Coated active material, positive electrode, and battery

Abstract

The coated active material (100) according to the present disclosure comprises a positive electrode active material (110) and a coating layer (120) that coats at least a part of the surface of the positive electrode active material (110). The coating layer (120) has 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 selection from the group consisting of Ca, Mg, Al, Y, Zr, and Nb. The second solid electrolyte has a composition different from that of the first solid electrolyte.

Description

Coated active material, positive electrode, and battery

[0001] The present disclosure relates to coated active materials, positive electrodes, and batteries.

[0002] In conventional batteries, electrolytes can be decomposed by active materials. When the electrolyte decomposes, a film of electrolyte decomposition products forms inside the electrodes. This leads to disadvantages such as an increase in the internal resistance of the battery and a decrease in the battery's cycle characteristics.

[0003] Coating an active material with an appropriate coating material can suppress electrolyte decomposition caused by the active material. For example, Patent Document 1 discloses coating a positive electrode active material with a solid electrolyte containing Li, Ti, M1, and F. M1 is at least one element selected from the group consisting of Ca, Mg, Al, Y, and Zr.

[0004] International Publication No. 2021 / 187391

[0005] There is a demand for improving the output characteristics of batteries using conventional active materials whose surfaces are coated with a coating material such as that disclosed in Patent Document 1.

[0006] The coated active material of the present disclosure comprises: a cathode active material; and a coating layer that coats at least a portion of a surface of the cathode active material, wherein the coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte, the first layer being located between the second layer and the cathode active material, the first solid electrolyte containing Li, Ti, M1, and F, where 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.

[0007] According to the present disclosure, it is possible to provide a coated active material that can improve the output characteristics of a battery.

[0008] Fig. 1 is a cross-sectional view showing a schematic configuration of a coated active material according to embodiment 1. Fig. 2 is a cross-sectional view showing a schematic configuration of a positive electrode according to embodiment 2. Fig. 3 is a cross-sectional view showing a schematic configuration of a battery according to embodiment 3.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0010] (Embodiment 1) Fig. 1 is a cross-sectional view showing a schematic configuration of a 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, in the form of particles. 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.

[0011] The first solid electrolyte is a solid electrolyte containing Li, Ti, M1, and F. M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb. The second solid electrolyte is a solid electrolyte having a different composition from the first solid electrolyte.

[0012] The first solid electrolyte is a fluoride solid electrolyte and has excellent oxidation resistance due to the high electronegativity of fluorine. When the positive electrode active material 110 is coated with the coating layer 120 having the first layer 111 containing the first solid electrolyte, direct contact between the positive electrode active material 110 and the electrolyte is prevented. This reduces decomposition of the electrolyte by the positive electrode active material 110.

[0013] The coating layer 120 further includes a second layer 112 containing a second solid electrolyte having a different composition from the first solid electrolyte. The second layer 112 is located outside the first layer 111 in the coated active material 100. A positive electrode containing the coated active material 100 is composed of a positive electrode material further containing a solid electrolyte and other materials, such as a conductive additive. By providing the coated active material 100 with such a second layer 112, the interfacial resistance between the coated active material 100 and other materials, such as the solid electrolyte, is reduced, thereby improving the output characteristics (e.g., discharge capacity and pulse discharge characteristics) of the battery. In this way, the coated active material 100 according to the first embodiment can achieve not only the improvement in battery characteristics due to the first layer 111 of the coating layer 120, but also the effect of improving output characteristics due to the reduction in interfacial resistance caused by the second layer 112.

[0014] In this embodiment, the second layer 112 is, for example, a layer including the outermost surface of the coated active material 100. In other words, the second layer 112 forms at least a portion of the outermost surface of the coated active material 100. With this configuration, the interface resistance between the coated active material 100 and other materials such as a solid electrolyte is more reliably reduced, thereby effectively improving the output characteristics of the battery. For example, the coated active material 100 according to the first embodiment can improve the discharge capacity of the battery and further improve the pulse discharge characteristics.

[0015] In the present embodiment, the first layer 111 is in contact with, for example, the positive electrode active material 110. With such a configuration, contact between the positive electrode active material 110 and the electrolyte is more reliably reduced, and the effect of improving the battery characteristics by the coating layer 120 can be more effectively exerted.

[0016] In the coating layer 120, the first layer 111 and the second layer 112 may be provided in contact with each other as shown in Fig. 1 , or another layer may be further included. That is, the coating layer 120 may further include another layer provided between the first layer 111 and the second layer 112, for example. The other layer may include, for example, another solid electrolyte having a composition different from the first solid electrolyte and the second solid electrolyte.

