Preparation method of high-exposure (010) crystal face morphology lithium manganese iron phosphate positive electrode material

Abstract

The application relates to a preparation method of a high-exposure (010) crystal face morphology lithium manganese iron phosphate positive electrode material. In view of the deficiency of the lithium manganese iron phosphate material in the aspect of the electric conductivity, the application provides a preparation method, ascorbic acid and a surfactant are introduced to carry out a hydrothermal reaction, and the hydrothermal reaction product is calcined to obtain the positive electrode material. The surfactant in the method has important dispersant and template effects, the prepared positive electrode material has a regular sheet layer, and the [010] crystal face has a shorter path, which is beneficial to accelerating the conduction rate of internal lithium ions and improving the electrochemical performance of the material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion cathode material, and particularly relates to a preparation method of a high-exposure (010) crystal face morphology lithium manganese iron phosphate cathode material, the high-exposure (010) crystal face morphology lithium manganese iron phosphate cathode material prepared by the method, a battery cathode comprising the cathode material, and a button cell. BACKGROUND

[0002] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the background of the present application and should not be taken as an acknowledgement or any form of suggestion that this information forms prior art that is publicly known.

[0003] Existing researches show that doping a certain proportion of manganese (Mn) in lithium iron phosphate can form a new type of phosphate lithium ion battery cathode material, lithium manganese iron phosphate LiMn x Fe 1-x PO4. Compared with lithium iron phosphate, the manganese-based material has a higher working voltage, so that the lithium manganese iron phosphate has a higher voltage platform. When the specific capacity is the same, the lithium manganese iron phosphate has a higher energy density, which is 10%-20% higher than that of the lithium iron phosphate under the same conditions, but the disadvantage is that the introduction of manganese significantly reduces the conductivity of the material, and further reduces the electrochemical performance.

[0004] In order to improve the Li + conductivity and electronic conductivity of the lithium manganese iron phosphate, the feasible ways include: (1) adopting effective carbon coating; (2) reducing the size of the lithium manganese iron phosphate particles to nanoscale; and (3) ion doping and crystal face growth control of the lithium manganese iron phosphate. For the above strategy (1), relevant researches show that, compared with the lithium iron phosphate material, in order to improve the conductivity, a proportion as high as 20-30wt% of carbon needs to be added in the preparation process of the lithium manganese iron phosphate, however, such a proportion of carbon coating will also reduce the power density of the battery. For the above strategy (2), only reducing the particle size cannot improve the energy density of the battery, improve the electrical performance, and reduce the compaction. In addition, the smaller particle size will greatly increase the specific surface area of the material, resulting in difficult processing and cost increase of the battery. Therefore, how to improve the conductivity, rate performance and cycle performance of the lithium manganese iron phosphate while ensuring the high energy density of the lithium manganese iron phosphate, and develop a lithium manganese iron phosphate with excellent comprehensive performance has important research and development significance. SUMMARY

[0005] The present application aims to improve the shortcomings of the prior art of the lithium manganese iron phosphate, and provide a high-exposure (010) crystal face special morphology lithium manganese iron phosphate Li x Fe 1-xLiMnxFe1-xPO4, wherein 0 The present application promotes the growth of (010) crystal face through hydrothermal method and with the aid of an inducing agent (surfactant), the synthesized powder is thin in thickness along

[010] direction, i.e. has higher (010) exposed surface, the material has high crystallinity, and based on this structure, the electrochemical performance of the lithium manganese iron phosphate positive electrode material is effectively improved. Through morphology improvement, the lithium manganese iron phosphate positive electrode material has higher lithium + higher lithium ion diffusion ability, lower charge transfer impedance and better stability.

[0006] In a first aspect, a preparation method of a lithium manganese iron phosphate positive electrode material with high (010) exposed crystal face morphology is provided, comprising the following steps:

[0007] Lithium salt, iron salt, manganese salt and phosphoric acid are weighed according to the stoichiometric ratio of each element in LiMnxFe1-xPO4&C, wherein 0

[0008] The surfactant is at least one selected from ethylene glycol (EG), polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB) and diethylene glycol (DEG).

