Preparation and application of lithium iron manganese phosphate material and its ferrous manganese phosphate precursor

Abstract

The application belongs to the field of positive electrode materials, and particularly relates to a preparation method of a ferromanganese phosphate precursor. A ferrous source, a manganese source and a phosphate source are subjected to a precipitation reaction to obtain a ferromanganese phosphate precipitate. The ferromanganese phosphate precipitate is subjected to a micro-oxidation treatment in an oxygen-containing atmosphere in advance, and then the micro-oxidation product is subjected to a carbon thermal reduction to obtain the ferromanganese phosphate precursor. The application further includes a method for preparing a lithium manganese iron phosphate active material from the precursor and an application. The process can effectively remove anions in the bulk phase, optimize the physical and chemical structure, and further improve the performance of the material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, specifically relating to the preparation of lithium iron manganese phosphate materials. Technical Background

[0002] With its advantages of low cost, long lifespan, and high stability, lithium iron phosphate (LFP) batteries have surpassed ternary lithium batteries in shipments since 2021, gaining market favor and occupying an increasing share of the lithium-ion battery cathode material market. However, LFP cathode materials have relatively low discharge voltage, and their discharge specific capacity is already close to the theoretical discharge capacity, meaning their energy density is approaching the theoretical limit. As an upgraded alternative, lithium manganese iron phosphate (LFP) cathode materials can significantly improve battery energy density compared to LFP, possessing great potential to replace LFP cathode materials. Among these methods, co-precipitation is the most commonly used method in the industry for preparing cathode material precursors.

[0003] For example, Chinese patent document CN102623699A discloses a method for synthesizing high-performance lithium iron phosphate, which includes the following steps: weighing lithium source, iron salt, and phosphate according to the elemental molar ratio Li:Fe:P = 1:1:1, weighing carbon source according to the elemental molar ratio Li:C greater than 1:1, crushing and uniformly stirring the mixture, heating it in a non-air or non-oxidizing atmosphere, calcining it at a constant temperature of 500-1000℃ for 1-100 hours, cooling it, and obtaining lithium iron phosphate powder.

[0004] For example, Chinese patent document CN1 15231543A discloses a method for preparing multi-carbon coated high-density lithium manganese iron phosphate, including the following steps: (1) mixing iron source, manganese source, phosphorus source, carbon source and additives, and synthesizing carbon and vanadium co-doped iron manganese phosphate precursor by co-precipitation method; sintering the obtained iron manganese phosphate precursor, removing all crystal water to obtain anhydrous iron manganese phosphate precursor; (2) adding lithium phosphate, supplementary phosphorus source, organic carbon source, dopant and deionized water to the anhydrous iron manganese phosphate precursor obtained in step (1), and then ball milling, wet sand milling, spray drying and sintering to obtain intermediate product; (3) adding deionized water and organic carbon source to the intermediate product obtained in step (2), and then ball milling, sand milling, spray drying, sintering and air jet pulverization to finally obtain the multi-carbon coated high-density lithium manganese iron phosphate material.

[0005] In summary, although the precipitation method is simple to operate, it faces problems such as metal ion oxidation during precipitation, washing and drying leading to component segregation, large washing wastewater volume and high impurity anion content, resulting in poor rate performance of the synthesized lithium manganese iron phosphate. Summary of the Invention

[0006] To address the problems of component segregation, high anionic impurity content, and unsatisfactory fast-charging performance encountered in the preparation of ferrous manganese phosphate precursors by existing precipitation methods, this invention provides a novel method for preparing ferrous manganese phosphate precursors (also known as manganese iron phosphate precursors or simply precursors), aiming to solve the problems of component segregation and high anionic impurity content.

[0007] The second objective of this invention is to provide a method for preparing lithium manganese iron phosphate materials using the prepared ferrous manganese phosphate precursor.

[0008] The third objective of this invention is to provide the lithium manganese iron phosphate material prepared by the aforementioned method and its application in lithium-ion batteries.

[0009] The fourth objective of this invention is to provide a lithium-ion battery comprising the prepared lithium manganese iron phosphate material, as well as its positive electrode and positive electrode material.

