Lithium ferric manganese phosphate precursor as well as preparation method and application thereof

Abstract

The invention relates to the technical field of lithium ion battery positive electrode materials, and particularly discloses a lithium iron manganese phosphate precursor and a preparation method and application thereof, the lithium iron manganese phosphate precursor comprises iron manganese mixed metal salt, a first precipitant and a second precipitant; the first precipitant is a carbonate solution or a bicarbonate solution, and the second precipitant is an ammonia water solution; the ammonia water solution and the iron-manganese mixed metal salt meet the requirement that the molar ratio of NH3.H2O to (Mn < 2 + > + Fe < 3 + >) is (2.0-3.5): 1. The reaction process for preparing the lithium ferric manganese phosphate precursor is simple to operate, and the prepared lithium ferric manganese phosphate precursor is excellent in stability in air, high in yield of iron and manganese elements and suitable for industrial popularization and application. And mixing the obtained ferric manganese phosphate precursor with a lithium salt, a phosphorus salt and an additive, and then grinding and mixing with a carbon source to prepare the lithium ferric manganese phosphate-carbon composite material with excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for lithium-ion batteries, and particularly relates to a lithium iron manganese phosphate precursor, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium iron manganese phosphate (LFMP) is widely used in the cathodes of lithium-ion batteries due to its advantages such as low cost, high safety, long cycle life, high voltage, and wide raw material sources, and combines the excellent rate performance of lithium iron phosphate and the high voltage platform of lithium manganese phosphate.

[0003] The synthesis methods of LFMP mainly include high-temperature solid-phase method and liquid-phase method. The liquid-phase method mainly includes hydrothermal method and co-precipitation method. The solid-phase method mainly involves solid-phase mixing of lithium source, manganese source, iron source, and phosphorus source, and then sintering at high temperature to form lithium iron manganese phosphate, while the liquid-phase method mainly synthesizes products by uniformly mixing soluble raw materials in a solution. Although the solid-phase method is simple, elements such as Mn and Fe cannot achieve atomic-level uniform mixing and are difficult to be uniformly distributed in the main structure of LFMP, resulting in a serious Jahn-Teller effect of Mn 3+ and affecting the cycle stability and rate performance of the battery. The synthesis of lithium iron manganese phosphate by the liquid-phase method can improve the uniformity of transition metals in LFMP. However, the hydrothermal method among them requires a high-temperature and high-pressure environment, has high requirements for production equipment, and has problems such as cumbersome production operations, poor safety, high energy consumption, and low production capacity; the co-precipitation method first synthesizes an iron manganese phosphate precursor by a wet method and then mixes it with a lithium source for sintering. This synthesis route has mild conditions, and the prepared product has uniform element distribution and precisely adjustable ratio, and is currently a favored route.

[0004] Chinese Patent CN119285457 provides an iron-manganese oxalate precursor, a preparation method, and a lithium iron manganese phosphate cathode material: Under the protection of an inert gas, an aqueous solution containing ammonium oxalate and an antioxidant is dropped into an aqueous solution containing a certain proportion of iron-manganese mixed salts and an antioxidant, so as to greatly reduce the yield of β-crystalline iron-manganese oxalate during the synthesis process and enable iron and manganese to achieve atomic-level mixing. However, the characteristics of the low main content of the iron-manganese oxalate precursor in this patent, the use of antioxidants and the protection of inert gas during the production process make its production process complex and costly. Chinese Patent CN113213545A provides a preparation method of a manganese iron carbonate precursor: Under the protection of an inert gas, a mixed metal salt solution, a carbonate solution, and an alkali solution are added to the reactor in parallel flow. Due to the intrinsically similar Ksp of manganese carbonate and ferrous carbonate, the uniform distribution of iron and manganese elements can be achieved. However, impurities such as residual alkali are easily introduced during the preparation of the carbonate precursor. Although, as described in Chinese Invention Patents CN113979486A, CN118255401A, etc., the content of sodium and sulfur in the carbonate precursor can be reduced by processes such as adding an acidic additive for washing and aging with an organic solvent, the preparation process is complex, the wastewater treatment is difficult, and the manganese iron carbonate is extremely easy to deteriorate when exposed to air, resulting in difficulties in its industrialization. In addition, the large volume change of manganese iron carbonate during the preparation of lithium iron manganese phosphate will seriously damage the powder compaction density of lithium iron manganese phosphate.

[0005] In view of this, there is an urgent need in the art for a preparation method of a lithium iron manganese phosphate precursor with a simple preparation process, atomic-level uniform distribution of iron and manganese elements, high air stability, suitable for industrial production, and good electrochemical performance. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a lithium iron manganese phosphate precursor, a preparation method, and an application thereof. In this method, an iron-manganese mixed metal salt solution and a second precipitant (ammonia water solution) with a certain concentration are respectively added to a first precipitant (carbonate or bicarbonate) bottom solution at the same time, and a coprecipitation reaction is carried out at a certain temperature. Then, through filtration, washing, and drying, a lithium iron manganese phosphate precursor is obtained. The precursor is mixed with a lithium salt, a phosphorus salt, and an additive, sintered, and then through two mixing and two sintering processes, a lithium iron manganese phosphate material with excellent performance can be obtained. The preparation process is simple and environmentally friendly, and is suitable for industrial promotion and application.

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

[0008] On the one hand, the present invention provides a lithium iron manganese phosphate precursor, which contains an iron-manganese mixed metal salt, a first precipitant, and a second precipitant; the first precipitant is a carbonate solution or a bicarbonate solution, and the second precipitant is an ammonia water solution; the ammonia water solution and the iron-manganese mixed metal salt satisfy NH3·H2O:(Mn2+ +Fe 3+ ) has a molar ratio of 2.0 - 3.5:1.

[0009] Further preferably, the aqueous ammonia solution and the iron-manganese mixed metal salt satisfy NH3·H2O:(Mn 2+ +Fe 3+ ) has a molar ratio of 2.23 - 3.35:1.

[0010] Preferably, the concentration of the first precipitant is 3.0 mol / L - 6.0 mol / L; the concentration of the second precipitant is 5.35 - 13.38 mol / L; the first precipitant and the iron-manganese mixed metal salt satisfy that the molar ratio of carbonate or bicarbonate to the total metal elements of iron and manganese is 0.4 - 0.8:1.

[0011] Preferably, the iron-manganese mixed metal salt includes an iron source and a manganese source; the iron source is trivalent iron, which is at least one of ferric nitrate, ferric sulfate, and ferric chloride; the manganese source is divalent manganese, which is at least one of manganese chloride, manganese acetate, and manganese sulfate; the total metal concentration in the iron-manganese mixed metal salt is 0.5 mol / L - 5 mol / L, and the molar ratio of Mn 2+ to Fe 3+ is x:y, where x is 0.5 - 0.9 and x + y = 1.

[0012] The present invention also provides a method for preparing the above lithium iron manganese phosphate precursor, comprising the following steps:

[0013] S1. Dissolve a certain amount of iron and manganese metal salts in pure water to obtain an iron-manganese mixed metal salt solution; dissolve a certain amount of carbonate or bicarbonate in pure water to obtain a first precipitant; add a certain amount of ammonia water to pure water to obtain a second precipitant;

[0014] S2. Drop the iron-manganese mixed metal salt solution and the second precipitant into the first precipitant simultaneously for coprecipitation reaction, and then filter, wash, and dry to obtain the lithium iron manganese phosphate precursor.

