A lithium iron manganese phosphate positive electrode material and a preparation method thereof

Abstract

This invention discloses a lithium manganese iron phosphate (LFP) cathode material and its preparation method, belonging to the field of lithium-ion battery technology. The LFP cathode material comprises at least LFP particles and a coating layer covering the LFP particles. The coating layer is made from an aluminum fluoride-integrated polyethylene thiophene-lithium polystyrene sulfonate compound. The coating layer acts as a physical barrier, forming a dynamic interface protection that directly inhibits manganese leaching and electrolyte erosion, reducing side reactions between the electrolyte and the cathode material. Simultaneously, it provides a more flexible transport channel for lithium ions and electrons, improving lithium ion transport efficiency while enhancing the conductivity of the cathode material, resulting in a structurally stable LFP cathode material with high rate performance and cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a lithium manganese iron phosphate cathode material and its preparation method. Background Technology

[0002] With the increasing popularity of new energy vehicles worldwide, the demand for power batteries is also growing. Furthermore, with the growth in public demand and the continuous iteration of technology, it is particularly urgent to develop a lithium-ion battery with high energy density, low cost, environmental friendliness, safety, and stability.

[0003] As a crucial component of lithium-ion batteries, cathode materials are key materials driving performance improvements. They not only determine the battery's energy density but also influence its cycle stability, safety, and cost. Common cathode materials currently include olivine-type lithium iron phosphate, layered lithium cobalt oxide, and lithium nickel oxide.

[0004] Lithium manganese iron phosphate (LMP) is a novel cathode material for lithium batteries. Compared to lithium iron phosphate (LFP) cathode materials, it boasts higher energy density, lower-temperature discharge capability, and more stable safety performance. However, LMP cathode materials exhibit poor conductivity and cycle stability. This is primarily due to the Jahn-Teller effect, which easily induces trivalent manganese ions during charge-discharge cycles, leading to crystal structure distortion. Furthermore, trivalent manganese ions are prone to disproportionation reactions under high-temperature or high-rate cycling conditions, generating divalent and tetravalent manganese ions. Divalent manganese ions readily dissolve in the electrolyte to form MnF2, while tetravalent manganese ions may undergo redox reactions with substances in the electrolyte, thus affecting electrolyte stability.

[0005] In addition, because the voltage plateau of the lithium manganese iron phosphate cathode material is close to the oxidation potential of conventional electrolytes, it promotes the decomposition of the electrolyte. Moreover, the moisture and acidic substances in the electrolyte will corrode the lithium manganese iron phosphate cathode material, causing side reactions and thus reducing the electrochemical activity of the lithium battery. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium manganese iron phosphate cathode material and its preparation method, so as to solve the problems of poor conductivity and easy side reaction with electrolyte in lithium manganese iron phosphate cathode material.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] In a first aspect, the present invention provides a lithium manganese iron phosphate cathode material, which includes at least lithium manganese iron phosphate particles and a coating layer covering the lithium manganese iron phosphate particles.

[0009] The coating material includes aluminum fluoride-integrated polyethylene dioxythiophene-lithium polystyrene sulfonate compound.

[0010] Preferably, the mass of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound is 4 to 6 wt% of the lithium manganese iron phosphate particles.

[0011] Preferably, the molar ratio of lithium, manganese, iron and phosphorus in the lithium manganese iron phosphate particles is (0.95~1.05):(0.5~0.7):(0.3~0.5):1.

[0012] Preferably, the lithium manganese iron phosphate particles are prepared by any one of the following methods: hydrothermal synthesis, sol-gel method, co-precipitation method, and high-temperature solid-phase method.

[0013] By adopting the above technical solution, a coating layer can be directly formed on the outside of lithium manganese iron phosphate particles to form a physical barrier, reducing the direct contact between the surface of lithium manganese iron phosphate particles and the electrolyte, thereby reducing the reactivity of lithium manganese iron phosphate cathode material with electrolyte. Moreover, the coating layer, as a dense physical barrier, can also reduce the possibility of manganese ions dissolving due to oxidation or structural distortion, thereby improving the cycle stability of cathode material.

[0014] The coating layer of this invention uses aluminum fluoride-integrated poly(ethylene thiophene)-lithium polystyrene sulfonate compound as raw material. Aluminum fluoride can act as a chemical buffer between the electrolyte and lithium manganese iron phosphate particles. Since hydrofluoric acid generated by electrolyte hydrolysis can corrode the lithium manganese iron phosphate cathode material, it can cause side reactions, exacerbate manganese dissolution, and lead to structural damage. Aluminum fluoride can preferentially react with the generated hydrofluoric acid to form coordination compounds, thereby reducing the direct corrosion of the cathode material by hydrofluoric acid and significantly reducing the occurrence of side reactions between the lithium manganese iron phosphate cathode material and the electrolyte. At the same time, aluminum fluoride can also enhance the overall structural stability of the cathode material by reducing oxygen vacancies on the surface of lithium manganese iron phosphate particles and inhibiting structural stress accumulation.

