Preparation method of lithium battery positive electrode material

Abstract

The invention discloses a preparation method of a lithium battery positive electrode material, and relates to the technical field of lithium battery processing. The preparation method comprises the following steps: step 1, preparing a precursor: dissolving nickel cobalt manganese metal salt in a water-ethanol mixed solvent to form a metal salt solution, dispersing a mesoporous SiO2 template in absolute ethyl alcohol to form a template suspension, mixing the metal salt solution with the template suspension, and carrying out a co-precipitation reaction under the assistance of ultrasonic waves; through cooperation of a water-ethanol double-solvent system and ultrasonic waves, the hydrolysis rate of metal ions is regulated and controlled, uniform mixing of molecular scales is achieved, the element distribution standard deviation is smaller than or equal to 1.2%, interface side reactions are reduced, the first coulombic efficiency is improved to 88%-89.5%, a mesoporous SiO2 template is combined with microwave sintering, the particle size is controlled to be 50-100 nm, and the mesoporous SiO2-based composite material is prepared. A surface layer porous structure (porosity is greater than or equal to 50%) is formed through vapor etching, the specific surface area reaches 60-80m < 2 > / g, the lithium ion diffusion coefficient is improved by more than 5 times, and the 5C rate capacity is improved by 40-50% compared with that of a traditional process.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery processing, and in particular to a method for preparing a lithium battery positive electrode material. Background Art

[0002] As the core power source for current portable electronic devices, new energy vehicles, and energy storage systems, lithium batteries rely on breakthroughs in key materials for performance improvement, especially cathode materials. Cathode materials directly determine the energy density, cycle life, and safety performance of batteries, and are one of the core directions of lithium battery technology research and development. Cathode materials represented by high-nickel ternary and lithium-rich manganese-based materials have become the mainstream development direction of the next generation of lithium batteries due to their higher specific capacity (>200mAh / g) and energy density (>700Wh / kg). However, the preparation process of such materials places extremely high demands on their crystal structure, particle morphology, and interface characteristics. Deviations in any link during the preparation process will lead to a significant decrease in the electrochemical performance of the material.

[0003] The traditional lithium battery cathode material preparation process has the following defects, such as uneven element distribution and poor structural stability. In the preparation of high nickel ternary precursor, Ni 2+ With Co 2+ 、Mn 2+ Differences in hydrolysis rates lead to elemental segregation, forming localized nickel-rich regions. This triggers interfacial side reactions during charge and discharge, resulting in low initial Coulombic efficiency, rapid cycle capacity decay, coarse particle size, and low ion transport efficiency. Conventional high-temperature sintering easily forms large particles, extending the lithium-ion diffusion path, resulting in poor rate performance, high interfacial impedance, and insufficient high-voltage adaptability. For high-voltage materials such as lithium cobalt oxide, conventional coating processes struggle to form a uniform, dense protective layer, leading to high interfacial impedance.

[0004] To this end, we provide a method for preparing a lithium battery positive electrode material to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a positive electrode material for a lithium battery. By combining ultrasound-assisted dual-solvent co-precipitation technology with microwave-induced nano-template sintering technology, the problems in the prior art of frequent interfacial side reactions caused by uneven distribution of metal elements and low lithium ion transmission efficiency caused by coarse particle size are solved.

[0006] To solve the above technical problems, the present invention is achieved through the following technical solutions: A method for preparing a positive electrode material for a lithium battery, comprising the following steps:

[0007] Step 1, precursor preparation: dissolving nickel, cobalt and manganese metal salts in a water-ethanol mixed solvent to form a metal salt solution, dispersing a mesoporous SiO2 template in anhydrous ethanol to form a template suspension, mixing the metal salt solution and the template suspension, and then performing a coprecipitation reaction under ultrasound assistance, controlling the pH value of the reaction system to gradually increase from an initial pH of 10.0-10.5 to 11.0-11.5 to obtain a metal hydroxide SiO2 composite precursor;

[0008] Step 2: Microwave template sintering: After the composite precursor is granulated, microwave sintering is performed in an air atmosphere containing water vapor. During the sintering process, the surface SiO2 template is etched by water vapor to form a gradient structure with a dense core and a porous surface. The template is then removed.

