A lithium iron manganese phosphate composite material and a preparation method thereof

Abstract

The application discloses a kind of lithium iron manganese phosphate composite material and preparation method thereof, belong to lithium ion battery cathode material technical field.The application includes the following steps: S1, MnCl2·4H2O and FeCl3·6H2O are dissolved in ethoxy acetic acid, and first solution is prepared;1, 3, 5-benzene tricarboxylic acid is added in anhydrous ethanol to prepare second solution;First solution is slowly added into second solution, then NaOH is added, and hydrothermal reaction is carried out, after cooling, centrifugal washing, drying, and manganese iron precursor is obtained;S2, SeO x @rGO-EDA is prepared;S3, manganese iron precursor, SeO x @rGO-EDA, lithium carbonate and ammonium dihydrogen phosphate are uniformly mixed, then calcined under nitrogen atmosphere, and lithium iron manganese phosphate composite material is obtained after cooling.SeO x The strong oxygen affinity of SeO can bind the active oxygen on the surface of LiFePO4, and the chemical adsorption effect can reduce the dissolution of manganese ions and improve the cycle stability of the composite material.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a lithium manganese iron phosphate composite material and a preparation method thereof. BACKGROUND

[0002] As a lithium ion battery cathode material, lithium iron phosphate (LiFePO4) has been reported since 1997, and has become an important choice in the field of power batteries and energy storage due to its stability and high safety of olivine structure. In its crystal structure, FeO6 octahedron and PO4 tetrahedron are connected by sharing vertices, lithium ions diffuse one-dimensionally along the direction, which endows the material with excellent thermal stability and cycle life, and high theoretical specific capacity. However, the intrinsic electronic conductivity is extremely low and the lithium ion diffusion rate is slow, which leads to insufficient high-rate performance, and the low tap density limits the volume energy density, which is difficult to meet the demand of high-power and compact applications. In view of the above problems, research focuses on multi-scale modification technology: carbon coating and bulk doping can improve the electrical conductivity; particle grading and morphology control can improve the density.

[0003] The patent application with the publication number CN114678526A discloses a preparation method of carbon-coated lithium iron phosphate composite material, which comprises the following steps: biomass is pulverized, and after pretreatment, biomass powder is obtained; the biomass powder is added to an aqueous iron salt solution, stirred, and then ammonia solution is added while stirring until no more precipitate is produced, and the precipitate is obtained by filtration and washing; under a protective atmosphere, the precipitate is treated by carbonization and activation to obtain a nano-sized product of iron oxide / carbon composite material; and then according to the stoichiometric ratio of lithium iron phosphate, the product is mixed with a lithium source and a phosphorus source, and high-temperature calcination is carried out under a protective atmosphere to obtain the product. However, the crystallinity of biomass carbon is usually low, and compared with the graphite carbon coating layer, its electronic conductivity may be insufficient, which is difficult to significantly improve the high-rate performance of lithium iron phosphate.

[0004] Therefore, it is an urgent problem to be solved to prepare a cathode material that can improve the actual specific capacity and cycle stability. SUMMARY

[0005] The application aims to provide a lithium manganese iron phosphate composite material and a preparation method thereof, so as to improve the actual specific capacity and cycle stability of the cathode material.

[0006] The object of the application can be achieved by the following technical solutions.

[0007] A lithium manganese iron phosphate composite material comprises lithium manganese iron phosphate and SeO xrGO-EDA; the lithium iron manganese phosphate comprises a manganese / iron-1,3,5-benzene tricarboxylic acid organic framework, a phosphorus source and a lithium source; the rGO is coated on SeO x The surface of the graphene oxide is etched by the EDA, and a core-shell structure is formed; adjacent rGO layers are covalently crosslinked by the EDA.