[0015] However, directly coating aluminum fluoride onto the surface of lithium manganese iron phosphate cathode material also presents significant problems. Because aluminum fluoride is an insulator, its coating layer hinders the cross-interface transport of electrons and lithium ions, leading to a decrease in the high-rate performance of the cathode material. Furthermore, aluminum fluoride itself is non-conductive, and given the already poor conductivity of lithium manganese iron phosphate, direct coating with aluminum fluoride further restricts electron transport paths, accelerating polarization and capacity decay. Therefore, this invention embeds aluminum fluoride within a poly(ethylene thiophene)-lithium polystyrene sulfonate compound.

[0016] Polyethylene dioxythiophene-polystyrene sulfonic acid (PEDIH-PPS) is a highly conductive polymer whose three-dimensional network structure can provide a continuous electron transport path on the surface of lithium manganese iron phosphate (LFP) particles, theoretically compensating for the insulation defects of aluminum fluoride. However, after incorporating PDIH-PPS with aluminum fluoride, it was found that the sulfonic acid groups in PDIH-PPS form hydrogen bonds with the surface groups of aluminum fluoride. This not only affects the dispersibility of aluminum fluoride in PDIH-PPS but also induces hydrolysis of aluminum fluoride in polar water. This not only fails to provide a chemical buffering effect but also generates new hydrofluoric acid, which corrodes the LFP cathode material. On the other hand, the strong polarity of the sulfonic acid groups causes their protons to compete with lithium ions in the electrolyte for migration, significantly reducing the diffusion rate of lithium ions. Therefore, the combination of PDIH-PPS with aluminum fluoride, a highly conductive polymer, and coating the surface of LFP cathode material provides very limited improvement in electronic conductivity.

[0017] To address this issue, this invention first lithium-encapsulates poly(ethylenedioxythiophene)-polystyrene sulfonic acid, then incorporates aluminum fluoride. In this process, the hydrogen ions of the sulfonic acid groups in the poly(ethylenedioxythiophene)-polystyrene sulfonic acid are replaced by lithium ions, directly eliminating the interference of protons on lithium ion transport. Furthermore, the binding energy between lithium ions and sulfonic acid groups is higher than that between hydrogen ions, thus forming a more stable ion transport channel without affecting its conductivity. Moreover, the lithium-encapsulation process regulates the pH value of the material, inhibiting the hydrolysis of aluminum fluoride. Simultaneously, lithium ions can form a passivation layer with aluminum fluoride, blocking direct contact between aluminum fluoride and water and reducing side reactions.

[0018] Finally, the aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound was used as a coating material to coat the surface of lithium manganese iron phosphate particles. This formed a dynamic interface protection, inhibiting manganese dissolution and electrolyte corrosion. The poly(ethylene dioxythiophene)-lithium polystyrene sulfonate provided an electronic pathway, while the aluminum fluoride optimized ion transport selectivity. The resulting coating layer, while physically blocking the electrons, provided a more flexible transport channel for lithium ions and electrons, improving the structural stability of the obtained cathode material, enhancing its rate performance, and reducing capacity decay.

[0019] Preferably, the raw materials for the aluminum fluoride-integrated polyethylene dioxythiophene-lithium polystyrene sulfonate compound include lithium polystyrene sulfonate, aluminum fluoride, and 3,4-ethylene dioxythiophene in a molar ratio of 1:(0.8-1):(1.2-1.8).

[0020] Preferably, the aluminum fluoride-intercalated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound is prepared according to the following method:

[0021] S1. Dissolve polystyrene sulfonic acid in water to prepare a premixed solution with a mass fraction of 10-20%; add lithium salt to the premixed solution, stir until no bubbles are generated, then add molecular sieve and let stand for 12-20 hours to obtain lithium polystyrene sulfonate solution.

[0022] S2. Aluminum fluoride is immersed in a strong acid solution for 2-3 hours, and then washed, neutralized and dried to obtain pretreated aluminum fluoride;

[0023] S3. Add pretreated aluminum fluoride to a lithium polystyrene sulfonate solution, ultrasonically disperse for 20-40 min, add 3,4-ethylenedioxythiophene, stir and disperse, then add an oxidant, continue stirring and reacting for 4-6 h, and finally wash, evaporate and dry to obtain the final product.