[0009] Step 3: Lithiation reaction: The sintered porous precursor is mixed with a lithium source and solid-phase sintered at high temperature in an oxygen atmosphere to obtain a lithium battery positive electrode material.

[0010] The present invention is further configured such that, in the water-ethanol mixed solvent, the volume ratio of water to ethanol is 3:1, the concentration of the metal salt solution is 1.0-1.5 mol / L, the pore size of the mesoporous SiO2 template is 3-10 nm, and the specific surface area is 500-1000 m 2 / g, and the added amount is 20%-40% of the precursor mass.

[0011] The present invention is further configured such that, in the coprecipitation reaction, the ultrasonic frequency is 20-40 kHz, the power density is 50-100 W / L, the reaction temperature is 40-60°C, a NaOH solution containing 5 vol% ammonia water (concentration 2.0-2.5 mol / L) is added dropwise, the initial pH is maintained for 30 minutes, and then the pH is increased to the target pH at a rate of 0.05-0.1 pH / min, and the total reaction time is 1.5-2.5 hours.

[0012] The present invention is further configured such that the microwave sintering conditions are: microwave frequency 2.45 GHz, heating rate 10-20°C / min, sintering temperature 700-900°C, insulation time 0.5-2h, water vapor content in the sintering atmosphere 5-10 vol%, and water vapor flow rate 30-80 mL / min.

[0013] The present invention is further configured such that in the granulation step, 1-5 wt% of polyvinyl alcohol (PVA) is added as a granulating agent, the wet granulation is passed through a 60-100 mesh sieve, and spherical particles of 5-20 μm are formed after drying.

[0014] The present invention is further configured such that, during the template removal, a 1-2 mol / L hydrochloric acid solution is used to dissolve the SiO2 template at 50-70°C with stirring for 1-3 hours, with a solid-liquid ratio of 1:8-1:12, and the template is washed to neutrality and then dried to obtain a porous precursor.

[0015] The present invention is further configured such that, in the lithiation reaction, the lithium source is LiOH·H2O or Li2CO3, the molar ratio of Li to transition metal (Ni+Co+Mn) is 1.03-1.07, the ball-to-material ratio during ball milling is 8-12:1, the rotation speed is 200-400 rpm, and the mixing time is 2-4 hours.

[0016] The present invention is further configured such that the conditions for the high-temperature solid-phase sintering are: oxygen flow rate 100-300 mL / min, heating rate 5-15° C. / min, sintering temperature 850-950° C., and holding time 8-12 h.

[0017] The present invention is further configured such that step three also includes a surface modification step: mixing the primary positive electrode material with 0.5-2wt% graphene or carbon nanotubes, surface coating the positive electrode material by ball milling or spray drying, and then heat treating the positive electrode material in an inert atmosphere at 300-500°C for 0.5-2h.

[0018] The present invention is further configured such that the primary particle size of the positive electrode material is 50-100 nm, the secondary particle size is 5-20 μm, and the specific surface area is 60-80 m 2 / g, surface porosity ≥50%, lithium ion diffusion coefficient ≥3.0×10 -10 cm 2 / s.

[0019] The present invention has the following beneficial effects:

[0020] 1. The present invention uses a water-ethanol dual solvent system in conjunction with ultrasound to regulate the hydrolysis rate of metal ions, achieve uniform mixing at the molecular scale, and reduce interfacial side reactions. The initial coulombic efficiency is increased to 88%-89.5%.

[0021] 2. The mesoporous SiO2 template of the present invention is combined with microwave sintering to control the particle size to 50-100nm, and water vapor etching forms a surface porous structure (porosity ≥ 50%) with a specific surface area of 60-80m 2 / g, the lithium ion diffusion coefficient is increased by more than 5 times, and the 5C rate capacity is increased by 40%-50% compared with the traditional process.

