Positive electrode functional material and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention provides a positive functional material and a preparation method thereof, a positive plate and a lithium ion battery. The preparation method comprises the following steps: S1, mixing raw materials including soluble metal salt, an organic ligand and a first organic solvent, and then sequentially carrying out pH regulation and coordination reaction to obtain a framework material; s2, mixing raw materials including a crown ether compound, a lithium supplement agent and a second organic solvent to obtain a mixed solution, dipping and absorbing the frame material in the mixed solution, and then drying the obtained dipping absorber to obtain a load material; and S3, mixing raw materials including the load material, a high-molecular polymer and a third organic solvent to obtain the positive electrode functional material. The prepared positive electrode functional material is attached to the surface of a lithium manganese iron phosphate material, so that the specific capacity and the cycling stability of the lithium manganese iron phosphate material can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular, to a positive electrode functional material, a preparation method thereof, a positive electrode sheet, and a lithium-ion battery. Background Art

[0002] With the continuous improvement of the technical requirements for safety performance in new energy vehicles, lithium iron phosphate batteries are increasingly widely used. However, the energy density of lithium iron phosphate batteries is relatively low and cannot meet the requirements of new energy vehicles for long endurance. Therefore, it is particularly urgent to find a battery with a higher energy density and better safety performance. Lithium manganese iron phosphate batteries are increasingly favored by battery manufacturers due to their higher voltage platform, energy density, and the ability to balance safety performance and other characteristics.

[0003] As a material obtained by introducing Mn ion doping modification to lithium iron phosphate material, lithium manganese iron phosphate material has an energy density 20% higher than that of lithium iron phosphate, which is also the greatest advantage of lithium manganese iron phosphate material. In addition, the advantages of lithium manganese iron phosphate material such as low cost, stability, and environmental friendliness also provide broad development prospects for this material. However, lithium manganese iron phosphate material itself has some serious drawbacks: for example, the J-T effect of Mn during charge and discharge causes lattice distortion and destroys the structural stability. As the charge and discharge continue, lithium ions repeatedly deintercalate / insert into the crystal particles, causing part of the crystal structure to collapse, part of the manganese ions to deintercalate from the structure and react with the electrolyte, and deposit on the surface of the negative electrode, damaging the SEI film on the surface of the negative electrode and causing the cyclic performance to continuously decrease. 3+ During the charge and discharge process, the J-T effect of Mn causes lattice distortion and destroys the structural stability. As the charge and discharge continue, lithium ions repeatedly deintercalate / insert into the crystal particles, causing part of the crystal structure to collapse, part of the manganese ions to deintercalate from the structure and react with the electrolyte, and deposit on the surface of the negative electrode, damaging the SEI film on the surface of the negative electrode and causing the cyclic performance to continuously decrease. Summary of the Invention

[0004] The main object of the present invention is to provide a positive electrode functional material, a preparation method thereof, a positive electrode sheet, and a lithium-ion battery to solve the problem of poor cyclic stability of lithium manganese iron phosphate positive electrode materials in the prior art.

[0005] To achieve the above object, according to one aspect of the present invention, a preparation method of a positive electrode functional material is provided. The preparation method includes the following steps: Step S1, mixing raw materials including soluble metal salts, organic ligands, and a first organic solvent, and then sequentially performing pH adjustment and coordination reaction to obtain a framework material; Step S2, mixing raw materials including a crown ether compound, a lithium supplement agent, and a second organic solvent to obtain a mixed solution, impregnating and absorbing the framework material in the mixed solution, and then drying the obtained impregnated and absorbed material to obtain a loaded material; Step S3, mixing the loaded material, a polymer, and a third organic solvent to obtain a positive electrode functional material.

[0006] The addition of crown ether substances helps to inhibit the dissolution of manganese ions in the lithium iron phosphate manganese material, capture the dissolved manganese ions, and prevent the manganese ions from consuming the electrolyte and damaging the SEI film structure. The addition of the lithium supplementing agent helps to supplement some of the lithium ions consumed during the formation of the SEI film during battery activation, thereby helping to improve the specific capacity and cycle stability of the battery. The addition of the polymer helps to enhance the interaction between the cathode functional material and the lithium iron phosphate manganese material, thereby helping the cathode functional material to uniformly adhere to the surface of the lithium iron phosphate manganese material, play a supporting role for the lithium iron phosphate manganese crystal, and help reduce the collapse of the crystal structure during the cycle.

[0007] Furthermore, the mass ratio of the above-mentioned crown ether compound to the lithium supplementing agent is (2-5):1; and / or, the mass ratio of the total mass of the crown ether compound and the lithium supplementing agent to the mass of the framework material is (5-16):(10-20); and / or, the mass ratio of the total mass of the crown ether compound and the lithium supplementing agent to the volume of the second organic solvent is (0.1-0.2 g):(1 mL).

[0008] Controlling the mass ratio of the crown ether compound to the lithium supplementing agent within the above range helps to enhance the synergistic effect between the two, thereby helping to further improve the functions of the cathode functional material in inhibiting the dissolution of manganese ions and supplementing lithium. Controlling the mass ratio of the total mass of the crown ether compound and the lithium supplementing agent to the mass of the framework material within the above range helps to further improve the functions of the cathode functional material in inhibiting the dissolution of manganese ions and supplementing lithium. Controlling the mass ratio of the total mass of the crown ether compound and the lithium supplementing agent to the volume of the second organic solvent within the above range helps to further improve the uniformity of the distribution of the crown ether compound and the lithium supplementing agent on the framework material.