[0024] Preferably, the lithium salt includes one or more combinations of lithium carbonate, lithium chloride, lithium nitrate and lithium sulfate; the molar ratio of lithium salt to polystyrene sulfonic acid is (0.4-0.6):1.

[0025] Preferably, the strong acid solution includes any one of nitric acid, hydrochloric acid, and sulfuric acid.

[0026] Preferably, the oxidant includes one or more combinations of sodium persulfate, ammonium persulfate, ferric sulfate, ferric chloride and hydrogen peroxide; the amount of oxidant added is 0.5 to 1% of the mass of 3,4-ethylenedioxythiophene.

[0027] By adopting the above technical solution, polystyrene sulfonic acid is first dissolved in water, and then a soluble lithium salt is added. At this time, lithium ions in the lithium salt undergo an ion exchange reaction with polystyrene sulfonic acid, and the lithium ions are transferred to polystyrene sulfonic acid. The resulting lithium polystyrene sulfonate solution is mixed with acidified aluminum fluoride. After strong acid treatment, new polar groups such as carboxyl groups can be introduced on the surface of aluminum fluoride, which can enhance the binding force between aluminum fluoride and lithium polystyrene sulfonate. A lithium polystyrene sulfonate adsorption layer is gradually formed on the surface of aluminum fluoride. Then, 3,4-ethylenedioxythiophene monomer is added. Under the interaction of π-π attraction and van der Waals forces, the monomer molecules are adsorbed on the surface of aluminum fluoride. Then, under the action of an oxidant, the monomer molecules use aluminum fluoride particles as templates to carry out in-situ oxidative polymerization on the surface to form a polyethylenedioxythiophene-lithium polystyrene sulfonate compound.

[0028] The aluminum fluoride-integrated poly(ethylenedioxythiophene)-lithium polystyrene sulfonate compound was prepared. It can directly act as a physical barrier to inhibit manganese dissolution and reduce the direct contact between the internal lithium manganese iron phosphate particles and the electrolyte. It can also improve the ion transport efficiency and electron transport efficiency of the lithium manganese iron phosphate cathode material, improve the interface performance, optimize the bonding force between aluminum fluoride and poly(ethylenedioxythiophene)-lithium polystyrene sulfonate, and solve the bonding barrier between the two, thus obtaining a high-performance lithium manganese iron phosphate cathode material.

[0029] Preferably, NiO is also bonded between the lithium manganese iron phosphate particles and the coating layer. x Buffer layer; the NiO x The buffer layer is made of NiO x Composed of nanoparticles.

[0030] Preferably, NiO x The mass of the buffer layer is 2 to 4 wt% of the lithium manganese iron phosphate particles.

[0031] Preferably, NiO x Nanoparticles were prepared by the following method: a soluble nickel salt was dissolved in water, the pH of the solution was adjusted to 8–10, and the mixture was stirred for 30–60 min. The resulting solution was then centrifuged, washed, dried, and calcined to obtain NiO. x Nanoparticles; soluble nickel salts include one or more combinations of nickel sulfate hexahydrate, nickel chloride hexahydrate, nickel nitrate hexahydrate, and nickel acetate tetrahydrate.

[0032] More preferably, NiO x The nanoparticles are nickel oxide hole nanoparticles; NiO x Nanoparticles are a mixture of NiO, NiOOH and Ni2O3. Due to the excessive oxygen content, a large number of Ni vacancies exist, causing NiO to exist in a non-stoichiometric form.

[0033] By adopting the above technical solution, a NiO layer is added between the lithium manganese iron phosphate particles and the coating layer formed by aluminum fluoride intercalated polyethylene dioxythiophene-lithium polystyrene sulfonate compound. x Buffer layer. NiO x As a transition metal oxide, NiO can synergistically work with the coating layer to suppress the erosion of the cathode material by the electrolyte and reduce the generation of interfacial side reactions. x NiO in the buffer layer x The porous structure of nanoparticles can serve as a lithium-ion pre-storage layer, shortening the diffusion distance of lithium ions from the electrolyte to the lithium manganese iron phosphate cathode material, thereby improving the rate performance and cycle performance of the obtained lithium manganese iron phosphate cathode material.

[0034] Moreover, NiO x The addition of a buffer layer can reduce the ability of the coating layer to induce oxygen vacancies, suppress the increase of oxygen vacancy concentration during long-term charge-discharge cycles, thereby improving structural stability, and NiO x The buffer layer can also form hydrogen bonds with the polar groups in the coating layer, which improves the adhesion of the coating layer to the surface of lithium manganese iron phosphate particles, thereby improving the capacity retention and high-rate performance of the obtained lithium manganese iron phosphate cathode material.

