is at least one selected from Ca, Mg, Al, Y, Zr, and Nb. The second solid electrolyte has a different composition from the first solid electrolyte.

Description

Technical Field

[0001] This disclosure relates to coated active materials, positive electrodes, and batteries. Background Technology

[0002] In traditional batteries, the electrolyte can sometimes be decomposed by the active materials. When the electrolyte decomposes, a film of electrolyte decomposition products forms inside the electrodes. This can lead to adverse effects such as increased internal resistance and decreased cycle performance of the battery.

[0003] If the active material is coated with a suitable coating material, the decomposition of the electrolyte caused by the active material can be suppressed. For example, Patent Document 1 discloses coating the positive electrode active material with a solid electrolyte containing Li, Ti, M1, and F. In addition, M1 is at least one element selected from Ca, Mg, Al, Y, and Zr.

[0004] Prior art literature

[0005] Patent Document 1: International Publication No. 2021 / 187391 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] Regarding conventional active materials whose surfaces are coated with a coating material, as disclosed in Patent Document 1, there is a need to improve the output characteristics of the battery.

[0008] Methods for solving problems

[0009] The coated active material disclosed herein has a positive electrode active material and a coating layer covering at least a portion of the surface of the positive electrode active material.

[0010] The coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte.

[0011] The first layer is located between the second layer and the positive electrode active material.

[0012] The first solid electrolyte comprises Li, Ti, M1, and F, wherein M1 is selected from at least one of Ca, Mg, Al, Y, Zr, and Nb.

[0013] The second solid electrolyte has a different composition than the first solid electrolyte.

[0014] The effects of the invention

[0015] According to this disclosure, a coated active material that can improve the output characteristics of a battery can be provided. Attached Figure Description

[0016] Figure 1This is a cross-sectional view showing the approximate structure of the coated active material in Embodiment 1.

[0017] Figure 2 This is a cross-sectional view showing the approximate structure of the positive electrode in Embodiment 2.

[0018] Figure 3 This is a cross-sectional view showing the general structure of the battery according to Embodiment 3. Detailed Implementation

[0019] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0020] (Implementation Method 1)

[0021] Figure 1 This is a cross-sectional view showing the general structure of the coated active material according to Embodiment 1 of the present disclosure. The coated active material 100 includes a positive electrode active material 110 and a coating layer 120. The positive electrode active material 110 is, for example, granular. The coating layer 120 coats at least a portion of the surface of the positive electrode active material 110. The coating layer 120 includes a first layer 111 and a second layer 112. The first layer 111 is located between the second layer 112 and the positive electrode active material 110. The first layer 111 is a layer containing a first solid electrolyte. The second layer 112 is a layer containing a second solid electrolyte.

[0022] The first solid electrolyte is a solid electrolyte containing Li, Ti, M1, and F. M1 is selected from at least one of Ca, Mg, Al, Y, Zr, and Nb. The second solid electrolyte is a solid electrolyte having a composition different from that of the first solid electrolyte.

[0023] The first solid electrolyte is a fluoride solid electrolyte, which exhibits excellent oxidation resistance due to the high electronegativity of fluorine. If the positive electrode active material 110 is coated with a coating layer 120 having a first layer 111 containing the first solid electrolyte, direct contact between the positive electrode active material 110 and the electrolyte can be prevented. This reduces the decomposition of the electrolyte caused by the positive electrode active material 110.

[0024] The coating layer 120 also has a second layer 112, which contains a second solid electrolyte having a different composition from the first solid electrolyte. The second layer 112 is located on the outer side of the coated active material 100 than the first layer 111. The positive electrode containing the coated active material 100 is, for example, made of a positive electrode material that also contains a solid electrolyte and conductive additives. By providing such a second layer 112 on the coated active material 100, the interfacial resistance between the coated active material 100 and other materials such as the solid electrolyte is reduced, thereby improving the battery's output characteristics (e.g., discharge capacity and pulse discharge characteristics). Thus, the coated active material 100 of Embodiment 1, in addition to improving battery characteristics through the first layer 111 of the coating layer 120, can also simultaneously improve output characteristics by reducing interfacial resistance through the second layer 112.

[0025] In this embodiment, the second layer 112 is, for example, the outermost layer containing the coated active material 100. That is, the second layer 112 forms at least a portion of the outermost surface of the coated active material 100. With this structure, the interfacial resistance between the coated active material 100 and other materials such as the solid electrolyte is more effectively reduced, thus effectively improving the battery's output characteristics. For example, the coated active material 100 of Embodiment 1 can increase the battery's discharge capacity, thereby improving pulse discharge characteristics.

[0026] In this embodiment, the first layer 111 is in contact with, for example, the positive electrode active material 110. With this structure, the contact between the positive electrode active material 110 and the electrolyte is more effectively reduced, thus allowing the improved battery characteristics brought about by the coating layer 120 to be more effectively utilized.

[0027] In the covering layer 120, the first layer 111 and the second layer 112 can be as follows: Figure 1 The layers shown are arranged in contact with each other and may further include other layers. That is, the coating layer 120 may also have other layers disposed between the first layer 111 and the second layer 112. The other layers may, for example, contain other solid electrolytes having a composition different from that of the first solid electrolyte and the second solid electrolyte.

[0028] The following provides a more detailed description of the positive electrode active material 110, the coating layer 120, the first solid electrolyte, and the second solid electrolyte.

[0029] The positive electrode active material 110 is, for example, a material containing lithium and transition metals that can absorb and release lithium.

