A method for preparing a lithium metal battery positive electrode material and a lithium metal battery

Abstract

The application relates to the technical field of batteries and discloses a preparation method of a lithium metal battery positive electrode material and a lithium metal battery. In the battery charging and discharging process, the positive electrode material provided by the application can reversibly undergo lithium ion deintercalation and redox reaction; during charging, lithium ions are deintercalated from a lithium iron phosphate crystal lattice and are embedded into a lithium metal negative electrode, Fe is oxidized into Fe; during discharging, lithium ions are deintercalated from the lithium metal negative electrode and are re-embedded into the FePO4 crystal lattice, Fe is reduced into Fe, and the mutual conversion between electric energy and chemical energy is realized. Composite doping modification replaces part of Fe in the crystal lattice with Ti, Zr, introduces crystal lattice defects, reduces the lithium ion deintercalation energy barrier, improves the lithium ion diffusion rate, the introduction of Ti and Zr elements can enhance the stability of the crystal lattice structure and inhibit the volume expansion in the charging and discharging process. 2+ 3+ 3+ 2+ 4+ 4+ 2+ ​​​​​​​

Description

Technical Field

[0001] This invention relates to a method for preparing a lithium metal battery cathode material and a lithium metal battery, which relates to the field of battery technology. It is applicable to the preparation of lithium-ion batteries and lithium metal batteries with high energy density and long cycle life, and can be widely used in electric vehicles, portable electronic devices, and large-scale energy storage power stations. Background Technology

[0002] Lithium iron phosphate (LiFePO4), as a cathode material for lithium-ion batteries, benefits from its high theoretical specific capacity (175 mAh / g) and stable operating voltage (approximately 3.2 V vs LiFePO4). + Lithium iron phosphate (LiFePO4) cathodes, with their outstanding advantages such as excellent chemical stability, low raw material cost, and environmental friendliness, have become one of the mainstream cathode materials in the fields of power batteries and energy storage batteries. With the development of new energy vehicles towards longer driving ranges and faster charging, and the increasing demands on battery cycle life for energy storage power stations, the need for performance optimization of battery systems based on lithium iron phosphate cathodes in terms of energy density, conductivity, and cycle stability is becoming increasingly urgent. Lithium metal batteries, due to the extremely high theoretical specific capacity (3860 mAh / g) and extremely low electrode potential (-3.04 V vs standard hydrogen electrode) of the lithium metal anode, have become a key technological direction for breaking through the energy density bottleneck of existing lithium-ion batteries. Combining lithium iron phosphate cathode materials with lithium metal anodes holds promise for constructing a new lithium metal battery system that combines high safety and high energy density.

[0003] The following problems still exist with existing technologies: 1. Lithium iron phosphate itself has extremely low electronic conductivity and lithium-ion diffusion coefficient, resulting in poor high-rate charge and discharge performance of the battery. In addition, during long-term cycling, the positive electrode material particles are prone to agglomeration and volume expansion, causing the electrode structure to collapse and significantly reducing the battery cycle life. 2. During the charging and discharging process of lithium metal batteries, uneven lithium deposition is prone to occur on the surface of the lithium metal negative electrode, forming lithium dendrites. The growth of lithium dendrites not only consumes electrolyte and lithium metal, leading to battery capacity decay, but may also puncture the separator and cause internal short circuits in the battery, posing serious safety hazards. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a lithium metal battery cathode material and a lithium metal battery, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: In a first aspect, this application provides a method for preparing a lithium metal battery cathode material, comprising the following steps: (1) Raw material pretreatment: Mix ammonium dihydrogen phosphate, ferric sulfate nonahydrate and citric acid in a molar ratio of 1:0.95-1.05:1.2-1.5, add deionized water to prepare a mixed solution with a concentration of 0.8-1.2 mol / L, stir at 40-50℃ for 30-60 min until completely dissolved to obtain the precursor mother liquor; (2) Composite doping modification: Add a dopant to the precursor mother liquor in step (1), wherein the dopant is a mixture of titanium source compound, zirconium source compound and copolymer compound; wherein the titanium source compound accounts for 1.5-6% of the theoretical mass of Fe element in the precursor mother liquor based on Ti element, the zirconium source compound accounts for 1.5-6% of the theoretical mass of Fe element in the precursor mother liquor based on Zr element, and the copolymer compound is poly(vinylpyrrolidone-co-acrylic acid), wherein the molar ratio of vinylpyrrolidone to acrylic acid is 2-4:1, and the molecular weight of the copolymer compound is 3000-15000, which accounts for 1.5-6% of the theoretical mass of Fe element in the precursor mother liquor; first add the titanium source compound and zirconium source compound to the precursor mother liquor, stir and disperse for 10-15 min, then add the above copolymer compound, continue to stir and disperse for 15-25 min until the system is uniform, and then adjust the pH value of the system to 4.5-5.5 with ammonia water; (3) Sol-gel preparation: Transfer the mixed solution after pH adjustment in step (2) to a constant temperature water bath, keep it at 60-70℃ and stir for 120-180 min to form a uniform and viscous sol, continue to heat to 80-90℃ and keep it at 80-90℃ for 4-6 h to obtain a dry gel; (4) Drying treatment: The dry gel described in step (3) is placed in a vacuum drying oven and dried at 105-120℃ for 8-12 hours to remove residual moisture and volatile impurities, and the dried precursor is obtained; (5) Segmented sintering: The dried precursor is placed in a tube furnace and pre-sintered at 350-400°C at a heating rate of 5-8°C / min under inert gas protection for 2-3 hours. Then, the temperature is raised to 750-850°C at a heating rate of 3-5°C / min and held for 4-6 hours for high-temperature sintering. After natural cooling to room temperature, the primary lithium metal battery cathode material is obtained. (6) Post-processing: The primary lithium metal battery cathode material is placed in a planetary ball mill, with ethanol as the dispersion medium, a ball-to-material ratio of 10-15:1, a rotation speed of 200-300 r / min, and ball milled for 2-4 h. Then, it is vacuum dried at 80-100℃ for 6-8 h to obtain the lithium metal battery cathode material.

[0006] Further, the titanium source compound in step (2) is at least one of tetrabutyl titanate and titanium isopropoxide, and the zirconium source compound is at least one of zirconium oxychloride and zirconium nitrate.

[0007] Further, the inert gas in step (5) is nitrogen or argon, the gas flow rate is 200-300 mL / min, and the grinding media of the planetary ball mill in step (6) is zirconia balls with a diameter of 3-5 mm.

