Ammonium manganese ferric phosphate and lithium manganese iron phosphate, preparation methods therefor, and uses thereof

Abstract

The present application relates to ammonium manganese ferric phosphate, lithium manganese iron phosphate, preparation methods therefor, and the uses thereof. The chemical formula of ammonium manganese ferric phosphate is (NH4)(3-2x-2y)FexMnyPO4·H2O, wherein 0<x≤0.5 and x+y<1. The ratio of the area of the diffraction peak of the (010) crystal plane to the area of the diffraction peak of the (121) crystal plane is less than 1.40. The ammonium manganese ferric phosphate does not contain SO4 2-, Cl-, Na+ and K+, or the ammonium manganese ferric phosphate contains at least one impurity ion amongst SO4 2-, Cl-, Na+ or K+, the concentration of any one impurity ion in the ammonium manganese ferric phosphate being less than 500 ppm. As a precursor of lithium manganese iron phosphate, the ammonium manganese ferric phosphate of the present can endow lithium manganese iron phosphate with a relatively high compacted density, and further enable lithium manganese iron phosphate to satisfy (Fe+Mn) / P<1, and therefore using lithium manganese iron phosphate as a positive electrode material in lithium ion batteries can improve the specific capacity and cycle performance.

Description

Ammonium manganese ferrophosphate, lithium manganese ferrophosphate and their preparation methods and applications

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 18, 2023, with application number 202311199268.8 and application name “Ammonium manganese ferrophosphate, lithium manganese ferrophosphate and preparation method and application thereof”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of lithium-ion batteries, and in particular to ammonium manganese iron phosphate, lithium manganese iron phosphate, and preparation methods and applications thereof. Background Art

[0003] Compared to lithium iron phosphate (LFP), lithium manganese iron phosphate (LMP) offers comparable specific capacity but a higher voltage platform, resulting in a 20% higher energy density. Therefore, LMP, as a next-generation upgrade to LFP, has become one of the most promising cathode active materials for lithium-ion batteries. Currently, mass-produced LMP cathode materials are mostly prepared using a high-temperature solid-phase method. Due to the wide variety of raw materials, batch instability is a common problem, and solid-phase mixing struggles to achieve atomic-level mixing of Fe, Mn, and P. Therefore, LMP cathode materials are currently primarily used in the two-wheeled vehicle sector.

[0004] In addition, the co-precipitation method to synthesize lithium manganese iron phosphate precursors containing Fe, Mn, and P will become the most promising route for lithium manganese iron phosphate. However, due to the different valence states of Fe and Mn, the types of synthesized precursors are also different. Among them, Mn 3+ In aqueous solution, disproportionation reaction easily occurs to generate Mn 2+ and MnO2, resulting in Fe x Mn 1-x The synthesis difficulty of PO4 is much greater than that of FePO4. 2+ 、Mn 2+ The precursor combined with P is easy to synthesize, but because (Fe+Mn) / P>1, an additional phosphorus source must be added during preparation, and it is impossible to truly achieve atomic-level mixing of all Fe, Mn, and P. Therefore, it is necessary to develop a lithium manganese iron phosphate precursor that is easy to synthesize and can achieve higher electrical performance.

[0005] Summary of the Invention

[0006] Based on this, it is necessary to provide an ammonium manganese iron phosphate, lithium manganese iron phosphate and their preparation method and application in response to the above problems; the ammonium manganese iron phosphate is used as a precursor of lithium manganese iron phosphate, which not only makes the lithium manganese iron phosphate have a higher compaction density, but also can make the (Fe+Mn) / P in the lithium manganese iron phosphate less than 1, and then the lithium manganese iron phosphate is used as a positive electrode material for lithium-ion batteries to improve the specific capacity and cycle performance.

[0007] An ammonium manganese ferric phosphate as a precursor of lithium manganese ferric phosphate, wherein the chemical formula of the ammonium manganese ferric phosphate is (NH4) (3-2x-2y) Fe x Mn y PO4·H2O, wherein 0<x≤0.5, x+y<1, the ratio of the diffraction peak area of ​​(010) crystal plane to the diffraction peak area of ​​(121) crystal plane is less than 1.40, and the ammonium manganese ferrous phosphate does not contain SO4 2- 、Cl - 、Na + and K + Alternatively, the ammonium manganese ferric phosphate includes SO4 2- 、Cl - 、Na + or K + At least one impurity ion in the ammonium manganese ferric phosphate, the concentration of any one impurity ion in the ammonium manganese ferric phosphate is less than 500ppm.

[0008] In one embodiment, 0.5<y<0.9.

[0009] In one embodiment, the total concentration of all impurity ions in the ammonium manganese ferric phosphate is less than 1000 ppm.

[0010] In one embodiment, the ammonium manganese ferric phosphate is in the form of flakes with a particle size of D 50 Less than 20μm.

[0011] A method for preparing the above-mentioned ammonium manganese ferric phosphate comprises the following steps:

[0012] The iron-manganese mixed salt solution is reacted with the carbonate solution to separate and obtain iron-manganese carbonate;

[0013] The phosphorus source solution is mixed with the iron manganese carbonate for secondary reaction, and ammonium manganese ferrophosphate is separated. The molar amount of the phosphorus source in the phosphorus source solution is 1 to 1.5 times the total molar amount of the iron source and the manganese source in the iron manganese mixed salt solution.

[0014] In one embodiment, the iron-manganese mixed salt solution includes an iron source, a manganese source and an antioxidant, wherein the molar ratio of the iron source to the manganese source is 1:9-1:1, and the mass of the antioxidant is 0.5%-2.0% of the mass of the iron source.

[0015] In one embodiment, the iron source is selected from at least one of ferrous sulfate, ferrous chloride, and ferric acetate;

[0016] And / or, the manganese source is at least one selected from manganese sulfate, manganese chloride, and manganese acetate;

[0017] And / or, the antioxidant is at least one selected from citric acid, ascorbic acid, formaldehyde, salicylic acid, and oxalic acid.

[0018] In one embodiment, the molar amount of the carbonate is 1 to 3 times the total molar amount of the iron source and the manganese source in the iron-manganese mixed salt solution, and the carbonate is selected from at least one of ammonium bicarbonate, sodium carbonate, and potassium carbonate.

[0019] In one embodiment, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, tripotassium phosphate, and phosphoric acid, and the phosphorus source contains ammonium ions.

