Lithium-containing transition metal oxide coated and doped positive electrode material and preparation method thereof

Abstract

The present invention provides a positive electrode material coated and doped with lithium-containing transition metal oxide and a preparation method thereof, belonging to the technical field of all-solid-state lithium batteries. The positive electrode material comprises a core positive electrode active material and an outer shell lithium-containing transition metal oxide coating layer, and at the same time, the transition metal is doped into the matrix of the positive electrode active material during the preparation process. When preparing the positive electrode material, the positive electrode active material and the coating layer material are first selectively matched according to their respective synthesis temperature ranges, and then the ratio of the lithium source and the transition metal oxide during the sintering process is regulated to obtain in situ a coated and doped positive electrode material with controllable composition and thickness and high coverage. The above-mentioned coating layer promotes the transmission of lithium ions at the interface between the positive electrode material and the solid electrolyte in the all-solid-state battery, effectively suppresses interfacial side reactions, and reduces interfacial resistance. At the same time, transition metal doping reduces the degree of lithium-nickel mixing of the positive electrode active material and improves its structural stability.

Description

Technical Field

[0001] The present invention relates to the technical field of all-solid-state lithium batteries, and in particular to a lithium-containing transition metal oxide-coated and doped positive electrode material and a preparation method thereof. Background Art

[0002] With the advancement of the times and the increasing demand, the development of all-solid-state lithium batteries has attracted great interest. All-solid-state lithium batteries primarily use non-flammable solid electrolytes and offer superior safety and higher energy density compared to traditional liquid lithium-ion batteries. The development of all-solid-state lithium batteries will be a key direction for the future development of electronic products and new energy vehicles.

[0003] In all-solid-state lithium batteries, improving the interfacial stability between the positive electrode active material and the solid electrolyte and the structural stability of the positive electrode active material are the key to developing high-performance all-solid-state lithium batteries. To this end, researchers have conducted a large number of modification explorations, such as lattice doping, surface coating, and core-shell structure construction. Among them, coating modification of the positive electrode active material has the best effect. Common coating materials include Al2O3, SiO2, Li4Ti5O 12 , LiNbO3, etc. Lithium-free coating materials usually have low lithium ion conductivity, which is not conducive to the transmission of lithium ions at the interface; lithium-containing coating materials have high lithium ion conductivity, but their preparation process is relatively cumbersome, and the raw materials required are mostly expensive organic metal alkoxides, which are difficult to mass-produce and apply.

[0004] The lithium-ion conductivity of the lithium-containing oxide solid electrolyte (e.g., Li 0.5 La 0.5 TiO3、Li7La3Zr2O 12 , LiTi2(PO4)3, etc.) as coating layers have many advantages. They have a wide electrochemical window, good compatibility with positive electrode active materials and solid electrolytes, and a relatively stable material structure. However, the usual coating methods for this type of material are liquid-phase sol-gel method or atomic layer deposition method. The thickness and uniformity of the coating layers prepared by these methods are difficult to control, the coating layer coverage is not high, and sometimes even expensive production equipment is required to achieve it. At the same time, excessively thick coating materials will also affect the improvement of battery performance, and modification of a single coating layer is not enough to improve the overall performance of all-solid-state lithium batteries. Constructing a synergistic modification of doping and coating is an effective strategy.