[0015] Preferably, the dropping conditions for the simultaneous dropping in step S2 are: dropping time 15 min - 120 min, dropping temperature 20°C - 30°C, and dropping stirring speed 200 rpm - 500 rpm;

[0016] Preferably, the coprecipitation conditions in step S2 are: temperature 40°C - 70°C, time 2 h - 8 h, pH 7.0 - 9.0; the drying conditions in step S2 are: drying temperature 80°C - 100°C, drying time 8 h - 12 h.

[0017] Preferably, the conductivity of the filtrate after washing in step S2 is lower than 300 μS / cm.

[0018] The present invention also provides an application of the above lithium iron manganese phosphate precursor or the lithium iron manganese phosphate precursor prepared by the above preparation method in the preparation of a lithium iron manganese phosphate-carbon composite material.

[0019] On the other hand, the present invention provides a method for preparing a lithium iron manganese phosphate-carbon composite material, comprising the following steps:

[0020] S1. Grinding and mixing the above lithium iron manganese phosphate precursor with a lithium salt, a phosphorus salt, and an additive in a liquid phase system and then drying, and sintering the dried powder in an inert atmosphere to obtain a prelithiated lithium iron manganese phosphate precursor;

[0021] S2. Taking the prelithiated lithium iron manganese phosphate precursor and a carbon source, grinding and mixing them in a liquid phase system and drying to obtain a precursor of the lithium iron manganese phosphate-carbon composite material;

[0022] S3. Sintering the precursor of the lithium iron manganese phosphate-carbon composite material under an inert gas protection atmosphere to obtain the lithium iron manganese phosphate-carbon composite material.

[0023] Preferably, the lithium salt described in step S1 includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate; the phosphorus salt includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, and lithium phosphate; the additive includes at least one of titanium dioxide, tetrabutyl titanate, magnesium hydroxide, magnesium oxide, magnesium acetate, magnesium nitrate, zirconium dioxide, zirconium hydroxide, niobium pentoxide, nickel acetate, and nickel oxide; the addition amount of the additive is 0-1.0% of the mass of the lithium iron manganese phosphate precursor and 0-1.0% of the mass of the finally formed lithium iron manganese phosphate.

[0024] Preferably, the lithium salt, the lithium iron manganese phosphate precursor, and the phosphorus salt described in step S1 satisfy a molar ratio of Li:(Mn + Fe):P of 1.1-1.0:1:1.1-1.0.

[0025] Preferably, the sintering conditions in step S1 are: temperature 400°C - 700°C, time 2h - 6h; the inert gas is any one of nitrogen, argon, and helium.

[0026] Preferably, the liquid phase system in steps S1 and S2 is any one of pure water, ethanol, and methanol.

[0027] Preferably, the grinding in steps S1 and S2 includes fine grinding and coarse grinding; the time of the coarse grinding is 30min - 60min, and the particle size D of the coarse grinding 50 is 1um - 2um; the time of the fine grinding is 60min - 120min, and the particle size D of the fine grinding 50It is 300 nm - 500 nm.

[0028] Specifically, the grinding refers to first performing rough grinding using a Rans grinding machine and then performing fine grinding using a sand mill.

[0029] Preferably, the drying in steps S1 and S2 is spray drying, and the inlet temperature of the spray drying is 250 - 270 °C, and the outlet temperature is 95 - 105 °C.

[0030] Preferably, the carbon source in step S2 is at least one of glucose, rock sugar, sucrose, fructose, polyethylene glycol, cyclodextrin, starch, and cellulose.

[0031] Preferably, the sintering conditions in step S3 are: temperature 675 °C - 780 °C, time 4 h - 10 h; the inert gas is any one of nitrogen, argon, and helium.

[0032] Preferably, the lithium iron manganese phosphate - carbon composite material in step S3 is subjected to classification and crushing treatment after sintering.

[0033] Preferably, the carbon content in the lithium iron manganese phosphate - carbon composite material in step S3 is 1.2% - 2.5%.

[0034] The present invention also provides an application of the above - mentioned lithium iron manganese phosphate precursor or the lithium iron manganese phosphate precursor prepared by the above - mentioned preparation method in improving the electrical performance of the lithium iron manganese phosphate - carbon composite material.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention draws on the lattice localization effect of layered double - metal hydroxide (LDH) and the ability of the interlayer to accommodate abundant coordinated anions / molecules. By simultaneously adding a mixed metal salt solution of trivalent iron and divalent manganese and an ammonia water solution with a certain concentration into a bottom liquid containing carbonate or bicarbonate, a coprecipitation reaction is carried out at a certain temperature, and then through filtration, washing, and drying, a lithium iron manganese phosphate precursor with atomic - level uniform distribution of iron and manganese elements and high stability in air is obtained. The molar ratio of Fe / Mn can be adjusted during the whole preparation process, and the recovery rate of iron and manganese elements can be as high as over 96%, which is very suitable for industrialization.

[0037] (2) The present invention mixes, sinters a self - made lithium iron manganese phosphate precursor with a lithium source, phosphoric acid, and an additive, and then remixes and grinds the sintered precursor with a carbon source and performs solid - phase sintering, and finally can prepare lithium iron manganese phosphate with excellent properties (electrochemical properties and cycling performance).

[0038] (3) The process for preparing the lithium iron manganese phosphate precursor in the present invention is simple, low - cost, has atomic - level uniform distribution of iron and manganese elements, high air stability, large specific surface area, low impurity content, and high activity.

[0039] (4) The preparation method of the lithium iron manganese phosphate precursor of the present invention does not use strong metal hydroxides. Instead, through the specific ratio between the second precipitating agent and iron and manganese elements, and specific coprecipitation conditions, the obtained lithium iron manganese phosphate precursor has better stability and can significantly improve the electrochemical performance of the lithium iron manganese phosphate-carbon composite material. The first precipitating agent carbonate, bicarbonate and the second precipitating agent NH₃·H₂O used in the present invention are all weak base precipitating agents. NH₃·H₂O acts as a precipitating agent and also as a complexing agent for metal ions. The synergistic effect of the weak base and the complexing agent is beneficial to reducing the nucleation rate of coprecipitation, making the reaction milder and more conducive to the coprecipitation of iron and manganese elements. Adding a strong base such as sodium hydroxide will cause the reaction rate to be too fast and easily result in a locally too high pH, which is not conducive to the coprecipitation of iron and manganese and ultimately affects the performance of the precursor. Description of the Drawings

[0040] Figure 1 XRD pattern of the lithium iron manganese phosphate precursor prepared in Example 1;

[0041] Figure 2 SEM image of the lithium iron manganese phosphate precursor prepared in Example 1;

[0042] Figure 3 SEM image of the lithium iron manganese phosphate prepared in Example 1;

[0043] Figure 4 Discharge curve of the lithium iron manganese phosphate prepared in Example 1;

[0044] Figure 5 1C discharge 100-cycle diagram of the lithium iron manganese phosphate prepared in Example 1. Detailed Embodiments

[0045] The present invention will be described below through specific examples to make the technical solutions of the present invention easier to understand and master. However, the present invention is not limited thereto. The described embodiments are only a part of the embodiments of the present invention, not all of the embodiments.

