Synthesis method of nano lithium manganese iron phosphate

Abstract

The invention provides a synthesis method of nano lithium iron manganese phosphate, which comprises the following steps: mixing and grinding ammonium iron manganese phosphate monohydrate or ammonium iron manganese phosphate and a lithium source, pre-calcining at low temperature to obtain an intermediate phase, greatly improving the grinding performance and grinding limit of the intermediate phase, and mixing and grinding the intermediate phase to obtain the nano lithium iron manganese phosphate. The lithium manganese iron phosphate with smaller primary particles and more uniform particle size distribution can be prepared, and the migration distance of lithium ions and electrons in the charging and discharging process is reduced, so that the rate capability and low-temperature performance of the lithium manganese iron phosphate are obviously improved. According to the invention, a coprecipitation method is adopted to prepare ammonium ferromanganese phosphate monohydrate, and then the ammonium ferromanganese phosphate monohydrate is taken as a raw material for grinding and low-temperature calcination to obtain a nanoscale precursor with uniformly mixed elements on a molecular level, small particle size and uniform particle size distribution, so that lithium ferromanganese phosphate with high crystallinity, controlled particle size and excellent rate capability can be synthesized.

Description

Technical Field

[0001] The present invention belongs to the field of cathode materials for lithium-ion batteries, and particularly relates to a method for synthesizing nano lithium iron manganese phosphate. Background Art

[0002] Lithium-ion batteries are indispensable energy storage devices in modern society and are widely used in fields such as digital products, electric vehicles, and grid energy storage. Lithium-ion batteries mainly consist of four main parts: a cathode material, an anode material, a separator, and an electrolyte. Among them, the cathode material plays an extremely important role in lithium-ion batteries. The cathode material is one of the key materials that determine the performance of lithium-ion batteries.

[0003] At present, there are mainly two types of cathode materials for lithium-ion batteries that are most widely used, namely lithium iron phosphate cathode materials and ternary lithium-ion battery cathode materials. Lithium iron phosphate has a low cost and excellent cycle stability and safety. However, due to its low theoretical capacity, the energy density of lithium-ion batteries is low; ternary cathode materials have a high energy density but a higher cost. At the same time, ternary lithium-ion batteries are prone to thermal runaway in extreme cases and have low safety.

[0004] Lithium iron manganese phosphate has received extensive attention due to its excellent performance: the material cost of lithium iron manganese phosphate is close to that of lithium iron phosphate. In terms of performance, compared with lithium iron phosphate materials, its energy density is higher; compared with ternary cathode materials, its safety performance is more excellent. However, the conductivity of the lithium iron manganese phosphate cathode material is only 10 -13 S / cm, and the lithium ion diffusion rate is 10 -15 cm 2 / S, which are 1 / 10 and 1 / 10000 of lithium iron phosphate respectively. Compared with the transition energy gap of 0.3 eV of lithium iron phosphate, the transition energy gap of electrons in lithium iron manganese phosphate is as high as 2 eV, which is basically an insulator. The low electron and ion mobility affects the capacity release and rate performance of the lithium iron manganese phosphate cathode material.

[0005] Nanostructuring is an effective solution to solve the low discharge capacity of the lithium iron manganese phosphate cathode material, and its principle is to reduce the transmission distance of lithium ions and electrons inside the material. In terms of material synthesis and preparation, the sol-gel method is an effective means to obtain nanomaterials, but due to its low production efficiency, it is difficult to solve the problem of material particle size at the industrial level. At present, the production of lithium iron phosphate mainly uses sanding to control the particle size of the material. Since the synthesis method of lithium iron manganese phosphate is similar to that of lithium iron phosphate, sanding is also very likely to play a role in controlling the particle size of the material during the synthesis of lithium iron manganese phosphate. However, whether using iron phosphate manganese or manganese iron (ammonium) as the precursor, the grinding performance of the raw materials is poor, resulting in an increase in grinding time or a relatively large final grinding particle size. Summary of the Invention

[0006] In view of the above technical problems, the purpose of the present invention is to provide a preparation method of a high-rate nano lithium iron manganese phosphate cathode material.

[0007] To achieve the above purpose, the present invention proposes the following solutions: The present invention provides a synthesis method of nano lithium iron manganese phosphate, including: (1) Mix ammonium iron manganese phosphate monohydrate or ammonium iron manganese phosphate with a lithium source, grind until the particle size D50 of the material is 500 - 1000 nm, and then dry to obtain a mixed material A; (2) Calcinate the mixed material A at a low temperature under air conditions to obtain a lithium iron manganese phosphate precursor; (3) Grind and mix the lithium iron manganese phosphate precursor with a carbon source, grind until the particle size D50 of the material is 100 - 400 nm, and then dry to obtain a mixed material B; (4) Sinter the mixed material B under a protective atmosphere to obtain nano lithium iron manganese phosphate.

