High-compaction lithium manganese iron phosphate material as well as preparation method and application thereof

Abstract

The invention discloses a high-compaction lithium manganese iron phosphate material as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, respectively preparing large-particle-size ferromanganese phosphate and small-particle-size ferromanganese phosphate through an oxidation-reduction reaction, then compounding the large-particle-size ferromanganese phosphate and the small-particle-size ferromanganese phosphate to serve as a precursor for synthesizing the lithium ferromanganese phosphate, and reacting the precursor with raw materials such as a lithium source to prepare the lithium ferromanganese phosphate. The two precursors with specific particle sizes are compounded, so that the small-particle-size precursor can effectively fill gaps of the large-particle-size precursor, the compaction density of the lithium manganese iron phosphate product is further improved, and meanwhile, excellent electrical properties can be realized.

Description

Technical Field

[0001] The invention relates to a high-density lithium manganese iron phosphate material and a preparation method and application thereof. Background Art

[0002] At present, the main lithium-ion cathode materials for power batteries are nickel-cobalt-manganese ternary cathode materials and lithium iron phosphate. The compaction density of ternary materials is generally 3.3g / cm 3 The above have higher energy density, but the cost is higher and unstable; lithium iron phosphate materials do not use precious metals, are low in cost, and have extremely stable structure and ultra-long cycle life, but the compaction density is relatively low, generally 2.3g / cm 3 The energy density is relatively low, and the existing technology development has reached the limit of its theoretical energy density, and it is difficult to significantly improve the long driving range that is increasingly required for power batteries.

[0003] As an upgraded version of lithium iron phosphate positive electrode material, lithium iron manganese phosphate material has the high voltage and higher energy density of ternary materials and the low cost, stable structure, good safety performance and long cycle of lithium iron phosphate materials. However, similar to lithium iron phosphate materials, the compaction density of lithium iron manganese phosphate positive electrode material is relatively low, which limits its application in high energy density lithium-ion power batteries. Improving the compaction density of lithium iron manganese phosphate positive electrode material is an effective way to improve battery energy density.

[0004] The primary particle porosity of the material produced by the traditional solid-phase synthesis method is large, and the material is not dense, resulting in a low compaction density that is difficult to reach 2.5g / cm 3 Because manganese is added to lithium manganese iron phosphate materials, the electronic conductivity is low and a smaller primary particle size is required. Simply increasing the particle size of the material to increase the compaction density will make it difficult for the material's electrical properties to be fully utilized. Summary of the invention

[0005] 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 both high compaction density and excellent electrical properties.

[0006] The present invention also provides an improved lithium manganese iron phosphate, which has both high compaction density and excellent electrical properties.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing lithium manganese iron phosphate, the preparation method comprising the following steps:

[0009] 1) causing a phosphorus source, a divalent manganese salt and manganese dioxide to undergo an oxidation-reduction reaction to generate monohydrated manganese phosphate, and reacting the monohydrated manganese phosphate with an iron source to obtain large-size ferromanganese phosphate; the large-size ferromanganese phosphate having a particle size of 200-1000 nm;

[0010] 2) causing a phosphorus source, a divalent manganese salt and manganese dioxide to undergo an oxidation-reduction reaction to generate monohydrated manganese phosphate, and reacting the monohydrated manganese phosphate with an iron source to obtain small-sized ferromanganese phosphate; the particle size of the small-sized ferromanganese phosphate is 50-150 nm;

[0011] 3) subjecting the large-particle manganese iron phosphate, the small-particle manganese iron phosphate, a lithium source, an optional organic carbon source, and an optional dopant to a high-temperature sintering reaction to obtain the lithium manganese iron phosphate;

[0012] The phosphorus source is selected from one or both of phosphate and phosphoric acid.

[0013] In some embodiments, the particle size of the large-particle manganese ferrophosphate is 400-600 nm.

[0014] In some embodiments, the particle size of the small-particle manganese ferrophosphate is 80-100 nm.

[0015] In some embodiments, the mass ratio of the large-particle size ferromanganese phosphate to the small-particle size ferromanganese phosphate is 1-4:6-9.

[0016] 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.

[0017] 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.

[0018] In some embodiments, the phosphorus source is a mixture of phosphate and phosphoric acid.

[0019] In some embodiments, in step 1), 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.

