Preparation method of lithium iron manganese phosphate material and lithium ion battery

Abstract

The invention relates to the technical field of electrode materials, and discloses a preparation method of a lithium iron manganese phosphate material and a lithium ion battery. The lithium iron manganese phosphate material is prepared by the following steps: performing in-situ growth in a cavity of polyethylene glycol-sucrose hybrid aerogel with a three-dimensional porous network structure to form a manganese iron phosphate precursor; the hybrid aerogel can control excessive agglomeration and disordered growth of ferromanganese phosphate precursor particles and avoid particle agglomeration, so that the finally formed lithium ferromanganese phosphate material particles are finer and more uniformly distributed, and an amorphous carbon-aluminum layer is formed during later calcination, so that the performance of the material is improved. The surface of lithium manganese iron phosphate particles is tightly coated with the composite material, electron transmission can be accelerated, particle pulverization can be reduced, meanwhile, corrosion of corrosive components in electrolyte can be inhibited, interface side reactions such as transition metal ion dissolution can be reduced, and finally the conductivity and cycling stability of the lithium ion battery are remarkably improved.

Description

TECHNICAL FIELD

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

[0002] The global emphasis on environmental protection and sustainable development is driving the transformation of energy structure to clean energy. Lithium ion batteries are widely used in 3C products, energy storage and power batteries due to their high energy density, long service life, good rate performance and low cost, and have become a research hotspot in new energy.

[0003] The positive electrode material determines the performance of the lithium battery. Commonly used ones are lithium cobaltate, ternary material and lithium iron phosphate. Among them, lithium iron phosphate is commercially mature, has the advantages of high safety, long service life and no pollution, but the working potential is low and the energy density is difficult to meet higher demand. Lithium iron phosphate has obvious defects: the olivine structure leads to slow diffusion of lithium ions, low electronic conductivity, poor electrode rate performance, rapid capacity attenuation during large current charging and discharging, and insufficient cycle stability, which limits its application in high-performance electric vehicles, large-scale energy storage and other fields with high requirements for power and service life. To improve the energy density and improve the defects of lithium iron phosphate, researchers replace part of the iron element with manganese to develop lithium manganese iron phosphate material. The addition of manganese improves the voltage platform and energy density, prolongs the endurance of electric vehicles, and the price of manganese is low, making the material cost flat or even lower than that of lithium iron phosphate. In addition, lithium manganese iron phosphate also effectively makes up the short board of low temperature performance of lithium iron phosphate. The capacity retention rate of traditional lithium iron phosphate battery is low in low temperature environment, while lithium manganese iron phosphate can still maintain good capacity under the same conditions. Moreover, it inherits the safety characteristics of lithium iron phosphate, has extremely high safety, can pass the rigorous full battery needle test, and does not catch fire or explode.

[0004] However, lithium manganese iron phosphate material also faces some challenges in practical application. For example, its conductivity is worse than that of lithium iron phosphate, and low electronic conductivity and ionic conductivity will lead to large internal resistance of the material during charging and discharging, affecting the rate performance of the battery, and the energy output and efficiency will decrease significantly in high-rate charging and discharging scenarios; at the same time, there are two voltage platforms, and the voltage difference between the platforms is large, which leads to unstable voltage change during battery charging and discharging, which may affect the stability of the electrical equipment, especially for electronic equipment that requires stable voltage output, additional circuit design is needed for adjustment, and its cycle stability needs to be improved, and the structure is prone to distortion after long-term charging and discharging cycles.

[0005] Therefore, it has become one of the important research contents in the field of lithium ion batteries to develop a preparation method of high-performance lithium manganese iron phosphate material to improve its cycle stability, ion conductivity and other performances. SUMMARY

[0006] The application aims to provide a preparation method of a lithium iron manganese phosphate material and a lithium ion battery.

[0007] The application aims to provide a preparation method of a lithium iron manganese phosphate material and a lithium ion battery. The application aims to provide a preparation method of a lithium iron manganese phosphate material and a lithium ion battery. Step 1: a lithium source is added to deionized water, and after stirring uniformly, a premix solution is obtained; Step 2: the lithium iron manganese phosphate precursor is ultrasonically dispersed in deionized water, and then the premix solution is added, ultrasonic dispersion is carried out at an ultrasonic frequency of 60-90 KHz for 3-5 h, and a mixed solution is obtained; Step 3: the mixed solution is added to an ethanol solution, and grinding is carried out until powder is obtained; Step 4: the powder is placed in a crucible and placed in a tube furnace filled with argon, the temperature is set to 700-800 DEG C, and sintering is carried out for 8-9 h, thereby obtaining the lithium iron manganese phosphate material.