[0020] In one embodiment, when the phosphorus source includes at least one of trisodium phosphate, tripotassium phosphate, and phosphoric acid, the ammonium ions in the phosphorus source are derived from at least one of diammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonia water.

[0021] In one embodiment, the secondary reaction is carried out under a protective atmosphere, the reaction temperature is 20° C.-80° C., and the reaction time is within 30 hours.

[0022] A lithium iron manganese phosphate prepared from the ammonium iron manganese phosphate as described above, wherein the chemical formula of the lithium iron manganese phosphate is Li n Fe x Mn y PO4, 0<x≤0.5, x+y<1, 1≤n<1.2.

[0023] A method for preparing the lithium manganese iron phosphate as described above comprises the following steps:

[0024] An intermediate product is prepared from a lithium source, a carbon source and the ammonium manganese ferric phosphate described above;

[0025] The intermediate product is calcined in an inert atmosphere to obtain lithium manganese iron phosphate.

[0026] In one embodiment, ammonium manganese ferric phosphate, a lithium source, and a carbon source are mixed and crushed, and then spray granulated to obtain an intermediate product.

[0027] In one embodiment, the molar amount of the lithium source is 1 to 1.2 times the molar amount of phosphorus in the ammonium manganese iron phosphate, and the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate;

[0028] And / or, the mass of the carbon source is 2%-14% of the total mass of the lithium source and the ammonium manganese ferric phosphate, and the carbon source is selected from at least one of glucose, sucrose, fructose, lactose, citric acid, starch, polyvinyl pyrrolidone, polyethylene glycol, polyacrylonitrile, phenolic resin, phenylalanine, graphite, graphene, graphene oxide, and carbon nanotubes.

[0029] In one embodiment, the calcination is selected from a multi-gradient heat treatment process, which includes: in the first stage, heating to 300℃-400℃ at 0.4℃ / min-1.6℃ / min, keeping warm for less than 3 hours, and in the second stage, heating to 600℃-800℃, keeping warm for 5h-20h.

[0030] The lithium manganese iron phosphate as described above is used as a positive electrode material for a lithium ion battery.

[0031] The ammonium manganese ferrous phosphate described in the present application, on the one hand, can make (Fe+Mn) / P<1 in the lithium manganese ferrous phosphate, thereby effectively avoiding excessive manganese ions and / or iron ions from blocking the lithium ion diffusion channel, thereby reducing the impedance of the lithium ion battery and improving the specific capacity and cycle performance; on the other hand, the ratio of the (010) crystal plane diffraction peak area to the (121) crystal plane diffraction peak area is controlled to be less than 1.40, and at the same time, the impurity ion concentration in the ammonium manganese ferrous phosphate is regulated to make the ammonium manganese ferrous phosphate free of SO4 2- 、Cl - 、Na + , K + or SO4 2- 、Cl - 、Na + , K + The concentration of any impurity ion in ammonium manganese iron phosphate is less than 500 ppm, which is beneficial to significantly improve the quality of lithium manganese iron phosphate, thereby further improving the specific capacity and cycle performance of lithium-ion batteries.

[0032] In addition, the present invention uses a two-step precipitation process to first prepare a particle with good sphericity and a particle size of D 50 Manganese iron carbonate with a particle size smaller than 20 μm is precipitated with a phosphorus source in a specific proportion to convert it into ammonium manganese iron phosphate with controllable particle size. This not only helps to increase the compaction density of lithium manganese iron phosphate, but also enables a more complete reaction of Fe, Mn, and P. The reaction process does not require pH control or the addition of a chelating agent, making the operation simple.

[0033] Therefore, the ammonium manganese iron phosphate described in the present application as a precursor of lithium manganese iron phosphate not only makes the lithium manganese iron phosphate have a higher compaction density, but also can make (Fe+Mn) / P in the lithium manganese iron phosphate less than 1, and then using lithium manganese iron phosphate as a positive electrode material for lithium-ion batteries can improve the specific capacity and cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a SEM image of ammonium manganese ferric phosphate provided in Example 1 of the present application at a magnification of 2000 times;

[0035] FIG2 is an XRD pattern of ammonium manganese ferrous phosphate provided in Example 1 of the present application;

[0036] FIG3 is a SEM image of the lithium manganese iron phosphate provided in Example 1 of the present application at a magnification of 1000 times;

[0037] FIG4 is an XRD pattern of lithium iron manganese phosphate provided in Example 1 of the present application;

[0038] FIG5 is a 0.2C charge-discharge curve of a button cell prepared with lithium manganese iron phosphate as the positive electrode material provided in Example 1 of the present application;

[0039] FIG6 is a SEM image of ammonium manganese ferric phosphate provided in Comparative Example 1 of the present application at a magnification of 2000 times;

[0040] FIG7 is an XRD diagram of ammonium manganese ferrous phosphate provided in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0041] To facilitate understanding of the present application, the present application will be described in more detail below. However, it should be understood that the present application can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present application. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present application. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0043] The present application provides ammonium manganese iron phosphate as a precursor of lithium manganese iron phosphate, the chemical formula of the ammonium manganese iron phosphate is (NH4) (3-2x-2y) Fe x Mn y PO4·H2O, wherein 0<x≤0.5, x+y<1, the ratio of the diffraction peak area of ​​(010) crystal plane to the diffraction peak area of ​​(121) crystal plane is less than 1.40, and the ammonium manganese ferrous phosphate does not contain SO4 2- 、Cl - 、Na + and K + Alternatively, the ammonium manganese ferric phosphate includes SO4 2- 、Cl - 、Na + or K +At least one impurity ion in the ammonium manganese ferric phosphate, the concentration of any impurity ion in the ammonium manganese ferric phosphate is less than 500 ppm. Preferably, 0.5<y<0.9, 0.975<x+y<1, more preferably 0.55<y<0.7.

[0044] The ammonium manganese ferrous phosphate described in the present application, on the one hand, can make (Fe+Mn) / P<1 in the lithium manganese ferrous phosphate, thereby effectively avoiding excessive manganese ions and / or iron ions from blocking the lithium ion diffusion channel, thereby reducing the impedance of the lithium ion battery and improving the specific capacity and cycle performance; on the other hand, the ratio of the (010) crystal plane diffraction peak area to the (121) crystal plane diffraction peak area is controlled to be less than 1.40, and at the same time, the impurity ion concentration in the ammonium manganese ferrous phosphate is regulated to make the ammonium manganese ferrous phosphate free of SO4 2- 、Cl - 、Na + , K + or SO4 2- 、Cl - 、Na + , K + The concentration of any impurity ion in ammonium manganese iron phosphate is less than 500 ppm, which is beneficial to significantly improve the quality of lithium manganese iron phosphate, thereby further improving the specific capacity and cycle performance of lithium-ion batteries.