[0009] Furthermore, the above-mentioned crown ether compound is selected from any one or more of 18-crown-6, 15-crown-5, and 12-crown-4; and / or, the lithium supplementing agent is an organic lithium salt, and preferably the organic lithium salt is selected from any one or more of lithium squarate, lithium oxalate, and lithium citrate; and / or, the second organic solvent is selected from any one or more of absolute ethanol, acetone, and absolute methanol; preferably, the second organic solvent is a combination of absolute ethanol and acetone, and the volume ratio of absolute ethanol to acetone is 1:(1-2).

[0010] 18-crown-6 has a larger ring and can better bind to larger ions such as Mn 2+ etc. Lithium squarate and lithium oxalate have high thermal stability and electrochemical stability, and can form a stable film layer on the surface of the cathode material, which helps to reduce the excessive consumption of lithium ions. Controlling the volume ratio of absolute ethanol to acetone within the above range helps to improve the uniformity and stability of the dispersion of the crown ether compound and the lithium supplementing agent on the framework material.

[0011] Further, the temperature of the above drying treatment is 60 to 90 °C; and / or, the time of the drying treatment is 3 to 4 h.

[0012] Controlling the temperature and time of the drying treatment within the above ranges helps to further improve the stability of the loaded material.

[0013] Further, in the above step S3, the mass ratio of the loaded material to the polymer is (0.1 to 1):(10 to 20); and / or, the mass ratio of the polymer to the volume of the third organic solvent is (5 to 10 g):(100 mL).

[0014] Controlling the mass ratio of the loaded material to the polymer within the above range helps to form a uniform, dense and highly functional film on the surface of the lithium iron phosphate manganese material. Controlling the mass ratio of the polymer to the volume of the third organic solvent within the above range helps to improve the uniformity and stability of the cathode functional material.

[0015] Further, the above polymer is selected from any one or more of polyethylene oxide, gelatin and ethyl polyacrylate; preferably, the polymer is a combination of gelatin and polyethylene oxide, and the mass ratio of gelatin to polyethylene oxide is 3:(7 to 8); and / or, the third organic solvent is selected from any one or more of acetonitrile, anisole, chloroform, dichloroethane, dimethylformamide, N-methylpyrrolidone, glycerol, propylene glycol and ethylene glycol; preferably, the third organic solvent is a combination of N-methylpyrrolidone and ethylene glycol, and the volume ratio of N-methylpyrrolidone to ethylene glycol is 1:(1 to 3); and / or, the time of the mixing treatment is 12 to 20 h; preferably, the mixing treatment is carried out under stirring, and the stirring speed of the mixing treatment is 300 to 400 rpm.

[0016] Controlling the mass ratio of gelatin to polyethylene oxide within the above range helps to fully exert the synergistic effect between the two, thereby helping to improve the mechanical strength and lithium ion transport performance of the cathode functional material. Controlling the volume ratio of N-methylpyrrolidone to ethylene glycol within the above range helps to improve the fluidity, dispersibility and stability of the glue solution. Controlling the time and stirring speed of the mixing treatment within the above ranges helps to improve the efficiency of the polymer to form a glue solution in the third solvent.

[0017] Further, in the above step S1, the molar ratio of the soluble metal salt to the organic ligand is (1-3):(1-2); and / or, the mass ratio of the soluble metal salt to the volume of the first organic solvent is (2-15 g):(10-20 mL); preferably, the soluble metal salt is selected from any one or more of aluminum chloride hexahydrate, iron phosphate, zinc sulfate, copper sulfate pentahydrate, aluminum nitrate nonahydrate, and nickel sulfate; and / or, the organic ligand is selected from any one or more of aminobenzoic acid amide, 2-methylimidazole, 1,3,5-benzenetricarboxylic acid, and terephthalic acid; and / or, the first organic solvent is selected from any one or more of N,N-dimethylformamide, ethanol, and water; preferably, the first organic solvent is a combination of N,N-dimethylformamide, ethanol, and water, and the volume ratio of N,N-dimethylformamide, ethanol, and water is (1-3):(1-2):1; and / or, an organic acid is used for pH adjustment, and the pH value of the solution after pH adjustment is 3-4; preferably, the organic acid is selected from any one or more of citric acid, acetic acid, and formic acid; and / or, the temperature of the coordination reaction is 150-200 °C; and / or, the time of the coordination reaction is 8-12 h.

[0018] Controlling the molar ratio of the soluble metal salt to the organic ligand within the above range helps to promote the effective coordination of metal ions with the organic ligand. Controlling the mass ratio of the soluble metal salt to the volume of the first organic solvent within the above range helps to improve the stability of the coordination reaction environment and the uniformity of the solution. Controlling the types of the soluble metal salt and the organic ligand within the above range helps to form a framework material with high porosity and a stable structure. Controlling the volume ratio of N,N-dimethylformamide, ethanol, and water within the above range helps the metal salt and the organic ligand to be uniformly dispersed and react in the solution, thereby helping to form a framework material with high porosity and a stable structure. Controlling the pH value of the solution, the temperature, and the time of the coordination reaction within the above range helps to form a framework material with high porosity, good stability, and functionality.

[0019] According to another aspect of the present invention, a positive electrode functional material is provided, and the positive electrode functional material is prepared by the foregoing preparation method.

[0020] The above positive electrode functional material has good stability and adhesion. Attaching the positive electrode functional material to the surface of the lithium iron manganese phosphate material helps to improve the specific capacity and cycle stability of the lithium iron manganese phosphate material.