[0008] Preferably, in step (1), the ammonium iron manganese phosphate monohydrate or ammonium iron manganese phosphate and the lithium source are proportioned according to the ratio of the total molar amount of manganese and iron to the molar amount of lithium in the lithium source of 1:1 - 1.03.

[0009] Preferably, the lithium source is one or more of lithium carbonate, lithium hydroxide and their hydrates.

[0010] Preferably, in step (2), the temperature of the low-temperature calcination is 400 - 500 °C; the time of the low-temperature calcination is 3 - 6 h.

[0011] Preferably, in step (3), the addition amount of the carbon source is 8 - 12% of the mass of the lithium iron manganese phosphate precursor; the carbon source is one or more of glucose, sucrose, polyethylene glycol, carbon black, graphene, polyvinyl alcohol, polypropylene alcohol, citric acid, cellulose, starch, maltodextrin, fructose, lactose, maltose, oxalic acid, ascorbic acid.

[0012] Preferably, in step (4), the sintering temperature is 600 - 800 °C; the sintering time is 4 h - 12 h; the protective atmosphere is a nitrogen atmosphere or an inert atmosphere.

[0013] Preferably, in step (1), the grinding is wet grinding; the drying is spray drying, freeze drying or drying.

[0014] Preferably, in step (3), the grinding is wet grinding; the drying is spray drying, freeze drying or drying.

[0015] Preferably, in step (1), the preparation method of the ammonium iron manganese phosphate monohydrate includes: Prepare a mixed salt solution A of manganese salt and iron salt; prepare a precipitant solution B containing a phosphorus source; prepare a reaction kettle bottom liquid C; Simultaneously add the mixed salt solution A and the precipitant solution B to the reaction kettle bottom liquid C, use ammonia water as a pH regulator, control the pH value of the reaction system to be 5-8, carry out stirring reaction, and continue stirring and aging after the feeding is completed; Perform solid-liquid separation and drying on the aged slurry to obtain ammonium manganese iron phosphate monohydrate NH 4 Mn x Fe 1-x PO 4 ·H 2 O, where 0 < x < 1.

[0016] Preferably, the precipitant solution B is prepared by dissolving a phosphorus source and ammonia water in water; the phosphorus source is selected from one or more of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid; The concentration of the phosphorus source is 0.5-2 mol / L; the concentration of the ammonia water is 0.5-2 mol / L.

[0017] Preferably, the total metal concentration in the mixed salt solution A is 0.5-2 mol / L.

[0018] Preferably, the pH value of the reaction kettle bottom liquid C is 5-8.

[0019] Preferably, the temperature of the reaction is from room temperature to 80 °C; the time for simultaneously adding the mixed salt solution A and the precipitant solution B to the reaction kettle bottom liquid C is 20 min-8 h.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The synthesis method of the present invention mixes ammonium manganese iron phosphate monohydrate with a lithium source and grinds them for low-temperature pre-calcination, so that the grinding performance and grinding limit of the intermediate phase are greatly improved. Then, mixing and grinding with the intermediate phase can prepare lithium iron manganese phosphate with smaller primary particles and more uniform particle size distribution, reduce the migration distance of lithium ions and electrons during charge and discharge, and significantly improve the rate performance and low-temperature performance of lithium iron manganese phosphate.

[0021] The synthesis method of the present invention uses the co-precipitation method to prepare ammonium manganese iron phosphate monohydrate, and then uses it as a raw material for grinding and low-temperature calcination to obtain a nano-level precursor with uniform mixing of elements at the molecular level, small particle size, and uniform particle size distribution, and further can synthesize lithium iron manganese phosphate with high crystallinity, controlled particle size, and excellent rate performance. Description of the Drawings

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0023] Figure 1 SEM image of the precursor obtained in step (6) of Example 1.

[0024] Figure 2 XRD pattern of the precursor obtained in step (6) of Example 1.

[0025] Figure 3 SEM images of the lithium iron manganese phosphate finished product obtained in Example 1 at different magnification ratios.

[0026] Figure 4 XRD pattern of the lithium iron manganese phosphate finished product obtained in Example 1.

[0027] Figure 5 Charge-discharge curves of the assembled battery in Example 1 at 0.1C and 1C.