[0020] In some embodiments, in step 2), based on the stoichiometric ratio of the divalent manganese salt, the phosphate is 0.8-1.1 equivalents, and the phosphoric acid is 0.05-0.15 equivalents.

[0021] 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; the manganese phosphate monohydrate particles are reacted with an iron source to obtain the large-particle size ferromanganese phosphate.

[0022] In some embodiments, in step 2), a phosphorus source, a divalent manganese salt and manganese dioxide are mixed to obtain a reaction mixture; the reaction mixture is ground to allow the reaction mixture to undergo an oxidation-reduction reaction 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 small-particle size manganese iron phosphate.

[0023] In some embodiments, in step 1), the reaction mixture is ground until its D50 particle size is less than 0.4 μm.

[0024] In some embodiments, in step 2), the reaction mixture is ground until its D50 particle size is less than 0.4 μm.

[0025] In some embodiments, 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, in step 2), 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.

[0027] 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 large-particle-size ferromanganese phosphate or small-particle-size ferromanganese phosphate.

[0028] 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%.

[0029] Furthermore, the mixing temperature is 20-40°C.

[0030] Furthermore, the grinding is performed in a sand mill.

[0031] Furthermore, the grinding temperature is 20-60°C.

[0032] Furthermore, the drying temperature is 100-120°C.

[0033] Furthermore, the sintering temperature is 500-800°C.

[0034] In some embodiments, in step 3), the large-particle manganese iron phosphate, small-particle manganese iron phosphate, lithium source, water, optional organic carbon source and optional dopant are subjected to sand milling, spray drying and high-temperature sintering reaction to obtain the lithium manganese iron phosphate.

[0035] In some embodiments, the material is sand-milled to a D50 particle size of less than 0.5 μm.

[0036] In some embodiments, the divalent manganese salt is selected from a combination of one or more of manganese sulfate, manganese chloride, and manganese nitrate.

[0037] 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.

[0038] In some embodiments, the lithium source is selected from one or more combinations of lithium carbonate, lithium hydroxide, lithium chloride, lithium sulfate, lithium nitrate, lithium dihydrogen phosphate, lithium hydrogen phosphate and lithium acetate.

[0039] 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.

[0040] 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%.

[0041] In some embodiments, the phosphate is present in the form of an aqueous phosphate solution.

[0042] In some embodiments, the divalent manganese salt is present in the form of a divalent manganese salt aqueous solution.

[0043] 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.

[0044] Furthermore, the lithium site dopant is selected from a combination of one or more of sodium, potassium and niobium.

[0045] Furthermore, the iron-site dopant is selected from a combination of one or more of vanadium, cobalt and titanium.

[0046] Furthermore, the phosphorus-site dopant is selected from one or both of boron and silicon.

[0047] Furthermore, the oxygen dopant is selected from one or both of fluorine and bromine.

[0048] The present invention also provides lithium manganese iron phosphate prepared by the above-mentioned preparation method of lithium manganese iron phosphate.

[0049] Furthermore, the compaction density of the lithium manganese iron phosphate is 2.5 g / cm 3 above.

[0050] Furthermore, the compaction density of the lithium manganese iron phosphate is 2.5-2.8 g / cm 3 .

[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 149-160 mAh / g at 0.1C, a discharge capacity of 138-145 mAh / g or more at 1C, and a capacity retention rate of 99.2%-99.9% after 200 cycles of charge and discharge at a rate of 1C. It can be seen that the lithium-ion battery has both excellent electrical properties and high compaction density.

[0053] Compared with the prior art, the present invention has the following advantages:

[0054] The present invention first prepares large-size ferromanganese phosphate and small-size ferromanganese phosphate respectively through redox reaction, and then compound the two, as precursors for the synthesis of lithium ferromanganese phosphate, and reacts them with raw materials such as lithium source to prepare lithium ferromanganese phosphate. The compounding of two precursors with specific particle sizes can achieve the small-size precursor effectively filling the gap of the large-size precursor, thereby improving the compaction density of the lithium ferromanganese phosphate product, and at the same time can achieve excellent electrical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a morphology picture of the small-particle ferromanganese phosphate prepared in Example 1;

[0056] Figure 2 This is a morphology picture of the large-particle ferromanganese phosphate prepared in Example 1;

[0057] Figure 3 This is a morphology picture of the lithium manganese iron phosphate prepared in Example 1;

[0058] Figure 4 The rate curve of the lithium manganese iron phosphate prepared in Example 1 at 0.1C and 1C;

[0059] Figure 5 This is a cycle curve of the lithium manganese iron phosphate prepared in Example 1 at 1C. DETAILED DESCRIPTION

[0060] 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.