[0035] Secondly, this invention provides a method for preparing lithium manganese iron phosphate cathode material, comprising the following process steps:

[0036] Aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound was added to deionized water, stirred and dispersed, and then lithium manganese iron phosphate particles were added. The mixture was soaked for 4-6 hours and then heat-treated at 110-130℃ for 2-3 hours to form a coating layer, thus obtaining lithium manganese iron phosphate cathode material.

[0037] Alternatively, NiO x Nanoparticles were dispersed in deionized water and then spin-coated onto the surface of lithium manganese iron phosphate particles. The mixture was then heat-treated at 120–150°C for 30–40 minutes to form NiO. x A buffer layer is formed to obtain pretreated lithium manganese iron phosphate particles.

[0038] Aluminum fluoride-integrated polyethylene thiophene-polystyrene sulfonate compound was added to deionized water, stirred and dispersed, and then pretreated lithium manganese iron phosphate particles were added and soaked for 4-6 hours. Then, it was heat-treated at 110-130℃ for 2-3 hours to form a coating layer, thus obtaining lithium manganese iron phosphate cathode material.

[0039] Preferably, the solid-liquid ratio of aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound to deionized water is 1 g: (2-4) mL.

[0040] Preferably, the lithium manganese iron phosphate particles do not undergo NiO treatment. x Nanoparticle pretreatment to form NiO x The buffer layer can also achieve the technical effects of this application.

[0041] By adopting the above technical solution, soluble nickel salts are dissolved in water, and then calcined to form NiO. x Nanoparticles containing NiO x A solution of nanoparticles is spin-coated onto the surface of lithium manganese iron phosphate particles, followed by heat treatment to form stable NiO. x A buffer layer is formed, and then the pretreated lithium manganese iron phosphate particles are impregnated in an aluminum fluoride-integrated polyethylene thiophene-lithium polystyrene sulfonate compound slurry to form a coating layer on the outermost layer, thereby obtaining a lithium manganese iron phosphate cathode material that can significantly suppress manganese dissolution and electrolyte side reactions. This cathode material also has good conductivity and cycle stability.

[0042] The beneficial effects of this invention are:

[0043] 1. The lithium manganese iron phosphate cathode material of the present invention also has a coating layer on its surface. The raw material of the coating layer includes an aluminum fluoride-integrated polyethylene dioxythiophene-lithium polystyrene sulfonate compound. On the one hand, the coating layer can act as a physical barrier, forming a dynamic interface protection, directly inhibiting the dissolution of manganese and the erosion of the electrolyte, and reducing the occurrence of side reactions between the electrolyte and the cathode material. On the other hand, the aluminum fluoride-integrated polyethylene dioxythiophene-lithium polystyrene sulfonate compound, after lithiation treatment and aluminum fluoride integration, can simultaneously provide a more flexible transport channel for lithium ions and electrons, improving the lithium ion transport efficiency while enhancing the conductivity of the cathode material, resulting in a structurally stable lithium manganese iron phosphate cathode material with high rate performance and cycle stability.

[0044] 2. In the lithium manganese iron phosphate cathode material of the present invention, NiO is further added between the lithium manganese iron phosphate particles and the coating layer. x The buffer layer provides a pathway for lithium-ion transport, reduces the generation of oxygen vacancies, improves structural stability, and increases the bonding force between lithium manganese iron phosphate particles and the coating layer, thereby improving the capacity retention of lithium manganese iron phosphate cathode materials. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] Preparation Example

[0047] Preparation Example 1: An aluminum fluoride-intercalated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound was prepared according to the following method:

[0048] S1. Dissolve 50 mmol of polystyrene sulfonic acid in water to prepare a premixed solution with a mass fraction of 15%; add 25 mmol of lithium carbonate to the premixed solution, stir until no bubbles are generated, then add silicon / aluminum molecular sieve and let stand for 12-20 h to obtain a lithium polystyrene sulfonate solution.

[0049] S2. 45 mmol of aluminum fluoride was impregnated with nitric acid for 2 hours, and then washed, neutralized and dried to obtain pretreated aluminum fluoride;

[0050] S3. Add pretreated aluminum fluoride to lithium polystyrene sulfonate solution, sonicate for 30 min, add 75 mmol of 3,4-ethylenedioxythiophene, stir and disperse, then add 0.1 g of ammonium persulfate, continue stirring and reacting for 5 h, and finally wash, evaporate and dry to obtain the product.

[0051] Preparation Example 2: An aluminum fluoride-intercalated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound was prepared according to the following method:

[0052] S1. Dissolve 50 mmol of polystyrene sulfonic acid in water to prepare a premixed solution with a mass fraction of 15%; add 20 mmol of lithium carbonate to the premixed solution, stir until no bubbles are generated, then add silicon / aluminum molecular sieve and let stand for 12-20 h to obtain a lithium polystyrene sulfonate solution.