[0009] Since the lithium manganese iron phosphate itself has lower electrical conductivity than lithium iron phosphate, the material particle size needs to be reduced to increase the electrical conductivity. In order to achieve the above effect, the surfactant is introduced in the hydrothermal reaction to play the role of dispersant and soft template, which inhibits the growth of the material in the

[010] direction and reduces the surface energy of the (010) crystal face. The crystal grain size and morphology of the sample are well controlled through the surfactant-induced crystal face growth technology to prepare the lithium manganese iron material with special morphology. Therefore, when the lithium manganese iron material is used as the positive electrode material of the lithium ion battery, the rate performance, coulombic efficiency, discharge capacity and cycle performance of the battery are greatly improved. In addition, the hydrothermal method and surfactant-assisted synthesis are adopted in the present application, and the particle size, morphology and crystal direction of the product are easy to control. The hydrothermal reaction is a low-temperature reaction, which has the advantages of fast reaction kinetics, short processing time, high phase purity and low calcination temperature after calcination. It has the characteristics of cost-effectiveness, environmental protection and easy commercial expansion.

[0010] Further, the above preparation method also has the following preferred schemes:

[0011] The lithium salt can be lithium hydroxide, lithium oxalate, lithium carbonate, lithium nitrate, lithium sulfate, lithium acetate, and the like. In one embodiment, lithium hydroxide is used.

[0012] The metal ion in the ionized iron salt should include ferrous ion. The iron salt can be ferrous chloride, ferrous nitrate, ferrous sulfate, ferrous oxalate, ferrous acetate, and the like. In one preferred embodiment, the acid radical in the manganese salt is the same as that in the iron salt. In one specific embodiment, the iron salt is ferrous sulfate and the manganese salt is manganese sulfate.

[0013] The phosphoric acid can be phosphoric acid, ammonium dihydrogen phosphate, monohydrogen ammonium phosphate, ammonium phosphate, and the like.

[0014] The specific steps for mixing the components are as follows:

[0015] The lithium salt solution A, the solution B containing iron and manganese salt, the phosphoric acid solution C, the solution D containing ascorbic acid and surfactant are prepared respectively. The solution C and the solution A are slowly added to the solution D in sequence and mixed uniformly to obtain the solution E. After the addition is completed, the stirring is continued for 25-50 min. The concentration of ascorbic acid in the solution E is controlled to be 0.004-0.006 g / ml, and the concentration of surfactant is controlled to be 0.008-0.030 g / ml. The solution B is slowly added to the solution E to obtain the solution F, and the stirring is continued for 25-50 min. During the stirring, the protective gas is continuously introduced, and the pH of the solution is controlled to be 5.5-6.5. In the above-obtained solution, the concentration of lithium element is 0.1-3 mol / L, and the molar ratio of phosphorus element, lithium element and iron / manganese element is phosphorus: iron / manganese: lithium = (0.99-1.03) : (0.98-1.03) : 3.

[0016] Further, the protective gas can be one of nitrogen, argon, hydrogen, helium, or a combination of multiple gases. The main purpose of introducing the protective gas is to prevent the ferrous ion and manganese ion in the solution from being oxidized.

[0017] In addition, after the hydrothermal reaction is completed, the solid part obtained by suction filtration needs to be washed, dried and then mixed with the carbon source. The washing can be performed with water, and the washing can be performed for 3 times or more. The hydrothermal product is obtained by vacuum drying.

[0018] The specific examples of the carbon source include glucose. In one embodiment, the hydrothermal product is mixed with glucose in a high-speed mixer, and alcohol is added to assist the mixing. The rotation speed of the mixture is 800-1200 rpm, and the mixing time is 20-40 min. After the mixing, the mixture is dried by vacuum drying or the like to completely evaporate the alcohol.

[0019] The mixed product is added into a tube furnace for calcination, the uniform speed heating mode is used in the calcination process, and the heating rate is, for example, 3-6℃ / min; the product after the calcination is cooled, ground, and sieved to obtain the carbon-coated lithium manganese iron phosphate positive electrode material LiMnxFe1-xPO4&C with the special morphology.

[0020] In a second aspect, the application provides the high-exposure (010) crystal face morphology lithium manganese iron phosphate positive electrode material prepared by the above method.

[0021] In a third aspect, the application provides a battery positive electrode comprising the positive electrode material of the second aspect.

[0022] The preparation method of the battery positive electrode is as follows:

[0023] The positive electrode material, the conductive agent, and the adhesive are mixed according to the mass ratio of 86-94:3-7:3-7 to obtain a positive electrode slurry, which is coated, punched, and vacuum dried to obtain the positive electrode material; the feasible conductive agent is, for example, KB, CNT, and SP; and the feasible adhesive is, for example, PVDF.

