High-compaction long-cycle lithium manganese iron phosphate material as well as preparation method and application thereof
The preparation of ferromanganese phosphate through redox reaction and the use of oxides and fluoride fluxes during high-temperature sintering process was solved, and the compaction density and circulation performance of lithium manganese ferromanganese phosphate material was achieved, achieving the effect of high compaction density and excellent electrical performance.
Patent Information
- Application Number
- CN202411640446.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-15
- Publication Date
- 2025-03-11
AI Technical Summary
The existing lithium manganese iron phosphate materials have shortcomings in compaction density and circulation performance, and it is difficult to achieve compaction density above 2.5g/cm3 and good circulation performance.
Ferromanganese phosphate is prepared by redox reaction, and oxides and fluoride are added as fluxes during high-temperature sintering to improve the compaction density and electrical properties of the material.
The high compaction density of lithium manganese iron phosphate material (above 2.5g/cm3) and excellent electrical and cycling performance are achieved, and the capacity and energy density of lithium-ion batteries are improved.
Smart Images
Figure CN119591071A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a high-density long-cycle lithium manganese iron phosphate material and a preparation method and application thereof. Background Art
[0002] Compared with other positive electrode materials, such as lithium cobalt oxide, high nickel ternary, spinel lithium manganese oxide, etc., lithium iron manganese phosphate has obvious advantages in cost, safety, low temperature performance, etc. However, since manganese is dominant in lithium iron manganese phosphate, manganese phosphate is an insulator, resulting in low electronic conductivity and low lithium ion diffusion rate. The reaction kinetics can usually be improved by reducing the primary particle size of the material through nano-nanoization, but this brings about the problem of small particle size and low compaction density in practical applications. Usually, the compaction density is difficult to reach 2.5g / cm 3 above.
[0003] The compaction density is closely related to the specific capacity of the electrode, internal resistance, charge and discharge efficiency, and cycle performance. Generally speaking, the greater the compaction density, the higher the capacity of the battery and the corresponding energy density. When the traditional solid phase, hydrothermal and gel methods are used to synthesize lithium manganese iron phosphate positive electrode materials, the materials have problems such as large primary particle porosity, small primary particle size, non-dense materials, and poor cycle performance. Therefore, it is very necessary to develop a lithium manganese iron phosphate material with both high compaction density and long cycle performance. Summary of the invention
[0004] In view of the shortcomings and deficiencies of the prior art, the present invention provides an improved method for preparing lithium manganese iron phosphate, which can prepare improved lithium manganese iron phosphate having high compaction density, excellent electrical properties and cycle performance.
[0005] The present invention also provides an improved lithium manganese iron phosphate, which has high compaction density, excellent electrical properties and cycle performance.
[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:
[0007] A method for preparing lithium manganese iron phosphate, the preparation method comprising the following steps:
[0008] 1) causing a phosphorus source, a divalent manganese salt and manganese dioxide to undergo an oxidation-reduction reaction to generate manganese phosphate monohydrate, and reacting the manganese phosphate monohydrate with an iron source to obtain ferromanganese phosphate;
[0009] 2) subjecting the ferromanganese phosphate, a lithium source, a flux, an optional organic carbon source, and an optional dopant to a high-temperature sintering reaction to obtain the lithium ferromanganese phosphate;
[0010] The phosphorus source is selected from one or both of phosphate and phosphoric acid;
[0011] The flux comprises oxides and fluorides; the oxides are selected from one or more combinations of magnesium oxide, titanium oxide, aluminum oxide, zirconium oxide, and boron oxide; the fluorides are selected from one or both of lithium fluoride and magnesium fluoride.
[0012] Preferably, the oxide is magnesium oxide; and the fluoride is lithium fluoride.
[0013] In some embodiments, the molar ratio of the oxide to the fluoride is 1-20:1-20.
[0014] Preferably, the molar ratio of the oxide to the fluoride is 1-5:1-10.
[0015] In some embodiments, the molar amount of the oxide is 0.1%-5.0% of the total molar amount of ferromanganese in the ferromanganese phosphate.
[0016] In some embodiments, the molar amount of the fluoride is 0.1%-2.0% of the total molar amount of ferromanganese in the ferromanganese phosphate.
[0017] In some embodiments, the oxide has a particle size of 0.01-5 μm.
[0018] In some embodiments, the particle size of the fluoride is 0.01-5 μm.