[0053] S2. 40 mmol of aluminum fluoride was impregnated with nitric acid for 2 hours, and then washed, neutralized and dried to obtain pretreated aluminum fluoride;

[0054] S3. Add pretreated aluminum fluoride to lithium polystyrene sulfonate solution, sonicate for 30 min, add 60 mmol of 3,4-ethylenedioxythiophene, stir and disperse, then add 0.08 g of ammonium persulfate, continue stirring and reacting for 5 h, and finally wash, evaporate and dry to obtain the product.

[0055] Preparation Example 3: An aluminum fluoride-intercalated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound was prepared according to the following method:

[0056] S1. Dissolve 50 mmol of polystyrene sulfonic acid in water to prepare a premixed solution with a mass fraction of 15%; add 30 mmol of lithium carbonate to the premixed solution, stir until no bubbles are generated, then add silicon / aluminum molecular sieve and let stand for 12-20 h to obtain a lithium polystyrene sulfonate solution.

[0057] S2. 50 mmol of aluminum fluoride was impregnated with nitric acid for 2 hours, and then washed, neutralized and dried to obtain pretreated aluminum fluoride;

[0058] S3. Add pretreated aluminum fluoride to lithium polystyrene sulfonate solution, sonicate for 30 min, add 90 mmol of 3,4-ethylenedioxythiophene, stir and disperse, then add 0.1 g of ammonium persulfate, continue stirring and reacting for 5 h, and finally wash, evaporate and dry to obtain the product.

[0059] Preparation Example 4: A fluoride-integrated poly(ethylenedioxythiophene)-lithium polystyrene sulfonate compound, which differs from Preparation Example 1 only in that the amount of aluminum fluoride added is 30 mmol.

[0060] Preparation Example 5: A fluoride-integrated poly(ethylenedioxythiophene)-lithium polystyrene sulfonate compound, which differs from Preparation Example 1 only in that the amount of aluminum fluoride added is 60 mmol.

[0061] Preparation Example 6: An aluminum fluoride-intercalated poly(ethylene dioxythiophene)-polystyrene sulfonic acid compound was prepared according to the following method:

[0062] S1. 45 mmol of aluminum fluoride was impregnated with nitric acid for 2 hours, and then washed, neutralized and dried to obtain pretreated aluminum fluoride;

[0063] S2. Dissolve 50 mmol of polystyrene sulfonic acid in water to prepare a premix with a mass fraction of 15%; add pretreated aluminum fluoride to the premix, sonicate for 30 min, add 75 mmol of 3,4-ethylenedioxythiophene, stir and disperse, then add 0.1 g of ammonium persulfate, continue stirring and reacting for 5 h, and finally wash, evaporate and dry to obtain the final product.

[0064] Preparation Example 7: A polyethylene dioxythiophene-lithium polystyrene sulfonate compound was prepared according to the following method:

[0065] S1. Dissolve 50 mmol of polystyrene sulfonic acid in water to prepare a premixed solution with a mass fraction of 15%; add 25 mmol of lithium carbonate to the premixed solution, stir until no bubbles are generated, then add silicon / aluminum molecular sieve and let stand for 12-20 h to obtain a lithium polystyrene sulfonate solution.

[0066] S2. Add 75 mmol of 3,4-ethylenedioxythiophene to a lithium polystyrene sulfonate solution, stir to disperse, then add 0.1 g of ammonium persulfate, continue stirring for 5 h, and finally wash, evaporate and dry to obtain the final product.

[0067] Preparation Example 8: An aluminum fluoride-intercalated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound was prepared according to the following method:

[0068] S1. Dissolve 50 mmol of polystyrene sulfonic acid in water to prepare a premixed solution with a mass fraction of 15%; add 25 mmol of lithium carbonate to the premixed solution, stir until no bubbles are generated, then add silicon / aluminum molecular sieve and let stand for 12-20 h to obtain a lithium polystyrene sulfonate solution.

[0069] S2. Add 45 mmol of aluminum fluoride to a lithium polystyrene sulfonate solution, sonicate for 30 min, add 75 mmol of 3,4-ethylenedioxythiophene, stir and disperse, then add 0.1 g of ammonium persulfate, continue stirring and reacting for 5 h, and finally wash, evaporate and dry to obtain the final product.

[0070] Example

[0071] Example 1: A lithium manganese iron phosphate cathode material was prepared according to the following method:

[0072] The aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound prepared in Preparation Example 1 was added to deionized water, wherein the solid-liquid ratio of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound to deionized water was 1 g: 3 mL.