[0008] Furthermore, the method for synthesizing the poly(vinylpyrrolidone-co-acrylic acid) includes the following steps: Step 1: Monomer pretreatment. Acrylic acid is treated with an alkaline solution to remove polymerization inhibitors, washed with water until neutral, and then purified by distillation. Vinylpyrrolidone is treated with a chromatography column to remove polymerization inhibitors, and the purified monomers are collected for later use. Step 2: Weigh the monomers according to the molar ratio of vinylpyrrolidone to acrylic acid 3:1, take 0.5%-1.5% of the total monomer mass of ammonium persulfate as an initiator, and 1-3 times the total monomer mass of deionized water; add deionized water to the reaction vessel, install stirring, condensation and nitrogen devices, and place it in a temperature control device; Step 3: Add the purified monomer to the reaction vessel, stir until dissolved, and then introduce nitrogen gas to remove oxygen from the system. Step 4: Dissolve the initiator in deionized water and add it dropwise to the reaction system under nitrogen protection. Heat the mixture to 65-75℃ and maintain stirring and nitrogen atmosphere for 4-6 hours. Step 5: After the reaction is complete, stop heating and continue to purge with nitrogen until the system cools down to obtain an aqueous solution of poly(vinylpyrrolidone-co-acrylic acid); Step 6: Add the above aqueous solution to 3-7 times its volume of anhydrous ethanol, stir to precipitate, let stand and separate the precipitate, and wash it several times with anhydrous ethanol. Step 7: Place the washed precipitate in a vacuum drying oven and dry it at 50-70℃ to obtain solid powder poly(vinylpyrrolidone-co-acrylic acid).

[0009] In a second aspect, this application also provides a lithium metal battery, which includes a positive electrode material prepared according to the lithium metal battery positive electrode material preparation method of the first aspect above, characterized in that it includes a positive electrode, a negative electrode, an electrolyte, a separator and a battery casing. The positive electrode is made by mixing the positive electrode material of the lithium metal battery with a binder and a conductive agent in a mass ratio of 80-85:5-8:5-7 and then coating it onto the surface of an aluminum foil current collector. The negative electrode is a lithium metal foil with a thickness of 50-100μm; The electrolyte is a homogeneous solution formed by dissolving lithium salt in an organic solvent; the diaphragm is a polypropylene / polyethylene composite porous diaphragm.

[0010] Furthermore, the lithium salt in the electrolyte is a mixture of lithium bis(trifluoromethanesulfonylimide) and lithium hexafluorophosphate, with a molar ratio of 1:0.5-1.0, and the concentration of the lithium salt in the electrolyte is 1.0-1.5 mol / L.

[0011] Furthermore, the organic solvent in the electrolyte is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1 to 1:2:2.

[0012] Furthermore, the binder is polyvinylidene fluoride or sodium carboxymethyl cellulose, and the conductive agent is at least one of conductive carbon black and carbon nanotubes.

[0013] Furthermore, the diaphragm has a pore size of 0.1-1.0 μm, a thickness of 10-20 μm, and a porosity of 40-60%. The battery casing is an aluminum-plastic composite film soft-pack casing. The battery's nominal voltage is 3.2-3.3V, and its operating temperature range is -20℃ to 60℃.

[0014] The present invention has the following beneficial effects: (1) This invention employs a synergistic composite modification technology of titanium, zirconium, and poly(vinylpyrrolidone-co-acrylic acid) copolymer (PVPAA). Titanium introduces defects through lattice substitution, and the amorphous carbon layer formed by the high-temperature transformation of the copolymer constructs a continuous electronic conduction network. The two work synergistically, combined with the optimization effect of segmented sintering on the crystal structure, to significantly improve the electronic conductivity of the cathode material, which can reach 1.2 × 10⁻⁶. -2 -3.2×10 -2 The S / cm ratio is increased by 2-3 orders of magnitude compared to undoped materials, effectively improving the battery's high-rate charge and discharge performance.

[0015] (2) The composite doping of titanium and zirconium in this invention can suppress lattice distortion during lithium ion insertion and extraction. The coordination anchoring effect of poly(vinylpyrrolidone-co-acrylic acid) ensures uniform distribution of doped elements and further enhances lattice stability. At the same time, the steric hindrance effect of the copolymer and the ball milling post-treatment work together to refine the material particles, and the particle size is controlled at 0.5-2μm, reducing agglomeration and volume expansion, so that the cathode material can still maintain the complete electrode structure after long-term cycling, significantly improving the battery capacity retention rate.

[0016] (3) In this invention, the synergistic modification of the cathode material and the optimized electrolyte system form a good match. The stable structure on the cathode side reduces interfacial side reactions and indirectly assists the electrolyte in forming a uniform, dense and highly ionicly conductive SEI film on the surface of the lithium metal anode. This effectively regulates the uniform deposition of lithium ions, inhibits the growth of lithium dendrites, and significantly improves the battery safety performance.

[0017] (4) The carbon layer derived from poly(vinylpyrrolidone-co-acrylic acid) can reduce the interface impedance of the positive electrode. Combined with the synergistic effect of the multi-electrolyte and the composite lithium salt in the electrolyte, it can further reduce the interfacial side reactions between the positive and negative electrodes and the electrolyte, reduce the charge transfer impedance, and significantly improve the battery reaction kinetics performance.

[0018] (5) Titanium and zirconium doping broadens the lithium-ion diffusion channel, and copolymer-assisted grain refinement shortens the ion transport path. The two and the electrolyte solvent ratio are optimized to form a synergistic effect, which effectively improves the ion transport capability of lithium iron phosphate at low temperature, and improves the discharge specific capacity of lithium metal battery at -20℃, thus solving the technical problem of poor low temperature performance of traditional lithium metal battery.

[0019] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the lithium metal battery structure provided by the present invention; Figure 2 The graphs show the cycle performance of lithium metal batteries assembled in Example 1 (curve A) and Comparative Example 1 (curve B) of the present invention. Figure 3 The image shows a scanning electron microscope (SEM) image of the surface morphology of the lithium metal battery negative electrode prepared according to an embodiment of the present invention. Figure 3 (a) is a scanning electron microscope (SEM) image of the surface morphology of the lithium metal battery negative electrode prepared in Example 2 of the present invention before cycling. Figure 3 (b) is a scanning electron microscope (SEM) image of the surface morphology of the lithium metal battery negative electrode prepared in Example 2 of the present invention after cycling. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Please see Figures 1-3As shown, the present invention relates to a method for preparing a positive electrode material for a lithium metal battery and a lithium metal battery.

[0024] Please see Figures 1-3 As shown, in a first aspect, the present invention provides a method for preparing a lithium metal battery cathode material, comprising the following steps: (1) Raw material pretreatment: Mix ammonium dihydrogen phosphate, ferric sulfate nonahydrate and citric acid in a molar ratio of 1:0.95-1.05:1.2-1.5, add deionized water to prepare a mixed solution with a concentration of 0.8-1.2 mol / L, stir at 40-50℃ for 30-60 min until completely dissolved to obtain the precursor mother liquor.

