A multi-modified lithium-rich cobalt-free single crystal material and a preparation method thereof

Abstract

The application discloses a kind of multiple modified lithium-rich cobalt-free single crystal materials, including doped lithium nickel manganese oxide base and its surface coating, the chemical general formula of doped lithium nickel manganese oxide base is Li x Ni y Mn z N 1‑y‑z O2, wherein: N is any one or several of Co, Mg element, 1 The material has excellent structural stability and electrochemical cycle stability. The preparation method of the multiple modified lithium-rich cobalt-free single crystal material is also disclosed, which physically mixes nickel manganese-based precursor, phosphate, lithium source and additive, and then sintering. Through one-step synthesis, metal ion doping and phosphate coating are simultaneously realized for multiple modification. The method is simple and easy to operate, which can significantly improve the electrochemical performance of lithium-rich cobalt-free material and has good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion battery manufacturing, and in particular relates to a multi-modified lithium-rich cobalt-free single crystal material and a preparation method thereof. Background Art

[0002] Lithium-rich manganese-based layered oxide materials, due to their high specific capacity and unique mixed layered crystal structure, have become a major research and development direction for lithium-ion battery cathode materials. Among them, lithium-rich cobalt-free single crystal materials have become a research focus for lithium-rich manganese-based materials due to their lower cost and higher energy density. However, similar to high-nickel cobalt-free materials, lithium-rich cobalt-free materials still face problems such as electrolyte corrosion and the formation of an interface film between the cathode and the electrolyte, resulting in rapid cycle decay and poor rate performance.

[0003] In order to solve these problems, the materials are mainly modified by methods such as doping and coating. However, the improvement space of a single modification method is limited and is not enough to meet the needs of practical applications. Therefore, seeking an efficient and reliable composite modification method is of great significance to the performance improvement of lithium-rich cobalt-free positive electrode materials. Metal ion doping can effectively improve the structural stability and rate performance of the material, and surface coating can effectively isolate it from contact with the electrolyte. However, in order to achieve the composite modification of the two at the same time, finding suitable modification materials and simple and easy-to-operate modification methods are the main difficulties in promoting the performance improvement and large-scale production application of lithium-rich cobalt-free materials in the future. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings and defects mentioned in the above background technology and provide a multi-modified lithium-rich, cobalt-free single crystal material and its preparation method. The present invention achieves metal ion doping and phosphate coating in a one-step process. This compositely modified lithium-rich, cobalt-free single crystal material exhibits excellent cycle stability and rate performance.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A multi-modified lithium-rich cobalt-free single crystal material, comprising a doped lithium nickel manganese oxide matrix and a surface coating thereof, wherein the chemical formula of the doped lithium nickel manganese oxide matrix is ​​Li x Ni y Mn z N 1-y-z O2, wherein: N is any one or more of Co and Mg elements, 1<x≤1.5, 0.9≤y+z≤1; the surface coating is LiCoPO4 or LiMgPO4.

[0007] Preferably, the weight of the surface coating is 1 to 10 wt% of the weight of the doped lithium nickel manganese oxide substrate.

[0008] Based on a general inventive concept, the present invention also provides a method for preparing a multi-modified lithium-rich cobalt-free single crystal material, comprising the following steps:

[0009] (1) dissolving nickel salt and manganese salt in pure water to obtain a nickel-manganese mixed solution, stirring to react, filtering and drying to obtain a nickel-manganese-based precursor;

[0010] (2) dispersing the nickel-manganese-based precursor, ammonium phosphate, lithium salt and additives in an organic solvent, ball milling and mixing until the organic solvent is completely volatilized, vacuum drying, and calcining at a high temperature in an air atmosphere to obtain the multi-modified lithium-rich cobalt-free single crystal material.

[0011] In the above preparation method, preferably, in step (1), sodium hydroxide and / or ammonia solution are used to control the pH of the nickel-manganese mixed solution to 8.5-10; the concentration of sodium hydroxide is 1-6 mol / L, and the concentration of ammonia solution is 4-10 mol / L.

[0012] Preferably, in step (1), the nickel-manganese-based precursor is nickel-manganese hydroxide Ni p Mn q (OH)2, where p+q=1.