[0019] In some embodiments, the phosphate is selected from one or two of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate and potassium dihydrogen phosphate.
[0020] In some embodiments, the molar amount of the phosphorus source is 5% to 15% in excess of the stoichiometric ratio of the divalent manganese salt.
[0021] In some embodiments, the phosphorus source is a mixture of phosphate and phosphoric acid.
[0022] Preferably, based on the stoichiometric ratio of the divalent manganese salt, the phosphate is 0.8-1.1 equivalents, and the phosphoric acid is 0.15-0.50 equivalents.
[0023] In some embodiments, in step 1), a phosphorus source, a divalent manganese salt and manganese dioxide are mixed to obtain a reaction mixture; the reaction mixture is ground to cause an oxidation-reduction reaction in the reaction mixture to generate manganese phosphate monohydrate, thereby obtaining a slurry containing manganese phosphate monohydrate; the slurry is separated to obtain manganese phosphate monohydrate particles; and the manganese phosphate monohydrate particles are reacted with an iron source to obtain the manganese ferrophosphate.
[0024] In some embodiments, in step 1), the reaction mixture is ground until its D50 particle size is less than 0.4 μm.
[0025] In some embodiments, in step 1), the ratio of the molar amount of manganese in the manganese phosphate monohydrate to the molar amount of iron in the iron source is 5-8:5-2.
[0026] In some embodiments, the manganese phosphate monohydrate particles and the iron source are dispersed and mixed in water, filtered, washed, dried and sintered to obtain the manganese ferrophosphate.
[0027] Preferably, the washing is performed with a phosphoric acid aqueous solution; more preferably, the mass concentration of the phosphoric acid aqueous solution used for washing is 0.5%-2%.
[0028] Furthermore, the mixing temperature is 20-40°C.
[0029] Furthermore, the grinding is performed in a sand mill.
[0030] Furthermore, the grinding temperature is 20-60°C.
[0031] Furthermore, the drying temperature is 100-120°C.
[0032] Furthermore, the sintering temperature is 500-800°C.
[0033] In some embodiments, in step 3), the manganese iron phosphate, lithium source, flux, water, optional organic carbon source and optional dopant are subjected to sand milling, spray drying and high-temperature sintering reaction to obtain the manganese iron lithium phosphate.
[0034] In some embodiments, in step 3), the material is sand-milled to a D50 particle size of less than 0.5 μm.
[0035] In some embodiments, the divalent manganese salt is selected from a combination of one or more of manganese sulfate, manganese chloride, and manganese nitrate.
[0036] In some embodiments, the iron source is selected from a combination of one or more of ferrous oxalate, ferrous acetate, ferric phosphate dihydrate, ferric phosphate, ferric oxide and ferrous sulfate.
[0037] In some embodiments, the lithium source is selected from a combination of one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium sulfate, lithium nitrate, lithium dihydrogen phosphate, lithium hydrogen phosphate and lithium acetate.
[0038] In some embodiments, the organic carbon source is selected from a combination of one or more of glucose, sucrose, fructose, citric acid, polyethylene glycol, polyvinyl pyrrolidone, ethylenediaminetetraacetic acid and ascorbic acid.
[0039] In some embodiments, the phosphoric acid is in the form of a phosphoric acid aqueous solution, and the mass concentration of the phosphoric acid aqueous solution is 10% to 70%.
[0040] In some embodiments, the phosphate is present in the form of an aqueous phosphate solution.
[0041] In some embodiments, the divalent manganese salt is present in the form of a divalent manganese salt aqueous solution.
[0042] In some embodiments, the dopant is selected from a combination of one or more of a lithium dopant, an iron dopant, a phosphorus dopant, and an oxygen dopant.
[0043] Furthermore, the lithium-site dopant is selected from a combination of one or more of sodium, potassium and niobium.
[0044] Furthermore, the iron-site dopant is selected from a combination of one or more of vanadium, cobalt and titanium.
[0045] Furthermore, the phosphorus-site dopant is selected from one or both of boron and silicon.
[0046] Furthermore, the oxygen dopant is selected from one or both of fluorine and bromine.
[0047] The present invention also provides lithium manganese iron phosphate prepared by the above-mentioned preparation method of lithium manganese iron phosphate.
[0048] Furthermore, the compaction density of the lithium manganese iron phosphate is 2.5 g / cm 3 above.