[0021] According to still another aspect of the present invention, a positive electrode sheet is provided, which includes a current collector and a positive electrode active layer, and the positive electrode active layer contains the foregoing positive electrode functional material and lithium iron manganese phosphate; preferably, the mass ratio of the positive electrode functional material to lithium iron manganese phosphate is (0.3-0.6):1.

[0022] Controlling the mass ratio of the positive electrode functional material to lithium iron manganese phosphate within the above range helps to form a uniform functional film on the surface of lithium iron manganese phosphate, which helps to support the lithium iron manganese phosphate crystal.

[0023] According to another aspect of the present invention, a lithium-ion battery is provided, including a positive electrode sheet, an electrolyte, and a negative electrode sheet, and the positive electrode sheet is the aforementioned positive electrode sheet.

[0024] The above lithium-ion battery has a high specific capacity and cycle stability.

[0025] Applying the technical solution of this application, in step S1, by mixing a soluble metal salt, an organic ligand, and a first organic solvent, and through pH adjustment and coordination reaction, a framework material with specific pores is formed, which helps to provide more loading active sites for crown ether compounds and lithium supplement agents. In step S2, by first mixing a crown ether compound, a lithium supplement agent, and a second organic solvent to form a mixed solution, then impregnating and absorbing the framework material in the mixed solution, and then drying the obtained impregnated and absorbed material to obtain a loaded material, which helps to improve the distribution uniformity of the crown ether compound and the lithium supplement agent in the framework material. The addition of crown ether substances helps to inhibit the dissolution of manganese ions in the lithium iron manganese phosphate material, capture the dissolved manganese ions, and prevent the manganese ions from consuming the electrolyte and destroying the SEI film structure. The addition of the lithium supplement agent helps to supplement some of the lithium ions consumed during the formation of the SEI film during battery activation, thereby helping to improve the specific capacity and cycle stability of the battery. In step S3, through the mixing treatment of the loaded material, a polymer, and a third organic solvent, the loaded material is uniformly dispersed in the sol formed by the polymer and the third organic solvent to form a positive electrode functional material. The addition of the polymer helps to improve the interaction between the positive electrode functional material and the lithium iron manganese phosphate material, thereby helping to make the positive electrode functional material uniformly adhere to the surface of the lithium iron manganese phosphate material, support the lithium iron manganese phosphate crystal, and help to reduce the collapse of the crystal structure during the cycle. Therefore, attaching the positive electrode functional material prepared by this application to the surface of the lithium iron manganese phosphate material helps to improve the specific capacity and cycle stability of the lithium iron manganese phosphate material. Specific Embodiments

[0026] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0027] As analyzed in the background technology of this application, there is a problem of poor cycle stability in the existing lithium iron manganese phosphate positive electrode material. To solve this problem, this application provides a positive electrode functional material and its preparation method, a positive electrode sheet, and a lithium-ion battery.

[0028] In a typical embodiment of the present application, a method for preparing a cathode functional material is provided. The preparation method includes the following steps: Step S1, mixing raw materials including a soluble metal salt, an organic ligand, and a first organic solvent, and then sequentially performing pH adjustment and coordination reaction to obtain a framework material; Step S2, mixing raw materials including a crown ether compound, a lithium supplement agent, and a second organic solvent to obtain a mixed solution, impregnating and absorbing the framework material in the mixed solution, and then drying the obtained impregnated and absorbed product to obtain a loaded material; Step S3, mixing raw materials including the loaded material, a polymer, and a third organic solvent to obtain a cathode functional material.

[0029] In Step S1, by mixing the soluble metal salt, the organic ligand, and the first organic solvent, and through pH adjustment and coordination reaction, a framework material with specific pores is formed, which helps to provide more loading active sites for the crown ether compound and the lithium supplement agent. In Step S2, by first mixing the crown ether compound, the lithium supplement agent, and the second organic solvent to form a mixed solution, then impregnating and absorbing the framework material in the mixed solution, and then drying the obtained impregnated and absorbed product to obtain a loaded material, it helps to improve the distribution uniformity of the crown ether compound and the lithium supplement agent in the framework material. The addition of the crown ether substance helps to inhibit the dissolution of manganese ions in the lithium iron phosphate manganese material, capture the dissolved manganese ions, and prevent the manganese ions from consuming the electrolyte and damaging the SEI film structure. The addition of the lithium supplement agent helps to supplement some of the lithium ions consumed during the formation of the SEI film during battery activation, thereby helping to improve the specific capacity and cycle stability of the battery. In Step S3, through the mixing treatment of the loaded material, the polymer, and the third organic solvent, the loaded material is uniformly dispersed in the sol formed by the polymer and the third organic solvent to form a cathode functional material. The addition of the polymer helps to improve the interaction between the cathode functional material and the lithium iron phosphate manganese material, thereby helping the cathode functional material to uniformly adhere to the surface of the lithium iron phosphate manganese material, play a supporting role for the lithium iron phosphate manganese crystal, and help to reduce the collapse of the crystal structure during the cycle process. Therefore, attaching the cathode functional material prepared in the present application to the surface of the lithium iron phosphate manganese material helps to improve the specific capacity and cycle stability of the lithium iron phosphate manganese material.

[0030] In an embodiment of the present application, in the above Step S2, the mass ratio of the crown ether compound to the lithium supplement agent is (2 - 5):1, specifically, it can be 2:1, 3:1, 4:1, 5:1, and the range values between any two ratios; and / or, the total mass ratio of the crown ether compound and the lithium supplement agent to the mass of the framework material is (5 - 16):(10 - 20); and / or, the total mass ratio of the crown ether compound and the lithium supplement agent to the volume of the second organic solvent is (0.1 - 0.2 g):(1 mL).