[0046] The endpoints and any values disclosed in the ranges in this document are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, between the endpoints of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this document. Unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" as used herein include both singular and plural referents. Numerical ranges expressed by endpoints include all values and fractions within the corresponding ranges, as well as the expressed endpoints.

[0047] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention. The experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials are all commercially available unless otherwise specified.

[0048] Example 1

[0049] Preparation of lithium iron manganese phosphate precursor:

[0050] Dissolve 119.96 g of anhydrous ferric sulfate (99.9%) and 152.10 g of manganese sulfate monohydrate (99.9%) in 750 ml of deionized water to obtain a mixed metal salt solution A. Then dissolve 76.5 g of (NH4)2CO3 (99.9%) (molar ratio CO3 2- :(Mn 2+ +Fe 3+ ) = 0.53:1) in 250 ml of deionized water to obtain a first precipitant carbonate solution B. Weigh 300.00 ml of 25 wt.% concentrated ammonia water and 300.00 ml of pure water to prepare a 6.69 mol / L ammonia water solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ ) = 2.68:1) to obtain a second precipitant ammonia water solution C.

[0051] At 30 °C, simultaneously drip the mixed metal salt solution A and the second precipitant ammonia water solution C into a 2 L three-necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The dripping time is 30 min. During the whole dripping process, the stirring speed is 350 rpm / min, and the pH of the reaction system is 8.07. After the dripping is completed, heat up to 60 °C and keep the temperature constant for 4 h. During the reaction process, the stirring speed is 350 rpm / min. After the reaction is completed, the product is filtered, washed and suction filtered until the conductivity of the filtrate < 300 μS / cm; place the filtered filter cake in a blast drying oven at 100 °C and dry for 12 h to finally obtain 158.34 g of lithium iron manganese phosphate precursor. Through detection and analysis, the C content of this precursor is 5.426%, the S content is 0.015%, the total content of Na and K impurities is 108.2 ppm, and the specific surface area is 136.04 m 2 / g; the Fe content is 20.51%, the Mn content is 30.35%. After calculation, its molar ratio Mn / Fe is 0.601:0.399, the Fe yield is 96.6%, and the Mn yield is 97.2%.

[0052] Perform XRD characterization on the obtained lithium iron manganese phosphate precursor, and the results are as Figure 1 . FromFigure 1 It can be known that the prepared lithium iron manganese phosphate precursor is a single phase as shown in the XRD pattern and can well conform to the standard pattern of MnCO3 (PDF card number 86-0172), indicating that the prepared lithium iron manganese phosphate precursor has a manganese carbonate structure, in which a part of Mn 2+ is replaced by Fe 3+ ions, resulting in a positively charged manganese carbonate structure, which is finally balanced by additional OH - or CO3 2- anion groups; after heating the obtained lithium iron manganese phosphate precursor in an air atmosphere at 300 °C for 4 h, it can still maintain its original structural characteristics, indicating its excellent air stability. At the same time, scanning electron microscopy was performed on the obtained lithium iron manganese phosphate precursor, and the results are as Figure 2 . From Figure 2 it can be seen that the prepared lithium iron manganese phosphate precursor is aggregated by primary spherical particles, and the size of the primary particles is relatively uniform, with a size of about 100 nm.

[0053] Preparation of lithium iron manganese phosphate:

[0054] The raw materials were fed according to the molar ratio of Li:(Fe+Mn):P = 1.06:1:1.03. 150.00 g of lithium iron manganese phosphate precursor, 54.30 g of lithium carbonate (99.5%), 165.11 g of ammonium dihydrogen phosphate (99%), and 1.50 g of magnesium carbonate were successively added to a 2 L measuring cup containing 800 mL of pure water, placed in a basket mill and ground at a speed of 2000 r / min for 30 min. After the slurry particle size reached 1-2 μm, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 400 nm, the slurry was spray-dried. After the spray drying was completed, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at a sintering temperature of 500 °C for 4 hours. After the tube furnace naturally cooled to 80 °C, the sintered material was crushed to obtain 205.8 g of pre-lithiated lithium iron manganese phosphate precursor.

[0055] 200.00 g of pre-lithiated lithium iron manganese phosphate precursor, 18.00 g of glucose, and 10.00 g of polyethylene glycol 20000 were successively added to a 2 L measuring cup containing 800 mL of pure water, placed in a basket mill and ground at a speed of 2000 r / min for 40 min. After the slurry particle size reached 1-2 μm, the slurry was introduced into a sand mill for fine grinding. After the slurry particle size reached 300 nm, the slurry was spray-dried. After the spray drying was completed, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering at a sintering temperature of 700 °C for 8 hours. After the tube furnace naturally cooled to 80 °C, the sintered material was crushed in stages to finally obtain LiFe with a carbon content of 1.52% 0.4 Mn0.6 PO4 / C composite material

[0056] For the obtained LiFe 0.4 Mn 0.6 PO4 / C composite material was characterized by scanning electron microscopy. It can be seen from Figure 3 it that the prepared lithium iron manganese phosphate material has relatively uniform particle size, and most of the primary particles are mainly concentrated around 200 - 300 m

[0057] Using the prepared LiFe 0.4 Mn 0.6 PO4 / C composite material as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, an electrode sheet was made. Using metallic lithium as the negative electrode, a button cell was assembled. At 2 - 4.3 V and 25 °C, under different charge-discharge current conditions, the initial reversible capacity was 155.8 mAh / g when charged and discharged at 0.1C, 153.6 mAh / g when charged and discharged at 0.2C, and 146.7 mAh / g when charged and discharged at 1C. And the capacity retention rate was 97.1% after 100 cycles at 1C

[0058] Example 2

[0059] Preparation of lithium iron manganese phosphate precursor

[0060] 89.97 g of anhydrous ferric sulfate (99.9%) and 177.45 g of manganese sulfate monohydrate (99.9%) were dissolved in 750 mL of deionized water to obtain a mixed metal salt solution A. Then 89.25 g of (NH4)2CO3 (99.9%) (molar ratio CO3 2- :(Mn 2+ +Fe 3+ ) = 0.62:1) was dissolved in 250 mL of deionized water to obtain a first precipitant carbonate solution B. 280.00 mL of 25 wt.% concentrated ammonia water and 280.00 mL of pure water were mixed to prepare a 6.69 mol / L ammonia water solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ ) = 2.50:1) to obtain a second precipitant ammonia water solution C

[0061] At 30 °C, the mixed metal salt solution A and the second precipitant ammonia water solution C were simultaneously dropped into a 2 L three-necked flask containing the first precipitant carbonate solution B by a peristaltic pump. The dropping time was 30 min. During the whole dropping process, the stirring speed was 350 rpm / min, and the pH of the reaction system was 8.29. After the dropping was completed, the temperature was raised to 60 °C and the reaction was carried out at a constant temperature for 4 h. During the reaction process, the stirring speed was 350 rpm / min. After the reaction was completed, the product was filtered, washed and suction-filtered until the conductivity of the filtrate < 300 μS / cm; the filtered cake was placed in a blast drying oven at 100 °C and dried for 12 h, and finally 160.34 g of lithium iron manganese phosphate precursor was obtained. Through detection and analysis, the C content of this precursor was 6.200%, the S content was 0.021%, the total content of Na and K impurities was 111.3 ppm, and the specific surface area was 148.95 m 2 / g; the Fe content was 15.28%, the Mn content was 34.87%. After calculation, the molar ratio of Mn / Fe was 0.699:0.301, the Fe yield was 97.5%, and the Mn yield was 96.9%.

