Modified lithium ion battery positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion battery positive electrode materials, and particularly relates to a modified lithium ion battery positive electrode material and a preparation method and application thereof. According to the invention, the doped metal element in the core layer can reduce lithium-nickel mixed arrangement, and meanwhile, the M-O bond energy is stronger, so that the structural stability is improved, the lattice spacing is enlarged, and the lithium ion transmission rate is improved. By means of solid electrolyte coating, direct contact between the core layer and the electrolyte can be prevented, side reaction between the core layer and the electrolyte and corrosion of decomposition products of the electrolyte on the core layer are prevented, and stability is improved; the solid electrolyte lithium ion conductivity is high, and the lithium ion transmission rate is increased; through continuous modification of the same metal elements, a consistent chemical environment is constructed inside and on the surface, a more uniform and stable interface is formed, uniform transmission of lithium ions is facilitated, interface impedance is reduced, voltage attenuation and capacity attenuation are effectively relieved, the rate performance is improved, and the cycle life is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to a modified lithium-ion battery cathode material, its preparation method, and its application. Background Technology

[0002] Common cathode materials for lithium-ion batteries include LiCoO2, LiMnO2, and LiNiO2, but each of these materials has its own drawbacks. A combination of the advantages and disadvantages of these three materials led to the development of ternary LiNiO2. x Co y Mn z O2 (NCM) cathode material. The charge-discharge performance and stability of ternary cathode materials mainly depend on the ratio of nickel, cobalt, and manganese elements in the material. Lithium-ion batteries are used in electric vehicles and energy storage systems. As the lithium-ion battery market continues to expand and the number of electric vehicles increases, the production of lithium-ion power batteries is also increasing. With the development of electric vehicles, low mileage can no longer meet people's needs. Therefore, finding materials with high energy density, high stability, and high safety performance is urgent.

[0003] Among numerous layered oxide cathode materials, high-nickel ternary cathode material LiNi x Co y Mn z O2 (X > 0.8) possesses high energy density and high electron transport rate, making it one of the most promising candidate materials for solving the problem of long-range electric vehicle driving. However, high-nickel materials also have some inherent problems, such as Ni... 2+ Excessive content can lead to severe cation mixing, resulting in continuous capacity decay, side reactions between the electrolyte and the cathode material, and the generation of microcracks, which in turn affect the structural stability and electrochemical performance of the cathode material. Summary of the Invention

[0004] The purpose of this invention is to provide a modified lithium-ion battery cathode material, its preparation method, and its applications. The modified cathode material provided by this invention exhibits excellent structural stability and electrochemical performance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a modified lithium-ion battery cathode material, comprising a core layer and a coating layer; The core layer is a ternary cathode material and doped metal elements in the ternary cathode material; The coating layer is made of a solid electrolyte. The solid electrolyte contains the same types of metal elements other than lithium as the doped metal elements.

[0006] Preferably, the ternary cathode material includes LiNi. x Coy Mn 1-x-y O2, where x+y≤1.

[0007] Preferably, the molar percentage of the metal element doped in the core layer is 0.1-5%.

[0008] Preferably, the solid electrolyte includes lithium aluminum titanium phosphate, lithium lanthanum zirconate, lithium lanthanum titanate, or lithium aluminum germanium phosphate.

[0009] Preferably, when the solid electrolyte is lithium titanium aluminum phosphate, the doped metal elements are titanium and aluminum; the molar ratio of titanium to aluminum is 0.5~2:1; When the solid electrolyte is lithium lanthanum zirconate, the doped metal elements are zirconium and lanthanum, and the molar ratio of zirconium to lanthanum is 0.5~2:1; When the solid electrolyte is lithium lanthanum titanate, the doped metal elements are titanium and lanthanum, and the molar ratio of titanium to lanthanum is 0.5~2:1; When the solid electrolyte is lithium aluminum germanium phosphate, the doped metal elements are germanium and aluminum, and the molar ratio of germanium to aluminum is 0.5~2:1.

[0010] Preferably, the thickness of the coating layer is 1~10 nm; the mass ratio of the core layer to the coating layer is 1:0.001~0.05; The particle size of the modified lithium-ion battery cathode material is 1~8μm.

[0011] This invention also provides a method for preparing the modified lithium-ion battery cathode material described in the above technical solution, comprising the following steps: Step 1: Provide the precursor material corresponding to the ternary cathode material; Step 2: Mix the raw materials corresponding to the doped metal elements, the precursor material, and the lithium source, and then sinter them to obtain the core material; Step 3: Mix the core material, solid electrolyte and solvent, and then dry and sinter them sequentially to obtain the modified lithium-ion battery cathode material.