[0017] The positive electrode active material 110, the coating layer 120, the first solid electrolyte, and the second solid electrolyte will be described in more detail below.

[0018] The positive electrode active material 110 is, for example, a material that contains lithium and a transition metal and is capable of absorbing and releasing lithium.

[0019] Examples of the positive electrode active material 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 a lithium-containing transition metal oxide or a lithium-containing transition metal phosphate as the positive electrode active material can reduce battery manufacturing costs and increase the 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 selected from 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 includes, for example, NCM.

[0020] The particles of the positive electrode active material 110 may be primary particles or secondary particles. The particles of the positive electrode active material 110 have an average particle size of, for example, 1 μm or more and 10 μm or less. 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, using a laser diffraction particle size distribution analyzer.

[0021] The first layer 111 of the coating layer 120 may consist essentially of the first solid electrolyte, or may consist solely of the first solid electrolyte. Here, "the first layer 111 consists essentially 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, the content may be 95% by mass or more.

[0022] As described above, the first solid electrolyte contained in the first layer 111 of the coating layer 120 contains Li, Ti, M1, and F. The first solid electrolyte may consist essentially of Li, Ti, M1, and F, or may consist only of Li, Ti, M1, and F. Here, "the first solid electrolyte consists essentially 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, the molar ratio may be 95% or more.

[0023] In the first solid electrolyte, the ratio of the amount of substance of Li to the total amount of substance 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.

[0024] M1 may be at least one selected from the group consisting of Ca, Mg, and Al, in which case the first solid electrolyte has excellent lithium ion conductivity.

[0025] M1 may be Al, in which case the first solid electrolyte has excellent lithium ion conductivity.

[0026] The first solid electrolyte may have a composition represented by the following formula (1): Li6-(4-4x+m1x)b(Ti 1-x M1 x ) b F6 Formula (1) Here, in the above formula (1), 0<x<1 and 0<b≦2 are satisfied. Note that m1 is the valence of M1.

[0027] When the first solid electrolyte has the composition represented by the above formula (1), the first solid electrolyte has excellent lithium ion conductivity.

[0028] The first solid electrolyte may not contain sulfur. According to the above configuration, generation of hydrogen sulfide gas can be prevented, thereby realizing a battery with improved safety.

[0029] As described above, the second layer 112 of the coating layer 120 is a layer containing a second solid electrolyte. The second layer 112 may, for example, be substantially free of a conductive additive. Here, "the second layer 112 is substantially free of a conductive additive" means that the content of the conductive additive in the second layer 112 is 0.1 mass % or less. The second layer 112 may be free of a conductive additive. Here, the conductive additive refers to a conductive additive used to reduce resistance in the positive electrode. Examples of the conductive additive 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 the conductive polymer compound include polyaniline, polypyrrole, and polythiophene.

[0030] The second layer 112 may consist essentially of the second solid electrolyte or may consist solely of the second solid electrolyte. Here, "the second layer 112 consists essentially 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, the content may be 95% by mass or more.

[0031] The second solid electrolyte contains, for example, a halide solid electrolyte. The second solid electrolyte may be a halide solid electrolyte. In this case, the second layer 112 has excellent lithium ion conductivity and can effectively reduce the interface 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.

[0032] The second solid electrolyte contains, for example, Li, M2, Y, and X. M2 is at least one element selected from the group consisting of metal elements and semimetal elements other than Li and Y. X is at least one element selected from the group consisting of 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 interface 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.

[0033] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0034] The term "metal element" includes all elements included in Groups 1 to 12 of the periodic table excluding hydrogen, and all elements included in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming an inorganic compound with a halogen element.

[0035] 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. M2 is preferably at least one selected from the group consisting of Ti, Hf, Zr, and In, and M2 may be Zr.

[0036] M2 may be at least one element selected from the group consisting of elements of Groups 3 to 13. M2 may be at least one element selected from the group consisting of Sc, Ti, Zr, Hf, Nb, Ta, W, Zn, Al, Ga, and In.

[0037] X may be Cl. In this case, the coated active material 100 can further improve the output characteristics of the battery.

[0038] The second solid electrolyte may have a composition represented by the following formula (2): d M2 e Y fX6 Formula (2) Here, M2 and X in the above formula (2) are as described above. Furthermore, in the above formula (2), 5.7<d+m2e+3f<6.3, d>0, e>0, and f≧0 are satisfied. Note that m2 is the valence of M2.

[0039] When the second solid electrolyte has the composition represented by the above formula (2), 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.

[0040] The second solid electrolyte may not contain sulfur. According to the above configuration, generation of hydrogen sulfide gas can be prevented, thereby realizing a battery with improved safety.

