Preparation method and application of ferromanganese phosphate

Abstract

The invention discloses a preparation method and application of ferromanganese phosphate. According to the method, by controlling the proportion of a manganese source, an iron source and a phosphorus source and reaction conditions in the preparation process, divalent manganese and divalent iron in the preparation process are firstly precipitated to generate manganese iron ammonium phosphate, then pH is adjusted, the temperature is raised, ammonium radicals are removed to generate manganwentzelite type manganese iron phosphate, and finally crystallization is carried out to convert the manganwentzelite type manganese iron phosphate into manganese iron phosphate. The whole preparation process does not need inert gas protection, no ammonia waste gas is discharged, the production cost is effectively reduced, and the method is environment-friendly. In addition, the method is short in synthesis period, low in cost and suitable for large-scale popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of battery materials, and specifically relates to a preparation method and application of ferromanganese phosphate. Background Art

[0002] Lithium iron manganese phosphate cathode material combines high energy density and high safety performance. It can be mixed with ternary materials to achieve cost reduction and efficiency improvement, and can also replace lithium iron phosphate to achieve a breakthrough in energy density. It is a highly promising next-generation cathode material. The preparation methods of lithium iron manganese phosphate can be divided into solid phase method and liquid phase method. Among them, the liquid phase method produces higher quality products and has become a research process for mainstream companies. The liquid phase method requires the preparation of lithium iron manganese phosphate precursors first, but there are currently no standardized precursors in the industry. Each type of precursor has its own advantages and there is a large space for research and development. Lithium iron manganese phosphate precursors can be divided into manganese iron oxides, manganese iron phosphates, manganese iron oxalates, etc. according to their types. Among them, manganese iron phosphate is the most studied type, which can be further subdivided into manganese iron phosphate, manganese iron phosphate, ammonium manganese iron phosphate and manganese iron pyrophosphate.

[0003] Most of the preparation methods of ferromanganese phosphate are to mix an iron source and a manganese source, then add a phosphorus source and an oxidant, and perform crystallization transformation under certain temperature and time conditions to obtain the target product ferromanganese phosphate. For example, Chinese patent CN115535992A discloses a preparation method, which uses iron powder, manganese carbonate and phosphoric acid to mix, and then obtains a ferromanganese phosphate precursor by grinding, spraying and calcining. The patent does not indicate whether the obtained precursor is a pure phase ferromanganese phosphate. Although the ratio of manganese, iron and phosphorus elements meets the design value, there may be impurities, which affects the compacted density and specific surface area of ​​the finished lithium ferromanganese phosphate. Chinese patent CN106981656B discloses a method for preparing battery-grade ferromanganese phosphate, which comprises preparing a low-concentration iron-manganese mixed solution, adding a low-concentration oxidant and a phosphate mixed solution, heating the reaction, and then adding a high-concentration iron-manganese mixed solution, stirring evenly, adding a high-concentration oxidant and a phosphate mixed solution, and finally adding phosphoric acid after the temperature reaction for transformation and crystallization to obtain battery-grade ferromanganese phosphate. However, the preparation process of this method is complicated and difficult to control, and is not suitable for industrialization.

[0004] The current synthesis method of ferromanganese phosphate has the problem of high content of impurity elements, which leads to poor performance of lithium ferromanganese phosphate obtained when it is used to prepare lithium ferromanganese phosphate. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a method for preparing ferromanganese phosphate and its application. A multi-step reaction is adopted to first synthesize ammonium ferromanganese phosphate, then deammonium ions are formed into red phosphorus manganese ore-type ferromanganese phosphate, and finally crystallized into ferromanganese phosphate. The multi-step reaction is conducive to removing impurity elements and improving the purity of the product. The preparation of pure phase ferromanganese phosphate as a precursor can simplify the subsequent production process of preparing lithium ferromanganese phosphate.