[0008] Further, in the first step, the lithium source is any one of lithium carbonate, lithium hydroxide, lithium nitrate or lithium oxalate.

[0009] Further, the mass ratio of the lithium source to the lithium iron manganese phosphate precursor is 1:1.1-1.2.

[0010] Further, the preparation method of the lithium iron manganese phosphate precursor comprises the following steps: A1: a phosphorus source, a manganese source and an iron source are added to deionized water to configure a metal salt solution; A2: polyethylene glycol-sucrose hybrid aerogel is dispersed in another portion of deionized water, and magnetic stirring is carried out for 10-15 min to obtain a colloidal solution; A3: the metal salt solution and the colloidal solution are added to a high-pressure hydrothermal reaction kettle, argon is introduced for 30-45 min, air is exhausted, the reaction kettle is sealed, the temperature is increased to 175-180 DEG C, and reaction is carried out for 4-5 h; after the reaction is completed, the pH value of the solution in the reaction kettle is tested, the product is suction filtered, the solid product is repeatedly washed with deionized water until the pH value is 6.5-7.5, and then the product is dried at a temperature of 60-70 DEG C for 10-12 h to obtain the lithium iron manganese phosphate precursor.

[0011] Further, in step A1, the phosphorus source is any one of phosphoric acid, sodium dihydrogen phosphate or ammonium dihydrogen phosphate; the manganese source is any one of manganese carbonate, manganese nitrate, manganese oxalate, manganese dioxide or trimanganese tetraoxide; and the iron source is any one of ferrous chloride, ferric nitrate or dihydrogen iron phosphate.

[0012] By the technical scheme, the polyethylene glycol-sucrose hybrid aerogel is used as a matrix for synthesizing manganese iron phosphate, and ions generated by dissociation of phosphorus source, manganese source and iron source are subjected to hydrothermal reaction in pores of the polyethylene glycol-sucrose hybrid aerogel to generate a manganese iron phosphate precursor.

[0013] Further, the preparation method of the polyethylene glycol-sucrose hybrid aerogel comprises the following steps: S1: adding tetrahydrofuran as a solvent into a reactor, adding polyethylene glycol, pentaerythritol glycidyl ether, and then adding sodium hydroxide aqueous solution, increasing the temperature to 35-40℃, stirring for 4-5h, removing unreacted substances and solvents after the reaction, and drying the product to obtain a polyethylene glycol modifier; S2: weighing the polyethylene glycol modifier and placing it in a reactor, adding deionized water and stirring uniformly, then adding a sucrose complex, increasing the temperature to 80-85℃, and stirring for 2-2.5h, collecting the product, placing the product in a polytetrafluoroethylene mold, and standing for 6-7h, then cooling the product in liquid nitrogen for 30-45min, and drying the frozen sample in a freeze dryer at-50℃ to-60℃ for 24-30h to obtain the polyethylene glycol-sucrose hybrid aerogel.

[0014] Further, in step S1, the mass fraction of the sodium hydroxide aqueous solution is 20-30%.

[0015] By the technical scheme, under the alkaline condition provided by sodium hydroxide, ring-opening reaction occurs between the polyepoxy groups in the structure of pentaerythritol glycidyl ether and the hydroxyl groups in the polyethylene glycol to form ether bonds, and the polyethylene glycol modifier containing a three-dimensional network structure is obtained, the alcohol hydroxyl groups on the polyethylene glycol modifier and the sucrose complex containing alcohol hydroxyl groups or carbonyl groups form a more compact network structure through hydrogen bonding, and the polyethylene glycol-sucrose hybrid aerogel containing a porous structure is finally obtained through freeze-drying technology.