[0013] Preferably, in step (1), the nickel salt and manganese salt are any one or more of acetate, sulfate and nitrate.

[0014] Preferably, the nickel salt and manganese salt concentrations in the nickel-manganese mixed solution are 2-5 mol / L respectively; and the stirring reaction time is 4-20 h.

[0015] Preferably, in step (2), the ammonium phosphate is any one or more of ammonium cobalt phosphate and ammonium magnesium phosphate; the lithium salt is any one or more of lithium hydroxide and lithium carbonate; the additive is any one or more of PVP, glucose, acetylene black, and graphene; and the organic solvent is any one or more of ethanol, ethylene glycol, methanol, and acetone.

[0016] Preferably, in step (2), the molar ratio of the nickel-manganese-based precursor: lithium in the lithium salt: ammonium phosphate: additive is 1: (1.04-1.07): (0.01-0.05): (0.01-0.05).

[0017] Preferably, in step (2), the temperature of the vacuum drying is 60-160° C., and the time of the vacuum drying is 4-20 h.

[0018] Preferably, in step (2), the temperature of the high-temperature calcination is 800-1300° C., and the time of the high-temperature calcination is 2-20 hours.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention physically mixes a nickel-manganese-based precursor with phosphate, a lithium source, and an additive, and subsequently sintering the mixture, thereby simultaneously achieving multiple modifications of metal ion doping and phosphate coating through a one-step synthesis. The method is simple and easy to operate, can significantly improve the electrochemical properties of lithium-rich cobalt-free materials, and has good application prospects.

[0021] 2. The lithium-rich, cobalt-free single crystal material modified by metal-doped phosphate coating of the present invention has excellent structural stability and electrochemical cycle stability; and the tap density of the single crystal structure is high, and its corresponding volume capacity is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is a high-magnification transmission image of the product in Example 1 of the present invention.

[0024] Figure 2 This is the cycle performance of the product in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0026] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0027] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0028] Example 1:

[0029] A multi-modified lithium-rich cobalt-free single crystal material LiCoPO4@Li 1.21 Ni 0.373 Mn 0.587 Co 0.04 O2, the preparation method thereof comprises the following steps:

[0030] (1) Dissolve 0.04 mol nickel sulfate and 0.06 mol manganese sulfate in 200 mL pure water and stir to dissolve to obtain a nickel-manganese mixed salt solution. Then add 4 mol / L sodium hydroxide and 8 mol / L ammonia solution to adjust the solution pH to 9-10. After continuous stirring for 10 hours, filter and dry to obtain nickel-manganese-based hydroxide Ni 0.4 Mn 0.6 (OH)2;

[0031] (2) Take 0.01 molNi 0.4 Mn 0.6 (OH)2, 0.0105molLiOH·H2O, 0.2mmolNH4CoPO4·H2O, and 0.2mmolPVP were added to a ball mill, and 40mL ethanol was added. The mixture was ball milled until the ethanol was completely evaporated. After vacuum drying at 100℃ for 6h, the mixture was calcined at 950℃ in a muffle furnace for 10h to obtain LiCoPO4@Li 1.21 Ni 0.373 Mn 0.587 Co 0.04 O2. High-magnification transmission image Figure 1 As shown, its single crystal structure can be seen, in which the mass fraction of the LiCoPO4 coating layer is 3.3%.

[0032] LiCoPO4@Li 1.21 Ni 0.373 Mn 0.587 Co 0.04 O2 cathode material powder was used as the active material. It was mixed with acetylene black (AB), a conductive agent, and polyvinylidene fluoride (PVDF), a binder, in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was used as the solvent, and the mixture was stirred in a small beaker at 800 rpm for 2 hours to produce a slurry. The slurry was coated onto a current collector aluminum foil using an automatic coater, placed flat on tempered glass, and dried in a vacuum drying oven at 85°C for 4 hours. Sheets were punched into 14mm diameter electrodes and dried in a vacuum drying oven at 105°C for 4 hours. The electrodes were then placed in an argon-filled glove box with a moisture and oxygen content below 0.1 ppm for 4 hours to reduce moisture adsorption during transfer. The cells were then assembled into CR2032 button cells in the glove box. The negative electrode consisted of a 16mm diameter, 0.5mm thick pure metal lithium sheet and an 18mm diameter Celgard 2300 porous polyethylene membrane as the separator.

