Lithium manganese iron phosphate material and preparation method thereof

Abstract

The invention discloses a lithium iron manganese phosphate material and a preparation method thereof, and belongs to the technical field of lithium batteries, dopamine doped lithium chloride is polymerized on the surfaces of lithium iron manganese phosphate particles to form a coating layer of polydopamine doped lithium chloride, then a titanium dioxide nanotube is used to form a deposition layer, and finally the deposited titanium dioxide nanotube is used as a growth substrate to prepare the lithium iron manganese phosphate material. Secondary coating of the polydopamine is realized, and the lithium manganese iron phosphate material is formed after carbonization. Lithium chloride and polydopamine form a chelate to promote crosslinking and inhibit volume expansion and fracture of particles, and a Li-N-C structure is utilized to construct a lithium ion migration channel, so that rapid transmission of lithium ions is realized, growth of lithium dendrites is inhibited, rate capability is improved, and cycle life of the battery is prolonged. Hydrogen bonds of polydopamine phenolic hydroxyl groups and hydroxyl groups on the surfaces of the titanium dioxide nanotubes are anchored and combined to synergistically cooperate to inhibit dissolution and side reaction of manganese ions, a complete covering layer is formed on the surfaces of lithium manganese iron phosphate particles, and the conductivity of the lithium manganese iron phosphate material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a lithium iron manganese phosphate material and a preparation method thereof. Background Art

[0002] Lithium iron manganese phosphate is a cathode material for lithium-ion batteries with advantages such as high energy density, high stability, high safety, and long cycle life. The demand for lithium iron manganese phosphate in the downstream industry has been increasing year by year, which has promoted the exploration of improving its performance. Although the introduction of manganese element has improved some properties of the original cathode material for lithium-ion batteries, it has also caused new problems such as low conductivity and manganese dissolution. Therefore, it is necessary to modify lithium iron manganese phosphate on the basis of mature industrial production to optimize the battery performance and promote the further development of the industry.

[0003] Under this background, the surface coating technology of lithium iron manganese phosphate materials has been gradually promoted. The main coating materials are polysaccharide organic carbon sources, and the coating methods include sol-gel method and mixed grinding, etc. However, in the existing technology, carbon coating often has certain limitations in conductivity due to the low degree of graphitization, and the conductivity of the cathode material will affect the rate performance of the battery; in addition, although carbon coating can play a role in physical protection and inhibit manganese dissolution to improve the cycle stability of the cathode material, during the charge and discharge cycle process, the carbon coating layer is prone to cracking or peeling off, which will also affect the cycle performance of the battery. Summary of the Invention

[0004] The present invention provides a lithium iron manganese phosphate material and a preparation method thereof, which can solve the problem of poor cycle performance of the lithium iron manganese phosphate material in the existing technology.

[0005] The purpose of the present invention can be achieved by the following technical solutions: The present invention provides a preparation method of a lithium iron manganese phosphate material, comprising the following steps: Step 1: Prepare a Tris-HCl buffer solution, add lithium iron manganese phosphate particles, and ultrasonically disperse for 2 - 4 h to obtain a dispersion. Add hydrochloric acid dopamine and lithium chloride to the dispersion, stir at room temperature with an open mouth for 12 - 24 h, and obtain primary particles after suction filtration and washing. The particles are lithium iron manganese phosphate coated with polydopamine doped with lithium element. Under alkaline conditions, hydrochloric acid dopamine will first automatically oxidize to form dopamine quinone, and then further react and polymerize to form polydopamine. The alkaline condition will consume the hydrogen ions generated during the polymerization process and promote the forward reaction. After adding lithium chloride, lithium ions will combine with the hydroxyl and amino groups in the dopamine structure to form Li - O and Li - N bonds, and dopamine and lithium ions form a chelate, further promoting the polymerization reaction of dopamine and making the formed polydopamine cross-linked structure more compact.