[0008] Further, the preparation method of the lithium iron manganese phosphate composite material comprises the following steps:

[0009] S1, dissolving MnCl2·4H2O and FeCl3·6H2O in ethoxy acetic acid to prepare a first solution; adding 1,3,5-benzene tricarboxylic acid into anhydrous ethanol to prepare a second solution; slowly adding the first solution into the second solution, and then adding NaOH, and performing hydrothermal reaction, and then performing centrifugal washing after cooling, and drying to obtain a manganese iron precursor;

[0010] S2, dissolving graphene oxide in deionized water to obtain a third solution; adding SeO2 into a 50% ethanol solution to obtain a fourth solution; uniformly mixing the third solution and the fourth solution, and adding an EDA (ethylene diamine) solution dropwise, and performing hydrothermal reaction, and then performing washing and freeze-drying to obtain SeO2@GO-EDA;

[0011] S3, uniformly grinding and mixing SeO2@GO-EDA and magnesium, heating and keeping warm in an argon environment, and then immersing in a hydrochloric acid solution after cooling; performing filtration and washing, and then performing freeze-drying to obtain SeO x rGO-EDA, 0X≤2;

[0012] S4, uniformly mixing the manganese iron precursor, SeO x rGO-EDA, lithium carbonate and ammonium dihydrogen phosphate, and then performing calcination under heating in a nitrogen atmosphere, and then obtaining the lithium iron manganese phosphate composite material after cooling.

[0013] Further, the amount ratio of the MnCl2·4H2O, the FeCl3·6H2O and the ethoxy acetic acid is (1-2.5) g:(0.25-1.25) g:(40-100) mL.

[0014] Further, the amount ratio of the 1,3,5-benzene tricarboxylic acid, the anhydrous ethanol and the NaOH is (0.5-2) g:(10-40) mL:(0.1-0.3) g.

[0015] Further, the hydrothermal reaction is performed at 160-180°C for 16-48h.

[0016] Further, the washing is performed by alternately washing with deionized water and ethanol for 3 times; and the drying is performed at 60-80°C for 12-24h.

[0017] Further, the graphene oxide, deionized water, SeO2, 50% ethanol solution and EDA are used in a ratio of (30-50) mg:(20-40) mL:(400-600) mg:(10-30) mL:(100-400) μL.

[0018] Further, the mass ratio of the SeO2@GO-EDA and magnesium is (0.8-1):(0.8-1).

[0019] Further, the heating and holding is at a rate of 1-5 ℃ / min to 650-700 ℃, and holding for 3-4 h.

[0020] Further, the concentration of the hydrochloric acid solution is 1 mol / L, and the immersion time is 18-24 h.

[0021] Further, the manganese iron precursor, SeO x @rGO-EDA, lithium carbonate and ammonium dihydrogen phosphate are used in a mass ratio of (30-45):(6-9):(3.5-5):(10-15).

[0022] Further, the heating and calcining is at a rate of 1-5 ℃ / min to 700-750 ℃, and calcining for 8-10 h.

[0023] The beneficial effects of the present application are:

[0024] (1) The present application provides a preparation method of a lithium manganese iron phosphate composite material, wherein the surface of lithium manganese iron phosphate (LMFP) particles is modified with SeO x @rGO-EDA functional units. Selenium (Se x / Se 4+ ) in SeO 6+ forms a Se-O-P or Se-O-M (M=Mn / Fe) covalent bond with the exposed oxygen atoms on the surface of LMFP particles, realizes chemical modification, and the residual carboxyl and hydroxyl groups on the edge of rGO are bonded with Mn 2+ / Fe 2+ on the surface of LMFP, thereby enhancing the interface bonding force.

[0025] (2) The present application uses a hydrothermal method to synthesize manganese / iron-1,3,5-benzene tricarboxylic acid organic framework (manganese iron precursor), and the high stability of the organic framework not only improves the stability of the composite material, but also provides a fast diffusion path for lithium ions due to the high specific surface area and regular channels of the organic framework, thereby improving the electronic conductivity; the introduction of manganese ions can improve the additional capacity of the battery; in addition, the chelation of the MOF (metal-organic framework) framework to iron ions can reduce the dissolution of iron during the cycle process, thereby prolonging the cycle life.

