Positive electrode material, preparation method thereof and application

Abstract

This application relates to a cathode material, a preparation method thereof, and an application. The cathode material includes a core and a coating layer coated on the surface of the core. The coating layer is in a composite state of crystalline phase - amorphous phase, and the amorphous phase is distributed on the outer surface of the cathode material. The lattice parameter c / a of the cathode material is 4.935 - 4.950; the chemical formula of the core is LiyNixCozMndAeDmO2, where 1 ≤ y ≤ 1.03, 0.5 ≤ x ≤ 0.96, 0 ≤ z ≤ 0.4, 0 ≤ d ≤ 0.4, 0.01 ≤ e < 0.1, 0.01 ≤ m < 0.1, A is selected from at least one of Mg, Al, Ca, and B, D is selected from at least one of Ti, Ce, Ta, Mo, and Zr, and the surface layer of the core is a rich X layer, where X is selected from at least one of P, S, Si, B, Al, Mg, Mo, Zr, and Nb; the crystalline phase is a lithium salt polyanion compound, and the amorphous phase is Li - M1 - M2 - O, where M1 is selected from at least one of P and S, and M2 is selected from at least one of Al, Mg, Mo, Zr, and Nb. The cathode material described in this application significantly improves the high-temperature cycle stability in a sulfide all-solid-state battery.

Description

Technical Field

[0001] The present application relates to the technical field of solid-state batteries, and particularly to a cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Compared with traditional liquid batteries, solid-state batteries avoid the safety hazards caused by the flammability and explosiveness of liquid electrolytes. At the same time, metallic lithium can be directly used as the battery anode, greatly reducing the amount of anode material used and significantly improving the energy density of the battery. Therefore, solid-state batteries are the key to achieving high battery safety and high energy density.

[0003] However, due to the electrochemical potential difference between the oxide cathode and the sulfide electrolyte, it is easy to cause the space charge layer effect and interfacial side reactions, especially in a high-temperature environment, the interfacial side reactions will be further aggravated, resulting in the attenuation of the high-temperature cycle capacity, which is not conducive to improving the high-temperature cycle performance of sulfide all-solid-state batteries. Summary of the Invention

[0004] Based on this, in view of the above problems, it is necessary to provide a cathode material, a preparation method thereof, and an application thereof; the cathode material can effectively inhibit interfacial side reactions in sulfide all-solid-state batteries and significantly improve the high-temperature cycle stability.

[0005] A cathode material includes a core and a coating layer coated on the surface of the core. The coating layer is in a composite state of crystalline phase - amorphous phase, and the amorphous phase is distributed on the outer surface of the cathode material. The lattice parameter c / a of the cathode material is 4.935 - 4.950;

[0006] The chemical formula of the core is Li y Ni x Co z Mn d A e D m O2, where 1≤y≤1.03, 0.5≤x≤0.96, 0≤z≤0.4, 0≤d≤0.4, 0.01≤e<0.1, 0.01≤m<0.1, A is selected from at least one of Mg, Al, Ca, B, D is selected from at least one of Ti, Ce, Ta, Mo, Zr, and the surface layer of the core is a X-rich layer, X is selected from at least one of P, S, Si, B, Al, Mg, Mo, Zr, Nb;

[0007] In the coating layer, the material of the crystalline phase is a lithium salt polyanion compound, and the material of the amorphous phase is Li-M1-M2-O, where M1 is selected from at least one of P, S, and M2 is selected from at least one of Al, Mg, Mo, Zr, Nb.

[0008] In one embodiment, in the amorphous phase, the molar ratio of Li to M1 and M2 is (0.5 - 1.5):(0.5 - 1):(0.05 - 0.1).

[0009] In one embodiment, the lithium salt polyanion compound is selected from at least one of Li3PO4, Li2HPO4, LiH2PO4, Li2SO4, Li2SO3, Li2SiO3, and Li3BO3.

[0010] In one embodiment, the mass of the amorphous phase is 0.1‰ - 5‰ of the core;

[0011] And / or, the mass of the non-oxygen element of the polyanion in the lithium salt polyanion compound is 0.2‰ - 2‰ of the core.

[0012] In one embodiment, the crystalline phase is an island structure, the island structure coats at least part of the surface of the core, and the average undulating thickness of the island structure is 1 nm - 20 nm;

[0013] And / or, the amorphous phase is distributed on the outer surface of the positive electrode material, and the average thickness of the amorphous phase is 1 nm - 20 nm;

[0014] And / or, the thickness ratio of the crystalline phase to the amorphous phase is 0.5:1 - 1.2:1;

[0015] And / or, the average thickness of the coating layer is 1 nm - 20 nm;

[0016] And / or, the ratio of the thickness of the X-rich layer to the radius of the core is 0.05:1 - 0.5:1.

[0017] In one embodiment, in the X-ray diffraction pattern of the positive electrode material, the intensity ratio of the diffraction peak of the (003) crystal plane to the diffraction peak of the (104) crystal plane is 1.70 - 2.40.

[0018] A method for preparing a positive electrode material as described above, comprising the following steps:

[0019] Using a coprecipitation reaction to prepare a hydroxide precursor containing doping element A and doping element D, mixing the hydroxide precursor with a first lithium source, and performing a first sintering in an oxygen-containing gas to obtain a first material, the chemical formula of the first material being Li y Ni x Co z Mn d A e D mO2, 1 ≤ y ≤ 1.03, 0.5 ≤ x ≤ 0.96, 0 ≤ z ≤ 0.4, 0 ≤ d ≤ 0.4, 0.01 ≤ e < 0.1, 0.01 ≤ m < 0.1;

[0020] Mix the first material with a polyanion compound and conduct a second sintering in an oxygen-containing gas to obtain a second material, wherein the temperature of the second sintering is greater than or equal to 550 °C;

[0021] Mix a second lithium source with a salt containing M1 and an oxide containing M2, and conduct a third sintering in an oxygen-containing gas to obtain the amorphous-phase material;

[0022] Mix the second material with the amorphous-phase material and conduct a fourth sintering in an oxygen-containing gas to obtain the positive electrode material, wherein the temperature of the fourth sintering is greater than or equal to 400 °C, and the temperature of the second sintering is greater than or equal to the temperature of the fourth sintering.

