A method for preparing a multi-stage doped manganese iron phosphate precursor

Abstract

This invention relates to the field of lithium-ion battery materials technology, and in particular to a method for multi-level doping of a manganese iron phosphate precursor, comprising the following steps: S1, preparing a ferrous salt solution, a manganese salt solution, and a copper salt solution; S2, adding the ferrous salt solution and the manganese salt solution to a first reaction vessel, adding a precipitant and a buffer, mixing and reacting, and introducing gas 1 to obtain an MFC precursor; S3, overflowing the MFC precursor from the first reaction vessel to a second reaction vessel, adding the ferrous salt solution, manganese salt solution, buffer, precipitant, and copper salt solution to the second reaction vessel, and introducing gas 1 to obtain an MFCC slurry; S4, purging the slurry washing vessel, introducing gas 2, adding a phosphoric acid solution to obtain an MFCP slurry; S5, after aging, washing, drying, and packaging, obtaining the finished MFCP precursor. This invention allows for multi-level doping and coating to improve the cycle stability and battery capacity of the material, and this process offers high production line flexibility and low cost.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials, and more particularly to a method for multi-level doping of manganese iron phosphate precursors. Background Technology

[0002] Precursors are key raw materials for the preparation of cathode materials. In the lithium battery cathode industry chain, the final performance of cathode materials will inherit the morphological and structural characteristics of their precursors. The quality of precursors (morphology, particle size, particle size distribution, specific surface area, impurity content, tap density, etc.) directly determines the physicochemical properties of cathode sintering products.

[0003] When applying for this invention, the applicant, after searching, discovered that a Chinese patent disclosed "a high-entropy doped lithium iron manganese phosphate cathode material with a hierarchical porous structure and a preparation method thereof," with application number "CN202311076408.2." This patent mainly involves S1, mixing an organic solvent and adding a carbon source, stirring until uniform to obtain a surface coating material; S2, mixing a lithium source, M source, iron source, manganese source, phosphorus source, carbon source, oxalic acid, and water, stirring until a clear solution is obtained, and adding a graphene solution dropwise to the clear solution to obtain a modified lithium iron manganese phosphate material; S3, mixing the modified lithium iron manganese phosphate material with the surface coating material, heating to evaporate the organic solvent, and obtaining a porous precursor.

[0004] However, the above preparation method is for preparing porous precursor structures. It requires slowly evaporating the organic solvent at a suitable temperature and then drying it. This is beneficial for forming a multi-level porous structure of micropores, mesopores and macropores inside the material. The operation is complicated and the process is cumbersome, resulting in a high degree of difficulty and cost in the preparation of the precursor. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for multi-level doping of manganese iron phosphate precursors.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for multi-level doping of manganese iron phosphate precursor, comprising the following steps:

[0007] S1. Iron crystals, manganese crystals, and copper crystals are dissolved in pure water to prepare ferrous salt solution, manganese salt solution, and copper salt solution, wherein the copper salt solution is a doping solution;

[0008] S2. Add ferrous salt solution and manganese salt solution to the first reaction vessel, add precipitant and buffer to mix and react, control the pH value in the first reaction vessel to 5-8, and introduce gas 1. React continuously at 25-40℃ to obtain MFC precursor, and stabilize the particle size of MFC precursor at 3-5μm.

[0009] S3. Adjust the internal temperature of the second reactor to 25-40℃, overflow the MFC precursor in the first reactor into the second reactor, add ferrous salt solution, manganese salt solution, buffer, precipitant and copper salt solution into the second reactor, control the pH value in the second reactor to 5-8, and introduce gas 1, continue the reaction overflow, and when the particle size increases to 10-12μm, cut to the slurry washing tank to obtain MFCC slurry;

[0010] S4. Drain the slurry washing vessel to a volume of 1 / 2 to 2 / 3. After rinsing, add 70-80℃ pure water to 2 / 3 of the slurry washing vessel and stir for 30 minutes. Repeat this process twice. Introduce gas 2 and add phosphoric acid solution to obtain MFCP slurry.

[0011] S5. After aging, washing, drying and packaging, the MFCP precursor product is obtained.

[0012] As a further description of the above technical solution:

[0013] The iron crystal in step S1 is ferrous sulfate, the manganese crystal in step S1 is manganese sulfate, and the copper crystal in step S1 is copper sulfate.

[0014] As a further description of the above technical solution:

[0015] The concentrations of the ferrous salt solution, manganese salt solution, and copper salt solution in step S1 are 1.5-3 mol / L.

[0016] As a further description of the above technical solution:

[0017] The precipitant in step S3 is ammonium bicarbonate with a concentration of 0.5-2 mol / L, and the buffer in step S3 is ammonia water with a concentration of 4-6 mol / L.

[0018] As a further description of the above technical solution:

[0019] In steps S2 and S3, gas 1 is CO, and in step S4, gas 2 is O3.