[0026] (3) The SeOx rGO-EDA, rGO (reduced graphene oxide) coated SeO2 in-situ generated via magnesium thermal reduction reaction x (0<x≤2), forming a core-shell structure; GO is reduced to rGO with stronger conductivity at high temperature; in addition, adjacent rGO layers are covalently cross-linked by ethylenediamine (EDA) molecules, and a three-dimensional continuous conductive network is constructed. The structure significantly improves the electronic conductivity, structural stability and electrochemical activity of the composite material.

[0027] (4) The oxygen-containing functional groups of the graphene oxide used in the application can cooperate with the amino groups of EDA to regulate the electrolyte decomposition path, form a dense and stable SEI film, and improve the stability of the lithium iron phosphate material; the graphene oxide acts as a SeO2 surface coating layer to synergistically inhibit oxygen release and structural degradation. In addition, the strong oxygen affinity of SeO2 can preferentially bind to the active oxygen on the surface of LiFePO4, and the chemical adsorption effect can inhibit the disproportionation reaction of manganese ions, reduce the dissolution of manganese ions, and improve the cycle stability of the composite material. x (4) The oxygen-containing functional groups of the graphene oxide used in the application can cooperate with the amino groups of EDA to regulate the electrolyte decomposition path, form a dense and stable SEI film, and improve the stability of the lithium iron phosphate material; the graphene oxide acts as a SeO2 surface coating layer to synergistically inhibit oxygen release and structural degradation. In addition, the strong oxygen affinity of SeO2 can preferentially bind to the active oxygen on the surface of LiFePO4, and the chemical adsorption effect can inhibit the disproportionation reaction of manganese ions, reduce the dissolution of manganese ions, and improve the cycle stability of the composite material. DETAILED DESCRIPTION

[0028] The specific embodiments of the application are described in detail below, but it should be understood that the protection scope of the application is not limited by the specific embodiments.

[0029] Example 1

[0030] This embodiment provides a lithium manganese iron phosphate composite material, which is prepared by the following steps:

[0031] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) are dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid is added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution is slowly added to the second solution under magnetic stirring, then 0.2 g of NaOH is added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; the sample is naturally cooled in the autoclave, centrifuged and collected, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0032] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, and ultrasonic dispersed, and then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor, and the reaction kettle was placed in an oven for hydrothermal reaction at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0033] S3, 300 mg of SeO2@GO-EDA and 300 mg of magnesium were ground and mixed uniformly, and then placed in a graphite crucible and heated in a tube furnace under an argon atmosphere, and the temperature was gradually increased at a rate of 5℃ / min until it reached 680℃, and then kept for 3 h; then the reaction product was cooled to room temperature, immersed in a hydrochloric acid solution with a concentration of 1 mol / L for 24 h; the obtained product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0034] S4, 35 parts by weight of manganese iron precursor, 8 parts by weight of SeO x @rGO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 730℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min, and then cooled to obtain a lithium manganese iron phosphate composite material.

[0035] Example 2

[0036] Compared with Example 1, the difference of this example is to increase the amount of manganese iron precursor and adjust the ratio of the use amount of the remaining components in S3, and the specific implementation steps are as follows:

[0037] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, and then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; after the sample was naturally cooled in the autoclave, it was centrifuged and collected, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0038] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, and ultrasonic dispersed, and then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor, and the reaction kettle was placed in an oven for hydrothermal reaction at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0039] S3, 300 mg of SeO2@GO-EDA and 300 mg of magnesium were ground and mixed uniformly, and then placed in a graphite crucible and heated in a tube furnace under an argon environment, and the temperature was gradually increased at a rate of 5℃ / min until it reached 680℃, and then kept for 3 h; then the reaction product was cooled to room temperature, immersed in a hydrochloric acid solution with a concentration of 1 mol / L for 24 h; the obtained product was separated by vacuum filtration technology, washed with deionized water for multiple times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0040] S4, 45 parts by weight of manganese iron precursor, 6 parts by weight of SeO x @rGO-EDA, 3.5 parts by weight of lithium carbonate, and 10 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 720℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min, and then cooled to obtain a lithium manganese iron phosphate composite material.