[0023] In one embodiment, the coprecipitation reaction includes adding a mixed salt solution and a precipitant to water and reacting in a protective gas to obtain a hydroxide precursor, wherein the molar concentration of the mixed salt in the mixed salt solution is 1 mol / L - 3 mol / L, the molar concentration of the precipitant in water is 5 mol / L - 10 mol / L, and the flow rate of the protective gas introduced is 2 L / min - 5 L / min.

[0024] In one embodiment, the polyanion compound is selected from at least one of polyanion compounds of lithium salts, ammonium dihydrogen phosphate, and silicic acid;

[0025] And / or, the mass of the polyanion compound is 1‰ - 7‰ of the first material;

[0026] And / or, the mass of the amorphous-phase material is 0.1‰ - 5‰ of the second material;

[0027] And / or, the molar ratio of Li in the second lithium source to M1 in the salt containing M1 and M2 in the oxide containing M2 is (0.5 - 1.5):(0.5 - 1):(0.05 - 0.1).

[0028] In one embodiment, the temperature of the first sintering is 800 °C - 1000 °C, and the time is 10 h - 20 h;

[0029] And / or, the temperature of the second sintering is 550 °C - 800 °C, and the time is 5 h - 10 h;

[0030] And / or, the temperature of the third sintering is 900 °C - 1200 °C, and the time is 4 h - 10 h;

[0031] And / or, the temperature of the fourth sintering is 400°C - 700°C, and the time is 5h - 10h.

[0032] A positive electrode sheet includes the positive electrode material as described above.

[0033] A sulfide solid-state battery includes the positive electrode sheet as described above.

[0034] The positive electrode material described in this application has a unique core-shell structure and lattice parameters. On the one hand, the inner core contains low-valence doped element A and high-valence doped element D, which can not only inhibit ion mixing, is beneficial to improving the capacity and initial Coulomb efficiency, but also can inhibit interfacial side reactions and enhance the reversibility of phase change. At the same time, the surface layer of the inner core is an X-rich layer, which can also enhance the bulk stability. On the other hand, the surface of the inner core is a uniform and continuous coating layer. Through the synergistic effect of the crystalline phase and amorphous phase in the coating layer, not only does the coating layer have the effect of a CEI-like film, which can effectively inhibit the interfacial side reaction between the sulfide electrolyte and the positive electrode, but also the polyanions and some non-oxygen elements in the coating layer can form strong covalent bonds with the oxygen atoms in the lattice structure of the inner core, which can inhibit the lattice structure collapse caused by deoxidation of the inner core. At the same time, the coating layer also has mechanical toughness, which can prevent particle cracking caused by drastic changes in lattice constants during cycling, thus ensuring high-temperature cycling stability.

[0035] Therefore, using the positive electrode material described in this application in a sulfide solid-state battery can significantly improve the capacity, initial Coulomb efficiency, and high-temperature cycling stability of the sulfide solid-state battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0037] Figure 1 It is a scanning electron microscope (SEM) comparison diagram of the positive electrode materials prepared in Example 1 and Comparative Example 1. Among them, a is the SEM diagram of the positive electrode material prepared in Example 1, and b is the SEM diagram of the positive electrode material prepared in Comparative Example 1;

[0038] Figure 2 It is an energy-dispersive X-ray spectroscopy (EDS) diagram of the element distribution of the positive electrode material prepared in Example 1. Among them, a is the image of the positive electrode material to be tested, and b is the mapping distribution image of phosphorus element;

[0039] Figure 3 It is a transmission electron microscope (TEM) diagram of the surface of the positive electrode material prepared in Example 1;

[0040] Figure 4 XRD (X-ray diffraction) comparison chart of the cathode materials prepared in Example 1 and Comparative Example 1. Among them, a is the X-ray diffraction spectrum of the cathode material prepared in Example 1, b is the X-ray diffraction spectrum of the cathode material prepared in Comparative Example 1, and c is the standard X-ray diffraction spectrum of lithium nickelate (PDF#74-0919);

[0041] Figure 5 Cross-sectional view of the cathode material prepared in Example 1;

[0042] Figure 6 Charge / voltage (dQ / dV) curve comparison chart of the solid-state batteries prepared in Example 1 and Comparative Example 1. Among them, a is the dQ / dV curve of the solid-state battery prepared in Example 1, and b is the dQ / dV curve of the solid-state battery prepared in Comparative Example 1;

[0043] Figure 7 Charge-discharge curve comparison chart of the solid-state batteries prepared in Example 1 and Comparative Example 1. Among them, a is the charge-discharge curve of the solid-state battery prepared in Example 1, and b is the charge-discharge curve of the solid-state battery prepared in Comparative Example 1;

[0044] Figure 8 High-temperature cycle curve comparison chart of the solid-state batteries prepared in Example 1 and Comparative Example 1. Among them, a is the high-temperature cycle curve of the solid-state battery prepared in Example 1, and b is the high-temperature cycle curve of the solid-state battery prepared in Comparative Example 1. Detailed implementation manners

[0045] For the convenience of understanding this application, the following will describe this application in more detail. However, it should be understood that this application can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure content of this application more thorough and comprehensive.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments or examples and are not intended to limit this application.

[0047] This application provides a cathode material, including a core and a coating layer coated on the surface of the core. The coating layer is a composite state of crystalline phase - amorphous phase, and the amorphous phase is distributed on the outer surface of the cathode material. The lattice parameter c / a of the cathode material is 4.935 - 4.950.