[0030] Examples of positive electrode active materials 110 include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, using lithium-containing transition metal oxides or lithium-containing transition metal phosphates as positive electrode active materials can reduce battery manufacturing costs and increase average discharge voltage. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. At least one of these positive electrode active materials can be used. In particular, lithium nickel cobalt manganese oxide (hereinafter referred to as "NCM") is a suitable positive electrode active material for combination with the coating layer 120 in Embodiment 1. Therefore, the positive electrode active material 110 may include, for example, NCM.

[0031] The particles of the positive electrode active material 110 can be primary or secondary particles. For example, the particles of the positive electrode active material 110 have an average particle size of 1 μm or more and 10 μm or less. The average particle size refers to the particle size (median particle size) at which the cumulative volume in the volumetric particle size distribution is 50%. The volumetric particle size distribution is determined, for example, by a laser diffraction particle size distribution measuring device.

[0032] The first layer 111 of the coating layer 120 may be substantially composed of the first solid electrolyte, or it may be composed solely of the first solid electrolyte. Here, "the first layer 111 is substantially composed of the first solid electrolyte" means that the content of the first solid electrolyte in the first layer 111 is 90% by mass or more. As an example, this content can be 95% by mass or more.

[0033] As described above, the first solid electrolyte contained in the first layer 111 of the coating layer 120 comprises Li, Ti, M1, and F. The first solid electrolyte may be substantially composed of Li, Ti, M1, and F, or it may be composed only of Li, Ti, M1, and F. Here, "the first solid electrolyte is substantially composed of Li, Ti, M1, and F" means that the molar ratio of the total mass of Li, Ti, M1, and F to the total mass of all elements constituting the first solid electrolyte is 90% or more. As an example, this molar ratio may be 95% or more.

[0034] In the first solid electrolyte, the ratio of the mass of Li to the total mass of Ti and M1 is, for example, 0.5 or more and 4.5 or less. When this ratio is within such a range, the first solid electrolyte exhibits excellent lithium-ion conductivity.

[0035] M1 can be at least one selected from Ca, Mg, and Al. In this case, the first solid electrolyte exhibits excellent lithium-ion conductivity.

[0036] M1 can be Al. In this case, the first solid electrolyte has excellent lithium-ion conductivity.

[0037] The first solid electrolyte may have a composition represented by the following formula (1).

[0038] Li 6-(4-4x+m1x)b (Ti 1-x M1 x ) b F6 ・・・Form (1)

[0039] Here, in the above equation (1), 0 < x < 1 and 0 < b ≤ 2 are satisfied. In addition, m1 is the valence of M1.

[0040] When the first solid electrolyte has the composition represented by the above formula (1), the first solid electrolyte has excellent lithium-ion conductivity.

[0041] The first solid electrolyte can be sulfur-free. Based on the above structure, the generation of hydrogen sulfide gas can be prevented. Therefore, a battery with improved safety can be achieved.

[0042] As described above, the second layer 112 of the coating layer 120 is a layer containing the second solid electrolyte. The second layer 112 may, for example, substantially not contain conductive additives. Here, "the second layer 112 substantially does not contain conductive additives" means that the proportion of conductive additives in the second layer 112 is 0.1% by mass or less. The second layer 112 may not contain conductive additives. Here, conductive additives refer to those used in the positive electrode to reduce resistance. Examples of conductive additives include carbon materials and conductive polymers. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymers include polyaniline, polypyrrole, and polythiophene.

[0043] The second layer 112 may be substantially composed of the second solid electrolyte, or it may be composed solely of the second solid electrolyte. Here, "the second layer 112 is substantially composed of the second solid electrolyte" means that the content of the second solid electrolyte in the second layer 112 is 90% by mass or more. As an example, this content can be 95% by mass or more.

[0044] The second solid electrolyte may be, for example, a halide solid electrolyte. In this case, the second layer 112 exhibits excellent lithium-ion conductivity and can effectively reduce the interfacial resistance between the coated active material 100 and other materials such as the solid electrolyte in the positive electrode. Therefore, in this case, the coated active material 100 can further improve the battery's output characteristics.

[0045] The second solid electrolyte, for example, comprises Li, M2, Y, and X. M2 is at least one element selected from metallic and half-metallic elements other than Li and Y. X is at least one selected from F, Cl, Br, and I. In this case, the second layer 112 containing the second solid electrolyte has excellent lithium-ion conductivity and can effectively reduce the interfacial resistance between the coated active material 100 and other materials such as the solid electrolyte in the positive electrode. Therefore, in this case, the coated active material 100 can further improve the output characteristics of the battery.

[0046] "Semi-metallic elements" include B, Si, Ge, As, Sb, and Te.

[0047] "Metallic elements" include all elements in Groups 1 to 12 of the periodic table except for hydrogen, and all elements in Groups 13 to 16 of the periodic table except for B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metallic elements are the group of elements that can become cations when forming inorganic compounds with halogen elements.

[0048] M2 may be selected from at least one 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. M2 is preferably selected from at least one of Ti, Hf, Zr, and In, and M2 may be Zr.

[0049] M2 can be at least one element selected from Groups 3 to 13. M2 can be at least one of Sc, Ti, Zr, Hf, Nb, Ta, W, Zn, Al, Ga, and In.

[0050] X can be Cl. In this case, the coated active material 100 can further improve the output characteristics of the battery.

[0051] The second solid electrolyte may have a composition represented by the following formula (2).

[0052] Li d M2 e Y f X6 ・・・Form (2)

[0053] Here, M2 and X in equation (2) are as described above. Furthermore, in equation (2), 5.7 < d + m2e + 3f < 6.3, d > 0, e > 0, and f ≥ 0 are satisfied. Additionally, m2 is the valence of M2.