[0025] (2) Composite doping modification: Add a dopant to the precursor mother liquor in step (1). The dopant is a mixture of titanium source compound, zirconium source compound and copolymer compound. The titanium source compound accounts for 1.5-6% of the theoretical mass of Fe in the precursor mother liquor based on Ti element, the zirconium source compound accounts for 1.5-6% of the theoretical mass of Fe in the precursor mother liquor based on Zr element, and the copolymer compound is poly(vinylpyrrolidone-co-acrylic acid). The molar ratio of vinylpyrrolidone to acrylic acid is 2-4:1, and the molecular weight of the copolymer compound is 3000-15000, which accounts for 1.5-6% of the theoretical mass of Fe in the precursor mother liquor. First, add the titanium source compound and zirconium source compound to the precursor mother liquor and stir and disperse for 10-15 min. Then add the above copolymer compound and continue to stir and disperse for 15-25 min until the system is uniform. Then adjust the pH value of the system to 4.5-5.5 with ammonia water. (3) Sol-gel preparation: Transfer the mixed solution after pH adjustment in step (2) to a constant temperature water bath, keep it at 60-70℃ and stir for 120-180 min to form a uniform and viscous sol, continue to heat to 80-90℃ and keep it at 80-90℃ for 4-6 h to obtain a dry gel.

[0026] (4) Drying treatment: Place the dry gel from step (3) in a vacuum drying oven and dry it at 105-120℃ for 8-12 hours to remove residual moisture and volatile impurities, and obtain the dried precursor.

[0027] (5) Segmented sintering: The dried precursor is placed in a tube furnace and pre-sintered at 350-400°C at a heating rate of 5-8°C / min under inert gas protection for 2-3 hours. Then, the temperature is raised to 750-850°C at a heating rate of 3-5°C / min and held for 4-6 hours for high-temperature sintering. After natural cooling to room temperature, the primary lithium metal battery cathode material is obtained. The inert gas is nitrogen or argon and the gas flow rate is 200-300 mL / min.

[0028] (6) Post-processing: The primary lithium metal battery cathode material is placed in a planetary ball mill, with ethanol as the dispersion medium, a ball-to-material ratio of 10-15:1, a rotation speed of 200-300 r / min, and ball milled for 2-4 h. Then, it is vacuum dried at 80-100℃ for 6-8 h to obtain the lithium metal battery cathode material. The grinding medium of the planetary ball mill is zirconium oxide balls with a diameter of 3-5 mm.

[0029] The specific synthesis steps of poly(vinylpyrrolidone-co-acrylic acid) are as follows: Step 1: Monomer pretreatment. Add 5% sodium hydroxide solution to acrylic acid, stir, and let stand to separate the layers. Discard the lower aqueous phase. Repeat twice. Wash with deionized water until neutral. Collect the fraction by vacuum distillation and store in the dark. Pass vinylpyrrolidone through a neutral alumina chromatography column and collect the eluent for later use.

[0030] Step 2: Weigh 100g of monomers at a molar ratio of vinylpyrrolidone to acrylic acid of 3:1, take 1.0% of the total monomer mass of ammonium persulfate as an initiator, and twice the total monomer mass of deionized water; add deionized water to a 250mL three-necked flask, install a mechanical stirrer, reflux condenser and nitrogen delivery tube, and place it in a constant temperature water bath.

[0031] Step 3: Add the weighed monomer to the flask, stir until completely dissolved, and then purge with high-purity nitrogen for 30 minutes to remove oxygen from the system.

[0032] Step 4: Dissolve ammonium persulfate in 10 mL of deionized water, and drop it into the flask through a constant pressure dropping funnel over 10 min under nitrogen protection. Heat the mixture to 70 °C and maintain stirring and nitrogen atmosphere for 4 h.

[0033] Step 5: After the reaction is complete, turn off the heating and continue to purge with nitrogen until the system cools to room temperature to obtain an aqueous solution of P(VP-co-AA).

[0034] Step 6: Slowly pour the aqueous solution into 5 times its volume of anhydrous ethanol, stir for 30 minutes to precipitate, let stand for 1 hour, filter and collect the precipitate, and wash it 3 times with anhydrous ethanol.

[0035] Step 7: Place the washed precipitate in a vacuum drying oven and dry it at 60°C for 12 hours to obtain a white solid powder P(VP-co-AA).

[0036] It should be noted that the cathode material prepared by this invention does not contain lithium in its initial state; it is essentially a lithium-intercalating iron-phosphate cathode material. Since the negative electrode of the battery uses lithium metal, the lithium source is provided by the negative electrode. During the first discharge process after battery assembly, the lithium metal negative electrode undergoes an oxidation reaction and releases lithium ions. These lithium ions migrate to the positive electrode side via the electrolyte and intercalate into the lattice of the lithium-free iron-phosphate cathode material, causing in-situ lithiation of the cathode material to generate the lithium iron phosphate active phase. Therefore, this invention eliminates the need to introduce an additional lithium source during the cathode material preparation stage, enabling the lithiation of the cathode active material to be completed during the first electrochemical process using a lithium metal negative electrode.

[0037] The cathode material prepared by this invention undergoes reversible lithium-ion intercalation / deintercalation and redox reactions during battery charging and discharging. During charging, lithium ions are extracted from the lithium iron phosphate lattice and intercalated into the lithium metal anode, while Fe... 2+ Oxidized to Fe 3+ During discharge, lithium ions are extracted from the lithium metal anode and re-inserted into the FePO4 lattice. 3+ Reduced to Fe 2+ This enables the interconversion of electrical energy and chemical energy.

[0038] Composite doping modification via Ti 4+ Zr 4+ Partial Fe in the lattice 2+ On the one hand, the introduction of lattice defects reduces the lithium-ion insertion / extraction energy barrier and increases the lithium-ion diffusion rate. On the other hand, the introduction of Ti and Zr elements can enhance the stability of the lattice structure and suppress volume expansion during charging and discharging. The conductive carbon network formed by the decomposition of citric acid during sintering works synergistically with the doping elements to construct a continuous electron transport channel, significantly improving the electronic conductivity of the material and improving the electrode reaction kinetics.

[0039] Please see Figures 1-3 As shown, in a second aspect, according to the first aspect above, the present invention also provides a lithium metal battery, including a positive electrode, a negative electrode, an electrolyte, a separator, and a battery casing. The battery casing is an aluminum-plastic composite film soft-pack casing. The nominal voltage of the battery is 3.2-3.3V, and the operating temperature range is -20℃ to 60℃.

