A method for using an alkaline environment to assist in the reduction and replenishment of waste lithium iron phosphate

Abstract

The present invention discloses a method for utilizing an alkaline environment to assist in the reduction and replenishment of lithium by waste lithium iron phosphate, and relates to the field of waste lithium-ion battery recycling and electrode material resource reuse. Based on the lower reduction potential of the reducing agent in the alkaline environment, the waste lithium iron phosphate powder is dispersed in an alkaline aqueous solution containing a reducing agent and lithium, and lithium iron phosphate with different lithium deficiency amounts is relithiated and repaired. Then, the solid-liquid separation is carried out and the relithiated lithium iron phosphate is thoroughly washed with deionized water, dried, and finally rapidly annealed to complete the entire regeneration process. This method overcomes the shortcomings of traditional recycling processes such as being cumbersome, high cost, and secondary pollution, and also avoids the special reaction conditions of other direct recycling processes such as high temperature and high pressure, reduces the operating temperature and time, and has a lower cost for battery recycling and regeneration.

Description

Technical Field

[0001] The present invention relates to the technical field of waste lithium iron phosphate recovery, and more specifically, to a method for utilizing an alkaline environment to assist in the reduction and replenishment of waste lithium iron phosphate. Background Art

[0002] Lithium iron phosphate (LiFePO4 / LFP), with its advantages of excellent stability, high safety, long cycle life, and low cost, is one of the most widely used materials in lithium-ion batteries. Its sales volume accounts for over 32% of the global lithium-ion battery market, and its demand in sectors such as new energy and base station energy storage is experiencing explosive growth. With the retirement of batteries and the increasing number of scrapped batteries, the recycling of the metal resources they contain and the environmental impact of used batteries on ecological sustainability have attracted considerable attention.

[0003] Traditional methods for recycling lithium battery materials include hydrometallurgy and pyrometallurgy, but neither method is suitable for large-scale regeneration of lithium iron phosphate. The general wet method uses acid (alkali) leaching, precipitation and other steps, which are not environmentally friendly and easily cause secondary pollution; the pyrometallurgical method consumes a lot of energy during the calcination process and has a limited recovery rate for lithium, especially for lithium iron phosphate, which has a low content of high-value metals and poor recycling economics. Compared with the former material leaching, direct lithium regeneration is a non-destructive repair technology that can repair the crystal structure of the material and restore its electrochemical properties without leaching treatment. This process can effectively reduce recycling costs, maximize the value of recycled materials and the closed-loop recovery of electrode materials.

[0004] The main reason for the capacity decay of lithium iron phosphate batteries is that a large amount of active lithium is lost in lithium iron phosphate, which leads to the formation of FePO4 phase during the cycle and leaves a large number of Li vacancy defects in lithium iron phosphate, which not only leads to Fe 2+ Oxidized to Fe 3+ , and induces Fe 2+ Some of them migrate to the Li site, generating Fe-Li para-site defects, blocking the Li + Therefore, to effectively regenerate lithium iron phosphate directly, the most critical step is to reduce Fe 3+ and Li +Re-embedded in lithium iron phosphate. Direct repair technology usually uses solid-phase repair method (high-temperature roasting) and liquid-phase repair method (hydrothermal or microwave heating), etc., by adding an appropriate amount of lithium source to perform in-situ reverse lithium replenishment, which can effectively repair and regenerate lithium iron phosphate, such as CN113072052A, CN102208707B and CN113629244A. High-temperature roasting mixes the lithium source with lithium iron phosphate and directly regenerates by solid-phase reduction, but the amount of lithium deficiency in lithium iron phosphate from different sources or specifications is different, and the need to accurately determine the element content in the material and the amount of lithium source supplementation has certain limitations. Liquid-phase lithium replenishment uses an "adaptive" lithium replenishment method, which does not require precise determination of the ratio of the lithium source, but the reaction time is long and the reaction temperature is relatively high. Some reactions still require high-voltage equipment. Summary of the Invention

[0005] In response to the shortcomings of the prior art, the present invention provides a method for using an alkaline environment to assist in the reduction and replenishment of lithium from waste lithium iron phosphate. Based on the advantageous areas in the E-pH diagram and the failure mechanism of lithium iron phosphate, this method shows that under alkaline conditions, the reducing agent has a lower reduction potential, and waste lithium iron phosphate can achieve rapid replenishment of liquid-phase lithium at a temperature below the boiling point of the solution and at an ambient pressure. Therefore, the entire lithium replenishment and repair process for waste lithium iron phosphate does not require additional high-temperature and high-pressure reaction vessels, simplifies operating facilities and processes, reduces the reaction temperature and reaction time, improves repair efficiency, and avoids the use of strong acids and strong bases.