[0022] 3. The microwave selective heating of the present invention shortens the sintering time from 8 hours to 1-2 hours, reduces energy consumption by 60%, and combines solvent recovery (ethanol recovery rate ≥ 95%) with template regeneration technology to significantly reduce production costs.

[0023] 4. The core-shell precursor is formed by gradient pH control in the present invention, and graphene / carbon nanotube coating can be used to reduce the interface impedance to ≤45Ω·cm 2 , inhibiting structural collapse under high pressure, and the capacity retention rate after 200 cycles reached 89.3%.

[0024] 5. The present invention is applicable to materials such as NCM523 / 622 / 811 by adjusting the metal ratio, template pore size and lithium source type, balancing the structural stability and capacity of systems with different nickel contents, and has strong universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a logical framework diagram of the method for preparing the positive electrode material for a lithium battery of the present invention;

[0026] Figure 2 The figure is a flow chart of the method for preparing the positive electrode material of a lithium battery of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0028] Example 1

[0029] See also Figure 1-2 A method for preparing a positive electrode material for a lithium battery comprises the following steps: Step 1: Precursor preparation: dissolving nickel, cobalt and manganese metal salts in a water-ethanol mixed solvent to form a metal salt solution, wherein the volume ratio of water to ethanol in the water-ethanol mixed solvent is 3:1, the concentration of the metal salt solution is 1.0-1.5 mol / L, the pore size of the mesoporous SiO2 template is 3-10 nm, and the specific surface area is 500-1000 m 2 / g, the addition amount is 20%-40% of the precursor mass, the mesoporous SiO2 template is dispersed in anhydrous ethanol to form a template suspension, the metal salt solution and the template suspension are mixed, and a coprecipitation reaction is carried out under the assistance of ultrasound. In the coprecipitation reaction, the ultrasonic frequency is 20-40kHz, the power density is 50-100W / L, the reaction temperature is 40-60°C, and a NaOH solution containing 5vol% ammonia water (concentration 2.0-2.5mol / L) is added dropwise. After the initial pH is maintained for 30min, it is increased to the target pH at a rate of 0.05-0.1pH / min. The total reaction time is 1.5-2.5h, and the pH value of the reaction system is controlled from the initial 10.0- 10.5 gradually increased to 11.0-11.5 to obtain a metal hydroxide SiO2 composite precursor; Step 2: Microwave template sintering: After the composite precursor is granulated, 1-5wt% of polyvinyl alcohol (PVA) is added as a granulating agent in the granulation step, and after wet granulation, it is sieved through a 60-100 mesh sieve and dried to form spherical particles of 5-20μm, which are microwave sintered in an air atmosphere containing water vapor. The microwave sintering conditions are: microwave frequency 2.45GHz, heating rate 10-20℃ / min, sintering temperature 700-900℃, insulation 0.5-2h, water vapor content in the sintering atmosphere is 5-10vol%, water vapor flow rate 30-80mL / min, during the sintering process, the surface SiO2 template is etched by water vapor to form a gradient structure of dense core and porous surface, and then the template is removed. During the template removal, 1-2 mol / L hydrochloric acid solution is used to dissolve the SiO2 template at 50-70 ° C and stirred for 1-3 hours, with a solid-liquid ratio of 1:8-1:12. After washing to neutrality, it is dried to obtain a porous precursor; Step 3: Lithiation reaction: In the lithiation reaction, the lithium source is LiOH·H2O or Li2CO3, the molar ratio of Li to transition metal (Ni+Co+Mn) is 1.03-1.07, the ball-to-material ratio is 8-12:1 during ball milling, the rotation speed is 200-400 rpm, and the mixing time is 2-4 hours. The sintered porous precursor is mixed with a lithium source and subjected to high-temperature solid-phase sintering in an oxygen atmosphere. The conditions for high-temperature solid-phase sintering are: oxygen flow rate 100-300 mL / min, heating rate 5-15°C / min, sintering temperature 850-950°C, and holding time 8-12h to obtain a lithium battery positive electrode material. Step three also includes a surface modification step: mixing the primary positive electrode material with 0.5-2wt% graphene or carbon nanotubes, coating the surface by ball milling or spray drying, and then heat treating in an inert atmosphere at 300-500°C for 0.5-2h. The primary particle size of the positive electrode material is 50-100nm, the secondary particle size is 5-20μm, and the specific surface area is 60-80m 2 / g, surface porosity ≥50%, lithium ion diffusion coefficient ≥3.0×10 -10 cm 2 / s.