[0016] Further, the preparation method of the sucrose complex comprises the following steps: H1: placing ethylenediaminetetraacetic dianhydride in a reactor, starting mechanical stirring, increasing the temperature to 120-130℃, adding sucrose and sodium bicarbonate, stirring for 6-7h, cooling to room temperature after the reaction, and obtaining a sucrose medium; H2: placing the sucrose medium in a reactor, dissolving by adding an ethanol aqueous solution, adding aluminum sulfate into the sucrose medium solution while stirring, increasing the temperature to 30-35℃, stirring and mixing for 4-6h, removing excess water, and then freeze-drying the product to obtain the sucrose complex.

[0017] Further, in step H2, the volume fraction of the ethanol aqueous solution is 10-20%.

[0018] Through the technical scheme, under the catalysis of sodium bicarbonate, the acid anhydride groups in ethylenediaminetetraacetic dianhydride and alcohol hydroxyl groups in sucrose structure undergo ring-opening esterification reaction to generate ester groups, and the carboxyl groups from ethylenediaminetetraacetic dianhydride are introduced into the sucrose medium, and then the sucrose medium and aluminum sulfate undergo coordination reaction in an acidic aqueous solution to form a sucrose complex.

[0019] Further, a lithium ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, and the positive electrode sheet includes the lithium iron manganese phosphate material prepared by the preparation method.

[0020] The present application has the following beneficial effects: (1) The lithium ion battery prepared by the present application has good rate performance and cycle stability, and the high performance makes the lithium ion battery have a broad application prospect in the field of new energy vehicles, energy storage power stations and other fields with strict requirements on battery performance.

[0021] (2) The present application synthesizes lithium manganese iron phosphate in situ in the cavity of the polyethylene glycol-sucrose hybrid aerogel, and the polyethylene glycol-sucrose hybrid aerogel with a three-dimensional porous network structure has abundant pores and surfaces, which can limit the excessive agglomeration and disordered growth of lithium manganese iron phosphate precursor particles. Metal ions in the metal salt solution are enriched in the pores or on the surface of the polyethylene glycol-sucrose hybrid aerogel, and through hydrothermal reaction, they are preferentially nucleated and grown in the network, finally controlling the size and dispersity of the precursor, avoiding particle agglomeration, and making the finally formed lithium manganese iron phosphate material particles finer and more uniform, which is beneficial to improving the ion conductivity and cycle stability of the material.

[0022] (3) The polyethylene glycol-sucrose hybrid aerogel prepared by the present application carbonizes during later calcination, forming an amorphous carbon-aluminum layer that tightly coats the surface of the lithium manganese iron phosphate particles. The carbon layer, as a conductive medium, can construct an electron conduction network throughout the particles, significantly reducing the inter-particle contact resistance, accelerating electron transport, and significantly improving the overall conductivity. At the same time, the aluminum source in the polyethylene glycol-sucrose hybrid aerogel cooperates with the carbon layer to construct a composite coating structure, inhibiting the volume expansion of lithium manganese iron phosphate during charge and discharge cycles and reducing particle pulverization. Meanwhile, the aluminum source can also modify the interface of the electrolyte, inhibit the corrosion of corrosive components in the electrolyte, reduce the interface side reactions such as transition metal ion dissolution, and improve the cycle stability, further improving the electrochemical activity of the electrode material.

[0023] Of course, implementing any product of the present application does not necessarily require achieving all the advantages described above at the same time. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required to be used in the description of the embodiments. Obviously, the drawings in the following description are only some of the embodiments of the present application, and all other drawings obtained by those of ordinary skill in the art without creative effort based on these drawings are within the scope of protection of the present application.

[0025] Figure 1 Scanning electron microscope image of the polyethylene glycol-sucrose hybrid aerogel of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0027] The lithium manganese iron phosphate material in the embodiments of the present application is prepared by the following method: Step one, preparation of sucrose complex: H1: 2.6 g of ethylenediaminetetraacetic dianhydride is placed in a reactor, mechanical stirring is started, the temperature is raised to 120℃, 3.5 g of sucrose and 0.05 g of sodium bicarbonate are added, and stirring reaction is carried out for 6 h. After the reaction is completed, the temperature is cooled to room temperature, and a sucrose medium is obtained. H2: 4.3 g of the sucrose medium is placed in a reactor, 100 mL of 10% ethanol aqueous solution is added for dissolution, 5.3 g of aluminum sulfate is slowly added into the sucrose medium solution while stirring, the temperature is raised to 30℃, stirring and mixing are carried out for 4 h, the excess water is removed, and then the product is freeze-dried to obtain the sucrose complex.