[0049] Furthermore, the compaction density of the lithium manganese iron phosphate is 2.5-2.8 g / cm 3 .
[0050] Furthermore, the primary particle size of the lithium manganese iron phosphate is 100-1000 nm.
[0051] The present invention also provides a lithium-ion battery, comprising a positive electrode material, wherein the positive electrode material comprises the above-mentioned lithium iron manganese phosphate.
[0052] Furthermore, the lithium-ion battery has a discharge capacity of 140-160 mAh / g at 0.1C, a discharge capacity of 130-145 mAh / g or more at 1C, and a capacity retention rate of 99.20%-99.99% after 200 cycles of charge and discharge at a rate of 1C. It can be seen that the lithium-ion battery has excellent electrical properties, cycle performance and high compaction density.
[0053] Compared with the prior art, the present invention has the following advantages:
[0054] The present invention first prepares ferromanganese phosphate through redox reaction, and then reacts it with raw materials such as lithium source to prepare lithium ferromanganese phosphate. When preparing lithium ferromanganese phosphate, specific types of oxides and fluorides are added as fluxes, which can effectively increase the primary particle size of the lithium ferromanganese phosphate product during the sintering reaction of the material, thereby improving the compaction density of the positive electrode material. In addition, the addition of flux can reduce the porosity of the positive electrode material, improve the uniformity of heating of each part during high-temperature sintering of the reaction raw materials, and effectively avoid the generation of impurities; in addition, when an organic carbon source is added for reaction, the flux can also increase the bonding strength between the lithium iron phosphate and the coated carbon layer, avoiding the subsequent processing technology such as crushing and grading to damage the carbon layer on the surface of the lithium iron phosphate, thereby further improving the electrical properties of the lithium iron phosphate.
[0055] The two flux components oxide and fluoride added in the present invention have a synergistic effect, and jointly improve the compaction density and electrical properties of the lithium iron manganese phosphate product. In the process of high-temperature sintering of lithium iron manganese phosphate materials, due to the different melting points of the components and poor mutual solubility, it is easy for the components to not fully melt each other. The sintered material has problems such as precipitation during the charge and discharge process and poor cycle performance. After adding the flux, the melting temperature of the material can be reduced, so that the components can fully react and fuse, avoiding the uncontrollable primary particle size of the material and the destruction of the carbon layer of the material caused by overburning. At the same time, the sintering temperature can be reduced to save energy. The oxide is selected as a flux to mainly act on the metal elements of the lithium iron manganese position of the material, reduce the activation energy to make it better fusion reaction, and the oxide of the present application is close to the ionic radius of the lithium iron manganese position, and can be better inserted into the atomic layer to stabilize the structure. When fluoride is present as a flux, it mainly acts on the oxygen position of the material, weakens the Li-O bond energy, and is beneficial to Li + Diffusion in the crystal lattice. BRIEF DESCRIPTION OF THE DRAWINGS
[0056] Figure 1 This is a morphology picture of the lithium manganese iron phosphate prepared in Example 1;
[0057] Figure 2 The rate curve of the lithium manganese iron phosphate prepared in Example 1 at 0.1C and 1C;
[0058] Figure 3 This is a cycle curve of the lithium manganese iron phosphate prepared in Example 1 at 1C. DETAILED DESCRIPTION
[0059] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.
[0060] Example 1
[0061] This embodiment provides a lithium manganese iron phosphate:
[0062] 1) Preparation of ferromanganese phosphate:
[0063] Weigh 48.07 kg of monoammonium phosphate and 35.32 kg of manganese sulfate monohydrate as raw materials, dissolve and filter them with 70.0 kg of pure water respectively, and add 6.26 kg of concentrated phosphoric acid (mass percentage is 13%) to the monoammonium phosphate solution;
[0064] Put the monoammonium phosphate and phosphoric acid solution into the feeding tank of the sand mill, set the sand mill speed to start the cycle, add the monohydrate manganese sulfate solution and 18.17 kg manganese dioxide in turn, and sand grind to a particle size D50 ≤ 0.4 μm;
[0065] The sand-milled slurry is put into a plate-and-frame filter press for filtration. After one washing, the byproduct ammonium sulfate is recovered. The filter cake is continuously washed with water until the conductivity is ≤500 μS / cm, and the filter cake (manganese phosphate monohydrate) is removed.