[0028] Figure 6 Charge-discharge curves of the assembled batteries in Example 1 and Comparative Example 1 at 1C. Detailed implementation manners

[0029] Precursors such as iron phosphate, manganese (ammonium) phosphate mixture, and manganese iron (ammonium) phosphate have low grinding efficiency and often a large grinding limit due to crystal structure and physical properties. As a result, it is difficult to obtain raw materials and products with the required particle size. Through research, the applicant can change the phase of the lithium iron manganese phosphate precursor and increase crystal defects by mixing ammonium manganese iron phosphate monohydrate with a lithium source and grinding at low temperature. The obtained intermediate-phase precursor contains amorphous components and a large number of defects, and its grinding performance is greatly improved. Furthermore, the grinding efficiency can be increased, the grinding limit size can be reduced, and the size of the material can be ground to a smaller particle size with a higher grinding efficiency, which is conducive to sintering to obtain a lithium iron manganese phosphate with a smaller particle size and improve the rate performance. Based on this important research finding, the applicant mixes ammonium manganese iron phosphate monohydrate or ammonium manganese iron phosphate with a lithium source and grinds to a material particle size D50 of 500 - 1000 nm, then calcines to obtain a precursor, and then mixes the precursor with a carbon source and grinds to a material particle size D50 of 100 - 400 nm, and finally sinters to obtain a nanoscale lithium iron manganese phosphate material, and the rate performance is significantly improved.

[0030] The present invention provides a method for synthesizing high-rate nano lithium iron manganese phosphate, including: (1) Mix ammonium iron manganese phosphate monohydrate or ammonium iron manganese phosphate with a lithium source, grind until the particle size D50 of the material is 500 - 1000 nm, and then dry to obtain a mixed material A; (2) Calcinate the mixed material A at a low temperature under air conditions to obtain a lithium iron manganese phosphate precursor; at least part or all of the obtained precursor forms a phase, and X-ray diffraction analysis shows that the precursor material is lithium iron manganese phosphate coexisting with a crystalline phase and an amorphous phase; (3) Grind and mix the lithium iron manganese phosphate precursor with a carbon source, grind until the particle size D50 of the material is 100 - 400 nm, and then dry to obtain a mixed material B; (4) Sinter the mixed material B under a protective atmosphere to obtain nanoscale lithium iron manganese phosphate.

[0031] In some preferred embodiments, in step (1), the ammonium iron manganese phosphate monohydrate or ammonium iron manganese phosphate and the lithium source are proportioned according to the ratio of the total molar amount of manganese and iron to the molar amount of lithium in the lithium source being 1:1 - 1.03.

[0032] In some preferred embodiments, the lithium source is one or more of lithium carbonate, lithium hydroxide and their hydrates.

[0033] In some preferred embodiments, in step (2), the temperature of the low-temperature calcination is 400 - 500 °C, such as 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, etc.; the time of the low-temperature calcination is 3 - 6 h, such as 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, etc.

[0034] In some preferred embodiments, in step (3), the addition amount of the carbon source is 8 - 12% of the mass of the lithium iron manganese phosphate precursor; the carbon source is one or more of glucose, sucrose, polyethylene glycol, carbon black, graphene, polyvinyl alcohol, polypropylene alcohol, citric acid, cellulose, starch, maltodextrin, fructose, lactose, maltose, oxalic acid, ascorbic acid.

[0035] In some preferred embodiments, in step (4), the temperature of the sintering is 600 - 800 °C; the sintering time is 4 h - 12 h; the protective atmosphere is a nitrogen atmosphere or an inert atmosphere.

[0036] In some preferred embodiments, in step (1), the grinding is wet grinding, and wet grinding can effectively avoid agglomeration and caking. The parameters of the wet grinding are conventional wet grinding parameters in the art, for example, the solid content is 20 - 60%, and the rotation speed is 1000 - 2000 rpm.

[0037] In some preferred embodiments, in step (1), the drying is spray drying, freeze drying or oven drying, and spray drying is further preferred, which has high productivity, low cost, and the obtained product is spherical with good fluidity.

[0038] In some preferred embodiments, in step (3), the grinding is wet grinding, and the parameters of the wet grinding are conventional wet grinding parameters in the art, for example, the solid content is 20 - 60%, and the rotation speed is 1000 - 2000 rpm.

[0039] In some preferred embodiments, in step (3), the drying is spray drying, freeze drying or oven drying, and spray drying is further preferred.

[0040] In some preferred embodiments, in step (1), the preparation method of ammonium iron manganese phosphate monohydrate includes: Preparing a mixed salt solution A of manganese salt and iron salt; preparing a precipitant solution B containing a phosphorus source; preparing a reaction kettle bottom liquid C; Synchronously adding the mixed salt solution A and the precipitant solution B to the reaction kettle bottom liquid C, using ammonia water as a pH regulator, controlling the pH value of the reaction system to be 5 - 8, carrying out stirring reaction, and continuing stirring and aging after the feeding is completed; the pH value can be 5, 5.5, 6, 6.5, 7, 7.5, 8, etc. The control of the pH value is beneficial to controlling the product morphology, and a higher pH value is beneficial to reducing the particle size of the product; Performing solid-liquid separation and drying on the aged slurry to obtain ammonium iron manganese phosphate monohydrate NH 4 Mn x Fe 1-x PO 4 ·H 2 O, where 0 < x < 1.

[0041] In some preferred embodiments, the precipitant solution B is prepared by dissolving a phosphorus source and ammonia water in water; the phosphorus source is selected from one or more of ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid; The concentration of the phosphorus source is 0.5 - 2 mol / L; the concentration of the ammonia water is 0.5 - 2 mol / L.