[0028] Step two, preparation of polyethylene glycol-sucrose hybrid aerogel: S1: 150 mL of tetrahydrofuran is added into a reactor as a solvent, 5.6 g of polyethylene glycol, 0.4 g of pentaerythritol glycidyl ether, and 2.8 mL of 20% sodium hydroxide aqueous solution are added, the temperature is raised to 35℃, stirring reaction is carried out for 4 h, after the reaction is completed, the unreacted substances and the solvent are removed, and the product is dried to obtain a polyethylene glycol modified substance; S2: 2.8 g of the polyethylene glycol modified substance is weighed and placed in a reactor, 120 mL of deionized water is added and stirred uniformly, 3.2 g of the sucrose complex is then added, the temperature is raised to 80℃, and the product is collected after stirring for 2 h. The product is placed in a polytetrafluoroethylene mold, and is left to stand for 6 h. Then, liquid nitrogen is used for cooling for 30 min, and the frozen sample is placed in a freeze-drying machine at-50℃ for drying for 24 h to obtain the polyethylene glycol-sucrose hybrid aerogel.

[0029] Figure 1 The scanning electron microscope image of the polyethylene glycol-sucrose hybrid aerogel can be seen from the figure. The polyethylene glycol-sucrose hybrid aerogel contains a large number of pores and presents a porous network appearance, which is conducive to the formation of manganese iron phosphate precursor in the cavity by subsequent phosphorus source, manganese source and iron source.

[0030] Step three, preparation of manganese iron phosphate precursor: A1: 0.3g of sodium dihydrogen phosphate, 0.1g of manganese carbonate and 0.4g of ferric nitrate were added to 20mL of deionized water to prepare a metal salt solution; A2: 2.2g of polyethylene glycol-sucrose hybrid aerogel was dispersed in 50mL of deionized water and magnetically stirred for 10min to obtain a colloidal solution; A3: The metal salt solution and the colloidal solution were added to a high-pressure hydrothermal reactor, argon was introduced for 30min, the air was exhausted, the reactor was sealed, the temperature was raised to 175℃, and the reaction was carried out for 5h. After the reaction, the pH value of the solution in the reactor was tested, the solid product was repeatedly washed with deionized water until the pH value was 7, and then dried at 60℃ for 12h to obtain the manganese iron phosphate precursor.

[0031] Step four, preparation of manganese iron phosphate lithium material: First step: 0.21g of lithium carbonate was dissolved in 3mL of deionized water, and after stirring uniformly, a premix solution was obtained; Second step: 0.23g of manganese iron phosphate precursor was ultrasonically dispersed in 5mL of deionized water, and then the premix solution was added. Ultrasonic dispersion was carried out at a frequency of 60KHz for 3h to obtain a mixed solution; Third step: The mixed solution was added to 5mL of ethanol solution and ground into powder; Fourth step: The powder was placed in a crucible and put into a tube furnace filled with argon, the temperature was set to 700℃, and sintering was carried out for 9h to obtain the manganese iron phosphate lithium material.

[0032] Example 2 First step: 0.21g of lithium carbonate was added to 3mL of deionized water, and after stirring uniformly, a premix solution was obtained; Second step: 0.24g of manganese iron phosphate precursor was ultrasonically dispersed in 6mL of deionized water, and then the premix solution was added. Ultrasonic dispersion was carried out at a frequency of 70KHz for 4h to obtain a mixed solution; Third step: The mixed solution was added to 6mL of ethanol solution and ground into powder; Fourth step: The powder was placed in a crucible and put into a tube furnace filled with argon, the temperature was set to 750℃, and sintering was carried out for 8.5h to obtain the manganese iron phosphate lithium material.

[0033] The preparation method of the manganese iron phosphate precursor is the same as that in Example 1.

[0034] Example 3 First step: 0.21 g of lithium carbonate was added to 3 mL of deionized water, and after stirring uniformly, a premix solution was obtained; Second step: 0.25 g of the manganese iron phosphate precursor was ultrasonically dispersed in 7 mL of deionized water, and then the premix solution was added. Ultrasonic dispersion was carried out at a frequency of 90 KHz for 3 h to obtain a mixed solution; Third step: The mixed solution was added to 7 mL of an ethanol solution, and grinding was carried out until a powder was obtained; Fourth step: The powder was placed in a crucible and placed in a tube furnace filled with argon, and the temperature was set to 800℃. Sintering was carried out for 8 h to obtain a lithium manganese iron phosphate material.