[0031] The addition of crown ether substances helps to inhibit the dissolution of manganese ions in the lithium iron manganese phosphate material, and the addition of a lithium supplementing agent helps to supplement some of the lithium ions consumed during the formation of the SEI film during battery activation. Controlling the mass ratio of the crown ether compound to the lithium supplementing agent within the above range helps to enhance the synergistic effect between the two, thereby helping to further improve the function of the cathode functional material in inhibiting the dissolution of manganese ions and the function of lithium supplementation, and further helping to improve the specific capacity and cycle stability of the lithium iron manganese phosphate material. Controlling the mass ratio of the total mass of the crown ether compound and the lithium supplementing agent to the mass of the framework material within the above range helps to further improve the function of the cathode functional material in inhibiting the dissolution of manganese ions and the function of lithium supplementation. Controlling the mass ratio of the total mass of the crown ether compound and the lithium supplementing agent to the volume of the second organic solvent within the above range helps to further improve the uniformity of the distribution of the crown ether compound and the lithium supplementing agent on the framework material.

[0032] In one embodiment of the present application, the above-mentioned crown ether compound is selected from any one or more of 18-crown-6, 15-crown-5, and 12-crown-4, and preferably the crown ether compound is 18-crown-6; and / or, the lithium supplementing agent is an organic lithium salt, and preferably the organic lithium salt is selected from any one or more of lithium squarate, lithium oxalate, and lithium citrate, and preferably the organic lithium salt is lithium squarate and / or lithium oxalate; and / or, the second organic solvent is selected from any one or more of absolute ethanol, acetone, and absolute methanol; preferably, the second organic solvent is a combination of absolute ethanol and acetone, and the volume ratio of absolute ethanol to acetone is 1:(1-2).

[0033] The crown ether compound has a cyclic structure and can form a stable coordination complex with metal ions (such as Mn 2+ ) to effectively adsorb and prevent the manganese ions dissolved on the surface of the cathode material. The ring of 18-crown-6 is larger and can better bind to larger ions such as Mn 2+ . The lithium supplementing agent is selected as an organic lithium salt, especially lithium squarate, lithium oxalate, and lithium citrate. These organic lithium salts can supplement the lithium ions consumed on the surface of the cathode material during the charge and discharge process of the battery and reduce the attenuation of the battery capacity caused by the loss of lithium ions. Lithium squarate and lithium oxalate have high thermal stability and electrochemical stability and can form a stable film layer on the surface of the cathode material, which helps to reduce the excessive consumption of lithium ions. The hydrophilicity of absolute ethanol helps to dissolve the crown ether compound and the lithium supplementing agent, while the hydrophobicity of acetone helps to dry the material. Controlling the volume ratio of absolute ethanol to acetone within the above range helps to improve the uniformity and stability of the dispersion of the crown ether compound and the lithium supplementing agent on the framework material.

[0034] In one embodiment of the present application, in the above step S1, the product after the coordination reaction is successively subjected to solid-liquid separation, washing, and drying to obtain the framework material. Preferably, the drying temperature is 80-120 °C.

[0035] In one embodiment of the present application, to further improve the stability of the supported material, it is preferred that the temperature of the above-mentioned drying treatment is 60 to 90 °C; and / or, the time of the drying treatment is 3 to 4 h.

[0036] In one embodiment of the present application, in the above-mentioned step S3, the mass ratio of the supported material to the polymer is (0.1 to 1):(10 to 20); and / or, the mass of the polymer to the volume of the third organic solvent is (5 to 10 g):(100 mL).

[0037] Controlling the mass ratio of the supported material to the polymer within the above range helps to form a uniform, dense and highly functional functional film on the surface of the lithium iron manganese phosphate material, thereby helping to improve the specific capacity and cycle stability of the lithium iron manganese phosphate material. Controlling the mass of the polymer to the volume of the third organic solvent within the above range helps to improve the uniformity and stability of the cathode functional material.

[0038] In one embodiment of the present application, the above-mentioned polymer is selected from any one or more of polyethylene oxide, gelatin and ethyl polyacrylate; preferably, the polymer is a combination of gelatin and polyethylene oxide, and the mass ratio of gelatin to polyethylene oxide is 3:(7 to 8); and / or, the third organic solvent is selected from any one or more of acetonitrile, anisole, chloroform, dichloroethane, dimethylformamide, N-methylpyrrolidone, glycerol, propylene glycol and ethylene glycol; preferably, the third organic solvent is a combination of N-methylpyrrolidone and ethylene glycol, and the volume ratio of N-methylpyrrolidone to ethylene glycol is 1:(1 to 3); and / or, the time of the mixing treatment is 12 to 20 h; preferably, the mixing treatment is carried out under stirring, and the stirring speed of the mixing treatment is 300 to 400 rpm.