[0048] Among them, the chemical formula of the core is Li y Nix Co z Mn d A e D m O₂, where 1 ≤ y ≤ 1.03, 0.5 ≤ x ≤ 0.96, 0 ≤ z ≤ 0.4, 0 ≤ d ≤ 0.4, 0.01 ≤ e < 0.1, 0.01 ≤ m < 0.1, A is selected from at least one of Mg, Al, Ca, and B, D is selected from at least one of Ti, Ce, Ta, Mo, and Zr, and the surface layer of the core is a rich-X layer, where X is selected from at least one of P, S, Si, B, Al, Mg, Mo, Zr, and Nb.

[0049] In the coating layer, the material of the crystalline phase is a lithium salt polyanion compound, and the material of the amorphous phase is Li-M1-M2-O, where M1 is selected from at least one of P and S, and M2 is selected from at least one of Al, Mg, Mo, Zr, and Nb.

[0050] The positive electrode material has a unique core-shell structure and lattice parameters. On the one hand, the core contains low-valence doping element A and high-valence doping element D. Among them, the low-valence element A is easily doped into the core lattice structure, which is beneficial to stabilizing the lattice structure, inhibiting ion mixing, and thus improving the capacity and first Coulomb efficiency; the high-valence element B tends to be pinned on the grain boundary surface, which is beneficial to inhibiting the interfacial side reaction and enhancing the phase change reversibility; at the same time, the surface layer of the core is a rich-X layer, which is beneficial to improving the structural stability and inhibiting the high-temperature interfacial side reaction.

[0051] On the other hand, the surface of the core is a uniform and continuous coating layer. Through the synergistic effect of the crystalline phase and the amorphous phase in the coating layer, not only does the coating layer have the effect of a CEI-like film, but also P and S in the coating layer have good compatibility with the sulfide electrolyte, which can effectively inhibit the interfacial side reaction between the sulfide electrolyte and the positive electrode. Moreover, the polyanion and some non-oxygen elements in the coating layer can form strong covalent bonds with the oxygen atoms in the core lattice structure, which can inhibit the lattice structure collapse caused by deoxidation of the core. At the same time, the coating layer also has mechanical toughness, which can prevent particle cracking caused by drastic changes in the lattice constant during cycling, thus ensuring high-temperature cycle stability.

[0052] It can be understood that c / a is the ratio of lattice parameter c to lattice parameter a. Since the doping elements enter the layered structure of the core, the lattice parameter c / a of the positive electrode material increases. When the lattice parameter c / a is 4.935 - 4.950, the structural stability of the positive electrode material is excellent. As a preference, the lattice parameter c / a of the positive electrode material includes but is not limited to any one value of 4.935, 4.94, 4.945, 4.95 or the range value between any two of them, and is preferably 4.94 - 4.95.

[0053] In the chemical formula of the preferred core, 1 ≤ y ≤ 1.02, 0.8 ≤ x ≤ 0.95, 0.05 ≤ z ≤ 0.2, 0.01 ≤ d ≤ 0.2, 0.01 ≤ e < 0.05, 0.01 ≤ m < 0.05, A is selected from at least one of Mg, Al, and B, and D is selected from at least one of Ti, Ta, and Zr; X is selected from at least one of P, S, Si, Al, Mg, and Zr.

[0054] In one embodiment, the ratio of the thickness of the X-rich layer to the radius of the core is 0.05:1 - 0.5:1, preferably 0.1:1 - 0.3:1.

[0055] In one embodiment, in the amorphous phase, the molar ratio of Li to M1 and M2 is (0.5 - 1.5):(0.5 - 1):(0.05 - 0.1), preferably (1 - 1.5):(0.5 - 0.7):(0.05 - 0.08). By adjusting the element ratio in the amorphous phase, it is beneficial to optimize the element content of the coating layer, thereby suppressing interfacial side reactions.

[0056] In one embodiment, the lithium salt polyanion compound is selected from at least one of Li3PO4, Li2HPO4, LiH2PO4, Li2SO4, Li2SO3, Li2SiO3, and Li3BO3, preferably Li3PO4, Li2SO4, and Li2SiO3, which is beneficial to further improve the mechanical toughness of the coating layer, suppress the generation of cracks in the cathode material under high voltage, and at the same time, the strong covalent bonds formed by the polyanions can inhibit the lattice structure collapse caused by material deoxidation, thereby further ensuring the high-temperature cycle stability.

[0057] In one embodiment, the mass fraction of the non-oxygen element of the polyanion in the lithium salt polyanion compound is 0.2‰ - 2‰ of the core, preferably 0.5‰ - 1.5‰. By adjusting the mass of the non-oxygen element of the polyanion in the lithium salt polyanion compound, it is beneficial to optimize the coating layer thickness, thereby obtaining higher ionic conductivity.

[0058] In one embodiment, the crystal phase is an island structure, the island structure covers at least part of the surface of the core, and the average undulating thickness of the island structure is 1 nm - 20 nm, preferably 1 nm - 15 nm. By controlling the thickness of the crystal phase, it is beneficial to obtain higher ionic conductivity, thereby improving the battery capacity performance.

[0059] In one embodiment, the mass fraction of the amorphous phase is 0.1‰ - 5‰ of the core, preferably 1‰ - 4‰. By adjusting the mass of the amorphous phase, it is beneficial to optimize the coating layer thickness, thereby obtaining higher ionic conductivity.

[0060] In one embodiment, the amorphous phase is distributed on the outer surface of the cathode material. It can be understood that the crystalline phase is surrounded and coated between the amorphous phase and the inner core surface, and the crystalline phase is in direct contact with the inner core surface. The crystalline phase can be partially or completely covered by the amorphous phase. When the crystalline phase is partially covered by the amorphous phase, the thickness of part of the crystalline phase is greater than the thickness of the amorphous phase surrounding it; when the crystalline phase is completely covered by the amorphous phase, preferably the thickness of the crystalline phase in contact with the amorphous phase surface is less than the thickness of the crystalline phase in contact with the inner core surface, so that the total thickness of the amorphous phase and its surface crystalline phase is close to the thickness of the crystalline phase in contact with the inner core surface, thereby making the coating layer more uniform.

