A method for recovering Li3Fe2(PO4)3 from retired lithium iron phosphate batteries and its application

Abstract

The application discloses a method for preparing Li3Fe2(PO4)3 from retired positive electrode powder of lithium iron phosphate battery, which comprises the following steps: mixing the active powder obtained by decomposing the positive electrode sheet with acid or alkali, and then adding an oxidizing agent to react to obtain a mixed solution; putting the mixed solution into a microwave reactor to react to obtain a Li3Fe2(PO4)3 precursor solution; centrifuging the precursor solution and washing it for multiple times, and then putting it into a muffle furnace to calcine after drying, and finally obtaining the powder-shaped Li3Fe2(PO4)3. The application can avoid the use of a large amount of strong acid and strong alkali in the traditional wet method, and can realize a short process, a simple preparation method, low cost, and direct regeneration of lithium battery positive electrode materials. After introducing an external field by the microwave method, the acid and the alkali promote the change of the structure of LiFePO4, and the recovery of lithium and iron elements is facilitated. In addition, after recycling, the application obtains the NASICON type Li3Fe2(PO4)3 with high ionic conductivity and stable structure as a positive electrode material to assemble a lithium ion battery, and it is found that the lithium ion battery has good reversible capacity and excellent capacity retention rate.

Description

Technical Field

[0001] This invention relates to the field of retired battery recycling, specifically to a method for preparing Li3Fe2(PO4)3 cathode material from retired lithium iron phosphate batteries and its application in lithium batteries. Background Technology

[0002] Lithium iron phosphate (LFP) batteries, due to their high operating voltage, long lifespan, high energy density, and lack of memory effect, have been widely used in new energy vehicles, starting power supplies, and electronic devices. However, with the rapid development of the electric vehicle industry, they are now facing a large-scale retirement of lithium-ion batteries. In 2020, China's new energy vehicle sales reached 1.367 million units, a year-on-year increase of 5.8%; in 2021, sales reached 1.521 million units, a year-on-year increase of 14.0%; and in 2022, sales reached a new high of 6.887 million units, a year-on-year increase of 93.4%. It is estimated that by 2025, the global number of new energy vehicles will reach 30 million, and the amount of retired lithium batteries will reach 2 million tons. The lifespan of lithium-ion power batteries is 3-5 years. The rapid development of the lithium battery market in recent years will inevitably drive the lithium battery recycling sector to maintain a similarly vigorous development for at least the next decade.

[0003] The recycling methods for retired lithium iron phosphate batteries can be mainly divided into direct repair methods and wet methods. Chinese patent CN114566727A addresses the repair and regeneration of retired lithium iron phosphate cathode powder. This involves removing impurities from the lithium iron phosphate powder at room temperature and activating it, then adding lithium and iron sources for ball milling, followed by spray drying and calcination to obtain the lithium iron phosphate product. This type of direct repair method mostly involves adding lithium to the separated cathode material to restore its physical and chemical properties, allowing it to be reused as a battery cathode material. Although this recycling process is relatively simple, it has low recycling efficiency, incomplete metal recovery, and high energy consumption. In particular, because impurities are not removed from the waste during the repair process, problems such as residual aluminum foil in the cathode material and reactions between the electrolyte and impurities in the waste can occur, significantly impacting the regenerated battery material.

[0004] Chinese patent CN116281916A discloses a wet process for the separate extraction and recovery of lithium metal and iron phosphate. The method involves mixing organic-free cathode material powder with a binder in a ball mill, followed by calcination, high-temperature vacuum reduction, distillation, and condensation to obtain lithium metal and iron-containing residue. The residue is then acid-leached with a precipitant, and calcined again to obtain battery-grade iron phosphate. The main problems with this type of wet process for full-element recovery are its excessively long process, cumbersome operation, and large reagent consumption. Furthermore, this method requires a significant amount of acid, making production emissions difficult to control and potentially causing secondary pollution.

[0005] Chinese patent CN115744940A proposes a wet selective lithium recovery method. This method involves adding hydrochloric acid and an oxidant to degraded lithium iron phosphate cathode powder after aluminum reduction, adjusting the pH with calcium oxide and liquid alkali, and then adding a calcium removal agent for carbonization and decomposition to obtain battery-grade lithium carbonate. While this type of selective lithium recovery wet process has advantages in lithium extraction efficiency and economic value compared to the all-element recovery method, the lithium extraction steps are overly cumbersome. It requires the addition of excessive amounts of acid and oxidant, along with corresponding alkali to neutralize the acid, increasing reagent consumption. Furthermore, this recovery method does not further process the iron phosphate in the waste residue, wasting valuable iron phosphate and causing some environmental pollution.