[0005] In view of this, there is an urgent need to develop a new type of high lithium ion conductivity transition metal oxide coating and a synergistic strategy of corresponding element doping to comprehensively solve the above problems. The high lithium ion conductivity lithium transition metal oxide coating can not only improve the transmission of lithium ions at the positive electrode interface, but also inhibit the oxidative decomposition of the solid electrolyte, thereby reducing the positive electrode interface impedance and solving the interface problem in all-solid-state lithium-ion batteries. Synergistically, transition metal element doping can expand the interlayer spacing of the positive electrode active material, reduce the degree of cation mixing, and further improve the structural stability of the positive electrode active material, which is beneficial to the long cycle performance of all-solid-state lithium batteries. At the same time, it is also necessary to develop a preparation process with a simple coating doping process, uniform coating layer thickness and high coverage, and easy large-scale production. At the same time, this process does not require expensive raw materials and equipment. These research findings will further promote the industrialization process of all-solid-state lithium batteries. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a positive electrode material coated and doped with lithium-containing transition metal oxide and a preparation method thereof, so as to solve the interface compatibility problem between the positive electrode material and the solid electrolyte of the all-solid-state lithium battery in the prior art, and at the same time make up for the limitations of single coating, and construct a synergistic strategy of coating and doping to improve the comprehensive performance of the all-solid-state lithium battery. In terms of preparation process, the present invention avoids the commonly used organic metal alkoxides and adopts cheap transition metal oxides as raw materials. At the same time, it avoids expensive equipment and cumbersome processes and adopts a simple in-situ one-step sintering preparation. The coating layer has a high lithium ion conductivity, increases the ability of lithium ion transmission at the interface between the positive electrode material and the solid electrolyte, avoids the oxidative decomposition of the solid electrolyte, inhibits the occurrence of interface side reactions, and thus reduces the interface impedance and electrode polarization. The doping of transition metals expands the interlayer spacing of the positive electrode active material matrix, reduces the degree of lithium nickel mixing, and thus enhances the structural stability of the positive electrode active material during long-term cycling. Using cheap raw materials and simple preparation methods, a positive electrode material with synergistic modification by coating and doping can be obtained at the same time. The coating layer has uniform thickness and high coverage. The positive electrode material is assembled into an all-solid-state lithium battery, which shows excellent performance and has good prospects for industrial production application.

[0007] Specifically, the positive electrode material comprises a core positive electrode active material and an outer shell lithium-containing transition metal oxide coating. The transition metal is doped into the matrix of the positive electrode active material during the preparation process. During preparation, the positive electrode active material and coating layer are selectively matched within their respective synthesis temperature ranges. By regulating the ratio of lithium source to transition metal oxide during sintering, a highly coated, doped positive electrode material with controllable composition and thickness is obtained in situ.

[0008] The coating layer is at least one of a lithium transition metal oxide Li-TM-O, a mixture of Li-TM-O and Li2O, and a mixture of Li-TM-O and Li2CO3 (whether Li2O or Li2CO3 is contained depends on the type and content of the lithium salt added during the synthesis process).

[0009] wherein TM is at least one of Sc, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, Mo, La, Ce, Yb, Hf, Ta, and W;

[0010] Doping is doping of corresponding transition metal elements in the coating layer;

[0011] The positive electrode active material is LiCoO2, LiNiO2, LiCo p Ni 1-p O2, LiMnO2, x Li2MnO3·(1-x)LiMO2, Li a Ni x Co y M 1-x-y O2, LiMn2O4, LiNi 0.5 Mn 1.5 At least one of O4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, LiFePO4, Li2CuO2, Li5FeO4, TiO2, Cr3O8, V2O5, TiS2, V2S3, FeS, FeS2, and MnO2;

[0012] LiCo p N i1-p In O2, 0≤p≤1,

[0013] In x Li2MnO3·(1-x)LiMO2, M is one of Ni, Co, and Mn.

[0014] Li a Ni x Co y M 1-x-y In O2, M is at least one element selected from Mn, Al, Mg, Fe, Hf, Zr, W, Nb, Sm, Ge, La, Ga, Cr, Cu, Zn, and Mo, wherein 0≤x≤1, 0≤y≤1, and 0.95 <a<1.03。

[0015] As mentioned above, the thickness of the coating layer is 2 to 50 nm; the diffusion depth of the doping element is 1 to 100 nm; the positive electrode active material is a single crystal or polycrystalline with a particle size of 2 to 20 μm; the coverage of the coating layer is above 80%; when the coating layer is a mixture of Li-TM-O and Li2O or Li-TM-O and Li2CO3, the content of Li2O or Li2CO3 accounts for 1% to 20% of the mass of Li-TM-O, preferably 2% to 15%.

[0016] The preparation method of the positive electrode material comprises the following steps:

[0017] S1: Selectively matching the positive electrode active material and the coating layer material according to their respective synthesis temperature ranges;

[0018] S2: adding a certain proportion of selected transition metal oxide source, lithium source and cathode active material precursor into a mixer and mixing them, and at the same time, adding a certain proportion of ethanol solvent to stir them evenly to prepare a mixture 1;

[0019] S3: placing the uniform mixture 1 slurry into an oven and drying it at 60-150° C. for 6-12 hours to prepare a dry mixture 2;

[0020] S4: sintering the dried mixture 2. In this process, the lithium source not only participates in the synthesis of the positive electrode active material, but also reacts with the transition metal oxide to in-situ synthesize a lithium-containing transition metal oxide coating layer on the surface of the positive electrode active material. After sintering, a sintered body 3 is obtained.