[0006] Step 2: Disperse the titanium dioxide nanotubes in a Tris-HCl buffer solution to form a suspension. Add the primary particles to the suspension, stir evenly, and then let it stand for 1-2 h. After the titanium dioxide nanotubes are completely deposited, filter and wash with water to remove the excess titanium dioxide nanotubes, obtaining secondary particles with titanium dioxide nanotubes deposited on the surface. The phenolic hydroxyl groups in polydopamine serve as the anchoring points for connecting titanium dioxide, adsorbing the titanium dioxide nanotubes and causing them to deposit on the particle surface.

[0007] Step 3: Disperse the secondary particles in a Tris-HCl buffer solution, add dopamine hydrochloride, and stir at room temperature for 12-24 h under open conditions. After suction filtration, washing, and drying, calcine at 700-750 °C for 1-2 h in an inert atmosphere to obtain the lithium iron manganese phosphate material. After titanium dioxide is deposited on the particle surface in Step 2, polydopamine will grow around it with it as the matrix, and there is a tight combination between titanium dioxide and polydopamine, forming a uniform and complete surface structure.

[0008] During the calcination in an inert atmosphere, the polydopamine in the coating layer will gradually carbonize. Compared with other carbon source materials, the structure of the cross-linked and polymerized polydopamine is ordered and contains nitrogen elements, enabling a relatively high degree of graphitization. After carbonization, an Li-N-C structure will be formed, which can supplement ions and build a lithium ion channel while promoting the rapid transmission of lithium ions.

[0009] Further, the pH of the Tris-HCl buffer solution is 8-9.

[0010] Further, the D50 of the lithium iron manganese phosphate particles is 0.5-1.5 μm.

[0011] Further, in Step 1, the mass fraction of the lithium iron manganese phosphate particles in the Tris-HCl buffer solution is 10-20 g / L.

[0012] Further, in Step 1, the dopamine hydrochloride is added to the dispersion liquid at a concentration of 0.5-2 g / L.

[0013] Further, in Step 1, the mass of lithium chloride is 6-10% of the mass of dopamine hydrochloride.

[0014] Further, the diameter of the titanium dioxide nanotubes is 5-10 nm; The concentration of the titanium dioxide nanotubes in the suspension is 0.1-0.5 g / L.

[0015] Titanium dioxide nanotubes with a smaller diameter can better adsorb and deposit on the surface of the particles, and their high specific surface area can provide a larger growth platform for the coating of polydopamine in Step 3, forming a complete coating layer. Moreover, the interlaced coating of titanium dioxide nanotubes and polydopamine can effectively inhibit the dissolution of manganese, suppress side reactions, and improve the cycle stability.

[0016] Further, in Step 2, the mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension is 20-40:1.

[0017] Further, in Step 3, the mass fraction of the secondary particles in the Tris-HCl buffer solution is 10-20 g / L, and the mass-volume ratio of dopamine hydrochloride to the Tris-HCl buffer solution is 0.5-2 g / L.

[0018] Further, the inert gas is one of argon and nitrogen.

[0019] The present invention also provides a lithium iron manganese phosphate material prepared by the above-described preparation method.

[0020] Advantages of the present invention: (1) In the present invention, dopamine self-polymerization is carried out on the surface of lithium iron manganese phosphate particles to form a polydopamine coating, and lithium chloride is doped to form a chelate to promote cross-linking. The tightly cross-linked polydopamine layer can relieve the volume expansion during the ion deintercalation process, avoid the rupture of particles, and utilize the Li-N-C structure to build a lithium ion migration channel, realizing the rapid transmission of lithium ions, inhibiting the growth of lithium dendrites, improving the rate performance, and extending the cycle life of the battery.

[0021] (2) In the preparation of the present invention, a layer of nano titanium dioxide nanotubes is deposited. The mechanical properties of the coating layer are enhanced by the high hardness and nanotube structure, and it cooperates with the polydopamine carbonized layer to block the direct contact of the electrolyte with lithium iron manganese phosphate, inhibiting the dissolution of manganese ions and side reactions. Polydopamine is anchored and combined with the hydroxyl groups on the surface of the titanium dioxide nanotubes through hydrogen bonds of phenolic hydroxyl groups, realizing the uniform deposition of nanotubes on the surface of polydopamine.