[0045] Preferably, the ratio of the diffraction peak area of ​​the (010) crystal plane to the diffraction peak area of ​​the (121) crystal plane is less than 1.20, which is beneficial to further improve the quality of lithium manganese iron phosphate and reduce the impact of impurities in lithium manganese iron phosphate on the electrolyte.

[0046] More preferably, the ammonium manganese ferric phosphate does not contain SO4 2- 、Cl - 、Na + and K + , which is more conducive to the production of high-quality lithium manganese iron phosphate.

[0047] When the ammonium manganese ferrophosphate includes SO4 2- 、Cl - 、Na + or K + When at least one impurity ion is present, preferably, the impurity ion SO4 2- or Cl - The concentration of impurity ions Na + or K + The concentration of the manganese phosphate is less than 200 ppm, and more preferably, the total concentration of all impurity ions in the manganese phosphate is less than 1000 ppm.

[0048] It should be noted that, due to the different types of metal salts and carbonates used in the preparation of ammonium manganese ferric phosphate, the impurity ions contained in the ammonium manganese ferric phosphate are also different.

[0049] Specifically, when the metal salt is selected from metal sulfate, the concentration of sulfate ion impurities in the ammonium manganese ferrous phosphate is less than 500 ppm; when the metal salt is selected from metal chloride, the concentration of chloride ion impurities in the ammonium manganese ferrous phosphate is less than 500 ppm; when the metal salt is selected from metal acetate, the concentration of acetate impurities in the ammonium manganese ferrous phosphate is less than 500 ppm; when the carbonate is selected from sodium carbonate, the concentration of sodium ion impurities in the ammonium manganese ferrous phosphate is less than 200 ppm; when the carbonate is selected from potassium carbonate, the concentration of potassium ion impurities in the ammonium manganese ferrous phosphate is less than 200 ppm.

[0050] As an example, the ammonium manganese ferric phosphate is in the form of flakes with a particle size of D 50 Less than 20 μm is beneficial to improving the compaction density of lithium manganese iron phosphate and thus improving the electrical performance.

[0051] The present application also provides a method for preparing the above-mentioned ammonium manganese ferrous phosphate, comprising the following steps:

[0052] S11, reacting the iron-manganese mixed salt solution with the carbonate solution to separate and obtain iron-manganese carbonate;

[0053] S12, mixing the phosphorus source solution with the iron manganese carbonate for a secondary reaction, and separating to obtain ammonium iron manganese phosphate, wherein the molar amount of the phosphorus source in the phosphorus source solution is 1 to 1.5 times the total molar amount of the iron source and the manganese source in the iron manganese mixed salt solution.

[0054] In step S11, a mixture of iron and manganese salt solution and carbonate solution is reacted once to obtain a product with good sphericity and particle size D 50 Manganese iron carbonate with a size less than 20 μm is beneficial for regulating the size of ammonium manganese iron phosphate.

[0055] Preferably, the molar amount of the carbonate is 1 to 3 times the total molar amount of the iron source and the manganese source in the iron-manganese mixed salt solution, which is conducive to the full reaction of the iron source and the manganese source to form iron-manganese carbonate.

[0056] Specifically, the carbonate is selected from soluble carbonates, more preferably at least one of ammonium bicarbonate, sodium carbonate, and potassium carbonate. When the carbonate is selected from ammonium bicarbonate, the molar amount of ammonium bicarbonate is preferably 2 to 3 times the total molar amount of the iron source and the manganese source in the iron-manganese mixed salt solution, considering that bicarbonate ions in the ammonium bicarbonate will simultaneously ionize and hydrolyze.

[0057] In one embodiment, the reaction mode of the iron-manganese mixed salt solution and the carbonate solution can be selected from the following three types: using the iron-manganese mixed salt solution as the base liquid, adding the carbonate solution under the protection of an inert gas to react for 1 hour to 10 hours to allow the reaction to proceed completely; or using water as the base liquid, adding the iron-manganese mixed salt solution and the carbonate solution at the same time, reacting for 1 hour to 10 hours to allow the reaction to proceed completely; or using the carbonate solution as the base liquid, adding the iron-manganese mixed salt solution under the protection of an inert gas to react for 1 hour to 10 hours to allow the reaction to proceed completely.

[0058] The iron-manganese mixed salt solution includes an iron source, a manganese source and an antioxidant, wherein the molar ratio of the iron source to the manganese source is 1:9-1:1, more preferably 1:2.4-1:1.2; the mass of the antioxidant is 0.5%-2.0% of the mass of the iron source, more preferably 0.5%-1.0%.

[0059] Specifically, the iron source is selected from at least one of ferrous sulfate, ferrous chloride, and ferric acetate.

[0060] The manganese source is selected from at least one of manganese sulfate, manganese chloride and manganese acetate.

[0061] The antioxidant is selected from at least one of citric acid, ascorbic acid, formaldehyde, salicylic acid and oxalic acid.

[0062] In one embodiment, the separation method after the primary reaction includes: allowing the mixed solution of the primary reaction to settle freely and removing the supernatant, thereby greatly reducing the concentration of impurity ions during the precipitation of manganese iron carbonate and reducing the amount of water used for washing, thereby facilitating the reduction of the concentration of impurity ions in the finished ammonium manganese iron phosphate, so that the concentration of impurity ions in the ammonium manganese iron phosphate is less than 1000 ppm.

[0063] In step S12, after obtaining a particle with good sphericity and particle size D 50 On the basis of manganese ferrous carbonate with particle size less than 20 μm, adding a specific proportion of phosphorus source can convert manganese ferrous carbonate precipitate into ammonium manganese ferrous phosphate with controllable particle size, that is, the morphology changes from spherical particles to flakes, while the overall particle size remains D 50 Less than 20 μm is not only beneficial to improving the compaction density of lithium manganese iron phosphate, but also can make the reaction of Fe, Mn and P more complete. The reaction process does not require pH control or the addition of chelating agents, and the operation is simple.

[0064] In one embodiment, the phosphorus source solution is preferably fed within 2 hours, which can effectively avoid problems such as enhanced crystallinity of manganese iron carbonate and incomplete precipitation conversion caused by long-term aging.