[0041] The mass ratio of the second solid electrolyte to the mass of the positive electrode active material 110 is, for example, greater than 0 mass% and not more than 5 mass%. When the second solid electrolyte is contained in the coated active material 100 at the above 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 mass of the positive electrode active material 110 may be not more than 3 mass%, or may be not more than 2 mass%. In this case, the coated active material 100 can further improve the output characteristics of the battery. Furthermore, the mass ratio of the second solid electrolyte to the mass of the positive electrode active material 110 may be not less than 0.1 mass%, or may be not less than 0.5 mass%. In this case, the coated active material 100 can further improve the output characteristics of the battery.

[0042] The ratio of the mass of the second solid electrolyte to the mass of the positive electrode active material 110 can be determined by measuring the masses by, for example, inductively coupled plasma mass spectrometry (ICP-MS).

[0043] The average thickness of the first layer 111 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, and more preferably 50 nm or less. By appropriately adjusting the average thickness of the first layer 111, the effect of improving the output characteristics of the battery can be enhanced. The average thickness of the first layer 111 can be calculated from a scanning transmission electron microscope (STEM) image obtained by STEM. The average thickness can be the average value of thicknesses at any multiple points (for example, five points).

[0044] 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 effect of improving the output characteristics of the battery can be enhanced. As with the first layer 111, the average thickness of the second layer 112 can be calculated from an STEM image obtained by STEM. The average thickness can be the average value of thicknesses at any multiple points (for example, five points).

[0045] The coated active material 100 according to the first embodiment has an average particle size of, for example, 1 μm or more and 10 μm or less. The average particle size of the coated active material 10 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, using a laser diffraction particle size distribution measuring device. When the thickness of the coating layer 120 is on the order of nanometers, 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.

[0046] The coated active material 100 according to the first embodiment can be produced, for example, by the following method.

[0047] First, the material of the first layer 111 is attached to the surface of the particles of the positive electrode active material 110. The material of the first layer 111 includes a first solid electrolyte.

[0048] The method for adhering the material of the first layer 111 to the surface of the positive electrode active material 110 is not particularly limited. For example, a mixture is obtained by mixing powder of the positive electrode active material 110 and powder of the material of the first layer 111 in an appropriate ratio. The mixture is then milled to impart mechanical energy to the mixture. A mixing device such as a ball mill can be used for the milling. To suppress oxidation of the material, the milling may be performed in a dry and inert atmosphere.

[0049] The first layer 111 may be manufactured by a dry particle compositing method. The treatment by the dry particle compositing method includes applying at least one mechanical energy selected from the group consisting of impact, compression, and shear to the positive electrode active material 110 and the material of the first layer 111.

[0050] Examples of devices that can impart mechanical energy to the mixture of the positive electrode active material 110 and the material of the first layer 111 include processing devices (particle composite devices) such as a ball mill, Mechanofusion (manufactured by Hosokawa Micron Corporation), and Nobilta (manufactured by Hosokawa Micron Corporation).

[0051] In either apparatus, the thickness of the first layer 111 can be controlled by adjusting conditions such as the rotation speed, processing time, and amount of material. Note that processing using the above apparatus is not essential. The first layer 111 may be produced by mixing the positive electrode active material 110 and the material for the first layer 111 using a mortar, a mixer, or the like. The material for the first layer 111 may be deposited on the surface of the positive electrode active material 110 by various methods such as a spray method, a spray-dry coating method, an electrodeposition method, an immersion method, or a mechanical mixing method using a disperser.

[0052] Next, the second layer 112 is formed by attaching a material for the second layer 112 to the surface of the particles on which the first layer 111 is formed on the surface of the positive electrode active material 110. The material for the second layer 112 includes a second solid electrolyte.

[0053] The method of adhering the material of the second layer 112 to the surface of the particles on which the first layer 111 is formed on the surface of the positive electrode active material 110 can be the same as the method exemplified above for forming the first layer 111.

[0054] (Embodiment 2) A positive electrode according to Embodiment 2 includes the coated active material according to Embodiment 1. The positive electrode according to Embodiment 2 can improve the output characteristics of a battery. For example, the positive electrode according to Embodiment 2 can improve the discharge capacity of a battery and further improve the pulse discharge characteristics.

[0055] 2 is a cross-sectional view showing a schematic configuration of a positive electrode 200 according to embodiment 2. The positive electrode 200 includes, for example, a positive electrode current collector 210 and a positive electrode active material layer 220 supported on the positive electrode current collector 210. The positive electrode active material layer 220 includes the coated active material 100 according to embodiment 1.

[0056] The positive electrode active material layer 220 may contain only the coated active material 100 according to the first embodiment as the positive electrode active material, or may further contain a positive electrode active material different from the coated active material 100 according to the first embodiment.