[0040] The positive electrode is made by mixing the positive electrode material of lithium metal battery with binder and conductive agent in a mass ratio of 80-85:5-8:5-7 and coating it onto the surface of aluminum foil current collector. The binder is polyvinylidene fluoride (PVDF) or sodium carboxymethyl cellulose (CMC), and the conductive agent is at least one of conductive carbon black (SuperP) and carbon nanotubes (CNTs).

[0041] The negative electrode is a lithium metal foil with a thickness of 50-100μm.

[0042] The electrolyte is a homogeneous solution of lithium salt dissolved in an organic solvent. The lithium salt in the electrolyte is a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate (LiPF6) in a molar ratio of 1:0.5-1.0. The concentration of lithium salt in the electrolyte is 1.0-1.5 mol / L. The organic solvent in the electrolyte is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1-1:2:2.

[0043] The diaphragm is a polypropylene / polyethylene composite porous diaphragm with a pore size of 0.1-1.0 μm, a thickness of 10-20 μm, and a porosity of 40-60%.

[0044] It should be noted that the working process of a lithium metal battery is based on the oxidation reaction of the lithium metal anode and the reduction reaction of the lithium iron phosphate cathode. During discharge, the lithium metal anode undergoes an oxidation reaction: Li-e - →Li + The generated lithium ions migrate to the positive electrode through the electrolyte and membrane; a reduction reaction occurs at the positive electrode: FePO4 + Li + +e - →LiFePO4, to achieve the discharge process. During charging, the electrode reaction proceeds in reverse. Lithium ions are extracted from the positive electrode and migrate to the negative electrode, where they are reduced and deposited as lithium metal on the surface of the negative electrode.

[0045] In accordance with the above two aspects, the present invention also provides an embodiment.

[0046] Implementation Plan (1) Equipment and reagents for preparing cathode materials a. Equipment: electronic balance (accuracy 0.0001g), constant temperature water bath, magnetic stirrer, ultrasonic disperser, vacuum drying oven, tube furnace, planetary ball mill, X-ray diffractometer (XRD), scanning electron microscope (SEM), laser particle size analyzer.

[0047] b. Reagents: Ammonium dihydrogen phosphate (NH4H2PO4, purity 99.7%), ferric sulfate nonahydrate (Fe2(SO4)39H2O, purity 99.5%), citric acid (C6H8O7, purity 99.8%), tetrabutyl titanate (C 16 H 36O4Ti (98% purity), zirconium oxychloride (ZrOCl2·8H2O, 99% purity), ammonia (25% mass concentration), ethanol (anhydrous, 99.9% purity), deionized water, vinylpyrrolidone (VP, ≥99.0% purity), acrylic acid (AA, ≥99.0% purity), ammonium persulfate (APS, ≥98.0% purity), sodium hydroxide (NaOH, ≥96.0% purity), and neutral alumina (100-200 mesh).

[0048] (2) Cathode material preparation steps a. Raw material pretreatment: Accurately weigh 11.50 g (0.1 mol) of NH4H2PO4, 27.80 g (0.1 mol) of FeSO47H2O, and 21.01 g (0.12 mol) of citric acid. Add 200 mL of deionized water and place in a 45°C constant temperature water bath. Stir magnetically for 45 min to obtain a transparent precursor mother liquor.

[0049] b. Composite doping modification: Weigh 0.52 g of tetrabutyl titanate (3.0% of the theoretical mass of Fe based on Ti) and 0.38 g of zirconium oxychloride (2.4% of the theoretical mass of Fe based on Zr). Dilute with 10 mL of ethanol and slowly drop into the precursor mother liquor. Disperse by sonication for 10 min. Then add 0.2 g of poly(vinylpyrrolidone-co-acrylic acid) (PVPAA, VP to AA molar ratio 3:1, molecular weight 5000-10000) and continue stirring and dispersing for 20 min until the system is uniformly mixed. Adjust the pH of the system to 5.0 with 25% ammonia water. After adjustment, continue stirring for 15 min to obtain the doped and modified mixture.

[0050] c. Sol-gel preparation: The mixed solution was transferred to a 65°C constant temperature water bath and stirred for 150 min to form a viscous sol. The temperature was then raised to 85°C and kept at that temperature for 5 h to evaporate the sol and obtain a dry gel.

[0051] d. Drying treatment: The dried gel was placed in a vacuum drying oven and dried at -0.09 MPa and 110℃ for 10 h to obtain the dried precursor powder.

[0052] e. Segmented sintering: The precursor powder is loaded into an alumina crucible, placed in a tube furnace, and argon gas is introduced (flow rate 250 mL / min). The temperature is increased to 380℃ at 6℃ / min and held for 2.5 h. The temperature was then increased to 800℃ at a rate of 4℃ / min, held for 5 hours, and then naturally cooled to room temperature to obtain the primary lithium metal battery cathode material.

[0053] f. Post-processing: The primary material was placed in a planetary ball mill, 50 mL of ethanol was added, the ball-to-material ratio was 12:1, the speed was 250 r / min, and the milling was carried out for 3 h. Then, it was vacuum dried at 90 °C for 7 h to obtain lithium metal battery cathode material. The average particle size was 1.2 μm according to laser particle size analysis.

[0054] (3) Lithium metal battery assembly equipment and reagents a. Equipment, including argon glove box, coating machine, vacuum drying oven, roller press, battery packaging machine, Blue Electric battery testing system, and electrochemical workstation.

[0055] b. Reagents: Polyvinylidene fluoride (PVDF), conductive carbon black (SuperP), carbon nanotubes (CNTs), N-methylpyrrolidone (NMP), lithium metal foil (99.9% purity), polypropylene / polyethylene composite membrane, lithium bis(trifluoromethanesulfonylimide) (LiTFSI, 99.9% purity), lithium hexafluorophosphate (LiPF6, 99.9% purity), ethylene carbonate (EC, 99.9% purity), dimethyl carbonate (DMC, 99.9% purity), ethyl methyl carbonate (EMC, 99.9% purity), aluminum foil current collector (18μm thickness), aluminum-plastic composite film.

[0056] (4) Lithium metal battery assembly steps a. Preparation of positive electrode sheet, First, weigh the positive electrode material, PVDF, SuperP and CNTs mixture (1:1) in a mass ratio of 82:6:6. Dissolve PVDF in NMP and stir for 30 minutes until completely dissolved. Add the conductive agent and stir for 45 minutes. Then add the positive electrode material and stir for 150 minutes to form a uniform slurry. Then, the slurry was coated onto the surface of the aluminum foil current collector to a thickness of 100 μm, vacuum dried at 120℃ for 14 h, and then cut into positive electrode sheets with a diameter of 14 mm after being pressed by a 6 MPa pressure roller, with a compaction density of 2.1 g / cm³. 3 .