[0022] (3) In the present invention, titanium dioxide nanotubes are used as the growth matrix, and polydopamine extends on its surface through π-π stacking and hydrogen bonds to form a complete covering layer, realizing the complete coating of lithium iron manganese phosphate particles. Polydopamine can be carbonized into a highly graphitized nitrogen-doped carbon layer, and its ordered structure can reduce the electron migration resistance, endowing the lithium iron manganese phosphate material with excellent electrical conductivity.

[0023] (4) The preparation process of the present invention does not require special equipment, the energy consumption of operations other than conventional carbonization and calcination is low, it will not increase the energy consumption additionally, the operation is simple, and it is easy to scale up production. Detailed implementation manners

[0024] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0025] Example 1 Prepare lithium iron manganese phosphate material: Step 1: Add 0.8 g of tris(hydroxymethyl)aminomethane into a beaker, then add 14.7 mL of 0.1 mol / L hydrochloric acid, add ultrapure water and stir. Detect that the pH is 8.5, and stop adding ultrapure water to obtain a Tris-HCl buffer solution.

[0026] Step 2: Commercially available lithium iron manganese phosphate particles (LiMn 0.5 Fe 0.5 PO4) with a D50 of 0.5 - 1.5 μm are added to the Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonically dispersed for 2 h to form a dispersion. Add dopamine hydrochloride and lithium chloride to the dispersion. The concentration of dopamine hydrochloride is 0.5 g / L, and the mass of lithium chloride is 6% of that of dopamine hydrochloride. Stir at room temperature for 12 h under open conditions, filter with suction, wash three times with ultrapure water to obtain primary particles, and remove the excess unpolymerized dopamine hydrochloride. The appearance is black.

[0027] Step 3: Commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm are added to the Tris-HCl buffer solution at a concentration of 0.1 g / L, and ultrasonically dispersed for 20 min to form a suspension. Add the primary particles and stir for 5 min, then let stand for 1 h. The mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension is 40:1. After filtration, wash three times with ultrapure water to remove the un-deposited titanium dioxide nanotubes to obtain secondary particles.

[0028] Step 4: The secondary particles are added to the Tris-HCl buffer solution at a mass fraction of 10 g / L, ultrasonically dispersed for 10 min, add dopamine hydrochloride at a concentration of 0.5 g / L, stir at room temperature for 12 h under open conditions, filter with suction, wash three times with ultrapure water, dry at 50 °C, and calcine at 700 °C for 2 h in an argon atmosphere to obtain the lithium iron manganese phosphate material.

[0029] Example 2 The difference from Example 1 is only that the mass of lithium chloride being 6% of that of dopamine hydrochloride is adjusted to 8%.

[0030] Prepare lithium iron manganese phosphate material: Step 1: Add 0.8 g of tris(hydroxymethyl)aminomethane into a beaker, then add 14.7 mL of 0.1 mol / L hydrochloric acid, add ultrapure water and stir. Detect the pH to be 8.5, stop adding ultrapure water, and obtain a Tris-HCl buffer solution.

[0031] Step 2: Commercially available lithium manganese iron phosphate particles (LiMn 0.5 Fe 0.5 PO4) with D50 of 0.5 - 1.5 μm are added into the Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion is carried out for 2 h to form a dispersion. Add dopamine hydrochloride and lithium chloride into the dispersion. The concentration of dopamine hydrochloride is 0.5 g / L, and the mass of lithium chloride is 8% of that of dopamine hydrochloride. Stir at room temperature for 12 h under open conditions, and perform suction filtration and wash three times with ultrapure water to obtain primary particles, removing the excess unpolymerized dopamine hydrochloride, with the appearance being black.