[0041] The remaining raw materials and preparation process are the same as those of Example 1.

[0042] Example 3

[0043] Compared with Example 1, the difference of this example is that the amount of manganese iron precursor is reduced and the amount ratio of the remaining components in S3 is adjusted, and the specific implementation steps are as follows:

[0044] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, and then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; after the sample was naturally cooled in the autoclave, it was centrifuged and collected, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0045] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, ultrasonically dispersed, and then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor, and the reaction kettle was placed in an oven for hydrothermal reaction at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0046] S3, 300 mg of SeO2@GO-EDA and 300 mg of magnesium were ground and mixed uniformly, placed in a graphite crucible, and heated in a tube furnace under an argon atmosphere, and the temperature was gradually increased at a rate of 5℃ / min until it reached 660℃, and then kept for 3 h; then the reaction product was cooled to room temperature and immersed in a 1 mol / L hydrochloric acid solution for 24 h; the product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0047] S4, 30 parts by weight of manganese iron precursor, 9 parts by weight of SeO x @rGO-EDA, 5 parts by weight of lithium carbonate, and 15 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at a rate of 5℃ / min to 710℃ for 8 h under high-purity nitrogen, and then cooled to obtain a lithium manganese iron phosphate composite material.

[0048] The remaining raw materials and preparation process are the same as those of Example 1.

[0049] Example 4

[0050] Compared with Example 1, the difference of this example is to adjust the mass ratio of SeO2@GO-EDA and magnesium, and the specific implementation steps are as follows:

[0051] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; the sample was naturally cooled in the autoclave, centrifuged, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0052] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, ultrasonically dispersed, and then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor, and the reaction kettle was placed in an oven for hydrothermal reaction at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0053] S3, 300 mg of SeO2@GO-EDA and 240 mg of magnesium were ground and mixed uniformly, placed in a graphite crucible, and heated in a tube furnace under an argon environment, and the temperature was gradually increased at a rate of 5℃ / min until it reached 690℃, and then kept for 3 h; then the reaction product was cooled to room temperature and immersed in a 1 mol / L hydrochloric acid solution for 24 h; the product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0054] S4, 35 parts by weight of manganese iron precursor, 8 parts by weight of SeO x @rGO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 740℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min, and then cooled to obtain a lithium manganese iron phosphate composite material.

[0055] The remaining raw materials and preparation process are the same as those of Example 1.

[0056] Example 5

[0057] Compared with Example 1, the difference of this example is to increase the amount of EDA and adjust the amount of other components in S2, and the specific implementation steps are as follows:

[0058] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; the sample was naturally cooled in the autoclave, centrifuged, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0059] S2, 35 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 400 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, ultrasonically dispersed, and then 400 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor, and the reaction kettle was placed in an oven for hydrothermal reaction at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0060] S3, 300 mg of SeO2@GO-EDA and 300 mg of magnesium were ground and mixed uniformly, placed in a graphite crucible, and heated in a tube furnace under an argon environment, and the temperature was gradually increased at a rate of 5℃ / min until it reached 700℃, and then kept for 3 h; then the reaction product was cooled to room temperature and immersed in a 1 mol / L hydrochloric acid solution for 24 h; the product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0061] S4, 35 parts by weight of manganese iron precursor, 8 parts by weight of SeO x @rGO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 750℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min, and then cooled to obtain a lithium manganese iron phosphate composite material.

[0062] The remaining raw materials and preparation process are the same as those of Example 1.