[0065] In one embodiment, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, trisodium phosphate, tripotassium phosphate, and phosphoric acid, and the phosphorus source contains ammonium ions.

[0066] Specifically, the phosphorus source can be directly selected from ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate; alternatively, when the phosphorus source includes at least one of trisodium phosphate, tripotassium phosphate, and phosphoric acid, the ammonium ions in the phosphorus source can be derived from ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate, or from ammonia water, or from a mixture of ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate and ammonia water. This application is not limited to this. Optionally, when the phosphorus source includes at least one of trisodium phosphate, tripotassium phosphate, and phosphoric acid, the phosphorus source also includes ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate, and during the secondary reaction, ammonia water is added to supplement ammonium ions for ammonium manganese iron phosphate.

[0067] In one embodiment, the secondary reaction is carried out under a protective atmosphere at a reaction temperature of 20°C-80°C, more preferably 20°C-50°C; and for a reaction time of less than 30 hours, more preferably 10 hours-15 hours. A stirring speed of 200 rpm-900 rpm is provided during the secondary reaction to ensure a more complete reaction. The protective atmosphere is selected from an inert gas, preferably at least one of nitrogen, helium, argon, and neon.

[0068] The present application also provides a lithium manganese iron phosphate prepared from the above-mentioned ammonium manganese iron phosphate, wherein the chemical formula of the lithium manganese iron phosphate is Li n Fe x Mn y PO4, 0<x≤0.5, x+y<1, 1≤n<1.2.

[0069] The ammonium manganese iron phosphate described in the present application is used as a precursor of lithium manganese iron phosphate, which not only makes the lithium manganese iron phosphate have a higher compaction density, but also can make (Fe+Mn) / P in the lithium manganese iron phosphate less than 1, thereby using the lithium manganese iron phosphate as a positive electrode material for lithium-ion batteries to improve the specific capacity and cycle performance.

[0070] The present application also provides a method for preparing the lithium manganese iron phosphate as described above, comprising the following steps:

[0071] S21, preparing an intermediate product from a lithium source, a carbon source, and the ammonium manganese ferric phosphate described above;

[0072] S22, calcining the intermediate product in an inert atmosphere to obtain lithium manganese iron phosphate.

[0073] In step S21, it is preferred to mix and crush ammonium manganese ferric phosphate, lithium source, and carbon source, and then spray granulate to obtain an intermediate product, wherein the particle size D after crushing is 50The preferred size is 0.1 μm-1 μm. According to actual product requirements, spray granulation is used to obtain an intermediate product with a certain particle size distribution, which is beneficial to the preparation of lithium manganese iron phosphate with a high compaction density.

[0074] Preferably, the molar amount of the lithium source is 1 to 1.2 times the molar amount of phosphorus in the ammonium manganese ferric phosphate, and the mass of the carbon source is preferably 2% to 14% of the total mass of the lithium source and the ammonium manganese ferric phosphate.

[0075] Specifically, the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate.

[0076] The carbon source is selected from at least one of glucose, sucrose, fructose, lactose, citric acid, starch, polyvinyl pyrrolidone, polyethylene glycol, polyacrylonitrile, phenolic resin, phenylalanine, graphite, graphene, graphene oxide, and carbon nanotubes.

[0077] In step S22, the calcination is preferably a multi-gradient heat treatment process, which includes: heating to 300-400°C at 0.4-1.6°C / min in the first stage and keeping warm for less than 3 hours; heating to 600-800°C in the second stage and keeping warm for 5-20 hours.

[0078] The lithium manganese iron phosphate described in the present application is used as a positive electrode material for lithium-ion batteries, which can make the lithium-ion batteries have excellent specific capacity and cycle performance.

[0079] Hereinafter, the ammonium manganese iron phosphate, lithium manganese iron phosphate, and their preparation methods and applications will be further described through the following specific examples.

[0080] Example 1

[0081] Take 667.25g of ferrous sulfate heptahydrate and 598.33g of manganese sulfate monohydrate to prepare an iron-manganese mixed salt solution with a concentration of 1 mol / L, where Mn 2+ with Fe 2+ The molar ratio is about 5.9:4.0; 948.68g of ammonium bicarbonate is prepared to prepare an ammonium bicarbonate solution with a concentration of 1mol / L, wherein the molar amount of ammonium bicarbonate is about 2 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 690.17g of ammonium dihydrogen phosphate is prepared to prepare an ammonium dihydrogen phosphate solution with a concentration of 1mol / L; the iron-manganese mixed salt solution is used as the base liquid, and the ammonium bicarbonate solution is passed into the reactor, and nitrogen is protected throughout the reaction. The feed is aged for 1h, and the supernatant is extracted; the remaining slurry is heated to 80°C, and the ammonium dihydrogen phosphate solution is passed. The feed is aged for 9h, solid-liquid separation and washing are carried out, and the ammonium ferric manganese phosphate powder is obtained. The main element detection and XRD analysis of the sample show that the chemical formula of the ammonium ferric manganese phosphate is (NH4)1.02 Fe 0.4 Mn 0.59 PO4·H2O, wherein the SEM image of the ammonium manganese ferric phosphate under the condition of 2000 times magnification is shown in Figure 1, and the XRD pattern is shown in Figure 2.

[0082] According to Li 1.025 Fe 0.4 Mn 0.59 Weigh ammonium manganese ferric phosphate, lithium carbonate, glucose and PEG, with glucose and PEG accounting for 5% and 7% of the total material respectively; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.4 μm, it was spray-dried to obtain D 50 The intermediate product was heat treated in a nitrogen atmosphere by heating the temperature to 370°C at 0.6°C / min, then to 650°C at 2°C / min, and then maintained at this temperature for 14 hours. Finally, the product was subjected to air flow milling to obtain a lithium manganese iron phosphate cathode material. The SEM image of the lithium manganese iron phosphate at 1000x magnification is shown in Figure 3, and the XRD pattern is shown in Figure 4.