[0039] Gelatin has good adhesiveness, which helps to enhance the adhesion of the positive electrode functional material on the surface of lithium iron phosphate manganese material. Polyethylene oxide is a commonly used lithium ion conductor, which helps to improve the lithium ion conductivity of the positive electrode functional material and the transmission efficiency of lithium ions between the positive and negative electrodes. Controlling the mass ratio of gelatin and polyethylene oxide within the above range helps to give full play to the synergistic effect between the two, thereby helping to improve the mechanical strength and lithium ion transmission performance of the positive electrode functional material, and thus helping to enhance the cycle stability and specific capacity of the battery. N-methylpyrrolidone is a polar solvent with good solubility and stability, which can promote the dissolution of the polymer and improve the uniformity of the glue solution; while ethylene glycol has a higher viscosity and better stability, which helps to improve the stability of the glue solution and promote the formation of the positive electrode functional material. Controlling the volume ratio of N-methylpyrrolidone and ethylene glycol within the above range helps to improve the fluidity, dispersibility and stability of the glue solution. Controlling the time and stirring speed of the mixing treatment within the above range helps to improve the efficiency of forming the glue solution of the polymer in the third solvent, thereby helping to further improve the dispersibility and stability of the glue solution.

[0040] In one embodiment of the present application, the above step S3 includes: step S31, performing a first mixing treatment on polyethylene oxide and N-methylpyrrolidone to obtain a sol D, and performing a second mixing treatment on gelatin and ethylene glycol to obtain a sol E; step S32, performing a third mixing treatment on the sol D and the sol E to obtain a glue solution F; step S33, performing a fourth mixing treatment on the glue solution F and the loading material to obtain a positive electrode functional material. The above first mixing treatment, second mixing treatment, third mixing treatment and fourth mixing treatment are all carried out under stirring conditions. The stirring speeds of the first mixing treatment, second mixing treatment, third mixing treatment and fourth mixing treatment are independently 300-400 rpm. The first mixing treatment and the second mixing treatment are carried out simultaneously. The times of the first mixing treatment and the second mixing treatment are independently 2-4 h. The time of the third mixing treatment is 2-4 h. The time of the fourth mixing treatment is 8-12 h.

[0041] In an embodiment of the present application, in the above step S1, the molar ratio of the soluble metal salt to the organic ligand is (1 to 3):(1 to 2); and / or, the mass of the soluble metal salt to the volume of the first organic solvent is (2 to 15 g):(10 to 20 mL); preferably, the soluble metal salt is selected from any one or more of aluminum chloride hexahydrate, iron phosphate, zinc sulfate, copper sulfate pentahydrate, aluminum nitrate nonahydrate, and nickel sulfate; and / or, the organic ligand is selected from any one or more of aminobenzoic acid amide, 2-methylimidazole, 1,3,5-benzenetricarboxylic acid, and terephthalic acid; and / or, the first organic solvent is selected from any one or more of N,N-dimethylformamide, ethanol, and water; preferably, the first organic solvent is a combination of N,N-dimethylformamide, ethanol, and water, and the volume ratio of N,N-dimethylformamide, ethanol, and water is (1 to 3):(1 to 2):1; and / or, an organic acid is used for pH adjustment, and the pH value of the solution after pH adjustment is 3 to 4; preferably, the organic acid is selected from any one or more of citric acid, acetic acid, and formic acid; and / or, the temperature of the coordination reaction is 150 to 200 °C; and / or, the time of the coordination reaction is 8 to 12 h.

[0042] Controlling the molar ratio of the soluble metal salt to the organic ligand within the above range helps to promote the effective coordination of metal ions with the organic ligand and helps to form a framework material with high porosity and a stable structure. Controlling the mass of the soluble metal salt to the volume of the first organic solvent within the above range helps to improve the stability of the coordination reaction environment and the uniformity of the solution, thus facilitating the formation of the framework material. Controlling the types of the soluble metal salt and the organic ligand within the above range helps to enhance the synergistic effect between the two, thus helping to form a framework material with high porosity and a stable structure. As a polar solvent, N,N-dimethylformamide helps to dissolve the soluble metal salt; ethanol and water provide a mild reaction environment to promote the coordination reaction of the organic ligand with metal ions. Controlling the volume ratio of N,N-dimethylformamide, ethanol, and water within the above range helps the metal salt and the organic ligand to be uniformly dispersed and react in the solution, thus helping to form a framework material with high porosity and a stable structure. Controlling the pH value of the solution, the temperature, and the time of the coordination reaction within the above range helps to form a framework material with high porosity, good stability, and functionality.

[0043] In another typical embodiment of the present application, a positive electrode functional material is provided, and the positive electrode functional material is prepared by the foregoing preparation method.

[0044] Since the above-mentioned positive electrode functional material is prepared by the preparation method of the present application, the positive electrode functional material has good stability and adhesion. Attaching the positive electrode functional material to the surface of the lithium iron manganese phosphate material helps to improve the specific capacity and cycle stability of the lithium iron manganese phosphate material.

[0045] In another typical embodiment of the present application, a positive electrode sheet is provided, which includes a current collector and a positive electrode active layer. The positive electrode active layer contains the aforementioned positive electrode functional material and lithium iron manganese phosphate; preferably, the mass ratio of the positive electrode functional material to lithium iron manganese phosphate is (0.3-0.6):1, specifically, it can be 0.3:1, 0.4:1, 0.5:1, 0.6:1, and the range values between any two ratios.

[0046] Controlling the mass ratio of the positive electrode functional material to lithium iron manganese phosphate within the above range helps to form a uniform functional film on the surface of the lithium iron manganese phosphate, helps to support the lithium iron manganese phosphate crystal, helps to reduce the collapse of the crystal structure during the cycle, inhibits the dissolution of manganese ions in the lithium iron manganese phosphate material, and supplements part of the lithium ions consumed during the formation of the SEI film during battery activation, thereby helping to improve the specific capacity and cycle stability of the positive electrode sheet.