[0066] According to the molar ratio of Mn / Fe=6 / 4, the filter cake, ferric phosphate dihydrate and pure water are dispersed, mixed and filtered, washed with a phosphoric acid aqueous solution with a mass concentration of about 1%, flash dried and calcined in a rotary kiln with the furnace temperature controlled at 650°C, and finally manganese iron phosphate with a total molar ratio of manganese iron to phosphorus of about 0.965 and a primary particle size of 200-250nm is obtained.
[0067] 2) Preparation of lithium manganese iron phosphate:
[0068] Add 1.80 kg of deionized water to a small sand mill material tank, turn on the sand mill, and sequentially add 661.00 g of ferromanganese phosphate, 171.66 g of lithium carbonate, 64.10 g of glucose monohydrate, 7.56 g of polyethylene glycol, magnesium oxide (particle size 20-30 nm, its molar amount accounts for 0.5% of the total molar amount of ferromanganese), and lithium fluoride (particle size 200-300 nm, its molar amount accounts for 0.5% of the total molar amount of ferromanganese) prepared above, and sand grind to a particle size D50 of the slurry ≤ 0.5 μm;
[0069] The sand-milled slurry was spray-dried into powder by using a spray machine with the air inlet temperature set at 240°C and the air outlet temperature set at 110°C. The powder was sintered in a roller furnace in a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 10 hours to obtain a calcined material.
[0070] The calcined material was pulverized by air flow until D50 was about 1.0 μm to obtain lithium manganese iron phosphate, whose SEM image is as follows: Figure 1 As shown, the primary particle size is about 200-300 nm.
[0071] Example 2
[0072] This embodiment provides a lithium manganese iron phosphate:
[0073] The method is basically the same as Example 1, except that in step 2), the molar amount of magnesium oxide is adjusted to 0.2% of the total molar amount of ferromanganese. The primary particle size of the lithium manganese iron phosphate finally obtained is about 200-250 nm.
[0074] Example 3
[0075] This embodiment provides a lithium manganese iron phosphate:
[0076] The method is basically the same as Example 1, except that in step 2), the molar amount of magnesium oxide is adjusted to 1.0% of the total molar amount of ferromanganese. The primary particle size of the lithium manganese iron phosphate finally obtained is about 300-400 nm.
[0077] Example 4
[0078] This embodiment provides a lithium manganese iron phosphate:
[0079] The method is basically the same as Example 1, except that in step 2), the molar amount of lithium fluoride is adjusted to 0.2% of the total molar amount of ferromanganese. The primary particle size of the lithium iron manganese phosphate finally obtained is about 200-250 nm.
[0080] Example 5
[0081] This embodiment provides a lithium manganese iron phosphate:
[0082] The method is basically the same as Example 1, except that in step 2), the molar amount of lithium fluoride is adjusted to 1.0% of the total molar amount of ferromanganese. The primary particle size of the lithium iron manganese phosphate finally obtained is about 300-500 nm.
[0083] Example 6
[0084] This embodiment provides a lithium manganese iron phosphate:
[0085] The method is basically the same as Example 1, except that in step 2), magnesium oxide is replaced by titanium oxide, and the molar amount thereof remains unchanged. The primary particle size of the lithium manganese iron phosphate finally obtained is about 200-300 nm.
[0086] Example 7
[0087] This embodiment provides a lithium manganese iron phosphate:
[0088] The method is basically the same as Example 1, except that in step 2), magnesium oxide is replaced by aluminum oxide, and the molar amount thereof remains unchanged. The primary particle size of the lithium manganese iron phosphate finally obtained is about 200-250 nm.
[0089] Example 8
[0090] This embodiment provides a lithium manganese iron phosphate:
[0091] The method is basically the same as Example 1, except that in step 2), magnesium oxide is replaced by zirconium oxide, and the molar amount thereof remains unchanged. The primary particle size of the finally obtained lithium manganese iron phosphate is about 200-250 nm.
[0092] Example 9
[0093] This embodiment provides a lithium manganese iron phosphate:
[0094] The method is basically the same as Example 1, except that in step 2), magnesium oxide is replaced by boron oxide, and the molar amount thereof remains unchanged. The primary particle size of the finally obtained lithium manganese iron phosphate is about 200-250 nm.