[0010] To obtain the ferrous manganese phosphate precursor, the main approach in the industry is precipitation in a protective atmosphere. This method can avoid the oxidation of ferrous iron to some extent, but it increases the difficulty of operation and the cost of equipment investment. Furthermore, the inventors have found that the product prepared by precipitation has a high content of anionic impurities. The presence of these impurities affects the rate performance of the material; however, existing technologies pay little attention to the problem of anionic impurities. Although cleaning processes can reduce the impurity content to some extent, it is difficult to remove anionic impurities trapped in the bulk phase and product, and it is also difficult to fundamentally solve the problem of component segregation. To address this problem, the present invention, after in-depth research, provides the following improved solution:

[0011] The method for preparing ferrous manganese phosphate precursor involves subjecting ferrous, manganese and phosphate sources to a precipitation reaction to obtain ferrous manganese phosphate precipitate. The ferrous manganese phosphate precipitate is then subjected to micro-oxidation treatment in an oxygen-containing atmosphere, followed by carbothermic reduction of the micro-oxidation product to obtain the ferrous manganese phosphate precursor.

[0012] For the preparation of ferrous manganese phosphate precursors, the industry's conventional understanding focuses on preventing oxidation, primarily through precipitation in a protective atmosphere. However, this invention breaks with this conventional understanding, providing a seemingly contradictory new approach. It innovatively performs micro-oxidation treatment on ferrous manganese phosphate precipitate in an oxygen-containing atmosphere. This effectively improves the material's microstructure and significantly reduces anionic impurities in the bulk phase. Further carbothermic reduction of these impurities synergistically modifies the material's physicochemical structure, reduces component segregation, and achieves limited hybridization, thereby significantly improving the performance of the prepared material, particularly its fast-charging performance.

[0013] In this invention, the ferrous source is a water-soluble ferrous salt; more specifically, it is at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0014] In this invention, the manganese source is a water-soluble divalent manganese salt, preferably at least one of manganese sulfate, manganese nitrite, and manganese chloride;

[0015] In this invention, the phosphate source is at least one of phosphoric acid, monoammonium dihydrogen phosphate, diammonium monohydrogen phosphate, and ammonium phosphate.

[0016] In this invention, the molar percentage of Mn / (Fe+Mn) in the ferrous and manganese sources is 55-90%, and more specifically 60-80%.

[0017] In this invention, the amount of phosphate source used is not less than the theoretical molar amount of the reaction, for example, it can be 1.1 to 2 times the theoretical molar amount.

[0018] In this invention, an alkaline component is also added to the precipitation reaction system;

[0019] In this invention, the pH during the precipitation reaction stage is 5.0–8.0, more preferably 6.5–7.2, and even more preferably 6.8–7.2. Under these conditions, in conjunction with the process described in this invention, it helps to further synergistically improve the anion content in the crystal lattice of the prepared material, and helps to improve the initial efficiency and overall performance of the final material.

[0020] In this invention, the precipitation reaction does not need to be carried out in a protective atmosphere; for example, it can be carried out in an air atmosphere.

[0021] In this invention, the obtained precipitate is innovatively micro-oxidized in an oxygen-containing atmosphere, which can reduce anionic impurities in the bulk phase of the material and help to combine with other processes to synergistically improve the fast-charging performance of the material.

[0022] In this invention, the oxygen-containing atmosphere includes at least one of air and oxygen.

[0023] In this invention, the oxygen-containing atmosphere may also contain a dilution gas, which includes at least one of nitrogen and an inert gas.

[0024] Preferably, the temperature of the micro-oxidation stage is 300–700°C;

[0025] Preferably, the micro-oxidation stage includes two gradient holding processes, wherein the first micro-oxidation holding temperature is 350–500℃, preferably 380–470℃; and the second micro-oxidation holding temperature is 500–650℃, preferably 530–620℃. This invention demonstrates that using the preferred process can further optimize the material structure, further improve the bulk anion removal effect, and also help improve its rate performance.

[0026] In this invention, the micro-oxidation time is 2–20 h;

[0027] In this invention, the micro-oxidation stage is a two-stage gradient heat preservation process, wherein the first stage of micro-oxidation heat preservation time is 1 to 4 hours, and the second stage of micro-oxidation heat preservation time is 1 to 4 hours.

[0028] In this invention, the micro-oxidized material is subjected to subsequent carbothermic reduction, which reduces high-valence elements such as iron to divalent states. In addition, it can achieve limited carbon hybridization, improve lattice and element segregation problems, and further synergistically improve the fast-charging performance of the prepared material.