[0073] After stirring and dispersing, lithium manganese iron phosphate particles obtained by hydrothermal synthesis are added, wherein the molar ratio of lithium, manganese, iron and phosphorus in the lithium manganese iron phosphate particles is 1:0.7:0.3:1. The mixture is soaked for 5 hours and then heat-treated at 120℃ for 2 hours to form a coating layer. The mass of aluminum fluoride intercalated polyethylene dioxythiophene-polystyrene sulfonate compound is controlled to be 5 wt% of the lithium manganese iron phosphate particles to obtain lithium manganese iron phosphate cathode material.

[0074] Example 2, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that the molar ratio of lithium, manganese, iron and phosphorus in the lithium manganese iron phosphate particles is 1.05:0.5:0.5:1; and the mass of the aluminum fluoride-integrated polyethylene dioxythiophene-polystyrene sulfonate compound prepared in Example 1 is controlled to be 4 wt% of the lithium manganese iron phosphate particles.

[0075] Example 3, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that the elemental molar ratio of lithium, manganese, iron and phosphorus in the lithium manganese iron phosphate particles is 0.95:0.6:0.4:1; and the mass of the aluminum fluoride-integrated polyethylene dioxythiophene-polystyrene sulfonate compound prepared in Example 1 is controlled to be 6 wt% of the lithium manganese iron phosphate particles.

[0076] Example 4, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that an equal amount of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 2 is used instead of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 1.

[0077] Example 5, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that an equal amount of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 3 is used instead of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 1.

[0078] Example 6, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that an equal amount of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 4 is used instead of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 1.

[0079] Example 7, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that an equal amount of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 5 is used instead of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 1.

[0080] Example 8, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that an equal amount of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 8 is used instead of the aluminum fluoride-integrated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 1.

[0081] Example 9, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that the mass of the aluminum fluoride-integrated polyethylene dioxythiophene-polystyrene sulfonate compound prepared in Example 1 is controlled to be 2 wt% of the lithium manganese iron phosphate particles.

[0082] Example 10, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that the mass of the aluminum fluoride-integrated polyethylene dioxythiophene-polystyrene sulfonate compound prepared in Example 1 is controlled to be 8 wt% of the lithium manganese iron phosphate particles.

[0083] Example 11: A lithium manganese iron phosphate cathode material was prepared according to the following method:

[0084] Nickel sulfate hexahydrate was dissolved in water, the pH of the solution was adjusted to 8.5, and the mixture was stirred for 60 minutes. The resulting solution was then centrifuged, washed, dried, and calcined to obtain NiO. x Nanoparticles;

[0085] The NiO obtained above x Nanoparticles were dispersed in deionized water and then spin-coated onto the surface of lithium manganese iron phosphate particles, wherein the molar ratio of lithium, manganese, iron, and phosphorus in the lithium manganese iron phosphate particles was 1:0.7:0.3:1. The mixture was then heat-treated at 140℃ for 40 min to form NiO. x Buffer layer, controlling NiO x The mass of the buffer layer is 3 wt% of the lithium manganese iron phosphate particles, thus obtaining pretreated lithium manganese iron phosphate particles.

[0086] The aluminum fluoride-integrated poly(ethylenedioxythiophene)-polystyrene sulfonate compound prepared in Preparation Example 1 was added to deionized water, wherein the solid-liquid ratio of the aluminum fluoride-integrated poly(ethylenedioxythiophene)-polystyrene sulfonate compound to deionized water was 1 g: 3 mL; after stirring and dispersing, pretreated lithium manganese iron phosphate particles were added and soaked for 6 h, and then heat-treated at 120 °C for 2 h to form a coating layer. The mass of the aluminum fluoride-integrated poly(ethylenedioxythiophene)-polystyrene sulfonate compound prepared in Preparation Example 1 was controlled to be 5 wt% of the lithium manganese iron phosphate particles, and lithium manganese iron phosphate cathode material was obtained.

[0087] Example 12, a lithium manganese iron phosphate cathode material, differs from Example 11 only in that the NiO content is controlled... x The mass of the buffer layer is 2 wt% of the lithium manganese iron phosphate particles.

[0088] Example 13, a lithium manganese iron phosphate cathode material, differs from Example 11 only in that the NiO content is controlled... x The mass of the buffer layer is 4 wt% of the lithium manganese iron phosphate particles.

[0089] Comparative Example

[0090] Comparative Example 1, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that an equal amount of the aluminum fluoride-integrated polyethylene dioxythiophene-polystyrene sulfonate compound prepared in Example 6 is used instead of the aluminum fluoride-integrated polyethylene dioxythiophene-polystyrene sulfonate compound prepared in Example 1.