[0012] Preferably, in step 2, the sintering includes performing a first sintering and a second sintering sequentially; The first sintering temperature is 300~700℃, and the holding time is 3~7h; The second sintering temperature is 600~900℃, and the holding time is 8~15h; the second sintering temperature is higher than the first sintering temperature. The sintering is carried out in an oxygen-containing atmosphere, which includes oxygen or air.

[0013] Preferably, in step 3, the sintering temperature is 200~600℃ and the holding time is 3~6h; The sintering is carried out in an oxygen-containing atmosphere, which includes oxygen or air.

[0014] The present invention also provides the application of the modified lithium-ion battery cathode material described in the above technical solution or the modified lithium-ion battery cathode material prepared by the preparation method described in the above technical solution in lithium-ion batteries.

[0015] This invention provides a modified lithium-ion battery cathode material, comprising a core layer and a coating layer; the core layer is a ternary cathode material and a doped metal element in the ternary cathode material; the coating layer is a solid electrolyte; the solid electrolyte contains the same type of metal element as the doped metal element except for lithium.

[0016] In this invention, the doped metal elements in the core layer can reduce lithium-nickel mixing, and the MO bond energy (M is the doped metal element) is stronger than the Ni-O, Co-O, and Mn-O bond energy. Therefore, it can improve the structural stability of the cathode material and increase the lattice spacing to enhance the lithium-ion transport rate. Coating the cathode material with a solid electrolyte not only prevents direct contact between the core material and the electrolyte, thus avoiding side reactions and corrosion from electrolyte decomposition products, but also significantly improves the material's stability during cycling. Furthermore, the strong lithium-ion conductivity of the solid electrolyte enhances the lithium-ion transport rate. During lithium-ion battery cycling, the solid electrolyte helps compensate for the loss of active lithium, further strengthening the stability of the cathode material's bulk and surface structure. Moreover, by controlling the types of metal elements other than lithium in the solid electrolyte to be the same as the doped metal elements, continuous modification with the same metal elements creates a consistent chemical environment inside and on the surface of the material, forming a more uniform and stable interface. This facilitates rapid and uniform lithium-ion transport at the electrode / electrolyte interface, reducing interface impedance and effectively mitigating voltage and capacity decay, thereby improving the material's rate performance and cycle life.

[0017] This invention provides a bulk-surface ion continuous modification strategy using ion doping and solid electrolyte coating. This strategy utilizes ions for doping in the bulk phase while simultaneously coating the surface with solid electrolyte, providing an effective new approach to improve the structural and interfacial stability and electrochemical performance of cathode materials.

[0018] This invention also provides a method for preparing the modified lithium-ion battery cathode material described in the above technical solution. This invention directly mixes the precursor, dopant, and lithium source, and prepares the core material through a one-step solid-state sintering process. The core material is then mixed with a solid electrolyte and subjected to a second sintering to obtain the modified lithium-ion battery cathode material. The preparation method is simple and suitable for industrial production. Attached Figure Description

[0019] Figure 1 EDS diagrams of the cathode materials obtained in Example 1 and Comparative Examples 1-3; Figure 2 The graph shows the charge-discharge cycle performance of the half-cells assembled from the composite materials of Example 1 and Comparative Examples 1-3 in the voltage range of 2.7-4.3V at a rate of 1C. Figure 3 The graph shows the charge-discharge performance of the half-cells assembled from the composite materials of Example 1 and Comparative Examples 1-3 at different rates (0.1C, 0.5C, 1C, 2C, 5C, 10C) within a voltage range of 2.7-4.3V. Figure 4 The graph shows the charge-discharge cycle performance of the half-cells obtained in Example 1 and Comparative Example 1 after 100 cycles at a voltage range of 2.7~4.3V, a rate of 1C, and a high temperature of 45°C. Figure 5 The graph shows the charge-discharge cycle performance of the full cells obtained in Example 1 and Comparative Example 1 after 100 cycles at a voltage range of 2.7 to 4.3 V and a rate of 1C. Figure 6 The graphs show the charge-discharge cycle performance of the half-cells obtained in Example 1 and Comparative Examples 1 and 4 at a high rate of 10C within a voltage range of 2.7 to 4.3V. Figure 7 The graph shows the charge-discharge cycle performance of the half-cell corresponding to Example 2 within a voltage range of 2.7~4.3V at a 1C rate. Figure 8 The graph shows the charge-discharge cycle performance of the half-cell corresponding to Example 3 within a voltage range of 2.7~4.3V at a 1C rate. Detailed Implementation

[0020] This invention provides a modified lithium-ion battery cathode material, comprising a core layer and a coating layer; The core layer is a ternary cathode material and doped metal elements in the ternary cathode material; The coating layer is made of a solid electrolyte. The solid electrolyte contains the same types of metal elements other than lithium as the doped metal elements.

