Microwave roasting repair method for positive electrode material of retired new energy lithium iron phosphate battery

Abstract

The invention relates to a microwave roasting repairing method for a positive electrode material of a decommissioned new energy lithium iron phosphate battery, and belongs to the technical field of repairing of decommissioned new energy batteries. The preparation method comprises the following steps: carrying out microwave impurity removal roasting after disassembling, crushing and sorting, adding a lithium source compound and a carbon source compound, carrying out mechanical ball milling on the mixed material, adding deionized water or absolute ethyl alcohol and other dispersion media, mixing to form uniform slurry, atomizing and drying the slurry, transferring the slurry into a microwave fluidized roasting furnace, and roasting to obtain the lithium ion battery cathode material. And naturally cooling or cooling to room temperature in a protective atmosphere, washing and drying to obtain the positive electrode material of the retired new energy lithium iron phosphate battery. According to the method disclosed by the invention, microwave heating and a fluidization technology are combined, and uniform deposition and coating of a carbon source pyrolytic carbon on the surfaces of LiFePO4 particles are ensured, so that the conductivity and the rate capability of the regenerated material are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of retired new energy battery repair technology, and in particular to a microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries. Background Technology

[0002] Lithium iron phosphate batteries have been widely used in electric vehicles, energy storage power stations and other fields due to their advantages such as high safety, long cycle life and relatively low cost.

[0003] As the first batch of power batteries put into the market gradually enters their retirement period, how to environmentally and economically recycle and process these retired batteries, and achieve high-value regeneration of their valuable components, especially cathode materials, has become a focus of attention in industry and academia. Traditional cathode material recycling methods mainly include pyrometallurgy and hydrometallurgy. Pyrometallurgy is energy-intensive, prone to lithium volatilization loss, and may produce harmful gases; hydrometallurgy has a long process and generates a large amount of acid and alkali waste liquid, posing an environmental pollution risk. In addition, some existing direct repair methods mostly use conventional electric heating roasting, which has problems such as uneven heating, long repair time, high energy consumption, and unsatisfactory recovery of the electrochemical performance of the recycled product. Therefore, developing a repair method that is short-process, low-energy, environmentally friendly, and produces high-performance recycled materials is of great significance. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a microwave calcination repair method for retired battery cathode materials, a highly efficient repair method based on the synergistic effect of microwave heating and fluidization technology. This method not only aims to shorten the process flow and reduce energy consumption, but also strives to achieve precise and uniform regeneration of materials at the microstructural level, ultimately obtaining high-quality regenerated cathode materials with performance comparable to virgin materials. The core innovation of this method lies in abandoning the traditional outside-to-inside heating method that relies on heat conduction. Instead, it utilizes the unique mechanism that microwaves can penetrate materials and generate instantaneous heat both inside and out simultaneously. This highly efficient heating mode is combined with fluidization technology to ensure extreme uniformity of the thermal and reaction fields, achieving efficient repair of lithium iron phosphate crystal structure defects and highly uniform reconstruction of the conductive carbon coating layer. Ultimately, this achieves the repair goals of a short process, low energy consumption, high quality, and environmentally friendly approach.

[0005] A microwave calcination repair method for cathode materials of retired new energy lithium iron phosphate batteries includes the following steps:

[0006] (1) Microwave purification and roasting:

[0007] The decommissioned cathode powder material obtained after dismantling, crushing and sorting is placed in a microwave calcination device and calcined to obtain the processed powder.

[0008] (2) Ingredient preparation and ball milling:

[0009] Lithium source compound and carbon source compound are added to the powder processed in step (1), and the mixture is mechanically ball-milled to obtain a fine powder with a fineness of -15 to -35 micrometers and a content of over 90%.

[0010] (3) Preparation of precursors by spray granulation:

[0011] The fine powder is mixed with a dispersion medium such as deionized water or anhydrous ethanol to form a uniform slurry. The slurry is then atomized and dried using a spray drying device to form spherical precursor particles with a porous microsphere structure.

[0012] (4) Microwave fluidized bed regeneration calcination:

[0013] The spherical precursor particles are transferred to a microwave fluidized bed roasting furnace for roasting to obtain the roasted material.

[0014] (5) Post-processing:

[0015] The calcined material is cooled naturally or to room temperature under a protective atmosphere, and then washed with deionized water to remove soluble salt byproducts generated during the reaction. The washed material is then dried to obtain the cathode material for retired new energy lithium iron phosphate batteries.