[0029] In this invention, micro-oxidation products and carbon sources are mixed and heated to achieve carbothermic reduction;

[0030] In this invention, the carbon source includes an organic carbon source, and further includes at least one of starch, glucose, citric acid, PEG, β-cyclodextrin, and sucrose;

[0031] In this invention, the carbon source is 0.3-5% of the weight of the micro-oxidation product, and more preferably 1-3%;

[0032] In this invention, the atmosphere during the carbothermic reduction stage is a protective atmosphere;

[0033] Preferably, the atmosphere in the carbothermic reduction stage also includes a reducing atmosphere;

[0034] In this invention, the temperature of carbothermic reduction is 350–600°C, preferably 400–500°C;

[0035] In this invention, the carbothermic reduction time is 1 to 4 hours.

[0036] The present invention also provides a ferrous manganese phosphate precursor prepared by the preparation method described above.

[0037] In this invention, the required active material can be prepared from the ferrous manganese phosphate precursor described herein using conventional methods.

[0038] For example, the present invention also provides a method for preparing the lithium iron manganese phosphate material, wherein a ferrous manganese phosphate precursor is prepared by the preparation method of the present invention, and then mixed with a lithium source and a coated carbon source and calcined to obtain the material.

[0039] In this invention, the lithium source includes at least one of lithium carbonate, lithium phosphate, and lithium dihydrogen phosphate;

[0040] In this invention, the carbon source used for coating is at least one selected from starch, glucose, citric acid, β-cyclodextrin, sucrose, and PEG.

[0041] In this invention, the coated carbon source is 5% to 15% of the weight of the ferrous manganese phosphate precursor.

[0042] In this invention, the calcination temperature is 300–900°C, preferably 650–800°C;

[0043] In this invention, the calcination time is 4 to 12 hours.

[0044] The present invention also provides a lithium iron manganese phosphate material prepared by the preparation method described above.

[0045] In this invention, the preparation method can endow the prepared lithium iron manganese phosphate material with special physicochemical characteristics, and the material with the characteristics obtained by the preparation method also has excellent electrochemical performance, especially fast charging performance.

[0046] The present invention also provides a positive electrode material for lithium-ion batteries, comprising a positive electrode active material, a binder and a conductive agent, wherein the positive electrode active material comprises the lithium iron manganese phosphate material described in the present invention.

[0047] The cathode material described in this invention, apart from the lithium iron manganese phosphate material prepared by the method of this invention, can have its other components and contents obtained and controlled based on conventional principles.

[0048] The present invention also provides a positive electrode for lithium-ion batteries, comprising a current collector and a positive electrode material composited thereon, wherein the positive electrode material is the positive electrode material described in the present invention.

[0049] The present invention also provides a lithium-ion battery comprising the positive electrode described herein.

[0050] Beneficial effects

[0051] This invention innovatively involves micro-oxidizing ferrous manganese phosphate precipitate in an oxygen-containing atmosphere and then further reducing it with carbothermal reduction. This process can synergistically and significantly reduce anionic impurities in the bulk phase, optimize the lattice and compositional uniformity, and thus significantly improve the performance of the prepared material, especially its fast-charging performance. Attached Figure Description

[0052] Figure 1 This is a SEM image of the iron manganese phosphate precursor prepared in Example 1.

[0053] Figure 2 The image shows the XRD pattern of the manganese ferrous phosphate precursor prepared in Example 1.

[0054] Figure 3 The image shows the XRD pattern of lithium manganese iron phosphate prepared in Example 1.

[0055] Figure 4 This is a rate-capacity graph of lithium manganese iron phosphate prepared in Example 1.

[0056] Figure 5 This is a cycle diagram of the lithium manganese iron phosphate prepared in Example 1.

[0057] Figure 6 The diagram shows a comparison of the sulfur content in the precursors obtained in Example 1 and Comparative Example 1. The sulfur content of the dried filter cake refers to the material obtained in step 1 of Example 1. The sulfur content of Example 1 and Comparative Example 1 refers to the sulfur content of the iron phosphate precursors obtained. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0059] The present invention provides an optional method for preparing lithium manganese iron phosphate, comprising the following steps:

[0060] Step (1): Weigh out a certain ratio of ferrous salt and manganese salt, add deionized water, and mix thoroughly to obtain solution A with a certain molar concentration; weigh out the corresponding phosphate salt, mix it with deionized water, and obtain solution B with a certain molar concentration; the molar ratio of transition metal ions in solution A to the molar ratio of phosphorus in solution B is 3:2; add solution B to solution A and stir thoroughly.