[0032] Step 3: Commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm are added into the Tris-HCl buffer solution at a concentration of 0.1 g / L, and ultrasonic dispersion is carried out for 20 min to form a suspension. Add the primary particles and stir for 5 min, then let it stand for 1 h. The mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension is 40:1. After filtration, wash three times with ultrapure water to remove the un-deposited titanium dioxide nanotubes, and obtain secondary particles.

[0033] Step 4: The secondary particles are added into the Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion is carried out for 10 min. Add dopamine hydrochloride at a concentration of 0.5 g / L, stir at room temperature for 12 h under open conditions, perform suction filtration and wash three times with ultrapure water, dry at 50 °C, and calcine at 700 °C for 2 h under an argon atmosphere to obtain the lithium manganese iron phosphate material.

[0034] Example 3 The difference from Example 1 is only that the mass of lithium chloride is adjusted from 6% to 10% of that of dopamine hydrochloride.

[0035] Preparation of lithium manganese iron phosphate material: Step 1: Add 0.8 g of tris(hydroxymethyl)aminomethane into a beaker, then add 14.7 mL of 0.1 mol / L hydrochloric acid, add ultrapure water and stir. Detect the pH to be 8.5, stop adding ultrapure water, and obtain a Tris-HCl buffer solution.

[0036] Step 2: Commercially available lithium manganese iron phosphate particles (LiMn 0.5 Fe 0.5PO4) was added to Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion was carried out for 2 h to form a dispersion. Dopamine hydrochloride and lithium chloride were added to the dispersion. The concentration of dopamine hydrochloride was 0.5 g / L, and the mass of lithium chloride was 10% of that of dopamine hydrochloride. Stirring was carried out at room temperature for 12 h under open conditions, and then filtration was carried out. After washing three times with ultrapure water, primary particles were obtained, and the excess unpolymerized dopamine hydrochloride was removed. The appearance was black.

[0037] Step 3: Commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm were added to Tris-HCl buffer solution at a concentration of 0.1 g / L, and ultrasonic dispersion was carried out for 20 min to form a suspension. Primary particles were added and stirred for 5 min, and then left to stand for 1 h. The mass ratio of primary particles to titanium dioxide nanotubes in the suspension was 40:1. After filtration, un-deposited titanium dioxide nanotubes were removed by washing three times with ultrapure water, and secondary particles were obtained.

[0038] Step 4: The secondary particles were added to Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion was carried out for 10 min. Dopamine hydrochloride was added at a concentration of 0.5 g / L, and stirring was carried out at room temperature for 12 h under open conditions. After filtration, washing was carried out three times with ultrapure water, drying was carried out at 50 °C, and calcination was carried out at 700 °C for 2 h under an argon atmosphere to obtain the lithium iron manganese phosphate material.

[0039] Example 4 The difference from Example 2 was only that in Step 2, the concentration of dopamine hydrochloride was adjusted from 0.5 g / L to 1.5 g / L, and the stirring at room temperature for 12 h was adjusted to 18 h.

[0040] Preparation of lithium iron manganese phosphate material: Step 1: 0.8 g of tris(hydroxymethyl)aminomethane was added to a beaker, and then 14.7 mL of 0.1 mol / L hydrochloric acid was added. Ultra-pure water was added and stirred. The pH was detected to be 8.5, and the addition of ultra-pure water was stopped to obtain Tris-HCl buffer solution.

[0041] Step 2: Commercially available lithium iron manganese phosphate particles (LiMn 0.5 Fe 0.5 PO4) with a D50 of 0.5 - 1.5 μm were added to Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion was carried out for 2 h to form a dispersion. Dopamine hydrochloride and lithium chloride were added to the dispersion. The concentration of dopamine hydrochloride was 1.5 g / L, and the mass of lithium chloride was 8% of that of dopamine hydrochloride. Stirring was carried out at room temperature for 18 h under open conditions, and then filtration was carried out. After washing three times with ultrapure water, primary particles were obtained, and the excess unpolymerized dopamine hydrochloride was removed. The appearance was black.