[0024] In a fourth aspect, the application provides a button cell battery comprising the battery positive electrode of the third aspect.

[0025] Preferably, the button cell battery is assembled as follows: a lithium sheet is used as the negative electrode material of the counter electrode, a microporous polypropylene film is used as the battery separator, the electrolyte is 1mol / L LiPF6, the solvent is a volume ratio of 1:1 of ethylene carbonate (EC) / dimethyl carbonate (DMC), and the 2032 type button cell battery is assembled in a glove box filled with dry high-purity argon and left to stand for 7-9h.

[0026] The above one or more technical solutions have the following beneficial effects:

[0027] The positive electrode material provided by the application has a volume distribution particle size of 0.1≤D50≤2um, D10>0.1um, and D90≤20um, which is close to the nanometer level and belongs to small particle size material; the surface morphology characterization based on SEM shows that the material has a relatively regular sheet structure, and the path in the

[010] crystal plane is shorter, which is a positive electrode material based on the growth control of the crystal plane to improve the electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings accompanying the specification of the application form part of the application and serve to provide a further understanding of the application. The exemplary embodiments of the application and their description serve to explain the application without imposing undue limitations on the application.

[0029] Figure 1The LiMn prepared in Example 1 0.6 Fe 0.4 SEM images of the surface morphology of PO4 & C samples;

[0030] Figures a and b show the material morphology at different scales.

[0031] Figure 2 The XRD diffraction pattern of the sample from Example 1;

[0032] Figure 3 The graph shows the initial charge-discharge performance of the button batteries of Example 1 and Comparative Example 1 at 25°C and 0.1C / 0.1C rate.

[0033] Figure 4 The graph shows the charge-discharge cycle performance of the button batteries of Example 1 and Comparative Example 1 at 25°C and 1C / 1C rate. Detailed Implementation

[0034] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0035] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0036] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0037] Example 1

[0038] Lithium hydroxide, ferrous sulfate, manganese sulfate, and phosphoric acid were weighed according to the stoichiometric ratio Li:Mn:Fe:P = 3:0.6:0.4:1. The weighed lithium hydroxide was added to deionized water and mixed thoroughly to obtain solution A, with a lithium salt concentration of 2.5 mol / L. Manganese sulfate and ferrous sulfate were separately dissolved in deoxygenated deionized water and stirred thoroughly to obtain solution B, where the combined concentration of manganese and ferrous ions was 1 mol / L. The above-mentioned phosphoric acid was added to deionized water to obtain phosphoric acid solution C. Appropriate amounts of ascorbic acid and surfactant PVP were weighed and added to deionized water, then stirred thoroughly to obtain solution D.

[0039] Under magnetic stirring, solutions C and A were slowly added sequentially to solution D and mixed thoroughly to obtain solution E. After all solutions were added, stirring continued for 30 minutes. Solution E contained 0.020 g / mL PVP and 0.005 g / mL ascorbic acid. Again under magnetic stirring, solution B was slowly added to solution E and mixed thoroughly to obtain solution F. After all solutions were added, stirring continued for 30 minutes. During stirring, nitrogen gas was continuously introduced into the reaction vessel to prevent the oxidation of manganese and ferrous ions in the solution. The pH of the solution system was maintained at 5.85 during stirring.

[0040] The solution F, after stirring, was transferred to a PTFE-lined stainless steel reactor and sealed. It was then placed in a constant temperature chamber at 180°C for a hydrothermal reaction for 12 hours. After the hydrothermal reaction was complete, the reactor was cooled to room temperature, and the solid fraction was obtained by filtration. The solid fraction was washed at least three times with deionized water and then vacuum dried to obtain the hydrothermal product LiMn. 0.6 Fe 0.4 PO4.

[0041] 8% (by weight) of glucose from the hydrothermal products was weighed and added to a high-speed mixer along with the hydrothermal products mentioned above. An appropriate amount of alcohol was added and mixed thoroughly at 1000 rpm for 35 minutes. After mixing, the solid fraction was separated and vacuum-dried at 100°C to allow the alcohol to evaporate completely, yielding the precursor. This precursor was placed in a tube furnace and calcined at 600°C for 10 hours under a nitrogen atmosphere at a rate of 3°C / min. After cooling to room temperature, it was ground and sieved to obtain the lithium manganese iron phosphate cathode material LiMn with this unique morphology. 0.6 Fe 0.4 PO4&C.