[0061] Preferably, the average thickness of the amorphous phase is 1 nm - 20 nm, preferably 1 nm - 15 nm. By controlling the thickness of the amorphous phase, it is beneficial to obtain higher ionic conductivity, thereby improving the battery capacity performance.

[0062] More preferably, the thickness ratio of the crystalline phase to the amorphous phase is 0.5:1 - 1.2:1, more preferably 0.8:1 - 1.1:1. By controlling the thickness ratio of the crystalline phase to the amorphous phase, it is beneficial to optimize the ionic conductivity and mechanical properties, thereby improving the interface stability.

[0063] In one embodiment, the average thickness of the coating layer is 1 nm - 20 nm, preferably 1 nm - 15 nm. By controlling the thickness of the coating layer to be ultra-thin nanoscale, it is beneficial to improve the ionic conductivity, thereby increasing the battery capacity.

[0064] In one embodiment, in the X-ray diffraction pattern of the cathode material, the intensity ratio of the diffraction peak of the (003) crystal plane to the diffraction peak of the (104) crystal plane is 1.70 - 2.40, preferably 1.90 - 2.40. Compared with the traditional cathode material, the intensity ratio of the diffraction peak of the (003) crystal plane to the diffraction peak of the (104) crystal plane increases. Therefore, the mixing degree of Li + and Ni 2+ is lower than that of the traditional cathode material, and the capacity and first Coulomb efficiency are improved.

[0065] The present application provides a preparation method of the cathode material as described above, including the following steps:

[0066] S1, preparing a hydroxide precursor containing doping element A and doping element D by coprecipitation reaction, mixing the hydroxide precursor with a first lithium source, and performing a first sintering in an oxygen-containing gas to obtain a first material. The chemical formula of the first material is Li y Ni x Co z Mn d A e D mO2, where 1 ≤ y ≤ 1.03, 0.5 ≤ x ≤ 0.96, 0 ≤ z ≤ 0.4, 0 ≤ d ≤ 0.4, 0.01 ≤ e < 0.1, 0.01 ≤ m < 0.1;

[0067] S2, Mix the first material with the polyanion compound and conduct a second sintering in an oxygen-containing gas to obtain a second material, where the temperature of the second sintering is greater than or equal to 550 °C;

[0068] S3, Mix a second lithium source with a salt containing M1 and an oxide containing M2, and conduct a third sintering in an oxygen-containing gas to obtain the amorphous material;

[0069] S4, Mix the second material with the amorphous material and conduct a fourth sintering in an oxygen-containing gas to obtain the cathode material, where the temperature of the fourth sintering is greater than or equal to 400 °C, and the temperature of the second sintering is greater than or equal to the temperature of the fourth sintering.

[0070] In step S1, the specific preparation process of the coprecipitation reaction is not limited in this application, and it can be prepared according to the conventional method. For example: Add the mixed salt solution and the precipitant to water and react in a protective gas to obtain a hydroxide precursor.

[0071] Preferably, the molar concentration of the mixed salt in the mixed salt solution is 1 mol / L - 3 mol / L, preferably 1 mol / L - 2 mol / L; the molar concentration of the precipitant in water is 5 mol / L - 10 mol / L, preferably 5 mol / L - 8 mol / L; the flow rate of the protective gas introduced is 2 L / min - 5 L / min, preferably 3 L / min - 5 L / min.

[0072] Specifically, the mixed salt includes a nickel salt, a cobalt salt, a manganese salt, a salt containing doping element A, and a salt containing doping element D. Among them, the nickel salt is preferably nickel sulfate hexahydrate; the cobalt salt is preferably cobalt sulfate heptahydrate; the manganese salt is preferably manganese sulfate monohydrate; A is selected from at least one of Mg, Al, Ca, and B. For example: When A is selected from Al, the salt containing doping element A is preferably aluminum sulfate octadecahydrate; D is selected from at least one of Ti, Ce, Ta, Mo, and Zr. For example: When D is selected from Zr, the salt containing doping element D is preferably zirconium sulfate tetrahydrate.

[0073] The precipitant includes but is not limited to sodium hydroxide, preferably sodium hydroxide; the protective gas includes but is not limited to at least one of nitrogen and argon, preferably nitrogen; the water is preferably deionized water.

[0074] The first lithium source includes but is not limited to at least one of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium sulfate, and lithium nitrate.

[0075] In one embodiment, the temperature of the first sintering is 800°C - 1000°C, preferably 800°C - 900°C; the time is 10h - 20h, preferably 12h - 18h.

[0076] In steps S2 to S4, by sequentially subjecting the first material to polyanion compound and amorphous phase sintering coating treatments and regulating the sintering temperature to satisfy a specific relationship, not only does the amorphous phase material form a molten state on the surface of the material, and a uniform and continuous crystal phase - amorphous phase composite coating layer is formed on the surface of the cathode material, achieving the effect of a CEI - like film with mechanical toughness, effectively suppressing the interfacial side reaction between the sulfide electrolyte and the cathode, and improving the structural stability, but also during the segmented sintering process, some elements in the coating layer diffuse into the inner core lattice structure and form strong covalent bonds with oxygen atoms in the lattice structure, thereby suppressing the collapse of the lattice structure caused by deoxidation of the inner core and ensuring that the inner core crystal structure is not damaged, improving the crystallinity of the material, and further ensuring the high - temperature cycle stability.

[0077] It should be noted that the preparation sequence of steps S2 and S3 in this application is not limited. Step S2 can be carried out first, followed by step S3; step S3 can be carried out first, followed by step S2; or steps S2 and S3 can be carried out simultaneously.