[0042] In some preferred embodiments, the total metal concentration in the mixed salt solution A is 0.5 - 2 mol / L.

[0043] In some preferred embodiments, the pH value of the bottom liquid C of the reaction kettle is 5 to 8, such as 5, 5.5, 6, 6.5, 7, 7.5, 8, etc. Controlling the pH value of the bottom liquid C of the reaction kettle is beneficial to improving the stability of the reaction system; further preferably, the bottom liquid C of the reaction kettle is prepared by dissolving one or more phosphorus sources selected from ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid in water and adjusting the pH with ammonia water; the concentration of the phosphorus source is 0 to 1 mol / L.

[0044] In some preferred embodiments, the temperature of the reaction is from room temperature to 80 °C; the time for simultaneously adding the mixed salt solution A and the precipitant solution B to the bottom liquid C of the reaction kettle is 20 min to 8 h.

[0045] In some preferred embodiments, the aging time is 20 min to 8 h.

[0046] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and in detail below in conjunction with the accompanying drawings of the specification and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0047] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0048] Unless otherwise specifically stated, various raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchases or can be prepared by existing methods.

[0049] Example 1: A method for preparing a high-rate nano lithium iron phosphate manganese cathode material, comprising: (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0050] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0051] (4) Add solutions A and B to the bottom liquid evenly with a peristaltic pump. During the dropping process, adjust the pH with ammonia water to control the pH of the reaction system to 8, the temperature to 60 °C, and the feeding time to 2 h. After the feeding is completed, continue to stir for an aging time of 2 h. After the reaction, ammonium manganese iron phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H2 O).

[0052] (5) Filter, wash, and dry the prepared ammonium iron manganese phosphate, add 1.03 mol of lithium carbonate and an appropriate amount of water, wet-grind the material, grind the D50 of the material to 500 nm, and then spray-dry the slurry.

[0053] (6) Calcinate the completely dried product at 450 °C under air conditions for 4 h to obtain a lithium iron manganese phosphate precursor. The SEM image of the precursor is as shown in Figure 1 shown, and the XRD pattern is as shown in Figure 2 shown. From Figure 1 it can be seen that the spray-dried precursor is mainly spherical-like, the size of the secondary particles is mainly between 2 and 10 μm, and the size of the primary particles is uniform, about 10 - 20 nm. From Figure 2 it can be seen that the XRD pattern of the precursor after calcination shows the characteristic peaks of lithium iron manganese phosphate, and at the same time, a peak envelope common to amorphous substances appears at about 2θ = 20°, indicating that the product contains partially crystalline lithium iron manganese phosphate and residual glassy substances.

[0054] (7) Add glucose accounting for 12% of the mass of the lithium iron manganese phosphate precursor and an appropriate amount of water to the prepared lithium iron manganese phosphate precursor, carry out wet-grinding and mixing, control the D50 of the material at 150 nm, and spray-dry the slurry.

[0055] (8) Sinter the spray-dried product at 700 °C under nitrogen protection for 10 h to obtain a lithium iron manganese phosphate product.

[0056] Characterize the product. The SEM image is as shown in Figure 3 shown. From Figure 3 it can be seen that the obtained lithium iron manganese phosphate material has uniform particle size and is a nanoscale material. The change of the secondary particles is not obvious, indicating that the sintering process will not damage the secondary particle structure, while the primary particles have grown compared with the precursor and reached about 80 nm. The XRD pattern is as shown in Figure 4 shown. It can be seen from the figure that a pure-phase lithium iron manganese phosphate is obtained.

[0057] Use the lithium iron manganese phosphate obtained in Example 1 as the active material of the cathode material, mix it with the conductive agent acetylene black (AB) and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, mix with N-methylpyrrolidone (NMP) as the solvent to prepare a cathode slurry, and coat it on an aluminum foil to obtain a cathode electrode sheet; use a lithium sheet as the anode and assemble it into a CR2025 type button cell in a glove box. The electrolyte solution is 1 M LiPF 6 , EC:DEC (volume ratio 4:6), and the separator is a commercial electrolyte separator with a diameter of 16 mm. Perform charge and discharge tests at 2.5 - 4.3 V at room temperature of 25 °C on a Chinese Neware battery test system.

[0058] The charge-discharge curves of the assembled battery at 0.1C and 1C are as follows Figure 5 shown. The charge-discharge plateau of this material is close to the lithium potential of manganese and iron. The plateau is stable and the ratio of the two is close to the manganese-iron ratio of the material, indicating that the material has good structural integrity. At a discharge rate of 0.1C, the capacity of the coin cell is 150.8 mAh / g, which is similar to that of mainstream products in the market. The discharge capacity at 1C is 146.8 mAh / g, only about 4 mAh / g different from the discharge capacity at 0.1C, showing its excellent rate performance. The discharge capacity of coin cells assembled with common non-rate-type materials in the market is generally lower than 140 mAh / g at 1C.