[0021] In this invention, the ternary cathode material preferably includes LiNi. x Co y Mn 1-x-y O2, where x+y≤1.

[0022] In this invention, the molar amount of the metal element doped in the core layer is preferably 0.1 to 5% of the total molar amount of metal elements other than lithium in the core layer, specifically 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.5%, and 5.0%.

[0023] In this invention, the solid electrolyte preferably comprises lithium aluminum titanium phosphate, lithium lanthanum zirconate, lithium lanthanum titanate, or lithium aluminum germanium phosphate. When the solid electrolyte is lithium aluminum titanium phosphate, the doping metal elements are titanium and aluminum; the molar ratio of titanium to aluminum is preferably 0.5 to 2:1, specifically 0.5:1, 1.0:1, 1.5:1, or 2.0:1. When the solid electrolyte is lithium lanthanum zirconate, the doping metal elements are zirconium and lanthanum, and the molar ratio of zirconium to lanthanum is preferably 0.5 to 2:1, specifically 0.5:1, 1.0:1, 1.5:1, or 2.0:1. :1; When the solid electrolyte is lithium lanthanum titanate, the doped metal elements are titanium and lanthanum, and the molar ratio of titanium to lanthanum is preferably 0.5~2:1, specifically 0.5:1, 1.0:1, 1.5:1, or 2.0:1; When the solid electrolyte is lithium aluminum germanium phosphate, the doped metal elements are germanium and aluminum, and the molar ratio of germanium to aluminum is preferably 0.5~2:1, specifically 0.5:1, 1.0:1, 1.5:1, or 2.0:1.

[0024] In this invention, the thickness of the coating layer is preferably 1~10nm, specifically 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, or 10nm; the mass ratio of the core layer to the coating layer is preferably 1:0.001~0.05, specifically 1:0.001, 1:0.005, 1:0.01, 1:0.02, 1:0.03, 1:0.04, or 1:0.05; and the particle size of the modified lithium-ion battery cathode material is preferably 1~8μm.

[0025] This invention also provides a method for preparing the modified lithium-ion battery cathode material described in the above technical solution, comprising the following steps: Step 1: Provide the precursor material corresponding to the ternary cathode material; Step 2: Mix the raw materials corresponding to the doped metal elements, the precursor material, and the lithium source, and then sinter them to obtain the core material; Step 3: Mix the core material, solid electrolyte and solvent, and then dry and sinter them sequentially to obtain the modified lithium-ion battery cathode material.

[0026] Step 1 of the present invention is to provide a precursor material corresponding to the ternary cathode material.

[0027] The present invention does not impose any special limitation on the preparation method of the precursor material, and any method known to those skilled in the art can be used.

[0028] In this invention, the precursor material is preferably prepared by a co-precipitation method, which preferably includes: mixing a soluble nickel source, a soluble cobalt source, a soluble manganese source and water to obtain a metal ion solution; using ammonia water as a base liquid, simultaneously adding the metal ion solution, sodium hydroxide solution and raw material ammonia water to the base liquid to carry out a co-precipitation reaction; and after aging, obtaining the precursor material.

[0029] In this invention, the soluble nickel source preferably includes at least one of nickel sulfate hexahydrate, nickel acetate, nickel nitrate, and nickel chloride; the soluble cobalt source preferably includes at least one of cobalt sulfate heptahydrate, cobalt acetate, cobalt nitrate, and cobalt chloride; and the soluble manganese source preferably includes at least one of manganese sulfate monohydrate, manganese acetate, manganese nitrate, and manganese chloride. This invention does not impose any particular limitation on the ratio of the soluble nickel source, soluble cobalt source, and soluble manganese source; the required raw materials can be taken according to the composition of the corresponding ternary cathode material. In this invention, the concentration of the metal ion solution is preferably 1~3 mol / L, specifically 1 mol / L, 2 mol / L, or 3 mol / L.

[0030] In this invention, the concentration of the sodium hydroxide solution is preferably 2-6 mol / L, specifically 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L; the concentration of the base solution is preferably 0.4-0.6 mol / L, specifically 0.4 mol / L, 0.5 mol / L, or 0.6 mol / L; and the concentration of the raw ammonia solution is preferably 2-3.5 mol / L, specifically 2 mol / L, 3 mol / L, or 3.5 mol / L.