[0057] The positive electrode active material layer 220 includes, for example, a solid electrolyte. Hereinafter, the solid electrolyte included in the positive electrode active material layer 220 will be referred to as a third solid electrolyte.

[0058] As shown in FIG. 2 , the positive electrode active material layer 220 includes a coated active material 100 and a material phase 221 composed of materials other than the coated active material 100. The material phase 221 includes, for example, a third solid electrolyte. In addition to the third solid electrolyte, the material phase 221 may further include a conductive additive, as described below. The positive electrode active material layer 220 has, for example, a sea-island structure in which the coated active material 100 is regarded as an island and the region of the material phase 221 containing the third solid electrolyte is regarded as a sea. When the positive electrode active material layer 220 has such a sea-island structure, the proportion of the conductive additive contained in the island is lower than the proportion of the conductive additive contained in the sea. Furthermore, in the interface region between the island and the sea, the proportion of the conductive additive 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 the conductive additive contained in the sea. That is, the second layer 112 may, for example, be substantially free of a conductive additive. Here, "the second layer 112 is substantially free of a conductive additive" means that the content of the conductive additive in the second layer 112 is 0.1 mass % or less. The second layer 112 does not need to contain a conductive additive. Because the first layer 111 and the second layer 112 are thin films, even if the first layer 111 and the second layer 112 are substantially free of a conductive additive, the interfacial resistance between the coated active material 100 and other materials such as the third solid electrolyte can be effectively reduced without increasing the resistance of the positive electrode 200.

[0059] In the interface region between the islands and the sea, whether the proportion of the conductive additive 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 the conductive additive contained in the material phase 221, which is the sea, can be confirmed by elemental mapping of a cross section including the interface between the coated active material 100 and the material phase 221 and its vicinity. The elemental map can be obtained by energy dispersive X-ray spectroscopy (STEM-EDX) combined with a scanning transmission electron microscope.

[0060] Examples of the third solid electrolyte 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 Li3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 Examples of the polymer solid electrolyte include a compound of a polymer compound having an ethylene oxide structure and a lithium salt. The lithium salt may 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 (3):

[0061] Li α M3 β X' γ In formula (3), α, β, and γ each independently represent a value greater than 0, M3 represents at least one element selected from the group consisting of metal elements and metalloid elements other than Li, and X′ represents at least one element selected from the group consisting of F, Cl, Br, and I.

[0062] "Metalloid elements" include B, Si, Ge, As, Sb, and Te.

[0063] The term "metal element" includes all elements included in Groups 1 to 12 of the periodic table excluding hydrogen, and all elements included in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming an inorganic compound with a halogen element.

[0064] The third solid electrolyte may be at least one selected from the group consisting of a sulfide solid electrolyte and a halide solid electrolyte, in which case the positive electrode 200 has excellent lithium ion conductivity.

[0065] The third solid electrolyte may be a halide solid electrolyte, in which case the positive electrode 200 has excellent lithium ion conductivity.

[0066] When the third solid electrolyte is a halide solid electrolyte, the third solid electrolyte may contain Cl.

[0067] The third solid electrolyte may not contain sulfur. According to the above configuration, generation of hydrogen sulfide gas can be prevented, thereby realizing a battery with improved safety.

[0068] The positive electrode active material layer 220 may contain other materials such as a conductive additive and a binder, as necessary.

[0069] The conductive additive is used to reduce the resistance of the positive electrode 200. Examples of the conductive additive include carbon materials and conductive polymer compounds. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of the conductive polymer compound include polyaniline, polypyrrole, and polythiophene. At least one selected from these conductive additives can be used.

[0070] The binder is used to improve the binding properties of the materials that make up the positive electrode 200. Examples of binders include polymer materials such as 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 selected from these binders can be used.

[0071] The positive electrode current collector 210 is a sheet or film made of a metal material such as aluminum, an aluminum alloy, stainless steel, titanium, or a titanium alloy. The sheet or film may be porous or non-porous. Examples of the sheet or film include metal foil and metal mesh. A carbon material may be applied to the surface of the positive electrode current collector 210 as a conductive auxiliary material.

[0072] The positive electrode 200 according to the second embodiment can be produced, for example, by mixing the material constituting the positive electrode active material layer 220 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.

[0073] (Embodiment 3) A battery according to Embodiment 3 includes the positive electrode according to Embodiment 2, a negative electrode, and a solid electrolyte layer. The solid electrolyte layer is disposed between the positive electrode and the negative electrode. By including the positive electrode according to Embodiment 2, the battery according to Embodiment 3 can improve its output characteristics. For example, the battery according to Embodiment 3 can improve its discharge capacity and further improve its pulse discharge characteristics.