[0030] Through the synergistic effect of a water-ethanol dual solvent system and ultrasonic cavitation, the hydrolysis rates of different metal ions are precisely controlled, achieving uniform mixing at the atomic level and fundamentally suppressing elemental segregation. With the help of microwave selective heating and the confinement effect of a mesoporous SiO2 template, the particle size is controlled at the nanoscale (50-100nm) and a three-dimensional, interconnected gradient pore structure is constructed, significantly shortening the lithium ion diffusion path. The above-mentioned technical combination effectively improves the material's layered structural stability, interfacial compatibility, and ion / electron transport efficiency, thereby addressing the core defects of traditional processes such as low first-time Coulombic efficiency, rapid cycle capacity decay, and poor rate performance.

[0031] Example 2

[0032] See also Figure 2 , NCM622 cathode material preparation process

[0033] Process parameters and implementation details

[0034] Target material: NCM622(LiNi 0.6 Co 0.2 Mn 0.2 O2)

[0035] Core adjustments: metal ion molar ratio, template addition amount, microwave sintering temperature

[0036] Step 1: Precursor preparation (ultrasound-assisted dual-solvent co-precipitation)

[0037] Raw material preparation

[0038] Metal salt solution: Weigh Ni(NO3)2·6H2O, Co(NO3)2·6H2O, and Mn(NO3)2·4H2O (molar ratio 6:2:2), dissolve in deionized water, add ethanol (water:ethanol = 3:1) to prepare a mixed solution with a concentration of 1.2 mol / L, and stir for 30 min until clear.

[0039] Template suspension: Take 30% of the precursor mass of mesoporous SiO2 (pore size 6nm, specific surface area 900m 2 / g), and added anhydrous ethanol for ultrasonic dispersion for 30 min (40 kHz, 200 W) to form a uniform suspension.

[0040] Coprecipitation reaction

[0041] The metal salt solution and the template suspension were transferred into a reactor equipped with an ultrasonic device, kept at a constant temperature of 50° C., and turned on the ultrasonic device (30 kHz, 75 W / L).

[0042] A 2.2 mol / L NaOH solution containing 5 vol% ammonia water was added dropwise at a rate of 8 mL / min. The initial pH was maintained at 10.2 for 30 min, and then increased to 11.3 at a rate of 0.08 pH / min (total reaction time 2 h). The stirring rate was 800 rpm.

[0043] Aging and separation: After the reaction, the mixture was aged at 55 ° C for 1.5 h, centrifuged (9000 rpm, 12 min), washed with deionized water 4 times (the conductivity of the washing liquid was <8 μS / cm), washed with ethanol once, and vacuum dried at 85 ° C for 12 h to obtain Ni 0.6 Co 0.2 Mn 0.2 (OH)2SiO2 composite precursor.

[0044] Step 2: Microwave template sintering

[0045] Granulation pretreatment

[0046] The precursor was mixed with 4 wt% PVA, and wet granulated with water. The mixture was passed through an 80-mesh sieve and dried at 70° C. for 5 h to form spherical particles of 10-15 μm.

[0047] Microwave sintering and template etching

[0048] The pellets were transferred to a 2.45 GHz microwave sintering furnace, and 8 vol% water vapor (air atmosphere) was introduced. The program was set as follows:

[0049] Room temperature → 100°C (5°C / min, 0.5h) → 300°C (10°C / min, 1h) → 850°C (15°C / min, keep warm for 1.5h, water vapor flow rate 60mL / min).

[0050] Template removal: 1.5 mol / L hydrochloric acid (solid-liquid ratio 1:10) was added to the sintered product, stirred at 60 °C for 2 h, centrifuged and washed until neutral (pH = 6.5), and vacuum dried at 80 °C for 10 h to obtain a porous precursor (Ni 0.6 Co 0.2 Mn 0.2 OOH, residual carbon content 1.2 wt%).