[0057] b. Electrolyte preparation: In an argon glove box, weigh LiTFSI and LiPF6 at a molar ratio of 1:0.8 and add them to a mixed solvent with a volume ratio of EC:DMC:EMC=1:1.5:1.5. Stir for 45 min until completely dissolved to obtain a 1.2 mol / L electrolyte.

[0058] c. Battery assembly: First, in an argon-filled glove box, lay the aluminum-plastic film shell flat, place the positive electrode plate inside, add 60 μL of electrolyte and soak for 5 minutes, cover with the separator and add 20 μL of electrolyte. Then, place the lithium metal negative electrode sheet (15mm in diameter), install the positive and negative electrode tabs, heat seal it for 5 seconds at 130℃ and 0.4MPa pressure using a packaging machine, and let it stand for 18 hours to complete the battery assembly.

[0059] (5) Performance testing methods a. Crystal structure testing: XRD instrument with CuKα rays, scanning range 10°-80°, scanning rate 5° / min, was used to analyze the crystal structure of the material.

[0060] b. Microscopic morphology testing: SEM instrument was used with an accelerating voltage of 10kV to observe the morphology of material particles and the surface state of lithium metal anode.

[0061] c. Electrochemical performance testing was conducted using the Blue Battery testing system. At 25°C, the battery was charged and discharged at a rate of 0.2C (charging cutoff voltage 3.6V, discharging cutoff voltage 2.0V) to test the initial charge-discharge specific capacity and cycle performance. Low-temperature discharge performance was tested at -20°C and a rate of 0.2C using an electrochemical workstation with a frequency range of 10... -2 -10 5 Hz, AC amplitude 5mV, to test the electrochemical impedance spectroscopy (EIS) of the battery.

[0062] Based on the above two aspects and implementation schemes, the present invention also provides the following embodiments and comparative examples.

[0063] Example 1

[0064] In this embodiment, tetrabutyl titanate and zirconium oxychloride are used as composite dopants to prepare lithium metal battery cathode materials and assemble lithium metal batteries. The specific parameters are as follows: (I) Cathode material preparation parameters a. Raw material molar ratio: NH4H2PO4:FeSO47H2O:citric acid = 1:1.0:1.3; b. Doping amount: Ti accounts for 3.6% of the theoretical mass of Fe, Zr accounts for 1.8%, and poly(vinylpyrrolidone-co-acrylic acid) accounts for 3.0%; c. Sol-gel temperature: 60℃, holding time: 180min, drying temperature: 115℃, drying time: 9h; d. Segmented sintering parameters: First stage 350℃, holding for 3h; Second stage 780℃, holding for 5.5h; e. Post-processing parameters: ball-to-material ratio 13:1, rotation speed 280 r / min, ball milling time 2.5 h, drying temperature 95 ℃, drying time 6.5 h.

[0065] (II) Parameters of Lithium Metal Batteries a. Positive electrode formulation: Positive electrode material:PVDF:SuperP:CNTs=83:5:6:6 (mass ratio); b. Electrolyte parameters: LiTFSI:LiPF6 = 1:0.7 (molar ratio), concentration 1.3 mol / L; solvent EC:DMC:EMC = 1:1:1 (volume ratio). c. Separator: PP / PE composite separator, 15μm thick, 50% porosity; d. Negative electrode: Lithium metal foil, 70μm thick.

[0066] (III) Performance Test Results a. Positive electrode material properties: Electronic conductivity 2.8 × 10⁻⁶ -2 S / cm, lithium-ion diffusion coefficient 8.5×10 -11 cm 2 / s, average particle size 1.0μm; b. Battery electrochemical performance: 0.2C initial discharge specific capacity 170mAh / g, coulombic efficiency 98.5%; 1C rate discharge specific capacity 158mAh / g, capacity retention after 1000 cycles 93.5%; -20℃ discharge specific capacity 149.5mAh / g (87.9% of room temperature capacity); charge transfer impedance 38Ω.

[0067] It should be noted that, in this embodiment, for the composite doping modification requirements of lithium metal battery cathode materials, poly(vinylpyrrolidone-co-acrylic acid) needs to have precise molecular weight control (5000-10000), a uniform copolymer structure, and strong coordination ability in order to achieve Ti 4+ Zr 4+ The anchoring dispersion and subsequent carbon layer coating are crucial. The core of the synthesis lies in: removing polymerization-inhibiting impurities through monomer pretreatment, controlling the polymerization rate by adjusting the amount of initiator and the reaction temperature, ensuring polymer purity through precipitation purification, and finally obtaining a functional copolymer adapted to the doping system. The synthesis process of poly(vinylpyrrolidone-co-acrylic acid) requires the determination of reagents and equipment in the early stage.

[0068] (a) Selection of reagents: Vinylpyrrolidone (VP, purity ≥99.0%): Provides N coordination sites, enhancing the binding force of metal ions; Acrylic acid (AA, purity ≥99.0%): provides carboxyl coordination sites to regulate the affinity-reluctance balance of the copolymer; Ammonium persulfate (APS, purity ≥98.0%): a water-soluble free radical initiator, suitable for aqueous solution polymerization systems; Sodium hydroxide (NaOH, purity ≥96.0%): used for the removal of acrylic acid polymerization inhibitors; Neutral alumina (100-200 mesh): used for impurity removal in vinylpyrrolidone chromatography; Anhydrous ethanol (purity ≥99.9%): precipitant to ensure effective polymer separation; Deionized water: a medium for polymerization reactions, with a conductivity ≤10μS / cm.

[0069] (II) Equipment Selection: 250mL three-necked flask (with standard ground glass joint, compatible with stirring, condensing and venting devices); Mechanical stirrer (speed range 0-500r / min, to ensure system homogeneity); Reflux condenser (spherical shape, effectively preventing monomer volatilization); Constant pressure dropping funnel (50mL, for precise control of initiator dropping rate); Constant temperature water bath (temperature control accuracy ±1℃, ensuring stable polymerization temperature); Vacuum drying oven (temperature control accuracy ±2℃, ultimate pressure ≤-0.095MPa); Buchner funnel and suction flask (with matching filter paper, used for sedimentation separation); Chromatography column (2cm inner diameter, 30cm length, used for VP purification).