[0031] In this invention, the preferred volume ratio of the metal ion solution, sodium hydroxide solution, and raw ammonia water is 2.8~3.2:0.8~1.2:1, specifically 3:1:1; the preferred volume ratio of the base solution and raw ammonia water is 3~6:1, specifically 3:1, 4:1, 5:1, or 6:1. In this invention, the preferred dropping rate of the metal ion solution is 0.96 mL / min; the preferred dropping rate of the sodium hydroxide solution is 0.96 mL / min; and the preferred dropping rate of the raw ammonia water is 0.48 mL / min.

[0032] In this invention, the coprecipitation is preferably carried out in a protective atmosphere, preferably nitrogen; the temperature of the coprecipitation reaction is preferably 45~65℃, specifically 45℃, 50℃, 55℃, 60℃, or 65℃; the pH value of the system is preferably controlled to be 9~11 during the coprecipitation reaction; the coprecipitation reaction is preferably carried out under stirring conditions, and the stirring speed is preferably 400~1200 rpm, specifically 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, or 1200 rpm. In this invention, the aging temperature is preferably 45~65℃, specifically 45℃, 50℃, 55℃, 60℃, or 65℃; the aging is preferably carried out under stirring conditions, and the stirring speed is preferably 200~500 rpm, specifically 200 rpm, 300 rpm, 400 rpm, or 500 rpm; the aging time is preferably 1~5 hours, specifically 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours. In this invention, after aging, filtration and drying are also preferably performed, and the drying temperature is preferably 80~120℃, specifically 80℃, 90℃, 100℃, 110℃, or 120℃; the drying time is preferably 12~24 hours, specifically 12 hours, 16 hours, 20 hours, or 24 hours.

[0033] After obtaining the precursor material, step 2 of the present invention involves mixing the raw material corresponding to the doped metal element, the precursor material, and the lithium source, and then sintering them to obtain the core material.

[0034] In this invention, the raw materials corresponding to aluminum preferably include at least one of aluminum hydroxide, aluminum nitrate, aluminum sulfate, and aluminum isopropoxide; the raw materials corresponding to titanium preferably include at least one of titanium hydroxide, titanium dioxide, and potassium titanium oxalate; the raw materials corresponding to lanthanum preferably include at least one of lanthanum hydroxide, lanthanum oxide, lanthanum nitrate, lanthanum acetate, and lanthanum chloride; the raw materials corresponding to zirconium preferably include at least one of zirconium hydroxide, zirconium dioxide, zirconium oxychloride, zirconium nitrate, and tetraisopropyl zirconate; and the raw materials corresponding to germanium preferably include at least one of germanium hydroxide and germanium dioxide.

[0035] In this invention, the lithium source preferably includes at least one selected from lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, and lithium acetate; the ratio of the molar amount of lithium in the lithium source to the total molar amount of metal elements in the precursor is 1.01~1.11:1. In this invention, the mixing method is preferably grinding, and the grinding method is preferably dry grinding or wet grinding; the grinding time is preferably 20~30 minutes.

[0036] In this invention, the sintering preferably includes a first sintering and a second sintering performed sequentially; the temperature of the first sintering is preferably 300~700℃, specifically 300℃, 400℃, 500℃, 600℃, or 700℃; the holding time is preferably 3~7h, specifically 3h, 4h, 5h, 6h, or 7h; the temperature of the second sintering is preferably 600~900℃, specifically 600℃, 700℃, 800℃, or 900℃; the holding time is preferably 8~15h, specifically 8h, 9h, 10h, 11h, 12h, 13h, 14h, or 15h; the heating rate of the sintering is preferably 4~10℃ / min, specifically 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min; the sintering is preferably carried out in an oxygen-containing atmosphere; the oxygen-containing atmosphere preferably includes oxygen or air.

[0037] After obtaining the core material, step 3 of the present invention involves mixing the core material, solid electrolyte, and solvent, and then drying and sintering them sequentially to obtain the modified lithium-ion battery cathode material.

[0038] In this invention, the mass ratio of the core material to the solid electrolyte is preferably 1:0.001~0.05. In this invention, the solvent preferably includes ethanol or isopropanol; the mixing is preferably carried out under stirring conditions. In this invention, the drying temperature is preferably 100°C. In this invention, the sintering temperature is preferably 200~600°C, specifically 200°C, 300°C, 400°C, 500°C, or 600°C; the holding time is preferably 3~6 hours, specifically 3 hours, 4 hours, 5 hours, or 6 hours; the sintering is preferably carried out in an oxygen-containing atmosphere; the oxygen-containing atmosphere preferably includes oxygen or air.