[0021] S5: annealing the sintered body 3 obtained in S4, so that the transition metal in the transition metal oxide diffuses into the matrix of the positive electrode active material, thereby obtaining the coated and doped positive electrode material.

[0022] As mentioned above, some of the lithium transition metal oxide coating materials in S1 need to be synthesized at high temperatures, so they need to be matched with positive electrode active materials that can be prepared by high temperature sintering, such as LiMn2O4, LiNi 0.5 Mn 1.5 O4, x Li2MnO3·(1-x)LiMO2 (M=Ni, Co, Mn) and some single crystal positive electrode active materials. Therefore, the synthesis temperature of the positive electrode active material and the synthesis temperature range of the coating layer material differ by 0 to 100°C, preferably by 0 to 50°C; for positive electrode materials and coating layer materials with a large difference in synthesis temperature range, the temperature can be adjusted by adding a sintering aid.

[0023] The transition metal oxide source in S2 includes at least one of scandium oxide, titanium oxide, vanadium oxide (including at least one of vanadium monoxide, vanadium dioxide, vanadium trioxide, and vanadium pentoxide), chromium oxide, copper oxide, zinc oxide, yttrium oxide, zirconium oxide, niobium oxide (including at least one of niobium monoxide, niobium dioxide, niobium trioxide, and niobium pentoxide), molybdenum oxide, lanthanum oxide, cerium oxide, ytterbium oxide, hafnium oxide, tantalum oxide (tantalum pentoxide), and tungsten oxide; the lithium source includes at least one of lithium carbonate, lithium oxide, lithium hydroxide, lithium nitrate, and lithium oxalate;

[0024] The mass ratio of the transition metal oxide source to the positive electrode active material precursor is 0.001 to 0.5:1, that is, the mass of the transition metal oxide is 0.1 to 50% of the mass of the positive electrode active material precursor, preferably 0.5 to 40%; the mass ratio of the lithium source to the positive electrode active material precursor is 1.05 to 1.9:1, that is, the mass excess percentage of the lithium source is 5 to 90%, preferably 6 to 70%.

[0025] The amount of ethanol solvent added in S2 is 4 to 8 L of anhydrous ethanol per kilogram of positive electrode material, preferably 4 to 6 L.

[0026] The sintering temperature of the mixture 2 in S4 is 700-1200° C., the heating rate is 1-10° C. / min, the sintering time is 8-18 hours, and the sintering atmosphere is oxygen, air or carbon dioxide.

[0027] The annealing rate of the sintered body 3 in S5 is 5 to 10° C. / min.

[0028] The positive electrode material is used as a positive electrode for all-solid-state lithium batteries, especially in the positive electrode material for all-solid-state lithium-ion batteries with sulfide solid electrolytes;

[0029] The solid electrolyte used in the all-solid-state lithium-ion battery is a sulfide solid electrolyte, specifically Li7P3S 11 、β-Li3PS4、Li6PS5Cl、Li 10 GeP2S 12 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , Li4SnS4 and any one of their doped and modified materials; the negative electrode material used in combination is any one of lithium metal, indium metal, lithium metal alloy, graphite, lithium titanate, silicon and silicon oxygen negative electrode and any one of their composite negative electrodes with carbon.

[0030] The beneficial effects of the above technical solution of the present invention are as follows:

[0031] 1. During the material preparation process, by controlling the addition amounts of lithium salt and transition metal oxide, a lithium-containing transition metal oxide coating layer with controllable thickness, uniformity, high coverage, and high lithium ion conductivity can be generated in situ on the surface of the positive electrode material while synthesizing the positive electrode material. Simultaneously, after high-temperature sintering and annealing, the transition metal elements in the coating diffuse into the matrix of the positive electrode active material, achieving the effect of element doping. This preparation method, which uses inexpensive raw materials and a simple one-step in-situ sintering process, can produce a positive electrode material with synergistic modification by coating and doping.

[0032] 2. The raw materials used in the present invention avoid commonly used organic metal alkoxides and adopt cheap transition metal oxides, while also avoiding the use of expensive equipment and cumbersome processes, which will be conducive to large-scale industrial production applications.