[0033] After the battery is assembled and aged for 12 hours, the charge and discharge tests at different potentials are carried out ( Figure 2The sample was activated at 0.1C for 3 cycles at a voltage of 2.0-4.6V and then cycled at 1C for 200 cycles. The discharge capacity after 200 cycles was 172.14 mAh g -1 , the capacity retention rate is 86.07%.

[0034] Example 2:

[0035] A multi-modified lithium-rich cobalt-free single crystal material LiMgPO4@Li 1.21 Ni 0.373 Mn 0.587 Mg 0.04 O2, the preparation method thereof comprises the following steps:

[0036] (1) Dissolve 0.04 mol nickel sulfate and 0.06 mol manganese sulfate in 200 mL pure water and stir to dissolve to obtain a nickel-manganese mixed salt solution. Then add 4 mol / L sodium hydroxide and 8 mol / L ammonia solution to adjust the solution pH to 9-10. After continuous stirring for 10 hours, filter and dry to obtain nickel-manganese-based hydroxide Ni 0.4 Mn 0.6 (OH)2;

[0037] (2) Take 0.01 molNi 0.4 Mn 0.6 (OH)2, 0.0105molLiOH·H2O, 0.2mmolNH4MgPO4, and 0.2mmolPVP were added to a ball mill, and 40mL ethanol was added. The mixture was ball milled until the ethanol was completely evaporated. After vacuum drying at 100℃ for 6h, the mixture was calcined at 950℃ in a muffle furnace for 10h to obtain LiMgPO4@Li 1.21 Ni 0.373 Mn 0.587 Mg 0.04 O2, wherein the mass fraction of the LiMgPO4 coating layer is 2.6%.

[0038] LiMgPO4@Li 1.21 Ni 0.373 Mn 0.587 Mg 0.04O2 cathode material powder was used as the active material. It was mixed with acetylene black (AB), a conductive agent, and polyvinylidene fluoride (PVDF), a binder, in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was used as the solvent, and the mixture was stirred in a small beaker at 800 rpm for 2 hours to produce a slurry. The slurry was coated onto a current collector aluminum foil using an automatic coater, placed flat on tempered glass, and dried in a vacuum drying oven at 85°C for 4 hours. Sheets were punched into 14mm diameter electrodes and dried in a vacuum drying oven at 105°C for 4 hours. The electrodes were then placed in an argon-filled glove box with a moisture and oxygen content below 0.1 ppm for 4 hours to reduce moisture adsorption during transfer. The cells were then assembled into CR2032 button cells in the glove box. The negative electrode consisted of a 16mm diameter, 0.5mm thick pure metal lithium sheet and an 18mm diameter Celgard 2300 porous polyethylene membrane as the separator.

[0039] After the battery was assembled and aged for 12 hours, charge and discharge tests were performed at different potentials. The sample was activated at 0.1C for 3 cycles at a voltage of 2.0-4.6V, and then cycled at 1C for 200 cycles. The discharge capacity after 200 cycles was 157.5mAhg -1 , the capacity retention rate is 78.2%.

[0040] Example 3:

[0041] A multi-modified lithium-rich cobalt-free single crystal material LiCoPO4@Li 1.21 Ni 0.387 Mn 0.593 Co 0.02 O2, the preparation method thereof comprises the following steps:

[0042] (1) Dissolve 0.04 mol nickel sulfate and 0.06 mol manganese sulfate in 200 mL pure water and stir to dissolve to obtain a nickel-manganese mixed salt solution. Then add 4 mol / L sodium hydroxide and 8 mol / L ammonia solution to adjust the solution pH to 9-10. After continuous stirring for 10 hours, filter and dry to obtain nickel-manganese-based hydroxide Ni 0.4 Mn 0.6 (OH)2;

[0043] (2) Take 0.01 molNi 0.4 Mn 0.6 (OH)2, 0.0105molLiOH·H2O, 0.1mmolNH4CoPO4·H2O, and 0.2mmolPVP were added to a ball mill, and 40mL ethanol was added. The mixture was ball milled until the ethanol was completely evaporated. After vacuum drying at 100℃ for 6h, the mixture was calcined at 950℃ in a muffle furnace for 10h to obtain LiCoPO4@Li 1.21 Ni0.387 Mn 0.593 Co 0.02 O2, wherein the mass fraction of the LiCoPO4 coating layer is 1.65%.