[0042] This embodiment describes the morphology of the aforementioned materials, such as... Figure 1 As shown, the above material is shorter in the

[010] crystal plane direction and the material is thinner. Figure 2 The XRD diffraction pattern of the above material shows that no obvious impurities were generated when compared with the standard sample card, proving that the above material has high purity.

[0043] Example 2

[0044] The difference from Example 1 is that, in this example, solution D is prepared as follows: Appropriate amounts of ascorbic acid and surfactant CTAB are weighed and added to deionized water, then mixed thoroughly to obtain solution D. Simultaneously, solution E contains 0.020 g / mL of CTAB and 0.005 g / mL of ascorbic acid.

[0045] Example 3

[0046] The difference between the embodiment 1 is that, in this embodiment, the solution D is prepared as follows: the appropriate amount of ascorbic acid and surfactant DEG are weighed, and then added into deionized water to mix uniformly to obtain the solution D. Meanwhile, the content of DEG in the solution E is 0.020 g / mL, and the content of ascorbic acid is 0.005 g / mL.

[0047] Embodiment 4

[0048] The difference between the embodiment 1 is that, in this embodiment, the solution D is prepared as follows: the appropriate amount of ascorbic acid and surfactant PVA are weighed, and then added into deionized water to mix uniformly to obtain the solution D. Meanwhile, the content of PVA in the solution E is 0.020 g / mL, and the content of ascorbic acid is 0.005 g / mL.

[0049] Embodiment 5

[0050] The lithium hydroxide, ferrous sulfate, manganese sulfate and phosphoric acid are weighed according to the stoichiometric ratio of Li:Mn:Fe:P = 3:0.4:0.6:1, respectively. The weighed lithium hydroxide is added into deionized water to mix uniformly to obtain the solution A, and the lithium salt concentration is 2.5 mol / L. The manganese sulfate and ferrous sulfate are separately dissolved in deoxygenated deionized water to mix uniformly to obtain the solution B, and the total concentration of manganese ions and ferrous ions is 1 mol / L. The above phosphoric acid is added into deionized water to obtain the phosphoric acid solution C. The appropriate amount of ascorbic acid and surfactant PVP are weighed, and then added into deionized water to mix uniformly to obtain the solution D.

[0051] Under the action of magnetic stirring, the solution C and the solution A are slowly added into the solution D in sequence to mix uniformly to obtain the solution E, and the stirring is continued for 50 min after all the solutions are added. The content of PVP in the solution E is 0.020 g / mL, and the content of ascorbic acid is 0.005 g / mL. Under the action of magnetic stirring, the solution B is slowly added into the solution E to mix uniformly to obtain the solution F, and the stirring is continued for 50 min after all the solutions are added. The nitrogen protection is continuously provided to the reaction container during the stirring process to avoid the oxidation of manganese ions and ferrous ions in the solution, and the pH of the solution system is controlled to be maintained at 6.5 during the stirring process.

[0052] The above solution F after the stirring is completed is transferred into a stainless steel reaction kettle with a polytetrafluoroethylene liner, sealed, and placed in a thermostat at 200°C to perform the hydrothermal reaction, and the holding time is 5 h. After the hydrothermal reaction is completed, the reaction kettle is cooled to room temperature, and the solid part is obtained by filtration, washed with deionized water for at least three times, and vacuum dried to obtain the hydrothermal product LiMn 0.6 Fe 0.4 PO4.

[0053] The hydrothermal product was mixed with 10% of the glucose by mass in a high-speed mixer, and an appropriate amount of alcohol was added to mix them uniformly. The mixture was mixed at 1200 rpm for 20 min. After the mixing was completed, the solid part was separated and vacuum dried at 100°C to fully evaporate the alcohol to obtain a precursor. The precursor was placed in a tube furnace and heated to 450°C at a rate of 3°C / min under a nitrogen atmosphere and maintained for 16 h. After cooling to room temperature, the product was ground and sieved to obtain the special-shaped lithium manganese iron phosphate positive electrode material LiMn 0.6 Fe 0.4 PO4&C.