[0061] Step (2): Add alkali solution to the solution in step (1), adjust the pH of the system to a certain range, and allow it to react for a certain period of time.

[0062] Step (3): Separate the slurry from step (2) into solid and liquid, then prepare the filter cake into a slurry with a certain solid content, and perform stirring and washing a certain number of times at a certain temperature. After washing, separate the slurry into solid and liquid.

[0063] Step (4): Dry the filter cake obtained in step (3), and then sinter the obtained powder sample in air at a certain temperature T1 and T2 for a certain time. After the furnace body cools to room temperature, take out the material; then mix the material with a certain mass of organic carbon source, and sinter it in an inert / reducing atmosphere at a certain temperature T3 for a certain time to obtain the manganese ferrous phosphate precursor; In step (4), T1 is 350-500℃, the sintering time is 1-4h, T2 is 500-650℃, and the sintering time is 1-4h; the organic carbon source is at least one of starch, glucose, citric acid, PEG, β-cyclodextrin, and sucrose, and the mass of the organic carbon source is 0.3%-5% of the mass of the manganese ferrous phosphate precursor product; the secondary sintering atmosphere is at least one of argon, nitrogen, argon-hydrogen mixture, and hydrogen; the sintering temperature T3 is 350-600℃; and the sintering time is 1-4h.

[0064] Step (5): After mixing the obtained manganese iron phosphate precursor with a certain proportion of lithium source and carbon source, the mixture is subjected to a combination of ball milling-sand milling-spraying-sintering process to obtain lithium manganese iron phosphate cathode material.

[0065] In step (1), the ferrous salt is at least one of ferrous sulfate, ferrous sulfate heptahydrate, ferrous chloride, ferrous chloride tetrahydrate, and ferrous nitrate; the manganese salt is at least one of manganese sulfate, manganese sulfate monohydrate, manganese nitrite, manganese chloride, and manganese chloride tetrahydrate; the molar ratio of the ferrous salt and the manganese salt is 2:8 to 8:2; the molar concentration of the transition metal ions in the ferrous-manganese salt mixed solution is in the range of 0.5 mol / L to 1.8 mol / L; the phosphate salt is at least one of phosphoric acid, monoammonium dihydrogen phosphate, diammonium monohydrogen phosphate, and ammonium phosphate; the molar concentration of phosphorus in the phosphate salt solution is in the range of 0.5 mol / L to 5 mol / L; and the addition method is direct pouring or addition at a certain flow rate. Furthermore, in step (1), the molar ratio of iron salt to manganese salt is 2:8 to 6:4, the molar concentration of transition metal ions in solution A is 1 mol / L to 1.5 mol / L, and the molar concentration of phosphorus in solution B is 1 mol / L to 2 mol / L.

[0066] In step (2), the alkaline solution is at least one of ammonia, an aqueous solution of sodium hydroxide, and an aqueous solution of sodium carbonate; the pH range is 5.0–8.0, and the reaction time is 1–6 h. Further, in step (2), the pH range is 6.0–7.5, and the reaction time is 2–4 h.

[0067] In step (3), the solid content is 5% to 20%; the washing temperature is 10 to 70°C; and the number of washing cycles is 2 to 5. Alternatively, the solid content ranges from 7% to 12%, the washing temperature is 40 to 60°C, and the number of washing cycles is 2 to 3.

[0068] In step (5), the lithium source is at least one of lithium carbonate, lithium phosphate, and lithium dihydrogen phosphate; the carbon source is at least one of starch, glucose, citric acid, PEG, β-cyclodextrin, and sucrose, and the proportion is 5% to 15% of the total carbon source mass relative to the mass of lithium manganese iron phosphate product.