[0062] Preparation of lithium iron manganese phosphate:

[0063] The raw materials were fed according to the molar ratio of Li:(Fe + Mn):P = 1.06:1:1.03. 150.00 g of lithium iron manganese phosphate precursor, 53.63 g of lithium carbonate (99.5%), 163.07 g of ammonium dihydrogen phosphate (99%), and 1.48 g of magnesium hydroxide were successively added to a 2 L measuring cup containing 800 mL of pure water, and placed in a basket mill and ground at a speed of 2000 r / min for 30 min. After the particle size of the slurry reached 1 - 2 μm, the slurry was introduced into a sand mill for fine grinding. After the particle size of the slurry reached 350 nm, the slurry was spray-dried. After the spray drying was completed, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering. The sintering temperature was 600 °C and the constant temperature was 4 hours. After the tube furnace naturally cooled to 80 °C, the sintered material was crushed to obtain 210.5 g of pre-lithiated lithium iron manganese phosphate precursor.

[0064] 200.00 g of pre-lithiated lithium iron manganese phosphate precursor, 18.00 g of rock sugar, and 5.00 g of starch were successively added to a 2 L measuring cup containing 800 mL of pure water, and placed in a basket mill and ground at a speed of 2000 r / min for 40 min. After the particle size of the slurry reached 1 - 2 μm, the slurry was introduced into a sand mill for fine grinding. After the particle size of the slurry reached 300 nm, the slurry was spray-dried. After the spray drying was completed, the dried and crushed material was placed in a tube furnace under a nitrogen atmosphere for sintering. The sintering temperature was 700 °C and the constant temperature was 8 hours. After the tube furnace naturally cooled to 80 °C, the sintered material was crushed in stages, and finally LiFe with a carbon content of 1.63% was obtained0.3 Mn 0.7 MnPO4 / C composite material

[0065] Using the prepared LiFe 0.3 Mn 0.7 PO4 / C composite material as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, an electrode sheet was made. Using metallic lithium as the negative electrode, a button cell was assembled. At 2 - 4.3 V and 25 °C, tests were carried out under different charge - discharge current conditions. The initial reversible capacity during charge - discharge at 0.1 C was 154.9 mAh / g, the initial reversible capacity during charge - discharge at 0.2 C was 152.8 mAh / g, the initial reversible capacity during charge - discharge at 1 C was 145.5 mAh / g, and the capacity retention rate after 100 cycles at 1 C was 96.5%.

[0066] Example 3

[0067] Preparation of lithium iron manganese phosphate precursor:

[0068] 59.98 g of anhydrous ferric sulfate (99.9%) and 202.81 g of manganese sulfate monohydrate (99.9%) were dissolved in 750 mL of deionized water to obtain a mixed metal salt solution A. Then, 102.00 g of (NH4)2CO3 (99.9%) (molar ratio CO3 2- :(Mn 2+ +Fe 3+ ) = 0.71:1) was dissolved in 250 mL of deionized water to obtain a first precipitant carbonate solution B. 270.00 mL of 25 wt.% concentrated ammonia water and 270.00 mL of pure water were mixed to prepare a 6.69 mol / L ammonia water solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ ) = 2.41:1), obtaining a second precipitant ammonia water solution C.

[0069] At 30 °C, the mixed metal salt solution A and the second precipitant ammonia water solution C were simultaneously added dropwise to a 2 L three - necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The dropping time was 30 min. During the whole dropping process, the stirring speed was 350 rpm / min, and the pH of the reaction system was 8.65. After the dropping was completed, the temperature was raised to 60 °C and kept at a constant temperature for 4 h. During the reaction process, the stirring speed was 350 rpm / min. After the reaction was completed, the product was filtered, washed, and suction - filtered until the conductivity of the filtrate < 300 μS / cm; the filtered cake was placed in a blast drying oven at 100 °C and dried for 12 h, finally obtaining 163.13 g of lithium iron manganese phosphate precursor. Through detection and analysis, the C content of this precursor was 6.973%, the S content was 0.023%, the total content of Na and K impurities was 119.7 ppm, and the specific surface area was 160.60 m2 / g; The Fe content is 10.13%, and the Mn content is 39.40%. After calculation, the molar ratio of Mn / Fe is 0.798:0.202, the Fe recovery rate is 98.4%, and the Mn recovery rate is 97.5%.

[0070] Preparation of lithium iron manganese phosphate:

[0071] Charge according to the molar ratio of raw materials Li:(Fe + Mn):P = 1.06:1:1.03. Add 150.00 g of lithium iron manganese phosphate precursor, 53.05 g of lithium carbonate (99.5%), 161.32 g of ammonium dihydrogen phosphate (99%), 0.85 g of titanium dioxide, and 0.75 g of niobium pentoxide into a 2 L measuring cup containing 800 mL of pure water in sequence. Place it in a basket mill and grind at a speed of 2000 r / min for 30 min. After the slurry particle size reaches 1 - 2 μm, transfer the slurry to a sand mill for fine grinding. After the slurry particle size reaches 300 nm, spray-dry this slurry. After the spray drying is completed, place the dried and crushed material in a tube furnace under a nitrogen atmosphere for sintering. The sintering temperature is 65

[0072] 0 °C, keep the temperature constant for 5 hours. After the tube furnace naturally cools down to 80 °C, crush the sintered material to obtain 208.3 g of pre-lithiated lithium iron manganese phosphate precursor.

[0073] Add 200.00 g of pre-lithiated lithium iron manganese phosphate precursor, 16.00 g of cyclodextrin, and 4.00 g of fructose into a 2 L measuring cup containing 800 mL of pure water in sequence. Place it in a basket mill and grind at a speed of 2000 r / min for 40 min. After the slurry particle size reaches 1 - 2 μm, transfer the slurry to a sand mill for fine grinding. After the slurry particle size reaches 300 nm, spray-dry this slurry. After the spray drying is completed, place the dried and crushed material in a tube furnace under a nitrogen atmosphere for sintering. The sintering temperature is 700 °C, keep the temperature constant for 6 hours. After the tube furnace naturally cools down to 80 °C, classify and crush the sintered material to finally obtain LiFe with a carbon content of 1.54% 0.2 Mn 0.8 PO4 / C composite material.

[0074] Using the prepared LiFe 0.2 Mn 0.8The PO4 / C composite material was used as the cathode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to prepare the electrode sheet. Using metallic lithium as the anode, a button cell was assembled. At 2 - 4.3 V and 25 °C, under different charge-discharge current conditions, the initial reversible capacity was 154.7 mAh / g when charged and discharged at 0.1 C, 152.5 mAh / g when charged and discharged at 0.2 C, and 145.6 mAh / g when charged and discharged at 1 C. And the capacity retention rate was 96.3% after 100 cycles at 1 C.