[0054] When the second solid electrolyte has the composition shown in formula (2) above, the second layer 112 containing the second solid electrolyte has excellent lithium-ion conductivity and can effectively reduce the interfacial resistance between the coated active material 100 and other materials such as the solid electrolyte in the positive electrode. Therefore, in this case, the coated active material 100 can further improve the output characteristics of the battery.

[0055] The second solid electrolyte can be sulfur-free. Based on the above structure, the generation of hydrogen sulfide gas can be prevented. Therefore, a battery with improved safety can be achieved.

[0056] The mass ratio of the second solid electrolyte to the positive electrode active material 110 is, for example, greater than 0% by mass and less than 5% by mass. When the coated active material 100 contains the second solid electrolyte in the above-mentioned mass ratio, the coated active material 100 can further improve the output characteristics of the battery. The mass ratio of the second solid electrolyte to the positive electrode active material 110 can be less than 3% by mass or less, or less than 2% by mass. In this case, the coated active material 100 can further improve the output characteristics of the battery. Alternatively, the mass ratio of the second solid electrolyte to the positive electrode active material 110 can be more than 0.1% by mass or more, or more than 0.5% by mass. In this case, the coated active material 100 can further improve the output characteristics of the battery.

[0057] The ratio of the mass of the second solid electrolyte to the mass of the positive electrode active material 110 can be determined, for example, by measuring the mass using inductively coupled plasma mass analysis (ICP-MS).

[0058] The average thickness of the first layer 111 is, for example, 1 nm or more and 150 nm or less. Preferably, the average thickness of the first layer 111 is 100 nm or less, more preferably 50 nm or less. By appropriately adjusting the average thickness of the first layer 111, the improvement in the output characteristics of the battery can be enhanced. The average thickness of the first layer 111 can be calculated from a TEM image obtained by scanning transmission electron microscopy (TEM). The average thickness can be the average of the thicknesses at any number of points (e.g., 5 points).

[0059] The average thickness of the second layer 112 is, for example, 1 nm or more and 150 nm or less. The average thickness of the first layer 111 is preferably 100 nm or less. By appropriately adjusting the average thickness of the second layer 112, the output characteristics of the battery can be improved. The average thickness of the second layer 112, like that of the first layer 111, can be calculated from a TEM image obtained by TEM. The average thickness can be the average of the thicknesses of any number of points (e.g., 5 points).

[0060] The coated active material 100 in Embodiment 1, for example, has an average particle size of 1 μm or more and 10 μm or less. The average particle size of the coated active material 100 refers to the particle size (median particle size) 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 distribution measuring device. When the thickness of the coating layer 120 is in the nanometer range, the average particle size of the coated active material 100 is approximately equal to the average particle size of the positive electrode active material 110.

[0061] The coated active material 100 of Embodiment 1 can be manufactured, for example, by the following method.

[0062] First, a first layer 111 of material is attached to the surface of the particles of the positive electrode active material 110. The first layer 111 of material contains a first solid electrolyte.

[0063] There are no particular limitations on the method for attaching the material of the first layer 111 to the surface of the positive electrode active material 110. For example, a mixture is obtained by mixing the powder of the positive electrode active material 110 and the powder of the material of the first layer 111 in an appropriate ratio. The mixture is then ground to impart mechanical energy to it. The grinding process can be performed using a mixing device such as a ball mill. To suppress the oxidation of the material, the grinding process can be performed in a dry and inert atmosphere.

[0064] The first layer 111 can be manufactured by a dry particle composite process. The process using the dry particle composite process involves imparting at least one mechanical energy selected from impact, compression, and shear to the materials of the positive electrode active material 110 and the first layer 111.

[0065] As a device capable of imparting mechanical energy to the mixture of positive electrode active material 110 and the first layer 111, examples of processing devices (particle composite devices) include ball mills, "Mechano Fusion" (manufactured by Hosokawa Micron Co., Ltd.), and "Nobilta" (manufactured by Hosokawa Micron Co., Ltd.).

[0066] In any apparatus, the thickness of the first layer 111 can be controlled by adjusting conditions such as rotation speed, processing time, and loading amount. Furthermore, the processing performed using the aforementioned apparatus is not mandatory. The first layer 111 can be manufactured by mixing the positive electrode active material 110 and the material of the first layer 111 using a mortar, mixer, or similar method. Alternatively, the material of the first layer 111 can be deposited on the surface of the positive electrode active material 110 using various methods such as spray coating, spray drying coating, electrolysis, impregnation, or mechanical mixing using a disperser.

[0067] Next, a second layer 112 is formed on the surface of the particles on the surface of the positive electrode active material 110 by attaching a material to the second layer 112. The material of the second layer 112 contains a second solid electrolyte.

[0068] In a method for attaching a second layer 112 to the surface of particles on which a first layer 111 is formed on the surface of a positive electrode active material 110, the above-described method, exemplified as a method for forming the first layer 111, can be used.

[0069] (Implementation Method 2)

[0070] The positive electrode of Embodiment 2 comprises the coated active material of Embodiment 1. The positive electrode of Embodiment 2 can improve the output characteristics of the battery. For example, the positive electrode of Embodiment 2 can increase the discharge capacity of the battery, thereby improving the pulse discharge characteristics.

[0071] Figure 2 This is a cross-sectional view showing the general structure of the positive electrode 200 in Embodiment 2. The positive electrode 200 includes, for example, a positive current collector 210 and a positive active material layer 220 supported on the positive current collector 210. The positive active material layer 220 contains the coated active material 100 of Embodiment 1.

[0072] The positive electrode active material layer 220 may contain only the coated active material 100 of Embodiment 1 as the positive electrode active material, or it may further contain a positive electrode active material different from the coated active material 100 of Embodiment 1.