[0006] To achieve the above purpose, the specific technical solutions adopted by the present invention are as follows:

[0007] (1) Waste lithium iron phosphate batteries are discharged, disassembled, soaked in N-methylpyrrolidone (NMP), stripped, filtered, dried, and ground to obtain the required lithium iron phosphate powder;

[0008] (2) mixing the powder with a lithium salt and a reducing agent aqueous solution adjusted to a pH of 8-12 to perform a reduction lithium supplementation reaction, wherein the temperature of the liquid phase lithium supplementation reaction is 50-80° C. and the reaction time is 0.5-1.5 h; the solid-liquid ratio of lithium iron phosphate to the solution volume is 2.5-30 g / L, the lithium salt in the lithium-containing aqueous solution is one of lithium hydroxide, lithium chloride, lithium nitrate, lithium sulfate, and lithium acetate, and the amount of the lithium salt is 0.01-0.5 mol / L. The lithium supplementation reaction is performed for a certain period of time, and then filtered and dried to obtain a repaired lithium iron phosphate precipitate;

[0009] (3) In order to further improve the crystallinity of the regenerated lithium iron phosphate, the repaired lithium iron phosphate is evenly mixed with the lithium source and the carbon source by ball milling. The resulting mixture is placed in an inert atmosphere such as argon or nitrogen and rapidly annealed to obtain the regenerated lithium iron phosphate.

[0010] Furthermore, in step (2), the acid for adjusting the pH value of the lithium-containing water and the reducing agent solution is one of hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, with a concentration of 0.5-2 mol / L; the base is one of sodium hydroxide and potassium hydroxide, with a concentration of 0.5-2 mol / L;

[0011] Furthermore, in step (2), the reducing agent is one of sodium nitrite, sodium sulfite, sodium hypophosphite, sodium phosphite, hydrogen peroxide, glucose, and sodium thiosulfate, and the amount used is 0.05-5 mol / L;

[0012] Furthermore, in step (3), the molar ratio of the lithium iron phosphate to the lithium source and the carbon source is 1: (1%-5%): (1%-15%), the lithium source is one of lithium hydroxide and lithium carbonate, and the carbon source is one of citric acid, glucose, and sucrose;

[0013] Furthermore, in step (3), the annealing temperature is 350-750°C, the heating rate is 2-10°C / min, and the sintering time is 3-8h;

[0014] Compared with the existing technology, the beneficial effects of the present invention are as follows:

[0015] The present invention discloses a method for utilizing an alkaline environment to assist in the reduction and replenishment of lithium from waste lithium iron phosphate. Under alkaline conditions, the reducing agent has a lower reduction potential, and the waste lithium iron phosphate can achieve rapid embedding of liquid-phase lithium at a temperature below the boiling point of the solution and at an ambient pressure. Combined with rapid annealing, the crystallinity of the material is further improved to obtain a positive electrode material with good electrochemical performance.

[0016] The present invention is based on the failure mechanism of lithium iron phosphate during the circulation process, and liquid phase repair replenishes the lost lithium to restore the composition and crystal structure of lithium iron phosphate waste. Compared with traditional lithium battery recovery methods, it will not destroy the original crystal structure of lithium iron phosphate, and there is no need to accurately determine the ratio of lithium source. The process is simple and the processing efficiency is high.