[0042] Step 3: Purchase commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm, add them to a Tris-HCl buffer solution at a concentration of 0.1 g / L, ultrasonically disperse for 20 min to form a suspension, add the primary particles, stir for 5 min, and then let it stand for 1 h. The mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension is 40:1. After filtration, wash three times with ultrapure water to remove the un-deposited titanium dioxide nanotubes, obtaining secondary particles.

[0043] Step 4: Add the secondary particles to a Tris-HCl buffer solution at a mass fraction of 10 g / L, ultrasonically disperse for 10 min, add dopamine hydrochloride at a concentration of 0.5 g / L, stir at room temperature with an open mouth for 12 h, perform suction filtration, wash three times with ultrapure water, dry at 50 °C, and calcine at 700 °C for 2 h under an argon atmosphere to obtain the lithium iron manganese phosphate material.

[0044] Example 5 The difference from Example 2 is only that in Step 2, the concentration of dopamine hydrochloride is adjusted from 0.5 g / L to 2 g / L, and the stirring at room temperature for 12 h is adjusted to 24 h.

[0045] Preparation of lithium iron manganese phosphate material: Step 1: Add 0.8 g of tris(hydroxymethyl)aminomethane to a beaker, then add 14.7 mL of 0.1 mol / L hydrochloric acid, add ultrapure water and stir. Detect that the pH is 8.5, and stop adding ultrapure water to obtain the Tris-HCl buffer solution.

[0046] Step 2: Purchase commercially available lithium iron manganese phosphate particles (LiMn 0.5 Fe 0.5 PO4) with a D50 of 0.5 - 1.5 μm, add them to a Tris-HCl buffer solution according to a mass fraction of 10 g / L, and ultrasonically disperse for 2 h to form a dispersion. Add dopamine hydrochloride and lithium chloride to the dispersion. The concentration of dopamine hydrochloride is 2 g / L, and the mass of lithium chloride is 8% of that of dopamine hydrochloride. Stir at room temperature with an open mouth for 24 h, perform suction filtration, wash three times with ultrapure water to obtain primary particles, and remove the excess un-polymerized dopamine hydrochloride. The appearance is black.

[0047] Step 3: Purchase commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm, add them to a Tris-HCl buffer solution at a concentration of 0.1 g / L, ultrasonically disperse for 20 min to form a suspension, add the primary particles, stir for 5 min, and then let it stand for 1 h. The mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension is 40:1. After filtration, wash three times with ultrapure water to remove the un-deposited titanium dioxide nanotubes, obtaining secondary particles.

[0048] Step 4: Add secondary particles into Tris-HCl buffer solution at a mass fraction of 10 g / L, ultrasonically disperse for 10 min, add dopamine hydrochloride at a concentration of 0.5 g / L, stir at room temperature with an open mouth for 12 h, filter, wash three times with ultrapure water, dry at 50 °C, and calcine at 700 °C for 2 h under an argon atmosphere to obtain the lithium iron manganese phosphate material.

[0049] Example 6 The difference from Example 4 is only that in Step 3, the mass ratio of primary particles to titanium dioxide nanotubes in the suspension is adjusted from 40:1 to 30:1.

[0050] Preparation of lithium iron manganese phosphate material: Step 1: Add 0.8 g of tris(hydroxymethyl)aminomethane into a beaker, then add 14.7 mL of 0.1 mol / L hydrochloric acid, add ultrapure water and stir. When the pH is detected to be 8.5, stop adding ultrapure water to obtain Tris-HCl buffer solution.