[0035] The preparation method of the manganese iron phosphate precursor is the same as that in Example 1.

[0036] Comparative Example 1 First step: 0.21 g of lithium carbonate was added to 3 mL of deionized water, and after stirring uniformly, a premix solution was obtained; Second step: 0.24 g of a commercially available manganese iron phosphate precursor was ultrasonically dispersed in 6 mL of deionized water, and then the premix solution was added. Ultrasonic dispersion was carried out at a frequency of 70 KHz for 4 h to obtain a mixed solution; Third step: The mixed solution was added to 6 mL of an ethanol solution, and grinding was carried out until a powder was obtained; Fourth step: The powder was placed in a crucible and placed in a tube furnace filled with argon, and the temperature was set to 750℃. Sintering was carried out for 8.5 h to obtain a lithium manganese iron phosphate material.

[0037] The commercially available manganese iron phosphate precursor was purchased from Hubei Gaobo Technology Co., Ltd.

[0038] Performance test (1) The lithium manganese iron phosphate materials prepared in Examples 1-3 and Comparative Example 1 were used as positive electrode materials of lithium ion batteries to prepare lithium ion batteries. The specific preparation method was as follows: 75 parts by weight of the lithium manganese iron phosphate material, 12 parts of graphene, and 10 parts of polyvinylidene fluoride were added to 4 parts of N-methyl pyrrolidone solvent, and stirring was carried out uniformly in a stirrer with a vacuum degree of -60 kPa to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on the surface of an aluminum foil, and was placed in a vacuum drying box at 80℃ for 6 h. After drying, rolling and slicing were carried out to obtain a positive electrode sheet; the positive electrode sheet, a graphite negative electrode sheet, an electrolyte, and a separator were combined, vacuum packaged, left to stand, formed, and divided to obtain a lithium ion battery.

[0039] The lithium ion battery was placed on a battery test system for charge-discharge cycle test; the test conditions were as follows: the charge-discharge rate was 1C and 8C, the voltage range was 2.5V-4.3V, one cycle was defined as one charge and one discharge, the discharge specific capacity, the discharge specific capacity after 200 cycles and the capacity retention rate were recorded, and the test results were shown in the following table: , Note: the discharge specific capacity (mAh / g) = discharge capacity (unit: mAh) / mass of lithium manganese iron phosphate material (unit: g); the capacity retention rate (%) after 200 cycles = discharge capacity at the 200th cycle / discharge capacity at the 1st cycle.

[0040] From the above data, it can be seen that the lithium batteries prepared by examples 1-3 have good rate performance and cycle stability; the discharge specific capacity of the lithium battery prepared by comparative example 1 at 1C rate and 8C rate is lower than that of examples 1-3, and the capacity retention rate after 200 cycles is less than 90%, which indicates that the rate performance and cycle stability of the lithium battery prepared by comparative example 1 are inferior to those of examples 1-3, because the commercially available manganese iron phosphate precursor used in comparative example 1 fails to form a carbon-aluminum coating layer.

[0041] (2) The electronic conductivity of the lithium manganese iron phosphate materials prepared by examples 1-3 and the lithium manganese iron phosphate material used in comparative example 1 was tested by an electronic conductivity tester; the test results were shown in the following table: From the above data, it can be seen that, compared with comparative example 1, the lithium manganese iron phosphate materials prepared by examples 1-3 have higher electronic conductivity and better conductivity performance; the lithium manganese iron phosphate material prepared by comparative example 1 fails to form a carbon-aluminum coating layer, has lower electronic conductivity and poorer conductivity performance.

[0042] The above content is only an example and description of the concept of the present application, and those skilled in the art can make various modifications or supplements or use similar ways to replace the described specific examples, as long as they do not deviate from the concept of the present application or exceed the scope defined by the present claims, and should belong to the protection scope of the present application.

