Method for preparing lithium manganese iron phosphate battery positive electrode material precursor by flash evaporation method

Abstract

The invention relates to a method for preparing a lithium manganese iron phosphate battery positive electrode material precursor by a flash evaporation method, which comprises the following steps: (1) co-precipitating a mixed solution: uniformly mixing ferrous sulfate and ultrapure water to obtain a ferrous sulfate solution; uniformly mixing manganese sulfate with ultrapure water to obtain a manganese sulfate solution; uniformly mixing the ferrous sulfate solution and the manganese sulfate solution, adding ammonia water to control the pH value, and stirring for reaction to obtain a coprecipitation solution; (2) carrying out solid-liquid separation on the coprecipitation solution, and washing with ultrapure water to obtain a solid precipitate; (3) adding pure water into the solid precipitate for slurrying, and then adding organic acid for dissolution reaction; after the reaction is finished, adding NH4H2PO4, and uniformly mixing and stirring to obtain MFCP slurry; and (4) carrying out spray flash evaporation treatment on the MFCP slurry, washing and drying to obtain the lithium iron manganese phosphate battery positive electrode material precursor. The method is easy to operate, various impurities and harmful substances in the system can be effectively removed, and the obtained product is good in performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery preparation, and particularly to a method for preparing a precursor of a cathode material for a lithium iron manganese phosphate battery by a flash evaporation method. Background Art

[0002] Lithium iron manganese phosphate (LMFP) is a new type of cathode material for lithium batteries and is active in the market due to its high energy density, excellent safety, and good low-temperature performance. Compared with lithium iron phosphate (LFP) batteries doped with manganese, its charging voltage is increased from 3.4V to 4.1V, and the theoretical energy density is increased by 20% compared with lithium iron phosphate batteries without manganese doping. This improvement is applied to the new energy vehicle industry, which not only improves the charging efficiency but also increases the cruising range, alleviating the problem of capacity reduction of lithium batteries at low temperatures. Manganese iron phosphate (MnxFe1-xPO4, 0 < x < 1) inherits the olivine structure of iron phosphate and has better chemical stability and thermodynamic stability.

[0003] At present, most of the lithium iron manganese phosphate precursors are prepared by the high-temperature solid-phase method. Since the various solid components in this method cannot be fully mixed in the system, the performance indicators cannot meet the use standards of commercial new energy vehicle batteries. Therefore, most of the products prepared by this method are used in low-end markets such as two-wheeled electric vehicles. Another preparation method is the co-precipitation method, which can uniformly disperse Fe, Mn, and P in the prepared lithium iron manganese phosphate precursor. However, this method has problems such as long preparation time, low yield, and easy introduction of impurities. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a precursor of a cathode material for a lithium iron manganese phosphate battery by a flash evaporation method with simple operation and good product performance.

[0005] To solve the above problems, a method for preparing a precursor of a cathode material for a lithium iron manganese phosphate battery by a flash evaporation method according to the present invention includes the following steps: ⑴ Co-precipitation of mixed solutions: Mix ferrous sulfate with ultrapure water evenly to obtain a ferrous sulfate solution with a ferrous ion concentration of 0.25 - 0.5 mol / L; mix manganese sulfate with ultrapure water evenly to obtain a manganese sulfate solution with a manganese ion concentration of 0.25 - 1.5 mol / L; after mixing the ferrous sulfate solution and the manganese sulfate solution evenly, add ammonia water at 30 - 40°C and control its pH value between 8.0 - 9.0, and obtain a co-precipitation solution after stirring and reacting; ⑵ The co-precipitation solution is subjected to solid-liquid separation and washed with ultrapure water to obtain a solid precipitate; ⑶ Add pure water to the solid precipitate at a mass ratio of 1:1 to make a slurry, and then add an organic acid to carry out a dissolution reaction; after the reaction is completed, add NH4H2PO4, mix and stir evenly to obtain MFCP slurry; (4) The MFCP slurry is treated by spray flash evaporation, washed and dried to obtain a precursor of the positive electrode material for a lithium manganese iron phosphate battery.

[0006] In the step (1), the molar ratio of ferrous sulfate to manganese sulfate is 4:6.

[0007] The stirring reaction speed in step (1) is 600-800 r / min, and the reaction time is 2-8 h.

[0008] In the step (2), the ultrapure water washing is performed for no less than 3 times.

