Rate type lithium iron phosphate positive electrode material, preparation method and battery thereof

Abstract

The invention discloses a rate type lithium iron phosphate positive electrode material, a preparation method and a battery thereof, firstly, iron phosphate is modified by dopamine hydrochloride, the surface activity of the iron phosphate is improved, subsequent doping of cobalt and magnesium is facilitated, meanwhile, excessive growth of crystal grains can be limited in high-temperature sintering, nitrogen and carbon are introduced into lithium iron phosphate, and the rate type lithium iron phosphate positive electrode material is prepared. A carbon-nitrogen coating layer is formed, so that the electronic conductivity is improved; then, isopropyl tri (dioctyl pyrophosphate acyloxy) titanate, cobalt oxide and magnesium oxide are adopted to prepare a doping agent, cobalt and magnesium are uniformly doped into lithium iron phosphate crystal lattices to form bulk phase doping, and cobalt and magnesium co-doping synergistically improves the electronic conductivity and structural stability of the lithium iron phosphate material; finally, a biomass carbon source beta-cyclodextrin is adopted for carbon coating, a uniform carbon layer is formed on the surface of the lithium iron phosphate, and the electrochemical performance of the lithium iron phosphate is further improved; the lithium iron phosphate material prepared by the method also has good electrochemical performance under high magnification.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium iron phosphate preparation, and more particularly to a rate type lithium iron phosphate cathode material, a preparation method thereof and a battery. BACKGROUND

[0002] In the field of new energy vehicles, high-rate lithium batteries greatly shorten the charging time of electric vehicles, helping to alleviate user anxiety about mileage and charging time, and improving the convenience of vehicle use; in the energy storage system, it can be applied to power grid peak shaving, large emergency power supply and distributed energy storage facilities to meet the demand for rapid charging and discharging to cope with power supply and demand imbalance; in the direction of industrial equipment and unmanned aerial vehicles, for portable devices that need frequent high-power output or rapid power supply, such as electric tools, unmanned aerial vehicles, etc., lithium batteries with high rate performance can significantly improve work efficiency. As the core part of the battery, the cathode material directly affects the energy density, rate performance and overall performance and cost of the battery. Therefore, developing a cathode material with excellent performance for lithium-ion batteries has become a key to promoting the sustainable and high-quality development of the electric vehicle industry and other energy storage power fields.

[0003] The cathode material has been widely studied and entered the mass application stage due to its low cost, environmental friendliness, long cycle life, safety and other advantages, and occupies more than half of the market share. Rate performance is a key indicator for phosphate cathode materials, and has an important influence on the performance of rapid charging and discharging of the battery in a short time. However, the poor electronic conductivity and lithium ion migration rate of lithium iron phosphate material restrict its rate performance, making it difficult to meet the power performance indicators of power lithium-ion batteries, which limits the application of lithium iron phosphate electrode material.

[0004] Therefore, improving the rate performance of lithium iron phosphate material has become one of the key research directions of lithium iron phosphate cathode material. At present, there are methods such as bulk doping, morphology control, crystal face coating of conductive layer and construction of three-dimensional conductive structure to accelerate lithium ion migration, shorten its diffusion path and improve electronic conductivity. For example, Chinese patent CN119674025A discloses a carbon-coated titanium-doped lithium iron phosphate cathode material and a preparation method thereof. The ferrous solution and the phosphorus source solution are mixed according to a certain proportion, hydrochloric acid dopamine is added, the pH is adjusted, then the titanium source solution is added, the mixture is stirred uniformly, the pH is continuously adjusted, and the titanium-embedded polydopamine-coated ferrous phosphate octahydrate is obtained. Then the titanium-embedded polydopamine-coated ferrous phosphate octahydrate is calcined in an inert gas atmosphere to obtain carbon-coated titanium-doped anhydrous ferrous phosphate. Finally, the carbon-coated titanium-doped anhydrous ferrous phosphate is mixed with lithium phosphate and a carbon source, ball milled, spray dried and calcined to obtain the carbon-coated titanium-doped lithium iron phosphate cathode material. The invention increases the stability of the precursor by using hydrochloric acid dopamine and its polymer polydopamine, provides a more uniform titanium source distribution for titanium doping of lithium iron phosphate, provides more abundant channels for electron transfer through titanium doping and carbon coating, and improves the electronic conductivity of the material.

[0005] For another example, Chinese patent CN116895748A discloses an LFMP@LFMCP composite material, which comprises an LFMP core and a LFMCP shell in-situ coated on the surface thereof; wherein the LFMP is magnesium-doped lithium iron phosphate; the LFMCP is magnesium-cobalt co-doped lithium iron phosphate; the electrochemical performance of the lithium iron phosphate material is improved by magnesium-cobalt co-doping and forming a core-shell structure. For another example, Chinese patent CN102227024A discloses a positive electrode material lithium iron phosphate suitable for power lithium ion batteries and a preparation method thereof. Lithium source compound, iron source and phosphorus acid source compound are mixed to obtain a lithium iron phosphate precursor mixture, then one or more than one of the compounds of doping elements manganese, cobalt, vanadium, nickel, aluminum, magnesium, calcium and zinc are added to the lithium iron phosphate precursor mixture to obtain a doped lithium iron phosphate precursor, then an organic carbon source and / or an inorganic carbon source are added to obtain a precursor of the positive electrode material lithium iron phosphate for power lithium ion batteries, and finally a protective gas or a reducing gas is introduced for high-temperature sintering to obtain the lithium iron phosphate suitable for the positive electrode material of power lithium ion batteries. The method improves the electronic conductivity of the material and enhances the electrochemical performance by metal compound doping and carbon coating.