[0059] Regarding the influence of calcination on the particle size of the material, the following conditional experiments were carried out. The raw materials used in the experiments were all the same batch of the same product: Scheme 1: S11. Filter, wash, and dry the ammonium manganese iron phosphate monohydrate prepared in Example 1, add 1.03 mol of lithium carbonate and an appropriate amount of water, wet-mill the material for 60 min, and spray-dry the slurry.

[0060] S12. Calcinate the completely dried product at 450°C in air for 4 h to obtain a lithium manganese iron phosphate precursor; S13. Add glucose accounting for 10% of the mass of the lithium manganese iron phosphate precursor and an appropriate amount of water to the obtained lithium manganese iron phosphate precursor, carry out batch wet-milling and mixing under the same conditions, and the grinding times are 60 min, 150 min, and 240 min respectively. Spray-dry the ground slurry, and the particle size of the obtained material is shown in Table 1.

[0061] Table 1 Scheme 2: S21. Filter, wash, and dry the ammonium manganese iron phosphate monohydrate prepared in Example 1. Calcinate the dried product at 450°C in air for 4 h to remove the crystal water and obtain ammonium manganese iron phosphate; S22. Add 1.03 mol of lithium carbonate, an appropriate amount of water, and 10% of glucose to ammonium manganese iron phosphate, carry out batch wet-milling and mixing under the same conditions, and the grinding times are 210 min, 320 min, and 650 min respectively. Spray-dry the ground slurry, and the particle size of the obtained material is shown in Table 2.

[0062] Among them, the wet-milling conditions in Step S13 and Step S22 are the same, with a solid content of 40% and a rotation speed of 1800 rpm.

[0063] Table 2 Analysis of the data in Table 1 and Table 2 reveals that by first grinding ammonium manganese iron phosphate and a lithium source and then performing low-temperature pre-calcination to prepare an intermediate precursor, and then grinding the precursor with a carbon source, compared to directly grinding the raw materials ammonium manganese iron phosphate, lithium source, and carbon source together, not only can the grinding efficiency be significantly improved, but also the particle size of the materials can be effectively reduced, achieving more effective control of the particle size of the material.

[0064] Example 2 A method for preparing a high-rate nano lithium manganese iron phosphate cathode material, comprising: (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0065] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 7 with ammonia water, and add this solution to a reaction kettle as the bottom liquid.

[0066] (4) Uniformly add solutions A and B to the bottom liquid using a peristaltic pump. During the dropping process, adjust the pH with ammonia water to control the pH of the reaction system to 7, the temperature to 60 °C, and the feeding time to 2 h. After the feeding is completed, continue stirring and aging for 2 h. After the reaction, ammonium manganese iron phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0067] (5) Filter, wash, and dry the prepared ammonium manganese iron phosphate, add 1.01 mol of lithium carbonate and an appropriate amount of water, perform wet sanding of the material for 4 h, grind the D50 of the material to 600 nm, and then spray-dry the slurry.

[0068] (6) Calcinate the completely dried product at 450 °C under air conditions to obtain a lithium manganese iron phosphate precursor.

[0069] (7) Add glucose accounting for 12% of the mass of the prepared lithium manganese iron phosphate precursor and an appropriate amount of water to the lithium manganese iron phosphate precursor, perform wet sanding and mixing for 1 h, control the D50 of the material at 250 nm, and spray-dry the slurry.

[0070] (8) Sinter the spray-dried product at 700 °C under nitrogen protection for 10 h to obtain a lithium manganese iron phosphate product.

[0071] Example 3 A method for preparing a high-rate nano lithium manganese iron phosphate cathode material, comprising: (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0072] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 6 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0073] (4) Uniformly add solutions A and B to the bottom liquid with a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system to 6, the temperature to 60 °C, and the feeding time to 2 h. After the feeding is completed, continuously stir and age for 2 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0074] (5) Filter, wash, and dry the obtained ammonium iron manganese phosphate, add 1.02 mol of lithium carbonate and an appropriate amount of water, wet-grind the material for 4 h, grind the D50 of the material to 800 nm, and spray-dry the slurry.

[0075] (6) Calcinate the completely dried product at 450 °C under air conditions to obtain the lithium iron manganese phosphate precursor.

[0076] (7) Add glucose accounting for 12% of the mass of the lithium iron manganese phosphate precursor and an appropriate amount of water to the obtained lithium iron manganese phosphate precursor, wet-grind and mix for 1 h, grind the particle size D50 of the material to 300 nm, and spray-dry the slurry.

[0077] (8) Sinter the spray-dried product at 700 °C under nitrogen protection for 10 h to obtain the lithium iron manganese phosphate product.