[0075] Example 4

[0076] Preparation of lithium iron manganese phosphate precursor:

[0077] 149.96 g of anhydrous ferric sulfate (99.9%) and 126.76 g of manganese sulfate monohydrate (99.9%) were dissolved in 750 mL of deionized water to obtain a mixed metal salt solution A. Then, 63.75 g of (NH4)2CO3 (99.9%) (molar ratio of CO3 2- :(Mn 2+ +Fe 3+ ) = 0.44:1) was dissolved in 250 mL of deionized water to obtain a first precipitant carbonate solution B. 310.00 mL of 25 wt.% concentrated ammonia water and 310.00 mL of pure water were mixed to prepare a 6.69 mol / L ammonia water solution (molar ratio of NH3·H2O:(Mn 2+ +Fe 3+ ) = 2.77:1), obtaining a second precipitant ammonia water solution C.

[0078] At 30 °C, the mixed metal salt solution A and the second precipitant ammonia water solution C were simultaneously added dropwise into a 2 L three-necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The dropping time was 30 min. During the whole dropping process, the stirring speed was 350 rpm / min, and the pH of the reaction system was 8.11. After the dropping was completed, the temperature was raised to 60 °C and kept at a constant temperature for 4 h. During the reaction process, the stirring speed was 350 rpm / min. After the reaction was completed, the product was filtered, washed, and suction filtered until the conductivity of the filtrate < 300 μS / cm; the filtered cake was placed in a blast drying oven at 100 °C and dried for 12 h, finally obtaining 157.09 g of lithium iron manganese phosphate precursor. Through detection and analysis, the C content of this precursor was 4.494%, the S content was 0.036%, the total content of Na and K impurities was 115.5 ppm, and the specific surface area was 123.24 m 2 / g; the Fe content was 25.77%, the Mn content was 25.38%. After calculation, the molar ratio of Mn / Fe was 0.500:0.500, the Fe yield was 96.4%, and the Mn yield was 96.8%.

[0079] Preparation of lithium iron manganese phosphate:

[0080] Charge the raw materials according to the molar ratio of Li:(Fe + Mn):P = 1.06:1:1.03. Add 150.00 g of lithium iron manganese phosphate precursor, 54.52 g of lithium carbonate (99.5%), 165.78 g of ammonium dihydrogen phosphate (99%), and 1.5 g of magnesium oxide into a 2 L measuring cup containing 800 mL of pure water in sequence. Place it in a basket mill and grind at a speed of 2000 r / min for 30 min. After the particle size of the slurry reaches 1 - 2 μm, transfer the slurry to a sand mill for fine grinding. After the particle size of the slurry reaches 350 nm, spray-dry this slurry. After the spray drying is completed, place the dried and crushed material in a tube furnace under a nitrogen atmosphere for sintering. The sintering temperature is 600 °C and keep it at a constant temperature for 4 hours. After the tube furnace naturally cools down to 80 °C, crush the sintered material to obtain 213.5 g of the prelithiated lithium iron manganese phosphate precursor.

[0081] Add 200.00 g of the prelithiated lithium iron manganese phosphate precursor, 18.00 g of glucose, and 4.00 g of rock sugar into a 2 L measuring cup containing 800 mL of pure water in sequence. Place it in a basket mill and grind at a speed of 2000 r / min for 40 min. After the particle size of the slurry reaches 1 - 2 μm, transfer the slurry to a sand mill for fine grinding. After the particle size of the slurry reaches 320 nm, spray-dry this slurry. After the spray drying is completed, place the dried and crushed material in a tube furnace under a nitrogen atmosphere for sintering. The sintering temperature is 700 °C and keep it at a constant temperature for 6 hours. After the tube furnace naturally cools down to 80 °C, perform graded crushing on the sintered material to finally obtain the LiFe 0.5 Mn 0.5 PO4 / C composite material with a carbon content of 1.61%.

[0082] Using the prepared LiFe 0.5 Mn 0.5 PO4 / C composite material as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to make an electrode sheet. Using metallic lithium as the negative electrode, assemble it into a button cell. At 2 - 4.3 V and 25 °C, test it under different charge and discharge current conditions. The initial reversible capacity for charge and discharge at 0.1C is 156.5 mAh / g, the initial reversible capacity for charge and discharge at 0.2C is 153.8 mAh / g, the initial reversible capacity for charge and discharge at 1C is 146.9 mAh / g, and the capacity retention rate after 100 cycles at 1C is 97.3%.

[0083] Example 5

[0084] Preparation of lithium iron manganese phosphate precursor:

[0085] Dissolve 242.39 g of iron(III) nitrate nonahydrate (99.5%) and 322.06 g of 50% manganese nitrate solution in 750 mL of deionized water to obtain a mixed metal salt solution A. Then dissolve 78.21 g of NH4HCO3 (99.9%) (molar ratio HCO3 - :(Mn 2+ +Fe 3+ ) = 0.66:1) in 500 mL of deionized water to obtain a first precipitating agent carbonate solution B. Weigh 375.00 mL of 25 wt.% concentrated ammonia water and 200.00 mL of pure water to prepare an 8.73 mol / L ammonia water solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ ) = 3.35:1) to obtain a second precipitating agent ammonia water solution C.

[0086] Under the condition of 30 °C, simultaneously drip the mixed metal salt solution A and the second precipitating agent ammonia water solution C into a 2 L three-necked flask containing the first precipitating agent carbonate solution B through a peristaltic pump. The dripping time is 15 min. During the whole dripping process, the stirring speed is 450 rpm / min, and the pH of the reaction system is 8.79. After the dripping is completed, raise the temperature to 70 °C and keep the temperature constant for 3 h. During the reaction process, the stirring speed is 450 rpm / min. After the reaction is completed, filter, wash, and suction-filter the product until the conductivity of the filtrate < 300 μS / cm; place the filtered cake in a blast drying oven at 100 °C and dry for 12 h to finally obtain 146.27 g of lithium iron manganese phosphate precursor. Through detection and analysis, the C content of this precursor is 4.475%, the total content of Na and K impurities is 128.7 ppm, and the specific surface area is 176.48 m 2 / g; the Fe content is 21.84%, the Mn content is 32.69%. After calculation, its molar ratio of Mn / Fe is 0.603:0.397, the Fe recovery rate is 95.1%, and the Mn recovery rate is 96.7%.

[0087] Preparation of lithium iron manganese phosphate:

[0088] The raw materials are fed in accordance with the molar ratio of Li:(Fe+Mn):P = 1.05:1:1.03. Successively add 140.00 g of lithium iron manganese phosphate precursor, 53.82 g of lithium carbonate (99.5%), 165.23 g of ammonium dihydrogen phosphate (99%), 0.76 g of zirconium dioxide, and 0.45 g of magnesium oxide into a 2 L measuring cup containing 800 mL of pure water. Place it in a basket mill and grind at a speed of 2000 r / min for 30 min. After the particle size of the slurry reaches 1 - 2 μm, transfer the slurry to a sand mill for fine grinding. After the particle size of the slurry reaches 360 nm, spray-dry this slurry. After the spray drying is completed, place the dried and crushed material in a tube furnace under a nitrogen atmosphere for sintering at a sintering temperature of 550 °C for 4 hours. After the tube furnace naturally cools down to 80 °C, crush the sintered material to obtain 205.6 g of pre-lithiated lithium iron manganese phosphate precursor.