[0078] In one embodiment, before mixing the first material with the polyanion compound for the second sintering, the first material is first crushed, which is beneficial for the polyanion compound to be uniformly coated on the surface of the first material.

[0079] Specifically, the temperature of the second sintering is 550°C - 800°C, preferably 650°C - 800°C; the time is 5h - 10h, preferably 8h - 10h.

[0080] The temperature of the third sintering is 900°C - 1200°C, preferably 1000°C - 1200°C; the time is 4h - 10h, preferably 8h - 10h.

[0081] The temperature of the fourth sintering is 400°C - 700°C, preferably 550°C - 700°C; the time is 5h - 10h, preferably 8h - 10h.

[0082] In one embodiment, the mass ratio of the polyanion compound to the first material is 1‰ - 7‰. Among them, the polyanion compound is selected from at least one of lithium salt - type polyanion compounds, ammonium dihydrogen phosphate, and silicic acid, and the lithium salt - type polyanion compound is selected from at least one of Li3PO4, Li2HPO4, LiH2PO4, Li2SO4, Li2SO3, Li2SiO3, and Li3BO3.

[0083] It should be noted that when the polyanion compound is selected from ammonium dihydrogen phosphate and silicic acid, under the condition of the second sintering temperature, a lithium salt polyanion compound coating layer is formed on the surface of the first material through the residual alkali reaction.

[0084] In one embodiment, the molar ratio of Li in the second lithium source to M1 in the M1-containing salt and M2 in the M2-containing oxide is (0.5 - 1.5):(0.5 - 1):(0.05 - 0.1), where the second lithium source includes but is not limited to at least one of lithium carbonate, lithium hydroxide, lithium chloride, lithium fluoride, lithium sulfate, and lithium nitrate; M1 is selected from at least one of P and S, and the M1-containing salt is preferably a polyanion compound containing M1, including but not limited to NH4H2PO4 and Li2SO4. For example, when M1 is selected from P, the M1-containing salt is preferably NH4H2PO4; M2 is selected from at least one of Al, Mg, Mo, Zr, and Nb. For example, when M2 is selected from Al, the M2-containing oxide is preferably alumina.

[0085] It can be understood that the first lithium source and the second lithium source can be the same or different, and the present application does not limit this.

[0086] In one embodiment, the mass ratio of the amorphous material to the second material is 0.1‰ - 5‰, which is beneficial to uniformly coating the amorphous material on the surface of the material under the sintering condition higher than the melting temperature of the amorphous material to form a continuous and uniform coating layer.

[0087] The present application provides a positive electrode sheet and a sulfide solid-state battery. It can be understood that the positive electrode sheet includes a current collector and a positive electrode active layer provided on the current collector, and the positive electrode active layer includes the positive electrode material as described above. Among them, the current collector includes but is not limited to a lithium foil.

[0088] It should be noted that the present application does not limit the specific components of the positive electrode active layer, the preparation method of the positive electrode sheet, and the type of the negative electrode sheet in the solid-state battery. The positive electrode active layer also includes a conductive agent and a binder; the positive electrode sheet can be prepared by a dry method or a wet method; the material of the negative electrode sheet in the solid-state battery includes but is not limited to metallic lithium, an alloy, graphite, or silicon.

[0089] Therefore, using the positive electrode material described in the present application in a sulfide solid-state battery can significantly improve the capacity, initial Coulomb efficiency, and high-temperature cycle stability of the sulfide solid-state battery.

[0090] It can be understood that the electrical devices using the above sulfide solid-state battery include but are not limited to electric vehicles, electric tools, electronic products, energy storage systems, and office equipment, etc., and the present application does not limit this.

[0091] Hereinafter, the positive electrode material, its preparation method and application will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only for illustrating the present application and should not be regarded as limiting the scope of the present application. For those conditions not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0092] Example 1

[0093] Dissolve nickel sulfate hexahydrate, cobalt sulfate heptahydrate, manganese sulfate monohydrate, zirconium sulfate tetrahydrate, and aluminum sulfate octadecahydrate in deionized water to prepare a mixed salt solution, where the molar ratio of nickel, cobalt, manganese, zirconium, and aluminum is 0.80:0.12:0.05:0.02:0.01, and the molar concentration of the mixed salt in the mixed salt solution is 2 mol / L. Then, add it to a reaction kettle containing deionized water through a peristaltic pump. At the same time, add sodium hydroxide to mix with the deionized water in the reaction kettle to form a sodium hydroxide solution with a concentration of 8 mol / L. Introduce nitrogen with a flow rate of 3 L / min as a protective gas, and stir at 50 °C for a co-precipitation reaction. Wash, filter by suction, and dry the reaction product to obtain a hydroxide precursor.

[0094] Uniformly mix 1 kg of the hydroxide precursor and 461 g of lithium hydroxide monohydrate in a mixer for 30 min, then transfer the mixture to a box furnace, introduce oxygen, and sinter at 850 °C for 12 h. After discharging, crush it to obtain the first material.

[0095] Mix NH4H2PO4, Al2O3, and Li2CO3 evenly and then transfer them to a box furnace. Introduce air and sinter at 1000 °C for 6 h to obtain an amorphous material Li-P-Al-O, where the molar ratio of Li:P:Al is 0.75:0.5:0.05.

[0096] Mix 800 g of the first material and 2.376 g of NH4H2PO4 in a high-speed mixer for 30 min, then transfer them to a box furnace, introduce oxygen, and sinter at 700 °C for 8 h to obtain the second material. The mass fraction of P in the second material relative to the first material is 0.8‰.

[0097] Mix 500 g of the second material and 1 g of the amorphous material evenly and then transfer them to a box furnace. Introduce oxygen and sinter at 550 °C for 8 h to obtain the positive electrode material. The mass fraction of the amorphous phase substance in the positive electrode material relative to the first material is 2‰.