[0006] In order to achieve the above object, the present invention provides a ferromanganese phosphate, the general chemical formula of which can be expressed as Mn1-xFexPO4·yH2O, 0<x≤0.4, 1.4≤y<2.0. The present invention also provides a method for preparing ferromanganese phosphate, which specifically comprises the following steps: (1) dissolving a soluble divalent iron source, a soluble divalent manganese source and an antioxidant in pure water, and adjusting the pH to ≤ 2.0 to form a mixed solution; Dissolve a soluble phosphorus source, a soluble ammonia source and a surfactant in pure water to form a base solution, and adjust the pH value of the base solution to 6.0-6.5; (2) Continue to stir the base liquid, slowly add the mixed solution to the base liquid, and add ammonia water to maintain the pH of the base liquid stable at 6.0-6.5 until the mixed solution is added dropwise, continue to stir for a period of time, and then perform multiple filtration and washing to obtain ammonium manganese iron phosphate; (3) Mixing ammonium manganese iron phosphate and pure water and stirring, then adjusting the pH to 3.0-5.0, heating to 80-99°C, keeping the temperature for 1-3 hours, and then filtering, washing and drying for multiple times to obtain red phosphorus manganese ore type manganese iron phosphate; (4) Mixing ferromanganese phosphate of erythritol type with pure water and keeping stirring, adding phosphoric acid and an oxidant, and heating to 80-99°C for 1-6 hours, controlling the pH of the reaction end point to be 2.0-5.0, and then obtaining pure phase ferromanganese phosphate after multiple filtration, washing and drying.

[0007] Preferably, in step (1), the soluble ferrous iron source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride and ferrous acetate. Further preferably, the soluble ferrous iron source is ferrous sulfate.

[0008] Preferably, in step (1), the soluble divalent manganese source is one or more of manganous sulfate, manganous nitrate, manganous chloride and manganous acetate. More preferably, the soluble divalent manganese source is manganous sulfate.

[0009] Preferably, in step (1), the antioxidant is one or more of citric acid, vitamin C, vitamin E and tea polyphenols. More preferably, the antioxidant is vitamin C.

[0010] Preferably, in step (1), the soluble phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, ammonium phosphate and sodium phosphate. Further preferably, the soluble phosphorus source is phosphoric acid, ammonium dihydrogen phosphate or a mixture thereof in any proportion.

[0011] Preferably, in step (1), the soluble ammonia source is one or more of ammonium phosphate, diammonium phosphate, diammonium hydrogen phosphate and ammonium sulfate. Further preferably, the soluble ammonia source is ammonium phosphate, ammonium sulfate or a mixture thereof in any proportion.

[0012] Preferably, in step (1), the surfactant is one or more of polyethylene glycol 200, polyethylene glycol 400, polyvinyl pyrrolidone, calcium stearate and butyl stearate. More preferably, the surfactant is polyethylene glycol 400 or polyvinyl pyrrolidone.

[0013] Preferably, in step (1), the soluble divalent iron source (calculated as Fe), the soluble divalent manganese source (calculated as Mn), the soluble phosphorus source (calculated as PO4 3- ) and soluble ammonia sources (in terms of NH4 + The molar ratio of (in terms of weight) is x: (1-x): (1.0~1.2): (1.0~1.2), where 0<x≤0.4.

[0014] Preferably, in step (1), the concentration of metal ions (Mn+Fe) in the mixed solution is 0.5-2 mol / L.

[0015] Preferably, in step (1), the antioxidant accounts for 0.1-5 wt % of the total mass of the raw materials (excluding pure water).

[0016] Preferably, in step (1), the surfactant accounts for 0.1-2 wt% of the total mass of the raw materials (excluding pure water).

[0017] Preferably, in step (1), sulfuric acid or phosphoric acid is used to adjust the pH value of the base solution, and more preferably, phosphoric acid is used for adjustment.

[0018] Preferably, in step (2), the stirring speed during the dropwise addition is 1000-1500 rpm.