[0061] Example 1

[0062] This embodiment provides a lithium manganese iron phosphate:

[0063] 1) Preparation of small particle size ferromanganese phosphate:

[0064] Weigh 68.47 kg of monoammonium phosphate and 50.30 kg of manganese sulfate monohydrate as raw materials, dissolve and filter them with 100.0 kg of pure water respectively, and add 6.65 kg of concentrated phosphoric acid (mass percentage is 10%) to the monoammonium phosphate solution;

[0065] 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 25.88 kg manganese dioxide in sequence, and sand grind to a particle size D50 ≤ 0.4 μm;

[0066] 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.

[0067] 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 600°C, and finally manganese iron phosphate with a total manganese iron to phosphorus molar ratio of about 0.975 and a primary particle size of 80-100nm is obtained.

[0068] 2) Preparation of large particle size ferromanganese phosphate:

[0069] Weigh 68.47 kg of monoammonium phosphate and 50.30 kg of manganese sulfate monohydrate as raw materials, dissolve and filter them with 100.0 kg of pure water respectively, and add 9.98 kg of concentrated phosphoric acid (mass percentage is 15%) to the monoammonium phosphate solution;

[0070] 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 25.88 kg manganese dioxide in sequence, and sand grind to a particle size D50 ≤ 0.4 μm;

[0071] 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.

[0072] 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 2%, flash dried and calcined in a rotary kiln with the furnace temperature controlled at 700°C, and finally manganese iron phosphate with a total molar ratio of manganese iron to phosphorus of about 0.950 and a primary particle size of 400-600nm is obtained.

[0073] 3) Preparation of lithium manganese iron phosphate:

[0074] Add 19 kg of deionized water to the sand mill material tank, turn on the sand mill, and add 1.31 kg of large-particle manganese ferrophosphate, 5.24 kg of small-particle manganese ferrophosphate (i.e., large particle size: small particle size is 2:8), 1.73 kg of lithium carbonate, 0.688 kg of glucose monohydrate, 0.08 kg of polyethylene glycol, and 113.95 g of cobalt acetate tetrahydrate prepared above in sequence, and sand grind until the particle size D50 of the slurry is ≤0.5 μm;

[0075] 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 8 hours to obtain a calcined material.

[0076] The calcined material is crushed by air flow until D50 is about 1.0 μm, so as to obtain cobalt-doped lithium manganese iron phosphate with a composite size of large and small particles, and a primary particle size of about 100-400 nm.

[0077] The obtained small particle size ferromanganese phosphate is as follows Figure 1 As shown. The obtained large particle size manganese iron phosphate is as follows Figure 2 The SEM image of the final cobalt-doped lithium manganese iron phosphate with a composite particle size is shown in Figure 3 shown.

[0078] Example 2

[0079] This embodiment provides a lithium manganese iron phosphate:

[0080] Steps 1) and 2) are the same as in Example 1;

[0081] 3) Preparation of lithium manganese iron phosphate:

[0082] Add 19 kg of deionized water to the sand mill material tank, turn on the sand mill, and add 0.655 kg of large-particle manganese ferrophosphate, 5.895 kg of small-particle manganese ferrophosphate (i.e., large particle size: small particle size is 1:9), 1.73 kg of lithium carbonate, 0.688 kg of glucose monohydrate, 0.081 kg of polyethylene glycol, and 113.95 g of cobalt acetate tetrahydrate prepared above in sequence, and sand grind until the particle size D50 of the slurry is ≤0.5 μm;

[0083] 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 8 hours to obtain a calcined material.

[0084] The calcined material is crushed by air flow until D50 is about 1.0 μm, thereby obtaining cobalt-doped lithium manganese iron phosphate with a composite size of large and small particles, and a primary particle size of about 80-400 nm.