[0098] Example 2

[0099] Dissolve nickel sulfate hexahydrate, cobalt sulfate heptahydrate, manganese sulfate monohydrate, aluminum sulfate octadecahydrate, and titanium sulfate in deionized water to prepare a mixed salt solution, where the molar ratio of nickel, cobalt, manganese, aluminum, and titanium is 0.81:0.12:0.05:0.01:0.01. Make the molar concentration of the mixed salt in the mixed salt solution 3 mol / L, and add it to a reaction kettle containing deionized water through a peristaltic pump. At the same time, add sodium hydroxide to mix with the deionized water in the reaction kettle to form a sodium hydroxide solution with a concentration of 6 mol / L. Introduce nitrogen with a flow rate of 5 L / min as a protective gas, and stir at 45 °C for a coprecipitation reaction. Wash, filter by suction, and dry the reaction product to obtain a hydroxide precursor.

[0100] Uniformly mix 1 kg of the hydroxide precursor and 410 g of lithium carbonate in a mixer for 30 min, then transfer the mixture to a box furnace, introduce oxygen, sinter at 800 °C for 12 h, and crush after discharging to obtain the first material.

[0101] Mix NH4H2PO4, ZrO2, and Li2CO3 evenly and then transfer them to a box furnace, introduce air, sinter at 1100 °C for 8 h to obtain an amorphous material Li-P-Zr-O, where the molar ratio of Li:P:Zr is 1:0.5:0.05.

[0102] Mix 800 g of the first material and 3.34 g of silicic acid in a high-speed mixer for 30 min, then transfer them to a box furnace, introduce oxygen, sinter at 700 °C for 8 h to obtain the second material. The mass fraction of Si in the second material relative to the first material is 1.5‰.

[0103] Mix 500 g of the second material and 1.5 g of the amorphous material evenly, then transfer them to a box furnace, introduce oxygen, sinter at 600 °C for 10 h to obtain a cathode material. The mass fraction of the amorphous substance in the cathode material relative to the first material is 3‰.

[0104] Example 3

[0105] Dissolve nickel sulfate hexahydrate, cobalt sulfate heptahydrate, manganese sulfate monohydrate, magnesium sulfate, and titanium sulfate in deionized water to prepare a mixed salt solution, where the molar ratio of nickel, cobalt, manganese, magnesium, and titanium is 0.90:0.06:0.02:0.01:0.01. Make the molar concentration of the mixed salt in the mixed salt solution 1 mol / L, and add it to a reaction kettle containing deionized water through a peristaltic pump. At the same time, add sodium hydroxide to mix with the deionized water in the reaction kettle to form a sodium hydroxide solution with a concentration of 5 mol / L. Introduce nitrogen with a flow rate of 3 L / min as a protective gas, and stir at 55 °C for a coprecipitation reaction. Wash, filter by suction, and dry the reaction product to obtain a hydroxide precursor.

[0106] Mix 1 kg of hydroxide precursor and 743 g of lithium chloride evenly in a mixer for 30 min, then transfer the mixture to a box furnace, introduce oxygen, sinter at 870 °C for 10 h, and crush the product after discharging to obtain the first material.

[0107] Mix Li2SO4 and MgO evenly and then transfer them to a box furnace, introduce air, sinter at 1000 °C for 10 h to obtain the amorphous material Li-S-Mg-O, where the molar ratio of Li:S:Mg is 1:0.5:0.08.

[0108] Mix 800 g of the first material and 5.48 g of Li2SO4 in a high-speed mixer for 30 min, then transfer the mixture to a box furnace, introduce oxygen, sinter at 750 °C for 10 h to obtain the second material, and the mass fraction of S in the second material relative to the first material is 2‰.

[0109] Mix 500 g of the second material and 2 g of the amorphous material evenly and then transfer the mixture to a box furnace, introduce oxygen, sinter at 650 °C for 10 h to obtain the cathode material, and the mass fraction of the amorphous substance in the cathode material relative to the first material is 4‰.

[0110] Example 4

[0111] The difference between Example 4 and Example 1 is that the molar ratio of nickel, cobalt, manganese, zirconium, and aluminum in the mixed salt solution is 0.81:0.12:0.05:0.01:0.01.

[0112] Example 5

[0113] The difference between Example 5 and Example 1 is that 800 g of the first material is mixed and sintered with 4.46 g of NH4H2PO4 to make the mass fraction of P in the second material relative to the first material 1.5‰.

[0114] Example 6

[0115] The difference between Example 6 and Example 1 is that 500 g of the second material is mixed and sintered with 2.5 g of the amorphous material to make the mass fraction of the amorphous substance in the cathode material relative to the first material 5‰.

[0116] Comparative Example 1

[0117] The difference between Comparative Example 1 and Example 1 is that the amorphous material was not prepared for secondary coating, and the second material was directly used as the cathode material.

[0118] Comparative Example 2

[0119] The difference between Comparative Example 2 and Example 1 is that nickel sulfate hexahydrate, cobalt sulfate heptahydrate, manganese sulfate monohydrate, and aluminum sulfate octadecahydrate are dissolved in deionized water to prepare a mixed salt solution, and the molar ratio of nickel, cobalt, manganese, and aluminum is 0.82:0.12:0.05:0.01.

[0120] Comparative Example 3

[0121] The difference between Comparative Example 3 and Example 1 is that nickel sulfate hexahydrate, cobalt sulfate heptahydrate, manganese sulfate monohydrate, and zirconium sulfate tetrahydrate are dissolved in deionized water to prepare a mixed salt solution, and the molar ratio of nickel, cobalt, manganese, and zirconium is 0.81:0.12:0.05:0.02.