[0091] Comparative Example 2, a lithium manganese iron phosphate cathode material, differs from Example 1 only in that an equal amount of the poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 7 is used to replace the aluminum fluoride-intercalated poly(ethylene dioxythiophene)-polystyrene sulfonate compound prepared in Example 1.

[0092] Comparative Example 3 is a lithium manganese iron phosphate cathode material, which differs from Example 1 only in that an equal amount of aluminum fluoride is used to replace the aluminum fluoride-integrated polyethylene dioxythiophene-lithium polystyrene sulfonate compound prepared in Example 1.

[0093] Comparative Example 4: A lithium manganese iron phosphate cathode material was prepared according to the following method:

[0094] Nickel sulfate hexahydrate was dissolved in water, the pH of the solution was adjusted to 8.5, and the mixture was stirred for 60 minutes. The resulting solution was then centrifuged, washed, dried, and calcined to obtain NiO. x Nanoparticles;

[0095] The NiO obtained above x Nanoparticles were dispersed in deionized water and then spin-coated onto the surface of lithium manganese iron phosphate particles, wherein the molar ratio of lithium, manganese, iron, and phosphorus in the lithium manganese iron phosphate particles was 1:0.7:0.3:1. The mixture was then heat-treated at 140℃ for 40 min to form NiO. x Buffer layer, controlling NiO x The buffer layer has a mass of 3 wt% of the lithium manganese iron phosphate particles, thus obtaining the lithium manganese iron phosphate cathode material.

[0096] Performance testing

[0097] According to the relevant records in GB / T 31467.3-2015 "Safety Requirements and Test Methods for Lithium-ion Power Battery Packs and Systems for Electric Vehicles", sample batteries were prepared using lithium manganese iron phosphate cathode material obtained in the examples and comparative examples as cathode materials.

[0098] Then, the specific capacity of the sample battery during its first discharge at room temperature and 1C rate, as well as its specific capacity after 500 cycles, were tested, and the capacity retention rate was calculated. Simultaneously, the specific capacity of the sample battery before and after 200 cycles at room temperature and 3C rate was tested, and the capacity retention rate was calculated.

[0099] The experimental results are shown in Table 1:

[0100] Table 1 Performance Test Results

[0101]

[0102] Combining Examples 1 and 8, it can be seen that the high-rate performance and cycle performance of Example 8 are lower than those of Example 1. The reason is that in the preparation process of the aluminum fluoride-polyethylenedioxythiophene-polystyrene sulfonate compound in Example 8, the aluminum fluoride was not acidified, resulting in a significant decrease in the content of polar groups on the surface of the aluminum fluoride. During the composite process with polyethylenedioxythiophene-polystyrene sulfonate, the interfacial bonding force is poor, and the aluminum fluoride is prone to agglomeration. In addition, it is also easy to detach during long-term cycling, enter the electrolyte, induce side reactions, and is not conducive to improving battery stability.

[0103] Combining Examples 1 and 11, it can be seen that the performance of Example 11 is improved compared to Example 1. This is because NiO is added to the lithium manganese iron phosphate cathode material obtained in Example 11. x The buffer layer can optimize the performance of the coating layer and provide a lithium-ion transport path, thereby improving the rate performance and cycle performance of lithium manganese iron phosphate cathode materials.

[0104] Combining Example 1 and Comparative Example 1, it can be seen that the high-rate performance and cycle performance of Comparative Example 1 are lower than those of Example 1. The reason is that the polyethylene dioxythiophene-polystyrene sulfonic acid in Comparative Example 1 has not undergone lithiation treatment. The strongly polar sulfonic acid groups contained therein will reduce the diffusion rate of lithium ions, affect the performance of the intercalated aluminum fluoride, and the improvement in conductivity is not obvious, resulting in a decrease in the performance of lithium-ion batteries.

[0105] Combining Example 1 and Comparative Example 2, it can be seen that the cycle performance of Comparative Example 2 is lower than that of Example 1. The reason is that the coating material in Comparative Example 2 is a polyethylene dioxythiophene-lithium polystyrene sulfonate compound, without intercalated aluminum fluoride. Its initial discharge specific capacity does not change much because the polyethylene dioxythiophene-lithium polystyrene sulfonate coating has a certain conductivity, which can compensate for the poor conductivity of the lithium manganese iron phosphate cathode material. However, the lack of aluminum fluoride, that is, the lack of a chemical buffer between the cathode material and the electrolyte, makes the erosion of the cathode material by the electrolyte more intense than that in Example 1, resulting in a decrease in cycle performance and high-rate performance.