[0047] In another typical embodiment of the present application, a preparation method of a positive electrode sheet is provided. The preparation method includes: dispersing the lithium iron manganese phosphate positive electrode slurry and the positive electrode functional material to obtain a mixed slurry, and coating the mixed slurry on the current collector and then drying it to obtain the positive electrode sheet. Preferably, a dispersion disk is used for dispersion treatment, and the linear velocity of the dispersion disk is 18-20 m / s; and / or, the dispersion treatment time is 4-6 h.

[0048] In another typical embodiment of the present application, a lithium ion battery is provided, which includes a positive electrode sheet, an electrolyte, and a negative electrode sheet, and the positive electrode sheet is the aforementioned positive electrode sheet.

[0049] Since the positive electrode sheet of the above lithium ion battery contains the positive electrode functional material of the present application, the lithium ion battery has a high specific capacity and cycle stability.

[0050] The beneficial effects of the present application will be further described below in conjunction with embodiments.

[0051] Example 1

[0052] S1. Weigh aluminum chloride hexahydrate and ammonium aminobenzoate according to a molar ratio of 3:2. Dissolve the soluble metal salt aluminum chloride hexahydrate in a mixed solution of N,N-dimethylformamide, ethanol, and water, where the volume ratio of N,N-dimethylformamide, ethanol, and water is 1:1:1. Sonicate for 40 min to form the first solution. The mass ratio of aluminum chloride hexahydrate to the volume of the mixed solution of N,N-dimethylformamide, ethanol, and water is 2 g:10 mL. Add the organic ligand ammonium aminobenzoate to the first solution and sonicate for 20 min to form the second solution. Adjust the pH of the second solution to 4 using acetic acid and sonicate for 20 min to form a suspension. Place the suspension in a reaction kettle and carry out a coordination reaction at 200 °C for 10 h. Naturally cool to room temperature, filter, wash with deionized water 3 times, and then dry to obtain the framework material;

[0053] S2. Weigh 18-crown-6 and lithium squarate according to a mass ratio of 3:1. Dissolve 18-crown-6 and lithium squarate in a mixed solution of anhydrous ethanol / acetone (volume ratio 1:1). The total mass ratio of 18-crown-6 and lithium squarate to the volume of the mixed solution of anhydrous ethanol / acetone is 0.2 g:1 mL to obtain the third solution. Use the above framework material to impregnate and absorb the third solution. The total mass ratio of 18-crown-6 and lithium squarate to the mass of the framework material is 5:20. Place the framework material that has absorbed the third solution in an 80 °C oven and bake for 4 h to obtain the loaded material. Dissolve polyethylene oxide in the solvent N-methylpyrrolidone and dissolve gelatin in the solvent ethylene glycol respectively. The mass ratio of gelatin to polyethylene oxide is 3:7, the volume ratio of N-methylpyrrolidone to ethylene glycol is 1:3, and the total mass ratio of polyethylene oxide and gelatin to the total volume of N-methylpyrrolidone and ethylene glycol is 5 g:100 mL. Stir at 300 rpm for 3 h to obtain sol D and sol E. Then mix sol D and sol E and continue to stir at 300 rpm for 3 h to obtain glue solution F. Add the loaded material to glue solution F. The mass ratio of the loaded material to the total mass of polyethylene oxide and gelatin is 0.1:20. Stir at 300 rpm for 10 h to obtain the positive electrode functional material.

[0054] S3. Add the above positive electrode functional material to the lithium iron manganese phosphate positive electrode slurry. The mass ratio of the positive electrode functional material to lithium iron manganese phosphate is 0.5:100. Disperse and homogenize for 6 h, and the linear speed of the dispersion disk is 20 m / s. Coat the slurry on the copper foil and dry to obtain the positive electrode sheet.

[0055] Example 2

[0056] The difference from Example 1 is as follows: S1. Weigh aluminum chloride hexahydrate and aminobenzoic acid amide according to a molar ratio of 3:2. Dissolve the soluble metal salt aluminum chloride hexahydrate in a mixed solution of N,N-dimethylformamide, ethanol, and water. The volume ratio of N,N-dimethylformamide, ethanol, and water is 3:2:1. Ultrasonic for 40 min to form the first solution. The mass ratio of aluminum chloride hexahydrate to the volume of the mixed solution of N,N-dimethylformamide, ethanol, and water is 2 g:10 mL. Add the organic ligand aminobenzoic acid amide to the first solution and ultrasonic for 20 min to form the second solution. Adjust the pH of the second solution to 3 with acetic acid and ultrasonic for 20 min to form a suspension. Place the suspension in a reaction kettle and carry out a coordination reaction at 200 °C for 10 h. Naturally cool to room temperature, filter, wash with deionized water three times, and then dry to obtain the framework material;

[0057] S2. Weigh 18-crown-6 and lithium oxalate according to a mass ratio of 3:1. Dissolve 18-crown-6 and lithium oxalate in a mixed solution of absolute ethanol / acetone (volume ratio 1:2). The total mass ratio of 18-crown-6 and lithium oxalate to the volume of the mixed solution of absolute ethanol / acetone is 0.2 g:1 mL to obtain the third solution. Use the above framework material to impregnate and absorb the third solution. The total mass ratio of 18-crown-6 and squaric acid lithium to the mass of the framework material is 5:20. Place the framework material after absorbing the third solution in an oven at 60 °C and bake for 4 h to obtain the loaded material. Dissolve polyethylene oxide in the solvent N-methylpyrrolidone and dissolve gelatin in the solvent ethylene glycol respectively. The mass ratio of gelatin to polyethylene oxide is 3:7. The volume ratio of N-methylpyrrolidone to ethylene glycol is 1:2. The total mass ratio of polyethylene oxide and gelatin to the total volume of N-methylpyrrolidone and ethylene glycol is 5 g:100 mL. Stir at 400 rpm for 4 h to obtain Sol D and Sol E. Then mix Sol D and Sol E and continue to stir at 400 rpm for 4 h to obtain the glue solution F. Add the loaded material to the glue solution F. The mass ratio of the loaded material to the total mass of polyethylene oxide and gelatin is 1:10. Stir at 400 rpm for 12 h to obtain the positive electrode functional material.