[0122] Comparative Example 4

[0123] The difference between Comparative Example 4 and Example 1 is that Al2O3 and Li2CO3 are mixed evenly and then transferred to a box furnace, air is introduced, and sintering is carried out at 1000 °C for 6 h to obtain an amorphous material Li-Al-O, where the molar ratio of Li:Al is 0.75:0.05.

[0124] Comparative Example 5

[0125] The difference between Comparative Example 5 and Example 1 is that NH4H2PO4 and Li2CO3 are mixed evenly and then transferred to a box furnace, air is introduced, and sintering is carried out at 1000 °C for 6 h to obtain an amorphous material Li-P-O, where the molar ratio of Li:P is 0.75:0.5.

[0126] Comparative Example 6

[0127] The difference between Comparative Example 6 and Example 1 is that the second sintering temperature is 400 °C and the time is 6 h, and the fourth sintering temperature is 300 °C and the time is 6 h.

[0128] Comparative Example 7

[0129] The difference between Comparative Example 7 and Example 1 is that the fourth sintering temperature is 750 °C.

[0130] The positive electrode materials prepared in Example 1 and Comparative Example 1 were subjected to SEM tests, and the results are shown in Figure 1 (a) and Figure 1 (b). It can be seen that the surface of the positive electrode after coating is smoother, indicating that the coating layer is thinner and more uniform.

[0131] The positive electrode material prepared in Example 1 was subjected to an EDS test, and the results are shown in Figure 2 As shown. It can be seen that the mapping of the P element almost overlaps with the shape of the positive electrode material particles, indicating the uniformity of the coating layer on the surface of the positive electrode material.

[0132] The surface of the positive electrode material prepared in Example 1 was subjected to a TEM test, and the results are asFigure 3 As shown, a coating layer with a thickness of about 5 nm - 10 nm can be clearly observed on the particle surface, and the surface is smooth, proving that the coating layer uniformly and completely coats the surface of the cathode material in the form of a film.

[0133] XRD tests were carried out on the cathode materials prepared in Example 1 and Comparative Example 1, and the results are as Figure 4 shown. It can be seen that there are no new diffraction peaks in the cathode material prepared in Example 1, indicating that the layered structure of the cathode material remains intact, and due to the small amount of coating, the coating layer does not affect the crystal structure of the cathode material.

[0134] The cathode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were subjected to characterization tests, and the results are shown in Table 1 and Table 2. Among them, the chemical formula was obtained based on ICP tests; the intensity ratio of the (003) crystal plane to the (104) crystal plane was obtained based on XRD tests; the cross-section of the cathode material prepared in Example 1 is as Figure 5 shown. Points were taken from the center to the outside of the cross-section in turn for EDS tests to obtain the elemental composition, and then the ratio of the thickness of the X-rich layer to the radius of the core can be calculated. The calculation results are shown in Table 1.

[0135] Table 1

[0136]

[0137] Table 2

[0138]

[0139]

[0140] According to Table 2, it can be seen that the I(003) / I(104) of the examples is larger than that of the comparative examples, indicating that the cation mixing is smaller.

[0141] The cathode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were made into cathode sheets and assembled into solid-state batteries for performance testing. The specific preparation methods and testing methods are as follows:

[0142] The cathode material, sulfide electrolyte Li6PS5Cl, and conductive agent VGCF were mixed evenly at a mass ratio of 85:15:1. The mixing method was ball milling, with a ball milling speed of 250 r / min, a ball milling time of 4 h, and a ball-to-material ratio of 4:1. After mixing evenly, a binder PTFE was added and ground into a sheet, and then kneaded and thinned on a hot roll press to obtain a cathode sheet. The mass of the binder was 1% of the mass of the mixed material. Graphite was used as the anode sheet. 150 mg of sulfide electrolyte Li6PS5Cl was weighed and evenly spread in the mold battery sleeve, and an electrolyte sheet was made at 200 MPa. Then, the cathode sheet and the anode sheet were placed on both sides of the electrolyte sheet, and the cathode, anode, and electrolyte sheet were laminated at 400 MPa to make a sulfide all-solid-state battery.

[0143] The sulfide all-solid-state batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were subjected to floating charge tests. The conditions of the floating charge test were to charge and discharge once at 0.1C within the voltage range of 2.5V - 4.25V, charge to 4.25V at 0.1C and then perform constant voltage charging for 10 h before discharging. The capacities in the constant voltage stage were statistically analyzed at different numbers of charge and discharge cycles, and the results are shown in Table 3.

[0144] Table 3

[0145]

[0146]

[0147] As can be seen from Table 3, the irreversible capacities of the sulfide all-solid-state batteries prepared in Examples 1 to 6 all decreased, indicating that the interfacial side reactions were effectively inhibited.

[0148] The sulfide all-solid-state batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were operated at a test pressure of about 100 MPa. The test conditions were at a high temperature of 60°C, and 0.1C, 0.2C, 0.5C, 1C, 2C, and 3C were respectively tested for two cycles and then restored to 0.5C for the test cycle. The voltage window was 2.5V - 4.25V; the test method for the potential difference was CV. The test results are shown in Table 4. Among them, the comparison charts of the test data of Example 1 and Comparative Example 1 are respectively as Figure 6 , Figure 7 , Figure 8 shown.

[0149] Table 4

[0150]

[0151] According to Figures 6 to 8As can be seen from Table 4, compared with Comparative Examples 1 to 7, the redox potential difference of the sulfide all-solid-state batteries prepared in Examples 1 to 6 is smaller, indicating that the interfacial side reactions are effectively inhibited, resulting in higher reversibility of the electrochemical reaction; the Coulombic efficiency of the first cycle is improved, and the charge and discharge capacity is increased, further indicating that the coating layer structure provided in this application effectively inhibits the interfacial side reactions; when cycled 100 times at a high temperature of 60 °C, the capacity can be maintained at about 85% at most, significantly improving the high-temperature cycle stability.

[0152] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0153] The above-described embodiments merely represent several implementation manners of this application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several modifications and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of the patent of this application should be subject to the appended claims.