[0019] Preferably, in step (2), the mixed solution is added to the base solution from below the liquid surface and the drop rate is 5-20 mL / min.

[0020] Preferably, in step (2), the stirring speed is reduced to 500 rpm after the dropwise addition is completed, and the stirring time is continued for 30 to 60 minutes.

[0021] Preferably, in step (2), the termination condition of the multiple filtration and washing is that the conductivity of the filtrate is ≤0.5 mS / cm.

[0022] Preferably, in step (3), the solid content of the ammonium manganese ferric phosphate and pure water after mixing is 10-20wt%.

[0023] Preferably, in step (3), the termination condition of the multiple filtration and washing is that the conductivity of the filtrate is ≤0.2 mS / cm.

[0024] Preferably, in step (4), the solid content of the ferromanganese phosphate of the erythromanganese ore type and pure water after mixing is 10-20 wt%.

[0025] Preferably, in step (4), the termination condition of the multiple filtration and washing is that the conductivity of the filtrate is ≤0.2 mS / cm.

[0026] Preferably, in step (4), the oxidant is one or more of hydrogen peroxide, sodium chlorate, sodium hypochlorite, high-purity oxygen, and nitric acid.

[0027] Preferably, in step (4), the oxidant accounts for 5-15 wt% of the total mass of the raw materials (hexachlorobenzene-type ferromanganese phosphate and the oxidant).

[0028] The present invention also provides an application of ferromanganese phosphate in preparing anode materials of batteries.

[0029] Preferably, the positive electrode material of the battery is lithium iron manganese phosphate, and the preparation method of lithium iron manganese phosphate comprises the following steps: (1) mixing a lithium source, ferromanganese phosphate, a carbon source and pure water and then sand-milling the mixture to obtain a slurry with a particle size D50 ≤ 300 nm; (2) spray drying the slurry to obtain a powder; (3) The powder is calcined, crushed and sieved under the protection of inert gas to obtain lithium manganese iron phosphate.

[0030] Preferably, in step (1), the molar ratio of the lithium source (calculated as Li) to the ferromanganese phosphate (calculated as Mn+Fe) is 1.0-1.05:1.0, and the carbon source accounts for 2-8 wt% of the total mass of the raw materials (excluding pure water).

[0031] The beneficial effects of the present invention are: The present invention first synthesizes ammonium ferromanganese phosphate hydrate, then adjusts the pH value and heats up to convert it into red phosphorus manganese ore type ferromanganese phosphate, and then crystallizes and transforms to obtain ferromanganese phosphate. Compared with the one-step direct synthesis of ferromanganese phosphate, the present invention has the advantages of less impurity content, high homogeneity of ferromanganese phosphorus element, good controllability, etc. In the process of synthesizing ferromanganese phosphate, the present invention does not need to introduce a protective atmosphere and does not emit ammonia waste gas, thereby reducing production costs and being environmentally friendly.

[0032] The present invention proposes a ferromanganese phosphate as a precursor. Compared with conventional single manganese source and iron source, the manganese and iron in ferromanganese phosphate are more evenly mixed, which can effectively inhibit the dissolution of manganese caused by the Jan-Taylor effect; compared with ammonium ferromanganese phosphate, ferromanganese phosphate does not contain ammonium ions, and will not release ammonia to affect the product quality during the synthesis of lithium iron manganese; compared with ferromanganese phosphate, ferromanganese phosphate can be adapted to mainstream lithium salts such as lithium carbonate and lithium hydroxide, and has good industrialization prospects. Based on the above advantages, the preparation of lithium iron manganese phosphate positive electrode material using ferromanganese phosphate as a precursor has the advantages of low cost and high quality, and is a very potential precursor material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the XRD pattern of the ammonium manganese ferrous phosphate prepared in Example 2.

[0034] Figure 2 This is the XRD spectrum of the ferromanganese phosphate of red phosphorus manganese ore prepared in Example 2.