[0006] The comprehensive use of these methods in the prior art can improve the rate performance of lithium iron phosphate material to a certain extent, but there are problems in the uniformity of doping and the stability of the material after doping modification. On this basis, it is of great significance to further study how to better improve the rate performance of lithium iron phosphate cathode material. SUMMARY

[0007] In view of the above, the application provides a rate type lithium iron phosphate positive electrode material, a preparation method and a battery thereof, the surface activity of iron phosphate is first improved, which is beneficial to subsequent doping, Co and Mg are uniformly doped, the crystal structure of lithium iron phosphate is more stable, and finally, a uniform carbon layer is formed on the surface of lithium iron phosphate, and the electrochemical performance of lithium iron phosphate is significantly improved.

[0008] The application provides a preparation method of a rate type lithium iron phosphate positive electrode material, characterized by comprising the following steps:

[0009] (1) dopa hydrochloride is added into Tris-HCl buffer solution, stirred uniformly, then iron phosphate is added and ultrasonic dispersion is carried out, and the mixture is left at room temperature, and then filtration, washing and vacuum drying are carried out to obtain modified iron phosphate;

[0010] (2) isopropyl tri(dioctyl pyrophosphoric acyloxy) titanate is added into an ethanol solution, stirred uniformly, then cobalt oxide and magnesium oxide are added, heated and stirred, and then filtration, washing and vacuum drying are carried out to obtain a doping agent;

[0011] (3) the modified iron phosphate, lithium carbonate, beta-cyclodextrin and the doping agent are mixed and ball milled, and vacuum drying is carried out to obtain dry particles;

[0012] (4) the dry particles are sintered under a nitrogen atmosphere, and naturally cooled to room temperature to obtain the rate type lithium iron phosphate positive electrode material.

[0013] The application first modifies iron phosphate with dopa hydrochloride, wherein the dopa hydrochloride contains catechol groups and amino groups, the catechol groups can be combined with Fe 3+ on the surface of iron phosphate through coordination to form a dopa-Fe 3+ complex and be adsorbed on the surface of iron phosphate particles; the amino group-NH2 interacts with functional groups such as -OH on the surface of iron phosphate through electrostatic interaction or hydrogen bonding to enhance adsorption stability; in a weak alkaline environment, dopa can undergo oxidative self-polymerization to form polydopamine, and the polydopamine formed by self-polymerization can form an organic coating layer on the surface of iron phosphate particles, which contains a large number of functional groups such as phenolic hydroxyl groups and amino groups, and these functional groups can act as active sites to enhance the interfacial reactivity of iron phosphate and provide a favorable environment for subsequent element doping.

[0014] Meanwhile, the polydopamine layer formed on the surface of iron phosphate will carbonize after high-temperature sintering and be converted into a nitrogen-doped carbon layer, nitrogen and carbon are introduced into lithium iron phosphate, and a C-N bond layer is formed; wherein, the carbon layer acts as a conductive network to directly improve the electronic conductivity of iron phosphate, nitrogen doping can significantly reduce the interfacial resistance of iron phosphate particles by introducing defect sites or changing the electronic structure of the carbon layer, and further enhance the electrochemical activity of the material; in addition, the polydopamine layer formed on the surface of iron phosphate will have a steric hindrance effect, which can limit the excessive growth of crystal grains in subsequent high-temperature sintering.

[0015] Then, the dopant is prepared with isopropyl tri(dioctyl pyrophosphoryl oxygen) titanate, cobalt oxide and magnesium oxide, wherein the isopropyl tri(dioctyl pyrophosphoryl oxygen) titanate is a long-chain molecule, which can form a barrier on the surface of the cobalt oxide and the magnesium oxide to avoid agglomeration, and can reduce the surface energy of the particles to reduce the tendency of spontaneous agglomeration, so that the cobalt oxide and the magnesium oxide are more uniformly distributed in the dopant and have good dispersibility and stability, and the cobalt and the magnesium are uniformly doped into the crystal lattice of the lithium iron phosphate to form a bulk doping, so that the crystal structure of the lithium iron phosphate is more stable.

[0016] Finally, the biomass carbon source β-cyclodextrin is used for carbon coating to form a uniform carbon layer on the surface of the lithium iron phosphate, and the electrochemical performance of the lithium iron phosphate is further improved, so that the surface carbon-coated lithium iron phosphate anode material with cobalt and magnesium co-doping and nitrogen doping is finally formed, and has excellent electrochemical performance.

[0017] In step (1), the concentration of the Tris-HCl buffer is 5-15 mmol / L, the pH is 8.5, and the amount used is 300-800 mL.

[0018] The Tris-HCl buffer affects the quality of the coating layer, and the suitable pH allows the hydrochloric acid dopamine to be uniformly coated on the surface of the iron phosphate particles.