[0063] Example 6

[0064] Compared with Example 1, the difference of this example is to reduce the amount of EDA and adjust the amount of other components in S2, and the specific implementation steps are as follows:

[0065] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; after the sample was naturally cooled in the autoclave, it was centrifuged and collected, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0066] S2, 50 mg of graphene oxide was dissolved in 40 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 600 mg of SeO2 was added to 20 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, ultrasonically dispersed, and then 100 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor, and the reaction kettle was placed in an oven for hydrothermal reaction at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0067] S3, 300 mg of SeO2@GO-EDA and 300 mg of magnesium were ground and mixed uniformly, placed in a graphite crucible, and heated in a tube furnace under an argon atmosphere, and the temperature was gradually increased at a rate of 5℃ / min until it reached 650℃, and then kept for 3 h; then the reaction product was cooled to room temperature and immersed in a 1 mol / L hydrochloric acid solution for 24 h; the product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0068] S4, 35 parts by weight of manganese iron precursor, 8 parts by weight of SeO x @rGO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 700℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min, and then cooled to obtain a lithium manganese iron phosphate composite material.

[0069] The remaining raw materials and preparation process are the same as those of Example 1.

[0070] Example 7

[0071] Compared with Example 1, the difference of this example is to adjust the amount of each component in S1, and the specific implementation steps are as follows:

[0072] S1, 2 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 1 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 80 mL of ethoxyacetic acid to prepare a first solution; 2 g of 1,3,5-benzene tricarboxylic acid was added to 30 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; the sample was naturally cooled in the autoclave, centrifuged, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0073] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, and ultrasonic dispersed, and then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor, and the reaction kettle was placed in an oven for hydrothermal reaction at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0074] S3, 300 mg of SeO2@GO-EDA and 300 mg of magnesium were ground and mixed uniformly, placed in a graphite crucible, and heated in a tube furnace under an argon environment, and the temperature was gradually increased at a rate of 5℃ / min until it reached 660℃, and then kept for 3 h; then the reaction product was cooled to room temperature and immersed in a hydrochloric acid solution with a concentration of 1 mol / L for 24 h; the obtained product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0075] S4, 35 parts by weight of manganese iron precursor, 8 parts by weight of SeO x @rGO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 720℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min, and then cooled to obtain a lithium manganese iron phosphate composite material.

[0076] The remaining raw materials and preparation process are the same as those of Example 1.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that EDA is not added, and the specific implementation steps are as follows:

[0079] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, and then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180℃ for 48 h; the sample was naturally cooled in the autoclave, centrifuged, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor;

[0080] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, and ultrasonically dispersed, and then placed in a reactor after stirring for 10 min, the reaction kettle was placed in an oven, and hydrothermal reaction was carried out at 180℃ for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO;

[0081] S3, 300 mg of SeO2@GO and 300 mg of magnesium were ground and mixed uniformly, and then placed in a graphite crucible and heated in a tube furnace under an argon atmosphere, and the temperature was gradually increased at a rate of 5℃ / min until it reached 680℃, and then kept at this temperature for 3 h; then the reaction product was cooled to room temperature and immersed in a hydrochloric acid solution with a concentration of 1 mol / L for 24 h; the obtained product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO (0 < X ≤ 2);

[0082] S4, 35 parts by weight of manganese-iron precursor, 4 parts by weight of SeO x @rGO, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at a rate of 5℃ / min to 730℃ for 8 h under high-purity nitrogen, and then cooled to obtain a manganese iron lithium phosphate composite material.

