A reduction method for regenerating a positive electrode material of a waste lithium iron phosphate battery

Abstract

The application discloses a kind of waste old lithium iron phosphate battery positive electrode material regeneration reduction methods, belong to waste lithium ion battery recycling and positive electrode material direct regeneration technical field.The present application is aimed at the technical problems of high cost of existing waste old lithium iron phosphate regeneration reducing agent, incomplete reduction, easy to introduce impurities, and low regeneration capacity, using dicyandiamide (C2H4N4) as special reducing agent, supporting specific regeneration process: waste old lithium iron phosphate, lithium supplement and dicyandiamide are mixed ball milled according to proportion, after drying, it is calcined in inert atmosphere in stages, and finally the regenerated lithium iron phosphate positive electrode material is obtained.The reducing agent of the application is low in cost, strong in reduction capacity, can completely eliminate FePO4 impurities, no impurities are introduced, the 0.1C discharge capacity of the regenerated material can reach 152~156 mAh·g⁻¹, close to the level of raw material;The supporting regeneration process is simple, environment-friendly and easy to industrialize, solves many defects of prior art, is suitable for large-scale recycling and regeneration of waste old lithium iron phosphate battery positive electrode material for power and energy storage, and has significant economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the technical field of waste lithium-ion battery recycling and direct regeneration of cathode materials, specifically relating to a reducing agent for regenerating waste lithium iron phosphate cathode materials and its regeneration method. Background Technology

[0002] Lithium iron phosphate (LFP) cathode materials possess advantages such as excellent cycle stability, high thermal stability, no heavy metal pollution, and low cost, and have been widely used in new energy vehicles, energy storage power stations, and other fields. As power batteries enter a large-scale retirement cycle, the resource recycling of spent LFP batteries has become an industry necessity.

[0003] Lithium iron phosphate (LiFePO4) undergoes structural degradation during long-term cycling, including lithium loss, Fe²⁺ oxidation to Fe³⁺, Fe-Li antisite defects, and FePO4 impurity phase formation. This leads to capacity decay, reduced rate performance, and increased polarization. Direct regeneration repair technology restores material performance in one step through lithium replenishment, reduction, and lattice reconstruction. It offers advantages such as a short process, low energy consumption, and preservation of the original material's microstructure, making it the most promising technology for industrialization.

[0004] The reduction step is the core of direct regeneration: the deteriorated Fe³⁺ must be efficiently reduced to Fe²⁺, eliminating the inert FePO₄ impurity phase and repairing the antisite defects. The reducing agents used in existing publicly available technologies mainly include: sodium sulfite, L-threonine, tartaric acid, citric acid, ascorbic acid, ferrous sulfate, ferrous oxalate, ferrous chloride, and ferrous lactate.

[0005] Existing reducing agents have the following obvious drawbacks: 1. Organic carboxylic acids (citric acid, tartaric acid, ascorbic acid) have high raw material costs and are prone to producing large amounts of organic residual carbon and acidic gases at high temperatures, affecting the purity and environmental friendliness of the materials.

[0006] 2. Ferrous salts (ferrous sulfate, ferrous oxalate) are prone to introducing impurities such as excess SO4²⁻ and Fe²⁺, which can cause the Li / Fe stoichiometric ratio to shift and affect the electrochemical performance of recycled materials.

[0007] 3. Some reducing agents have limited reducing capacity and cannot completely eliminate the FePO4 impurity phase, resulting in low regeneration capacity.

[0008] 4. The overall cost of the reagents is relatively high, which restricts the economic benefits of large-scale regeneration.

[0009] Therefore, developing a specialized reducing agent that is low-cost, has strong reducing power, introduces no impurities, is environmentally friendly, and is compatible with high-temperature calcination is of key significance for improving the economics and product quality of direct regeneration of waste lithium iron phosphate. Summary of the Invention

[0010] This invention addresses the problems of high cost, incomplete reduction, easy introduction of impurities, and low regeneration capacity of existing waste lithium iron phosphate regeneration reducing agents. It provides a highly efficient and low-cost reducing agent with dicyandiamine (C2H4N4) as the core, along with a stable and controllable direct regeneration method.