[0019] In step (1), the mass ratio of the hydrochloric acid dopamine to the iron phosphate is 0.5-2:10.

[0020] The amount of the hydrochloric acid dopamine and the iron phosphate needs to be appropriate to obtain the modified iron phosphate with good dispersibility, stability and surface activity, and the lithium iron phosphate material with a balance between conductivity and active material ratio; if the amount of the hydrochloric acid dopamine is too large, the viscosity of the reaction system will increase, the dispersibility of the iron phosphate will decrease, the doping effect of the doping elements will be poor, and after carbonization, the carbon-nitrogen coating layer of the lithium iron phosphate coating will be too thick, which will hinder the migration of electrons and reduce the rate performance and other electrochemical performance of the lithium iron phosphate; if the amount of the hydrochloric acid dopamine is too small, the surface of the iron phosphate particles will not be fully modified, and the dispersibility, stability and surface activity will be insufficient, which is not conducive to the doping of the doping elements, and at the same time, the carbon-nitrogen coating layer after carbonization will be too thin, the electronic conductivity will be low, and the electrochemical performance of the lithium iron phosphate will be poor.

[0021] In step (1), the power of the ultrasonic dispersion is 200-500 W, the frequency is 50-70 kHz, and the time is 1-2 h; the room temperature standing time is 8-16 h.

[0022] In step (2), the mass ratio of the isopropyl tri(dioctyl pyrophosphoryl oxygen) titanate, the cobalt oxide, the magnesium oxide and the ethanol solution is 0.05-0.2:1-2:1-2:10-50.

[0023] The dopant of the application is prepared alone, and the good dispersibility and surface activity of the modified iron phosphate enable cobalt and magnesium to be uniformly doped; meanwhile, the cobalt oxide and magnesium oxide as active components modify the stability and conductivity of the lithium iron phosphate, and the synergistic effect of cobalt and magnesium forms a uniform and continuous conductive network with the internal carbon-nitrogen coating layer and the surface carbon coating layer, which together improves the electrochemical properties of the lithium iron phosphate, such as electronic conductivity, specific capacity, rate performance, etc. The amount of isopropyl tri(dioctyl pyrophosphoryloxy) titanate that is too small may lead to poor interface bonding of the substances, easy agglomeration, and poor uniform doping, which is not conducive to the formation of a uniform and continuous conductive network; the amount of isopropyl tri(dioctyl pyrophosphoryloxy) titanate that is too large may form an excessive organic layer, which is not conducive to the subsequent synthesis reaction and affects the performance of the lithium iron phosphate, and even introduces impurities; the amount of cobalt and magnesium also needs to be appropriate, too little cannot achieve good results, and too much is not conducive to the stability of the lithium iron phosphate, and even blocks the electron transport channel and reduces the electrochemical properties of the lithium iron phosphate; therefore, appropriate amounts of isopropyl tri(dioctyl pyrophosphoryloxy) titanate, cobalt oxide and magnesium oxide can better form a uniformly dispersed dopant, which is more conducive to uniformly doping cobalt and magnesium into the lithium iron phosphate, so that a uniform and continuous conductive network is formed, and the stability, electronic conductivity, specific capacity and rate performance of the lithium iron phosphate are improved.

[0024] In step (2), the ethanol solution is an ethanol aqueous solution with a concentration of 70-95wt%.

[0025] In step (2), the temperature of the heating and stirring is 70-90℃, and the time is 0.5-2h.

[0026] In step (3), the mass ratio of the total mass of the modified iron phosphate and lithium carbonate to the mass of the β-cyclodextrin and the dopant is 1:0.02-0.1:0.005-0.02, and the molar ratio of iron to lithium is 1:1.0-1.1.

[0027] The amount of cobalt and magnesium, the carbon-nitrogen coating layer and the surface carbon coating layer form a uniform and continuous conductive network, which together improves the electrochemical properties of the lithium iron phosphate, and the amount of each substance needs to be controlled to maximize the synergistic effect, so that the stability of the lithium iron phosphate is not insufficient, the coating layer is not defective, and the electron transport channel is not blocked and lengthened due to an unbalanced content of a certain element.

[0028] In step (3), the specific conditions of the ball milling are as follows: the rotation speed is 200-500rpm, the ball milling medium is anhydrous ethanol, the ratio of the material to the liquid is 1:1-2, the grinding ball is a zirconium oxide ball, the ratio of the ball to the material is 5-15:1, and the ball milling time is 3-6h.

[0029] In step (4), the sintering temperature is 600-800℃, and the sintering time is 8-12h.

[0030] The application discloses a lithium iron phosphate positive electrode material with a high rate capability.

[0031] The application discloses a battery, and the positive electrode material of the battery is the lithium iron phosphate positive electrode material with the high rate capability.