[0051] Step 2: Commercially available lithium iron manganese phosphate particles (LiMn 0.5 Fe 0.5 PO4) with a D50 of 0.5 - 1.5 μm are added into Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonically dispersed for 2 h to form a dispersion. Add dopamine hydrochloride and lithium chloride into the dispersion. The concentration of dopamine hydrochloride is 1.5 g / L, and the mass of lithium chloride is 8% of that of dopamine hydrochloride. Stir at room temperature under open conditions for 18 h, filter, wash three times with ultrapure water to obtain primary particles, and remove the excess unpolymerized dopamine hydrochloride. The appearance is black.

[0052] Step 3: Commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm are added into Tris-HCl buffer solution at a concentration of 0.1 g / L, ultrasonically dispersed for 20 min to form a suspension, add primary particles, stir for 5 min, and then let stand for 1 h. The mass ratio of primary particles to titanium dioxide nanotubes in the suspension is 30:1. Filter and wash three times with ultrapure water to remove the undeposited titanium dioxide nanotubes to obtain secondary particles.

[0053] Step 4: Add secondary particles into Tris-HCl buffer solution at a mass fraction of 10 g / L, ultrasonically disperse for 10 min, add dopamine hydrochloride at a concentration of 0.5 g / L, stir at room temperature with an open mouth for 12 h, filter, wash three times with ultrapure water, dry at 50 °C, and calcine at 700 °C for 2 h under an argon atmosphere to obtain the lithium iron manganese phosphate material.

[0054] Example 7 The difference from Example 4 is only that in Step 3, the mass ratio of primary particles to titanium dioxide nanotubes in the suspension is adjusted from 40:1 to 20:1.

[0055] Preparation of lithium iron manganese phosphate material: Step 1: Add 0.8 g of tris(hydroxymethyl)aminomethane into a beaker, then add 14.7 mL of 0.1 mol / L hydrochloric acid, add ultrapure water and stir. Detect that the pH is 8.5, stop adding ultrapure water, and obtain a Tris-HCl buffer solution.

[0056] Step 2: Commercially available lithium manganese iron phosphate particles (LiMn 0.5 Fe 0.5 PO4) with a D50 of 0.5 - 1.5 μm are added into the Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion is carried out for 2 h to form a dispersion. Add dopamine hydrochloride and lithium chloride into the dispersion. The concentration of dopamine hydrochloride is 1.5 g / L, and the mass of lithium chloride is 8% of that of dopamine hydrochloride. Stir at room temperature for 18 h under open conditions, filter, wash three times with ultrapure water, and obtain primary particles, removing the excess unpolymerized dopamine hydrochloride. The appearance is black.

[0057] Step 3: Commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm are added into the Tris-HCl buffer solution at a concentration of 0.1 g / L, and ultrasonic dispersion is carried out for 20 min to form a suspension. Add the primary particles, stir for 5 min, and then let it stand for 1 h. The mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension is 20:1. After filtration, wash three times with ultrapure water to remove the un-deposited titanium dioxide nanotubes, and obtain secondary particles.

[0058] Step 4: The secondary particles are added into the Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion is carried out for 10 min. Add dopamine hydrochloride at a concentration of 0.5 g / L, stir at room temperature for 12 h under open conditions, filter, wash three times with ultrapure water, dry at 50 °C, and calcine at 700 °C for 2 h under an argon atmosphere to obtain the lithium manganese iron phosphate material.

[0059] Comparative Example 1 The difference from Example 1 is only that lithium chloride is not added in Step 2 of this comparative example.

[0060] Preparation of lithium manganese iron phosphate material: Step 1: Add 0.8 g of tris(hydroxymethyl)aminomethane into a beaker, then add 14.7 mL of 0.1 mol / L hydrochloric acid, add ultrapure water and stir. Detect that the pH is 8.5, stop adding ultrapure water, and obtain a Tris-HCl buffer solution.

[0061] Step 2: Commercially available lithium manganese iron phosphate particles (LiMn 0.5 Fe 0.5PO4) was added to Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion was carried out for 2 h to form a dispersion. Dopamine hydrochloride with a concentration of 0.5 g / L was added to the dispersion, and stirring was carried out at room temperature for 12 h under open conditions. After suction filtration and washing three times with ultrapure water, primary particles were obtained, removing the excess unpolymerized dopamine hydrochloride, and the appearance was black.