[0069] The following is a typical solution:

[0070] Example 1

[0071] Step (1):

[0072] Weigh 0.36 mol of manganese sulfate and 0.24 mol of ferrous sulfate, add 270 g of deionized water and stir well to obtain solution A. Weigh 0.416 mol of monoammonium phosphate (ammonium dihydrogen phosphate) and 240 g of water, stir well to obtain solution B. Then add solution B to solution A to obtain mixed solution C. Slowly add ammonia water to solution C, control the pH of the reaction endpoint to 7.0, react in air for 3 hours, and then filter the slurry. Mix the obtained filter cake with 200 g of water at 60 °C and wash three times. After washing, filter the mixture. Place the filter cake in a forced-air drying oven at 80 °C for 12 hours to obtain ferrous manganese phosphate precipitate (dried filter cake).

[0073] Step (2):

[0074] Step 2-1:

[0075] The precipitated material of ferrous manganese phosphate was transferred to a muffle furnace (air atmosphere) and sintered at 600°C for 3 hours.

[0076] Step 2-2:

[0077] The material was removed, and 2% of its weight of starch was added to the product and mixed evenly. The mixture was then sintered at 500°C for 3 hours under an argon atmosphere to obtain the ferrous manganese phosphate precursor (hereinafter referred to as the precursor).

[0078] Step (3):

[0079] 30g of the obtained precursor, lithium phosphate (the molar ratio of lithium to transition elements in the precursor was 1.03:1), and 3g of glucose were subjected to a combined ball milling-sand milling-spraying process to obtain a lithium manganese iron phosphate precursor. The obtained precursor was sintered at 650℃ for 8 hours under an argon atmosphere to obtain the lithium manganese iron phosphate cathode material. The SEM image of the precursor is attached. Figure 1 As shown, the XRD pattern of its precursor is attached. Figure 2 As shown.

[0080] Example 2

[0081] Weigh 0.4 mol manganese sulfate and 0.1 mol ferrous sulfate, add 300 g deionized water and stir until homogeneous to obtain solution A. Weigh 0.343 mol monoammonium phosphate and 170 g water, stir until homogeneous to obtain solution B. Then add solution B to solution A to obtain mixed solution C. Slowly add an aqueous solution of sodium carbonate to solution C, controlling the pH of the reaction endpoint to 7.0. After reacting in air for 4 hours, filter the slurry. Mix the resulting filter cake with 600 g water at 40 °C and wash four times. After washing, filter again. Place the filter cake in a forced-air drying oven and dry at 80 °C for 12 hours. Then transfer the material to a muffle furnace (in air atmosphere) and sinter at 550 °C for 3 hours.

[0082] The material was removed, and 1% by weight of fumaric acid was added to the product and mixed evenly. The mixture was then sintered at 450°C for 2 hours under an argon atmosphere to obtain the manganese ferrous phosphate precursor.

[0083] 20g of the obtained precursor, lithium phosphate (the molar ratio of lithium to transition elements in the precursor was 1.02:1), and 2.5g of glucose were subjected to a ball milling-sand milling-spraying process to obtain a lithium manganese iron phosphate precursor. The obtained precursor was then sintered at 700℃ for 6 hours under an argon atmosphere to obtain the lithium manganese iron phosphate cathode material.

[0084] Example 3

[0085] Weigh 0.25 mol of manganese chloride and 0.15 mol of ferrous chloride, add 300 g of deionized water and stir well to obtain solution A. Weigh 0.34 mol of diammonium hydrogen phosphate and 180 g of water, stir well to obtain solution B. Then add solution B to solution A to obtain mixed solution C. Slowly add ammonia water to solution C, controlling the pH of the reaction endpoint to 6.5. After reacting in air for 3 hours, filter the slurry.

[0086] The obtained filter cake was mixed with 400g of water and washed three times at 50℃. After washing, the mixture was filtered. The filter cake was dried in a forced-air drying oven at 80℃ for 12h, and then transferred to a muffle furnace (air atmosphere) and sintered at 550℃ for 2h. The material was removed, and 3% by weight of β-cyclodextrin was added to the product and mixed evenly. The mixture was then sintered at 400℃ for 2h under an argon atmosphere to obtain the ferrous manganese phosphate precursor.

[0087] 20g of the obtained precursor, lithium phosphate (the molar ratio of lithium to transition elements in the precursor was 1.03:1), and 1.5g of glucose were subjected to a ball milling-sand milling-spraying process to obtain a lithium manganese iron phosphate precursor. The obtained precursor was then sintered at 750℃ for 4 hours under an argon atmosphere to obtain the lithium manganese iron phosphate cathode material.