[0016] Further, the roasting conditions in step (1) are as follows: under air atmosphere conditions, the material is heated to a temperature range of 600℃-675℃ by microwave radiation, and held at this temperature for 1min-5min.

[0017] Further, the lithium source compound in step (2) is preferably lithium carbonate or lithium hydroxide, and the amount of lithium source compound added is controlled according to the stoichiometric ratio so that the molar ratio of lithium to iron (Li / Fe) in the final product is between 1.00 and 1.05.

[0018] Further, the carbon source compound in step (2) is preferably glucose, sucrose or citric acid, and the amount of the carbon source compound added is 3%-10% of the mass of the powder after treatment in step (1).

[0019] Furthermore, the ball milling time in step (2) is 1h-3h.

[0020] Furthermore, the solid content of the homogeneous slurry described in step (3) is 30%-50%.

[0021] Furthermore, the air inlet temperature of the spray drying process described in step (3) is controlled between 180°C and 220°C.

[0022] Further, the calcination conditions in step (4) are as follows: under an inert protective atmosphere, gas is introduced to keep the precursor particles in a stable fluidized state; microwave energy is used to rapidly and uniformly heat the fluidized material to a target temperature of 800℃-900℃, and the temperature is maintained at this high temperature for 10min-20min.

[0023] Furthermore, the retired new energy lithium iron phosphate battery cathode material obtained in step (5) has a first discharge specific capacity of more than 155 mAh / g at a rate of 0.1C after installation, and a capacity retention rate of more than 87% after 600 cycles.

[0024] The advantages of this invention, particularly the significant benefits it brings by employing microwave roasting technology, are as follows:

[0025] 1. Microwave and fluidization technologies work synergistically to achieve ultimate uniformity: By combining microwave heating with fluidization technology, the material is in a dynamic suspension state in the reactor, with each particle directly exposed to the microwave field, resulting in extremely uniform heating and completely eliminating the cold center and temperature dead zones inherent in static roasting. Simultaneously, fluidization separates the particles, effectively preventing agglomeration at high temperatures and greatly enhancing the gas-solid phase mass transfer process. This ensures uniform deposition and coating of carbon from the carbon source pyrolysis onto the surface of LiFePO4 particles, thereby significantly improving the conductivity and rate performance of the recycled material.

[0026] 2. Bulk heating and selective heating effects ensure repair quality: Microwaves have a preferential heating effect on carbon and polar substances (such as LiFePO4 precursors), realizing "bulk heating" inside the material. This eliminates the temperature difference between the inside and outside of the material caused by heat conduction in traditional external heating methods, allowing the crystal repair reaction to occur uniformly throughout the entire particle. This effectively avoids the phenomenon of surface overheating and incomplete internal repair, resulting in a well-integrity crystal structure in the regenerated product.

[0027] 3. The process is simple, efficient, and environmentally friendly: the entire process does not require the use of strong acids or alkalis, avoiding the problem of large-scale waste liquid treatment. Rapid microwave treatment also reduces the volatilization loss of active lithium components at high temperatures, improving material recovery rates.

[0028] 4. High energy utilization and significantly shortened roasting time: Microwaves can directly act on the material molecules, causing them to heat up instantly, avoiding the energy loss process of traditional resistance furnaces where the furnace chamber is heated first and then transferred to the material through thermal radiation and convection. The time required to rise from room temperature to the target temperature is only one-third or even less than that of traditional methods, and the holding time is also significantly reduced, resulting in a significant decrease in overall energy consumption. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of the microwave calcination repair method for the cathode material of retired lithium iron phosphate batteries according to the present invention. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0031] A microwave calcination repair method for cathode materials of retired new energy lithium iron phosphate batteries, such as... Figure 1 As shown, it includes the following steps:

[0032] (1) Microwave purification and roasting:

[0033] The decommissioned cathode powder material, obtained after dismantling, crushing, and sorting, is placed in a microwave calcination device. Under air atmosphere conditions, the material is heated to a temperature range of 600℃-675℃ by microwave radiation and held at this temperature for 1-5 minutes to obtain the processed powder. During this process, residual binders, conductive agents, and trace amounts of electrolyte and other organic impurities in the powder material are decomposed and oxidized and removed under the combined action of selective microwave heating and oxygen. Microwave heating has the characteristic of volumetric heating, which enables the material to heat up rapidly both inside and out simultaneously, shortening the processing time and avoiding the loss of active lithium and sintering of the material structure that may be caused by prolonged high temperatures due to slow heat conduction in traditional external heating methods.