[0073] The positive electrode active material layer 220 may contain, for example, a solid electrolyte. Hereinafter, the solid electrolyte contained in the positive electrode active material layer 220 will be referred to as the third solid electrolyte.

[0074] Positive electrode active material layer 220, for example Figure 2As shown, the positive electrode active material layer 220 is composed of a coated active material 100 and a material phase 221, which is composed of materials other than the coated active material 100. The material phase 221 may, for example, contain a third solid electrolyte. In addition to the third solid electrolyte, the material phase 221 may also contain conductive additives, as described later. The positive electrode active material layer 220 has, for example, an island structure, where the coated active material 100 is considered an island, and the region containing the material phase 221 containing the third solid electrolyte is considered a sea. In the case where the positive electrode active material layer 220 has such an island structure, the proportion of conductive additives contained in the island is lower than the proportion of conductive additives contained in the sea. Furthermore, in the interface region between the island and the sea, the proportion of conductive additives contained in the coating layer 120 (i.e., the first layer 111 and / or the second layer 112) constituting the interface on the island side is lower than the proportion of conductive additives contained in the sea. That is, the second layer 112 may, for example, substantially not contain conductive additives. Here, "the second layer 112 substantially does not contain conductive additives" means that the proportion of conductive additives in the second layer 112 is less than 0.1% by mass. The second layer 112 may not contain conductive additives. Since the first layer 111 and the second layer 112 are thin films, even if the first layer 111 and the second layer 112 substantially do not contain conductive additives, the resistance of the positive electrode 200 will not increase, and the interfacial resistance between the coated active material 100 and other materials such as the third solid electrolyte can be effectively reduced.

[0075] Furthermore, in the interface region between the island and the sea, whether the proportion of conductive additives contained in the coating layer 120 (i.e., the first layer 111 and / or the second layer 112) constituting the interface on the island side is lower than the proportion of conductive additives contained in the material phase 221, which is the sea, can be confirmed by performing elemental mapping on the interface containing the coated active material 100 and the material phase 221 and its adjacent cross-section. The elemental map can be obtained by using energy-dispersive X-ray spectroscopy (STEM-EDX) with a scanning transmission electron microscope.

[0076] Examples of third-generation solid electrolytes include halide solid electrolytes, sulfide solid electrolytes, polymeric solid electrolytes, and complexed hydride solid electrolytes. Examples of sulfide solid electrolytes include Li₂S-P₂S₅, Li₂S-SiS₂, Li₂S-B₂S₃, Li₂S-GeS₂, and Li₂S-P₂S₅. 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12Examples of polymeric solid electrolytes include polymeric compounds with an ethylene oxide structure and lithium salt compounds. Lithium salts can be selected from at least one of LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. Examples of complexed hydride solid electrolytes include LiBH4-LiI and LiBH4-P2S5. Halide solid electrolytes can be materials represented by the following formula (3).

[0077] Li α M3 β X' γ ...Form (3)

[0078] In equation (3), α, β and γ are each independently greater than 0, M3 is selected from at least one of the metallic and half-metallic elements other than Li, and X' is selected from at least one of F, Cl, Br and I.

[0079] "Semi-metallic elements" include B, Si, Ge, As, Sb, and Te.

[0080] "Metallic elements" include all elements in Groups 1 to 12 of the periodic table except for hydrogen, and all elements in Groups 13 to 16 of the periodic table except for B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metallic elements are the group of elements that can become cations when forming inorganic compounds with halogen elements.

[0081] The third solid electrolyte can be selected from at least one of sulfide solid electrolytes and halide solid electrolytes. In this case, the positive electrode 200 has excellent lithium-ion conductivity.

[0082] The third solid electrolyte can be a halide solid electrolyte. In this case, the positive electrode 200 exhibits excellent lithium-ion conductivity.

[0083] When the third solid electrolyte is a halide solid electrolyte, the third solid electrolyte may contain Cl.

[0084] The third solid electrolyte can be sulfur-free. Based on the above structure, the generation of hydrogen sulfide gas can be prevented. Therefore, a battery with improved safety can be achieved.

[0085] The positive electrode active material layer 220 may contain conductive additives, adhesives, or other materials as needed.

[0086] Conductive additives are used to reduce the resistance of the positive electrode at 200Ω. Examples of conductive additives include carbon materials and conductive polymers. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymers include polyaniline, polypyrrole, and polythiophene. At least one of these conductive additives may be used.

[0087] An adhesive is used to improve the adhesion of the materials constituting the positive electrode 200. Examples of adhesives include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one of these adhesives may be used.

[0088] The positive current collector 210 is, for example, a sheet or film made of metallic materials such as aluminum, aluminum alloy, stainless steel, titanium, or titanium alloy. The sheet or film can be porous or non-porous. Metal foil, metal mesh, etc., can be used as the sheet or film. Carbon material can be coated on the surface of the positive current collector 210 as a conductive auxiliary material.

[0089] The positive electrode 200 of Embodiment 2 can be made as follows: a positive electrode slurry is prepared by mixing the material constituting the positive electrode active material layer 220 with a solvent, the positive electrode slurry is coated on the positive electrode current collector 210 to form a coating film, and then the coating film is dried.

[0090] (Implementation Method 3)

[0091] The battery of Embodiment 3 includes a positive electrode, a negative electrode, and a solid electrolyte layer as in Embodiment 2. The solid electrolyte layer is disposed between the positive and negative electrodes. By including the positive electrode of Embodiment 2, the battery of Embodiment 3 can improve its output characteristics. For example, the battery of Embodiment 3 can increase its discharge capacity, thereby improving its pulse discharge characteristics.