[0088] Example 4

[0089] Weigh 0.7 mol manganese chloride and 0.3 mol ferrous chloride, add 250 g of deionized water and stir until homogeneous to obtain solution A. Weigh 0.687 mol monoammonium phosphate and 80 g of water, stir until homogeneous to obtain solution B. Then add solution B to solution A to obtain mixed solution C. Slowly add an aqueous solution of sodium hydroxide to solution C, controlling the pH at the reaction endpoint to 7.0. After reacting in air for 3 hours, filter the slurry. Mix the resulting filter cake with 250 g of water and wash at 55°C for a total of 4 times. After washing, filter again. Place the filter cake in a forced-air drying oven and dry at 90°C for 12 hours. Then transfer the material to a muffle furnace (in air atmosphere) and sinter at 550°C for 4 hours.

[0090] The material was removed, and 3.5% of its weight of starch was added to the product and mixed evenly. The mixture was then sintered at 500°C for 3 hours under an argon atmosphere to obtain the manganese ferrous phosphate precursor.

[0091] 20g of the obtained precursor, lithium phosphate (the molar ratio of lithium to transition elements in the precursor is 1.03:1), and 1.5g of glucose were subjected to a ball milling-sand milling-spraying process to obtain a lithium manganese iron phosphate precursor. The obtained precursor was sintered at 700℃ for 6 hours under an argon atmosphere to obtain the lithium manganese iron phosphate cathode material.

[0092] Example 5

[0093] Compared with Example 1, the only difference is that in step 2-1, the micro-oxidation stage is subjected to two-stage heat preservation treatment, that is, the precipitated material is sintered at 400°C for 1 hour before being sintered at 550°C for 1 hour; other operations and parameters are the same as in Example 1.

[0094] Comparative Example 1

[0095] Compared with Example 1, the only difference is that the air sintering process of step 2-1 in step 2 is missing. That is, the ferrous manganese phosphate precipitate of step 1 is directly subjected to step 2-2 and subsequent treatments. All other operations and parameters are the same as in Example 1.

[0096] Comparative Example 2

[0097] Compared with Example 1, the only difference is that in step 2-1 of step 2, the air atmosphere is replaced with argon gas, and all other operations and parameters are the same as in Example 1.

[0098] Comparative Example 3

[0099] Compared with Example 1, the only difference is that in step 2, step 2-2 is not performed, and the product of step 2-1 is directly processed in step 3 and subsequent steps. All other operations and parameters are the same as in Example 1.

[0100] Comparative Example 4

[0101] Compared with Example 1, the only difference is that in step 2-2 of step 2, starch is not added and the atmosphere is changed to 5v% H2-Ar. All other operations and parameters are the same as in Example 1.

[0102] test

[0103] Weigh the corresponding substances according to the mass ratio of active material (prepared in each case): binder (PVDF): conductive agent (conductive carbon black) = 8:1:1, add a certain amount of N-methylpyrrolidone and grind and mix. Coat the uniformly ground slurry onto aluminum foil and dry it in a vacuum oven at 120℃ for 12 hours to obtain the positive electrode sheet. Then cut the electrode sheet into 12mm round pieces and assemble them into CR2025 button half-cells in a high-purity argon glove box. Place the assembled button half-cells in a constant temperature environment at 25℃ and conduct electrochemical performance tests at charge and discharge cutoff voltages of 2.5-4.5V.

[0104] The magnification data is shown in Table 1:

[0105] Table 1

[0106]

[0107] The retention rate after 100 cycles at 25℃ is shown in Table 2:

[0108]

[0109] Through Tables 1 and 2 and Figures 1-6 It is understood that the preparation process described in this invention can effectively optimize the structure of the material, reduce its lattice anionic impurities, and effectively improve its initial efficiency and stability.

Claims

1. A method for preparing a ferrous manganese phosphate precursor, characterized in that, Ferrous manganese phosphate precipitate was prepared by precipitation reaction of ferrous source, manganese source and phosphate source. The ferrous manganese phosphate precipitate was pre-treated by micro-oxidation in an oxygen-containing atmosphere. Then, the micro-oxidation product and carbon source were mixed and heated to carry out carbothermic reduction to obtain ferrous manganese phosphate precursor. The oxygen-containing atmosphere includes at least one of air and oxygen. The temperature during the micro-oxidation stage is 300~700℃; the micro-oxidation time is 2~4h. The carbon source includes organic carbon sources; the carbon source accounts for 0.3-5% of the weight of the micro-oxidation products. The temperature for carbothermal reduction is 350~600℃.