[0070] The specific synthesis process of poly(vinylpyrrolidone-co-acrylic acid) is as follows: First, monomer pretreatment removes key impurities: Acrylic acid (AA) purification: Take 50 mL of acrylic acid and place it in a 100 mL separatory funnel. Add an equal volume of 5 wt% NaOH aqueous solution, shake vigorously for 5 min, and let stand to separate the layers. Discard the lower aqueous phase (containing the polymerization inhibitor hydroquinone). Repeat this alkaline washing operation twice, and then wash with deionized water until the pH of the aqueous phase is 7.0. Transfer the purified acrylic acid to a distillation flask and distill under reduced pressure at 60 °C and -0.09 MPa. Collect the distillate and store it in a sealed container away from light (to prevent self-polymerization).

[0071] Vinylpyrrolidone (VP) purification: Pack neutral alumina into a chromatography column and pre-wash the column bed with deionized water until the eluent is clear; slowly pour 50 mL of VP into the top of the column, controlling the flow rate at 1-2 drops / second, collect the eluent (to remove the polymerization inhibitor), and seal for later use.

[0072] Secondly, the polymerization reaction allows for precise control of molecular weight and tool structure: Ingredient calculation: Weigh 10.0g of mixed monomers (7.8g of VP and 2.2g of AA) at a molar ratio of VP to AA of 3:1; the amount of initiator APS is 1.0% of the total monomer mass (i.e., 0.1g); the amount of deionized water is twice the total monomer mass (i.e., 20.0mL).

[0073] Reaction system setup: Add 20.0 mL of deionized water to a 250 mL three-necked flask, install a mechanical stirrer, reflux condenser and nitrogen delivery tube in sequence, and place it in a constant temperature water bath; turn on the stirrer (200 r / min), and introduce high-purity nitrogen (purity ≥99.99%) for 30 min to completely remove oxygen from the system (to avoid oxygen inhibiting polymerization).

[0074] Addition of monomers and initiators: Slowly inject the purified mixed monomers into the flask and stir for 10 min until completely dissolved; dissolve 0.1 g APS in 5 mL of deionized water, transfer it to a constant pressure dropping funnel, and add it dropwise into the reaction system at a uniform rate over 10 min under nitrogen protection.

[0075] Polymerization conditions control: Heat to 70℃, maintain stirring speed of 250r / min, and continuously introduce nitrogen atmosphere for 4h reaction; observe the viscosity change of the system during the process, and stop heating when the solution becomes uniformly viscous, continue to introduce nitrogen atmosphere until the system cools to room temperature to obtain PVPAA aqueous solution.

[0076] Then, purification and drying are performed to ensure the purity and morphology of the polymer: Precipitation separation: Slowly pour the cooled PVPAA aqueous solution into 5 times the volume (about 125 mL) of anhydrous ethanol, turn on magnetic stirring (300 r / min) for 30 min, and a white flocculent precipitate will be formed; let stand for 1 h to allow the precipitate to settle completely, and collect the precipitate by vacuum filtration using a Buchner funnel.

[0077] Washing and impurity removal: The precipitate was washed three times with anhydrous ethanol, 50 mL each time, and stirred for 10 min before filtration to remove unreacted monomers and residual initiators.

[0078] Drying and shaping: The washed precipitate was transferred to a vacuum drying oven, and the temperature was set to 60℃ and the pressure to -0.09MPa for 12 hours. After drying, a white solid powder PVPAA was obtained and sealed for storage.

[0079] Finally, molecular weight verification was performed: the molecular weight of the polymer was tested by gel permeation chromatography (GPC) with N,N-dimethylformamide (DMF) as the mobile phase, a flow rate of 1.0 mL / min, and a column temperature of 30 °C. The number average molecular weight of the target product was controlled within the range of 5000-10000, and the dispersity was ≤1.8 to ensure its uniform dispersion and coordination efficiency in the doped system.

[0080] Example 2

[0081] This embodiment uses titanium isopropoxide and zirconium nitrate as composite dopants to prepare lithium metal battery cathode materials and assemble lithium metal batteries. The specific parameters are as follows: (I) Cathode material preparation parameters 1. Raw material molar ratio: NH4H2PO4:FeSO47H2O:citric acid = 1:1.05:1.4; 2. Doping amount: Ti accounts for 5.4% of the theoretical mass of Fe, Zr accounts for 3.6%, and poly(vinylpyrrolidone-co-acrylic acid) accounts for 3.6%; 3. Sol-gel temperature: 70℃, holding time: 120 min; drying temperature: 120℃, drying time: 8 h; 4. Segmented sintering parameters: First stage 400℃, holding for 2 hours; Second stage 820℃, holding for 4.5 hours; 5. Post-processing parameters: ball-to-material ratio 14:1, rotation speed 220 r / min, ball milling time 3.5 h; drying temperature 100℃, drying time 6 h.

[0082] (II) Parameters of Lithium Metal Batteries 1. Positive electrode formulation: Positive electrode material: CMC: SuperP: CNTs = 84:7:5:4 (mass ratio); 2. Electrolyte parameters: LiTFSI:LiPF6 = 1:0.9 (molar ratio), concentration 1.4 mol / L; solvent EC:DMC:EMC = 1:2:2 (volume ratio). 3. Separator: PP / PE composite separator, 18μm thick, 55% porosity; 4. Negative electrode: Lithium metal foil, 90μm thick.

[0083] (III) Performance Test Results 1. Positive electrode material properties: Electronic conductivity 3.2 × 10⁻⁶ -2 S / cm, lithium-ion diffusion coefficient 9.2×10 -11 cm 2 / s, average particle size 0.8μm; 2. Battery electrochemical performance: 0.2C initial discharge specific capacity 172 mAh / g, coulombic efficiency 98.8%, 1C rate discharge specific capacity 161 mAh / g, capacity retention after 1000 cycles 94.2%, -20℃ discharge specific capacity 153.8 mAh / g (89.4% of room temperature capacity); charge transfer impedance 35 Ω. Please refer to [link / reference]. Figure 3 , Figure 3 (a) is a scanning electron microscope (SEM) image of the surface morphology of the lithium metal battery negative electrode prepared in this embodiment before cycling. Figure 3 (b) Scanning electron microscope (SEM) image of the surface morphology of the lithium metal battery anode prepared in this embodiment after cycling.

[0084] Example 3

[0085] Compared to Example 1, except that in the b. composite doping modification sub-step of (2) cathode material preparation step, the amount of PVPAA is reduced to 0.15g, all other steps are the same as in Example 1.

[0086] Comparative Example 1

[0087] To verify the superiority of the technical solution of the present invention, comparative example 1 is set up, with the following specific parameters: a. Cathode material: No dopants were added, and the other preparation parameters were the same as in Example 1; b. Electrolyte: Single LiPF6 lithium salt, concentration 1.0 mol / L, solvent EC:DMC = 1:1 (volume ratio); c. The remaining battery parameters are the same as in Example 1.