[0083] Example 2

[0084] Take 500.44g of ferrous sulfate heptahydrate and 689.60g of manganese sulfate monohydrate to prepare an iron-manganese mixed salt solution with a concentration of 1 mol / L, where Mn 2+ with Fe 2+ The molar ratio of the reaction mixture is about 6.8:3.0; 1138.42g of ammonium bicarbonate is prepared to prepare an ammonium bicarbonate solution with a concentration of 1.2mol / L, wherein the molar amount of ammonium bicarbonate is about 2.45 times the total molar amount of the iron source and the manganese source in the iron-manganese mixed salt solution; 828.20g of ammonium dihydrogen phosphate is prepared to prepare an ammonium dihydrogen phosphate solution with a concentration of 1.2mol / L; the metal mixed salt and the ammonium bicarbonate solution are simultaneously introduced into a reactor filled with pure water, and nitrogen is passed throughout the reaction. The feed is aged for 2h, and the supernatant is extracted; the remaining slurry is heated to 70°C, and the ammonium dihydrogen phosphate solution is introduced. The feed is aged for 8h, solid-liquid separation is performed, washing is performed, and drying is performed in an oven at 75°C for 24h to obtain ammonium ferric manganese phosphate powder. The chemical formula of the ammonium ferric manganese phosphate is (NH4) according to the main element detection and XRD analysis of the sample. 1.04 Fe 0.3 Mn 0.68 PO4·H2O.

[0085] According to Li 1.026 Fe 0.3 Mn 0.68 Weigh ammonium manganese ferric phosphate, lithium carbonate and sucrose, with sucrose accounting for 10% of the total material; mix the above materials evenly and wet grind them to D 50After the particle size was reduced to 0.2 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat-treated in a nitrogen atmosphere, the temperature is increased to 380° C. at 0.7° C. / min, the temperature is kept for 1 hour, the temperature is then increased to 670° C. at 2° C. / min, the temperature is kept for 14 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0086] Example 3

[0087] Take 333.63g of ferrous sulfate heptahydrate and 780.87g of manganese sulfate monohydrate to prepare a 1mol / L iron-manganese mixed salt solution, where Mn 2+ with Fe 2+ The molar ratio of is about 7.7:2.0; 1233.30g of ammonium bicarbonate is taken to prepare an ammonium bicarbonate solution with a concentration of 1.3mol / L, wherein the molar amount of ammonium bicarbonate is about 2.68 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 897.22g of ammonium dihydrogen phosphate is taken to prepare an ammonium dihydrogen phosphate solution with a concentration of 1.3mol / L; the ammonium bicarbonate solution is used as the base liquid, and the iron-manganese mixed salt solution is passed into the reactor, and nitrogen protection is passed throughout the reaction. The feed is aged for 3h, and the supernatant is extracted; the remaining slurry is heated to 60°C, and the ammonium dihydrogen phosphate solution is passed. The feed is aged for 7h, solid-liquid separation and washing are carried out, and the ammonium ferric manganese phosphate powder is obtained. The main element detection and XRD analysis of the sample show that the chemical formula of the ammonium ferric manganese phosphate is (NH4) 1.06 Fe 0.2 Mn 0.77 PO4·H2O.

[0088] According to Li 1.027 Fe 0.2 Mn 0.77 Weigh ammonium manganese ferric phosphate, lithium carbonate, glucose and PVP, with glucose and PVP accounting for 6% and 4% of the total materials respectively; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.3 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat-treated in a nitrogen atmosphere, the temperature is increased to 390° C. at 0.8° C. / min, the temperature is kept for 1.5 hours, the temperature is then increased to 690° C. at 3° C. / min, the temperature is kept for 12 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0089] Example 4

[0090] Take 166.81g of ferrous sulfate heptahydrate and 872.14g of manganese sulfate monohydrate to prepare a 1mol / L iron-manganese mixed salt solution, where Mn 2+ with Fe2+ The molar ratio of is about 8.6:1.0; 1138.42g of ammonium bicarbonate is taken to prepare an ammonium bicarbonate solution with a concentration of 1.2mol / L, wherein the molar amount of ammonium bicarbonate is about 2.5 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 897.22g of ammonium dihydrogen phosphate is taken to prepare an ammonium dihydrogen phosphate solution with a concentration of 1.3mol / L; the iron-manganese mixed salt solution is used as the base liquid, and the ammonium bicarbonate solution is passed into the reactor, and nitrogen protection is passed throughout the reaction. The feed is aged for 4h, and the supernatant is extracted; the remaining slurry is heated to 50°C, and the ammonium dihydrogen phosphate solution is passed. The feed is aged for 6h, solid-liquid separation and washing are carried out, and the ammonium ferric manganese phosphate powder is obtained. The main element detection and XRD analysis of the sample show that the chemical formula of the ammonium ferric manganese phosphate is (NH4) 1.08 Fe 0.1 Mn 0.86 PO4·H2O.

[0091] According to Li 1.028 Fe 0.1 Mn 0.86 Weigh ammonium manganese ferric phosphate, lithium carbonate, and PEG, with PEG accounting for 7.5% of the total material; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.4 μm, it was spray-dried to obtain D 50 The intermediate product is 3μm-15μm; the intermediate product is heat treated in a nitrogen atmosphere, the temperature is increased to 400°C at 1°C / min, and then the temperature is increased to 700°C at 4°C / min, and the temperature is kept for 10 hours. Finally, the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0092] Example 5

[0093] Take 834.06g of ferrous sulfate heptahydrate and 507.06g of manganese sulfate monohydrate to prepare an iron-manganese mixed salt solution with a concentration of 1 mol / L, where Mn 2+ with Fe 2+ The molar ratio of the reaction mixture is about 4.9:5.0; 1138.42g of ammonium bicarbonate is taken to prepare an ammonium bicarbonate solution with a concentration of 1.2mol / L, wherein the molar amount of ammonium bicarbonate is about 2.4 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 966.24g of ammonium dihydrogen phosphate is taken to prepare an ammonium dihydrogen phosphate solution with a concentration of 1.4mol / L; the iron-manganese mixed salt solution is used as the base liquid, and the ammonium bicarbonate solution is passed into the reactor, and nitrogen is protected throughout the reaction. The feed is aged for 1h, and the supernatant is extracted; the remaining slurry is heated to 40°C, and the ammonium dihydrogen phosphate solution is passed into the reactor. The feed is aged for 5h, solid-liquid separation is performed, washing is performed, and the ammonium ferric manganese phosphate powder is obtained. The main element detection and XRD analysis of the sample show that the chemical formula of the ammonium ferric manganese phosphate is (NH4)1.02 Fe 0.5 Mn 0.49 PO4·H2O.