[0033] 3. The coating layer containing lithium transition metal oxide provided by the present invention has high lithium ion conductivity, increases the ability of lithium ion transmission at the interface between the positive electrode material and the solid electrolyte, avoids the oxidative decomposition of the solid electrolyte, suppresses the occurrence of interfacial side reactions, and thus reduces the interface impedance and electrode polarization. The doping of transition metals expands the interlayer spacing of the positive electrode active material matrix, reduces the degree of lithium nickel mixing, and thus enhances the structural stability of the positive electrode active material during long-term cycling. The positive electrode material is assembled into an all-solid-state lithium battery, which exhibits low interfacial impedance, high charge and discharge specific capacity, good rate performance, ultra-long high-voltage cycle stability and high capacity retention.

[0034] In summary, the present invention can improve the shortcomings of existing all-solid-state lithium-ion battery positive electrode materials, improve the solid-solid interface problems and poor positive electrode structure stability that restrict their development, so that the positive electrode materials can be better applied to all-solid-state lithium batteries. At the same time, it also has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the structure of the positive electrode material coated and doped with lithium-containing transition metal oxide of the present invention;

[0036] Figure 2 Schematic diagram of the preparation process of the lithium-containing transition metal oxide-coated and doped positive electrode material of the present invention;

[0037] Figure 3 This is a flow chart of the preparation process of the lithium-containing transition metal oxide-coated and doped positive electrode material of the present invention;

[0038] Figure 4 XRD test results of polycrystalline NCM811 and polycrystalline NCM811@Li7TaO6 prepared in Comparative Example 1 and Example 1 of the present invention;

[0039] Figure 5 HRTEM test results of polycrystalline NCM811 and polycrystalline NCM811@Li7TaO6 prepared in Comparative Example 1 and Example 1 of the present invention, wherein (a) is the polycrystalline NCM811 prepared in Comparative Example 1, and (b) is the polycrystalline NCM811@Li7TaO6 prepared in Example 1;

[0040] Figure 6 The results of electrochemical performance testing of all-solid-state lithium-ion batteries assembled with polycrystalline NCM811 and polycrystalline NCM811@Li7TaO6 prepared in Comparative Example 1 and Example 1 of the present invention, wherein (a) is a comparison diagram of the initial charge and discharge performance, (b) is a comparison diagram of the rate performance, and (c) is a comparison diagram of the cycle performance. DETAILED DESCRIPTION

[0041] In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, a detailed description will be given below with reference to the accompanying drawings and specific embodiments.

[0042] The present invention provides a lithium-containing transition metal oxide-coated and doped positive electrode material and a preparation method thereof.

[0043] like Figure 1 As shown, the positive electrode material includes a core positive electrode active material and an outer shell lithium-containing transition metal oxide coating layer. At the same time, the transition metal is doped into the matrix of the positive electrode active material during the preparation process.

[0044] The coating layer is at least one of a lithium transition metal oxide Li-TM-O, a mixture of Li-TM-O and Li2O, and a mixture of Li-TM-O and Li2CO3.

[0045] wherein TM is at least one of Sc, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, Mo, La, Ce, Yb, Hf, Ta, and W;

[0046] Doping is doping of corresponding transition metal elements in the coating layer;

[0047] The positive electrode active material is LiCoO2, LiNiO2, LiCo p Ni 1-p O2, LiMnO2, x Li2MnO3·(1-x)LiMO2, Li a Ni x Co y M 1-x-y O2, LiMn2O4, LiNi 0.5 Mn 1.5At least one of O4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, LiFePO4, Li2CuO2, Li5FeO4, TiO2, Cr3O8, V2O5, TiS2, V2S3, FeS, FeS2, and MnO2;

[0048] LiCo p N i1-p In O2, 0≤p≤1,

[0049] In x Li2MnO3·(1-x)LiMO2, M is one of Ni, Co, and Mn.

[0050] Li a Ni x Co y M 1-x-y In O2, M is at least one element selected from Mn, Al, Mg, Fe, Hf, Zr, W, Nb, Sm, Ge, La, Ga, Cr, Cu, Zn, and Mo, wherein 0≤x≤1, 0≤y≤1, and 0.95 <a<1.03。

[0051] like Figure 2 and Figure 3 As shown, the preparation method of the positive electrode material includes the following steps:

[0052] S1: Selectively matching the positive electrode active material and the coating layer material according to their respective synthesis temperature ranges;

[0053] S2: adding a certain proportion of selected transition metal oxide source, lithium source and cathode active material precursor into a mixer and mixing them, and at the same time, adding a certain proportion of ethanol solvent to stir them evenly to prepare a mixture 1;

[0054] S3: placing the uniform mixture 1 slurry into an oven and drying it at 60-150° C. for 6-12 hours to prepare a dry mixture 2;

[0055] S4: sintering the dried mixture 2. In this process, the lithium source not only participates in the synthesis of the positive electrode active material, but also reacts with the transition metal oxide to in-situ synthesize a lithium-containing transition metal oxide coating layer on the surface of the positive electrode active material. After sintering, a sintered body 3 is obtained.