[0032] The application at least has the following beneficial effects:

[0033] (1) First, the surface activity of the iron phosphate is improved by modifying the iron phosphate with dopamine hydrochloride, which is beneficial to the subsequent doping of cobalt and magnesium, and can limit the excessive growth of the crystal grains in the high-temperature sintering and introduce nitrogen and carbon into the lithium iron phosphate to form a carbon-nitrogen coating layer, thereby improving the electronic conductivity and the electrochemical performance of the lithium iron phosphate;

[0034] (2) Then, the dopant is prepared by using isopropyl tris (dioctyl pyrophosphoric acyloxy) titanate, cobalt oxide and magnesium oxide, the cobalt oxide and the magnesium oxide of the dopant are uniformly dispersed, the cobalt and the magnesium are uniformly doped into the lithium iron phosphate crystal lattice to form a bulk doping, and the lithium iron phosphate crystal structure is more stable; the cobalt and the magnesium are co-doped to improve the electronic conductivity and the structural stability of the lithium iron phosphate material, and improve the electrochemical performance of the lithium iron phosphate material;

[0035] (3) Finally, the biomass carbon source beta-cyclodextrin is used for carbon coating to form a uniform carbon layer on the surface of the lithium iron phosphate, and the electrochemical performance of the lithium iron phosphate is further improved;

[0036] (4) The lithium iron phosphate positive electrode material with the high rate capability prepared by the application has uniform cobalt and magnesium co-doping, a carbon-nitrogen coating layer in the lithium iron phosphate and a uniform carbon coating layer on the surface of the lithium iron phosphate, the uniform and continuous conductive network is formed by the synergistic effect of the cobalt and the magnesium, the internal carbon-nitrogen coating layer and the surface carbon coating layer, the electrochemical performance of the lithium iron phosphate is significantly improved, the discharge specific capacity of the lithium iron phosphate is greater than or equal to 173 mAh / g at 25 DEG C and 0.1 C, and the discharge specific capacity of the lithium iron phosphate is greater than or equal to 140 mAh / g at 25 DEG C and 20 C, and the lithium iron phosphate has good discharge specific capacity and rate performance. DETAILED DESCRIPTION

[0037] The embodiments of the application will be described in more detail below. The application can be implemented in various forms, and should not be interpreted as being limited to the embodiments set forth herein, but rather the embodiments are provided to make the application more thorough and complete. It should be understood that the embodiments of the application are only for exemplary purposes, and are not used to limit the protection scope of the application.

[0038] Embodiment 1:

[0039] The embodiments of the application are implemented according to the following technical solutions, including the following steps:

[0040] (1) Dopamine hydrochloride is added to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stirred uniformly, and then iron phosphate is added, wherein the mass ratio of dopamine hydrochloride to iron phosphate is 1:10, and then ultrasonic dispersion is carried out under the condition of a power of 300 W and a frequency of 55 kHz for 1 h, and then the mixture is left to stand at room temperature for 12 h, and then suction filtration is carried out, and then the obtained product is washed with anhydrous ethanol and deionized water three times, and then vacuum drying is carried out at 80 DEG C, so as to obtain modified iron phosphate;

[0041] (2) Isopropyl tris (dioctyl pyrophosphoric acyl oxygen) titanate is added to 95 wt% of an ethanol aqueous solution, stirred uniformly, and then cobalt oxide and magnesium oxide are added, wherein the mass ratio of isopropyl tris (dioctyl pyrophosphoric acyl oxygen) titanate, cobalt oxide, magnesium oxide and the ethanol solution is 0.1:1:2:30, and then stirring is carried out at 80 DEG C for 1 h, and then suction filtration is carried out, and then the obtained product is washed with anhydrous ethanol three times, and then vacuum drying is carried out at 80 DEG C, so as to obtain a dopant;

[0042] (3) The modified iron phosphate, lithium carbonate, beta-cyclodextrin and the dopant are mixed and ball milled, wherein the mass ratio of the total mass of the modified iron phosphate and lithium carbonate to the mass of the beta-cyclodextrin and the dopant is 1:0.05:0.01, and the molar ratio of iron to lithium is 1:1.05, and then vacuum drying is carried out, so as to obtain dry particles; wherein the specific conditions of ball milling are as follows: the rotating speed is 300 rpm, the ball milling medium is anhydrous ethanol, the ratio of the material to the liquid is 1:1.5, the grinding ball is a zirconium oxide ball, the ratio of the ball to the material is 10:1, and the ball milling time is 4 h;

[0043] (4) The dry particles are sintered under a nitrogen atmosphere, wherein the sintering temperature is 700 DEG C, the sintering time is 10 h, and then natural cooling is carried out to room temperature, so as to obtain a rate type lithium iron phosphate positive electrode material.

[0044] Example 2:

[0045] The embodiment of the application is implemented according to the following technical scheme, which comprises the following steps:

[0046] (1) Dopamine hydrochloride is added to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stirred uniformly, and then iron phosphate is added, wherein the mass ratio of dopamine hydrochloride to iron phosphate is 1:10, and then ultrasonic dispersion is carried out under the condition of a power of 300 W and a frequency of 55 kHz for 1 h, and then the mixture is left to stand at room temperature for 12 h, and then suction filtration is carried out, and then the obtained product is washed with anhydrous ethanol and deionized water three times, and then vacuum drying is carried out at 80 DEG C, so as to obtain modified iron phosphate;

[0047] (2) adding isopropyl tri(dioctyl pyrophosphoryl oxy) titanate into 90wt% ethanol aqueous solution, stirring uniformly, then adding cobalt oxide and magnesium oxide, wherein the mass ratio of isopropyl tri(dioctyl pyrophosphoryl oxy) titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.1:1.5:1.5:30, stirring at 80℃ for 1h, then suction filtering, washing with anhydrous ethanol for 3 times, and vacuum drying at 80℃ to obtain a dopant;