[0044] LiCoPO4@Li 1.21 Ni 0.387 Mn 0.593 Co 0.02 O2 positive electrode material powder as an active material, a conductive agent acetylene black (AB), and a binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 8:1:1, N-methyl pyrrolidone (NMP) was used as a solvent, the mixture was stirred in a small beaker at a speed of 800 r / min for 2 h to obtain a slurry. The slurry was coated on a current collector aluminum foil using an automatic coating machine, placed on a tempered glass, and transferred to a vacuum drying oven at 85°C for drying for 4 h. After punching, a 14 mm diameter electrode was prepared and dried in a vacuum drying oven at 105°C for 4 h. The moisture content and oxygen content were both less than 0.1 ppm, and the argon atmosphere was filled. The electrode was placed in a glove box for 4 h to reduce the adsorbed moisture during the transfer process. Then, a CR2032 button cell was assembled in the glove box. The battery used a pure metal lithium sheet with a diameter of 16 mm and a thickness of 0.5 mm as the negative electrode, and a porous polyethylene film with a diameter of 18 mm and a model number of Celgard2300 as the separator.

[0045] After the battery was assembled and aged for 12 h, the charge and discharge test at different potentials was performed. The sample was activated at 0.1C for 3 cycles at a voltage of 2.0-4.6V, and then cycled at 1C for 200 cycles. The discharge specific capacity after 200 cycles was 155.9 mAhg -1 , and the capacity retention rate was 76.8%.

[0046] Example 4:

[0047] A LiCoPO4@Li 1.21 Ni 0.373 Mn 0.587 Co 0.04 O2, the preparation method comprising the following steps:

[0048] (1) 0.04 mol of nickel sulfate and 0.06 mol of manganese sulfate were dissolved in 200 mL of pure water to obtain a nickel-manganese mixed salt solution. Then, 4 mol / L of sodium hydroxide and 8 mol / L of ammonia solution were added to adjust the pH of the solution to 9-10. After continuous stirring for 10 h, the nickel-manganese-based hydroxide Ni 0.4 Mn 0.6 (OH)2 was filtered and dried;

[0049] (2) 0.01 mol of Ni0.4 Mn 0.6 (OH)2, 0.0105molLiOH·H2O, 0.3mmolNH4CoPO4·H2O, and 0.2mmolPVP were added to a ball mill, and 40mL ethanol was added. The mixture was ball milled until the ethanol was completely evaporated. After vacuum drying at 100℃ for 6h, the mixture was calcined at 950℃ in a muffle furnace for 10h to obtain LiCoPO4@Li 1.21 Ni 0.373 Mn 0.587 Co 0.06 O2, wherein the mass fraction of the LiCoPO4 coating layer is 4.95%.

[0050] LiCoPO4@Li 1.21 Ni 0.373 Mn 0.587 Co 0.04 O2 cathode material powder was used as the active material. It was mixed with acetylene black (AB), a conductive agent, and polyvinylidene fluoride (PVDF), a binder, in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was used as the solvent, and the mixture was stirred in a small beaker at 800 rpm for 2 hours to produce a slurry. The slurry was coated onto a current collector aluminum foil using an automatic coater, placed flat on tempered glass, and dried in a vacuum drying oven at 85°C for 4 hours. Sheets were punched into 14mm diameter electrodes and dried in a vacuum drying oven at 105°C for 4 hours. The electrodes were then placed in an argon-filled glove box with a moisture and oxygen content below 0.1 ppm for 4 hours to reduce moisture adsorption during transfer. The cells were then assembled into CR2032 button cells in the glove box. The negative electrode consisted of a 16mm diameter, 0.5mm thick pure metal lithium sheet and an 18mm diameter Celgard 2300 porous polyethylene membrane as the separator.