[0017] (1) Compared with other direct regeneration methods, the present invention can react at low temperature (50-80°C) and ambient pressure (1atm), which reduces the reaction temperature and time, and has lower energy consumption. In addition, the entire lithium replenishment and repair process does not require special reaction conditions such as high temperature and high pressure, and the battery recycling and regeneration cost is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a process flow chart of the present invention;

[0019] Figure 2 The XRD patterns and regeneration schematic diagrams of lithium iron phosphate with different lithium deficiency degrees before and after reduction and repair in Example 1 of the present application;

[0020] Figure 3 This is a cycle and rate performance diagram of waste lithium iron phosphate, reduced lithium-supplemented lithium iron phosphate, and annealed regenerated lithium iron phosphate in Example 1 of this application. DETAILED DESCRIPTION

[0021] The following description sets forth numerous specific details to facilitate a thorough understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the present invention. Therefore, the present invention is not limited to the specific implementations disclosed below.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0023] Example 1

[0024] (1) Discharging, disassembling, soaking in N-methylpyrrolidone (NMP), stripping, and drying the waste lithium iron phosphate battery, and grinding it to obtain the required positive electrode material (LiFePO4);

[0025] (2) Weigh the required waste lithium iron phosphate powder and add it to a mixed clear solution of lithium hydroxide and sodium sulfite adjusted to a pH of 10 to perform a reduction and lithium replenishment reaction. The pH-adjusted solution is 1 mol / L sulfuric acid or 1 mol / L sodium hydroxide solution, wherein the concentration of lithium hydroxide is 0.1 mol / L, the concentration of the reducing agent sodium sulfite is 0.2 mol / L, the solid-liquid ratio is 2.5 g / L, the temperature is 50°C, and the reaction time is 1.5 hours. After the reaction is completed, the lithium iron phosphate powder after lithium replenishment and repair is obtained by filtration and drying.

[0026] (3) The repaired lithium iron phosphate powder was added with 3% LiOH as a lithium source and 5% citric acid as a carbon source, ball-milled at 500 rpm for 1 h, and the mixed powder was placed in an argon atmosphere and heated to 650 °C at a rate of 2 °C / min for 5 h to obtain regenerated lithium iron phosphate, and its electrochemical properties were tested.

[0027] Figure 2 The XRD diagram of the lithium iron phosphate after reduction and lithium supplementation and rapid annealing regeneration in this embodiment can be seen from the figure. Its diffraction peaks correspond to the lithium iron phosphate standard card (JCPDS:81-1173), and the peak shape is sharp without any impurity peaks (a) and the schematic diagram of the lithium supplementation structure (b).

[0028] Figure 3The performance curves of the cycle (a) and rate (b) of the waste, reduced lithium supplemented and rapidly annealed lithium iron phosphate in this embodiment are shown. It can be seen from the figure that the discharge capacity of the reduced lithium supplemented and annealed lithium iron phosphate in the first cycle at 1C is 123.2mAh g -1 、146.6mAh g -1 Significantly higher than the 102.7mAh g of waste lithium iron phosphate -1 At 1C, 5C, and 10C rates, the discharge capacity of the lithium iron phosphate after reduction, lithium replenishment, and annealing regeneration is 121.8 mAh g -1 , 118.9mAh g -1 、102.6mAh g -1 and 144.6mAh g -1 、141.1mAh g -1 、121.6mAh g -1 , while the discharge capacity of waste lithium iron phosphate is 112.4 mAh g -1 、103.1mAh g -1 、80.7mAh g -1 , through the method of the present invention, the regenerated lithium iron phosphate shows good electrochemical properties.

[0029] Example 2

[0030] (1) Discharging, disassembling, soaking in N-methylpyrrolidone (NMP), stripping, and drying the waste lithium iron phosphate battery, and grinding to obtain the required positive electrode material (LiFePO4); (2) Weighing the required waste lithium iron phosphate powder and adding it to a mixed clear solution of lithium nitrate and sodium nitrite with a pH value of 11, to carry out a reduction and lithium replenishment reaction. The solution used to adjust the pH is 0.5 mol / L nitric acid or 0.5 mol / L sodium hydroxide solution, wherein the concentration of lithium nitrate is 0.1 mol / L, the concentration of reducing agent sodium nitrite is 0.3 mol / L, the solid-liquid ratio is 5 g / L, the temperature is 60°C, and the reaction time is 1 hour. After the reaction is completed, the lithium iron phosphate powder is filtered and dried to obtain the lithium replenishment and repaired lithium iron phosphate powder.