[0048] (3) mixing the modified iron phosphate, lithium carbonate, β-cyclodextrin and the dopant and ball milling, wherein the mass ratio of the total mass of the modified iron phosphate and the lithium carbonate to the mass of the β-cyclodextrin and the dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, and vacuum drying to obtain dry particles; wherein the specific conditions of the ball milling are as follows: the rotation speed is 300rpm, the ball milling medium is anhydrous ethanol, the solid-liquid ratio is 1:1.5, the grinding ball is zirconium oxide ball, the ball-to-material ratio is 10:1, and the ball milling time is 4h;

[0049] (4) sintering the dry particles under a nitrogen atmosphere, wherein the sintering temperature is 700℃, the sintering time is 10h, and the sintering is naturally cooled to room temperature to obtain a rate type lithium iron phosphate positive electrode material.

[0050] Example 3:

[0051] The embodiment of the application is implemented according to the following technical scheme, comprising the following steps:

[0052] (1) adding dopamine hydrochloride into 500mL Tris-HCl buffer solution with a concentration of 10mmol / L and a pH of 8.5, stirring uniformly, then adding iron phosphate, wherein the mass ratio of dopamine hydrochloride to iron phosphate is 1:10, then ultrasonic dispersion is carried out under the condition that the power is 300W and the frequency is 55kHz for 1h, then the system is left to stand at room temperature for 12h, suction filtering, washing with anhydrous ethanol and deionized water for 3 times in turn, and vacuum drying at 80℃ to obtain modified iron phosphate;

[0053] (2) adding isopropyl tri(dioctyl pyrophosphoryl oxy) titanate into 90wt% ethanol aqueous solution, stirring uniformly, then adding cobalt oxide and magnesium oxide, wherein the mass ratio of isopropyl tri(dioctyl pyrophosphoryl oxy) titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.1:2:1:30, stirring at 80℃ for 1h, then suction filtering, washing with anhydrous ethanol for 3 times, and vacuum drying at 80℃ to obtain a dopant;

[0054] (3) mixing modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant by ball milling, wherein the mass ratio of the total mass of modified iron phosphate and lithium carbonate to the mass of β-cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, vacuum drying to obtain dry particles; wherein the specific conditions of ball milling are: rotation speed is 300 rpm, ball milling medium is anhydrous ethanol, solid-liquid ratio is 1:1.5, grinding ball is zirconium oxide ball, ball-to-material ratio is 10:1, ball milling time is 4 h;

[0055] (4) sintering the dry particles under a nitrogen atmosphere, wherein the sintering temperature is 700 DEG C, the sintering time is 10 h, and the natural cooling to room temperature to obtain a rate type lithium iron phosphate positive electrode material.

[0056] Example 4

[0057] The embodiment of the application is implemented according to the following technical scheme, comprising the following steps:

[0058] (1) adding dopamine hydrochloride into 800 mL Tris-HCl buffer solution with a concentration of 5 mmol / L and a pH of 8.5, stirring uniformly, then adding iron phosphate, wherein the mass ratio of dopamine hydrochloride to iron phosphate is 0.5:10, then ultrasonic dispersion is carried out under the condition of a power of 300 W and a frequency of 55 kHz for 1 h, then standing at room temperature for 12 h, then suction filtration, then washing with anhydrous ethanol and deionized water for 3 times respectively, and then vacuum drying at 80 DEG C to obtain modified iron phosphate;

[0059] (2) adding isopropyl tri(dioctyl pyrophosphoryloxy) titanate into 80 wt% ethanol aqueous solution, stirring uniformly, then adding cobalt oxide and magnesium oxide, wherein the mass ratio of isopropyl tri(dioctyl pyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.2:1.5:2:50, then stirring at 70 DEG C for 2 h, then suction filtration, then washing with anhydrous ethanol for 3 times, and then vacuum drying at 80 DEG C to obtain a dopant;

[0060] (3) mixing modified iron phosphate, lithium carbonate, β-cyclodextrin and dopant by ball milling, wherein the mass ratio of the total mass of modified iron phosphate and lithium carbonate to the mass of β-cyclodextrin and dopant is 1:0.1:0.005, the molar ratio of iron to lithium is 1:1.05, vacuum drying to obtain dry particles; wherein the specific conditions of ball milling are: rotation speed is 300 rpm, ball milling medium is anhydrous ethanol, solid-liquid ratio is 1:1.5, grinding ball is zirconium oxide ball, ball-to-material ratio is 10:1, ball milling time is 4 h;

[0061] (4) sintering the dry particles under a nitrogen atmosphere, wherein the sintering temperature is 700 DEG C, the sintering time is 10 h, and the natural cooling to room temperature to obtain a rate type lithium iron phosphate positive electrode material.