[0051] After the battery was assembled and aged for 12 hours, charge and discharge tests were performed at different potentials. The sample was activated at 0.1C for 3 cycles at a voltage of 2.0-4.6V, and then cycled at 1C for 200 cycles. The discharge capacity after 200 cycles was 163.3mAhg -1 , the capacity retention rate is 80.8%.

[0052] Comparative Example 1:

[0053] A positive electrode material Li 1.21 Ni 0.4 Mn 0.6 The preparation method of O2 comprises the following steps:

[0054] (1) Dissolve 0.04 mol nickel sulfate and 0.06 mol manganese sulfate in 200 mL pure water and stir to dissolve to obtain a nickel-manganese mixed salt solution. Then add 4 mol / L sodium hydroxide and 8 mol / L ammonia solution to adjust the solution pH to 9-10. After continuous stirring for 10 hours, filter and dry to obtain nickel-manganese-based hydroxide Ni 0.4 Mn 0.6 (OH)2;

[0055] (2) Take 0.01 molNi 0.4 Mn 0.6 (OH)2, 0.0105molLiOH·H2O, and 0.2mmolPVP were added to a ball mill, and 40mL ethanol was added. The mixture was ball milled until the ethanol was completely evaporated. After drying at 100℃ in vacuum for 6h, the mixture was calcined at 950℃ in a muffle furnace for 10h to obtain Li 1.21 Ni 0.4 Mn 0.6 O2.

[0056] Li 1.21 Ni 0.4 Mn 0.6 O2 cathode material powder was used as the active material. It was mixed with acetylene black (AB), a conductive agent, and polyvinylidene fluoride (PVDF), a binder, in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was used as the solvent, and the mixture was stirred in a small beaker at 800 rpm for 2 hours to produce a slurry. The slurry was coated onto a current collector aluminum foil using an automatic coater, placed flat on tempered glass, and dried in a vacuum drying oven at 85°C for 4 hours. Sheets were punched into 14mm diameter electrodes and dried in a vacuum drying oven at 105°C for 4 hours. The electrodes were then placed in an argon-filled glove box with a moisture and oxygen content below 0.1 ppm for 4 hours to reduce moisture adsorption during transfer. The cells were then assembled into CR2032 button cells in the glove box. The negative electrode consisted of a 16mm diameter, 0.5mm thick pure metal lithium sheet and an 18mm diameter Celgard 2300 porous polyethylene membrane as the separator.

[0057] After the battery was assembled and aged for 12 hours, charge and discharge tests were performed at different potentials. The sample was activated at 0.1C for 3 cycles at a voltage of 2.0-4.6V, and then cycled at 1C for 200 cycles. The discharge capacity after 200 cycles was 96.0mAhg -1 , the capacity retention rate is 48.6%.

[0058] Comparative Example 2:

[0059] A positive electrode material Li3PO4@Li 1.21 Ni 0.4 Mn 0.6The preparation method of O2 comprises the following steps:

[0060] (1) Dissolve 0.04 mol nickel sulfate and 0.06 mol manganese sulfate in 200 mL pure water and stir to dissolve to obtain a nickel-manganese mixed salt solution. Then add 4 mol / L sodium hydroxide and 8 mol / L ammonia solution to adjust the solution pH to 9-10. After continuous stirring for 10 hours, filter and dry to obtain nickel-manganese-based hydroxide Ni 0.4 Mn 0.6 (OH)2;

[0061] (2) Take 0.01 molNi 0.4 Mn 0.6 (OH)2, 0.0105molLiOH·H2O, 0.2mmolNH4H2PO4, and 0.2mmolPVP were added to a ball mill, and 40mL ethanol was added. The mixture was milled until the ethanol was completely evaporated. After drying at 100℃ in a vacuum oven for 6h, the mixture was calcined at 950℃ in a muffle furnace for 10h to obtain Li3PO4@Li 1.21 Ni 0.4 Mn 0.6 O2.