[0092] Figure 3 This is a cross-sectional view showing the general structure of the battery 300 according to Embodiment 3. The battery 300 includes a positive electrode 310, a negative electrode 330, and a solid electrolyte layer 320 disposed between the positive electrode 310 and the negative electrode 330. The positive electrode 310 is the positive electrode 200 of Embodiment 2. With this structure, the battery 300 can improve its output characteristics.

[0093] The battery 300 in embodiment 3 can be an all-solid-state battery.

[0094] The negative electrode 330 contains a negative electrode active material. The negative electrode active material is a material capable of absorbing and releasing lithium. Examples of negative electrode active materials capable of absorbing and releasing lithium include lithium titanate, graphite, silicon, silicon-containing oxides, zinc alloys, lithium metal, and lithium alloys. At least one of these negative electrode active materials can be used.

[0095] The negative electrode 330 may contain conductive additives, binders, and other materials. As conductive additives and binders, materials that can be used in the positive electrode 310 can also be used in the negative electrode 330.

[0096] The solid electrolyte layer 320 contains a solid electrolyte. The solid electrolyte can be a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, a complex hydride solid electrolyte, etc. The solid electrolyte layer 320 can be formed from multiple solid electrolytes having different compositions. The solid electrolyte layer 320 can be a stack of multiple solid electrolyte membranes.

[0097] (Other implementation methods)

[0098] (Postscript)

[0099] Based on the above description of the embodiments, the following technical solution is disclosed.

[0100] (Technical Solution 1)

[0101] A coated active material having a positive electrode active material and a coating layer covering at least a portion of the surface of the positive electrode active material.

[0102] The coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte.

[0103] The first layer is located between the second layer and the positive electrode active material.

[0104] The first solid electrolyte comprises Li, Ti, M1, and F, wherein M1 is selected from at least one of Ca, Mg, Al, Y, Zr, and Nb.

[0105] The second solid electrolyte has a different composition than the first solid electrolyte.

[0106] This structure can improve the battery's output characteristics.

[0107] (Technical Solution 2)

[0108] According to the coated active material described in technical solution 1

[0109] The second layer is the outermost layer containing the coated active material.

[0110] This structure can effectively improve the battery's output characteristics.

[0111] (Technical Solution 3)

[0112] According to the coated active material described in technical solution 1 or 2

[0113] The first layer is in contact with the positive electrode active material.

[0114] This structure can effectively improve the battery's output characteristics.

[0115] (Technical Solution 4)

[0116] According to any one of technical solutions 1 to 3, the coated active material,

[0117] In the first solid electrolyte, the mass ratio of Li to the total mass of Ti and M1 is 0.5 or more and 4.5 or less.

[0118] Therefore, the first solid electrolyte has excellent lithium-ion conductivity.

[0119] (Technical Solution 5)

[0120] According to any one of technical solutions 1 to 4, the coated active material,

[0121] M1 is selected from at least one of Ca, Mg and Al.

[0122] Therefore, the first solid electrolyte has excellent lithium-ion conductivity.

[0123] (Technical Solution 6)

[0124] According to the coated active material described in technical solution 5

[0125] M1 is Al.

[0126] Therefore, the first solid electrolyte has excellent lithium-ion conductivity.

[0127] (Technical Solution 7)

[0128] According to any one of technical solutions 1 to 6, the coated active material,

[0129] The first solid electrolyte has a composition represented by the following formula (1),

[0130] Li 6-(4-4x+m1x)b (Ti 1-x M1 x ) b F6 ・・・Form (1)

[0131] In equation (1),

[0132] Satisfying 0 < x < 1 and 0 < b ≤ 2, and

[0133] The m1 is the valence of the M1.

[0134] Therefore, the first solid electrolyte has excellent lithium-ion conductivity.

[0135] (Technical Solution 8)

[0136] According to any one of technical solutions 1 to 7, the coated active material,

[0137] The second layer does not actually contain conductive additives.

[0138] This structure allows for further improvement in the battery's output characteristics.

[0139] (Technical Solution 9)

[0140] According to any one of technical solutions 1 to 8, the coated active material,

[0141] The second solid electrolyte contains a halide solid electrolyte.

[0142] This structure allows for further improvement in the battery's output characteristics.

[0143] (Technical Solution 10)

[0144] According to the coated active material described in technical solution 9

[0145] The second solid electrolyte is a halide solid electrolyte.

[0146] This structure allows for further improvement in the battery's output characteristics.

[0147] (Technical Solution 11)

[0148] According to any one of technical solutions 1 to 10, the coated active material,

[0149] The second solid electrolyte contains Li, M2, Y, and X.

[0150] M2 is at least one element selected from metallic and half-metallic elements other than Li and Y.

[0151] X is selected from at least one of F, Cl, Br and I.

[0152] This structure allows for further improvement in the battery's output characteristics.

[0153] (Technical Solution 12)

[0154] The coated active material according to any one of technical solutions 1 to 11,

[0155] The second solid electrolyte has a composition represented by the following formula (2),

[0156] Li d M2 e Y f X6 ・・・Form (2)

[0157] In equation (2),

[0158] M2 is at least one element selected from metallic and half-metallic elements other than Li and Y.

[0159] X is selected from at least one of F, Cl, Br and I.

[0160] It satisfies 5.7 < d + m²e + 3f < 6.3, d > 0, e > 0, and f ≥ 0, and

[0161] The m2 is the valence of the M2.

[0162] This structure allows for further improvement in the battery's output characteristics.

[0163] (Technical Solution 13)

[0164] According to the coated active material described in technical solution 11 or 12

[0165] The M2 is selected from at least one 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.

[0166] This structure allows for further improvement in the battery's output characteristics.

[0167] (Technical Solution 14)

[0168] According to any one of technical solutions 11 to 13, the coated active material,

[0169] X is Cl.