[0035] Figure 3 This is the XRD pattern of the ferromanganese phosphate prepared in Example 2.

[0036] Figure 4 This is the XRD spectrum of the lithium manganese iron phosphate prepared in Example 2. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further explained below in conjunction with specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The protection scope of the present invention shall be subject to the contents recorded in the claims. Any modification or replacement made by a person skilled in the art to the technical solution of the present invention without creative work shall fall within the protection scope of the present invention.

[0038] Example 1 (1) Preparation of ferromanganese phosphate 6.08g of ferrous sulfate, 9.06g of manganous sulfate, 0.04g of ascorbic acid and 200ml of pure water were uniformly mixed, and then the pH value was adjusted to 0.5 to form a mixed solution. 9.8g of phosphoric acid, 13.21g of ammonium sulfate and 0.04g of polyvinyl pyrrolidone were dissolved in 500ml of pure water to form a base liquid, and the base liquid was continuously stirred at 1000rpm. The mixed solution was pumped into the base liquid at a rate of 10ml / min from below the liquid surface, and ammonia water was pumped into the base liquid at the same time to maintain the pH of the base liquid at 6.0. After the mixed solution was added, the stirring speed was reduced to 500rpm and the stirring was continued for 60min, and then the filtrate was filtered and washed several times until the conductivity of the filtrate was ≤0.5mS / cm to obtain ammonium manganese iron phosphate. Ammonium manganese iron phosphate and pure water are mixed to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, nitric acid is added to adjust the pH value of the slurry to 5.0, the temperature is raised to 80℃ and kept for 1h, and the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then vacuum dried to obtain red phosphorus manganese ore type manganese iron phosphate. Red phosphorus manganese ore type manganese iron phosphate is mixed with pure water to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid and 0.77g hydrogen peroxide are added at the same time, the temperature is raised to 80℃ and kept for 1h, so that the reaction end point pH=2.0, the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then dried to obtain pure phase manganese iron phosphate.

[0039] (2) Preparation of lithium manganese iron phosphate 17.55 g of ferromanganese phosphate, 3.81 g of lithium carbonate, 0.57 g of sucrose and pure water were mixed and sand-milled until the slurry D50 was ≤ 300 nm, and then spray-dried, calcined at 700° C. for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium ferromanganese phosphate positive electrode material.

[0040] Example 2 (1) Preparation of ferromanganese phosphate 6.07g of ferrous sulfate, 9.06g of manganous sulfate, 0.39g of ascorbic acid and 100ml of pure water were uniformly mixed, and then the pH value was adjusted to 0.8 to form a mixed solution. 10.29g of phosphoric acid, 13.87g of ammonium sulfate and 0.39g of polyvinyl pyrrolidone were dissolved in 500ml of pure water to form a base liquid, and the base liquid was continuously stirred at 1200rpm. The mixed solution was pumped into the base liquid at a rate of 10ml / min from below the liquid surface, and ammonia water was pumped into the base liquid at the same time to maintain the pH of the base liquid at 6.2. After the mixed solution was added, the stirring speed was reduced to 500rpm and the stirring was continued for 60min, and then the filtrate was filtered and washed several times until the conductivity of the filtrate was ≤0.5mS / cm to obtain ammonium manganese iron phosphate. Ammonium manganese iron phosphate and pure water are mixed to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, nitric acid is added to adjust the pH value of the slurry to 3.0, the temperature is raised to 90℃ and kept for 2h, and the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then vacuum dried to obtain red phosphorus manganese ore type manganese iron phosphate. Red phosphorus manganese ore type manganese iron phosphate is mixed with pure water to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid and 1.62g hydrogen peroxide are added at the same time, the temperature is raised to 90℃ and kept for 3h, so that the reaction end point pH=3.0, the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then dried to obtain pure phase manganese iron phosphate.