[0020] As a further description of the above technical solution:

[0021] In step S2, the kernel MFC precursor is Mn. x Fe (1-x) CO3, where 0.30 ≤ x < 0.70, and the MFCC precursor doped in step S3 is Mn. x Fe y Cu (1-x-y) CO3, where 0.30≤x<0.70, 0.30≤y<0.70, and x+y<1.

[0022] As a further description of the above technical solution:

[0023] The MFCP precursor is mixed with a lithium source and sintered to obtain the cathode material.

[0024] The present invention has the following beneficial effects:

[0025] Compared with existing technologies, this method for multi-stage doping of manganese iron phosphate precursors involves the following steps: In the first stage, ferrous salt solution and manganese salt solution are added to a first reactor to obtain a core MFC precursor; in the second stage, the MFC precursor in the first reactor overflows into a second reactor, and ferrous salt solution, manganese salt solution, and doping solution are added to obtain a doped MFCC precursor; finally, phosphoric acid solution is added for displacement, and the doping of the manganese iron phosphate precursor is completed. This method allows for multi-stage doping and coating to improve the cycle stability of materials and battery capacity, and the process line is highly flexible and low-cost. Attached Figure Description

[0026] Figure 1 This is a flowchart of a method for multi-level doping of manganese iron phosphate precursor proposed in this invention;

[0027] Figure 2 This is an enlarged electron microscope image of the MFCP manganese iron phosphate precursor, which is a method for multi-level doping of manganese iron phosphate precursor proposed in this invention. Detailed Implementation

[0028] Reference Figures 1-2 The present invention provides a method for multi-level doping of manganese iron phosphate precursor, comprising the following steps:

[0029] S1. Iron crystals, manganese crystals, and copper crystals are dissolved in pure water to prepare ferrous salt solutions, manganese salt solutions, and copper salt solutions. The iron crystals are one or more of ferrous sulfate, ferrous chloride, and ferrous nitrate; the manganese crystals are one or more of manganese sulfate, copper chloride, and copper nitrate; and the copper crystals are one or more of copper sulfate, copper chloride, and copper nitrate. These solutions are then mixed with pure water to obtain solutions containing Fe. 2+ Mn 2+ Cu 2+ The concentrations of the ferrous salt solution, manganese salt solution and copper salt solution obtained are 1.5-3 mol / L, preferably 2 mol / L. The copper salt solution is a dopant solution. According to the actual needs of the battery, the copper crystal can be replaced by elements such as cobalt, niobium, titanium, zirconium, and tungsten to make different dopant solutions to meet the needs of different battery scenarios.

[0030] S2. Add the ferrous salt solution and manganese salt solution to the first reaction vessel, and add a precipitant and a buffer to mix and react. The precipitant is one or more of ammonium bicarbonate, ammonium carbonate, and sodium bicarbonate with a concentration of 0.5-2 mol / L, which provides carbonate ions. The buffer is one or more of ammonia water, disodium ethylenediaminetetraacetate, and glycine with a concentration of 4-6 mol / L. Control the pH value in the first reaction vessel to 5-8, and introduce gas 1, which is a reducing gas, such as CO, to prevent Mn from entering the reactor. 2+ Fe 2+ Oxidation, along with the introduction of gas 1, ensures crystal form and prevents collapse, while also facilitating subsequent replacement with phosphate. The reaction is carried out continuously at 25-40℃ to obtain the MFC precursor, with the particle size of the MFC precursor stably controlled at 3-5 μm. Specifically, pure water and ammonia are added to the first reactor, maintaining the internal temperature at 35℃ and the ammonia concentration in the bottom liquid at 0.30 mol / L. Then, ferrous salt and manganese salt solutions are introduced into the first reactor, with a ferrous salt solution flow rate: manganese salt solution flow rate = 4:6. Ammonium bicarbonate as a precipitant and ammonia as a buffer are added and mixed for reaction. During the reaction, the pH value inside the first reactor is controlled at 6.50±0.10, and the ammonia concentration is 0.25-0.30 mol / L. CO gas is introduced during the reaction for protection against Mn. 2+ Fe 2+ Oxidation yields a kernel MFC precursor with a reaction particle size of 4-5 μm. The kernel MFC precursor is Mn. x Fe (1-x) CO3, where 0.30 ≤ x < 0.70;