[0083] The remaining raw materials and preparation process are the same as those of Example 1.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 1 is that SeO2 is not added, and the specific implementation steps are as follows:

[0086] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, and then 0.2 g of NaOH was added, and then transferred to a stainless steel autoclave and placed in an oven at 180℃ for 48 h; the sample was naturally cooled in the autoclave, centrifuged, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80℃ for 24 h to obtain a manganese-iron precursor;

[0087] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor. The reaction kettle was placed in an oven, and hydrothermal reaction was carried out at 180℃ for 12 h. After the reaction was completed, the sample was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain GO-EDA;

[0088] S3, 300 mg of GO-EDA and 300 mg of magnesium were ground and mixed uniformly, and then placed in a graphite crucible and heated in a tube furnace under an argon atmosphere. The temperature was gradually increased at a rate of 5℃ / min until it reached 680℃, and then kept at this temperature for 3 h. Subsequently, the reaction product was cooled to room temperature and immersed in a 1 mol / L hydrochloric acid solution for 24 h. The obtained product was separated by vacuum filtration technology, washed with deionized water for multiple times until the pH value was 7, and finally freeze-dried for 12 h to obtain rGO-EDA.

[0089] S4, 35 parts by weight of manganese iron precursor, 6 parts by weight of rGO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 730℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min. After cooling, a lithium manganese iron phosphate composite material was obtained.

[0090] The remaining raw materials and preparation process were the same as those of Example 1.

[0091] Comparative Example 3

[0092] The difference between this comparative example and Example 1 is that only graphene oxide is added in S2. The specific implementation steps are as follows:

[0093] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution. 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution. The first solution was slowly added to the second solution under magnetic stirring, and then 0.2 g of NaOH was added. The sample was transferred to a stainless steel autoclave and placed in an oven at 180℃ for 48 h. After the sample was naturally cooled in the autoclave, it was centrifuged and washed with deionized water and ethanol alternately for 3 times. The sample was dried in an oven at 80℃ for 24 h to obtain a manganese iron precursor.

[0094] S2, 35 parts by weight of manganese iron precursor, 3 parts by weight of graphene oxide, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 750℃ for 8 h under high-purity nitrogen at a rate of 5℃ / min. After cooling, a lithium manganese iron phosphate composite material was obtained.

[0095] The remaining raw materials and preparation process are the same as those of Example 1.

[0096] Comparative Example 4

[0097] This comparative example is compared with Example 1, the difference is that no magnesium hot reaction is carried out, and the specific implementation steps are as follows:

[0098] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 1 g of 1,3,5-benzene tricarboxylic acid was added to 20 mL of anhydrous ethanol to prepare a second solution; the first solution was slowly added to the second solution under magnetic stirring, then 0.2 g of NaOH was added, transferred to a stainless steel autoclave, and placed in an oven at 180°C for 48 h. The sample was naturally cooled in the autoclave, centrifuged and collected, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80°C for 24 h to obtain a manganese-iron precursor;

[0099] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, and ultrasonic dispersed, then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor. The reaction kettle was placed in an oven and hydrothermally reacted at 180°C for 12 h. After the reaction was completed, it was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0100] S3, 35 parts by weight of manganese-iron precursor, 8 parts by weight of SeO2@GO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, and then calcined at 750°C under high-purity nitrogen at a rate of 5°C / min for 8 h. After cooling, a manganese iron lithium phosphate composite material was obtained.

[0101] The remaining raw materials and preparation process are the same as those of Example 1.

[0102] Comparative Example 5

[0103] This comparative example is compared with Example 1, the difference is that no manganese / iron-1,3,5-benzene tricarboxylic acid organic framework is formed, and the specific implementation steps are as follows:

[0104] S1, 1.5 g of manganese chloride tetrahydrate (MnCl2·4H2O) and 0.5 g of iron chloride hexahydrate (FeCl3·6H2O) were dissolved in 60 mL of ethoxyacetic acid to prepare a first solution; 0.2 g of NaOH was added, transferred into a stainless steel autoclave, and placed in an oven at 180°C for 48 h; after the sample was naturally cooled in the autoclave, it was centrifuged and collected, washed with deionized water and ethanol alternately for 3 times, and dried in an oven at 80°C for 24 h to obtain a manganese-iron precursor;