[0041] (2) Preparation of lithium manganese iron phosphate 17.55 g of ferromanganese phosphate, 3.81 g of lithium carbonate, 0.97 g of glucose and pure water were mixed and sand-milled until the slurry D50 was ≤ 300 nm, and then spray-dried, calcined at 700° C. for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium ferromanganese phosphate positive electrode material.

[0042] Example 3 (1) Preparation of ferromanganese phosphate 5.40g of ferrous nitrate, 12.53g of manganous nitrate, 2.16g of ascorbic acid and 50ml of pure water were uniformly mixed, and then the pH value was adjusted to 1.0 to form a mixed solution. 10.78g of phosphoric acid, 14.54g of ammonium sulfate and 0.86g of polyvinyl pyrrolidone were dissolved in 500ml of pure water to form a base liquid, and the base liquid was continuously stirred at 1500rpm. The mixed solution was pumped into the base liquid at a rate of 10ml / min from below the liquid surface, and ammonia water was pumped into the base liquid at the same time to maintain the pH of the base liquid at 6.5. After the mixed solution was added, the stirring speed was reduced to 500rpm and the stirring was continued for 45min, and then the filtrate was filtered and washed several times until the conductivity of the filtrate was ≤0.5mS / cm to obtain ammonium manganese iron phosphate. Ammonium manganese iron phosphate and pure water are mixed to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, sulfuric acid is added to adjust the pH value of the slurry to 4.0, the temperature is raised to 99°C and kept warm for 3h, and the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then vacuum dried to obtain red phosphorus manganese ore type manganese iron phosphate. Red phosphorus manganese ore type manganese iron phosphate is mixed with pure water to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid and 2.58g hydrogen peroxide are added at the same time, the temperature is raised to 99°C and kept warm for 6h, the pH value of the reaction end point is 4.0, the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then dried to obtain pure phase manganese iron phosphate.

[0043] (2) Preparation of lithium manganese iron phosphate 17.55 g of ferromanganese phosphate, 3.81 g of lithium carbonate, 1.60 g of glucose and pure water were mixed and sand-milled until the slurry D50 was ≤ 300 nm, and then spray-dried, calcined at 700° C. for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium ferromanganese phosphate positive electrode material.

[0044] Example 4 (1) Preparation of ferromanganese phosphate 5.40g of ferrous nitrate, 12.53g of manganous nitrate, 1.37g of ascorbic acid and 67ml of pure water were uniformly mixed, and then the pH value was adjusted to 1.5 to form a mixed solution. 11.76g of phosphoric acid, 15.86g of ammonium sulfate and 0.23g of polyvinyl pyrrolidone were dissolved in 500ml of pure water to form a base liquid, and the base liquid was continuously stirred at 1000rpm. The mixed solution was pumped into the base liquid at a rate of 10ml / min from below the liquid surface, and ammonia water was pumped into the base liquid at the same time to maintain the pH of the base liquid at 6.3. After the mixed solution was added, the stirring speed was reduced to 500rpm and the stirring was continued for 60min, and then the filtrate was filtered and washed several times until the conductivity of the filtrate was ≤0.5mS / cm to obtain ammonium manganese iron phosphate. Ammonium manganese iron phosphate and pure water are mixed to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, hydrochloric acid is added to adjust the pH value of the slurry to 3.5, the temperature is raised to 95℃ and kept warm for 1.5h, and the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then vacuum dried to obtain red phosphorus manganese ore type manganese iron phosphate. Red phosphorus manganese ore type manganese iron phosphate is mixed with pure water to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid and 1.99g hydrogen peroxide are added at the same time, the temperature is raised to 95℃ and kept warm for 4h, the pH value of the reaction end point is 5.0, the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then dried to obtain pure phase manganese iron phosphate.

[0045] (2) Preparation of lithium manganese iron phosphate 17.55 g of ferromanganese phosphate, 3.81 g of lithium carbonate, 0.77 g of polyethylene glycol and pure water were mixed and sand-milled until the slurry D50 was ≤ 300 nm, and then spray-dried, calcined at 700° C. for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium ferromanganese phosphate positive electrode material.