[0074] 3 is a cross-sectional view showing a schematic configuration of a 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 according to Embodiment 2. With this configuration, the battery 300 can have improved output characteristics.

[0075] The battery 300 according to the third embodiment may be an all-solid-state battery.

[0076] The negative electrode 330 includes a negative electrode active material. The negative electrode active material is a material capable of absorbing and desorbing lithium. Examples of negative electrode active materials capable of absorbing and desorbing lithium include lithium titanate, graphite, silicon, silicon-containing oxides, zinc alloys, lithium metal, and lithium alloys. At least one selected from these negative electrode active materials can be used.

[0077] The negative electrode 330 may contain other materials such as a conductive additive, a binder, etc. Materials that can be used for the positive electrode 310 as the conductive additive and the binder can also be used for the negative electrode 330.

[0078] The solid electrolyte layer 320 includes a solid electrolyte. Examples of the solid electrolyte that can be used include a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. The solid electrolyte layer 320 may be formed of a plurality of solid electrolytes having different compositions. The solid electrolyte layer 320 may also be a stack of a plurality of solid electrolyte films.

[0079] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0080] (Technology 1) A coated active material comprising: a cathode active material; and a coating layer that coats at least a portion of a surface of the cathode active material, wherein the coating layer has a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte, the first layer being located between the second layer and the cathode active material, the first solid electrolyte containing Li, Ti, M1, and F, where M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb, and the second solid electrolyte having a different composition from the first solid electrolyte.

[0081] With this configuration, the output characteristics of the battery can be improved.

[0082] (Technology 2) The coated active material according to Technology 1, wherein the second layer is a layer including the outermost surface of the coated active material.

[0083] With this configuration, the output characteristics of the battery can be effectively improved.

[0084] (Technology 3) The coated active material according to Technology 1 or 2, wherein the first layer is in contact with the positive electrode active material.

[0085] With this configuration, the output characteristics of the battery can be effectively improved.

[0086] (Technology 4) The coated active material according to any one of Technologies 1 to 3, wherein in the first solid electrolyte, a ratio of the amount of substance of Li to the total amount of substance of Ti and the M1 is 0.5 or more and 4.5 or less.

[0087] This provides the first solid electrolyte with excellent lithium ion conductivity.

[0088] (Technology 5) The coated active material according to any one of Technologies 1 to 4, wherein M1 is at least one selected from the group consisting of Ca, Mg, and Al.

[0089] This provides the first solid electrolyte with excellent lithium ion conductivity.

[0090] (Technology 6) The coated active material according to Technology 5, wherein M1 is Al.

[0091] This provides the first solid electrolyte with excellent lithium ion conductivity.

[0092] (Technology 7) The first solid electrolyte has a composition represented by the following formula (1): Li6-(4-4x+m1x)b(Ti 1-x M1 x ) b F6 Formula (1) wherein, in the formula (1), 0<x<1 and 0<b≦2 are satisfied, and m1 is the valence of M1.

[0093] This provides the first solid electrolyte with excellent lithium ion conductivity.

[0094] (Technology 8) The coated active material according to any one of Technologies 1 to 7, wherein the second layer does not substantially contain a conductive additive.

[0095] With this configuration, the output characteristics of the battery can be further improved.

[0096] (Technology 9) The coated active material according to any one of Technologies 1 to 8, wherein the second solid electrolyte contains a halide solid electrolyte.

[0097] With this configuration, the output characteristics of the battery can be further improved.

[0098] (Technology 10) The coated active material according to Technology 9, wherein the second solid electrolyte is a halide solid electrolyte.

[0099] With this configuration, the output characteristics of the battery can be further improved.

[0100] (Technology 11) The coated active material according to any one of technologies 1 to 10, wherein the second solid electrolyte contains Li, M2, Y, and X, wherein M2 is at least one element selected from the group consisting of metal elements and semi-metal elements other than Li and Y, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0101] With this configuration, the output characteristics of the battery can be further improved.

[0102] (Technology 12) The second solid electrolyte has a composition represented by the following formula (2): Li d M2 e Y f X6 Formula (2) wherein, in the formula (2), the M2 is at least one element selected from the group consisting of metal elements and semi-metal elements other than Li and Y, the X is at least one element selected from the group consisting of F, Cl, Br, and I, 5.7<d+m2e+3f<6.3, d>0, e>0, and f≧0 are satisfied, and the m2 is a valence of the M2.

[0103] With this configuration, the output characteristics of the battery can be further improved.

[0104] (Technology 13) The coated active material according to Technology 11 or 12, wherein M2 is 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.