[0106] Combining Examples 1, 3, and 4, it can be seen that the performance of Comparative Examples 3 and 4 is significantly lower than that of Example 1. This is because the aluminum fluoride coating and NiO in Comparative Example 3... x The poor conductivity of the buffer layer also limits its effect on improving the structural stability of the material, resulting in a decline in the performance of the lithium-ion battery.

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0108] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A lithium manganese iron phosphate cathode material, characterized in that, The lithium manganese iron phosphate cathode material includes at least lithium manganese iron phosphate particles and a coating layer covering the lithium manganese iron phosphate particles. The raw material for the coating layer includes an aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound.

2. The lithium iron phosphate cathode material according to claim 1, characterized in that, The mass of the aluminum fluoride-embedded poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound is 4-6 wt% of the lithium manganese iron phosphate particles.

3. The lithium iron phosphate cathode material according to claim 1, characterized in that, The raw materials for the aluminum fluoride-embedded polyethylene dioxythiophene-lithium polystyrene sulfonate compound include lithium polystyrene sulfonate, aluminum fluoride, and 3,4-ethylene dioxythiophene in a molar ratio of 1:(0.8-1):(1.2-1.8).

4. The lithium iron phosphate cathode material according to claim 3, characterized in that, The aluminum fluoride-intercalated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound was prepared by the following method: S1. Dissolve polystyrene sulfonic acid in a solvent to prepare a premixed solution with a mass fraction of 10-20%; add lithium salt to the premixed solution, stir until no bubbles are generated, then add molecular sieve and let stand for 12-20 hours to obtain a lithium polystyrene sulfonate solution. S2. Aluminum fluoride is immersed in a strong acid solution for 2-3 hours, and then washed, neutralized and dried to obtain pretreated aluminum fluoride; S3. Add pretreated aluminum fluoride to a lithium polystyrene sulfonate solution, ultrasonically disperse for 20-40 min, add 3,4-ethylenedioxythiophene, stir and disperse, then add an oxidant, continue stirring and reacting for 4-6 h, and finally wash, evaporate and dry to obtain the final product.

5. The lithium iron phosphate cathode material according to claim 4, characterized in that, The lithium salt includes one or more combinations of lithium carbonate, lithium chloride, lithium nitrate and lithium sulfate; the molar ratio of the lithium salt to polystyrene sulfonic acid is (0.4-0.6):

1.

6. The lithium iron phosphate cathode material according to claim 1, characterized in that, The molar ratio of lithium, manganese, iron and phosphorus in the lithium manganese iron phosphate particles is (0.95~1.05):(0.5~0.7):(0.3~0.5):

1.

7. The lithium iron phosphate cathode material according to claim 1, characterized in that, NiO is also bonded between the lithium manganese iron phosphate particles and the coating layer. x Buffer layer; the NiO x The buffer layer is made of NiO x Composed of nanoparticles.

8. The lithium iron phosphate cathode material according to claim 7, characterized in that, The NiO x The mass of the buffer layer is 2 to 4 wt% of the lithium manganese iron phosphate particles.

9. The lithium iron phosphate cathode material according to claim 7, characterized in that, The NiO x Nanoparticles were prepared by the following method: Soluble nickel salts were dissolved in water, the pH of the solution was adjusted to 8–10, and the mixture was stirred for 30–60 minutes. The resulting solution was then centrifuged, washed, dried, and calcined to obtain NiO. x Nanoparticles; the soluble nickel salt includes one or more combinations of nickel sulfate hexahydrate, nickel chloride hexahydrate, nickel nitrate hexahydrate, and nickel acetate tetrahydrate.

10. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, The process includes the following steps: Aluminum fluoride-embedded poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound is added to deionized water, stirred and dispersed, and then lithium manganese iron phosphate particles are added. The mixture is soaked for 4-6 hours and then heat-treated at 110-130°C for 2-3 hours to form a coating layer, thereby obtaining the lithium manganese iron phosphate cathode material according to any one of claims 1-6. Alternatively, NiO x Nanoparticles were dispersed in deionized water and then spin-coated onto the surface of lithium manganese iron phosphate particles. The mixture was then heat-treated at 120–150°C for 30–40 minutes to form NiO. x A buffer layer is formed to obtain pretreated lithium manganese iron phosphate particles. Aluminum fluoride-integrated poly(ethylene dioxythiophene)-lithium polystyrene sulfonate compound is added to deionized water, stirred and dispersed, and then pretreated lithium manganese iron phosphate particles are added and soaked for 4-6 hours. Then, the mixture is heat-treated at 110-130°C for 2-3 hours to form a coating layer, thereby obtaining the lithium manganese iron phosphate cathode material as described in any one of claims 7-9.

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