Claims

1. A cathode material for a solid-state battery, characterized in that, The positive electrode material includes a core and a coating layer coated on the surface of the core. The coating layer is in a composite state of crystalline phase - amorphous phase, and the amorphous phase is distributed on the outer surface of the positive electrode material. The lattice parameter c / a of the positive electrode material is 4.935 - 4.950; The chemical formula of the core is Li y Ni x Co z Mn d A e D m O2, where 1 ≤ y ≤ 1.03, 0.5 ≤ x ≤ 0.96, 0 ≤ z ≤ 0.4, 0 ≤ d ≤ 0.4, 0.01 ≤ e < 0.1, 0.01 ≤ m < 0.1, A is selected from at least one of Mg, Al, Ca, and B, D is selected from at least one of Ti, Ce, Ta, Mo, and Zr, and the surface layer of the core is a rich X layer, and X is selected from at least one of P, S, Si, B, Al, Mg, Mo, Zr, and Nb; In the coating layer, the material of the crystalline phase is a lithium salt polyanion compound, and the material of the amorphous phase is Li-M1-M2-O, where M1 is selected from at least one of P and S, and M2 is selected from at least one of Al, Mg, Mo, Zr, and Nb. The molar ratio of Li to M1 and M2 is (0.5 - 1.5):(0.5 - 1):(0.05 - 0.1).

2. The cathode material according to claim 1, characterized in that, In the amorphous phase, the molar ratio of Li to M1 and M2 is (1 - 1.5):(0.5 - 0.7):(0.05 - 0.08).

3. The cathode material according to claim 1, characterized in that, The lithium salt polyanion compound is selected from at least one of Li3PO4, Li2HPO4, LiH2PO4, Li2SO4, Li2SO3, Li2SiO3, and Li3BO3.

4. The cathode material according to any one of claims 1 to 3, characterized in that, The mass of the amorphous phase is 0.1‰ - 5‰ of the core; and / or, the mass of the non-oxygen element of the polyanion in the lithium salt polyanion compound is 0.2‰ - 2‰ of the core.

5. The cathode material according to any one of claims 1 to 3, characterized in that, The crystalline phase is in an island structure, the island structure coats at least part of the surface of the core, and the average undulating thickness of the island structure is 1 nm - 20 nm; and / or, the amorphous phase is distributed on the outer surface of the positive electrode material, and the average thickness of the amorphous phase is 1 nm - 20 nm; and / or, the thickness ratio of the crystalline phase to the amorphous phase is 0.5:1 - 1.2:1; and / or, the average thickness of the coating layer is 1 nm - 20 nm; and / or, the ratio of the thickness of the X-rich layer to the radius of the core is 0.05:1 - 0.5:

1.

6. The cathode material according to claim 1, characterized in that, In the X-ray diffraction pattern of the positive electrode material, the intensity ratio of the diffraction peak of the (003) crystal plane to the diffraction peak of the (104) crystal plane is 1.70 - 2.

40.

7. A method for preparing a cathode material according to any one of claims 1 to 6, characterized in that, It includes the following steps: A hydroxide precursor containing dopant element A and dopant element D is prepared by a coprecipitation reaction. The hydroxide precursor is mixed with a first lithium source and subjected to a first sintering in an oxygen-containing gas to obtain a first material, and the chemical formula of the first material is Li y Ni x Co z Mn d A e D m O2, where 1 ≤ y ≤ 1.03, 0.5 ≤ x ≤ 0.96, 0 ≤ z ≤ 0.4, 0 ≤ d ≤ 0.4, 0.01 ≤ e < 0.1, 0.01 ≤ m < 0.1; Mix the first material with the polyanion compound and perform a second sintering in an oxygen-containing gas to obtain a second material, where the temperature of the second sintering is greater than or equal to 550°C; Mix the second lithium source with the salt containing M1 and the oxide containing M2, and perform a third sintering in an oxygen-containing gas to obtain the material of the amorphous phase; Mix the second material with the material of the amorphous phase and perform a fourth sintering in an oxygen-containing gas to obtain the positive electrode material, where the temperature of the fourth sintering is greater than or equal to 400°C, and the temperature of the second sintering is greater than or equal to the temperature of the fourth sintering.

8. The method for preparing the cathode material according to claim 7, wherein, The coprecipitation reaction includes adding a mixed salt solution and a precipitant to water and reacting in a protective gas to obtain a hydroxide precursor, where the molar concentration of the mixed salt in the mixed salt solution is 1 mol / L - 3 mol / L, the molar concentration of the precipitant in water is 5 mol / L - 10 mol / L, and the flow rate of the protective gas introduced is 2 L / min - 5 L / min.

9. The preparation method of the cathode material according to claim 7, wherein The polyanion compound is selected from at least one of lithium salt polyanion compounds, ammonium dihydrogen phosphate, and silicic acid; and / or, the mass of the polyanion compound is 1‰ - 7‰ of the first material; and / or, the mass of the amorphous material is 0.1‰ - 5‰ of the second material; and / or, the molar ratio of Li in the second lithium source to M1 in the M1-containing salt and M2 in the M2-containing oxide is (0.5 - 1.5):(0.5 - 1):(0.05 - 0.1).

10. The preparation method of the cathode material according to claim 7, wherein, The temperature of the first sintering is 800°C - 1000°C, and the time is 10h - 20h; and / or, the temperature of the second sintering is 550°C - 800°C, and the time is 5h - 10h; and / or, the temperature of the third sintering is 900°C - 1200°C, and the time is 4h - 10h; and / or, the temperature of the fourth sintering is 400°C - 700°C, and the time is 5h - 10h.

11. A positive electrode sheet, characterized in that, It includes the positive electrode material according to any one of claims 1 to 6.

12. A sulfide solid-state battery, characterized in that, It includes the positive electrode sheet according to claim 11.

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