[0062] Step 3: Commercially available titanium dioxide nanotubes with a diameter of 5 - 10 nm were added to Tris-HCl buffer solution at a concentration of 0.1 g / L, and ultrasonic dispersion was carried out for 20 min to form a suspension. The primary particles were added and stirred for 5 min, then left standing for 1 h. The mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension was 40:1. After filtration, it was washed three times with ultrapure water to remove the undeposited titanium dioxide nanotubes, and secondary particles were obtained.

[0063] Step 4: The secondary particles were added to Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion was carried out for 10 min. Dopamine hydrochloride was added at a concentration of 0.5 g / L, and stirring was carried out at room temperature for 12 h under open conditions. After suction filtration, it was washed three times with ultrapure water and dried at 50 °C, and then calcined at 700 °C for 2 h under an argon atmosphere to obtain the lithium iron manganese phosphate material.

[0064] Comparative Example 2 The difference from Example 1 is only that titanium dioxide nanotubes are not deposited in this comparative example.

[0065] Preparation of lithium iron manganese phosphate material: Step 1: 0.8 g of tris(hydroxymethyl)aminomethane was added to a beaker, and then 14.7 mL of 0.1 mol / L hydrochloric acid was added. Ultra-pure water was added and stirred. The pH was detected to be 8.5, and the addition of ultra-pure water was stopped to obtain Tris-HCl buffer solution.

[0066] Step 2: Commercially available lithium iron manganese phosphate particles (LiMn 0.5 Fe 0.5 PO4) with a D50 of 0.5 - 1.5 μm was added to Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion was carried out for 2 h to form a dispersion. Dopamine hydrochloride and lithium chloride were added to the dispersion. The concentration of dopamine hydrochloride was 0.5 g / L, and the mass of lithium chloride was 6% of that of dopamine hydrochloride. Stirring was carried out at room temperature for 12 h under open conditions. After suction filtration and washing three times with ultrapure water, primary particles were obtained, removing the excess unpolymerized dopamine hydrochloride, and the appearance was black.

[0067] Step 3: The primary particles were added to Tris-HCl buffer solution at a mass fraction of 10 g / L, and ultrasonic dispersion was carried out for 10 min. Dopamine hydrochloride was added at a concentration of 0.5 g / L, and stirring was carried out at room temperature for 12 h under open conditions. After suction filtration, it was washed three times with ultrapure water and dried at 50 °C, and then calcined at 700 °C for 2 h under an argon atmosphere to obtain the lithium iron manganese phosphate material.

[0068] Comparative Example 3 In this comparative example, the lithium iron manganese phosphate material was directly prepared by co - grinding lithium iron manganese phosphate particles and glucose followed by high - temperature calcination.

[0069] Preparation of lithium iron manganese phosphate material: Step 1: Mix commercially available lithium iron manganese phosphate particles (LiMn 0.5 Fe 0.5 PO4) with the carbon source glucose. The mass of glucose is 10% of the total mass of lithium iron manganese phosphate particles and glucose. Add pure water according to a solid content of 50% and mix and stir - grind. The particle size after grinding is 300 - 400 nm; Step 2: Spray - dry the ground lithium iron manganese phosphate particles and calcine them at 700 °C for 2 h under a nitrogen atmosphere to obtain the lithium iron manganese phosphate material.