[0170] This structure allows for further improvement in the battery's output characteristics.

[0171] (Technical Solution 15)

[0172] The coated active material according to any one of technical solutions 1 to 14,

[0173] The mass ratio of the second solid electrolyte to the mass of the positive electrode active material is greater than 0% by mass and less than 5% by mass.

[0174] This structure allows for further improvement in the battery's output characteristics.

[0175] (Technical Solution 16)

[0176] According to any one of technical solutions 1 to 15, the coated active material,

[0177] The average thickness of the first layer is greater than 1 nm and less than 150 nm.

[0178] This structure allows for further improvement in the battery's output characteristics.

[0179] (Technical Solution 17)

[0180] The coated active material according to any one of technical solutions 1 to 16,

[0181] The average thickness of the second layer is greater than 1 nm and less than 150 nm.

[0182] This structure allows for further improvement in the battery's output characteristics.

[0183] (Technical Solution 18)

[0184] A positive electrode comprising the coated active material as described in any one of technical solutions 1 to 17.

[0185] This structure allows for further improvement in the battery's output characteristics.

[0186] (Technical Solution 19)

[0187] A positive electrode comprising a positive electrode active material layer consisting of a coated active material and a material phase other than the coated active material.

[0188] The coated active material has a positive electrode active material and a coating layer covering at least a portion of the surface of the positive electrode active material.

[0189] The coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte.

[0190] The first layer is located between the second layer and the positive electrode active material.

[0191] The first solid electrolyte comprises Li, Ti, M1, and F, wherein M1 is selected from at least one of Ca, Mg, Al, Y, Zr, and Nb.

[0192] The second solid electrolyte has a different composition than the first solid electrolyte.

[0193] The material phase contains a third solid electrolyte.

[0194] In the interface region between the coated active material and the material phase, the proportion of conductive additives contained in the coating layer is lower than the proportion of conductive additives contained in the material phase.

[0195] This structure allows for further improvement in the battery's output characteristics.

[0196] (Technical Solution 20)

[0197] According to the positive electrode described in technical solution 19

[0198] In the first solid electrolyte, the mass ratio of Li to the total mass of Ti and M1 is 0.5 or more and 4.5 or less.

[0199] Therefore, the first solid electrolyte has excellent lithium-ion conductivity.

[0200] (Technical Solution 21)

[0201] According to the positive electrode described in technical solution 19 or 20

[0202] The first solid electrolyte has a composition represented by the following formula (1),

[0203] Li 6-(4-4x+m1x)b (Ti 1-x M1 x ) b F6 ・・・Form (1)

[0204] Here, in equation (1),

[0205] Satisfying 0 < x < 1 and 0 < b ≤ 2, and

[0206] The m1 is the valence of the M1.

[0207] Therefore, the first solid electrolyte has excellent lithium-ion conductivity.

[0208] (Technical Solution 22)

[0209] According to any one of technical solutions 19 to 21, the positive electrode,

[0210] The second solid electrolyte contains a halide solid electrolyte.

[0211] This structure allows for further improvement in the battery's output characteristics.

[0212] (Technical Solution 23)

[0213] According to any one of technical solutions 19 to 22, the positive electrode,

[0214] The second solid electrolyte contains Li, M2, Y, and X.

[0215] M2 is at least one element selected from metallic and half-metallic elements other than Li and Y.

[0216] X is selected from at least one of F, Cl, Br and I.

[0217] This structure allows for further improvement in the battery's output characteristics.

[0218] (Technical Solution 24)

[0219] According to any one of technical solutions 19 to 23, the positive electrode,

[0220] The second solid electrolyte has a composition represented by the following formula (2),

[0221] Li d M2 e Y f X6 ・・・Form (2)

[0222] Here, in equation (2),

[0223] M2 is at least one element selected from metallic and half-metallic elements other than Li and Y.

[0224] X is selected from at least one of F, Cl, Br and I.

[0225] It satisfies 5.7 < d + m²e + 3f < 6.3, d > 0, e > 0, and f ≥ 0, and

[0226] The m2 is the valence of the M2.

[0227] This structure allows for further improvement in the battery's output characteristics.

[0228] (Technical Solution 25)

[0229] According to any one of technical solutions 19 to 24, the positive electrode,

[0230] The average thickness of the first layer is greater than 1 nm and less than 150 nm.

[0231] This structure allows for further improvement in the battery's output characteristics.

[0232] (Technical Solution 26)

[0233] According to any one of technical solutions 19 to 25, the positive electrode,

[0234] The average thickness of the second layer is greater than 1 nm and less than 150 nm.

[0235] This structure allows for further improvement in the battery's output characteristics.

[0236] (Technical Solution 27)

[0237] A battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode as described in technical solution 18.

[0238] This structure can improve the battery's output characteristics.

[0239] (Technical Solution 28)

[0240] A battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, as described in any one of technical solutions 19 to 26.

[0241] This structure can improve the battery's output characteristics.

[0242] Example

[0243] The present disclosure will now be described in more detail with reference to the embodiments. The embodiments described below are merely examples and are not intended to limit the scope of the disclosure.

[0244] (Example 1)

[0245] [Preparation of the first solid electrolyte]

[0246] Under an argon atmosphere with a dew point below -60°C, LiF, TiF4, and AlF3, used as raw material powders, were weighed in a molar ratio of LiF:TiF4:AlF3 = 2.7:0.3:0.7. They were pulverized and mixed in a mortar to obtain a mixture. The mixture was then ground using φ5mm zirconia balls and a planetary ball mill (Fridge, P-7 type) at 500 rpm for 12 hours. This yielded a product containing Li... 2.7 Ti 0.3 Al 0.7 F6 is a powdered first solid electrolyte. Hereinafter, Li... 2.7 Ti 0.3 Al 0.7 F6 is denoted as "LTAF".