[0056] S5: annealing the sintered body 3 obtained in S4, so that the transition metal in the transition metal oxide diffuses into the matrix of the positive electrode active material, thereby obtaining the coated and doped positive electrode material.

[0057] The positive electrode material is used as the positive electrode of an all-solid-state lithium battery. The solid electrolyte used in combination with the positive electrode material in the all-solid-state lithium-ion battery is a sulfide solid electrolyte, and the negative electrode material used in combination is any one of lithium metal, indium metal, lithium metal alloy, graphite, lithium titanate, silicon and silicon oxide negative electrodes and their composite negative electrodes with carbon.

[0058] The following describes this with reference to specific embodiments.

[0059] Example 1

[0060] This embodiment provides a positive electrode material coated and doped with lithium transition metal oxide and a preparation method thereof, wherein the positive electrode active material is polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), particle size 12μm, lithium-containing transition metal oxide coating layer composition is Li-Ta-O, specifically Li7TaO6, coating layer thickness is 10nm, Ta element is doped into polycrystalline NCM811 matrix material, its diffusion depth is 20nm. The specific preparation includes the following steps:

[0061] The precursor of the polycrystalline NCM811 cathode active material, tantalum pentoxide (Ta2O5 by mass is 15% of the NCM811 precursor), and lithium hydroxide (LiOH·H2O by mass excess is 20%) are added to a mixer and mixed. Simultaneously, a certain proportion of ethanol solvent is added to ensure uniform mixing (the amount of ethanol solution added is calculated based on the amount of cathode material, with 5L of anhydrous ethanol used per kilogram of cathode material). The mixed slurry is then placed in an oven and dried at 100°C for 10 hours. The dried mixture is then sintered at 900°C in air for 10 hours at a heating rate of 8°C / min. Finally, the resulting sintered body is annealed at a rate of 7°C / min. This results in a Ta-doped polycrystalline NCM811 cathode material coated with the lithium transition metal oxide Li7TaO6.

[0062] Example 2

[0063] This embodiment provides a positive electrode material coated and doped with lithium transition metal oxide and a preparation method thereof, wherein the positive electrode active material is polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), particle size 10μm, lithium-containing transition metal oxide coating layer composition of Li-Nb-O, specifically LiNb3O8, coating layer thickness 2nm, Nb element doped into the polycrystalline NCM811 matrix material, its diffusion depth is 8nm. The specific preparation includes the following steps:

[0064] The precursor of the polycrystalline NCM811 cathode active material, niobium pentoxide (Nb2O5 by mass is 2% of the NCM811 precursor), and lithium hydroxide (LiOH·H2O by mass excess of 10%) are added to a mixer and mixed. Simultaneously, a certain proportion of ethanol solvent is added to ensure uniform mixing (the amount of ethanol solution added is calculated based on the amount of cathode material, with 5L of ethanol solution used per kilogram of cathode material). The mixed slurry is then placed in an oven and dried at 90°C for 9 hours. The dried mixture is then sintered at 800°C in air for 10 hours at a heating rate of 10°C / min. Finally, the resulting sintered body is annealed at a rate of 10°C / min. This results in a polycrystalline NCM811 cathode material containing a lithium transition metal oxide (LiNb3O8) coating and Nb doping.

[0065] Example 3

[0066] This embodiment provides a positive electrode material coated and doped with lithium transition metal oxide and a preparation method thereof, wherein the positive electrode active material is polycrystalline LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), with a particle size of 10 μm, the composition of the lithium-containing transition metal oxide coating layer is Li-YO, specifically LiYO2, the coating layer thickness is 20 nm, and the Y element is doped into the polycrystalline NCM811 matrix material, and its diffusion depth is 30 nm. The specific preparation includes the following steps:

[0067] The precursor of the polycrystalline NCM811 cathode active material, yttrium oxide (Y2O3 by mass is 30% of the NCM811 precursor), and lithium carbonate (Li2CO3 by mass is 50% in excess) are added to a mixer and mixed. Simultaneously, a certain proportion of ethanol solvent is added to ensure uniform mixing (the amount of ethanol solution added is calculated based on the amount of cathode material, with 5L of anhydrous ethanol used per kilogram of cathode material). The mixed slurry is then placed in an oven and dried at 80°C for 10 hours. The dried mixture is then sintered at 850°C in a carbon dioxide atmosphere for 15 hours at a heating rate of 8°C / min. Finally, the resulting sintered body is annealed at a rate of 10°C / min. This results in a polycrystalline NCM811 cathode material containing a lithium transition metal oxide (LiYO2) coating and Y doping.