[0062] Example 5

[0063] The embodiment of the present application is implemented according to the following technical scheme, comprising the following steps:

[0064] (1) Dopamine hydrochloride is added into 300 mL Tris-HCl buffer solution with a concentration of 15 mmol / L and a pH of 8.5, and stirred uniformly, then iron phosphate is added, wherein the mass ratio of dopamine hydrochloride to iron phosphate is 2:10, then ultrasonic dispersion is carried out under the condition of a power of 300 W and a frequency of 55 kHz for 1 h, and then the mixture is left to stand at room temperature for 12 h, and then filtered, washed with anhydrous ethanol and deionized water for 3 times, and dried at 80 DEG C under vacuum to obtain modified iron phosphate;

[0065] (2) Isopropyl tri (dioctyl pyrophosphoric acyl oxygen) titanate is added into 70 wt% ethanol aqueous solution, and stirred uniformly, then cobalt oxide and magnesium oxide are added, wherein the mass ratio of isopropyl tri (dioctyl pyrophosphoric acyl oxygen) titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.05:1:1:10, and then stirred at 90 DEG C for 0.5 h, and then filtered, washed with anhydrous ethanol for 3 times, and dried at 80 DEG C under vacuum to obtain a dopant;

[0066] (3) The modified iron phosphate, lithium carbonate, beta-cyclodextrin and the dopant are mixed and ball milled, wherein the mass ratio of the total mass of the modified iron phosphate and lithium carbonate to the mass of the beta-cyclodextrin and the dopant is 1:0.02:0.02, and the molar ratio of iron to lithium is 1:1.05, and then dried under vacuum to obtain dry particles; wherein the specific conditions of ball milling are as follows: the rotation speed is 300 rpm, the ball milling medium is anhydrous ethanol, the ratio of material to liquid is 1:1.5, the grinding ball is zirconium oxide ball, the ratio of ball to material is 10:1, and the ball milling time is 4 h;

[0067] (4) The dry particles are sintered under a nitrogen atmosphere, wherein the sintering temperature is 700 DEG C, the sintering time is 10 h, and then the mixture is naturally cooled to room temperature to obtain a rate type lithium iron phosphate positive electrode material.

[0068] Comparative Example 1: Iron phosphate is not modified:

[0069] The embodiment of the present application is implemented according to the following technical scheme, comprising the following steps:

[0070] (1) Isopropyl tri (dioctyl pyrophosphoric acyl oxygen) titanate is added into 90 wt% ethanol aqueous solution, and stirred uniformly, then cobalt oxide and magnesium oxide are added, wherein the mass ratio of isopropyl tri (dioctyl pyrophosphoric acyl oxygen) titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.1:1:2:30, and then stirred at 80 DEG C for 1 h, and then filtered, washed with anhydrous ethanol for 3 times, and dried at 80 DEG C under vacuum to obtain a dopant;

[0071] (2) mixing modified iron phosphate, lithium carbonate, beta cyclodextrin and dopant by ball milling, wherein the mass ratio of the total mass of modified iron phosphate and lithium carbonate to the mass of beta cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, the dopant is obtained by mixing cobalt oxide and magnesium oxide at a mass ratio of 2:1, and vacuum drying to obtain dry particles; wherein the specific conditions of ball milling are: the rotation speed is 300 rpm, the ball milling medium is anhydrous ethanol, the solid-liquid ratio is 1:1.5, the grinding ball is zirconium oxide ball, the ball-to-material ratio is 10:1, and the ball milling time is 4h;

[0072] (4) sintering the dry particles under a nitrogen atmosphere, wherein the sintering temperature is 700 DEG C, the sintering time is 10h, and the natural cooling to room temperature to obtain a lithium iron phosphate positive electrode material of the rate type.

[0073] Comparative Example 2: the dopant is cobalt oxide and magnesium oxide, and is directly mixed with modified iron phosphate, lithium carbonate and beta cyclodextrin by ball milling:

[0074] The embodiment of the application is implemented according to the following technical scheme, comprising the following steps:

[0075] (1) adding dopamine hydrochloride into 500mL Tris-HCl buffer solution with a concentration of 10mmol / L and a pH of 8.5, stirring uniformly, then adding iron phosphate, wherein the mass ratio of dopamine hydrochloride to iron phosphate is 1:10, then performing ultrasonic dispersion under the condition of a power of 300W and a frequency of 55kHz for 1h, then standing at room temperature for 12h, then performing suction filtration, then washing with anhydrous ethanol and deionized water for 3 times respectively, and then performing vacuum drying at 80 DEG C to obtain modified iron phosphate;

[0076] (2) mixing modified iron phosphate, lithium carbonate, beta cyclodextrin and dopant by ball milling, wherein the mass ratio of the total mass of modified iron phosphate and lithium carbonate to the mass of beta cyclodextrin and dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, the dopant is obtained by mixing cobalt oxide and magnesium oxide at a mass ratio of 2:1, and vacuum drying to obtain dry particles; wherein the specific conditions of ball milling are: the rotation speed is 300 rpm, the ball milling medium is anhydrous ethanol, the solid-liquid ratio is 1:1.5, the grinding ball is zirconium oxide ball, the ball-to-material ratio is 10:1, and the ball milling time is 4h;

[0077] (4) sintering the dry particles under a nitrogen atmosphere, wherein the sintering temperature is 700 DEG C, the sintering time is 10h, and the natural cooling to room temperature to obtain a lithium iron phosphate positive electrode material of the rate type.