[0039] The present invention also provides the application of the modified lithium-ion battery cathode material described in the above technical solution or the modified lithium-ion battery cathode material prepared by the preparation method described in the above technical solution in lithium-ion batteries.

[0040] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0041] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0042] Example 1 Using nickel sulfate, cobalt sulfate, and manganese sulfate as raw materials, with the molar ratio of Ni, Co, and Mn being 0.9:0.05:0.05, the raw materials and water were mixed to prepare a 750 mL metal ion solution with a concentration of 2 mol / L. NaOH was weighed and prepared into a 250 mL NaOH solution with a concentration of 4 mol / L, based on a metal ion to OH- molar ratio of 1:2. A 250 mL ammonia solution with a concentration of 3.5 mol / L was also prepared. Using 1500 mL of 0.5 mol / L ammonia solution as the base solution, the metal ion solution, sodium hydroxide solution, and raw material ammonia solution obtained above were simultaneously added dropwise to the base solution (the dropping rates of the three were 0.96 mL / min, 0.96 mL / min, and 0.48 mL / min, respectively). The pH value of the reaction was controlled at 11, the temperature at 55℃, and the stirring speed at 900 rpm. After the addition was completed, the mixture was aged at 400 rpm for 3 hours, filtered, and the resulting precipitate was dried at 120℃ for 12 hours to obtain Ni. 0.9 Co 0.05 Mn 0.05 (OH)2 precursor; Using TiO2, Al(OH)3, the precursor prepared above, and LiOH·H2O as raw materials, the ratio of the molar amount of lithium in LiOH·H2O to the total molar amount of metal elements in the precursor is 1.05:1, and the molar ratio of TiO2, Al(OH)3 and LiOH·H2O is 0.0025:0.0025:1.05; First, LiOH·H2O and the precursor were added to a mortar, then TiO2 and Al(OH)3 were added to the mortar and ground for 30 min. After that, the mixture was placed in a tube furnace and sintered at 450℃ for 3 h in an oxygen atmosphere, and then sintered at 730℃ for 10 h with a heating rate of 5℃ / min to obtain the core material (where the molar ratio of titanium to aluminum is 1:1, and the molar amount of the doped metal element accounts for 0.5% of the total molar amount of metal elements other than lithium in the core layer). The core material prepared above and LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3) Add it to ethanol at a mass ratio of 1:0.005 and stir for 30 min. After stirring, put it in a forced-air drying oven and dry at 100℃ for 3 h. Put the dried sample into a tube furnace and sinter at 400℃ for 5 h in an oxygen atmosphere to finally obtain the modified cathode material (PC955 AT@LATP), wherein the thickness of the coating layer is 7~8 nm and the particle size of the modified cathode material is 3~5 μm.

[0043] Example 2 (1) Using ZrO2, La(OH)3, and the nickel-cobalt-manganese hydroxide precursor (Ni) prepared in Example 1 0.9 Co 0.05 Mn 0.05 Using ZrO2 and LiOH·H2O (Aladdin, 98%) as raw materials, the lithium source and nickel-cobalt-manganese hydroxide precursor with a molar ratio of 1.05:1 were first added to a mortar. Then, ZrO2 and La(OH)3 (the molar ratio of ZrO2, La(OH)3 and LiOH·H2O was 0.0025:0.0025:1.05) were added to the mortar and ground for 30 min. After that, it was placed in a tube furnace and sintered at 450℃ for 3 h in an oxygen atmosphere, and then sintered at 730℃ for 10 h with a heating rate of 5℃ / min. Finally, the core material was obtained (where the molar ratio of zirconium and lanthanum was 1:1, and the molar amount of doped metal elements accounted for 0.5% of the total molar amount of metal elements other than lithium in the core layer). (2) Using the core material prepared above and LLZO (Li7La3Zr2O) 12 (National Pharmaceutical Group, 99.99%) was added to ethanol at a mass ratio of 1:0.005. The mixture was stirred in ethanol for 30 min. After stirring, it was placed in a forced-air drying oven and dried at 100℃ for 3 h. The dried sample was then placed in a tube furnace and heated at 400℃ for 5 h in an oxygen atmosphere to finally obtain Zr-La doped and LLZO coated lithium-ion battery cathode material (PC955 LZ@LLZO). The coating thickness was 6~8 nm and the particle size was 3~5 μm.