[0046] Example 5 (1) Preparation of ferromanganese phosphate 2.54g of ferrous chloride, 10.07g of manganous chloride, 1.33g of ascorbic acid and 67ml of pure water were uniformly mixed, and then the pH value was adjusted to 1.0 to form a mixed solution. 10.78g of phosphoric acid, 14.54g of ammonium sulfate and 0.57g of polyvinyl pyrrolidone were dissolved in 500ml of pure water to form a base liquid, and the base liquid was continuously stirred at 1500rpm. The mixed solution was pumped into the base liquid at a rate of 10ml / min from below the liquid surface, and ammonia water was pumped into the base liquid at the same time to maintain the pH of the base liquid at 6.4. After the mixed solution was added, the stirring speed was reduced to 500rpm and the stirring was continued for 60min, and then the filtrate was filtered and washed several times until the conductivity of the filtrate was ≤0.5mS / cm to obtain ammonium manganese iron phosphate. Ammonium manganese iron phosphate and pure water are mixed to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid is added to adjust the pH value of the slurry to 4.5, the temperature is raised to 88°C and kept warm for 2.5h, and the filtrate is filtered and washed several times until the conductivity of the filtrate is ≤0.2mS / cm, and then vacuum dried to obtain red phosphorus manganese ore type manganese iron phosphate. Red phosphorus manganese ore type manganese iron phosphate is mixed with pure water to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid and 1.27g hydrogen peroxide are added at the same time, the temperature is raised to 88°C and kept warm for 5h, the pH value of the reaction end point is 4.5, the filtrate is filtered and washed several times until the conductivity of the filtrate is ≤0.2mS / cm, and then dried to obtain pure phase manganese iron phosphate.

[0047] (2) Preparation of lithium manganese iron phosphate 17.55 g of ferromanganese phosphate, 3.81 g of lithium carbonate, 0.38 g of dextrin and pure water were mixed and sand-milled until the slurry D50 was ≤ 300 nm, and then spray-dried, calcined at 700° C. for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium ferromanganese phosphate positive electrode material.

[0048] Example 6 (1) Preparation of ferromanganese phosphate 2.54g of ferrous chloride, 10.07g of manganous chloride, 1.52g of ascorbic acid and 67ml of pure water were uniformly mixed, and then the pH value was adjusted to 0.9 to form a mixed solution. 10.78g of phosphoric acid, 14.54g of ammonium sulfate and 0.57g of polyvinyl pyrrolidone were dissolved in 500ml of pure water to form a base liquid, and the base liquid was continuously stirred at 1250rpm. The mixed solution was pumped into the base liquid at a rate of 10ml / min from below the liquid surface, and ammonia water was pumped into the base liquid at the same time to maintain the pH of the base liquid at 6.1. After the mixed solution was added, the stirring speed was reduced to 500rpm and the stirring was continued for 60min, and then the filtrate was filtered and washed several times until the conductivity of the filtrate was ≤0.5mS / cm to obtain ammonium manganese iron phosphate. Ammonium manganese iron phosphate and pure water are mixed to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid is added to adjust the pH value of the slurry to 3.8, the temperature is raised to 92°C and kept warm for 2.0h, and the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then vacuum dried to obtain red phosphorus manganese ore type manganese iron phosphate. Red phosphorus manganese ore type manganese iron phosphate is mixed with pure water to form a slurry with a solid content of 10wt%, the slurry is continuously stirred at 1000rpm, phosphoric acid and 1.62g hydrogen peroxide are added at the same time, the temperature is raised to 92°C and kept warm for 5h, the pH value of the reaction end point is 3.5, the filtrate is filtered and washed for multiple times until the conductivity of the filtrate is ≤0.2mS / cm, and then dried to obtain pure phase manganese iron phosphate.