[0094] According to Li 1.030 Fe 0.5 Mn 0.49 Weigh ammonium manganese ferrophosphate, lithium carbonate, and PVP, with PVP accounting for 5.50% of the total material; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.5 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat-treated in a nitrogen atmosphere, the temperature is increased to 400°C at 1.2°C / min, the temperature is kept for 1 hour, the temperature is then increased to 710°C at 5°C / min, the temperature is kept for 9 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0095] Example 6

[0096] Take 477.14g of ferrous chloride tetrahydrate and 700.60g of manganese chloride tetrahydrate to prepare an iron-manganese mixed salt solution with a concentration of 1 mol / L, where Mn 2+ with Fe 2+ The molar ratio of the reaction mixture is about 5.9:4.0; 635.94g of sodium carbonate is prepared to prepare a sodium carbonate solution with a concentration of 1mol / L, wherein the molar amount of sodium carbonate is about 1.14 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 792.36g of diammonium hydrogen phosphate is prepared to prepare a diammonium hydrogen phosphate solution with a concentration of 1mol / L; the iron-manganese mixed salt solution is used as the base liquid, and the sodium carbonate solution is passed into the reactor. The reaction is protected by nitrogen throughout the process. The feed is aged for 2h and the supernatant is extracted; the remaining slurry is heated to 30°C, and the diammonium hydrogen phosphate solution is passed. The feed is aged for 6h, solid-liquid separation and washing are performed, and the powder is dried in an oven at 75°C for 24h to obtain ammonium ferric manganese phosphate powder. The chemical formula of the ammonium ferric manganese phosphate is (NH4) according to the main element detection and XRD analysis of the sample. 1.02 Fe 0.4 Mn 0.59 PO4·H2O.

[0097] According to Li 1.031 Fe 0.4 Mn 0.59 Weigh ammonium manganese ferric phosphate, lithium carbonate, glucose and PEG, with glucose and PEG accounting for 5% and 7% of the total material respectively; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.6 μm, it was spray-dried to obtain D 50The intermediate product is 3 μm-15 μm in size; the intermediate product is heat treated in a nitrogen atmosphere, the temperature is increased to 370° C. at a rate of 0.6° C. / min, and then the temperature is increased to 650° C. at a rate of 2° C. / min, and the heat is maintained for 14 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0098] Example 7

[0099] Take 417.43g of ferric acetate monohydrate and 867.62g of manganese acetate tetrahydrate to prepare a 1mol / L iron-manganese mixed salt solution, where Mn 2+ with Fe 2+ The molar ratio is about 5.9:4.0; 995.11g of potassium carbonate is prepared into a potassium carbonate solution with a concentration of 1.2mol / L, wherein the molar amount of potassium carbonate is about 1.26 times the total molar amount of the iron source and the manganese source in the iron-manganese mixed salt solution; 2736.86g of trisodium phosphate dodecahydrate is prepared into a trisodium phosphate solution with a concentration of 1.2mol / L, and 6mol of ammonia water is added and mixed evenly; the iron-manganese mixed salt solution is used as the base liquid, and the potassium carbonate solution is passed into the reactor, and nitrogen is protected throughout the reaction. The feed is aged for 2h, and the supernatant is extracted; the remaining slurry is kept warm to 20°C, and trisodium phosphate solution is passed into the feed. The feed is aged for 6h, solid-liquid separation and washing are carried out, and the ammonium manganese ferrous phosphate powder is obtained. The main element detection and XRD analysis of the sample show that the chemical formula of the ammonium manganese ferrous phosphate is (NH4) 1.02 Fe 0.4 Mn 0.59 PO4·H2O.

[0100] According to Li 1.032 Fe 0.4 Mn 0.59 Weigh ammonium manganese ferric phosphate, lithium carbonate and sucrose, with sucrose accounting for 10% of the total material; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.7 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat-treated in a nitrogen atmosphere, the temperature is increased to 380° C. at 0.7° C. / min, the temperature is kept for 1 hour, the temperature is then increased to 650° C. at 2° C. / min, the temperature is kept for 14 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0101] Example 8

[0102] Take 667.25g of ferrous sulfate heptahydrate and 598.33g of manganese sulfate monohydrate to prepare an iron-manganese mixed salt solution with a concentration of 1 mol / L, where Mn 2+ with Fe 2+The molar ratio is about 5.9:4.0; 1078.01g of potassium carbonate is prepared to prepare a potassium carbonate solution with a concentration of 1.3mol / L, wherein the molar amount of potassium carbonate is about 1.31 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 2077.30g of tripotassium phosphate trihydrate is prepared to prepare a tripotassium phosphate solution with a concentration of 1.3mol / L, and 6mol of ammonia water is added and mixed evenly; the iron-manganese mixed salt solution is used as the base liquid, and the potassium carbonate solution is passed into the reactor, and nitrogen protection is passed throughout the reaction. The feed is aged for 2h, and the supernatant is extracted; the remaining slurry is heated to 30°C, and the tripotassium phosphate solution is passed, and the feed is aged for 6h, solid-liquid separation and washing are carried out, and it is dried in a 75°C oven for 24h to obtain ammonium manganese ferrous phosphate powder. The chemical formula of the ammonium manganese ferrous phosphate is (NH4) through main element detection and XRD analysis of the sample. 1.02 Fe 0.4 Mn 0.59 PO4·H2O.

[0103] According to Li 1.033 Fe 0.4 Mn 0.59 Weigh ammonium manganese ferric phosphate, lithium carbonate, glucose and PVP, with glucose and PVP accounting for 6% and 4% of the total materials respectively; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.8 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat-treated in a nitrogen atmosphere, the temperature is increased to 390° C. at 0.8° C. / min, the temperature is kept for 1.5 hours, the temperature is then increased to 670° C. at 3° C. / min, the temperature is kept for 12 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0104] Example 9

[0105] Take 477.14g of ferrous chloride tetrahydrate and 700.60g of manganese chloride tetrahydrate to prepare an iron-manganese mixed salt solution with a concentration of 1 mol / L, where Mn 2+ with Fe 2+The molar ratio is about 5.9:4.0; 995.11g of potassium carbonate is prepared into a potassium carbonate solution with a concentration of 1.2mol / L, wherein the molar amount of potassium carbonate is about 1.37 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 451.60ml of phosphoric acid is prepared into a phosphoric acid solution with a concentration of 1.1mol / L, and 6mol of ammonia water is added and mixed evenly; the iron-manganese mixed salt solution is used as the base liquid, and the potassium carbonate solution is passed into the reactor, and nitrogen is protected throughout the reaction. The feed is aged for 2h, and the supernatant is extracted; the remaining slurry is heated to 40°C, and the phosphoric acid solution is passed, and the feed is aged for 6h, solid-liquid separation and washing are carried out, and the ammonium manganese ferrous phosphate powder is obtained. The main element detection and XRD analysis of the sample show that the chemical formula of the ammonium manganese ferrous phosphate is (NH4) 1.02 Fe 0.4 Mn 0.59 PO4·H2O.