[0031] (3) The repaired lithium iron phosphate powder was added with 3% LiOH as a lithium source and 10% citric acid as a carbon source, ball milled at 500 rpm for 1 h, and the mixed powder was placed in an argon atmosphere and heated to 750 °C at a rate of 5 °C / min for 3 h to obtain regenerated lithium iron phosphate, and its electrochemical properties were tested.

[0032] Example 3

[0033] (1) Discharging, disassembling, soaking in N-methylpyrrolidone (NMP), stripping, and drying the waste lithium iron phosphate battery, and grinding to obtain the required positive electrode material (LiFePO4); (2) Weighing the required waste lithium iron phosphate powder and adding it to a mixed clear solution of lithium hydroxide and glucose with a pH value of 10.5 to carry out a reduction and lithium replenishment reaction. The solution used to adjust the pH value is 1 mol / L hydrochloric acid or 1 mol / L potassium hydroxide solution, wherein the concentration of lithium hydroxide is 0.3 mol / L, the concentration of the reducing agent glucose is 0.4 mol / L, the solid-liquid ratio is 5 g / L, the temperature is 80°C, and the reaction time is 0.5 h. After the reaction is completed, the lithium iron phosphate powder is filtered and dried to obtain the lithium replenishment and repaired lithium iron phosphate powder.

[0034] (3) The repaired lithium iron phosphate powder was added with 5% LiOH as a lithium source and 2% citric acid as a carbon source, ball-milled at 500 rpm for 1 h, and the mixed powder was placed in an argon atmosphere and heated to 650 °C at a rate of 2 °C / min for calcination for 3 h to obtain regenerated lithium iron phosphate, and its electrochemical properties were tested.

Claims

1. A method for reducing and replenishing lithium by using an alkaline environment to assist waste lithium iron phosphate, characterized in that: The following steps are involved: (1) Lithium iron phosphate batteries with different failure levels are completely discharged, disassembled, soaked in N-methylpyrrolidone for stripping, filtered, dried, and ground to obtain the desired lithium iron phosphate powder; (2) placing the lithium iron phosphate powder obtained in step (1) in a mixed solution containing lithium and a reducing agent with a pH value of 8-12, and performing a liquid-phase reduction lithium replenishment reaction, wherein the liquid-phase lithium replenishment reaction temperature is 50-80° C., the reaction time is 0.5-1.5 h, the solid-liquid ratio of lithium iron phosphate to the solution volume is 2.5-30 g / L, the lithium salt of the lithium-containing aqueous solution is one of lithium hydroxide, lithium chloride, lithium nitrate, lithium sulfate, and lithium acetate, and its molar concentration is 0.01-0.5 mol / L, and after the reaction is completed, filtering and drying to obtain the repaired lithium iron phosphate solid; (3) The lithium iron phosphate repaired in step (2) is mixed with a lithium source and a carbon source by ball milling, and is placed in an argon or nitrogen inert atmosphere at a selected temperature for rapid annealing to obtain lithium iron phosphate with good electrochemical properties.

2. The method of claim 1, wherein the method comprises the following steps: In step (2), the reducing agent is one of sodium nitrite, sodium sulfite, sodium hypophosphite, sodium phosphite, hydrogen peroxide, glucose, and sodium thiosulfate, and the amount used is 0.05-5 mol / L.

3. The method of claim 1, wherein the method comprises the following steps: In step (2), the acid for adjusting the pH value of the aqueous solution containing lithium and reducing agent is one of hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid, with a concentration of 0.5-2 mol / L; the base is one of sodium hydroxide and potassium hydroxide, with a concentration of 0.5-2 mol / L.

4. The method of claim 1, wherein the method comprises the following steps: In step (3), the molar ratio of the lithium iron phosphate to the lithium source and the carbon source is 1: (1%-5%): (1%-15%), the lithium source is one of lithium hydroxide and lithium carbonate, and the carbon source is one of citric acid, glucose, and sucrose.

5. The method of claim 1, wherein the method comprises the following steps: In step (3), the annealing temperature is 350-750°C, the heating rate is 2-10°C / min, and the sintering time is 3-8h.

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