[0105] S2, 40 mg of graphene oxide was dissolved in 20 mL of deionized water to obtain a third solution by stirring and ultrasonic dispersion; 500 mg of SeO2 was added to 10 mL of 50% ethanol solution to obtain a fourth solution by stirring and ultrasonic dispersion; the third solution and the fourth solution were mixed, stirred, and ultrasonic dispersed, and then 200 μL of EDA solution was added dropwise, stirred for 10 min, and then placed in a reactor; the reaction kettle was placed in an oven, and hydrothermal reaction was carried out at 180°C for 12 h; after the reaction was completed, the product was washed with deionized water and ethanol alternately for 3 times, and freeze-dried for 24 h to obtain SeO2@GO-EDA;

[0106] S3, 300 mg of SeO2@GO-EDA and 300 mg of magnesium were ground and mixed uniformly, placed in a graphite crucible, and heated in a tube furnace under argon environment; the temperature was gradually increased at a rate of 5°C / min until it reached 690°C, and then kept for 3 h; then the reaction product was cooled to room temperature, immersed in a hydrochloric acid solution with a concentration of 1 mol / L for 24 h; the obtained product was separated by vacuum filtration technology, washed with deionized water for several times until the pH value was 7, and finally freeze-dried for 12 h to obtain SeO x @rGO-EDA (0 < X ≤ 2);

[0107] S4, 35 parts by weight of the manganese-iron precursor, 8 parts by weight of SeO x @rGO-EDA, 4 parts by weight of lithium carbonate, and 12 parts by weight of ammonium dihydrogen phosphate were uniformly mixed, calcined at 740°C for 8 h under high-purity nitrogen at a rate of 5°C / min, and cooled to obtain a lithium manganese iron phosphate composite material.

[0108] The remaining raw materials and preparation process were the same as those of Example 1.

[0109] Performance test

[0110] Lithium iron phosphate, acetylene black and polytetrafluoroethylene were added into N-methylpyrrolidone in a mass ratio of 80:12:8, ground and mixed uniformly, the slurry was coated on the surface of aluminum foil, dried at 100 DEG C for 24h to obtain a positive electrode sheet, lithium metal sheet was used as the negative electrode, polypropylene microporous membrane was used as the separator, 1mol / L LiPF6 organic solution was used as the electrolyte, the solvent used in the organic solution was a mixed solution of dimethyl carbonate and ethylene carbonate, and the battery was assembled in a glove box. The capacity test and cycle test of the prepared battery were carried out according to SJ / T 11797-2022 respectively; the test results are shown in Table 1:

[0111] Table 1

[0112]

[0113] As can be seen from Table 1, examples 2-7 are compared with example 1, the only difference is that the component ratio is adjusted within a reasonable range, from the results, the prepared lithium manganese iron phosphate composite can improve the specific capacity and cycle performance of the battery; compared with example 1, example 2 increases the amount of manganese iron precursor, which means that the content of iron is increased, which destroys the balance of iron, lithium and phosphorus atoms, resulting in a downward trend of battery performance compared with example 1; compared with example 1, increasing the amount of EDA in example 5 will hinder the transmission path of lithium ions, reducing the specific capacity of the battery; compared with example 1, example 7 increases the molar ratio of iron and manganese in the manganese iron precursor, resulting in unstable structure of the manganese iron precursor, which will cause the decline of the subsequent performance test results.

[0114] Comparative examples 1-3 are compared with example 1, the difference is that SeO x The adjustment of raw material components in the preparation process of rGO-EDA can improve the stability of EDA and graphene oxide by forming a dense and stable SEI film; SeO x Not only can improve the electronic conductivity, but also can reduce the dissolution of manganese ions, improve the cycle stability of the battery; thus leading to the decline of battery performance of comparative examples 1-3 compared with example 1. Compared with example 1, comparative example 4 does not perform magnesium thermal reaction, GO cannot form rGO with stronger conductivity, and SeO2 cannot further improve the conductivity, resulting in a decrease in the specific capacity of the battery. Compared with example 1, comparative example 5 does not form manganese / iron-1,3,5-benzene-1,3,5-tricarboxylic acid organic framework, at this time the stability of lithium iron phosphate material decreases, and manganese iron ions will accelerate the dissolution, and the battery performance decreases more.