[0044] Example 3 (1) Using TiO2, La(OH)3, and the nickel-cobalt-manganese hydroxide precursor (Ni) prepared in Example 1 0.9 Co 0.05 Mn 0.05 Using (OH)2 and lithium source LiOH·H2O (Aladdin, 98%) as raw materials, lithium source and nickel cobalt manganese hydroxide precursor with a molar ratio of 1.05:1 were first added to a mortar. Then TiO2 and La(OH)3 (the molar ratio of TiO2, La(OH)3 and LiOH·H2O was 0.0025:0.0025:1.05) were added to the mortar and ground for 30 min. Then it was placed in a tube furnace and sintered at 450℃ for 3 h in an oxygen atmosphere, and then sintered at 730℃ for 10 h with a heating rate of 5℃ / min. Finally, the core material was obtained (where the molar ratio of titanium and lanthanum was 1:1, and the molar amount of doped metal elements accounted for 0.5% of the total molar amount of metal elements other than lithium in the core layer). (2) Using the core material prepared above and LLTO (Li 0.33 La 0.56TiO3 (Sinopharm, 99.99%) was added to ethanol at a ratio of 1:0.005 and stirred in ethanol for 30 min. After stirring, the sample was placed in a forced-air drying oven and dried at 100℃ for 3 h. The dried sample was then placed in a tube furnace and heated at 400℃ for 5 h in an oxygen atmosphere to finally obtain Ti-La doped and LLTO coated lithium-ion battery cathode material (PC955 LT@LLTO). The coating thickness was 7~8 nm and the particle size was 3~5 μm.

[0045] Comparative Example 1 The precursor was obtained according to Example 1. The precursor and LiOH·H2O were mixed at a molar ratio of 1.05:1, ground for 30 min, and placed in a tube furnace. In an oxygen atmosphere, the mixture was first sintered at 450°C for 3 h, and then sintered at 730°C for 10 h. The heating rate was 5°C / min, and pure NCM955 cathode material (PC955) was obtained.

[0046] Comparative Example 2 The core material was prepared according to the method in Example 1, and the core material was used directly as the positive electrode material (PC955 AT).

[0047] Comparative Example 3 Pure NCM955 cathode material was prepared according to the method of Comparative Example 1; The pure NCM955 cathode material prepared above and LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3) Add 0.5% by mass to ethanol and stir for 30 min. After stirring, place it in a forced-air drying oven and dry at 100℃ for 3 h. Place the dried sample in a tube furnace and sinter at 400℃ for 5 h in an oxygen atmosphere to finally obtain the cathode material (PC955 LATP), wherein the thickness of the coating layer is 7~8 nm and the particle size of the cathode material is 3~5 μm.

[0048] Comparative Example 4 The core material (PC955 AT) was prepared according to the method described in Example 1; The PC955 AT and LLZO(Li7La3Zr2O) prepared above were used. 12 The sample was added to ethanol at a mass ratio of 1:0.005 and stirred for 30 minutes. After stirring, it was placed in a forced-air drying oven and dried at 100°C for 3 hours. The dried sample was then placed in a tube furnace and sintered at 400°C for 5 hours in an oxygen atmosphere to finally obtain the cathode material (PC955 AT@LLZO).

[0049] Performance testing Test Example 1 Figure 1 EDS images of the cathode materials obtained in Example 1 and Comparative Examples 1-3 are shown, where (a) corresponds to the NCM955 precursor, (b) corresponds to NCM955 (Comparative Example 1), (c) corresponds to NCM955 AlTi doping (Comparative Example 2), (d) corresponds to NCM955 LATP coating (Comparative Example 3), (e) corresponds to NCM955 AlTi doping and LATP coating (Example 1), and (f) is the EDS of NCM955 AlTi doping and LATP coating. from Figure 1 It can be seen that the secondary particle size of the four samples is between 3 and 5 μm. Among them, the NCM955 AlTi-doped and LATP-coated samples have better crystallinity, with more uniform and dense primary particle size and a smooth surface. The NCM955 sample, however, shows obvious small particles on its surface, which may be residual lithium material formed from contact with air. To determine the elemental distribution, energy-dispersive X-ray spectroscopy (EDS) analysis was performed on the four NCM cathode materials. Figure 1 As can be observed in (f), elements such as Ni, Co, Mn, O, Ti, Al and P are all uniformly distributed on the surface of the material.