[0068] Example 4

[0069] This embodiment provides a positive electrode material coated and doped with lithium transition metal oxide and a preparation method thereof, wherein the positive electrode active material is single crystal LiNi 0.6 Co 0.2 Mn 0.2O2 (NCM622), particle size 4μm, lithium-containing transition metal oxide coating layer composition of Li-La-Ti-O, coating layer thickness of 5nm, La and Ti elements co-doped into single crystal NCM622 matrix material, the diffusion depth of which is 10nm. The specific preparation includes the following steps:

[0070] The precursor of the positive electrode active material single crystal NCM622, lanthanum oxide (La2O3 by mass is 5% of the NCM622 precursor), titanium oxide (TiO2 by mass is 10% of the NCM622 precursor), and lithium carbonate (Li2CO3 by mass excess is 30%) are added to a mixer and mixed. Simultaneously, a certain proportion of ethanol solvent is added to ensure uniform mixing (the amount of ethanol solution added is calculated based on the amount of positive electrode material, with 5L of anhydrous ethanol used per kilogram of positive electrode material). The mixed slurry is then placed in an oven and dried at 80°C for 12 hours. The dried mixture is then sintered at 1000°C in an oxygen atmosphere for 15 hours at a heating rate of 5°C / min. Finally, the resulting sintered body is annealed at a rate of 5°C / min. This results in a single crystal NCM622 positive electrode material containing a lithium transition metal oxide Li-La-Ti-O coating and co-doped with La and Ti.

[0071] Example 5

[0072] This embodiment provides a positive electrode material coated and doped with lithium transition metal oxide and a preparation method thereof, wherein the positive electrode active material is LiNi 0.5 Mn 1.5 O4, the particle size is 10μm, the composition of the lithium transition metal oxide coating layer is Li-La-Zr-O, the coating layer thickness is 8nm, La and Zr elements are co-doped into LiNi 0.5 Mn 1.5 The O4 matrix material has a diffusion depth of 15nm. The specific preparation includes the following steps:

[0073] The positive electrode active material LiNi 0.5 Mn 1.5The precursor of O4, lanthanum oxide (the mass of La2O3 is 7% of the mass of the LiCoO2 precursor), zirconium oxide (the mass of ZrO2 is 15% of the mass of the LiCoO2 precursor) and lithium hydroxide (the mass excess percentage of LiOH·H2O is 40%) are added to the mixer for mixing. At the same time, a certain proportion of ethanol solvent is added to stir it evenly (the amount of ethanol solution is added according to the amount of positive electrode material, and 5L of anhydrous ethanol is used for each kilogram of positive electrode material). The mixed slurry is placed in an oven and dried at 80°C for 8h. The dried mixture is then sintered at 1100°C in an oxygen atmosphere for 12h with a heating rate of 5°C / min. Finally, the obtained sintered body is annealed at an annealing rate of 6°C / min. Finally, a LiNi containing lithium transition metal oxide Li-La-Zr-O coated and La and Zr co-doped is formed. 0.5 Mn 1.5 O4 positive electrode material.

[0074] Comparative Example 1

[0075] This comparative example provides an uncoated and undoped polycrystalline NCM811 positive electrode material and a preparation method thereof, wherein the preparation method of the positive electrode material is the same as that of Example 1, except that no transition metal oxide is added and the lithium salt is not excessive, thereby forming an uncoated and undoped polycrystalline NCM811 positive electrode material.

[0076] Comparative Example 2

[0077] This comparative example provides an uncoated and undoped single-crystal NCM622 positive electrode material and a preparation method thereof, wherein the preparation method of the positive electrode material is the same as that of Example 4, except that no transition metal oxide is added and the lithium salt is not excessive, thereby forming an uncoated and undoped single-crystal NCM622 positive electrode material.