[0058] S3. Add the above positive electrode functional material to the lithium iron phosphate manganese positive electrode slurry. The mass ratio of the positive electrode functional material to lithium iron phosphate manganese is 0.6:100. Disperse and homogenize for 6 h. The linear velocity of the dispersion disk is 20 m / s. Coat the slurry on the copper foil and dry to obtain the positive electrode sheet.

[0059] Example 3

[0060] The difference from Example 1 is that the temperature of the coordination reaction is 150 °C and the time is 12 h, and finally the positive electrode sheet is obtained.

[0061] Example 4

[0062] The difference from Example 1 is that the mass ratio of the positive electrode functional material to lithium iron manganese phosphate is 0.3:100, and finally a positive electrode sheet is obtained.

[0063] Example 5

[0064] The difference from Example 1 is that the mass ratio of the positive electrode functional material to lithium iron manganese phosphate is 0.1:100, and finally a positive electrode sheet is obtained.

[0065] Example 6

[0066] The difference from Example 1 is that the mass ratio of the positive electrode functional material to lithium iron manganese phosphate is 0.9:100, and finally a positive electrode sheet is obtained.

[0067] Example 7

[0068] The difference from Example 1 is that the mass ratio of 18-crown-6 to lithium squarate is 5:1, and finally a positive electrode sheet is obtained.

[0069] Example 8

[0070] The difference from Example 1 is that the mass ratio of 18-crown-6 to lithium squarate is 8:1, and finally a positive electrode sheet is obtained.

[0071] Example 9

[0072] The difference from Example 1 is that the total mass of 18-crown-6 and lithium squarate to the mass of the framework material is 16:10, and finally a positive electrode sheet is obtained.

[0073] Example 10

[0074] The difference from Example 1 is that the total mass of 18-crown-6 and lithium squarate to the mass of the framework material is 2:20, and finally a positive electrode sheet is obtained.

[0075] Example 11

[0076] The difference from Example 1 is that the mass of the loading material to the total mass of polyethylene oxide and gelatin is 1:10, and finally a positive electrode sheet is obtained.

[0077] Example 12

[0078] The difference from Example 1 is that the mass of the loading material to the total mass of polyethylene oxide and gelatin is 1:50, and finally a positive electrode sheet is obtained.

[0079] Example 13

[0080] The difference from Example 1 is that the mass ratio of gelatin to polyethylene oxide is 3:8, and finally a positive electrode sheet is obtained.

[0081] Example 14

[0082] The difference from Example 1 is that the mass ratio of gelatin to polyethylene oxide is 3:9, and a positive electrode sheet is finally obtained.

[0083] Example 15

[0084] The difference from Example 1 is that the temperature of the coordination reaction is 220 °C and the time is 6 h, and a positive electrode sheet is finally obtained.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that the addition of 18-crown-6 is cancelled, and a positive electrode sheet is finally obtained.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that the addition of lithium squarate is cancelled, and a positive electrode sheet is finally obtained.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that the addition of 18-crown-6 and lithium squarate is cancelled, and a positive electrode sheet is finally obtained.

[0091] Performance Test

[0092] The positive electrode sheets prepared in the examples and comparative examples were assembled with a graphite negative electrode into a battery. Under the test conditions of 2.0 - 4.5 V, the 0.2C discharge specific capacity, 1C discharge specific capacity at 25 °C, and the capacity retention rate after 200 cycles at 25 °C, a rate of 1C, a voltage range of 2.5 - 4.5 V, and a cut-off current of 0.05 mA were tested. The test results are shown in Table 1.

[0093] Table 1

[0094]

[0095] It can be seen from the data in Table 1 that compared with the test results of the comparative examples, the materials prepared in the examples have better structural performance, better discharge performance, and higher cycling efficiency. The batteries made of the materials prepared in the examples have excellent electrochemical performance.

[0096] From the above description, it can be seen that the above examples of the present invention achieve the following technical effects:

[0097] In step S1, by mixing a soluble metal salt, an organic ligand, and a first organic solvent, and through pH adjustment and coordination reaction, a framework material with specific pores is formed, which helps to provide more loading active sites for crown ether compounds and lithium supplement agents. In step S2, by first mixing a crown ether compound, a lithium supplement agent, and a second organic solvent to form a mixed solution, then impregnating and absorbing the framework material in the mixed solution, and then drying the obtained impregnated and absorbed material, a loaded material is obtained, which helps to improve the distribution uniformity of the crown ether compound and the lithium supplement agent in the framework material. The addition of the crown ether substance helps to inhibit the dissolution of manganese ions in the lithium iron phosphate manganese material, capture the dissolved manganese ions, and prevent the manganese ions from consuming the electrolyte and damaging the SEI film structure. The addition of the lithium supplement agent helps to supplement some of the lithium ions consumed during the formation of the SEI film during battery activation, thereby helping to improve the specific capacity and cycle stability of the battery. In step S3, through the mixing treatment of the loaded material, a polymer, and a third organic solvent, the loaded material is uniformly dispersed in the sol formed by the polymer and the third organic solvent to form a positive electrode functional material. The addition of the polymer helps to improve the interaction between the positive electrode functional material and the lithium iron phosphate manganese material, thereby helping to make the positive electrode functional material uniformly adhere to the surface of the lithium iron phosphate manganese material, play a supporting role for the lithium iron phosphate manganese crystal, and help to reduce the collapse of the crystal structure during the cycle. Therefore, attaching the positive electrode functional material prepared in this application to the surface of the lithium iron phosphate manganese material helps to improve the specific capacity and cycle stability of the lithium iron phosphate manganese material.