[0085] Example 3

[0086] This embodiment provides a lithium manganese iron phosphate:

[0087] Steps 1) and 2) are the same as in Example 1;

[0088] 3) Preparation of lithium manganese iron phosphate:

[0089] Add 19 kg of deionized water to the sand mill material tank, turn on the sand mill, and add 1.965 kg of large-particle manganese ferrophosphate, 4.585 kg of small-particle manganese ferrophosphate (i.e., large particle size: small particle size is 3:7) prepared above, 1.73 kg of lithium carbonate, 0.688 kg of glucose monohydrate, 0.081 kg of polyethylene glycol, and 113.95 g of cobalt acetate tetrahydrate in sequence, and sand grind until the particle size D50 of the slurry is ≤0.5 μm;

[0090] The slurry after sand grinding was spray dried by using a spray machine, and the air inlet temperature of the spray machine was set to 240°C and the air outlet temperature was set to 110°C. The slurry was spray dried into powder, and the powder was sintered in a roller furnace under a nitrogen atmosphere at a sintering temperature of 750°C and a sintering time of 6 hours to obtain a calcined material;

[0091] The calcined material is crushed by air flow until D50 is about 1.0 μm, so as to obtain cobalt-doped lithium manganese iron phosphate with a composite size of large and small particles, and a primary particle size of about 100-400 nm.

[0092] Example 4

[0093] This embodiment provides a lithium manganese iron phosphate:

[0094] Steps 1) and 2) are the same as in Example 1;

[0095] 3) Preparation of lithium manganese iron phosphate:

[0096] Add 19 kg of deionized water to the sand mill material tank, turn on the sand mill, and add 2.62 kg of large-particle manganese ferrophosphate, 3.93 kg of small-particle manganese ferrophosphate (i.e., large particle size: small particle size is 4:6), 1.73 kg of lithium carbonate, 0.688 kg of glucose monohydrate, 0.081 kg of polyethylene glycol, and 113.95 g of cobalt acetate tetrahydrate prepared above in sequence, and sand grind until the particle size D50 of the slurry is ≤0.5 μm;

[0097] 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 8 hours to obtain a calcined material.

[0098] The calcined material is crushed by air flow until D50 is about 1.0 μm, so as to obtain cobalt-doped lithium manganese iron phosphate with a composite size of large and small particles, and a primary particle size of about 100-400 nm.

[0099] Comparative Example 1

[0100] This comparative example provides a lithium manganese iron phosphate:

[0101] 1) Preparation of large particle size ferromanganese phosphate:

[0102] Same as step 2 of Example 1);

[0103] 2) Preparation of lithium manganese iron phosphate:

[0104] The process is basically the same as step 3 of Example 1, except that 1.31 kg of large-particle manganese iron phosphate and 5.24 kg of small-particle manganese iron phosphate are replaced with 6.55 kg of large-particle manganese iron phosphate (i.e., only large-particle manganese iron phosphate is added, and small-particle manganese iron phosphate is not added). Finally, large-particle cobalt-doped lithium manganese iron phosphate is obtained, with a primary particle size of about 400 nm.

[0105] Comparative Example 2

[0106] This comparative example provides a lithium manganese iron phosphate:

[0107] 1) Preparation of small particle size ferromanganese phosphate:

[0108] Same as step 1 in Example 1);

[0109] 2) Preparation of lithium manganese iron phosphate:

[0110] The process is basically the same as step 3 of Example 1, except that 1.31 kg of large-particle ferromanganese phosphate and 5.24 kg of small-particle ferromanganese phosphate are replaced with 6.55 kg of small-particle ferromanganese phosphate (i.e., only small-particle ferromanganese phosphate is added without large-particle ferromanganese phosphate). Finally, small-particle cobalt-doped lithium manganese phosphate is obtained, with a primary particle size of about 100 nm.

[0111] Comparative Example 3

[0112] This comparative example provides a lithium manganese iron phosphate:

[0113] 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:

[0114] According to the Mn / Fe molar ratio of 6 / 4, 9.77 kg of manganese (III) phosphate monohydrate and 7.24 kg of 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 temperature of 600° C. to obtain a manganese iron phosphate precursor;

[0115] 2) Preparation of lithium manganese iron phosphate:

[0116] The process is basically the same as step 3) of Example 1, except that 1.31 kg of large-particle ferromanganese phosphate and 5.24 kg of small-particle ferromanganese phosphate are replaced with 6.55 kg of the ferromanganese phosphate precursor prepared in step 1).

[0117] Comparative Example 4

[0118] This comparative example provides a lithium manganese iron phosphate:

[0119] The large-particle cobalt-doped lithium manganese iron phosphate obtained in Comparative Example 1 and the small-particle cobalt-doped lithium manganese iron phosphate obtained in Comparative Example 2 were mechanically mixed in a mass ratio of 2:8 to obtain a lithium manganese iron phosphate product with a composite of large and small particle sizes (i.e., the two were directly blended).