[0078] Comparative Example 3

[0079] This comparative example provides a non-coated and doped LiNi 0.5 Mn 1.5 O4 positive electrode material and preparation method thereof, wherein the preparation method of the positive electrode material is the same as that of Example 5, except that no transition metal oxide is added, lithium salt is not excessive, and uncoated and doped LiNi is formed 0.5 Mn 1.5 O4 positive electrode material.

[0080] Table 1 Parameter settings of Examples 1-5 and Comparative Examples 1-3

[0081]

[0082] Material phase detection

[0083] Figure 4XRD detection proves that the polycrystalline NCM811@Li7TaO6 material prepared in Example 1 contains the Li7TaO6 phase (marked with plum blossoms) corresponding to the lithium-containing transition metal oxide coating material, and the corresponding standard card number is PDF#82-0898.

[0084] Figure 5 HRTEM detection found that there was no coating layer on the surface of the polycrystalline NCM811 prepared in Comparative Example 1, while a relatively uniform coating layer of about 10 nm thick was formed on the surface of the polycrystalline NCM811@Li7TaO6 prepared in Example 1.

[0085] Assembly of an all-solid-state lithium-ion battery, wherein the all-solid-state lithium-ion battery comprises a lithium-indium alloy negative electrode, a Li6PS5Cl sulfide solid electrolyte, and the positive electrode material prepared in Examples 1-5 or Comparative Examples 1-3. The specific assembly process is as follows: first, 200 mg of the Li6PS5Cl sulfide solid electrolyte is loaded into a Φ10 mm mold and pressed into an intermediate layer at a pressure of 200 MPa; then, 10 mg of a composite positive electrode material (composed of 7 mg of the above-prepared positive electrode active material and 3 mg of the Li6PS5Cl sulfide solid electrolyte) is added to one end of the intermediate layer and pressed into shape at a pressure of 200 MPa; finally, a certain amount of lithium-indium alloy negative electrode is added to the other end of the intermediate layer, and the all-solid-state lithium-ion battery is assembled at a pressure of 370 MPa.

[0086] Material performance test, test temperature is 25℃, voltage range is 2.6-4.4V vs.Li + / Li. Full battery at 0.1C (1C = 170mAg -1 ) at a current density of 0.5C; the rate performance test was carried out at different current densities of 0.2C, 0.5C, 0.8C, 1C, 2C and 3C; the ultra-long cycle performance test was carried out at a current density of 1C, and the capacity retention rate after 1000 cycles was recorded.

[0087] Figure 6 The results of electrochemical performance testing of all-solid-state lithium-ion batteries assembled with polycrystalline NCM811 and polycrystalline NCM811@Li7TaO6 prepared in Comparative Example 1 and Example 1 are shown. Figure 6 a is the comparison chart of the first charge and discharge performance; Figure 6 b is a comparison chart of rate performance; Figure 6 c is a comparison chart of cycle performance.

[0088] Table 2 Performance test data of all-solid-state lithium-ion batteries of Examples 1-5 and Comparative Examples 1-3

[0089]

[0090] From the above data analysis, it can be seen that the all-solid-state lithium-ion battery composed of the positive electrode material coated and doped with the lithium-containing transition metal oxide of the present application has a good charge and discharge specific capacity, high rate performance and stable long cycle performance compared to the uncoated sample. This is due to the lithium-containing transition metal oxide coating and doping of the present invention. The coating increases the ability of lithium ions to transfer at the interface between the positive electrode material and the solid electrolyte, avoids the oxidative decomposition of the solid electrolyte, inhibits the occurrence of interfacial side reactions, and thus reduces the interface impedance and electrode polarization. The doping of transition metals expands the interlayer spacing of the positive electrode active material matrix, reduces the degree of lithium nickel mixing, and thus enhances the structural stability of the positive electrode active material during long-term cycling.