[0054] Example 6

[0055] Lithium hydroxide, ferrous sulfate, manganese sulfate, and phosphoric acid were weighed according to the stoichiometric ratio Li:Mn:Fe:P = 3:0.6:0.4:1. The weighed lithium hydroxide was added to deionized water and mixed uniformly to obtain solution A, with a lithium salt concentration of 2.5 mol / L. The manganese sulfate and ferrous sulfate were separately dissolved in deoxygenated deionized water and stirred to mix uniformly to obtain solution B, with a total manganese ion and ferrous ion concentration of 1 mol / L. The above phosphoric acid was added to deionized water to obtain phosphoric acid solution C. An appropriate amount of ascorbic acid and surfactant PVP were added to deionized water and stirred to mix uniformly to obtain solution D.

[0056] Under the action of magnetic stirring, solution C and solution A were slowly added to solution D in sequence and mixed uniformly to obtain solution E. After all the solutions were added, stirring was continued for 25 min. The PVP content in solution E was 0.020 g / mL, and the ascorbic acid content was 0.005 g / ml. Under the action of magnetic stirring, solution B was slowly added to solution E, and solution F was obtained by fully mixing. After all the solutions were added, stirring was continued for 25 min. Nitrogen was continuously introduced into the reaction container during the stirring process to prevent the manganese ions and ferrous ions in the solution from being oxidized. The pH of the solution system was maintained at 5.5 during the stirring process.

[0057] The above solution F after stirring was transferred to a stainless steel reaction kettle lined with polytetrafluoroethylene and sealed, and placed in a constant temperature oven at 150°C for hydrothermal reaction, with a holding time of 15 h. After the hydrothermal reaction was completed, the reaction kettle was cooled to room temperature, and the solid part was obtained by filtration. The solid part was washed with deionized water at least three times and vacuum dried to obtain the hydrothermal product LiMn 0.6 Fe 0.4 PO4.

[0058] The glucose with a mass of 6% of the hydrothermal product was weighed and added into the high-speed mixer together with the hydrothermal product, and an appropriate amount of alcohol was added to mix them uniformly. The mixture was mixed at a speed of 800 rpm for 40 min. After mixing, the solid part was separated and vacuum dried at 100°C to fully evaporate the alcohol to obtain the precursor. The precursor was placed in a tube furnace and heated to 750°C at a rate of 6°C / min under a nitrogen atmosphere and kept for 8 h. After cooling to room temperature, the material was ground and sieved to obtain the special-shaped lithium manganese iron phosphate positive electrode material LiMn 0.6 Fe 0.4 PO4&C.

[0059] Comparative Example 1

[0060] The difference between Example 1 and Comparative Example 1 is that the solution D is prepared as follows: an appropriate amount of ascorbic acid is weighed and added into deionized water to mix uniformly to obtain solution D. At the same time, the ascorbic acid content in solution E is 0.005 g / ml.

[0061] The high-exposure (010) crystal face morphology lithium manganese iron phosphate positive electrode materials prepared in Examples 1-4 and Comparative Example 1 were used as battery positive electrode materials to prepare button cells for electrochemical performance testing. The preparation method is as follows:

[0062] a. The positive electrode slurry was prepared by stirring according to the ratio of positive electrode material: conductive agent (SP): adhesive (PVDF) = 90:5:5 to form a uniformly dispersed positive electrode slurry. The prepared slurry was coated, punched, and vacuum dried. Lithium metal was used as the negative electrode material of the counter electrode, and a microporous polypropylene film was used as the battery separator. Ethylene carbonate (EC) / dimethyl carbonate (DMC) with a solvent volume ratio of 1:1 and 1 mol / L LiPF6 were used as the electrolyte. The 2032 type button cell was assembled in a glove box filled with dry high-purity argon and left to stand for 8 h.

[0063] b. The button cell after standing was charged and discharged at a rate of 0.1C at an ambient temperature of 25°C and a voltage of 2.5-4.5V. The electrochemical performance of the positive electrode material provided in the above examples was tested. The first discharge efficiency was calculated as follows: first efficiency = first discharge specific capacity / first charge specific capacity*100%.

[0064] c. The positive electrode material in the above examples was tested for cycle performance at 25°C and 2.5-4.5V with 1C charge / 1C discharge. The capacity retention rate after 100 cycles was calculated as follows: capacity retention rate = 100th discharge specific capacity / first discharge specific capacity*100%. The results are shown in Table 1.