[0051] Step 3: Lithiation reaction and surface modification

[0052] Lithium source mixing

[0053] Li2CO3 was weighed according to Li / (Ni+Co+Mn)=1.06 and mixed with the porous precursor by ball milling (ball-to-material ratio 10:1, 350 rpm, 3 h) to form a uniform mixture.

[0054] High temperature solid phase sintering

[0055] The mixture was heated to 900°C at a rate of 10°C / min in a tube furnace under an oxygen atmosphere (200 mL / min), kept at that temperature for 10 h, and passed through a 150-mesh sieve after cooling to obtain the primary product of NCM622.

[0056] Surface coating

[0057] The primary product was mixed with 1.5 wt% carbon nanotubes (CNTs) by spray drying (inlet air temperature 180°C, atomization pressure 0.3 MPa), and the resulting powder was heat-treated in argon at 400°C for 1 h to form a CNTs coating layer.

[0058] Performance test results

[0059] Physical characterization

[0060] Particle morphology: primary particles 60-90nm, secondary particles 8-15μm, specific surface area 72m 2 / g, surface porosity 55%, core porosity 15%.

[0061] Crystal structure: (003) / (104)=1.3 in the XRD pattern, no NiO impurity peak, and the layered structure integrity is 20% better than that of the traditional process.

[0062] Electrochemical performance

[0063] First coulombic efficiency: 88.5% (about 85% for traditional NCM622 process).

[0064] Cycle stability: 86% capacity retention after 500 cycles at 0.5C (75% for traditional process).

[0065] Rate performance: 10C rate discharge capacity 165mAh / g (conventional process 120mAh / g), lithium ion diffusion coefficient 3.5×10 -10 cm 2 / s(traditional technology<10 -10 cm 2 / s).

[0066] Interface impedance: 38Ω·cm 2 (Traditional coating process> 200Ω·cm 2 ), thanks to the uniform distribution of the CNTs conductive network.

[0067] Example 3

[0068] See also Figure 2 , NCM523 cathode material preparation process

[0069] Process parameters and implementation details

[0070] Target material: NCM523(LiNi0.5 Co 0.2 Mn 0.3 O2)

[0071] Core adjustments: metal ion molar ratio, microwave sintering heating rate, lithiation reaction ball milling speed

[0072] Step 1: Precursor preparation (ultrasound-assisted dual-solvent co-precipitation)

[0073] Raw material preparation

[0074] Metal salt solution: According to the molar ratio of Ni(NO3)2·6H2O, Co(NO3)2·6H2O, and Mn(NO3)2·4H2O of 5:2:3, weigh the corresponding metal salts and dissolve them in deionized water. Then add ethanol (water:ethanol volume ratio of 3:1) to prepare a metal salt solution with a concentration of 1.3 mol / L. Stir for 40 minutes until completely dissolved.

[0075] Template suspension: Weigh 25% of the precursor mass of mesoporous SiO2 (pore size 8nm, specific surface area 700m 2 / g), and anhydrous ethanol was added for ultrasonic dispersion for 40 minutes (ultrasonic frequency of 35 kHz, power of 250 W) to form a uniform template suspension.

[0076] Coprecipitation reaction

[0077] The metal salt solution and the template suspension were transferred to a reactor equipped with an ultrasonic device, the reaction temperature was maintained at 55° C., and ultrasound was turned on (ultrasonic frequency was 35 kHz, power density was 80 W / L).

[0078] A 2.3 mol / L NaOH solution containing 5 vol% ammonia was added dropwise at a rate of 6 mL / min. The initial pH was set to 10.3 and maintained for 30 minutes. The pH was then raised to 11.2 at a rate of 0.06 pH / min. The total reaction time was 2 hours and the stirring rate was 700 rpm.