[0034] (2) Ingredient preparation and ball milling:

[0035] Lithium source compound and carbon source compound are added to the powder after treatment in step (1), and the mixture is mechanically ball-milled for 1-3 hours to obtain fine powder. The lithium source compound is preferably lithium carbonate or lithium hydroxide, and the amount of lithium source compound added is controlled according to the stoichiometric ratio so that the molar ratio of lithium to iron (Li / Fe) in the final product is between 1.00 and 1.05. The carbon source compound is preferably glucose, sucrose or citric acid, and the amount of carbon source compound added is 3%-10% of the mass of the powder after treatment in step (1). This step aims to achieve uniform mixing and refinement of materials to achieve the required particle size distribution, while completely avoiding the negative impact of metal impurities introduced by traditional metal ball milling on the purity of recycled materials.

[0036] (3) Preparation of precursors by spray granulation:

[0037] The fine powder is mixed with a dispersion medium such as deionized water or anhydrous ethanol to form a uniform slurry with a solid content of 30% to 50%. The slurry is then atomized and dried using a spray drying device. The inlet air temperature of the spray dryer is controlled between 180℃ and 220℃ to form spherical precursor particles with a porous microsphere structure. The spherical precursor obtained in this step not only has good flowability and high bulk density, but its porous structure also provides a huge reaction specific surface area and convenient mass transfer channels for the subsequent microwave calcination process, which is conducive to the full progress of the reaction.

[0038] (4) Microwave fluidized bed regeneration calcination:

[0039] The spherical precursor particles are transferred to a microwave fluidized bed roasting furnace for roasting. Under an inert protective atmosphere, such as high-purity nitrogen or argon, the precursor particles are kept in a stable fluidized state. Microwave energy is used to rapidly and uniformly heat the fluidized material to a target temperature of 800℃-900℃, and this temperature is maintained for 10-20 minutes to obtain the roasted material. Under these conditions, the amorphous FePO4 and other phases in the precursor undergo an efficient solid-phase reaction with the lithium source, regenerating well-crystallized and regularly shaped lithium iron phosphate crystals. Simultaneously, the carbon source compound pyrolyzes at high temperature, forming a continuous and uniform conductive carbon coating layer on the surface of the lithium iron phosphate particles.

[0040] (5) Post-processing:

[0041] The calcined material is cooled naturally or to room temperature under a protective atmosphere; then it is washed with deionized water to remove soluble salt byproducts generated during the reaction. The washed material is then dried to obtain the cathode material for retired new energy lithium iron phosphate batteries.

[0042] After the recycled material is installed, the initial discharge specific capacity at 0.1C rate is higher than 155mAh / g, and the capacity retention rate is more than 87% after 600 cycles.

[0043] Example 1

[0044] The retired cathode powder was obtained from a company in Zhejiang Province after mechanical dismantling, crushing, and physical sorting.

[0045] A microwave calcination repair method for cathode materials of retired new energy lithium iron phosphate batteries includes the following steps:

[0046] (1) Microwave purification and roasting:

[0047] The decommissioned cathode powder material obtained after dismantling, crushing and sorting is placed in a microwave calcination device. Under air atmosphere conditions, the material is heated to a temperature range of 650°C by microwave radiation and held at this temperature for 3 minutes to obtain the processed powder.

[0048] (2) Ingredient preparation and ball milling:

[0049] Add 0.8% lithium carbonate by mass to the powder processed in step (1), control the Li / Fe molar ratio to be 1.02, add 5% sucrose by mass of the powder, and grind the mixture in a zirconium oxide stirred mill for 2 hours to obtain a mixed fine powder with a particle size of -25 micrometers and a content of 90%.

[0050] (3) Preparation of precursors by spray granulation:

[0051] The fine powder is mixed with a dispersion medium such as deionized water or anhydrous ethanol to form a uniform slurry with a solid content of 40%. The slurry is then atomized and dried using a spray drying device. The inlet air temperature of the spray dryer is controlled at 200°C to form spherical precursor particles with a porous microsphere structure.