[0106] According to Li 1.0 Fe 0.4 Mn 0.59 Weigh ammonium manganese ferric phosphate, lithium carbonate, and PEG, with PEG accounting for 7.50% of the total material; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.9 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat-treated in a nitrogen atmosphere, the temperature is increased to 400° C. at 1° C. / min, and then the temperature is increased to 670° C. at 4° C. / min, and the heat is maintained for 10 hours. Finally, the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0107] Example 10

[0108] Take 417.43g of ferric acetate monohydrate and 867.62g of manganese acetate tetrahydrate to prepare a 1mol / L iron-manganese mixed salt solution, where Mn 2+ with Fe 2+ The molar ratio of is about 5.9:4.0; 763.13g of sodium carbonate is prepared to prepare a sodium carbonate solution with a concentration of 1.2mol / L, wherein the molar amount of sodium carbonate is about 1.18 times the total molar amount of the iron source and manganese source in the iron-manganese mixed salt solution; 966.24 of ammonium dihydrogen phosphate is prepared to prepare a diammonium phosphate solution with a concentration of 1.4mol / L; the iron-manganese mixed salt solution is used as the base liquid, and the sodium carbonate solution is passed into the reactor, and nitrogen is protected throughout the reaction. The feed is aged for 2h, and the supernatant is extracted; the remaining slurry is heated to 50°C, and the diammonium dihydrogen phosphate solution is passed. The feed is aged for 6h, solid-liquid separation and washing are carried out, and the ammonium ferric manganese phosphate powder is obtained. The main element detection and XRD analysis of the sample show that the chemical formula of the ammonium ferric manganese phosphate is (NH4) 1.02 Fe0.4 Mn 0.59 PO4·H2O.

[0109] According to Li 1.19 Fe 0.4 Mn 0.59 Weigh ammonium manganese ferrophosphate, lithium carbonate, and PVP, with PVP accounting for 5.50% of the total material; mix the above materials evenly and wet grind them to D 50 After the particles were reduced to 1 μm, they were spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat-treated in a nitrogen atmosphere, the temperature is increased to 400°C at 1.2°C / min, the temperature is kept for 1 hour, the temperature is then increased to 690°C at 5°C / min, the temperature is kept for 9 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0110] Comparative Example 1

[0111] An iron-manganese mixed salt solution and an ammonium dihydrogen phosphate solution were prepared in the same ratio as in Example 1; 8 L of pure water was added to the reactor as a base liquid, and the iron-manganese mixed salt solution, ammonium dihydrogen phosphate, and 10 mol / L of alkali were simultaneously fed into the reactor. Nitrogen was passed throughout the reaction process to protect the reaction, and the pH of the reaction process was controlled to be 5-7 and the temperature was 60 ° C. After the feeding was completed, the mixture was aged for 9 h, solid-liquid separation was performed, washing was performed, and the mixture was dried in an oven at 75 ° C for 24 h to obtain ammonium manganese ferrous phosphate powder. The chemical formula of the ammonium manganese ferrous phosphate was NH4Fe by main element detection and XRD analysis of the sample. 0.4 Mn 0.60 PO4·H2O. The SEM image of the ammonium manganese ferric phosphate at a magnification of 2000 times is shown in FIG6 , and the XRD pattern is shown in FIG7 .

[0112] According to Li 1.030 Fe 0.4 Mn 0.60 Weigh ammonium manganese ferric phosphate, lithium carbonate, glucose and PEG, with glucose and PEG accounting for 5% and 7% of the total material respectively; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.4 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat treated in a nitrogen atmosphere, the temperature is increased to 370° C. at a rate of 0.6° C. / min, and then the temperature is increased to 650° C. at a rate of 2° C. / min, and the heat is maintained for 14 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0113] Comparative Example 2

[0114] An iron-manganese mixed salt solution was prepared using the same ratio as in Example 1; 451.60 ml of phosphoric acid was used to prepare a phosphoric acid solution with a concentration of 1.1 mol / L; 8 L of pure water was added to the reactor as a base liquid, and the prepared iron-manganese mixed salt solution, phosphoric acid, and 5 mol / L ammonia water were simultaneously fed into the reactor. Nitrogen was passed throughout the reaction process to protect the reaction, and the pH of the reaction process was controlled to be 5-7 and the temperature was 60 ° C. After the feeding was completed, the mixture was aged for 9 h, solid-liquid separation was performed, washing was performed, and the mixture was dried in an oven at 75 ° C for 24 h to obtain ammonium manganese ferrous phosphate powder. The chemical formula of the ammonium manganese ferrous phosphate was NH4Fe by main element detection and XRD analysis of the sample. 0.4 Mn 0.60 PO4·H2O.

[0115] According to Li 1.030 Fe 0.4 Mn 0.60 Weigh ammonium manganese ferric phosphate, lithium carbonate, glucose and PEG, with glucose and PEG accounting for 5% and 7% of the total material respectively; mix the above materials evenly and wet grind them to D 50 After the particle size was reduced to 0.4 μm, it was spray-dried to obtain D 50 The intermediate product is 3 μm-15 μm in size; the intermediate product is heat treated in a nitrogen atmosphere, the temperature is increased to 370° C. at a rate of 0.6° C. / min, and then the temperature is increased to 650° C. at a rate of 2° C. / min, and the heat is maintained for 14 hours, and finally the lithium manganese iron phosphate positive electrode material is obtained by air flow pulverization.

[0116] The ammonium manganese ferric phosphate provided by Example 1-10 and Comparative Example 1-2 were subjected to XRD, SEM, impurity ion detection, and particle size detection, respectively. The results are shown in Table 1.

[0117] Table 1

[0118] The electrochemical performance of the lithium manganese iron phosphate positive electrode materials provided in Examples 1-10 and Comparative Examples 1-2 was tested, and the results are shown in Table 2.