[0105] With this configuration, the output characteristics of the battery can be further improved.

[0106] (Technology 14) The coated active material according to any one of Techniques 11 to 13, wherein X is Cl.

[0107] With this configuration, the output characteristics of the battery can be further improved.

[0108] (Technology 15) The coated active material according to any one of Technologies 1 to 14, wherein a ratio of the mass of the second solid electrolyte to the mass of the positive electrode active material is greater than 0 mass % and is 5 mass % or less.

[0109] With this configuration, the output characteristics of the battery can be further improved.

[0110] (Technology 16) The coated active material according to any one of Technologies 1 to 15, wherein the average thickness of the first layer is 1 nm or more and 150 nm or less.

[0111] With this configuration, the output characteristics of the battery can be further improved.

[0112] (Technology 17) The coated active material according to any one of Technologies 1 to 16, wherein the second layer has an average thickness of 1 nm or more and 150 nm or less.

[0113] With this configuration, the output characteristics of the battery can be further improved.

[0114] (Technology 18) A positive electrode comprising the coated active material according to any one of technologies 1 to 17.

[0115] With this configuration, the output characteristics of the battery can be improved.

[0116] (Technology 19) A positive electrode including a positive electrode active material layer made of a coated active material and a material phase excluding the coated active material, wherein the coated active material includes a positive electrode active material and a coating layer coating at least a portion of a surface of the positive electrode active material, the coating layer having a first layer including a first solid electrolyte and a second layer including a second solid electrolyte, the first layer being located between the second layer and the positive electrode active material, the first solid electrolyte including Li, Ti, M1, and F, wherein M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb, the second solid electrolyte having a different composition from the first solid electrolyte, and the material phase including a third solid electrolyte, wherein at an interface region between the coated active material and the material phase, a proportion of a conductive additive contained in the coating layer is lower than a proportion of a conductive additive contained in the material phase.

[0117] With this configuration, the output characteristics of the battery can be improved.

[0118] (Technology 20) The positive electrode according to Technology 19, wherein in the first solid electrolyte, a ratio of the amount of substance of Li to the total amount of substance of Ti and the M1 is 0.5 or more and 4.5 or less.

[0119] This provides the first solid electrolyte with excellent lithium ion conductivity.

[0120] (Technology 21) The first solid electrolyte has a composition represented by the following formula (1): Li6-(4-4x+m1x)b(Ti 1-x M1 x ) b F6 Formula (1) wherein, in the formula (1), 0<x<1 and 0<b≦2 are satisfied, and the m1 is the valence of the M1.

[0121] This provides the first solid electrolyte with excellent lithium ion conductivity.

[0122] (Technology 22) The positive electrode according to any one of Techniques 19 to 21, wherein the second solid electrolyte contains a halide solid electrolyte.

[0123] With this configuration, the output characteristics of the battery can be further improved.

[0124] (Technology 23) The positive electrode according to any one of Techniques 19 to 22, wherein the second solid electrolyte contains Li, M2, Y, and X, wherein M2 is at least one element selected from the group consisting of metal elements and semimetal elements other than Li and Y, and X is at least one element selected from the group consisting of F, Cl, Br, and I.

[0125] With this configuration, the output characteristics of the battery can be further improved.

[0126] (Technology 24) The second solid electrolyte has a composition represented by the following formula (2): Li d M2 e Y f X6 Formula (2) wherein, in the formula (2), M2 is at least one element selected from the group consisting of metal elements and semimetal elements other than Li and Y, X is at least one element selected from the group consisting of F, Cl, Br, and I, 5.7<d+m2e+3f<6.3, d>0, e>0, and f≧0 are satisfied, and m2 is a valence of M2.

[0127] With this configuration, the output characteristics of the battery can be further improved.

[0128] (Technology 25) The positive electrode according to any one of technologies 19 to 24, wherein the average thickness of the first layer is 1 nm or more and 150 nm or less.

[0129] With this configuration, the output characteristics of the battery can be further improved.

[0130] (Technology 26) The positive electrode according to any one of Technologies 19 to 25, wherein the average thickness of the second layer is 1 nm or more and 150 nm or less.

[0131] With this configuration, the output characteristics of the battery can be further improved.

[0132] (Technology 27) A battery comprising: the positive electrode according to Technology 18; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0133] With this configuration, the output characteristics of the battery can be improved.

[0134] (Technology 28) A battery comprising: the positive electrode according to any one of technologies 19 to 26; a negative electrode; and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

[0135] With this configuration, the output characteristics of the battery can be improved.

[0136] The present disclosure will be described in more detail below using examples. The following examples are merely examples of embodiments, and are not intended to limit the scope of the present disclosure.