[0089] Successively add 200.00 g of pre-lithiated lithium iron manganese phosphate precursor, 15.00 g of glucose, and 7.00 g of cellulose into a 2 L measuring cup containing 800 mL of pure water. Place it in a basket mill and grind at a speed of 2000 r / min for 40 min. After the particle size of the slurry reaches 1 - 2 μm, transfer the slurry to a sand mill for fine grinding. After the particle size of the slurry reaches 320 nm, spray-dry this slurry. After the spray drying is completed, place the dried and crushed material in a tube furnace under a nitrogen atmosphere for sintering at a sintering temperature of 730 °C for 4 hours. After the tube furnace naturally cools down to 80 °C, crush the sintered material in stages to finally obtain a LiFe 0.4 Mn 0.6 PO4 / C composite material.

[0090] Using the prepared LiFe 0.4 Mn 0.6 PO4 / C composite material as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder to make an electrode sheet. Using metallic lithium as the negative electrode, assemble it into a button cell. At 2 - 4.3 V and 25 °C, test under different charge-discharge current conditions. The initial reversible capacity for charge-discharge at 0.1C is 155.7 mAh / g, the initial reversible capacity for charge-discharge at 0.2C is 153.1 mAh / g, the initial reversible capacity for charge-discharge at 1C is 145.9 mAh / g, and the capacity retention rate after 100 cycles at 1C is 96.9%.

[0091] Example 6

[0092] Preparation of lithium iron manganese phosphate precursor:

[0093] Dissolve 97.32 g of anhydrous ferric chloride (99%) and 178.11 g of manganese chloride tetrahydrate (99%) in 750 mL of deionized water to obtain a mixed metal salt solution A. Then dissolve 89.94 g of (NH4)2CO3 (99.9%) (molar ratio CO3 2- :(Mn 2+ +Fe 3+ ) = 0.62:1) in 250 mL of deionized water to obtain a first precipitant carbonate solution B. Weigh 250.00 mL of 25 wt.% concentrated ammonia water and 75.00 mL of pure water to prepare a 10.29 mol / L ammonia water solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ ) = 2.23:1), to obtain a second precipitant ammonia water solution C.

[0094] Under the condition of 30 °C, simultaneously drip the mixed metal salt solution A and the second precipitant ammonia water solution C into a 2 L three-necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The dripping time is 60 min. During the whole dripping process, the stirring speed is 250 rpm / min, and the pH of the reaction system is 7.64. After the dripping is completed, heat up to 45 °C and keep the temperature constant for reaction for 8 h. During the reaction process, the stirring speed is 250 rpm / min. After the reaction is completed, the product is filtered, washed and suction filtered until the conductivity of the filtrate < 300 μS / cm; place the filtered cake in a blast drying oven at 100 °C for drying for 12 h to finally obtain 165.51 g of lithium iron manganese phosphate precursor. Through detection and analysis, the C content of this precursor is 6.083%, the Cl - content is 112 ppm, the total content of Na and K impurities is 123.1 ppm, and the specific surface area is 126.43 m 2 / g; the Fe content is 19.51%, the Mn content is 28.87%. After calculation, its molar ratio of Mn / Fe is 0.601:0.399, the Fe yield is 96.1%, and the Mn yield is 96.7%.

[0095] Preparation of lithium iron manganese phosphate:

[0096] The raw materials are fed in according to the molar ratio of Li:(Fe+Mn):P = 1.06:1:1.02. 160.00 g of lithium iron manganese phosphate precursor, 55.09 g of lithium carbonate (99.5%), 165.90 g of ammonium dihydrogen phosphate (99%), 0.58 g of nickel acetate, and 0.85 g of magnesium oxide are successively added to a 2 L measuring cup containing 800 mL of pure water, and placed in a planetary ball mill to grind at a speed of 2000 r / min for 30 min. After the particle size of the slurry reaches 1-2 um, the slurry is introduced into a sand mill for fine grinding. After the particle size of the slurry reaches 360 nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 600 °C for 4 hours. After the tubular furnace naturally cools down to 80 °C, the sintered material is crushed to obtain 215.8 g of pre-lithiated lithium iron manganese phosphate precursor.

[0097] 200.00 g of pre-lithiated lithium iron manganese phosphate precursor, 18.00 g of rock sugar, and 10.00 g of polyethylene glycol are successively added to a 2 L measuring cup containing 800 mL of pure water, and placed in a planetary ball mill to grind at a speed of 2000 r / min for 40 min. After the particle size of the slurry reaches 1-2 um, the slurry is introduced into a sand mill for fine grinding. After the particle size of the slurry reaches 320 nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 730 °C for 4 hours. After the tubular furnace naturally cools down to 80 °C, the sintered material is classified and crushed to finally obtain a LiFe 0.4 Mn 0.6 PO4 / C composite material with a carbon content of 1.58%.

[0098] Using the prepared LiFe 0.4 Mn 0.6 PO4 / C composite material as the cathode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, an electrode sheet is made. Using metallic lithium as the anode, a coin cell is assembled. At 2-4.3 V and 25 °C, different charge-discharge current conditions are used for testing. The initial reversible capacity for charge-discharge at 0.1 C is 155.6 mAh / g, the initial reversible capacity for charge-discharge at 0.2 C is 153.3 mAh / g, the initial reversible capacity for charge-discharge at 1 C is 145.5 mAh / g, and the capacity retention rate after 100 cycles at 1 C is 96.6%.

[0099] Comparative Example 1

[0100] Preparation of lithium iron manganese phosphate precursor:

[0101] Compared with Example 1, the difference is that the amount of ammonium carbonate used is 122.51 g (molar ratio CO3 2- :(Mn2+ +Fe 3+ ) = 0.85:1).

[0102] Dissolve 119.96 g of anhydrous ferric sulfate (99.9%) and 152.10 g of manganese sulfate monohydrate (99.9%) in 750 mL of deionized water to obtain a mixed metal salt solution A. Then dissolve 122.51 g of (NH4)2CO3 (99.9%) (molar ratio of CO3 2- :(Mn 2+ +Fe 3 + ) = 0.85:1) in 250 mL of deionized water to obtain a first precipitant carbonate solution B. Weigh 300.00 mL of 25 wt.% concentrated ammonia water and 300.00 mL of pure water to prepare a 6.69 mol / L ammonia water solution (molar ratio of NH3·H2O:(Mn 2+ +Fe 3+ ) = 2.68:1), to obtain a second precipitant ammonia water solution C.

[0103] Under the condition of 30 °C, simultaneously drip the mixed metal salt solution A and the second precipitant ammonia water solution C into a 2 L three-necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The dripping time is 30 min. During the whole dripping process, the stirring speed is 350 rpm / min, and the pH of the reaction system is 7.38. After the dripping is completed, heat up to 60 °C and keep the temperature constant for 4 h. During the reaction process, the stirring speed is 350 rpm / min. After the reaction is completed, the product is filtered, washed and suction-filtered until the conductivity of the filtrate < 300 μS / cm; place the filtered cake in a blast drying oven at 100 °C and dry it for 12 h to finally obtain 168.34 g of lithium iron manganese phosphate precursor. Through detection and analysis, the C content of this precursor is 8.029%, the S content is 0.542%, the total content of Na and K impurities is 5129.1 ppm, and the specific surface area is 238.51 m 2 / g; the Fe content is 19.36%, the Mn content is 28.42%. After calculation, its molar ratio of Mn / Fe is 0.599:0.401, the Fe recovery rate is 97.0%, and the Mn recovery rate is 96.8%.