[0088] Performance test results: Electronic conductivity of the cathode material is 3.5 × 10⁻⁶. -9 S / cm, the battery's initial discharge capacity at 0.2C is 158mAh / g, the capacity retention rate after 1000 cycles is 72.3%, the discharge capacity at -20℃ is 110.6mAh / g (70.0% of the room temperature capacity), the charge transfer impedance is 85Ω, and obvious lithium dendrites appear on the surface of the lithium metal anode after cycling.

[0089] Comparative Example 2

[0090] To verify the superiority of the technical solution of the present invention, a comparative example 2 is also provided, with the following specific parameters:

[0091] a. Cathode material: Only Ti dopant was added (Ti element accounts for 3.6% of Fe element mass), without Zr and poly(vinylpyrrolidone-co-acrylic acid), and the other preparation parameters were the same as in Example 1; b. The electrolyte parameters are the same as in Example 1; c. The remaining battery parameters are the same as in Example 1.

[0092] Performance test results: Electronic conductivity of the cathode material is 1.2 × 10⁻⁶. -5 S / cm, battery initial discharge specific capacity at 0.2C is 143mAh / g, capacity retention after 1000 cycles is 70.6%, discharge specific capacity at -20℃ is 100.1mAh / g (69.9% of room temperature capacity), charge transfer impedance is 78Ω.

[0093] Comparative Example 3

[0094] To verify the superiority of the technical solution of the present invention, comparative example 3 is also provided, with the following specific parameters: a. Cathode material: Only Zr dopant was added (Zr element accounts for 1.8% of Fe element mass), without Ti and poly(vinylpyrrolidone-co-acrylic acid), and the other preparation parameters were the same as in Example 1; b. The electrolyte parameters are the same as in Example 1; c. The remaining battery parameters are the same as in Example 1.

[0095] Performance test results: Electronic conductivity of the cathode material is 8.5 × 10⁻⁶. -6 S / cm, battery initial discharge specific capacity at 0.2C is 152mAh / g, capacity retention after 1000 cycles is 62.5%, discharge specific capacity at -20℃ is 106.4mAh / g (70.0% of room temperature capacity), and charge transfer impedance is 81Ω.

[0096] Comparative Example 4

[0097] To verify the superiority of the technical solution of the present invention, comparative example 4 is also provided, with the following specific parameters: a. Positive electrode material: Add Ti and Zr dopants (same as in Example 1), without poly(vinylpyrrolidone-co-acrylic acid), use equal amounts and proportions of commercially available polyvinylpyrrolidone and polyacrylic acid with a molecular weight of 5000 to replace PVPAA, and the remaining preparation parameters are the same as in Example 1; b. The electrolyte parameters are the same as in Example 1; c. The remaining battery parameters are the same as in Example 1.

[0098] Performance test results: Electronic conductivity of the cathode material is 4.2 × 10⁻⁶. -4 S / cm, battery initial discharge specific capacity at 0.2C is 149mAh / g, capacity retention after 1000 cycles is 71.1%, discharge specific capacity at -20℃ is 108.8mAh / g (73.0% of room temperature capacity), charge transfer impedance is 65Ω.

[0099] Please see Figure 2 , Figure 2 The cycle performance of the lithium metal batteries assembled in Example 1 (curve A) and Comparative Example 1 (curve B) of the present invention is shown; further, the performance between the examples and the comparative examples is summarized in Table 1.

[0100] Table 1:

[0101] Explanation of synergistic effect: The synergistic effect of poly(vinylpyrrolidone-co-acrylic acid) (PVPAA) with Ti and Zr is based on a three-dimensional mechanism of structural regulation, interface optimization, and enhanced conduction: the N atom of the VP unit in the copolymer forms a "NO" cooperative coordination site with the O atom of the AA unit, which can effectively anchor Ti. 4+ Zr 4+ To suppress its aggregation and achieve uniform doping, Ti 4+ By substituting Fe in the crystal lattice3+ Stable olivine structure, Zr 4+ Interstitial doping strengthens the lattice framework; during high-temperature sintering, the copolymer transforms into a uniformly coated amorphous carbon layer, which synergistically enhances electronic conductivity with the lattice defects introduced by Ti doping. Simultaneously, the steric hindrance effect of its molecular chains refines the lithium iron phosphate grains. Combined with the lithium-ion diffusion channels broadened by Zr and the ion migration barrier lowered by Ti, this accelerates lithium-ion transport. This synergistic effect significantly improves material performance: cycle stability is greatly enhanced, capacity retention is significantly improved after long-term cycling, and structural stability at high temperatures is also significantly improved; rate performance is effectively optimized, with a significant increase in capacity output at high-rate discharge; and electronic conductivity and lithium-ion diffusion capacity are both improved by orders of magnitude.

[0102] All three are indispensable: The absence of Ti leads to lattice instability due to Fe. 3+ Migration distortion occurs, and capacity decay is accelerated during cycling; the absence of Zr makes the lattice prone to Li degradation at high temperatures. + Significant expansion occurs during insertion / extraction, leading to particle breakage and electrolyte wetting failure; without copolymers, Ti and Zr easily agglomerate to form impurity phases that disrupt the crystal lattice and cannot form a uniform carbon layer, resulting in the breakage of the electronic conduction network and limiting performance improvement.

[0103] Copolymers were chosen instead of homopolymers such as polyvinylpyrrolidone (PVP) and polyacrylic acid (PAA). PVP contains only nitrogen (N) coordination sites, resulting in weak binding to metal ions and low carbon conversion, making it difficult to guarantee doping uniformity and carbon layer quality. While PAA contains strongly coordinating carboxyl groups, its excessively polar molecular chains easily form localized gels, leading to uneven dispersion, and high-temperature decomposition can leave impurities that damage the crystal lattice. In contrast, copolymers enhance binding through synergistic coordination at two nitrogen (NO) sites, achieving a balance between molecular chain affinity and hydrophobicity to prevent gelation, resulting in high-purity and uniform carbon layer coating. This synergistic enhancement effect is unattainable with single homopolymers.

[0104] In addition, infrared spectroscopy was performed on the PVPAA provided in Example 1 after small molecules were removed by dialysis, and the results are shown in Table 2.

[0105] Table 2:

[0106] As can be seen, infrared spectroscopy confirmed the presence of the required functional groups in PVPAA, indicating that the synthesis process was successful.

[0107] In summary, this invention, through composite doping modification of cathode materials and optimization of preparation methods, combined with the design of lithium metal battery electrolyte systems and structures, simultaneously solves the technical problems of poor electronic conductivity, insufficient cycle stability, lithium dendrite growth, and poor electrolyte compatibility in existing technologies, significantly improving the electrochemical performance and safety performance of batteries.