[0119] Table 2

[0120] Combining Table 1 and Table 2 and Figure 5, it can be seen that compared with Comparative Examples 1 and 2, the D of the ammonium manganese ferric phosphate provided in Examples 1 to 8 and 10 of the present application is 50 Less than 15μm, impurity ions SO4 2- or Cl - The concentration of impurity ions Na + or K +The concentration is less than about 200ppm, (Fe+Mn) / P<1, the small particle size can effectively improve the sand milling efficiency, the impurity ion concentration is low, and these soluble impurity ions can be prevented from dissolving in the electrolyte, thereby affecting the capacity. The molar amount of phosphorus is greater than the sum of the molar amounts of iron and manganese metal ions, which is beneficial to avoid excessive manganese ions and / or iron ions blocking the lithium ion diffusion channel and reducing impedance. Therefore, the manganese iron phosphate lithium positive electrode material prepared using the manganese iron ammonium phosphate provided in Examples 1 to 8 and 10 as a precursor has a higher compaction density, specific capacity and cycle performance. In particular, Example 9 was found to have Cl - and K + The concentration is basically 0. Compared with Examples 1-8 and Example 10, the lithium manganese iron phosphate positive electrode material prepared using the ammonium manganese iron phosphate provided in Example 9 as a precursor has a higher compaction density and excellent specific capacity and cycle performance.

[0121] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0122] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. Ammonium manganese iron phosphate as a precursor of lithium manganese iron phosphate, wherein: The chemical formula of the ammonium manganese ferric phosphate is (NH4) (3-2x-2y) Fe x Mn y PO4·H2O, wherein 0<x≤0.5, x+y<1, the ratio of the diffraction peak area of ​​(010) crystal plane to the diffraction peak area of ​​(121) crystal plane is less than 1.40, and the ammonium manganese iron phosphate does not contain SO4 2- , Cl - 、Na + and K + Alternatively, the ammonium manganese ferrophosphate includes SO4 2- , Cl - 、Na + or K + At least one impurity ion in the ammonium manganese ferric phosphate, and the concentration of any impurity ion in the ammonium manganese ferric phosphate is less than 500ppm.

2. Ammonium ferric manganese phosphate according to claim 1, wherein 0.5＜y＜0.9。 3. Ammonium ferric manganese phosphate according to claim 1, wherein The total concentration of all impurity ions in the ammonium manganese ferric phosphate is less than 1000 ppm.

4. The ammonium manganese ferric phosphate according to any one of claims 1 to 3, wherein The ammonium manganese ferric phosphate is in the form of flakes with a particle size of D 50 Less than 20μm.

5. A method for preparing ammonium manganese ferric phosphate according to any one of claims 1 to 4, wherein: The steps include: The iron-manganese mixed salt solution is reacted with the carbonate solution to separate iron-manganese carbonate; The phosphorus source solution is mixed with the iron manganese carbonate for secondary reaction, and ammonium iron manganese phosphate is separated. The molar amount of the phosphorus source in the phosphorus source solution is 1 to 1.5 times the total molar amount of the iron source and the manganese source in the iron manganese mixed salt solution.

6. The method for preparing ammonium ferric manganese phosphate according to claim 5, wherein: The iron-manganese mixed salt solution comprises an iron source, a manganese source and an antioxidant, wherein the molar ratio of the iron source to the manganese source is 1:9-1:1, and the mass of the antioxidant is 0.5%-2.0% of the mass of the iron source.

7. The method for preparing ammonium ferric manganese phosphate according to claim 6, wherein: The iron source is selected from at least one of ferrous sulfate, ferrous chloride and ferrous acetate; And / or, the manganese source is at least one selected from manganese sulfate, manganese chloride, and manganese acetate; And / or, the antioxidant is selected from at least one of citric acid, ascorbic acid, formaldehyde, salicylic acid and oxalic acid.

8. The method for preparing ammonium ferromanganese phosphate according to claim 5, wherein: The molar amount of the carbonate is 1 to 3 times the total molar amount of the iron source and the manganese source in the iron-manganese mixed salt solution, and the carbonate is selected from at least one of ammonium bicarbonate, sodium carbonate, and potassium carbonate.

9. The method for preparing ammonium ferromanganese phosphate according to claim 5, wherein: The phosphorus source is selected from at least one of diammonium phosphate, diammonium phosphate, trisodium phosphate, tripotassium phosphate, and phosphoric acid, and the phosphorus source contains ammonium ions.

10. The method for preparing ammonium ferric manganese phosphate according to claim 9, wherein: When the phosphorus source includes at least one of trisodium phosphate, tripotassium phosphate, and phosphoric acid, the ammonium ions in the phosphorus source are derived from at least one of diammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonia water.

11. The method for preparing ammonium ferric manganese phosphate according to claim 5, wherein: The secondary reaction is carried out under a protective atmosphere, the reaction temperature is 20° C.-80° C., and the reaction time is within 30 hours.

12. A lithium manganese iron phosphate prepared from the ammonium manganese iron phosphate according to any one of claims 1 to 4, wherein: The chemical formula of the lithium manganese iron phosphate is Li n Fe x Mn y PO4, 0<x≤0.5, x+y<1, 1≤n<1.

2.

13. A method for preparing lithium manganese iron phosphate as claimed in claim 12, wherein: The steps include: An intermediate product is prepared from a lithium source, a carbon source and the ammonium manganese iron phosphate according to any one of claims 1 to 5; The intermediate product is calcined in an inert atmosphere to obtain lithium manganese iron phosphate.

14. The method for preparing lithium manganese iron phosphate according to claim 13, wherein: The ammonium manganese ferric phosphate, lithium source and carbon source are mixed and crushed and then spray granulated to obtain an intermediate product.

15. The method for preparing lithium manganese iron phosphate according to claim 13 or claim 14, wherein: The molar amount of the lithium source is 1 to 1.2 times the molar amount of phosphorus in the ammonium manganese iron phosphate, and the lithium source is selected from at least one of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate; And / or, the mass of the carbon source is 2%-14% of the total mass of the lithium source and the ammonium manganese ferric phosphate, and the carbon source is selected from at least one of glucose, sucrose, fructose, lactose, citric acid, starch, polyvinyl pyrrolidone, polyethylene glycol, polyacrylonitrile, phenolic resin, phenylalanine, graphite, graphene, graphene oxide, and carbon nanotubes.

16. The method for preparing lithium manganese iron phosphate according to claim 13, wherein: The calcination is selected from a multi-gradient heat treatment process, which includes: in the first stage, the temperature is increased to 300°C-400°C at 0.4°C / min-1.6°C / min, and the temperature is kept for less than 3 hours; in the second stage, the temperature is increased to 600°C-800°C, and the temperature is kept for 5h-20h.

17. The lithium iron manganese phosphate as claimed in claim 12 is used as a positive electrode material for a lithium ion battery.

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