[0070] Perform performance tests on the batteries assembled with the lithium iron manganese phosphate materials prepared in Examples 1 - 7 and Comparative Examples 1 - 3. The detection refers to the standard of T / CIAPS0029—2023 "Lithium Iron Manganese Phosphate Cathode Material for Lithium - Ion Batteries". The results are shown in Table 1:

[0071] As can be seen from Table 1, as the addition amount of lithium chloride in the coating layer increases, both its capacity and rate performance are significantly improved, and it can promote the cross - linking of polydopamine, making the coating layer structure more compact and uniform, which can improve the conductivity of the material. However, after adding too much lithium chloride, due to the insufficient stability of the Li - N - C structure, its cycle stability decreases. Examples 4 and 5 increased the proportion of polydopamine on the basis of Example 2. When the carbon content in the coating layer increases, the conductivity of the material is improved, but too high a coating layer proportion will reduce the capacity of the material. Under the conditions of Example 4, its comprehensive performance is the best. In Examples 6 and 7, as the amount of titanium dioxide nanotubes increases, the effect of suppressing side reactions is significantly improved, and the cycle performance of the battery is improved. The capacity retention rate can reach up to 99.1% after 500 cycles at 1C. Compared with Example 1, in Comparative Example 1, when no lithium chloride is added to the coating layer material, the specific capacity of the lithium iron manganese phosphate material is lower, and its conductivity also decreases. When no titanium dioxide nanotube deposition is added, the conductivity and cycle performance of Comparative Example 2 are obviously inferior to those of Example 1. Comparative Example 3 is a conventional carbon - coating technology in the prior art. From the performance test results of Comparative Example 3, the performance indexes of the materials in the examples of the present invention are all superior to those of Comparative Example 3, and they have excellent electrochemical performance.

[0072] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0073] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of lithium iron manganese phosphate material, characterized in that, It includes the following steps: Step 1: Dispersing lithium iron manganese phosphate particles in a Tris-HCl buffer solution to form a dispersion liquid, adding dopamine hydrochloride and lithium chloride, stirring at room temperature with an open mouth for 12 - 24 h, and obtaining primary particles after suction filtration and washing; Step 2: Dispersing titanium dioxide nanotubes in a Tris-HCl buffer solution to form a suspension, adding the primary particles, stirring evenly, standing for 1 - 2 h, and obtaining secondary particles after filtration and washing; Step 3: Dispersing the secondary particles in a Tris-HCl buffer solution, adding dopamine hydrochloride, stirring at room temperature with an open mouth for 12 - 24 h, drying after suction filtration and washing, and calcining at 700 - 750 °C for 1 - 2 h in an inert atmosphere to obtain a lithium iron manganese phosphate material.

2. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that, The pH of the Tris-HCl buffer solution is 8 - 9.

3. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that, The D50 of the lithium iron manganese phosphate particles is 0.5 - 1.5 μm.

4. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that, In Step 1, the mass fraction of the lithium iron manganese phosphate particles in the Tris-HCl buffer solution is 10 - 20 g / L.

5. The preparation method of the lithium iron manganese phosphate material according to claim 1, wherein In Step 1, the dopamine hydrochloride is added to the dispersion liquid at a concentration of 0.5 - 2 g / L.

6. The preparation method of a lithium iron manganese phosphate material according to claim 1, characterized in that, In Step 1, the mass of the lithium chloride is 6 - 10% of the mass of the dopamine hydrochloride.

7. The preparation method of the lithium iron manganese phosphate material according to claim 1, wherein The diameter of the titanium dioxide nanotubes is 5 - 10 nm; The concentration of the titanium dioxide nanotubes in the suspension is 0.1 - 0.5 g / L.

8. The preparation method of the lithium iron manganese phosphate material according to claim 1, characterized in that, In Step 2, the mass ratio of the primary particles to the titanium dioxide nanotubes in the suspension is 20 - 40:

1.

9. The preparation method of the lithium iron manganese phosphate material according to claim 1, wherein In Step 3, the mass fraction of the secondary particles in the Tris-HCl buffer solution is 10 - 20 g / L, and the mass-volume ratio of the dopamine hydrochloride to the Tris-HCl buffer solution is 0.5 - 2 g / L.

10. A lithium iron manganese phosphate material, characterized in that, The lithium iron manganese phosphate material is prepared by using the preparation method of the lithium iron manganese phosphate material according to any one of claims 1 - 9.

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