[0050] Test Example 2 Electrochemical performance tests were conducted on the cathode materials obtained in Example 1 and Comparative Examples 1-4. The positive electrode material was assembled into a half-cell. The assembly process was as follows: the prepared positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) were mixed evenly in a mortar at a weight ratio of 8:1:1. An appropriate amount of N-methyl-2-pyrrolidone (NMP) organic solvent was added, and the mixture was ground to form a smooth paste without obvious particles and bubbles. The paste was coated onto fresh aluminum foil using a spatula and then dried in a vacuum oven at 100°C for 12 hours. After drying, the coated foil was cut into positive electrode sheets with a diameter of 12 mm. Using 1 mol / L LiPF6 / ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) (EC:EMC:DMC = 1:1:1 volume ratio) / 1 wt% vinylene carbonate (VC) as the electrolyte, a polypropylene microporous membrane as the separator, and a lithium sheet as the negative electrode, a 2025 type coin cell was assembled in an argon-filled dry glove box.

[0051] Figure 2 To ensure the assembled half-cell operates within a voltage range of 2.7–4.3V, it is subjected to 1C (1C = 200 mA·g) at a voltage of 1C. -1 ) Rate charge-discharge cycle performance curves; from Figure 2 It can be seen that after 100 cycles, the discharge specific capacity of the PC955, PC955AT, PC955LATP, and PC955AT@LATP samples was 132.25 mAh·g.-1 147.17mAh·g -1 150.03mAh·g -1 183.44mAh·g -1 The capacity retention rates were 66.13%, 72.06%, 71.55%, and 90.18%, respectively. It can be seen that Al and Ti doping, as well as LATP coating, significantly improved the cycling stability of the material. Compared with PC955, the PC955 AT@LATP material exhibited a discharge specific capacity 51.29 mAh·g higher after 100 cycles. -1 .

[0052] Figure 3 The charge-discharge performance curves of the assembled half-cell at different rates (0.1C, 0.5C, 1C, 2C, 5C, 10C) within the voltage range of 2.7~4.3V are shown in Table 1. Table 1 Rate performance test results (mAh·g) -1 )

[0053] from Figure 3 It can be seen that the rate performance of NCM955 after bulk or surface aluminum / titanium modification is superior to that of pure PC955. Specifically, the discharge specific capacity of the LATP-coated PC955 LATP and PC955 AT@LATP samples at different current densities is higher than that of the uncoated samples. This is attributed to the Li in the LATP coating layer. + This is because the concentration gradient will migrate to lower concentrations to fill lithium vacancies in the cathode material.

[0054] Figure 4 The graphs show the charge-discharge cycle performance of the half-cells obtained in Example 1 and Comparative Example 1 after 100 cycles at a voltage range of 2.7–4.3 V, a rate of 1 C, and a high temperature of 45 °C. It can be seen that after 100 cycles at 45 °C, the discharge specific capacity of the PC955 and PC955AT@LATP samples is 144.10 mAh·g⁻¹. -1 and 164.11mAh·g -1 The capacity retention rates were 67.17% and 80.08%, respectively; it can be seen that the doping / coating strategy provided by the present invention can significantly improve the high-temperature cycling stability of the material.

[0055] Following the battery assembly method above, replace the lithium-ion negative electrode with a graphite negative electrode to assemble a full battery. Figure 5The graphs show the charge-discharge cycle performance of the full cells obtained in Example 1 and Comparative Example 1 after 100 cycles at a voltage range of 2.7–4.3 V and a rate of 1C. It can be seen that the discharge specific capacity of the PC955 and PC955 AT@LATP samples is 142.59 mAh·g. -1 and 171.94mAh·g -1 The capacity retention rates were 82.94% and 93.30%, respectively. It can be seen that the doping / coating strategy provided by this invention significantly improves the cycling stability of the material.

[0056] Figure 6 The graphs show the charge-discharge cycle performance of the half-cells obtained in Example 1 and Comparative Examples 1 and 4 at a high rate of 10C within a voltage range of 2.7–4.3V. It can be seen that at a high rate of 10C, the discharge specific capacity of the PC955, PC955 AT@LLZO, and PC955AT@LATP samples after 50 cycles is 126.10 mAh·g. -1 150.02mAh·g -1 and 182.19mAh·g -1 The capacity retention rates were 81%, 88.35%, and 104.29%, respectively. The discharge specific capacity of the PC955 and PC955 AT@LATP samples after 100 cycles was 89.44 mAh·g⁻¹. -1 and 169.97mAh·g -1 The capacity retention rates were 57.49% and 97.3%, respectively. The PC955 AT@LATP sample had a discharge specific capacity of 140.97 mAh·g after 150 cycles. -1 With a capacity retention rate of 80.7%, it can be seen that the present invention uses a continuous ion modification strategy of bulk-surface ion doping and solid electrolyte coating to form a bulk-surface ion modification strategy, and controls the dopant elements in the core layer and the metal elements in the coating layer to be the same, which can further improve the cycling stability of the material at high rates.