[0011] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows.

[0012] A method for regenerating cathode materials from waste lithium iron phosphate batteries, comprising the following steps: S1. Old lithium iron phosphate, with lithium carbonate added at a Li / Fe ratio of 1.05 to 1.2:1; S2. Mass ratio: waste lithium iron phosphate: dicyandiamine = 1: 0.1~2; S3. Add anhydrous ethanol and ball mill at 200–450 r / min for 0.5–6 h; S4. After drying, calcine in stages under a nitrogen atmosphere: hold at 200-450℃ for 2-4 h + hold at 500-900℃ for 6-12 h; S5. Natural cooling yields recycled lithium iron phosphate.

[0013] Further improvements and optimizations to the above technical solution resulted in a Li / Fe ratio of 1.12:1 and a waste lithium iron phosphate to dicyandiamine ratio of 1:0.5.

[0014] A further optimization is that, in step S3, ball milling is performed at 350 r / min for 2 hours.

[0015] Further improvements and optimizations to the above technical solution resulted in a Li / Fe ratio of 1.15:1 and a waste lithium iron phosphate to dicyandiamine ratio of 1:1.

[0016] Further optimizations are made in step S3, ball milling at 400 r / min for 1 h; and in step S4, after drying, calcination is carried out in stages under a nitrogen atmosphere: holding at 450℃ for 3 h + holding at 700℃ for 7 h.

[0017] Further improvements and optimizations to the above technical solution resulted in a Li / Fe ratio of 1.08:1 and a waste lithium iron phosphate to dicyandiamine ratio of 1:0.2.

[0018] Further optimizations are made in step S3, ball milling at 250 r / min for 6 h; and in step S4, after drying, calcination is carried out in stages under a nitrogen atmosphere: holding at 250℃ for 3 h + holding at 600℃ for 10 h.

[0019] Further improvements and optimizations to the above technical solution resulted in a Li / Fe ratio of 1.1:1 and a waste lithium iron phosphate to dicyandiamine ratio of 1:1.5.

[0020] Further optimizations include: in step S3, ball milling at 450 r / min for 0.5 h; and in step S4, after drying, calcination in stages under a nitrogen atmosphere: holding at 300℃ for 4 h + holding at 650℃ for 9 h.

[0021] The progress and advantages of this invention compared with the prior art are as follows:

[0022] 1. The reducing agent has low cost and significant economic benefits; dicyandiamine is a bulk chemical raw material with ample market supply and a unit price far lower than commonly used reducing agents such as citric acid, ascorbic acid, L-threonine, and ferrous lactate, which can reduce the cost of regenerative agents by more than 30%.

[0023] 2. Strong reducing ability, no impurity phase residue; mild and continuous release of reducing atmosphere, which can completely eliminate FePO4 impurity phases caused by deterioration, no impurity peaks in XRD, and high lattice purity.

[0024] 3. No impurities are introduced, and the material has high purity; it does not contain sulfur, phosphorus, halogens, or transition metal impurities, and the decomposition products are N2, NH3, CO2, H2O, etc., with no residue after calcination.

[0025] 4. Excellent electrochemical performance, close to that of virgin materials; the 0.1C discharge capacity of recycled materials can reach 156 mAh•g⁻¹, with high coulombic efficiency and low polarization, and can be directly used to remanufacture batteries.

[0026] 5. The process is simple, environmentally friendly, and easy to industrialize; the process is short, the equipment is universal, there is no acidic waste liquid, no heavy metal pollution, which meets the requirements of green manufacturing and is suitable for large-scale continuous production. Attached Figure Description

[0027] Figure 1 XRD patterns of waste lithium iron phosphate and recycled lithium iron phosphate in Example 1.