[0006] Therefore, there is a need for a method to recover cathode materials from retired lithium iron phosphate batteries. This method should ensure recovery efficiency and control costs while shortening experimental steps and cycles, enabling the recovery of all elements through a simple process, and resulting in batteries with good performance. In view of this, the present invention is proposed. Summary of the Invention

[0007] The purpose of this invention is to propose a method for recycling retired lithium iron phosphate batteries to obtain Li3Fe2(PO4)3 as a positive electrode material for lithium-ion batteries.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing Li3Fe2(PO4)3 cathode material, comprising the following steps:

[0010] (1) Prepare an acid or base solution, wherein the concentration of the acid or base is 0.5 ~ 3.5 mol L. -1 ;

[0011] (2) Dissolve the retired lithium iron phosphate cathode powder in the acid or alkali solution in step (1); the solid-liquid ratio of the acid or alkali to the retired lithium iron phosphate cathode powder is 1:3 ~ 1:15, to obtain solution I;

[0012] (3) Add an oxidant dropwise to solution I from step (2) while stirring. The molar ratio of the oxidant to the decommissioned lithium iron phosphate cathode powder is 1:0.5~3 to obtain solution II.

[0013] (4) The solution II from step (3) is placed in a microwave reactor for reaction. The solution after reaction is centrifuged, and the precipitate is washed with water and ethanol multiple times and then dried to obtain the precursor material.

[0014] (5) The precursor material is placed in an air atmosphere and subjected to high-temperature calcination reaction in a muffle furnace to obtain Li3Fe2(PO4)3 cathode material.

[0015] The acid is any one of HCl, HNO3, H2SO4, and CH3COOH, and the base is any one of NaOH, LiOH, and KOH, which can better dissolve the crystal structure of lithium iron phosphate. Furthermore, in order to better disrupt the crystal structure of lithium iron phosphate without causing its basic framework to disintegrate, the concentration of the acid or base is selected from 0.5 ~ 3.5 mol L. -1 .

[0016] The oxidant is any one of H2O2, KMnO4, and KClO3.

[0017] The power of the microwave reaction is 50 ~ 500 W, and the reaction time is 0.1 ~ 2 h.

[0018] The temperature conditions for the high-temperature reaction are 600 ~ 900℃.

[0019] The application of the Li3Fe2(PO4)3 material in lithium-ion battery cathode materials.

[0020] The specific application steps are as follows: For button cell fabrication, a slurry is prepared by mixing Li3Fe2(PO4)3, acetylene black, and PVDF in a mass ratio of 8:1:1. This slurry is then coated onto aluminum foil and dried in a forced-air drying oven at 60°C for 6 hours, followed by drying in a vacuum drying oven at 100°C for 12 hours. Small circular electrode sheets are then prepared by rolling and cutting for button cell fabrication. The button cell assembly is carried out in a glove box filled with argon gas, with water and oxygen content less than 0.1 ppm. A lithium metal sheet is used as the negative electrode, a polypropylene microporous membrane as the separator, and a 1 mol / L electrolyte. -1 LiPF6 / ethylene carbonate (EC) + dimethyl carbonate (DMC) (volume ratio 1:1).

[0021] Compared with existing technologies, this application has the following advantages and features:

[0022] (1) The process flow of the present invention realizes that the operation of retired lithium iron phosphate batteries is simple, short, and low-energy, which is suitable for industrial application.

[0023] (2) The present invention applies an external field through microwave reaction, which can achieve high recycling rate of lithium and iron metal elements, greatly shorten the recycling process, and regenerate them into new cathode materials more efficiently.

[0024] (3) The Li3Fe2(PO4)3 cathode material obtained by the process scheme of the present invention has good electrochemical performance. Experiments have confirmed that the Li3Fe2(PO4)3 (NASICON type structure) synthesized by this method has high discharge capacity, good reversibility and cycle life, and can be used for electrochemical energy storage.

[0025] This invention utilizes microwave reaction and simple experimental procedures to directly recycle decommissioned lithium iron phosphate cathode powder into NASICON-type cathode materials with high ionic conductivity and stable structure, which can be used to synthesize lithium-ion battery cathode materials with stable performance and high specific capacity. Attached Figure Description

[0026] Figure 1 The X-ray diffraction (XRD) patterns of Li3Fe2(PO4)3 obtained after acid treatment in Example 1 and alkaline treatment in Example 5 are shown.

[0027] Figure 2 The image shows a scanning electron microscope (SEM) image of the Li3Fe2(PO4)3 material obtained after acid treatment in Example 1.

[0028] Figure 3 The results of the cycle performance test of the Li3Fe2(PO4)3 lithium-ion battery obtained after acid treatment in Example 1 at a rate of 0.2 C are shown. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] Example 1

[0031] S1 dissolves retired lithium iron phosphate cathode powder in 1.5 mol L at a solid-liquid ratio of 1:3. -1 Solution I was obtained by dissolving the HCl solution.