[0057] Test Example 3 Following the above process of assembling half-cells, the electrochemical performance of the composite materials obtained in Examples 2 and 3 were tested respectively. Figure 4 The half-cell obtained in Example 2 operates within a voltage range of 2.7~4.3V at 1C (1C = 200mA·g). -1 ) Rate charge-discharge cycle performance curves; from Figure 4 It can be seen that after 100 cycles, the discharge specific capacity of the Zr-La doped / LLZO coated sample and the pure sample are 171.81 mAh·g, respectively. -1 and 132.25mAh·g -1The capacity retention rates were 86.15% and 66.13%, respectively. It can be seen that the synergistic strategy of Zr-La doping and LLZO coating significantly improved the cycling stability of the material.

[0058] Figure 5 The half-cell obtained in Example 3 operates within a voltage range of 2.7~4.3V at 1C (1C = 200mA·g). -1 ) Rate charge-discharge cycle performance curves; from Figure 5 It can be seen that after 100 cycles, the discharge specific capacity of the Ti-La doped / LLTO coated sample and the pure sample are 169.94 mAh·g. -1 and 132.25mAh·g -1 The capacity retention rates were 86.88% and 66.13%, respectively. It can be seen that the synergistic strategy of Ti-La doping and LLTO coating significantly improved the cycling stability of the material.

[0059] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A modified lithium-ion battery cathode material, characterized in that, Includes the core layer and the cladding layer; The core layer is a ternary cathode material and doped metal elements in the ternary cathode material; The coating layer is made of a solid electrolyte. The solid electrolyte contains the same types of metal elements other than lithium as the doped metal elements.

2. The modified lithium-ion battery cathode material according to claim 1, characterized in that, The ternary cathode material includes LiNi. x Co y Mn 1-x-y O2, where x+y≤1.

3. The modified lithium-ion battery cathode material according to claim 1, characterized in that, The molar amount of the metal element doped in the core layer accounts for 0.1 to 5% of the total molar amount of metal elements other than lithium in the core layer.

4. The modified lithium-ion battery cathode material according to claim 1, characterized in that, The solid electrolyte includes lithium aluminum titanium phosphate, lithium lanthanum zirconate, lithium lanthanum titanate, or lithium aluminum germanium phosphate.

5. The modified lithium-ion battery cathode material according to claim 4, characterized in that, When the solid electrolyte is lithium titanium aluminum phosphate, the doped metal elements are titanium and aluminum; the molar ratio of titanium to aluminum is 0.5~2:1; When the solid electrolyte is lithium lanthanum zirconate, the doped metal elements are zirconium and lanthanum, and the molar ratio of zirconium to lanthanum is 0.5~2:1; When the solid electrolyte is lithium lanthanum titanate, the doped metal elements are titanium and lanthanum, and the molar ratio of titanium to lanthanum is 0.5~2:1; When the solid electrolyte is lithium aluminum germanium phosphate, the doped metal elements are germanium and aluminum, and the molar ratio of germanium to aluminum is 0.5~2:

1.

6. The modified lithium-ion battery cathode material according to claim 1, characterized in that, The thickness of the coating layer is 1~10 nm; the mass ratio of the core layer to the coating layer is 1:0.001~0.05; The particle size of the modified lithium-ion battery cathode material is 1~8μm.

7. The method for preparing the modified lithium-ion battery cathode material according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1: Provide the precursor material corresponding to the ternary cathode material; Step 2: Mix the raw materials corresponding to the doped metal elements, the precursor material, and the lithium source, and then sinter them to obtain the core material; Step 3: Mix the core material, solid electrolyte and solvent, and then dry and sinter them sequentially to obtain the modified lithium-ion battery cathode material.

8. The preparation method according to claim 7, characterized in that, In step 2, the sintering includes performing a first sintering and a second sintering in sequence; The first sintering temperature is 300~700℃, and the holding time is 3~7h; The second sintering temperature is 600~900℃, and the holding time is 8~15h; the second sintering temperature is higher than the first sintering temperature. The sintering is carried out in an oxygen-containing atmosphere, which includes oxygen or air.

9. The preparation method according to claim 7, characterized in that, In step 3, the sintering temperature is 200~600℃ and the holding time is 3~6h; The sintering is carried out in an oxygen-containing atmosphere, which includes oxygen or air.

10. The application of the modified lithium-ion battery cathode material according to any one of claims 1 to 6 or the modified lithium-ion battery cathode material prepared by the preparation method according to any one of claims 7 to 9 in lithium-ion batteries.

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