[0028] Figure 2 Charge-discharge curves of regenerated lithium iron phosphate in Example 1. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1 A method for regenerating cathode materials from waste lithium iron phosphate batteries, comprising the following steps: S1. Old lithium iron phosphate, with lithium carbonate added at a ratio of Li / Fe = 1.12:1; S2. Mass ratio: waste lithium iron phosphate: dicyandiamine = 1:0.5; S3. Add anhydrous ethanol and ball mill at 350 r / min for 2 h; S4. After drying, calcinate in stages under a nitrogen atmosphere: hold at 350℃ for 4 h + hold at 650℃ for 8 h; S5. Natural cooling yields recycled lithium iron phosphate.

[0031] Performance testing: No FePO4 impurity phase, pure phase olivine LiFePO4 structure; 0.1C discharge capacity: 156 mAh•g⁻¹; no corrosion on aluminum foil / current collector, no impurities in materials.

[0032] Advantages of this embodiment: Compared to Comparative Example 1, it has lower cost, more thorough reduction, no residual carbon, and a capacity increase of 9 mAh•g⁻¹; compared to Comparative Example 2, it has no excessive Fe impurities introduced, no lattice distortion, no residual impurities, and a capacity increase of 11 mAh•g⁻¹, with superior structure and electrochemical performance of the recycled material.

[0033] Example 2 A method for regenerating cathode materials from waste lithium iron phosphate batteries, comprising the following steps: S1. Lithium supplementation to Li / Fe = 1.15:1; S2. Mass ratio: Waste lithium iron phosphate: dicyandiamine = 1:1; S3. Ball milling: 400 r / min, 1 h; S4. Calcination: Hold at 450℃ for 2 h + hold at 700℃ for 7 h; S5. Atmosphere: Argon.

[0034] Performance testing: No FePO4 impurity phase; 0.1C discharge capacity: 154 mAh•g⁻¹.

[0035] Advantages of this embodiment: Compared to Comparative Example 1, the reduction is more complete, there is no acidic gas pollution, and the capacity is increased by 7 mAh•g⁻¹; compared to Comparative Example 2, no metal impurities are introduced, the crystal form is more complete, the capacity is increased by 9 mAh•g⁻¹, and the reproducibility and stability are better.

[0036] Example 3 A method for regenerating cathode materials from waste lithium iron phosphate batteries, comprising the following steps: S1. Lithium supplementation to Li / Fe = 1.05:1; S2. Mass ratio: Waste lithium iron phosphate: dicyandiamine = 1:0.2; S3. Ball milling: 200 r / min, 6 h; S4. Calcination: Hold at 250℃ for 4 h + hold at 500℃ for 12 h; S5. Atmosphere: Nitrogen.

[0037] Performance testing: No obvious FePO4 impurity phase; 0.1C discharge capacity: 152 mAh•g⁻¹.

[0038] Advantages of this embodiment: Compared to Comparative Example 1, it requires less reagent, has lower cost, no organic carbon residue, and increases capacity by 5 mAh•g⁻¹; compared to Comparative Example 2, it has no impurity interference, a more regular crystal lattice, and increases capacity by 7 mAh•g⁻¹, making it more economical.

[0039] Example 4 A method for regenerating cathode materials from waste lithium iron phosphate batteries, comprising the following steps: S1. Lithium supplementation to Li / Fe = 1.10:1; S2. Mass ratio: Waste lithium iron phosphate: dicyandiamine = 1:1.5; S3. Ball milling: 450 r / min, 0.5 h; S4. Calcination: Hold at 300℃ for 4 h + hold at 650℃ for 9 h; S5. Atmosphere: Nitrogen.

[0040] Performance testing: Pure phase structure, no impurities; 0.1C discharge capacity: 153 mAh•g⁻¹.

[0041] Advantages of this embodiment: Compared to Comparative Example 1, it has higher mixing efficiency, lower energy consumption, more uniform reduction, and a capacity increase of 6 mAh•g⁻¹; compared to Comparative Example 2, it has no metal impurities introduced, more complete crystallization, and a capacity increase of 8 mAh•g⁻¹, making it more suitable for efficient industrial production.