[0032] S2 H2O2 is added to solution I with the oxidant and lithium iron phosphate in a molar ratio of 1:2, and the mixture is stirred to obtain solution II;

[0033] S3. Solution II was placed in a microwave reactor and reacted at a power of 160 W for 30 min. After the reaction, the solution was centrifuged, and the resulting black precipitate was washed three times with deionized water and ethanol respectively and then dried to obtain the precursor.

[0034] S4 The precursor was calcined in air at 800°C for 2 hours to obtain a red powder, which is the Li3Fe2(PO4)3 material.

[0035] S5 The electrode was prepared using the Li3Fe2(PO4)3 material obtained in Example 1 by the following method:

[0036] The specific application steps are as follows: The Li3Fe2(PO4)3 material obtained in Example 1 is mixed with acetylene black and PVDF in a mass ratio of 8:1:1 to prepare a slurry. The slurry is then coated onto aluminum foil and dried in a forced-air drying oven at 60°C for 6 hours, followed by drying in a vacuum drying oven at 100°C for 12 hours. Small circular electrode sheets are then prepared by rolling and cutting for use in button cell manufacturing. The button cell assembly is carried out in a glove box filled with argon gas and with water and oxygen content less than 0.1 ppm. A lithium metal sheet is used as the negative electrode, a polypropylene microporous membrane as the separator, and a 1 mol / L electrolyte. -1 LiPF6 / ethylene carbonate (EC) + dimethyl carbonate (DMC) (volume ratio 1:1).

[0037] Example 2

[0038] S1 dissolves retired lithium iron phosphate cathode powder in 2.5 mol L at a solid-liquid ratio of 1:5. -1 Solution I was obtained from the HNO3 solution;

[0039] S2 H2O2 is added to solution I with the oxidant and lithium iron phosphate in a molar ratio of 1:2, and mixed solution II is obtained.

[0040] S3. Solution II was placed in a microwave reactor and reacted at a power of 160 W for 30 min. After the reaction, the solution was centrifuged, and the resulting black precipitate was washed three times with deionized water and ethanol respectively and then dried to obtain the precursor.

[0041] S4 The precursor was calcined in air at 800°C for 2 hours to obtain a red powder, which is the Li3Fe2(PO4)3 material.

[0042] The electrode preparation method for the red powder recovered in S5 is consistent with that in Example 1.

[0043] Example 3

[0044] S1 dissolves retired lithium iron phosphate cathode powder in 2.5 mol L at a solid-liquid ratio of 1:8. -1 Mixed solution I was obtained by dissolving H2SO4 in the solution.

[0045] S2 H2O2 was added to mixed solution I with the oxidant and lithium iron phosphate in a molar ratio of 1:2.5 to obtain mixed solution II;

[0046] S3. Mixed solution II was placed in a microwave reactor and reacted at a power of 160 W for 45 min. After the reaction, the solution was centrifuged, and the resulting black precipitate was washed three times with deionized water and ethanol respectively and then dried to obtain the precursor.

[0047] S4 The precursor was calcined in air at 800°C for 2 hours to obtain a red powder, which is the Li3Fe2(PO4)3 material.

[0048] The electrode preparation method for the red powder recovered in S5 is consistent with that in Example 1.

[0049] Example 4

[0050] S1 dissolves retired lithium iron phosphate cathode powder in 2.5 mol L at a solid-liquid ratio of 1:5. -1 Mixed solution I was obtained by reacting CH3COOH solution with the solution.

[0051] S2 H2O2 was added to mixed solution I with the oxidant and lithium iron phosphate in a molar ratio of 1:2.5 to obtain mixed solution II;

[0052] S3. Mixed solution II was placed in a microwave reactor and reacted at a power of 160 W for 30 min. After the reaction, the solution was centrifuged, and the resulting black precipitate was washed three times with deionized water and ethanol respectively and then dried to obtain the precursor.

[0053] S4 The precursor was calcined in air at 800°C for 2 hours to obtain a red powder, which is the Li3Fe2(PO4)3 material.

[0054] The electrode preparation method for the red powder recovered in S5 is consistent with that in Example 1.

[0055] Example 5

[0056] S1 dissolves retired lithium iron phosphate cathode powder in 2.5 mol L at a solid-liquid ratio of 1:5. -1 Mixed solution I was obtained by dissolving NaOH in the solution.

[0057] S2 H2O2 was added to mixed solution I with the oxidant and lithium iron phosphate in a molar ratio of 1:2.5 to obtain mixed solution II;

[0058] S3. Mixed solution II was placed in a microwave reactor and reacted at a power of 320 W for 15 min. After the reaction, the solution was centrifuged, and the resulting black precipitate was washed three times with deionized water and ethanol respectively and then dried to obtain the precursor.