[0095] Example 10
[0096] This embodiment provides a lithium manganese iron phosphate:
[0097] The method is basically the same as Example 1, except that in step 2), lithium fluoride is replaced by magnesium fluoride, and the molar amount thereof remains unchanged. The primary particle size of the finally obtained lithium manganese iron phosphate is about 300 nm.
[0098] Comparative Example 1
[0099] This comparative example provides a lithium manganese iron phosphate:
[0100] The method is basically the same as Example 1, except that in step 2), lithium fluoride is not added, and the molar amount of magnesium oxide is adjusted to 1.0% of the total molar amount of ferromanganese. The primary particle size of the lithium manganese iron phosphate finally obtained is about 200-300 nm.
[0101] Comparative Example 2
[0102] This comparative example provides a lithium manganese iron phosphate:
[0103] The method is basically the same as Example 1, except that in step 2), magnesium oxide is not added, and the molar amount of lithium fluoride is adjusted to 1.0% of the total molar amount of ferromanganese. The primary particle size of the lithium iron manganese phosphate finally obtained is about 250-300 nm.
[0104] Comparative Example 3
[0105] This comparative example provides a lithium manganese iron phosphate:
[0106] 1) Without performing a redox reaction of manganese, manganese (III) phosphate monohydrate is prepared by reacting manganese trioxide with phosphoric acid, and then reacting with ferric phosphate dihydrate to prepare a manganese ferrophosphate precursor:
[0107] According to the Mn / Fe molar ratio of 6 / 4, 9.77 kg of manganese (III) phosphate monohydrate and iron phosphate dihydrate were dispersed and mixed with pure water, filtered, and the filter cake was washed with a phosphoric acid aqueous solution with a mass concentration of about 1%, and then dried and calcined in a rotary kiln at a controlled furnace temperature of 650° C. to obtain a manganese iron phosphate precursor;
[0108] 2) Preparation of lithium manganese iron phosphate:
[0109] The process is basically the same as step 2) of Example 1, except that the ferromanganese phosphate is replaced by the ferromanganese phosphate precursor prepared in step 1).
[0110] The lithium manganese iron phosphate positive electrode material (LMFP / C) prepared in the above embodiments and comparative examples is configured with conductive carbon nanotubes, conductive carbon black, binder polyvinylidene fluoride, and solvent N-methylpyrrolidone to form a positive electrode slurry, wherein the mass ratio of the LMFP / C positive electrode material to the conductive carbon nanotubes, conductive carbon black, and binder polyvinylidene fluoride is 91.5:1.5:1.0:6; the positive electrode slurry is coated on aluminum foil, followed by vacuum baking, punching, and finally making a LMFP / C positive electrode sheet. LMFP / C is used as the positive electrode, the lithium sheet is used as the negative electrode, and the EC / DMC / EMC solution of 1mol / L LiPF6 is used as the electrolyte to assemble a button battery, and the battery is charged and discharged (the charge and discharge window is 2.5V~4.3V), and the electrical properties of the lithium manganese iron phosphate can be obtained. The results are shown in Table 1 below.
[0111] Table 1 Performance of each embodiment and comparative example
[0112]
[0113]
[0114] As can be seen from Table 1, the two flux components oxide and fluoride added in the present invention have a synergistic effect, and jointly improve the compaction density and electrical properties of the lithium iron manganese phosphate product. The present invention first prepares ferromanganese phosphate through an oxidation-reduction reaction, and then reacts it with raw materials such as a lithium source to prepare lithium iron manganese phosphate. When preparing lithium iron manganese phosphate, specific types of oxides and fluorides are added as fluxes, so that the lithium iron manganese phosphate can have a high compaction density, excellent electrical properties and cycle performance.
[0115] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.
[0116] The endpoints and any values of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.
Claims
1. A method for preparing lithium manganese iron phosphate, characterized in that: The preparation method comprises the following steps: 1) causing a phosphorus source, a divalent manganese salt and manganese dioxide to undergo an oxidation-reduction reaction to generate manganese phosphate monohydrate, and reacting the manganese phosphate monohydrate with an iron source to obtain ferromanganese phosphate; 2) subjecting the ferromanganese phosphate, a lithium source, a flux, an optional organic carbon source, and an optional dopant to a high-temperature sintering reaction to obtain the lithium ferromanganese phosphate; The phosphorus source is selected from one or both of phosphate and phosphoric acid; The flux comprises oxides and fluorides; the oxides are selected from one or more combinations of magnesium oxide, titanium oxide, aluminum oxide, zirconium oxide, and boron oxide; the fluorides are selected from one or both of lithium fluoride and magnesium fluoride.