Claims

1. A method for preparing lithium manganese iron phosphate material, characterized in that: The following steps are involved: Step 1: Add the lithium source to deionized water and stir evenly to obtain a premixed solution; Step 2: ultrasonically disperse the ferromanganese phosphate precursor in deionized water, then add the premixed solution, and ultrasonically disperse it at an ultrasonic frequency of 60-90 kHz for 3-5 hours to obtain a mixed solution; Step 3: Add the mixed solution to the ethanol solution and grind it into powder; Step 4: Place the powder in a crucible, put it into a tubular furnace filled with argon, set the temperature to 700-800°C, and sinter for 8-9 hours to obtain lithium manganese iron phosphate material.

2. The method for preparing a lithium iron manganese phosphate material according to claim 1, wherein: In the first step, the lithium source is any one of lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxalate.

3. The method for preparing a lithium manganese iron phosphate material according to claim 1, wherein: The mass ratio of the lithium source to the ferromanganese phosphate precursor is 1:1.1-1.

2.

4. The method for preparing a lithium iron manganese phosphate material according to claim 1, wherein: The preparation method of the ferromanganese phosphate precursor comprises the following steps: A1: Add phosphorus source, manganese source and iron source to deionized water to prepare a metal salt solution; A2: Disperse the polyethylene glycol-sucrose hybrid aerogel in another portion of deionized water and stir magnetically for 10-15 minutes to obtain a colloidal solution; A3: Add the metal salt solution and colloidal liquid to a high-pressure hydrothermal reactor, introduce argon for 30-45 minutes, exhaust the air, seal the reactor, raise the temperature to 175-180°C, and react for 4-5 hours. After the reaction is completed, test the pH value of the solution in the reactor, filter the product, and repeatedly wash the solid product with deionized water to a pH of 6.5-7.

5. Then, dry it at 60-70°C for 10-12 hours to obtain a manganese iron phosphate precursor.

5. The method for preparing a lithium iron manganese phosphate material according to claim 4, characterized in that: In step A1, the phosphorus source is any one of phosphoric acid, sodium dihydrogen phosphate, and ammonium dihydrogen phosphate; the manganese source is any one of manganese carbonate, manganese nitrate, manganese oxalate, manganese dioxide, and manganese tetraoxide; and the iron source is any one of ferrous chloride, ferric nitrate, and ferric phosphate dihydrate.

6. The method for preparing a lithium iron manganese phosphate material according to claim 4, characterized in that: The preparation method of the polyethylene glycol-sucrose hybrid aerogel comprises the following steps: S1: Add tetrahydrofuran as a solvent to a reactor, add polyethylene glycol and pentaerythritol glycidyl ether, and then add a sodium hydroxide aqueous solution, increase the temperature to 35-40°C, stir and react for 4-5 hours, and after the reaction is completed, remove the unreacted material and solvent, and dry the product to obtain a polyethylene glycol modified product; S2: Weigh the polyethylene glycol modification and place it in a reactor, add deionized water, stir evenly, then add the sucrose complex, then raise the temperature to 80-85°C, keep stirring for 2-2.5 hours, collect the product, place the product in a polytetrafluoroethylene mold, let it stand for 6-7 hours, then cool it with liquid nitrogen for 30-45 minutes, and place the frozen sample in a freeze dryer at -50°C to -60°C and dry it for 24-30 hours to obtain polyethylene glycol-sucrose hybrid aerogel.

7. The method for preparing a lithium iron manganese phosphate material according to claim 6, characterized in that: In step S1, the mass fraction of the sodium hydroxide aqueous solution is 20-30%.

8. The method for preparing a lithium iron manganese phosphate material according to claim 6, characterized in that: The preparation method of the sucrose complex comprises the following steps: H1: Place ethylenediaminetetraacetic acid dianhydride in a reactor, start mechanical stirring, raise the temperature to 120-130°C, add sucrose and sodium bicarbonate, stir and react for 6-7 hours, and after the reaction is completed, cool to room temperature to obtain a sucrose medium; H2: Place the sucrose medium in a reactor, add ethanol aqueous solution to dissolve it, add aluminum sulfate to the sucrose medium solution while stirring, raise the temperature to 30-35°C, stir and mix for 4-6 hours, remove excess water, and then freeze-dry the product to obtain a sucrose complex.

9. The method for preparing a lithium iron manganese phosphate material according to claim 8, characterized in that: In step H2, the volume fraction of the ethanol aqueous solution is 10-20%.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the positive electrode sheet comprises a lithium manganese iron phosphate material prepared by the preparation method according to any one of claims 1 to 9.

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