[0062] Li3PO4@Li 1.21 Ni 0.4 Mn 0.6 O2 cathode material powder was used as the active material. It was mixed with acetylene black (AB), a conductive agent, and polyvinylidene fluoride (PVDF), a binder, in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was used as the solvent, and the mixture was stirred in a small beaker at 800 rpm for 2 hours to produce a slurry. The slurry was coated onto a current collector aluminum foil using an automatic coater, placed flat on tempered glass, and dried in a vacuum drying oven at 85°C for 4 hours. Sheets were punched into 14mm diameter electrodes and dried in a vacuum drying oven at 105°C for 4 hours. The electrodes were then placed in an argon-filled glove box with a moisture and oxygen content below 0.1 ppm for 4 hours to reduce moisture adsorption during transfer. The cells were then assembled into CR2032 button cells in the glove box. The negative electrode consisted of a 16mm diameter, 0.5mm thick pure metal lithium sheet and an 18mm diameter Celgard 2300 porous polyethylene membrane as the separator.

[0063] After the battery was assembled and aged for 12 hours, charge and discharge tests were performed at different potentials. The sample was activated at 0.1C for 3 cycles at a voltage of 2.0-4.6V, and then cycled at 1C for 200 cycles. The discharge capacity after 200 cycles was 125.2mAhg -1 , the capacity retention rate is 65.5%.

[0064] In summary, the present invention successfully achieves a one-step synthesis of a multi-modified lithium-rich, cobalt-free single crystal cathode material by in-situ phosphate compounding of a lithium-rich, cobalt-free material precursor, combined with subsequent lithiation sintering. This composite material effectively improves the structural stability and electrochemical cycling stability of the lithium-rich, cobalt-free single crystal.

[0065] The above contents are only basic descriptions of the concept of the present invention, and any equivalent transformations made according to the technical solution of the present invention shall fall within the protection scope of the present invention.

Claims

1. A multi-modified lithium-rich cobalt-free single crystal material, characterized in that: The invention comprises a doped lithium nickel manganese oxide matrix and a surface coating thereof, wherein the chemical formula of the doped lithium nickel manganese oxide matrix is ​​Li x Ni y Mn z N 1-y-z O2, wherein: N is Mg element, 1<x≤1.5, 0.9≤y+z≤1; the surface coating is LiMgPO4; the weight of the surface coating is 1-10wt% of the weight of the doped lithium nickel manganese oxide matrix.

2. A method for preparing the multi-modified lithium-rich cobalt-free single crystal material according to claim 1, characterized in that: The following steps are involved: (1) dissolving nickel salt and manganese salt in pure water to obtain a nickel-manganese mixed solution, stirring to react, filtering and drying to obtain a nickel-manganese-based precursor; using sodium hydroxide and / or ammonia solution to control the pH of the nickel-manganese mixed solution to be 8.5-10; (2) dispersing the nickel-manganese-based precursor, ammonium phosphate, lithium salt and additives in an organic solvent, ball milling and mixing until the organic solvent is completely volatilized, vacuum drying at 60-160° C., and calcining at a high temperature of 800-1300° C. in an air atmosphere to obtain the multi-modified lithium-rich cobalt-free single crystal material; The molar ratio of the nickel-manganese-based precursor: lithium in the lithium salt: ammonium phosphate: additive is 1: (1.04-1.07): (0.01-0.05): (0.01-0.05), and the ammonium phosphate is magnesium ammonium phosphate.

3. The preparation method according to claim 2, characterized in that In step (1), the concentration of sodium hydroxide is 1-6 mol / L, and the concentration of ammonia solution is 4-10 mol / L.

4. The preparation method according to claim 2, characterized in that In step (1), the nickel-manganese-based precursor is nickel-manganese hydroxide Ni p Mn q (OH)2, where p+q=1.

5. The preparation method according to claim 2, characterized in that In step (1), the nickel salt and manganese salt are any one or more of acetate, sulfate and nitrate.

6. The preparation method according to claim 2, characterized in that In step (1), the nickel salt and manganese salt concentrations in the nickel-manganese mixed solution are 2-5 mol / L respectively; and the stirring reaction time is 4-20 h.

7. The preparation method according to claim 2, characterized in that In step (2), the lithium salt is any one or more of lithium hydroxide and lithium carbonate; the additive is any one or more of PVP, glucose, acetylene black, and graphene; and the organic solvent is any one or more of ethanol, ethylene glycol, methanol, and acetone.

8. The preparation method according to any one of claims 2 to 7, characterized in that In step (2), the vacuum drying time is 4-20 hours; the high-temperature calcination time is 2-20 hours.

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