[0042] Example 5 A method for regenerating cathode materials from waste lithium iron phosphate batteries, comprising the following steps: S1. Lithium supplementation until Li / Fe = 1.2:1; S2. Mass ratio: Waste lithium iron phosphate: dicyandiamine = 1:2; S3. Ball milling: 300 r / min, 3 h; S4. Calcination: Hold at 200℃ for 4 h + hold at 900℃ for 6 h; S5. Atmosphere: Nitrogen.

[0043] Performance testing: High crystallinity, no impurities; 0.1C discharge capacity: 155 mAh•g⁻¹.

[0044] Advantages of this embodiment: Compared to Comparative Example 1, the reduction window is wider, high-temperature crystallization is more complete, and the capacity is increased by 8 mAh•g⁻¹; compared to Comparative Example 2, there is no stoichiometric shift, no impurity phase residue, and the capacity is increased by 10 mAh•g⁻¹, with better material structural stability and cycling performance.

[0045] Comparative Example 1 (Citrate Reducing Agent) Citric acid was used as a reducing agent, and the ratio of waste lithium iron phosphate to citric acid was 1:0.5 (mass ratio). The remaining ball milling, calcination, and lithium replenishment processes were the same as in Example 1.

[0046] Results: Trace amounts of FePO4 impurity phase still exist; 0.1C discharge capacity is 147 mAh•g⁻¹; high cost; trace amounts of residual carbon.

[0047] Comparative Example 2 (Ferrous Oxalate Reducing Agent) Ferrous oxalate was used as the reducing agent, and the ratio of waste lithium iron phosphate to ferrous oxalate was 1:0.5 (mass ratio). The other conditions were the same as in Example 1.

[0048] Results: Excessive Fe impurities were introduced, causing a deviation in the Li / Fe ratio; the FePO4 phase was not completely eliminated; the 0.1C discharge capacity was 145 mAh•g⁻¹; and significant lattice distortion was observed.

[0049] The above description represents the preferred embodiment of the present invention. It should be noted that, for those skilled in the art, various modifications and improvements can be made without departing from the principles and core ideas of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for regenerating cathode materials from waste lithium iron phosphate batteries, comprising the following steps: S1. Old lithium iron phosphate, with lithium carbonate added at a Li / Fe ratio of 1.05 to 1.2:1; S2. Mass ratio: waste lithium iron phosphate: dicyandiamine = 1: 0.1~2; S3. Add anhydrous ethanol and ball mill at 200–450 r / min for 0.5–6 h; S4. After drying, calcine in stages under a nitrogen atmosphere: hold at 200-450℃ for 2-4 h + hold at 500-900℃ for 6-12 h; S5. Natural cooling yields recycled lithium iron phosphate.

2. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 1, characterized in that, Li / Fe = 1.12:1, waste lithium iron phosphate: dicyandiamine = 1:0.

5.

3. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 2, characterized in that, In step S3, ball mill at 350 r / min for 2 h.

4. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 1, characterized in that, Li / Fe = 1.15:1, waste lithium iron phosphate: dicyandiamine = 1:

1.

5. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 4, characterized in that, In step S3, ball milling is performed at 400 r / min for 1 h; in step S4, after drying, the mixture is calcined in stages under a nitrogen atmosphere: 450℃ for 3 h + 700℃ for 7 h.

6. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 1, characterized in that, Li / Fe = 1.08:1, waste lithium iron phosphate: dicyandiamine = 1:0.

2.

7. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 6, characterized in that, In step S3, ball milling is performed at 250 r / min for 6 h; in step S4, after drying, the mixture is calcined in stages under a nitrogen atmosphere: 250℃ for 3 h + 600℃ for 10 h.

8. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 1, characterized in that, Li / Fe = 1.1:1, waste lithium iron phosphate: dicyandiamine = 1:1.

5.

9. The reduction method for regenerating waste lithium iron phosphate battery cathode material according to claim 8, characterized in that, In step S3, ball milling is performed at 450 r / min for 0.5 h; in step S4, after drying, the mixture is calcined in stages under a nitrogen atmosphere: held at 300℃ for 4 h + held at 650℃ for 9 h.

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