2. The method for preparing the ferrous manganese phosphate precursor as described in claim 1, characterized in that, The ferrous source is a water-soluble ferrous salt; The manganese source is a water-soluble divalent manganese salt.

3. The method for preparing the ferrous manganese phosphate precursor as described in claim 1, characterized in that, The ferrous source is at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate; The manganese source is at least one of manganese sulfate, manganese nitrite, and manganese chloride; Phosphate sources include at least one of phosphoric acid, monoammonium dihydrogen phosphate, diammonium monohydrogen phosphate, and ammonium phosphate. The molar percentage of Mn / (Fe+Mn) in ferrous and manganese sources is 55-90%; Alkaline components were also added to the precipitation reaction system; The pH during the precipitation reaction stage is 5.0~8.

0.

4. The method for preparing the ferrous manganese phosphate precursor as described in claim 3, characterized in that, The molar percentage of Mn / (Fe+Mn) in ferrous and manganese sources is 60-80%.

5. The method for preparing the ferrous manganese phosphate precursor as described in claim 1, characterized in that, The oxygen-containing atmosphere also contains a dilution gas, which includes at least one of nitrogen and an inert gas.

6. The method for preparing the ferrous manganese phosphate precursor as described in claim 1, characterized in that, The micro-oxidation stage includes two gradient heat preservation processes. The first micro-oxidation heat preservation temperature is 350~500℃, and the second micro-oxidation heat preservation temperature is 500~650℃.

7. The method for preparing the ferrous manganese phosphate precursor as described in claim 6, characterized in that, The micro-oxidation stage includes two gradient heat preservation processes. The first micro-oxidation heat preservation temperature is 380~470℃, and the second micro-oxidation heat preservation temperature is 530~620℃.

8. The method for preparing the ferrous manganese phosphate precursor as described in claim 6, characterized in that, The micro-oxidation stage consists of two gradient heat preservation processes, where the first micro-oxidation heat preservation time is 1~4h and the second micro-oxidation heat preservation time is 1~4h.

9. The method for preparing the ferrous manganese phosphate precursor as described in claim 1, characterized in that, The carbon source includes at least one of starch, glucose, citric acid, PEG, β-cyclodextrin, and sucrose; The atmosphere during the carbothermic reduction stage is a protective atmosphere.

10. The method for preparing the ferrous manganese phosphate precursor as described in claim 9, characterized in that, The atmosphere in the carbothermic reduction stage also includes a reducing atmosphere.

11. The method for preparing the ferrous manganese phosphate precursor as described in claim 1, characterized in that, The temperature for carbothermal reduction is 400~500℃.

12. The method for preparing the ferrous manganese phosphate precursor as described in claim 1, characterized in that, The carbothermal reduction time is 1~4 hours.

13. A method for preparing lithium iron manganese phosphate material, characterized in that, The ferrous manganese phosphate precursor is prepared by the preparation method described in any one of claims 1 to 12, and then mixed with a lithium source and a coated carbon source and calcined to obtain the final product.

14. The preparation method according to claim 13, characterized in that, The lithium source includes at least one of lithium carbonate, lithium phosphate, and lithium dihydrogen phosphate; The carbon source for coating is at least one of starch, glucose, citric acid, β-cyclodextrin, sucrose, and PEG. The carbon source for coating is 5% to 15% of the weight of the ferrous manganese phosphate precursor; The roasting temperature is 300~900℃.

15. The preparation method according to claim 14, characterized in that, The roasting temperature is 650~800℃; The roasting time is 4 to 12 hours.

16. A lithium iron manganese phosphate material prepared by the preparation method according to any one of claims 13 to 15.

17. A positive electrode material for lithium-ion batteries, comprising a positive electrode active material, a binder, and a conductive agent, characterized in that, The positive electrode active material includes the lithium iron manganese phosphate material as described in claim 16.

18. A positive electrode for a lithium-ion battery, comprising a current collector and a positive electrode material composited thereon, characterized in that, The cathode material is the cathode material as described in claim 17.

19. A lithium-ion battery, characterized in that, It includes the positive electrode as described in claim 18.

Images