[0049] (2) Preparation of lithium manganese iron phosphate 17.54 g of ferromanganese phosphate, 3.81 g of lithium carbonate, 1.17 g of glucose and pure water were mixed and sand-milled until the slurry D50 was ≤ 300 nm, and then spray-dried, calcined at 700° C. for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium ferromanganese phosphate positive electrode material.

[0050] Comparative Example 1 3.81 g of lithium carbonate, 6.03 g of iron phosphate, 4.58 g of manganese tetraoxide, 6.90 g of ammonium dihydrogen phosphate, 1.85 g of glucose and 54 g of pure water were mixed, then added to a sand mill and sand-milled to a slurry D50 ≤ 300 nm, and then spray-dried, calcined at 700 ° C for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium manganese iron phosphate positive electrode material.

[0051] Comparative Example 2 3.81 g of lithium carbonate, 4.52 g of iron phosphate, 5.26 g of manganese tetraoxide, 8.05 g of ammonium dihydrogen phosphate, 2.14 g of sucrose and 55 g of pure water were mixed, then added to a sand mill and sand-milled to a slurry D50 ≤ 300 nm, and then spray-dried, calcined at 700 ° C for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium manganese iron phosphate positive electrode material.

[0052] Comparative Example 3 3.81 g of lithium carbonate, 3.02 g of iron phosphate, 6.09 g of manganese tetraoxide, 9.20 g of ammonium dihydrogen phosphate, 2.46 g of polyethylene glycol and 57 g of pure water were mixed, then added to a sand mill and sand-milled to a slurry D50 ≤ 300 nm, and then spray-dried, calcined at 700 ° C for 10 h under a nitrogen atmosphere, crushed and sieved to obtain a lithium manganese iron phosphate positive electrode material.

[0053] The above-mentioned lithium manganese iron phosphate positive electrode material, polyvinylidene fluoride (PVDF), Super-p conductive carbon black and N-methylpyrrolidone were homogenized, wherein the mass ratio of positive electrode material, PVDF and Super-p was 90:5:5, and the solid content of the slurry was 30%. Then, the circular electrode piece was obtained by coating, drying and punching, and finally, the circular electrode piece, diaphragm and lithium sheet were assembled into a button battery in a glove box for testing. The button battery was charged and discharged in the voltage range of 2.5~4.5 V.

[0054] The prepared ferromanganese phosphate and lithium iron manganese phosphate were subjected to performance tests, and the results are shown in Table 1 and Table 2. It can be seen from the data in the table that when the ferromanganese phosphate prepared by the present invention is used to prepare lithium iron manganese phosphate material, its compaction density and electrical properties are higher than those of the comparative example, and its specific surface area is lower than that of the comparative example, indicating that using high-purity ferromanganese phosphate as a precursor of lithium iron manganese phosphate can improve its physical and chemical properties and electrical properties.

[0055] Table 1 Test results of ferromanganese phosphate

[0056] Table 2 Test results of lithium manganese iron phosphate

Claims

1. A method for preparing ferromanganese phosphate, characterized in that: The following steps are involved: (1) dissolving a soluble divalent iron source, a soluble divalent manganese source and an antioxidant in pure water to form a mixed solution; dissolving a soluble phosphorus source, a soluble ammonia source and a surfactant in pure water to form a base solution; (2) continuously stirring the base liquid, adding the mixed solution to the base liquid until the mixed solution is added dropwise, continuing to stir for a period of time, and then performing multiple filtration and washing to obtain ammonium manganese iron phosphate; (3) Mixing ammonium manganese iron phosphate and pure water and stirring, then adjusting the pH to 3.0-5.0, heating to 80-99°C, keeping the temperature for 1-3 hours, and then filtering, washing and drying for multiple times to obtain red phosphorus manganese ore type manganese iron phosphate; (4) Mixing ferromanganese phosphate of erythritol type with pure water and keeping stirring, adding phosphoric acid and an oxidant, and heating to 80-99°C for 1-6 hours, controlling the pH of the reaction end point to be 2.0-5.0, and then obtaining pure phase ferromanganese phosphate after multiple filtration, washing and drying.