[0065] Table 1

[0066]

[0067] From the above Table 1, compared with Comparative Example 1, the electric performance (initial efficiency and discharge specific capacity) and cycle performance of the positive electrode material prepared in Examples 1-6 are obviously improved; and the positive electrode material also exhibits good cycle performance at 1C rate, which also indicates that the rate performance is improved. The reasons for the effects achieved in the above examples are as follows. In the present application, the surfactant is used to induce the directional growth of crystal faces, and under the action of the hydrothermal method, the sheet-shaped lithium manganese iron phosphate positive electrode material with uniform particle size, good dispersity, thin thickness along the

[010] direction and preferential exposure of (010) plane is obtained, the internal conductivity of the lithium manganese iron phosphate material is improved, the volume resistivity of the lithium manganese iron phosphate material is effectively reduced, the internal electronic conductivity and Li + transmission speed, thereby improving the electrochemical performance of the material.

[0068] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the principles and spirit of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a lithium manganese iron phosphate cathode material with high exposure (010) crystal plane morphology, characterized in that, The steps include: according to LiMn 0.6 Fe 0.4 The stoichiometric ratio of each element in PO4&C is determined by weighing lithium salt, iron salt, manganese salt, and phosphoric acid, which are then added to water along with ascorbic acid and surfactant and mixed thoroughly. The uniformly mixed solution is transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 150-200℃ for 5-15 hours. The hydrothermal reaction product is then mixed with the carbon source and calcined at 450-750℃ for 6-16 hours to obtain the above-mentioned cathode material. The surfactant is selected from at least one of polyvinyl alcohol, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, and diethylene glycol; The concentration of ascorbic acid is 0.004~0.006 g / ml, and the concentration of surfactant is 0.008-0.030 g / ml; The carbon source is glucose; the hydrothermal product is mixed with glucose and then added to a high-speed mixer, and alcohol is added to assist in mixing. The mass of glucose is 6-10% of the hydrothermal product. The mixing speed is 800-1200 rpm and the mixing time is 20-40 min. After mixing, the mixture is dried by vacuum drying to completely evaporate the alcohol.

2. The preparation method according to claim 1, characterized in that, The lithium salt is lithium hydroxide; the iron salt is ferrous sulfate; and the manganese salt is manganese sulfate.

3. The preparation method according to claim 1, characterized in that, The specific steps for mixing all components are as follows: Prepare lithium salt solution A, iron and manganese salt solution B, phosphoric acid solution C, and ascorbic acid and surfactant mixture solution D separately. Slowly add solution C and solution A to solution D in sequence and mix thoroughly to obtain solution E. After the addition is complete, continue stirring for 25-50 min. Control the concentration of ascorbic acid in solution E to be 0.004~0.006 g / ml and the concentration of surfactant to be 0.008-0.030 g / ml. Slowly add solution B to solution E to obtain solution F and continue stirring for 25-50 min. During the stirring process, continuously introduce protective gas and control the pH of the solution to be 5.5-6.

5. In the above-obtained solution F, the concentration of lithium element is 0.1~3 mol / L, and the molar ratio of phosphorus, lithium, and iron / manganese element is phosphorus: iron / manganese: lithium = (0.99~1.03): (0.98~1.03):

3.

4. The preparation method according to claim 3, characterized in that, The protective gas is nitrogen.

5. The preparation method according to claim 1, characterized in that, After the hydrothermal reaction is completed, the solid part obtained by filtration needs to be washed, dried and then mixed with the carbon source. The washing is performed three or more times, and the hydrothermal product is obtained by vacuum drying.

6. The preparation method according to claim 1, characterized in that, The calcination process employs a uniform heating method, with a heating rate of 3~6℃ / min.

7. The lithium manganese iron phosphate cathode material with high exposure (010) crystal plane morphology prepared by the method of any one of claims 1-6.

8. A battery positive electrode, characterized in that, The positive electrode of the battery comprises the positive electrode material according to claim 7; the preparation method of the positive electrode of the battery is as follows: A positive electrode slurry is prepared by mixing positive electrode material, conductive agent, and adhesive in a mass ratio of 86~94:3~7:3~7. The slurry is then coated, stamped, and vacuum dried to obtain the positive electrode material. The conductive agent is conductive graphite, and the adhesive is polyvinylidene fluoride.

9. A button battery, characterized in that, The button battery is assembled as follows: the button battery has the positive electrode as described in claim 8, uses a lithium metal sheet as the negative electrode material, and uses a polypropylene film with micropores as the battery separator; the electrolyte is 1 mol / L LiPF6, and the solvent is ethylene carbonate / dimethyl carbonate with a volume ratio of 1:1; the 2032 type button battery is assembled in a glove box filled with dry high-purity argon gas and left to stand for 7-9 hours.

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