[0120] 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.

[0121] Table 1 Performance of each embodiment and comparative example

[0122]

[0123] As can be seen from Table 1, the present invention first prepares large-particle ferromanganese phosphate and small-particle ferromanganese phosphate respectively through redox reaction, and then compound the two, as the precursor for the synthesis of lithium ferromanganese phosphate, and reacts them with raw materials such as lithium source to prepare lithium ferromanganese phosphate. The compounding of two precursors with specific particle sizes can achieve the small-particle precursor to effectively fill the gap of the large-particle precursor, thereby improving the compaction density of the lithium ferromanganese phosphate product, and at the same time can achieve excellent electrical properties. However, large-particle lithium ferromanganese phosphate, small-particle lithium ferromanganese phosphate, or directly blending the two, or preparing the ferromanganese phosphate precursor without redox reaction, cannot achieve both excellent electrical properties and high compaction density.

[0124] 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.

[0125] 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 monohydrated manganese phosphate, and reacting the monohydrated manganese phosphate with an iron source to obtain large-size ferromanganese phosphate; the large-size ferromanganese phosphate having a particle size of 200-1000 nm; 2) causing a phosphorus source, a divalent manganese salt and manganese dioxide to undergo an oxidation-reduction reaction to generate monohydrated manganese phosphate, and reacting the monohydrated manganese phosphate with an iron source to obtain small-sized ferromanganese phosphate; the particle size of the small-sized ferromanganese phosphate is 50-150 nm; 3) subjecting the large-particle manganese iron phosphate, the small-particle manganese iron phosphate, a lithium source, an optional organic carbon source, and an optional dopant to a high-temperature sintering reaction to obtain the lithium manganese iron phosphate; The phosphorus source is selected from one or both of phosphate and phosphoric acid.

2. The method for preparing lithium iron manganese phosphate according to claim 1, characterized in that: The mass ratio of the large-particle ferromanganese phosphate to the small-particle ferromanganese phosphate is 1-4:6-9; and / or the particle size of the large-particle ferromanganese phosphate is 400-600nm, and the particle size of the small-particle ferromanganese phosphate is 80-100nm.

3. 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.

4. 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.

5. The method for preparing lithium iron manganese phosphate according to claim 4, characterized in that: In step 1), 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; and / or, in step 2), based on the stoichiometric ratio of the divalent manganese salt, the phosphate is 0.8-1.1 equivalents, and the phosphoric acid is 0.05-0.15 equivalents.

6. 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; the manganese phosphate monohydrate particles are reacted with an iron source to obtain the large-particle ferromanganese phosphate; and / or, in step 2), 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; the manganese phosphate monohydrate particles are reacted with an iron source to obtain the small-particle ferromanganese phosphate.

7. The method for preparing lithium manganese iron phosphate according to claim 6, characterized in that: In step 1), the reaction mixture is ground until the D50 particle size is less than 0.4 μm; and / or, in step 2), the reaction mixture is ground until the D50 particle size is less than 0.4 μm.

8. 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 2), 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.

9. The method for preparing lithium manganese iron phosphate according to claim 1, characterized in that: In step 3), the large-particle manganese iron phosphate, small-particle manganese iron phosphate, lithium source, water, optional organic carbon source and optional dopant are subjected to sand milling, spray drying and high-temperature sintering reaction to obtain the lithium manganese iron phosphate.

10. The method for preparing lithium manganese iron phosphate according to claim 9, characterized in that: Sand grind the material until its D50 particle size is less than 0.5 μm.

11. 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.

12. 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.

13. Lithium manganese iron phosphate prepared by the method for preparing lithium manganese iron phosphate according to any one of claims 1 to 12.

14. The lithium manganese iron phosphate according to claim 13, characterized in that: The compaction density of the lithium manganese iron phosphate is 2.5 g / cm 3 Preferably, the compaction density of the lithium manganese iron phosphate is 2.5-2.8 g / cm 3 .

15. 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 13 or 14.

16. The lithium ion battery according to claim 15, characterized in that: The lithium ion battery has a discharge specific capacity of 149-160 mAh / g at 0.1C, a discharge specific capacity of 138-145 mAh / g or more at 1C, and a capacity retention rate of 99.2%-99.9% after 200 cycles of charge and discharge at a 1C rate.

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