[0115] The above disclosure is only a few specific embodiments of the present application, but the embodiments of the present application are not limited to this, any changes that can be thought of by those skilled in the art should fall within the protection scope of the present application.

Claims

1. A lithium iron manganese phosphate composite material, characterized in that, SeO including lithium manganese iron phosphate and surface modification of lithium manganese iron phosphate x @rGO-EDA; The manganese iron lithium phosphate comprises a manganese / iron-1,3,5-benzene tricarboxylic acid organic framework, a phosphorus source and a lithium source; The rGO is coated on SeO x The surface forms a core-shell structure, and adjacent rGO sheets are covalently cross-linked by EDA to form SeO x @rGO-EDA, 0 < X≤ 2.

2. A method for producing a lithium iron manganese phosphate composite material, characterized by, The method for preparing the manganese iron lithium phosphate composite material as claimed in claim 1 comprises the following steps: S1, dissolving MnCl2.4H2O and FeCl3.6H2O in ethoxy acetic acid to prepare a first solution; adding 1,3,5-benzene tricarboxylic acid into anhydrous ethanol to prepare a second solution; slowly adding the first solution into the second solution, and then adding NaOH, and then performing hydrothermal reaction, and then performing centrifugal washing after cooling, and then drying to obtain a manganese iron precursor; S2, dissolving graphene oxide in deionized water to obtain a third solution; adding SeO2 into a 50% ethanol solution to obtain a fourth solution; mixing the third solution and the fourth solution uniformly, and then adding EDA solution dropwise, and then performing hydrothermal reaction, and then performing washing and freeze-drying to obtain SeO2@GO-EDA; S3, grinding and mixing SeO2@GO-EDA and magnesium uniformly, heating and keeping warm under argon environment, immersing in hydrochloric acid solution after cooling; filtering and washing, freeze-drying to obtain SeO2@rGO-EDA, 0X≤2. x @rGO-EDA, 0X≤2. S4, the manganese iron precursor, SeO x @After the rGO-EDA, lithium carbonate and ammonium dihydrogen phosphate are uniformly mixed, they are calcined under nitrogen, and the lithium manganese iron phosphate composite material is obtained after cooling.

3. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The amount ratio of the MnCl2.4H2O, the FeCl3.6H2O and the ethoxy acetic acid is (1-2.5) g:(0.25-1.25) g:(40-100) mL.

4. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The amount ratio of the 1,3,5-benzene tricarboxylic acid, the anhydrous ethanol and the NaOH is (0.5-2) g:(10-40) mL:(0.1-0.3) g.

5. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The hydrothermal reaction is performed at 160-180℃ for 16-48h; the washing is performed by alternately washing with deionized water and ethanol for 3 times; and the drying is performed at 60-80℃ for 12-24h.

6. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The amount ratio of the graphene oxide, the deionized water, the SeO2, the 50% ethanol solution and the EDA is (30-50) mg:(20-40) mL:(400-600) mg:(10-30) mL:(100-400) μL.

7. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The mass ratio of the SeO2@GO-EDA and the magnesium is (0.8-1):(0.8-1).

8. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The heating and holding is performed at a rate of 1-5℃ / min to 650-700℃, and the holding is performed for 3-4h; and the temperature rising calcination is performed at a rate of 1-5℃ / min to 700-750℃ for 8-10h.

9. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The concentration of the hydrochloric acid solution is 1 mol / L, and the immersion time is 18-24h.

10. The method for preparing the lithium manganese iron phosphate composite material according to claim 2, characterized in that, The manganese iron precursor, SeO x @The mass ratio of rGO-EDA, lithium carbonate, ammonium dihydrogen phosphate is (30-45):(6-9):(3.5-5):(10-15).

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