[0104] It can be seen from the experimental results that when using too much carbonate, the iron and manganese recovery rates of the final lithium iron manganese phosphate precursor are relatively high, the carbon content is also high, and the iron-manganese ratio is close to the theoretical value, but the impurity content of the precursor is high.

[0105] Preparation of lithium iron manganese phosphate:

[0106] The raw materials are fed in a molar ratio of Li:(Fe + Mn):P = 1.06:1:1.03. 160.00 g of lithium iron manganese phosphate precursor, 54.41 g of lithium carbonate (99.5%), 165.45 g of ammonium dihydrogen phosphate (99%), and 1.5 g of magnesium carbonate are successively added to a 2 L measuring cup containing 800 mL of pure water, and placed in a planetary ball mill to grind at a speed of 2000 r / min for 30 min. After the slurry particle size reaches 1 - 2 μm, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 400 nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 500 °C for 4 hours. After the tubular furnace naturally cools down to 80 °C, the sintered material is crushed to obtain 208.9 g of pre-lithiated lithium iron manganese phosphate precursor.

[0107] 200.00 g of pre-lithiated lithium iron manganese phosphate precursor, 18.00 g of glucose, and 10.00 g of polyethylene glycol 20000 are successively added to a 2 L measuring cup containing 800 mL of pure water, and placed in a planetary ball mill to grind at a speed of 2000 r / min for 40 min. After the slurry particle size reaches 1 - 2 μm, the slurry is introduced into a sand mill for fine grinding. After the slurry particle size reaches 300 nm, the slurry is spray-dried. After the spray drying is completed, the dried and crushed material is placed in a tubular furnace under a nitrogen atmosphere for sintering at a sintering temperature of 700 °C for 8 hours. After the tubular furnace naturally cools down to 80 °C, the sintered material is classified and crushed to finally obtain LiFe 0.4 Mn 0.6 PO4 / C composite material with a carbon content of 1.52%.

[0108] Using the prepared LiFe 0.4 Mn 0.6 PO4 / C composite material as the positive electrode material, acetylene black as the conductive agent, and polytetrafluoroethylene as the binder, an electrode sheet is made. Using metallic lithium as the negative electrode, a coin cell is assembled. At 2 - 4.3 V and 25 °C, different charge-discharge current conditions are used for testing. The initial reversible capacity during charge-discharge at 0.1C is 151.4 mAh / g, the initial reversible capacity during charge-discharge at 0.2C is 149.1 mAh / g, the initial reversible capacity during charge-discharge at 1C is 140.1 mAh / g, and the capacity retention rate after 100 cycles at 1C is 82.3%.

[0109] Comparative Example 2

[0110] Preparation of lithium iron manganese phosphate precursor:

[0111] Compared with Example 1, the difference is that the amount of ammonium carbonate used is 50.45 g (molar ratio CO3 2- :(Mn 2++Fe 3+ ) = 0.35:1).

[0112] Dissolve 119.96 g of anhydrous ferric sulfate (99.9%) and 152.10 g of manganese sulfate monohydrate (99.9%) into 750 mL of deionized water to obtain a mixed metal salt solution A. Then dissolve 50.45 g of (NH4)2CO3 (99.9%) (molar ratio CO3 2- :(Mn 2+ +Fe 3+ ) = 0.35:1) into 250 mL of deionized water to obtain a first precipitant carbonate solution B. Weigh 300.00 mL of 25 wt.% concentrated ammonia water and 300.00 mL of pure water to prepare a 6.69 mol / L ammonia water solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ ) = 2.68:1) to obtain a second precipitant ammonia water solution C.

[0113] Under the condition of 30 °C, simultaneously drip the mixed metal salt solution A and the second precipitant ammonia water solution C into a 2 L three-necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The dripping time is 30 min. During the whole dripping process, the stirring speed is 350 rpm / min, and the pH of the reaction system is 7.38. After the dripping is completed, raise the temperature to 60 °C and keep the temperature constant for reaction for 4 h. During the reaction process, the stirring speed is 350 rpm / min. After the reaction is completed, filter, wash and suction-filter the product until the conductivity of the filtrate < 300 μS / cm; place the filtered cake in a blast drying oven at 100 °C and dry for 12 h to finally obtain 143.73 g of lithium iron manganese phosphate precursor. After detection and analysis, the C content of this precursor is 4.015%, the S content is 0.476%, the total content of Na and K impurities is 126.4 ppm, and the specific surface area is 76.33 m 2 / g; the Fe content is 21.23%, the Mn content is 27.04%. After calculation, its molar ratio Mn / Fe is 0.564:0.436, the Fe recovery rate is 90.8%, and the Mn recovery rate is 78.6%.

[0114] It can be seen from the experimental results that too little use of carbonate results in low recovery rates of iron and manganese elements in the final lithium iron manganese phosphate precursor, inaccurate iron-manganese ratio (theoretical value Mn / Fe = 6:4), and high S impurity content.

[0115] Comparative Example 3

[0116] Preparation of lithium iron manganese phosphate precursor:

[0117] Compared with Example 1, the difference is that the amount of ammonia water used is 450 mL (molar ratio NH3·H2O:(Mn 2+ +Fe3+ ) = 4.01:1).

[0118] Dissolve 119.96 g of anhydrous ferric sulfate (99.9%) and 152.10 g of manganese sulfate monohydrate (99.9%) into 750 mL of deionized water to obtain a mixed metal salt solution A. Then dissolve 76.5 g of (NH4)2CO3 (99.9%) (molar ratio CO3 2- :(Mn 2+ +Fe 3+ ) = 0.53:1) into 250 mL of deionized water to obtain a first precipitant carbonate solution B. Weigh 450.00 mL of 25 wt.% concentrated ammonia water and 450.00 mL of pure water to prepare a 6.69 mol / L ammonia water solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ ) = 4.01:1), to obtain a second precipitant ammonia water solution C.

[0119] Under the condition of 30 °C, simultaneously drip the mixed metal salt solution A and the second precipitant ammonia water solution C into a 2 L three-necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The dripping time is 30 min. During the whole dripping process, the stirring speed is 350 rpm / min, and the pH of the reaction system is 9.64. After the dripping is completed, heat up to 60 °C and keep the temperature constant for reaction for 4 h. During the reaction process, the stirring speed is 350 rpm / min. After the reaction is completed, the product is filtered, washed and suction filtered until the conductivity of the filtrate < 300 μS / cm; place the filtered filter cake in a blast drying oven at 100 °C and dry for 12 h to finally obtain 144.65 g of lithium iron manganese phosphate precursor. Through detection and analysis, the C content of this precursor is 5.288%, the S content is 0.316%, the total content of Na and K impurities is 2131.5 ppm, and the specific surface area is 194.35 m 2 / g; the Fe content is 21.76%, the Mn content is 23.61%. After calculation, its molar ratio of Mn / Fe is 0.524:0.476, the Fe yield is 93.7%, and the Mn yield is 69.1%.

[0120] It can be seen from the experimental results that excessive ammonia water makes the pH value of the reaction system increase, the iron and manganese yields are low, ultimately resulting in the imbalance of the iron and manganese ratio (the theoretical value of Mn / Fe = 6:4), inaccurate ratio, and relatively high impurity content in the precursor.

[0121] Comparative Example 4

[0122] Preparation of lithium iron manganese phosphate precursor:

[0123] Compared with Example 1, the difference is that the dosage of ammonia water is 175 mL (molar ratio NH3·H2O:(Mn 2++Fe 3+ )=1.56:1).