[0091] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A lithium-containing transition metal oxide coated and doped positive electrode material, characterized in that: It includes a core positive electrode active material and an outer shell containing a lithium transition metal oxide coating layer. At the same time, the transition metal is doped into the matrix of the positive electrode active material during the preparation process; The coating layer contains at least one of lithium transition metal oxide Li-TM-O, a mixture of Li-TM-O and Li2O, and a mixture of Li-TM-O and Li2CO3. wherein TM is at least one of Sc, Ti, V, Cr, Cu, Zn, Y, Zr, Nb, Mo, La, Ce, Yb, Hf, Ta, and W; Doping is doping of corresponding transition metal elements in the coating layer; The positive electrode active material is LiCoO2, LiNiO2, LiCo p Ni 1-p O2, LiMnO2, x Li2MnO3·(1-x)LiMO2, Li a Ni x Co y M 1-x-y O2, LiMn2O4, LiNi 0.5 Mn 1.5 At least one of O4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, LiFePO4, Li2CuO2, and Li5FeO4; LiCo p Ni 1-p In O2, 0≤p≤1, In x Li2MnO3·(1-x)LiMO2, M is one of Ni, Co, and Mn. Li a Ni x Co y M 1-x-y In O2, M is at least one element selected from Mn, Al, Mg, Fe, Hf, Zr, W, Nb, Sm, Ge, La, Ga, Cr, Cu, Zn, and Mo, wherein 0≤x≤1, 0≤y≤1, and 0.95 <a<1.03; The thickness of the coating layer is 2 to 50 nm; the diffusion depth of the doping element is 1 to 100 nm; The method for preparing the positive electrode material comprises the following steps: S1: Selectively matching the positive electrode active material and the coating layer material according to their respective synthesis temperature ranges; S2: adding a certain proportion of selected transition metal oxide source, lithium source and cathode active material precursor into a mixer and mixing them, and at the same time, adding a certain proportion of ethanol solvent to stir them evenly to prepare a mixture 1; S3: placing the uniform mixture 1 slurry into an oven and drying it at 60-150° C. for 6-12 hours to prepare a dry mixture 2; S4: sintering the dried mixture 2. In this process, the lithium source not only participates in the synthesis of the positive electrode active material, but also reacts with the transition metal oxide to in-situ synthesize a lithium-containing transition metal oxide coating layer on the surface of the positive electrode active material. After sintering, a sintered body 3 is obtained. S5: annealing the sintered body 3 obtained in S4, so that the transition metal in the transition metal oxide diffuses into the matrix of the positive electrode active material, thereby obtaining the coated and doped positive electrode material.

2. The lithium-containing transition metal oxide coated and doped positive electrode material according to claim 1, characterized in that: The positive electrode active material is a single crystal or polycrystal with a particle size of 2 to 20 μm; the coverage of the coating layer is above 80%; when the coating layer is a mixture of Li-TM-O and Li2O or Li-TM-O and Li2CO3, the content of Li2O or Li2CO3 accounts for 1% to 20% of the mass of Li-TM-O.

3. The lithium-containing transition metal oxide coated and doped positive electrode material according to claim 1, characterized in that The synthesis temperature of the positive electrode active material in S1 differs from that of the coating layer material in a range of 0 to 100°C.

4. The lithium-containing transition metal oxide coated and doped positive electrode material according to claim 1, characterized in that The transition metal oxide source in S2 includes at least one of scandium oxide, titanium oxide, vanadium oxide, chromium oxide, copper oxide, zinc oxide, yttrium oxide, zirconium oxide, niobium oxide, molybdenum oxide, lanthanum oxide, cerium oxide, ytterbium oxide, hafnium oxide, tantalum oxide and tungsten oxide; the lithium source includes at least one of lithium carbonate, lithium oxide, lithium hydroxide, lithium nitrate and lithium oxalate; The mass ratio of the transition metal oxide source to the positive electrode active material precursor is 0.001 to 0.5:1; the mass ratio of the lithium source to the positive electrode active material precursor is 1.05 to 1.9:

1.

5. The lithium-containing transition metal oxide coated and doped positive electrode material according to claim 1, characterized in that: The added amount of the ethanol solvent is 4 to 8 L of anhydrous ethanol per kilogram of positive electrode material.

6. The lithium-containing transition metal oxide coated and doped positive electrode material according to claim 1, characterized in that: The sintering temperature of the mixture 2 in S4 is 700-1200° C., the heating rate is 1-10° C. / min, the sintering time is 8-18 hours, and the sintering atmosphere is oxygen, air or carbon dioxide.

7. The lithium-containing transition metal oxide coated and doped positive electrode material according to claim 1, characterized in that: The annealing rate of the sintered body 3 in S5 is 5-10° C. / min.

8. The lithium-containing transition metal oxide coated and doped positive electrode material according to claim 1, characterized in that: The positive electrode material is used as the positive electrode of an all-solid-state lithium battery. The solid electrolyte used in combination with the positive electrode material in the all-solid-state lithium-ion battery is a sulfide solid electrolyte, and the negative electrode material used in combination is any one of lithium metal, indium metal, lithium metal alloy, graphite, lithium titanate, silicon and silicon oxide negative electrodes and their composite negative electrodes with carbon.

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