[0078] Example 4 Preparation method of high-rate nano lithium iron manganese phosphate cathode material, including: (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0079] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 5 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0080] (4) Add solution A and B evenly into the bottom solution with a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system to be 5, the temperature to be 60 °C, and the feeding time to be 2 h. After the feeding is completed, continue stirring and aging for 2 h. After the reaction is completed, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0081] (5) Filter, wash, and dry the obtained ammonium iron manganese phosphate, add 1.02 mol of lithium carbonate and an appropriate amount of water, wet-mill the material for 4 h, grind the D50 of the material to 1000 nm, and spray-dry the slurry.

[0082] (6) Calcinate the completely dried product at 450 °C under air conditions for 4 h to obtain the lithium iron manganese phosphate precursor.

[0083] (7) Add glucose accounting for 12% of the mass of the lithium iron manganese phosphate precursor and an appropriate amount of water to the obtained lithium iron manganese phosphate precursor, wet-mill and mix for 1 h, grind the particle size D50 of the material to 400 nm, and spray-dry the slurry.

[0084] (8) Sinter the spray-dried product at 700 °C under nitrogen protection for 4 h to obtain the lithium iron manganese phosphate product.

[0085] Example 5 Preparation method of high-rate nano lithium iron manganese phosphate cathode material, including: (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0086] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom solution.

[0087] (4) Add solution A and B evenly into the bottom solution with a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system to be 8, the temperature to be 60 °C, and the feeding time to be 2 h. After the feeding is completed, continue stirring and aging for 2 h. After the reaction is completed, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0088] (5) Filter, wash, and dry the prepared ammonium iron manganese phosphate, add 1.03 mol of lithium carbonate and an appropriate amount of water, wet-grind the material, grind the D50 of the material to 500 nm, and then spray-dry the slurry.

[0089] (6) Calcinate the completely dried product at 500 °C under air conditions for 3 h to obtain the lithium iron manganese phosphate precursor.

[0090] (7) Add glucose accounting for 12% of the mass of the prepared lithium iron manganese phosphate precursor and an appropriate amount of water to the prepared lithium iron manganese phosphate precursor, perform wet-grinding and mixing, control the D50 of the material at 150 nm, and spray-dry the slurry.

[0091] (8) Sinter the spray-dried product at 720 °C under nitrogen protection for 4 h to obtain the lithium iron manganese phosphate product.

[0092] Example 6 Preparation method of high-rate nano lithium iron manganese phosphate cathode material, comprising: (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0093] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0094] (4) Uniformly add solutions A and B to the bottom liquid with a peristaltic pump, adjust the pH with ammonia water during the dropping process, control the pH of the reaction system at 8, the temperature at 60 °C, and the feeding time at 2 h. After the feeding is completed, continuously stir for an aging time of 2 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0095] (5) Filter, wash, and dry the prepared ammonium iron manganese phosphate, add 1.03 mol of lithium carbonate and an appropriate amount of water, wet-grind the material, grind the D50 of the material to 500 nm, and then spray-dry the slurry.

[0096] (6) Calcinate the completely dried product at 400 °C under air conditions for 6 h to obtain the lithium iron manganese phosphate precursor.

[0097] (7) Add glucose accounting for 12% of the mass of the prepared lithium iron manganese phosphate precursor and an appropriate amount of water to the prepared lithium iron manganese phosphate precursor, perform wet-grinding and mixing, control the D50 of the material at 150 nm, and spray-dry the slurry; (8) The spray-dried product is sintered at 600 °C under nitrogen protection for 12 h to obtain the lithium iron manganese phosphate product.

[0098] Example 7 A method for preparing a high-rate nano lithium iron manganese phosphate cathode material, comprising: (1) 1.6 mol of manganese sulfate and 0.4 mol of ferrous sulfate heptahydrate are dissolved in 1 L of water to obtain solution A; (2) 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water are dissolved in 1 L of water to obtain solution B.

[0099] (3) 0.1 mol of ammonium dihydrogen phosphate is dissolved in 1 L of water, and the pH is adjusted to 8 with ammonia water. This solution is added to the reaction kettle as the bottom liquid.

[0100] (4) Solutions A and B are uniformly added to the bottom liquid with a peristaltic pump. During the dropping process, the pH is adjusted with ammonia water to control the pH of the reaction system to be 8, the temperature to be 50 °C, and the feeding time to be 4 h. After the feeding is completed, continuous stirring and aging are carried out for 3 h. After the reaction, ammonium manganese iron phosphate monohydrate (NH 4 Mn 0.8 Fe 0.2 PO 4 ·H 2 O) is obtained.

[0101] (5) The obtained ammonium manganese iron phosphate is filtered, washed, and dried, 1.02 mol of lithium carbonate and an appropriate amount of water are added, the material is wet-milled, and after the D50 of the material is ground to 500 nm, the slurry is spray-dried.

[0102] (6) The completely dried product is calcined at 450 °C under air conditions for 4 h to obtain the lithium iron manganese phosphate precursor.