[0052] (4) Microwave fluidized bed regeneration calcination:

[0053] The spherical precursor particles are transferred to a microwave fluidized bed roasting furnace for roasting. Nitrogen gas is introduced to keep the precursor particles in a stable fluidized state. The microwave source is started to rapidly and uniformly heat the fluidized material to 850°C using microwave energy, and then hold it at this high temperature for 15 minutes.

[0054] (5) Post-processing:

[0055] The calcined material was naturally cooled to room temperature; then, it was washed with deionized water to remove soluble salt byproducts generated during the reaction. The washed material was then dried to obtain the cathode material for retired new energy lithium iron phosphate batteries.

[0056] The cathode material prepared in this embodiment, after being installed in a device, exhibits an initial discharge specific capacity of over 156.5 mAh / g at a 0.1C rate, and a capacity retention rate of over 88.4% after 600 cycles.

[0057] Example 2

[0058] We obtained the positive electrode powder from retired lithium iron phosphate batteries provided by a company in Fujian.

[0059] A microwave calcination repair method for cathode materials of retired new energy lithium iron phosphate batteries includes the following steps:

[0060] (1) Microwave purification and roasting:

[0061] The decommissioned cathode powder material obtained after dismantling, crushing and sorting is placed in a microwave calcination device. Under air atmosphere conditions, the material is heated to a temperature range of 675°C by microwave radiation and held at this temperature for 5 minutes to obtain the processed powder.

[0062] (2) Ingredient preparation and ball milling:

[0063] Add 1.1% lithium carbonate by mass to the powder processed in step (1), control the Li / Fe molar ratio to be 1.05, add 10% sucrose by mass of the powder, and grind the mixture in a zirconium oxide stirred mill for 3 hours to obtain a 90% mixed fine powder with a particle size of -30 micrometers.

[0064] (3) Preparation of precursors by spray granulation:

[0065] The fine powder is mixed with a dispersion medium such as deionized water or anhydrous ethanol to form a uniform slurry with a solid content of 35%. The slurry is then atomized and dried using a spray drying device. The inlet air temperature of the spray dryer is controlled at 180°C to form spherical precursor particles with a porous microsphere structure.

[0066] (4) Microwave fluidized bed regeneration calcination:

[0067] The spherical precursor particles are transferred to a microwave fluidized bed roasting furnace for roasting. Nitrogen gas is introduced to keep the precursor particles in a stable fluidized state. The microwave source is turned on, and the fluidized material is heated rapidly and uniformly to 900°C using microwave energy, and held at this high temperature for 12 minutes.

[0068] (5) Post-processing:

[0069] The calcined material was naturally cooled to room temperature; then, it was washed with deionized water to remove soluble salt byproducts generated during the reaction. The washed material was then dried to obtain the cathode material for retired new energy lithium iron phosphate batteries.

[0070] The cathode material prepared in this embodiment, after being installed in a device, exhibits an initial discharge specific capacity of over 158.8 mAh / g at a 0.1C rate, and a capacity retention rate of over 87.4% after 600 cycles.

[0071] Example 3

[0072] We obtained the positive electrode powder from retired lithium iron phosphate batteries provided by a company in Anhui.

[0073] A microwave calcination repair method for cathode materials of retired new energy lithium iron phosphate batteries includes the following steps:

[0074] (1) Microwave purification and roasting:

[0075] The decommissioned cathode powder material obtained after dismantling, crushing and sorting is placed in a microwave calcination device. Under air atmosphere conditions, the material is heated to a temperature range of 600°C by microwave radiation and held at this temperature for 2.5 minutes to obtain the processed powder.

[0076] (2) Ingredient preparation and ball milling:

[0077] Add 0.9% lithium carbonate by mass to the powder processed in step (1), control the Li / Fe molar ratio to be 1.00, add 5.5% sucrose by mass of the powder, and grind the mixture in a ceramic ball mill for 2 hours to obtain a fine powder with a particle size of -35 and a content of 90%.

[0078] (3) Preparation of precursors by spray granulation:

[0079] The fine powder is mixed with a dispersion medium such as deionized water or anhydrous ethanol to form a uniform slurry with a solid content of 35%. The slurry is then atomized and dried using a spray drying device. The inlet air temperature of the spray dryer is controlled at 190°C to form spherical precursor particles with a porous microsphere structure.