2. The method for preparing ferromanganese phosphate according to claim 1, wherein: The pH of the mixed solution in step (1) is ≤2.0; the pH value of the base solution is 6.0-6.5; sulfuric acid or phosphoric acid is used to adjust the pH value of the base solution.

3. The method for preparing ferromanganese phosphate according to claim 1, wherein: In step (1), the soluble ferrous iron source is one or more of ferrous sulfate, ferrous nitrate, ferrous chloride and ferrous acetate; The soluble divalent manganese source is one or more of manganous sulfate, manganous nitrate, manganous chloride and manganous acetate; The antioxidant is one or more of citric acid, vitamin C, vitamin E and tea polyphenols; The soluble phosphorus source is one or more of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate, disodium hydrogen phosphate, ammonium phosphate and sodium phosphate; The soluble ammonia source is one or more of ammonium phosphate, diammonium phosphate, diammonium hydrogen phosphate and ammonium sulfate; the surfactant is one or more of polyethylene glycol 200, polyethylene glycol 400, polyvinyl pyrrolidone, calcium stearate and butyl stearate.

4. The method for preparing ferromanganese phosphate according to claim 1, wherein: In step (1), the soluble divalent iron source is calculated as Fe, the soluble divalent manganese source is calculated as Mn, and the soluble phosphorus source is calculated as PO4 3- Soluble ammonia source is calculated as NH4 + The molar ratio is x: (1-x): (1.0~1.2): (1.0~1.2), where 0<x≤0.4; The concentration of metal ions Mn+Fe in the mixed solution is 0.5-2 mol / L, the antioxidant accounts for 0.1-5 wt% of the total mass of the raw materials, and the surfactant accounts for 0.1-2 wt% of the total mass of the raw materials.

5. The method for preparing ferromanganese phosphate according to claim 1, characterized in that: In step (2), the stirring speed is 1000-1500 rpm during the dropwise addition process, the mixed solution is added to the base solution from below the liquid surface and the dropwise addition rate is 5-20 mL / min, the stirring speed is reduced to 300-500 rpm after the dropwise addition is completed, the continued stirring time is 30-60 min, and the termination condition of the multiple filtration and washing is that the filtrate conductivity is ≤0.5 mS / cm.

6. The method for preparing ferromanganese phosphate according to claim 1, characterized in that: In step (2), during the process of adding the mixed solution, ammonia water is added simultaneously to maintain the pH value of the base solution stable at 6.0-6.

5.

7. The method for preparing ferromanganese phosphate according to claim 1, characterized in that: In step (3), the solid content of the ammonium manganese ferric phosphate and pure water after mixing is 10-20wt%, the termination condition of the multiple filtration and washing is that the conductivity of the filtrate is ≤0.2mS / cm, and the drying method is vacuum drying.

8. The method for preparing ferromanganese phosphate according to claim 1, characterized in that: In step (4), the solid content of the ferromanganese phosphate of the pyrophosphate type and pure water after mixing is 10-20 wt %, and the termination condition of the multiple filtration and washing is that the conductivity of the filtrate is ≤0.2 mS / cm; The oxidant is one or more of hydrogen peroxide, perchloric acid, sodium hypochlorite, oxygen, ozone and nitric acid, and the oxidant accounts for 5-15wt% of the total mass of the raw materials.

9. A ferromanganese phosphate, characterized in that: A ferromanganese phosphate prepared by the preparation method according to any one of claims 1 to 8, wherein the general chemical formula is Mn 1-x Fe x PO4·yH2O, 0<x≤0.4, 1.4≤y<2.

0.

10. A positive electrode material, characterized in that: Including the ferromanganese phosphate described in claim 9.

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