[0103] (7) 10% of glucose based on the mass of the lithium iron manganese phosphate precursor and an appropriate amount of water are added to the obtained lithium iron manganese phosphate precursor, and wet-milling and mixing are carried out to control the D50 of the material to be about 150 nm, and the slurry is spray-dried.

[0104] (8) The spray-dried product is sintered at 700 °C under nitrogen protection for 10 h to obtain the lithium iron manganese phosphate product.

[0105] Example 8 A method for preparing a high-rate nano lithium iron manganese phosphate cathode material, comprising: (1) 0.4 mol of manganese sulfate and 1.6 mol of ferrous sulfate heptahydrate are dissolved in 1 L of water to obtain solution A; (2) 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water are dissolved in 1 L of water to obtain solution B.

[0106] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, add ammonia water to adjust the pH to 8, and add this solution to the reaction kettle as the bottom liquid.

[0107] (4) Uniformly add solutions A and B to the bottom liquid using a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system to 8, the temperature to 80 °C, and the feeding time to 30 min. After the feeding is completed, continuously stir and age for 1 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.2 Fe 0.8 PO 4 ·H 2 O) is obtained.

[0108] (5) Filter, wash, and dry the obtained ammonium iron manganese phosphate, add 1.03 mol of lithium carbonate and an appropriate amount of water, wet-grind the material, grind the D50 of the material to 300 nm, and then spray-dry the slurry.

[0109] (6) Calcinate the completely dried product at 450 °C under air conditions for 4 h to obtain the lithium iron manganese phosphate precursor.

[0110] (7) Add glucose accounting for 8% of the mass of the lithium iron manganese phosphate precursor and an appropriate amount of water to the obtained lithium iron manganese phosphate precursor, carry out wet-grinding and mixing, control the D50 of the material to be about 120 nm, and spray-dry the slurry.

[0111] (8) Sinter the spray-dried product at 700 °C under nitrogen protection for 10 h to obtain the lithium iron manganese phosphate product.

[0112] Example 9 Preparation method of high-rate nano lithium iron manganese phosphate cathode material, including: (1) Dissolve 1.8 mol of manganese sulfate and 0.2 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0113] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, add ammonia water to adjust the pH to 8. Add this solution to the reaction kettle as the bottom liquid.

[0114] (4) Uniformly add solutions A and B to the bottom liquid using a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system to 8, the temperature to 25 °C, and the feeding time to 6 h. After the feeding is completed, continuously stir and age for 6 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.9 Fe 0.1 PO4 ·H 2 O).

[0115] (5) Filter, wash, and dry the prepared ammonium iron manganese phosphate, add 1.01 mol of lithium carbonate and an appropriate amount of water, subject the material to wet sanding, grind the D50 of the material to 500 nm, and then spray-dry the slurry.

[0116] (6) Calcinate the completely dried product at 450 °C under air conditions for 4 h to obtain the lithium iron manganese phosphate precursor.

[0117] (7) Add glucose accounting for 12% of the mass of the lithium iron manganese phosphate precursor and an appropriate amount of water to the prepared lithium iron manganese phosphate precursor, conduct wet sanding and mixing, control the D50 of the material at 150 nm, and spray-dry the slurry.

[0118] (8) Sinter the spray-dried product at 700 °C under nitrogen protection for 10 h to obtain the lithium iron manganese phosphate product.

[0119] Example 10 The difference between this example and Example 1 is only that in steps (5) and (7), the drying method of the slurry is drying by baking.

[0120] Comparative Example 1 A method for preparing a lithium iron manganese phosphate cathode material, comprising: (1) Dissolve 1.2 mol of manganese sulfate and 0.8 mol of ferrous sulfate heptahydrate in 1 L of water to obtain solution A; (2) Dissolve 2 mol of ammonium dihydrogen phosphate and 320 g of 25% ammonia water in 1 L of water to obtain solution B.

[0121] (3) Dissolve 0.1 mol of ammonium dihydrogen phosphate in 1 L of water, adjust the pH to 8 with ammonia water, and add this solution to the reaction kettle as the bottom liquid.

[0122] (4) Uniformly add solutions A and B to the bottom liquid with a peristaltic pump. During the dropping process, adjust the pH with ammonia water, control the pH of the reaction system at 8, the temperature at 60 °C, and the feeding time at 2 h. After the feeding is completed, continue stirring and aging for 2 h. After the reaction, ammonium iron manganese phosphate monohydrate (NH 4 Mn 0.6 Fe 0.4 PO 4 ·H 2 O) is obtained.

[0123] (5) Filter, wash, and dry the prepared ammonium iron manganese phosphate monohydrate, calcine it at 450 °C for 4 h to remove the crystal water, and obtain ammonium iron manganese phosphate; (6) Add 1.03 mol of lithium carbonate, 12% of the mass of ammonium iron manganese phosphate of glucose, and an appropriate amount of water to ammonium iron manganese phosphate. Wet-grind the material. After grinding the D50 of the material to about 180 nm, spray-dry the slurry.