[0137] Example 1 Preparation of First Solid Electrolyte In an argon atmosphere having a dew point of -60°C or less, raw material powders LiF, TiF, and AlF were weighed in a molar ratio of LiF:TiF:AlF = 2.7:0.3:0.7. These were pulverized and mixed in a mortar to obtain a mixture. Thereafter, the mixture was milled using a φ5 mm zirconia ball and a planetary ball mill (Fritsch, P-7 model) at 500 rpm for 12 hours. As a result, Li 2.7 Ti 0.3 Al 0.7 A powdery first solid electrolyte having a composition of LiF was obtained. 2.7 Ti 0.3 Al 0.7 F6 is written as "LTAF".

[0138] [Preparation of Second Solid Electrolyte] In an argon atmosphere having a dew point of -60°C or less, raw material powders LiCl, ZrCl4, and YCl3 were weighed in a molar ratio of LiCl:ZrCl4:YCl3 = 2.5:0.5:0.5. These were pulverized and mixed in a mortar to obtain a mixture. Thereafter, the mixture was milled using a φ5 mm zirconia ball and a planetary ball mill (manufactured by Fritsch, Model P-7) at 500 rpm for 12 hours. As a result, Li 2.5 Zr 0.5 Y0.5 A powdery second solid electrolyte having a composition of LiCl was obtained. 2.5 Zr 0.5 Y 0.5 Cl6 is abbreviated as "LZYC".

[0139] [Preparation of Coated Cathode Active Material] An NCM powder (average particle size 5 μm) was prepared as the cathode active material. 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 compressive shear treatment using a particle compositer (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, the NCM and the first solid electrolyte were mixed in a mass ratio of 100:3, and the mixture was treated under the conditions of a rotation speed of 6000 rpm and a treatment time of 50 min. This resulted in a cathode active material (a cathode active material with a first layer) having a first coating layer formed on its surface.

[0140] A second solid electrolyte was attached to the surface of the particles of the positive electrode active material with the first layer to form a second coating layer. The second coating layer was formed by compressive shear treatment using a particle compositer (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, the positive electrode active material with the first layer and the second solid electrolyte were mixed so that the mass ratio of NCM to second solid electrolyte was 100:0.5. The mixture was treated under conditions of a rotation speed of 6000 rpm and a treatment time of 50 minutes. This formed the second coating layer, and the coated active material of Example 1 was obtained.

[0141] [Preparation of Positive Electrode Composite] The coated active material, the third solid electrolyte, and the conductive additive were mixed in an agate mortar to prepare a positive electrode composite. The mass ratio of the coated active material, the third solid electrolyte, and the conductive additive was coated active material:third solid electrolyte:conductive additive = 64:34:2. LZYC was used as the third solid electrolyte. Carbon nanofiber (manufactured by Showa Denko K.K.) was used as the conductive additive.

[0142] [Preparation of Negative Electrode Mixture] A mixture of LiYBrCl (hereinafter referred to as "LYBC") as a solid electrolyte and LiTiO as a negative electrode active material was mixed in a dry argon atmosphere. 12The negative electrode mixture was prepared by mixing the negative electrode active material (average particle size 2.5 μm) and the 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 nanofiber (manufactured by Showa Denko K.K.) was used as the conductive additive.

[0143] [Battery Fabrication] 63.3 mg of a positive electrode composite, 50.9 mg of LZYC, 60.0 mg of LYBC, and 82.3 mg of a negative electrode composite were stacked in this order in an insulating outer cylinder having an inner diameter of 9.4 mm. The positive electrode composite, solid electrolyte, and negative electrode composite were press-molded at a pressure of 720 MPa. This produced a laminate having a positive electrode, an electrolyte layer, and a negative electrode. Next, stainless steel current collectors were placed on the top and bottom of the laminate, and current collector leads were attached to the current collectors. Finally, the insulating outer cylinder was sealed using an insulating ferrule to isolate the interior of the insulating outer cylinder from the outside atmosphere.

[0144] [Battery Evaluation] (Measurement of Initial Discharge Capacity) The initial discharge capacity of the battery of Example 1 was measured by the following method. After constant current charging at a current of 0.05 C until the voltage reached 2.6 V, constant current discharging was performed at a current of 0.01 C until the voltage reached 1.5 V. The discharge capacity measured at this time was considered to be the initial discharge capacity. The rest time between charging and discharging was 60 minutes. Charging and discharging were performed at a temperature condition of 25°C (ambient temperature). The results are shown in Table 1.