[0080] (4) Microwave fluidized bed regeneration calcination:

[0081] The spherical precursor particles are transferred to a microwave fluidized bed roasting furnace for roasting. Nitrogen gas is introduced to keep the precursor particles in a stable fluidized state. The microwave source is turned on, and the fluidized material is heated rapidly and uniformly to 890°C using microwave energy, and held at this high temperature for 15.5 minutes.

[0082] (5) Post-processing:

[0083] The calcined material is cooled naturally or to room temperature under a protective atmosphere; then it is washed with deionized water to remove soluble salt byproducts generated during the reaction. The washed material is then dried to obtain the cathode material for retired new energy lithium iron phosphate batteries.

[0084] The cathode material prepared in this embodiment, after being installed in a device, exhibits an initial discharge specific capacity of over 160.2 mAh / g at a 0.1C rate, and a capacity retention rate of over 87.9% after 600 cycles.

[0085] Comparative Example 1

[0086] A microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries differs from the operation steps in Example 3 in step (4):

[0087] This comparative example was calcined using conventional static calcination methods: the precursor particles were loaded into a corundum crucible, placed in the same box-type resistance furnace, heated to 850°C under nitrogen protection, and held at this temperature for 120 minutes.

[0088] The obtained material was tested and found to have an initial discharge specific capacity of 138.4 mAh / g and a capacity retention rate of 71.9% after 600 cycles. Sintering was observed between the particles, and the battery performance was lower than that of Example 3.

[0089] This comparison shows that even with extended roasting time, traditional resistance furnace heating methods cannot achieve the same repair effect as microwave roasting due to inherent defects in the heating method.

Claims

1. A method for microwave calcination repair of cathode materials in retired new energy lithium iron phosphate batteries, characterized in that, Includes the following steps: (1) Microwave purification and roasting: The decommissioned cathode powder material obtained after dismantling, crushing and sorting is placed in a microwave calcination device and calcined to obtain the processed powder. (2) Ingredient preparation and ball milling: Lithium source compound and carbon source compound are added to the powder processed in step (1), and the mixture is mechanically ball-milled to obtain a fine powder with a fineness of -15 to -35 micrometers and a content of over 90%. (3) Preparation of precursors by spray granulation: The fine powder is mixed with a dispersion medium such as deionized water or anhydrous ethanol to form a uniform slurry. The slurry is then atomized and dried using a spray drying device to form spherical precursor particles with a porous microsphere structure. (4) Microwave fluidized bed regeneration calcination: The spherical precursor particles are transferred to a microwave fluidized bed roasting furnace for roasting to obtain the roasted material. (5) Post-processing: The calcined material is cooled naturally or to room temperature under a protective atmosphere, and then washed with deionized water to remove soluble salt byproducts generated during the reaction. The washed material is then dried to obtain the cathode material for retired new energy lithium iron phosphate batteries.

2. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, The roasting conditions in step (1) are as follows: under air atmosphere conditions, the material is heated to a temperature range of 600℃-675℃ by microwave radiation and held at this temperature for 1min-5min.

3. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, The lithium source compound in step (2) is preferably lithium carbonate or lithium hydroxide. The amount of lithium source compound added is controlled according to the stoichiometric ratio so that the molar ratio of lithium to iron (Li / Fe) in the final product is between 1.00 and 1.

05.

4. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, The carbon source compound in step (2) is preferably glucose, sucrose or citric acid, and the amount of the carbon source compound added is 3%-10% of the mass of the powder after treatment in step (1).

5. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, The ball milling time in step (2) is 1h-3h.

6. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, The solid content of the homogeneous slurry described in step (3) is 30%-50%.

7. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, The air inlet temperature for spray drying in step (3) is controlled between 180℃ and 220℃.

8. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, The calcination conditions in step (4) are as follows: under an inert protective atmosphere, gas is introduced to keep the precursor particles in a stable fluidized state; microwave energy is used to rapidly and uniformly heat the fluidized material to a target temperature of 800℃-900℃, and the temperature is maintained at this high temperature for 10min-20min.

9. The microwave calcination repair method for the cathode material of retired new energy lithium iron phosphate batteries according to claim 1, characterized in that, After the retired lithium iron phosphate battery cathode material obtained in step (5) is installed, the first discharge specific capacity at 0.1C rate is higher than 155mAh / g, and the capacity retention rate is higher than 87% after 600 cycles.

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