[0079] Aging and separation: After the reaction, the mixture was aged at 58 ° C for 1.2 hours, then centrifuged (speed of 8500 rpm, time for 13 minutes), washed with deionized water 5 times (until the conductivity of the washing liquid is less than 9 μS / cm), washed once with ethanol, and finally dried in a vacuum drying oven at 82 ° C for 13 hours to obtain Ni 0.5 Co 0.2 Mn 0.3 (OH)2SiO2 composite precursor.

[0080] Step 2: Microwave template sintering

[0081] Granulation pretreatment

[0082] The dried composite precursor was mixed with 2 wt % of polyvinyl alcohol (PVA), and an appropriate amount of deionized water was added for wet granulation. The mixture was passed through a 70-mesh sieve and dried at 65° C. for 5.5 hours to form spherical particles of 6-18 μm.

[0083] Microwave sintering and template etching

[0084] The spherical particles were placed in a 2.45 GHz microwave sintering furnace, and an air atmosphere containing 6 vol% water vapor was introduced. The sintering program was set as follows:

[0085] The temperature was raised from room temperature to 100°C at a rate of 8°C / min and kept at this temperature for 0.5 h;

[0086] Heating was carried out from 100°C to 300°C at a rate of 10°C / min and kept at this temperature for 1 hour;

[0087] The temperature was raised from 300°C to 820°C at a heating rate of 18°C / min and kept at this temperature for 1.8 hours, during which the water vapor flow rate was controlled at 40 mL / min.

[0088] Template removal: The sintered product was added to a 1.2 mol / L hydrochloric acid solution (solid-liquid ratio of 1:9) and stirred at 55 °C for 2.5 hours to dissolve the SiO2 template. The solution was then centrifuged and washed until it became neutral (pH = 6.8). Finally, the product was dried in a vacuum drying oven at 80 °C for 11 hours to obtain a porous precursor (Ni 0.5 Co 0.2 Mn 0.3 OOH, residual carbon content is 0.8 wt%).

[0089] Step 3: Lithiation reaction and surface modification

[0090] Lithium source mixing

[0091] LiOH·H2O was weighed as a lithium source according to a molar ratio of Li / (Ni+Co+Mn)=1.04 and added into a ball mill together with the porous precursor. The ball-to-material ratio was set to 9:1, the ball milling speed was 320 rpm, and the ball milling time was 3.5 hours to ensure that the two were fully mixed.

[0092] High temperature solid phase sintering

[0093] The mixed materials were transferred to a box furnace, and heated to 920°C at a rate of 8°C / min in an oxygen atmosphere (oxygen flow rate of 150 mL / min), kept warm for 9 hours, and then cooled and passed through a 120-mesh sieve to obtain the primary NCM523 product.

[0094] Surface coating

[0095] The NCM523 primary product was mixed with 0.8 wt% graphene by planetary ball milling (rotation speed of 380 rpm, time of 40 minutes) and then heat treated in an argon atmosphere at 350 ° C for 1.5 hours to form a uniform graphene coating.

[0096] Performance test results

[0097] Physical characterization

[0098] Particle morphology: primary particle size is between 70-95nm, secondary particle size is 7-16μm, and specific surface area is 65m 2 / g, the surface porosity reaches 52% and the core porosity is 12%.

[0099] Crystal structure: The XRD pattern shows that the (003) / (104) peak intensity ratio is 1.25, and there is no obvious impurity phase peak, indicating that the material has a good layered crystal structure.

[0100] Electrochemical performance

[0101] First Coulombic efficiency: reached 87.8%, higher than the 84% of the traditional NCM523 process.

[0102] Cycling stability: After 400 cycles at a 1C rate, the capacity retention rate is 87%, while the capacity retention rate of the traditional process is about 72%.

[0103] Rate performance: The discharge capacity at 5C rate is 170mAh / g, while the traditional process is only 130mAh / g, and the lithium ion diffusion coefficient is 3.2×10 -10 cm 2 / s, which is better than the lithium ion diffusion coefficient of traditional processes.

[0104] Interface impedance: Interface impedance reduced to 42Ω·cm 2 , while the interface impedance of traditional coating process is usually greater than 220Ω·cm 2 , which is due to the good conductivity of the graphene coating.