[0009] In step (3), the organic acid is acetic acid (CH3COOH), and the molar ratio of the organic acid to the sum of manganese and iron is 1:3.

[0010] In step (3), the molar ratio of NH4H2PO4 to ferromanganese is 1:1.

[0011] The dissolution reaction conditions in step (3) are a temperature of 30-40° C. and a reaction time of 1 h.

[0012] The temperature of the spray flash treatment in step (4) is 260-500°C.

[0013] Compared with the prior art, the present invention has the following advantages: 1. The organic acid added after coprecipitation, filtration and washing in the present invention plays a role of buffering strong acid in the solution, which helps to form a coprecipitate with uniform composition, and by controlling the ratio of ferromanganese to phosphorus source, a particle size D50 range of 240±10μm is prepared, meeting the requirements for preparing battery-grade high-purity ferromanganese phosphate precursor.

[0014] 2. The present invention uses formic acid / acetic acid to convert Fe 2+ Oxidized to Fe 3+ The obtained product does not contain impurities such as Fe(OH)3 colloid, and the added phosphorus source (NH4H2PO4) contains amine substances, which can make Fe 2+ , Mn 2+ The metal ions are better coordinated to generate manganese iron phosphate precursor.

[0015] 3. The flash evaporation process used in the present invention can effectively remove various impurities and harmful substances in the system, such as salt, organic matter, etc.

[0016] 4. The process of the present invention is short and the operation is simple. The prepared precursor component of the positive electrode material of lithium manganese iron phosphate battery has uniform particle size distribution and high tap density, and the product has good physical and chemical indicators: the particle size control range is 200nm to 250nm; the tap density is greater than 2.5g / cm 3 ; Resistivity <100Ω·cm 3 ; Specific surface area is 21±2m 2 / g; discharge capacity ≥158mAh / g; room temperature energy density ≥210Wh / kg; cycle life>3000 times; room temperature rate performance 3C / 1C capacity ratio ≥88%. DETAILED DESCRIPTION

[0017] A method for preparing a positive electrode material precursor of a lithium manganese iron phosphate battery by a flash evaporation method comprises the following steps: ⑴ Co-precipitation of mixed solution: Mix ferrous sulfate and ultrapure water evenly to obtain a ferrous sulfate solution with an iron ion concentration of 0.25-0.5 mol / L; mix manganese sulfate and ultrapure water evenly to obtain a manganese sulfate solution with a manganese ion concentration of 0.25-1.5 mol / L; the molar ratio of ferrous sulfate to manganese sulfate is 4:6. After the ferrous sulfate solution and the manganese sulfate solution are evenly mixed, add ammonia water at 30-40°C, control the pH value between 8.0-9.0, and stir at a speed of 600-800 r / min for 2-8 hours to obtain a coprecipitation solution.

[0018] (2) The coprecipitation solution is subjected to solid-liquid separation, and the sulfate ions are washed with ultrapure water to obtain a solid precipitate. The number of ultrapure water washings is not less than 3 times.

[0019] ⑶ Pure water was added to the solid precipitate at a mass ratio of 1:1 to make a slurry, and then an organic acid was added to dissolve the precipitate. The reaction temperature was 30-40°C and the reaction time was 1 hour. After the reaction, NH4H2PO4 was added and the mixture was mixed and stirred to obtain MFCP slurry.

[0020] Wherein: the organic acid is acetic acid (CH3COOH), and the molar ratio of the organic acid to the sum of manganese and iron is 1:3. The molar ratio of NH4H2PO4 to the sum of manganese and iron is 1:1.

[0021] (4) The MFCP slurry is treated by spray flash evaporation at 260-500°C, and then washed and dried to obtain a precursor of the positive electrode material for a lithium manganese iron phosphate battery.

[0022] Flash evaporation forms a fluidized bed through hot air and atomized MFCP slurry, exchanging heat and water, thus achieving an efficient and rapid drying process.

[0023] Example 1 A method for preparing a positive electrode material precursor of a lithium manganese iron phosphate battery by a flash evaporation method comprises the following steps: ⑴ Co-precipitation of mixed solution: Mix 84g of ferrous sulfate and 1L of ultrapure water evenly to obtain a ferrous sulfate solution; mix 126g of manganese sulfate and 1L of ultrapure water evenly to obtain a manganese sulfate solution; after the ferrous sulfate solution and the manganese sulfate solution are evenly mixed, add 150mL of ammonia water at 30-40°C, control the pH value between 8.0 and 9.0, and stir the reaction at a speed of 600-800r / min for 4h to obtain a coprecipitation solution.