[0108] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a lithium metal battery cathode material, characterized in that, Includes the following steps: (1) Raw material pretreatment: Mix ammonium dihydrogen phosphate, ferric sulfate nonahydrate and citric acid in a molar ratio of 1:0.95-1.05:1.2-1.5, add deionized water to prepare a mixed solution with a concentration of 0.8-1.2 mol / L, stir at 40-50℃ for 30-60 min until completely dissolved to obtain the precursor mother liquor; (2) Composite doping modification: Add a dopant to the precursor mother liquor in step (1). The dopant is a mixture of titanium source compound, zirconium source compound and copolymer compound. The titanium source compound accounts for 1.5-6% of the theoretical mass of Fe in the precursor mother liquor based on Ti element, the zirconium source compound accounts for 1.5-6% of the theoretical mass of Fe in the precursor mother liquor based on Zr element, and the copolymer compound is poly(vinylpyrrolidone-co-acrylic acid). The molar ratio of vinylpyrrolidone to acrylic acid is 2-4:1, and the molecular weight of the copolymer compound is 3000-15000, which accounts for 1.5-6% of the theoretical mass of Fe in the precursor mother liquor. First, add the titanium source compound and zirconium source compound to the precursor mother liquor and stir and disperse for 10-15 min. Then add the copolymer compound and continue to stir and disperse for 15-25 min until the system is uniform. Then adjust the pH of the system to 4.5-5.5 with ammonia water. (3) Sol-gel preparation: Transfer the mixed solution after pH adjustment in step (2) to a constant temperature water bath, keep it at 60-70℃ and stir for 120-180 min to form a uniform and viscous sol, continue to heat to 80-90℃ and keep it at 80-90℃ for 4-6 h to obtain a dry gel; (4) Drying treatment: The dry gel described in step (3) is placed in a vacuum drying oven and dried at 105-120℃ for 8-12 hours to remove residual moisture and volatile impurities, and the dried precursor is obtained; (5) Segmented sintering: The dried precursor is placed in a tube furnace and pre-sintered at 350-400°C at a heating rate of 5-8°C / min under inert gas protection for 2-3 hours. Then, the temperature is raised to 750-850°C at a heating rate of 3-5°C / min and held for 4-6 hours for high-temperature sintering. After natural cooling to room temperature, the primary lithium metal battery cathode material is obtained. (6) Post-processing: The primary lithium metal battery cathode material is placed in a planetary ball mill, with ethanol as the dispersion medium, a ball-to-material ratio of 10-15:1, a rotation speed of 200-300 r / min, and ball milled for 2-4 h. Then, it is vacuum dried at 80-100℃ for 6-8 h to obtain the lithium metal battery cathode material.

2. The method for preparing a lithium metal battery cathode material according to claim 1, characterized in that, The titanium source compound mentioned in step (2) is at least one of tetrabutyl titanate and titanium isopropoxide, and the zirconium source compound is at least one of zirconium oxychloride and zirconium nitrate.

3. The method for preparing a lithium metal battery cathode material according to claim 1, characterized in that, The inert gas mentioned in step (5) is nitrogen or argon, and the gas flow rate is 200-300 mL / min. The grinding media of the planetary ball mill mentioned in step (6) is zirconia balls with a diameter of 3-5 mm.

4. The method for preparing a lithium metal battery cathode material according to claim 1, characterized in that, The method for synthesizing the poly(vinylpyrrolidone-co-acrylic acid) includes the following steps: Step 1: Monomer pretreatment. Acrylic acid is treated with an alkaline solution to remove polymerization inhibitors, washed with water until neutral, and then purified by distillation. Vinylpyrrolidone is treated with a chromatography column to remove polymerization inhibitors, and the purified monomers are collected for later use. Step 2: Weigh the monomers according to the molar ratio of vinylpyrrolidone to acrylic acid 3:1, take 0.5%-1.5% of the total monomer mass of ammonium persulfate as an initiator, and 1-3 times the total monomer mass of deionized water; add deionized water to the reaction vessel, install stirring, condensation and nitrogen devices, and place it in a temperature control device; Step 3: Add the purified monomer to the reaction vessel, stir until dissolved, and then introduce nitrogen gas to remove oxygen from the system. Step 4: Dissolve the initiator in deionized water and add it dropwise to the reaction system under nitrogen protection. Heat the mixture to 65-75℃ and maintain stirring and nitrogen atmosphere for 4-6 hours. Step 5: After the reaction is complete, stop heating and continue to purge with nitrogen until the system cools down to obtain an aqueous solution of poly(vinylpyrrolidone-co-acrylic acid); Step 6: Add the above aqueous solution to 3-7 times its volume of anhydrous ethanol, stir to precipitate, let stand and separate the precipitate, and wash it several times with anhydrous ethanol. Step 7: Place the washed precipitate in a vacuum drying oven and dry it at 50-70℃ to obtain solid powder poly(vinylpyrrolidone-co-acrylic acid).

5. A lithium metal battery, comprising a positive electrode material prepared according to any one of claims 1-4, characterized in that, Includes positive electrode, negative electrode, electrolyte, separator and battery casing; The positive electrode is made by mixing the positive electrode material of the lithium metal battery with a binder and a conductive agent in a mass ratio of 80-85:5-8:5-7 and then coating it onto the surface of an aluminum foil current collector. The negative electrode is a lithium metal foil with a thickness of 50-100μm; The electrolyte is a homogeneous solution formed by dissolving lithium salt in an organic solvent; the diaphragm is a polypropylene / polyethylene composite porous diaphragm.

6. A lithium metal battery according to claim 5, characterized in that, The lithium salt in the electrolyte is a mixture of lithium bis(trifluoromethanesulfonylimide) and lithium hexafluorophosphate, with a molar ratio of 1:0.5-1.0, and the concentration of the lithium salt in the electrolyte is 1.0-1.5 mol / L.

7. A lithium metal battery according to claim 5, characterized in that, The organic solvent in the electrolyte is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1 to 1:2:

2.

8. A lithium metal battery according to claim 5, characterized in that, The binder is polyvinylidene fluoride or sodium carboxymethyl cellulose, and the conductive agent is at least one of conductive carbon black and carbon nanotubes.

9. A lithium metal battery according to claim 5, characterized in that, The diaphragm has a pore size of 0.1-1.0μm, a thickness of 10-20μm, and a porosity of 40-60%. The battery casing is an aluminum-plastic composite film soft-pack casing. The battery's nominal voltage is 3.2-3.3V, and its operating temperature range is -20℃ to 60℃.

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