[0145] [Measurement of Pulse Discharge Voltage at -40°C] The pulse discharge voltage of the battery of Example 1 at -40°C was measured by the following method. The battery was charged to 2.6 V at 25°C and 0.05 C, then placed in a thermostatic chamber at -40°C, and after 2 hours, discharged at 0.07 C, and the voltage was measured after 0.5 seconds and 1 second. The results are shown in Table 1.

[0146] (Example 2) In preparing the coated active material, when forming the second layer, the cathode active material with the first layer and the second solid electrolyte were mixed so that the mass ratio of NCM to second solid electrolyte was 100:1. Except for this change, the coated active material and battery of Example 2 were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0147] Example 3 In preparing the coated active material, when forming the second layer, the cathode active material with the first layer and the second solid electrolyte were mixed so that the mass ratio of NCM to the second solid electrolyte was 100:2. Except for this change, the coated active material and battery of Example 3 were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0148] (Comparative Example 1) In the preparation of the coated active material, the second layer was not formed. That is, only the first layer was formed on the surface of the NCM to prepare the coated active material of Comparative Example 1. Except for this change, the coated active material and battery of Comparative Example 1 were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0149]

[0150] The "initial discharge capacity ratio" in Table 1 is a value obtained by normalizing the initial discharge capacity with the initial discharge capacity of Comparative Example 1.

[0151] As shown in Table 1, the initial discharge capacities of the batteries of Examples 1 to 3 were greater than the initial discharge capacity of the battery of Comparative Example 1.

[0152] The pulse discharge voltages at -40°C of the batteries of Examples 1 to 3 were higher than the pulse discharge voltage at -40°C of the battery of Comparative Example 1.

[0153] As described above, the coated active material coated with a coating layer having a first layer and a second layer was able to improve the battery output characteristics more than the coated active material coated with a coating layer consisting of only the first layer.

[0154] The technology of the present disclosure is useful for, for example, lithium ion secondary batteries.

Claims

1. A coated active material comprising a positive electrode active material and a coating layer that covers at least a part of the surface of the positive electrode active material, the coating layer having a first layer containing a first solid electrolyte and a second layer containing a second solid electrolyte, the first layer being positioned between the second layer and the positive electrode active material, the first solid electrolyte containing Li, Ti, M1, and F, where M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb, and the second solid electrolyte having a composition different from that of the first solid electrolyte.

2. The coated active material according to claim 1, wherein the second layer is a layer including the outermost surface of the coated active material.

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

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

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

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

7. The first solid electrolyte has a composition represented by the following formula (1): Li6-(4-4x+m1x)b(Ti 1-x M1 x ). b F6... Formula (1) Here, in the formula (1), 0 < x < 1 and 0 < b ≤ 2 are satisfied, and m1 is the valence of M1. The coated active material according to claim 1.

8. The coated active material according to claim 1, wherein the second layer substantially does not contain a conductive assistant.

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

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

11. The coated active material according to claim 1, wherein the second solid electrolyte contains Li, M2, Y, and X, M2 is at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Y, and X is at least one selected from the group consisting of F, Cl, Br, and I.

12. The second solid electrolyte has a composition represented by the following formula (2): Li d M2 e Y f X6 ··· Formula (2) Here, in the formula (2), M2 is at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Y, X is at least one selected from the group consisting of F, Cl, Br, and I, 5.7 < d + m2e + 3f < 6.3, d > 0, e > 0, and f ≧ 0 are satisfied, and m2 is the valence of M2. The coated active material according to claim 1.

13. The coated active material according to claim 11, wherein M2 is 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.

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

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

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

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

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 composed of a coated active material and a material phase excluding the coated active material, wherein the coated active material comprises a positive electrode active material and a coating layer covering at least a part 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 contains Li, Ti, M1, and F, where M1 is at least one selected from the group consisting of Ca, Mg, Al, Y, Zr, and Nb, the second solid electrolyte has a composition different from that of the first solid electrolyte, the material phase contains a third solid electrolyte, and in the interface region between the coated active material and the material phase, the proportion of the conductive auxiliary agent contained in the coating layer is lower than the proportion of the conductive auxiliary agent contained in the material phase. Positive electrode.

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

21. The first solid electrolyte has a composition represented by the following formula (1): Li6-(4-4x+m1x)b(Ti 1-x M1 x ). b F6... Formula (1) Here, in the formula (1), 0 < x < 1 and 0 < b ≤ 2 are satisfied, and m1 is the valence of M1. The positive electrode according to claim 19.

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

23. The second solid electrolyte contains Li, M2, Y, and X, M2 is at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Y, and X is at least one selected from the group consisting of F, Cl, Br, and I. Positive electrode according to claim 19.

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

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

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

27. A battery comprising the positive electrode according to claim 18, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode.

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

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