[0024] (2) The coprecipitation solution was separated into solid and liquid and washed three times with ultrapure water to obtain solid precipitates of Fe(OH)3 and Mn(OH)2.

[0025] ⑶ Add 0.5L pure water to the solid precipitate to make it slurry, then add 20mL CH3COOH to dissolve it, the reaction temperature is 30~40℃, and the reaction time is 1h. After the reaction is completed, add 155g NH4H2PO4, mix and stir evenly to obtain MFCP slurry.

[0026] (4) The MFCP slurry was treated by spray flash evaporation at 400°C, washed three times with deionized water and dried to obtain 225g of lithium manganese iron phosphate battery positive electrode material precursor.

[0027] Example 2 A method for preparing a positive electrode material precursor of a lithium manganese iron phosphate battery by a flash evaporation method comprises the following steps: ⑴ Co-precipitation of mixed solution: Mix 112g of ferrous sulfate and 1L of ultrapure water evenly to obtain a ferrous sulfate solution; mix 168g of manganese sulfate and 1L of ultrapure water evenly to obtain a manganese sulfate solution; after the ferrous sulfate solution and the manganese sulfate solution are evenly mixed, add 200mL of ammonia water at 30-40°C, control the pH value between 8.0 and 9.0, and stir at a speed of 800r / min for 8h to obtain a coprecipitation solution.

[0028] (2) The coprecipitation solution was separated into solid and liquid and washed three times with ultrapure water to obtain solid precipitates of Fe(OH)3 and Mn(OH)2.

[0029] ⑶ Add 1L pure water to the solid precipitate to make it slurry, then add 30mL CH3COOH to dissolve it, the reaction temperature is 30~40℃, and the reaction time is 1h. After the reaction is completed, add 212g NH4H2PO4, mix and stir evenly to obtain MFCP slurry.

[0030] (4) The MFCP slurry was treated by spray flash evaporation at 500°C, washed three times with deionized water and dried to obtain 325g of lithium manganese iron phosphate battery positive electrode material precursor.

Claims

1. A method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method, comprising the following steps: ⑴ Co-precipitation of mixed solution: The ferrous sulfate and ultrapure water are mixed evenly to obtain a ferrous sulfate solution with an iron ion concentration of 0.25-0.5 mol / L; manganese sulfate and ultrapure water are mixed evenly to obtain a manganese sulfate solution with a manganese ion concentration of 0.25-1.5 mol / L; after the ferrous sulfate solution and the manganese sulfate solution are mixed evenly, ammonia water is added at 30-40° C., the pH value is controlled between 8.0-9.0, and the coprecipitation solution is obtained after stirring the reaction; (2) the coprecipitation solution is subjected to solid-liquid separation and washed with ultrapure water to obtain a solid precipitate; ⑶ Add pure water to the solid precipitate at a mass ratio of 1:1 to make a slurry, and then add an organic acid to carry out a dissolution reaction; after the reaction is completed, add NH4H2PO4, mix and stir evenly to obtain MFCP slurry; (4) The MFCP slurry is treated by spray flash evaporation, washed and dried to obtain a precursor of the positive electrode material for a lithium manganese iron phosphate battery.

2. The method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method as claimed in claim 1, characterized in that: In the step (1), the molar ratio of ferrous sulfate to manganese sulfate is 4:

6.

3. The method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method according to claim 1, characterized in that: The stirring reaction speed in step (1) is 600-800 r / min, and the reaction time is 2-8 h.

4. The method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method according to claim 1, characterized in that: In the step (2), the ultrapure water washing is performed for no less than 3 times.

5. The method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method as claimed in claim 1, characterized in that: In step (3), the organic acid is acetic acid, and the molar ratio of the organic acid to the sum of manganese and iron is 1:

3.

6. The method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method according to claim 1, characterized in that: In step (3), the molar ratio of NH4H2PO4 to ferromanganese is 1:

1.

7. The method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method as claimed in claim 1, characterized in that: The dissolution reaction conditions in step (3) are a temperature of 30-40° C. and a reaction time of 1 h.

8. The method for preparing a positive electrode material precursor for a lithium manganese iron phosphate battery by a flash evaporation method as claimed in claim 1, characterized in that: The temperature of the spray flash treatment in step (4) is 260-500°C.