[0031] S3. Adjust the internal temperature of the second reactor to 25-40℃. Overflow the MFC precursor from the first reactor into the second reactor. Add ferrous salt solution, manganese salt solution, buffer, precipitant, and copper salt solution to the second reactor. The precipitant is one or more of ammonium bicarbonate, ammonium carbonate, and sodium bicarbonate with a concentration of 0.5-2 mol / L, which provides carbonate ions. The buffer is one or more of ammonia water, disodium ethylenediaminetetraacetate, and glycine with a concentration of 4-6 mol / L. Control the pH value in the second reactor to 5-8 and introduce gas 1, which is CO, a reducing gas. Continue the overflow reaction until the particle size reaches 10-12 μm. Transfer the mixture to the washing tank to obtain MFCC slurry. Specifically, add pure water and ammonia water to the second reactor and control the internal temperature of the second reactor to 35℃. The ammonia concentration of the bottom liquid is 0.30 mol / L. The MFC precursor obtained in the first reactor overflows into the second reactor. Then, ferrous salt solution, manganese salt solution, copper salt solution, ammonium bicarbonate solution, and ammonia are introduced into the second reactor. The flow rates of the ferrous salt solution, manganese salt solution, and copper salt solution are 4:5:1, and the pH in the second reactor is controlled at 6.5 ± 0.1. During the reaction, CO is introduced; CO has reducing properties and can protect the ions in the solution from oxidation. The overflow continues until the particle size reaches 10-11 μm, at which point the reaction is switched to a washing reactor. The washing reactor is the next stage after the second reactor, and solution transfer can be performed via overflow. After the washing reactor reaches the specified liquid level, it is replaced to switch the solution in the second reactor to another washing reactor, ensuring the reaction does not stop. The function of the washing reactor is to replace impurities and convert carbonate ions to phosphate ions, obtaining a slurry doped with the MFCC precursor, Mn. x Fe y Cu (1-x-y) CO3, where 0.30≤x<0.70, 0.30≤y<0.70, and x+y<1;

[0032] S4. The washing vessel is purged, with the purging volume being 1 / 2 to 2 / 3 of the vessel's volume, preferably 1 / 2. After purging, pure water at 70-80℃ is added to 2 / 3 of the vessel's volume. The mixture is stirred for 30 minutes. This process is repeated multiple times, preferably twice. Gas 2, a strong oxidizing gas (such as O3), is then introduced. When ozone is introduced into the liquid and a phosphoric acid solution is added in an ozone-containing atmosphere, carbonate ions can be replaced with phosphate ions, thus preparing the MFCP slurry. This process route, which first forms carbonate and then converts it to phosphate, helps avoid the formation of impurity phases and ensures the performance of the final material.

[0033] S5. After aging, washing, drying and packaging, the MFCP precursor product is obtained.

[0034] The cathode material is obtained by sintering the MFCP precursor with a lithium source.

[0035] Working principle: In the first stage, the prepared ferrous salt solution and manganese salt solution are added to the first reactor to obtain the core MFC precursor. In the second stage, the MFC precursor in the first reactor overflows to the second reactor and ferrous salt solution, manganese salt solution and doping solution are added to obtain the doped MFCC precursor. Finally, phosphoric acid solution is added for displacement, and the doping of the manganese iron phosphate precursor is completed.

[0036] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for multi-level doping of manganese iron phosphate precursor, characterized in that: Includes the following steps: S1. Iron crystals, manganese crystals, and copper crystals are dissolved in pure water to prepare ferrous salt solution, manganese salt solution, and copper salt solution, wherein the copper salt solution is a doping solution; S2. Add ferrous salt solution and manganese salt solution to the first reaction vessel, and add ammonium bicarbonate (0.5-2 mol / L) as a precipitant and ammonia (4-6 mol / L) as a buffer to mix and react. Control the pH value in the first reaction vessel to 5-8, and introduce CO. React continuously at 25-40℃ to obtain the MFC precursor. The particle size of the MFC precursor is stably controlled at 3-5 μm, and the core MFC precursor is Mn. x Fe (1-x) CO3, where 0.30 ≤ x < 0.70; S3. Adjust the internal temperature of the second reactor to 25-40℃. Overflow the MFC precursor from the first reactor into the second reactor. Add ferrous salt solution, manganese salt solution, ammonia water with a concentration of 4-6 mol / L as a buffer, ammonium bicarbonate with a concentration of 0.5-2 mol / L as a precipitant, and copper salt solution into the second reactor. Control the pH value in the second reactor to 5-8 and introduce CO. Continue the overflow reaction until the particle size reaches 10-12 μm. Transfer the mixture to a slurry washing tank to obtain MFCC slurry. The MFCC precursor is Mn. x Fe y Cu (1-x-y) CO3, where 0.30≤x<0.70, 0.30≤y<0.70, and x+y<1; S4. Drain the slurry washing tank to a volume of 1 / 2 to 2 / 3. After rinsing, add 70-80℃ pure water to 2 / 3 of the tank volume and stir for 30 minutes. Repeat this process twice. Then, introduce O3 and add phosphoric acid solution to obtain MFCP slurry. S5. After aging, washing, drying and packaging, the MFCP precursor product is obtained.

2. The method for multi-level doping of a manganese iron phosphate precursor according to claim 1, characterized in that: The iron crystal in step S1 is ferrous sulfate, the manganese crystal in step S1 is manganese sulfate, and the copper crystal in step S1 is copper sulfate.

3. The method for multi-level doping of a manganese iron phosphate precursor according to claim 1, characterized in that: The concentrations of the ferrous salt solution, manganese salt solution, and copper salt solution in step S1 are 1.5-3 mol / L.

4. The method for multi-level doping of a manganese iron phosphate precursor according to claim 1, characterized in that: The MFCP precursor is mixed with a lithium source and sintered to obtain the cathode material.

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