2. The method for preparing lithium iron manganese phosphate according to claim 1, characterized in that: The molar ratio of the oxide to the fluoride is 1-20:1-20; preferably, the molar ratio of the oxide to the fluoride is 1-5:1-10.
3. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The molar amount of the oxide accounts for 0.1%-5.0% of the total molar amount of ferromanganese in the ferromanganese phosphate; and / or the molar amount of the fluoride accounts for 0.1%-2.0% of the total molar amount of ferromanganese in the ferromanganese phosphate.
4. The method for preparing lithium iron manganese phosphate according to claim 1, characterized in that: The particle size of the oxide is 0.01-5 μm; and / or the particle size of the fluoride is 0.01-5 μm.
5. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The phosphate is selected from one or two of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate and potassium dihydrogen phosphate; and / or, based on the stoichiometric ratio of the divalent manganese salt, the molar amount of the phosphorus source is 5%-15% excess.
6. The method for preparing lithium iron manganese phosphate according to claim 1, characterized in that: The phosphorus source is a mixture of phosphate and phosphoric acid; preferably, based on the stoichiometric ratio of the divalent manganese salt, the phosphate is 0.8-1.1 equivalents, and the phosphoric acid is 0.15-0.50 equivalents.
7. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: In step 1), a phosphorus source, a divalent manganese salt and manganese dioxide are mixed to obtain a reaction mixture; the reaction mixture is ground to cause an oxidation-reduction reaction in the reaction mixture to generate manganese phosphate monohydrate, thereby obtaining a slurry containing manganese phosphate monohydrate; the slurry is separated to obtain manganese phosphate monohydrate particles; and the manganese phosphate monohydrate particles are reacted with an iron source to obtain the manganese ferrophosphate.
8. The method for preparing lithium iron manganese phosphate according to claim 7, characterized in that: In step 1), the reaction mixture is ground until the D50 particle size is less than 0.4 μm.
9. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: In step 1), the ratio of the molar amount of manganese in the manganese phosphate monohydrate to the molar amount of iron in the iron source is 5-8:5-2; and / or, in step 3), the manganese iron phosphate, lithium source, flux, water, optional organic carbon source and optional dopant are sand milled, spray dried and sintered at high temperature to obtain the manganese iron lithium phosphate.
10. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The divalent manganese salt is selected from a combination of one or more of manganese sulfate, manganese chloride, and manganese nitrate; and / or the iron source is selected from a combination of one or more of ferrous oxalate, ferrous acetate, ferric phosphate dihydrate, ferric phosphate, ferric oxide, and ferrous sulfate; and / or the lithium source is selected from a combination of one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium sulfate, lithium nitrate, lithium dihydrogen phosphate, lithium hydrogen phosphate, and lithium acetate; and / or the organic carbon source is selected from a combination of one or more of glucose, sucrose, fructose, citric acid, polyethylene glycol, polyvinyl pyrrolidone, ethylenediaminetetraacetic acid, and ascorbic acid.
11. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: The phosphoric acid is present in the form of a phosphoric acid aqueous solution, the mass concentration of the phosphoric acid aqueous solution is 10% to 70%; and / or the phosphate is present in the form of a phosphate aqueous solution; And / or, the divalent manganese salt exists in the form of a divalent manganese salt aqueous solution.
12. Lithium manganese iron phosphate prepared by the method for preparing lithium manganese iron phosphate according to any one of claims 1 to 11.
13. The lithium manganese iron phosphate according to claim 12, characterized in that: The compaction density of the lithium manganese iron phosphate is 2.5-2.8 g / cm 3 ; and / or, the primary particle size of the lithium manganese iron phosphate is 100-1000nm.
14. A lithium ion battery comprising a positive electrode material, characterized in that: The positive electrode material includes the lithium manganese iron phosphate as described in claim 12 or 13.
15. The lithium ion battery according to claim 14, characterized in that: The lithium ion battery has a discharge specific capacity of 140-160 mAh / g at 0.1C, a discharge specific capacity of 130-145 mAh / g or more at 1C, and a capacity retention rate of 99.20%-99.99% after 200 cycles of charge and discharge at a 1C rate.