[0098] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode functional material, characterized in that: The preparation method comprises the following steps: Step S1, mixing raw materials including a soluble metal salt, an organic ligand and a first organic solvent, and then sequentially performing pH adjustment and coordination reaction to obtain a framework material; Step S2, mixing raw materials including a crown ether compound, a lithium supplement agent and a second organic solvent to obtain a mixed solution, immersing the framework material in the mixed solution for absorption, and then drying the obtained immersion absorbent to obtain a load material; Step S3, mixing the raw materials including the load material, the high molecular polymer and the third organic solvent to obtain the positive electrode functional material.

2. The preparation method according to claim 1, characterized in that: In the step S2, the mass ratio of the crown ether compound to the lithium replenisher is (2-5):1; and / or, the mass ratio of the crown ether compound and the lithium replenisher to the mass of the framework material is (5-16):(10-20); and / or, the mass ratio of the crown ether compound and the lithium replenisher to the volume of the second organic solvent is (0.1-0.2 g):(1 mL).

3. The preparation method according to claim 1 or 2, characterized in that: The crown ether compound is selected from any one or more of 18-crown-6, 15-crown-5 and 12-crown-4; And / or, the lithium supplement is an organic lithium salt, preferably the organic lithium salt is selected from any one or more of lithium squarate, lithium oxalate and lithium citrate; And / or, the second organic solvent is selected from any one or more of anhydrous ethanol, acetone and anhydrous methanol; preferably, the second organic solvent is a combination of anhydrous ethanol and acetone, and the volume ratio of the anhydrous ethanol to the acetone is 1:(1-2).

4. The preparation method according to any one of claims 1 to 3, characterized in that The drying temperature is 60-90° C. and / or the drying time is 3-4 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In the step S3, the mass ratio of the support material to the high molecular weight polymer is (0.1-1):(10-20); and / or the mass ratio of the high molecular weight polymer to the volume of the third organic solvent is (5-10 g):(100 mL).

6. The preparation method according to any one of claims 1 to 5, characterized in that The high molecular polymer is selected from any one or more of polyethylene oxide, gelatin and polyethyl acrylate; preferably, the high molecular polymer is a combination of gelatin and polyethylene oxide, and the mass ratio of the gelatin to the polyethylene oxide is 3:(7-8); And / or, the third organic solvent is selected from any one or more of acetonitrile, anisole, chloroform, ethylene dichloride, dimethylformamide, N-methylpyrrolidone, glycerol, propylene glycol and ethylene glycol; preferably, the third organic solvent is a combination of N-methylpyrrolidone and ethylene glycol, and the volume ratio of the N-methylpyrrolidone to the ethylene glycol is 1:(1-3); And / or, the mixing treatment time is 12 to 20 hours; preferably, the mixing treatment is carried out in a stirring state, and the stirring speed of the mixing treatment is 300 to 400 rpm.

7. The preparation method according to any one of claims 1 to 6, characterized in that In the step S1, the molar ratio of the soluble metal salt to the organic ligand is (1-3):(1-2); And / or, the ratio of the mass of the soluble metal salt to the volume of the first organic solvent is (2-15 g): (10~20mL); Preferably, the soluble metal salt is selected from any one or more of aluminum chloride hexahydrate, iron phosphate, zinc sulfate, copper sulfate pentahydrate, aluminum nitrate nonahydrate and nickel sulfate; and / or, the organic ligand is selected from any one or more of aminobenzoic acid amine, 2-methylimidazole, 1,3,5-benzenetricarboxylic acid and terephthalic acid; And / or, the first organic solvent is selected from any one or more of N,N-dimethylformamide, ethanol and water; preferably, the first organic solvent is a combination of N,N-dimethylformamide, ethanol and water, and the volume ratio of the N,N-dimethylformamide, the ethanol and the water is (1-3):(1-2):1; And / or, an organic acid is used for the pH adjustment, and the pH value of the solution after the pH adjustment is 3 to 4; preferably, the organic acid is selected from any one or more of citric acid, acetic acid and formic acid; And / or, the temperature of the coordination reaction is 150-200° C.; and / or, the time of the coordination reaction is 8-12 hours.

8. A positive electrode functional material, characterized in that: The positive electrode functional material is prepared by the preparation method described in any one of claims 1 to 7.

9. A positive electrode sheet, comprising a current collector and a positive electrode active layer, characterized in that: The positive electrode active layer contains the positive electrode functional material according to claim 8 and lithium iron manganese phosphate; preferably, the mass ratio of the positive electrode functional material to the lithium iron manganese phosphate is (0.3-0.6):

1.

10. A lithium ion battery comprising a positive electrode, an electrolyte and a negative electrode, characterized in that: The positive electrode sheet is the positive electrode sheet according to claim 9.

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