[0124] (7) Sinter the spray-dried product under nitrogen protection at 700 °C for 10 h to obtain a lithium iron manganese phosphate product.

[0125] Assemble the obtained lithium iron manganese phosphate product into a button cell in the same manner as in Example 1, and perform charge-discharge tests at 2.5 - 4.3 V at a rate of 1C at room temperature of 25 °C on a China Neware battery test system. The charge-discharge curves are as Figure 6 shown. It can be seen from Figure 6 that the rate performance corresponding to the sample of Example 1 is better than that of Comparative Example 1.

[0126] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for synthesizing lithium iron manganese phosphate nanometer, characterized in that, it includes: (1) Mix ammonium iron manganese phosphate monohydrate or ammonium iron manganese phosphate with a lithium source, grind until the particle size D50 of the material is 500 - 1000 nm, and then dry to obtain a mixed material A; (2) Calcinate the mixed material A under air conditions at low temperature to obtain a lithium iron manganese phosphate precursor; (3) Grind and mix the lithium iron manganese phosphate precursor with a carbon source, grind until the particle size D50 of the material is 100 - 400 nm, and then dry to obtain a mixed material B; (4) Sinter the mixed material B under a protective atmosphere to obtain nanoscale lithium iron manganese phosphate.

2. The method for synthesizing lithium iron manganese phosphate nanometer according to claim 1, characterized in that, in step (1), the ammonium iron manganese phosphate monohydrate or ammonium iron manganese phosphate and the lithium source are proportioned according to the ratio of the total molar amount of manganese and iron to the molar amount of lithium in the lithium source of 1:1 - 1.03; and / or, the lithium source is one or more of lithium carbonate, lithium hydroxide and their hydrates.

3. The method for synthesizing lithium iron manganese phosphate nanometer according to claim 1, characterized in that, in step (2), the temperature of the low-temperature calcination is 400 - 500 °C; the time of the low-temperature calcination is 3 - 6 h.

4. The method for synthesizing lithium iron manganese phosphate nanometer according to claim 1, characterized in that, in step (3), the addition amount of the carbon source is 8 - 12% of the mass of the lithium iron manganese phosphate precursor; and / or, the carbon source is one or more of glucose, sucrose, polyethylene glycol, carbon black, graphene, polyvinyl alcohol, polypropylene alcohol, citric acid, cellulose, starch, maltodextrin, fructose, lactose, maltose, oxalic acid, ascorbic acid.

5. The method for synthesizing lithium iron manganese phosphate nanometer according to claim 1, characterized in that, in step (4), the temperature of the sintering is 600 - 800 °C; the sintering time is 4 h - 12 h; the protective atmosphere is a nitrogen atmosphere or an inert atmosphere.

6. The method for synthesizing lithium iron manganese phosphate nanometer according to claim 1, characterized in that, in step (1), the grinding is wet grinding; the drying is spray drying, freeze drying or drying; in step (3), the grinding is wet grinding; the drying is spray drying, freeze drying or drying.

7. The method for synthesizing lithium iron manganese phosphate nanometer according to claim 1, characterized in that, in step (1), the preparation method of the ammonium iron manganese phosphate monohydrate includes: Preparing a mixed salt solution A of a manganese salt and an iron salt; preparing a precipitant solution B containing a phosphorus source; preparing a reaction kettle bottom liquid C; Simultaneously adding the mixed salt solution A and the precipitant solution B to the reaction kettle bottom liquid C, using ammonia water as a pH regulator, controlling the pH value of the reaction system to be 5 - 8, carrying out a stirring reaction, and continuing to stir and age after the feeding is completed; The aged slurry is subjected to solid-liquid separation and drying to obtain ammonium iron manganese phosphate monohydrate NH 4 Mn x Fe 1-x PO 4 ·H 2 O, where 0 < x < 1.

8. The method for synthesizing lithium iron manganese phosphate nanometer according to claim 7, characterized in that, the precipitant solution B is prepared by dissolving a phosphorus source and ammonia water in water; the phosphorus source is selected from one or more of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid. The concentration of the phosphorus source is 0.5 - 2 mol / L; the concentration of the ammonia water is 0.5 - 2 mol / L.

9. The synthesis method of nano lithium iron manganese phosphate as claimed in claim 7, characterized in that, the total metal concentration in the mixed salt solution A is 0.5 - 2 mol / L; the pH value of the reaction kettle bottom liquid C is 5 - 8.

10. The synthesis method of nano lithium iron manganese phosphate as claimed in claim 7, characterized in that, the temperature of the reaction is from room temperature to 80 °C; the time for simultaneously adding the mixed salt solution A and the precipitant solution B into the reaction kettle bottom liquid C is 20 min - 8 h.

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