[0124] 119.96 g of anhydrous ferric sulfate (99.9%) and 152.10 g of monohydrated manganese sulfate (99.9%) were dissolved in 750 mL of deionized water to obtain a mixed metal salt solution A. Then 76.5 g of (NH4)2CO3 (99.9%) (molar ratio of CO3 2- :(Mn 2+ +Fe 3+ )=0.53:1) was dissolved in 250mL of deionized water to obtain the first precipitant carbonate solution B. 175.00mL of 25wt.% concentrated ammonia water and 175.00mL of pure water were weighed to prepare a 6.69mol / L ammonia solution (molar ratio NH3·H2O:(Mn 2+ +Fe 3+ )=1.56:1), and obtain the second precipitant ammonia solution C.

[0125] At 30°C, the mixed metal salt solution A and the second precipitant ammonia solution C were simultaneously added dropwise to a 2L three-necked flask containing the first precipitant carbonate solution B through a peristaltic pump. The addition time was 30min. During the entire addition process, the stirring speed was 350rpm / min, and the pH of the reaction system was 6.49. After the addition was completed, the temperature was raised to 60°C and the reaction was kept at a constant temperature for 4h. During the reaction, the stirring speed was 350rpm / min. After the reaction was completed, the product was filtered, washed and filtered until the filtrate conductivity was <300μS / cm; the filtered filter cake was placed in a 100°C blast drying oven and dried for 12h, and finally 147.50g of lithium iron manganese phosphate precursor was obtained. After detection and analysis, the C content of the precursor was 4.237%, the S content was 0.031%, the Na and K impurity content was 109.4ppm in total, and the specific surface area was 107.52m 2 / g; the Fe content is 20.95%, the Mn content is 25.53%, and after calculation, the molar ratio of Mn / Fe is 0.553:0.447, the Fe yield is 92.0%, and the Mn yield is 76.2%.

[0126] It can be seen from the experimental results that too low ammonia water reduces the pH value of the reaction system and the Mn yield is low, which ultimately causes an imbalance in the iron-manganese ratio (theoretical value Mn / Fe=6:4) and an inaccurate ratio.

[0127] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A lithium iron manganese phosphate precursor, characterized in that: It contains an iron-manganese mixed metal salt, a first precipitant and a second precipitant; the first precipitant is a carbonate solution or a bicarbonate solution, and the second precipitant is an ammonia water solution; the ammonia water solution and the iron-manganese mixed metal salt satisfy that NH3·H2O:(Mn 2+ +Fe 3+ ) is a molar ratio of 2.0 - 3.5:

1.

2. The lithium iron manganese phosphate precursor according to claim 1, wherein: The concentration of the first precipitating agent is 3.0 mol / L - 6.0 mol / L; the concentration of the second precipitating agent is 5.35 - 13.38 mol / L; the first precipitating agent and the iron-manganese mixed metal salt satisfy: CO3 2- or HCO3 - and the molar ratio with (Mn 2+ + Fe 3+ ) is 0.4 - 0.8:

1.

3. The lithium iron manganese phosphate precursor according to claim 1, characterized in that: The iron-manganese mixed metal salt contains an iron source and a manganese source; the iron source is trivalent iron, which is at least one of iron nitrate, iron sulfate, and iron chloride; the manganese source is divalent manganese, which is at least one of manganese chloride, manganese acetate, manganese sulfate, and manganese nitrate; the total metal concentration in the iron-manganese mixed metal salt is 0.5 mol / L - 5 mol / L, and Mn 2+ and Fe 3+ have a molar ratio of x:y, where x is 0.5 - 0.9 and x + y = 1.

4. A method for preparing the lithium iron manganese phosphate precursor according to any one of claims 1 to 3, characterized in that: It includes the following steps: S1. Dissolve a certain amount of iron and manganese metal salts in pure water to obtain an iron-manganese mixed metal salt solution; dissolve a certain carbonate or bicarbonate in pure water to obtain a first precipitant; add a certain amount of ammonia water to pure water to obtain a second precipitant; S2. Drop the iron-manganese mixed metal salt solution and the second precipitant into the first precipitant simultaneously for coprecipitation reaction, and then filter, wash, and dry to obtain the lithium iron manganese phosphate precursor.

5. The preparation method according to claim 4, characterized in that: The dropping conditions for the simultaneous dropping in step S2 are: dropping time 15 min - 120 min, dropping temperature 20°C - 30°C, dropping stirring speed 200 rpm - 500 rpm; the coprecipitation conditions in step S2 are: temperature 40°C - 70°C, time 2 h - 8 h, pH 7.0 - 9.0; the drying conditions in step S2 are: drying temperature 80°C - 100°C, drying time 8 h - 12 h.

6. Application of the lithium iron manganese phosphate precursor according to any one of claims 1 - 3 or the lithium iron manganese phosphate precursor prepared by the preparation method according to any one of claims 4 - 5 in the preparation of a lithium iron manganese phosphate-carbon composite material.

7. A method for preparing a lithium iron manganese phosphate-carbon composite material, characterized in that: It includes the following steps: S1. Grind and mix the lithium iron manganese phosphate precursor according to any one of claims 1 - 3 with a lithium salt, a phosphorus salt, and an additive in a liquid phase system and then dry it. Sinter the dried powder in an inert atmosphere to obtain a prelithiated lithium iron manganese phosphate precursor; S2. Take the prelithiated lithium iron manganese phosphate precursor and a carbon source to grind and mix them in a liquid phase system and dry them to obtain a precursor of the lithium iron manganese phosphate-carbon composite material; S3. Sinter the precursor of the lithium iron manganese phosphate-carbon composite material in an inert gas protection atmosphere to obtain the lithium iron manganese phosphate-carbon composite material.

8. The preparation method according to claim 7, wherein: The lithium salt described in step S1 includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate; the phosphorus salt includes at least one of ammonium dihydrogen phosphate, ammonium hydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, and lithium phosphate; the additive includes at least one of titanium dioxide, tetrabutyl titanate, magnesium hydroxide, magnesium oxide, magnesium acetate, magnesium nitrate, zirconium dioxide, zirconium hydroxide, niobium pentoxide, nickel acetate, and nickel oxide; the addition amount of the additive is 0 - 1.0% of the mass of the lithium iron manganese phosphate precursor.

9. The preparation method according to claim 7, characterized in that: The lithium salt, lithium iron manganese phosphate precursor, and phosphorus salt described in step S1 satisfy a molar ratio of Li:(Mn+Fe):P of 1.1-1.0:1:1.1-1.0; the liquid phase system described in steps S1 and S2 is any one of pure water, ethanol, and methanol; the grinding described in steps S1 and S2 includes fine grinding and coarse grinding, the time for the coarse grinding is 30 min - 60 min, and the particle size D 50 for the coarse grinding is 1 μm - 2 μm; the time for the fine grinding is 60 min - 120 min, and the particle size D 50 for the fine grinding is 300 nm - 500 nm.

10. Application of the lithium iron manganese phosphate precursor according to any one of claims 1 - 3 or the lithium iron manganese phosphate precursor prepared by the preparation method according to any one of claims 4 - 5 in improving the electrical performance of the lithium iron manganese phosphate-carbon composite material.

Images