[0247] [Preparation of the second solid electrolyte]

[0248] Under an argon atmosphere with a dew point below -60°C, LiCl, ZrCl4, and YCl3, as raw material powders, were weighed in a molar ratio of LiCl:ZrCl4:YCl3 = 2.5:0.5:0.5. They were pulverized and mixed in a mortar to obtain a mixture. The mixture was then ground using φ5mm zirconia balls and a planetary ball mill (Fridge, P-7 type) at 500 rpm for 12 hours. This yielded a product containing Li... 2.5 Zr 0.5 Y 0.5 The second solid electrolyte is a powdered form of Cl6. Below, Li... 2.5 Zr 0.5 Y 0.5 Cl6 is denoted as "LZYC".

[0249] [Preparation of coated positive electrode active material]

[0250] As the positive electrode active material, NCM powder (average particle size 5 μm) was prepared. A first solid electrolyte was attached to the surface of the NCM particles to form a first coating layer. The first coating layer was formed by compression shearing using a particle recombination device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, NCM and the first solid electrolyte were mixed at a mass ratio of 100:3, and the mixture was treated at a rotation speed of 6000 rpm and a treatment time of 50 min. This yielded a positive electrode active material with a first coating layer formed on its surface (positive electrode active material with a first layer).

[0251] A second solid electrolyte is attached to the surface of particles containing a first layer of positive electrode active material to form a second coating layer. This second coating layer is formed by compression shearing using a particle recombination apparatus (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, the positive electrode active material containing the first layer and the second solid electrolyte are mixed at a mass ratio of NCM to the second solid electrolyte of 100:0.5. The mixture is treated at a rotation speed of 6000 rpm and a processing time of 50 min. This forms the second coating layer, resulting in the coated active material of Example 1.

[0252] [Preparation of the positive electrode mixture]

[0253] The positive electrode mixture was prepared by mixing the coated active material, the third solid electrolyte, and the conductive additive in an agate mortar. The mass ratio of the coated active material, the third solid electrolyte, and the conductive additive was 64:34:2. LZYC was used as the third solid electrolyte. Carbon nanofibers (manufactured by Showa Denko Corporation) were used as the conductive additive.

[0254] [Preparation of the negative electrode mixture]

[0255] Under a dry argon atmosphere, Li3YBr2Cl4 (hereinafter referred to as "LYBC") is used as the solid electrolyte, and Li4Ti5O is used as the negative electrode active material. 12 The negative electrode mixture was prepared by mixing the negative electrode active material (average particle size 2.5 μm) and a conductive additive in an agate mortar. The mass ratio of the negative electrode active material, solid electrolyte, and conductive additive was 64:34:2. Carbon nanofibers (manufactured by Showa Denko Co., Ltd.) were used as the conductive additive.

[0256] [Battery manufacturing]

[0257] Within an insulating outer cylinder with an inner diameter of 9.4 mm, 63.3 mg of positive electrode mixture, 50.9 mg of LZYC, 60.0 mg of LYBC, and 82.3 mg of negative electrode mixture are sequentially stacked. The positive electrode mixture, solid electrolyte, and negative electrode mixture are then pressurized and molded at 720 MPa. This creates a laminate containing a positive electrode, an electrolyte layer, and a negative electrode. Next, stainless steel current collectors are placed on the top and bottom of the laminate, and current collector leads are installed on the current collectors. Finally, an insulating ring is used to seal the insulating outer cylinder, isolating its interior from the external atmosphere.

[0258] [Battery Evaluation]

[0259] (Determination of initial discharge capacity)

[0260] The initial discharge capacity of the battery in Example 1 was determined using the following method. The battery was charged at a constant current of 0.05C until the voltage reached 2.6V, and then discharged at a constant current of 0.01C until the voltage reached 1.5V. The discharge capacity measured at this point was considered the initial discharge capacity. The pause time between charging and discharging was 60 minutes. Charging and discharging were performed at a temperature of 25°C (ambient temperature). The results are shown in Table 1.

[0261] [Determination of pulse discharge voltage at -40℃]

[0262] The pulse discharge voltage of the battery in Example 1 at -40°C was determined using the following method. The battery was charged to 2.6V at 0.05C at 25°C, then placed in a constant temperature bath at -40°C. After 2 hours, it was discharged at 0.07C, and the voltage was measured after 0.5 seconds and 1 second. The results are shown in Table 1.

[0263] (Example 2)

[0264] In the fabrication of the coated active material, during the formation of the second layer, the positive electrode active material with the first layer and the second solid electrolyte were mixed at a mass ratio of NCM to the second solid electrolyte of 100:1. Except for this change, the coated active material and battery of Example 2 were fabricated using the same method as in Example 1, and the results were evaluated. The results are shown in Table 1.

[0265] (Example 3)

[0266] In the fabrication of the coated active material, during the formation of the second layer, the positive electrode active material with the first layer and the second solid electrolyte were mixed at a mass ratio of NCM to the second solid electrolyte of 100:2. Except for this change, the coated active material and battery of Example 3 were fabricated using the same method as in Example 1, and the results were evaluated. The results are shown in Table 1.

[0267] (Comparative Example 1)

[0268] In the fabrication of the coated active material, no second layer was formed. That is, only the first layer was formed on the surface of the NCM to produce the coated active material of the comparative example. Except for this change, the coated active material and battery of Comparative Example 1 were fabricated using the same method as in Example 1, and evaluated. The results are shown in Table 1.