[0078] Comparative Example 3: the dopant is cobalt oxide, and is directly mixed with modified iron phosphate, lithium carbonate and beta cyclodextrin by ball milling:

[0079] The embodiment of the application is implemented according to the following technical scheme, comprising the following steps:

[0080] (1) Dopamine hydrochloride was added to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stirred uniformly, and then iron phosphate was added, wherein the mass ratio of dopamine hydrochloride to iron phosphate was 1:10, then ultrasonic dispersion was carried out under the condition of a power of 300 W and a frequency of 55 kHz for 1 h, and then the mixture was left to stand at room temperature for 12 h, filtered, washed with anhydrous ethanol and deionized water three times in turn, and vacuum dried at 80 DEG C to obtain modified iron phosphate;

[0081] (2) Isopropyl tri(dioctyl pyrophosphoryloxy) titanate was added to 90 wt% of an ethanol aqueous solution, stirred uniformly, and then cobalt oxide was added, wherein the mass ratio of isopropyl tri(dioctyl pyrophosphoryloxy) titanate, cobalt oxide and the ethanol solution was 0.1:3:30, and then the mixture was stirred at 80 DEG C for 1 h, filtered, washed with anhydrous ethanol three times, and vacuum dried at 80 DEG C to obtain a dopant;

[0082] (3) The modified iron phosphate, lithium carbonate, beta-cyclodextrin and the dopant were mixed and ball milled, wherein the mass ratio of the total mass of the modified iron phosphate and lithium carbonate to the mass of the beta-cyclodextrin and the dopant was 1:0.05:0.01, the molar ratio of iron to lithium was 1:1.05, and vacuum drying was performed to obtain dry particles; wherein the ball milling was performed under the following conditions: a rotation speed of 300 rpm, anhydrous ethanol as the ball milling medium, a solid-liquid ratio of 1:1.5, zirconium oxide balls as the grinding balls, a ball-to-material ratio of 10:1, and a ball milling time of 4 h;

[0083] (4) The dry particles were sintered under a nitrogen atmosphere, wherein the sintering temperature was 700 DEG C, the sintering time was 10 h, and natural cooling was performed to room temperature to obtain a rate-type lithium iron phosphate positive electrode material.

[0084] In the comparative example 4, the dopant was magnesium oxide, which was directly mixed and ball milled with the modified iron phosphate, lithium carbonate and beta-cyclodextrin:

[0085] The embodiment of the present application is implemented according to the following technical scheme, which comprises the following steps:

[0086] (1) Dopamine hydrochloride was added to 500 mL of Tris-HCl buffer solution with a concentration of 10 mmol / L and a pH of 8.5, stirred uniformly, and then iron phosphate was added, wherein the mass ratio of dopamine hydrochloride to iron phosphate was 1:10, then ultrasonic dispersion was carried out under the condition of a power of 300 W and a frequency of 55 kHz for 1 h, and then the mixture was left to stand at room temperature for 12 h, filtered, washed with anhydrous ethanol and deionized water three times in turn, and vacuum dried at 80 DEG C to obtain modified iron phosphate;

[0087] (2) adding isopropyl tri(dioctyl pyrophosphoryloxy) titanate into 90wt% ethanol aqueous solution, stirring uniformly, then adding magnesium oxide, wherein the mass ratio of isopropyl tri(dioctyl pyrophosphoryloxy) titanate, magnesium oxide and ethanol solution is 0.1:3:30, stirring at 80℃ for 1h, then suction filtering, washing with anhydrous ethanol for 3 times, vacuum drying at 80℃ to obtain a dopant;

[0088] (3) mixing modified iron phosphate, lithium carbonate, β-cyclodextrin and the dopant and ball milling, wherein the mass ratio of the total mass of modified iron phosphate and lithium carbonate to the mass of β-cyclodextrin and the dopant is 1:0.05:0.01, the molar ratio of iron to lithium is 1:1.05, vacuum drying to obtain dry particles; wherein the specific conditions of ball milling are: rotation speed is 300rpm, ball milling medium is anhydrous ethanol, solid-liquid ratio is 1:1.5, grinding ball is zirconium oxide ball, ball-to-material ratio is 10:1, ball milling time is 4h;

[0089] (4) sintering the dry particles under nitrogen atmosphere, wherein the sintering temperature is 700℃, the sintering time is 10h, naturally cooling to room temperature to obtain a rate type lithium iron phosphate positive electrode material.

[0090] The lithium iron phosphate positive electrode materials obtained in the above examples and comparative examples are subjected to a button cell test: the lithium iron phosphate positive electrode material, acetylene black and polyvinylidene fluoride obtained are dissolved in an appropriate amount of N-methyl pyrrolidone solvent according to a mass ratio of 8:1:1, uniformly mixed and coated on an aluminum foil, vacuum dried and then cut into an electrode sheet with a diameter of 14mm by a slicing machine, with a surface density of 8mg / cm 2 , to prepare a positive electrode sheet; a lithium metal sheet is used as a negative electrode; a separator is an imported polypropylene microporous membrane (Celgard 2400); an electrolyte is a 1mol / L LiPF6 solution, and a solvent is a mixed solution of ethylene carbonate (EC):dimethyl carbonate (DMC)=1:1 in volume ratio, which is assembled into a button cell (CR2032) in an argon-filled glove box, and then the assembled battery is subjected to charge and discharge test in a blue cell test system. The discharge specific capacity at 0.1C rate and the discharge specific capacity at 20C rate of the examples and comparative examples at 25℃ are shown in Table 1.