[0105] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all details in detail, nor do they limit the invention to only the specific implementation methods described. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can better understand and utilize the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium battery, characterized in that: The following steps are involved: Step 1: Precursor preparation A nickel-cobalt-manganese metal salt is dissolved in a water-ethanol mixed solvent to form a metal salt solution, a mesoporous SiO2 template is dispersed in anhydrous ethanol to form a template suspension, the metal salt solution and the template suspension are mixed, and then a coprecipitation reaction is carried out under ultrasound assistance, and the pH value of the reaction system is controlled to gradually increase from an initial pH of 10.0-10.5 to 11.0-11.5 to obtain a metal hydroxide SiO2 composite precursor; Step 2: Microwave template sintering After the composite precursor is granulated, microwave sintering is performed in an air atmosphere containing water vapor. During the sintering process, the surface SiO2 template is etched by the water vapor to form a gradient structure of dense core and porous surface, and then the template is removed; Step 3: Lithiation reaction The sintered porous precursor is mixed with a lithium source and solid-phase sintered at high temperature in an oxygen atmosphere to obtain a lithium battery positive electrode material.

2. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: In the water-ethanol mixed solvent, the volume ratio of water to ethanol is 3:1, the concentration of the metal salt solution is 1.0-1.5 mol / L; the pore size of the mesoporous SiO2 template is 3-10 nm, and the specific surface area is 500-1000 m 2 / g, and the added amount is 20%-40% of the precursor mass.

3. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: In the coprecipitation reaction, the ultrasonic frequency is 20-40 kHz, the power density is 50-100 W / L, the reaction temperature is 40-60° C., a NaOH solution with a concentration of 2.0-2.5 mol / L is added dropwise, the initial pH is maintained for 30 minutes, and then the pH is raised to the target pH at a rate of 0.05-0.1 pH / min. The total reaction time is 1.5-2.5 hours. The NaOH solution contains 5% ammonia water by volume.

4. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: The microwave sintering conditions are as follows: microwave frequency 2.45 GHz, heating rate 10-20° C. / min, sintering temperature 700-900° C., insulation time 0.5-2 h, water vapor content in the sintering atmosphere 5%-10% by volume, and water vapor flow rate 30-80 mL / min.

5. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: In the granulation step, 1% to 5% by mass of polyvinyl alcohol is added as a granulating agent, and after wet granulation, the granules are sieved through a 60-100 mesh sieve and dried to form spherical particles of 5-20 μm.

6. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: In the template removal, a 1-2 mol / L hydrochloric acid solution is used to dissolve the SiO2 template at 50-70°C with stirring for 1-3 hours, with a solid-liquid ratio of 1:8-1:

12. The template is washed to neutrality and then dried to obtain a porous precursor.

7. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: In the lithiation reaction, the lithium source is LiOH·H2O or Li2CO3, the molar ratio of Li to transition metal (Ni+Co+Mn) is 1.03-1.07, the ball-to-material ratio during ball milling is 8-12:1, the rotation speed is 200-400 rpm, and the mixing time is 2-4 hours.

8. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: The conditions for the high-temperature solid-phase sintering are: oxygen flow rate 100-300 mL / min, heating rate 5-15° C. / min, sintering temperature 850-950° C., and holding time 8-12 h.

9. The method for preparing a positive electrode material for a lithium battery according to claim 1, wherein: The step three also includes a surface modification step: mixing the primary positive electrode material with graphene or carbon nanotubes, coating the surface by ball milling or spray drying, and then heat treating in an inert atmosphere at 300-500° C. for 0.5-2 hours; the amount of graphene or carbon nanotubes added is 0.5%-2% of the mass of the primary positive electrode material.

10. The method for preparing a positive electrode material for a lithium battery according to any one of claims 1 to 9, characterized in that: The primary particle size of the positive electrode material is 50-100 nm, the secondary particle size is 5-20 μm, and the specific surface area is 60-80 m 2 / g, surface porosity ≥50%, lithium ion diffusion coefficient ≥3.0×10 -10 cm 2 / s.

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