[0269] Table 1

[0270]

[0271] The “Initial Discharge Capacity Ratio” in Table 1 is a value obtained by standardizing the initial discharge capacity using the initial discharge capacity of Comparative Example 1.

[0272] As shown in Table 1, the initial discharge capacity of the batteries in Examples 1 to 3 exceeded that of the battery in Comparative Example 1.

[0273] The pulse discharge voltage of the batteries in Examples 1-3 at -40°C is higher than that of the battery in Comparative Example 1 at -40°C.

[0274] As described above, compared with a coated active material that is coated by a coating layer consisting of only a first layer, a coated active material that is coated by a coating layer having a first layer and a second layer can improve the output characteristics of the battery.

[0275] Industry availability

[0276] The technology disclosed herein can be used, for example, in lithium-ion secondary batteries.

Claims

1. A coated active material comprising a positive electrode active material and a coating layer covering at least a portion of the surface of the positive electrode active material. The coating layer has 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 comprises Li, Ti, M1, and F, wherein, M1 is selected from at least one of Ca, Mg, Al, Y, Zr, and Nb. The second solid electrolyte has a different composition than the first solid electrolyte.

2. The coated active material according to claim 1, The second layer is the outermost layer containing the coated active material.

3. The coated active material according to claim 1, The first layer is in contact with the positive electrode active material.

4. The coated active material according to claim 1, In the first solid electrolyte, the mass ratio of Li to the total mass of Ti and M1 is 0.5 or more and 4.5 or less.

5. The coated active material according to claim 1, M1 is selected from at least one of Ca, Mg and Al.

6. The coated active material according to claim 5, M1 is Al.

7. The coated active material according to claim 1, The first solid electrolyte has a composition represented by the following formula (1), Li 6-(4-4x+m1x)b (Ti 1-x M1 x ) b F6... Formula (1) in, In the above formula (1), Satisfying 0 < x < 1 and 0 < b ≤ 2, and The m1 is the valence of the M1.

8. The coated active material according to claim 1, The second layer does not actually contain conductive additives.

9. The coated active material according to claim 1, The second solid electrolyte contains a halide solid electrolyte.

10. The coated active material according to claim 9, The second solid electrolyte is a halide solid electrolyte.

11. The coated active material according to claim 1, The second solid electrolyte contains Li, M2, Y, and X. M2 is at least one element selected from metallic and half-metallic elements other than Li and Y. X is selected from at least one of F, Cl, Br and I.

12. The coated active material according to claim 1, The second solid electrolyte has a composition represented by the following formula (2), Li d M2 e Y f X6 ··· Equation (2) in, In the above equation (2), M2 is at least one element selected from metallic and half-metallic elements other than Li and Y. X is selected from at least one of F, Cl, Br and I. It satisfies 5.7 < d + m²e + 3f < 6.3, d > 0, e > 0, and f ≥ 0, and The m2 is the valence of the M2.

13. The coated active material according to claim 11, The M2 is selected from at least one 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.

14. The coated active material according to claim 11, X is Cl.

15. The coated active material according to claim 1, The mass ratio of the second solid electrolyte to the mass of the positive electrode active material is greater than 0% by mass and less than 5% by mass.

16. The coated active material according to claim 1, The average thickness of the first layer is greater than 1 nm and less than 150 nm.

17. The coated active material according to claim 1, The average thickness of the second layer is greater than 1 nm and less than 150 nm.

18. A positive electrode comprising the coated active material according to any one of claims 1 to 17.

19. A positive electrode comprising a positive electrode active material layer consisting of a coated active material and a material phase other than the coated active material. The coated active material has a positive electrode active material and a coating layer covering at least a portion of the surface of the positive electrode active material. The coating layer has 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 comprises Li, Ti, M1, and F, wherein, M1 is selected from at least one of Ca, Mg, Al, Y, Zr, and Nb. The second solid electrolyte has a different composition than the first solid electrolyte. The material phase contains a third solid electrolyte. In the interface region between the coated active material and the material phase, the proportion of conductive additives contained in the coating layer is lower than the proportion of conductive additives contained in the material phase.

20. The positive electrode according to claim 19, In the first solid electrolyte, the mass ratio of Li to the total mass of Ti and M1 is 0.5 or more and 4.5 or less.

21. The positive electrode according to claim 19, The first solid electrolyte has a composition represented by the following formula (1), Li 6-(4-4x+m1x)b (Ti 1-x M1 x ) b F6... Formula (1) Here, in equation (1), Satisfying 0 < x < 1 and 0 < b ≤ 2, and The m1 is the valence of the M1.

22. The positive electrode according to claim 19, The second solid electrolyte contains a halide solid electrolyte.

23. The positive electrode according to claim 19, The second solid electrolyte contains Li, M2, Y, and X. M2 is at least one element selected from metallic and half-metallic elements other than Li and Y. X is selected from at least one of F, Cl, Br and I.

24. The positive electrode according to claim 19, The second solid electrolyte has a composition represented by the following formula (2), Li d M2 e Y f X6 ··· Formula (2) Here, in equation (2), M2 is at least one element selected from metallic and half-metallic elements other than Li and Y. X is selected from at least one of F, Cl, Br and I. It satisfies 5.7 < d + m²e + 3f < 6.3, d > 0, e > 0, and f ≥ 0, and The m2 is the valence of the M2.

25. The positive electrode according to claim 19, The average thickness of the first layer is greater than 1 nm and less than 150 nm.

26. The positive electrode according to claim 19, The average thickness of the second layer is greater than 1 nm and less than 150 nm.

27. A battery comprising a positive electrode, a negative electrode as described in claim 18, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

28. A battery comprising a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode, as described in any one of claims 19 to 26.

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