[0091] As shown in Table 1, the rate type lithium iron phosphate positive electrode material prepared in the present application has excellent electrochemical performance, compared with Comparative Examples 1-4, Examples 1-5 have higher discharge specific capacity and capacity retention rate at 0.1C and 20C rates, the discharge specific capacity thereof at 25℃, 0.1C is ≥173mAh / g, and the discharge specific capacity thereof at 25℃, 20C is ≥140mAh / g, which fully proves that the present application can significantly improve the discharge performance and rate performance of lithium iron phosphate.

[0092] The iron phosphate of the comparative example 1 is not modified, and the electrochemical performance of the obtained lithium iron phosphate positive electrode material is obviously reduced, which proves that the modification of the iron phosphate has an important role in improving the electrochemical performance of the lithium iron phosphate positive electrode material; the comparative example 2 is not mixed and modified with isopropyl tri(dioctyl pyrophosphoric acyloxy) titanate, and the electrochemical performance of the obtained lithium iron phosphate positive electrode material is obviously reduced, which proves that the prepared dopant has better dispersibility and doping performance, and plays a crucial role in improving the electrochemical performance of the lithium iron phosphate positive electrode material; the electrochemical performance of the comparative example 3 and the comparative example 4 is low, which fully proves that the synergistic effect of cobalt and magnesium is better than the doping effect of single cobalt element or magnesium element; in summary, the uniform cobalt-magnesium co-doping, and the combined effect of the carbon-nitrogen coating layer inside the lithium iron phosphate and the uniform carbon coating layer on the surface of the lithium iron phosphate make the specific capacity, rate performance and other electrochemical performances of the lithium iron phosphate material obviously improved.

[0093] Table 1 Performance test results of products of examples and comparative examples

[0094]

[0095] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a rate-type lithium iron phosphate cathode material, characterized in that, The method comprises the following steps: (1) adding dopamine hydrochloride into Tris-HCl buffer solution, stirring uniformly, adding iron phosphate, ultrasonic dispersion, standing at room temperature, suction filtration, washing, vacuum drying to obtain modified iron phosphate; (2) adding isopropyl tri(dioctyl pyrophosphoryloxy) titanate into ethanol solution, stirring uniformly, adding cobalt oxide and magnesium oxide, heating and stirring, then suction filtration, washing, vacuum drying to obtain a dopant; (3) mixing the modified iron phosphate, lithium carbonate, β-cyclodextrin and the dopant, ball milling, vacuum drying to obtain dry particles; (4) sintering the dry particles under nitrogen atmosphere, naturally cooling to room temperature to obtain a rate type lithium iron phosphate positive electrode material.

2. The preparation method of the one kind of the ratio type lithium iron phosphate positive electrode material according to claim 1, characterized in that, In step (1), the concentration of the Tris-HCl buffer solution is 5-15 mmol / L, the pH is 8.5, and the amount is 300-800 mL.

3. The preparation method of the one kind of the ratio type lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the mass ratio of dopamine hydrochloride to iron phosphate is 0.5-2:

10.

4. The preparation method of the specific capacity type lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the ultrasonic dispersion power is 200-500 W, the frequency is 50-70 kHz, and the time is 1-2 h; the standing time at room temperature is 8-16 h.

5. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), the mass ratio of isopropyl tri(dioctyl pyrophosphoryloxy) titanate, cobalt oxide, magnesium oxide and ethanol solution is 0.05-0.2:1-2:1-2:10-50.

6. The method of claim 1 or 5, wherein the method is characterized by: In step (2), the ethanol solution is an ethanol aqueous solution with a concentration of 70-95 wt%.

7. The method for preparing a rate-multiply lithium iron phosphate cathode material according to claim 1, characterized in that, In step (2), the heating and stirring temperature is 70-90℃, and the time is 0.5-2 h.

8. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), the mass ratio of the total mass of the modified iron phosphate and lithium carbonate to the mass of the β-cyclodextrin and the dopant is 1:0.02-0.1:0.005-0.02, wherein the molar ratio of iron to lithium is 1:1.0-1.

1.

9. The method for preparing a rate-multiplying lithium iron phosphate cathode material according to claim 1, characterized in that, In step (3), the ball milling specific conditions are: rotation speed is 200-500 rpm, ball milling medium is anhydrous ethanol, solid-liquid ratio is 1:1-2, grinding ball is zirconium oxide ball, ball-to-material ratio is 5-15:1, and ball milling time is 3-6 h.

10. The method of claim 1, wherein the lithium iron phosphate cathode material is prepared by the steps of: mixing a lithium source, an iron source, and a phosphate source; and heating the mixture to a temperature of 600-800°C for 2-10 hours. In step (4), the sintering temperature is 600-800℃, and the sintering time is 8-12 h.

11. A rate-type lithium iron phosphate cathode material, characterized in that, The rate type lithium iron phosphate positive electrode material is prepared by the preparation method of any one of claims 1-10.

12. A battery, characterized by The positive electrode material of the battery is the rate type lithium iron phosphate positive electrode material of claim 11.

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