[0059] S4 The precursor was calcined in air at 800°C for 2 hours to obtain a red powder, which is the Li3Fe2(PO4)3 material.

[0060] The electrode preparation method for the red powder recovered in S5 is consistent with that in Example 1.

[0061] Example 6

[0062] S1 dissolves retired lithium iron phosphate cathode powder in 1.5 mol L at a solid-liquid ratio of 1:10. -1 In LiOH solution, mixed solution I is obtained;

[0063] S2 H2O2 is added to mixed solution I with the oxidant and lithium iron phosphate in a molar ratio of 1:2 to obtain mixed solution II;

[0064] S3. Mixed solution II was placed in a microwave reactor and reacted at a power of 160 W for 30 min. After the reaction, the solution was centrifuged, and the resulting black precipitate was washed three times with deionized water and ethanol respectively and then dried to obtain the precursor.

[0065] S4 The precursor was calcined in air at 800°C for 2 hours to obtain a red powder, which is the Li3Fe2(PO4)3 material.

[0066] The electrode preparation method for the red powder recovered in S5 is consistent with that in Example 1.

[0067] Example 7

[0068] S1 dissolves retired lithium iron phosphate cathode powder in 2.5 mol L at a solid-liquid ratio of 1:15. -1 Mixed solution I was obtained by dissolving KOH in the solution.

[0069] S2 H2O2 is added to mixed solution I with the oxidant and lithium iron phosphate in a molar ratio of 1:2 to obtain mixed solution II;

[0070] S3. Mixed solution II was placed in a microwave reactor and reacted at a power of 160 W for 30 min. After the reaction, the solution was centrifuged, and the resulting black precipitate was washed three times with deionized water and ethanol respectively and then dried to obtain the precursor.

[0071] S4 The precursor was calcined in air at 800°C for 2 hours to obtain a red powder, which is the Li3Fe2(PO4)3 material.

[0072] The electrode preparation method for the red powder recovered in S5 is consistent with that in Example 1.

[0073] The structural and electrochemical characterization analyses of Li3Fe2(PO4)3 obtained after acid and alkali treatments are as follows:

[0074] Test results of Examples 1 and 5

[0075] Figure 1 The X-ray diffraction patterns of Li3Fe2(PO4)3 obtained after acid treatment in Example 1 and alkaline treatment in Example 5 are shown. It can be seen that they are in perfect agreement with the standard diffraction card PDF card #80-1515, indicating good crystallinity.

[0076] Figure 2 SEM testing was performed on the Li3Fe2(PO4)3 material obtained after acid treatment in Example 1: The scanning electron microscope image of Li3Fe2(PO4)3 at 10,000x magnification shows that its surface is relatively rough and clearly presents a sponge-like texture. Its loose and porous structure can provide sufficient space for lithium ion insertion and extraction.

[0077] Figure 3 Cyclic tests were conducted at 0.2C on the Li3Fe2(PO4)3 material obtained after acid treatment in Example 1, showing that the sample has good cyclic stability.

[0078] Finally, it should be noted that the above examples are only for helping to understand the method and core ideas of the present invention. They are not intended to limit the scope of the invention's substantive technical content. Those skilled in the art can make various improvements to the invention to optimize the solution. Any modifications and alterations made without departing from the principles of the invention should be included within the scope of the claims of the present invention.

Claims

1. A method for recovering Li3Fe2(P04)3 from decommissioned lithium iron phosphate batteries, characterized in that, The steps are as follows: (1) preparing an acid or base solution, the concentration of the acid or base being 0.5 ~ 3.5 mol L -1 ; (2) the retired lithium iron phosphate positive electrode powder is dissolved in the acid or alkali solution in step (1); the solid-liquid ratio of the acid or alkali to the retired lithium iron phosphate positive electrode powder is 1:3-1:15, to obtain solution I; (3) the solution I in step (2) is added with an oxidizing agent drop by drop while stirring, the molar ratio of the oxidizing agent to the retired lithium iron phosphate positive electrode powder is 1:0.5-3, to obtain solution II; (4) the solution II in step (3) is placed in a microwave reactor for reaction, the power of the microwave reaction is 50-500 W, the reaction time is 0.1-2 h, the solution after reaction is centrifuged, the precipitate is washed with water and ethanol for multiple times and dried, to obtain a precursor material; (5) the precursor material is placed in a muffle furnace for high-temperature calcination reaction in an air atmosphere, to obtain a Li3Fe2(PO4)3 positive electrode material.

2. The method of claim 1, wherein: The acid is any one of HCl, HNO3, H2SO4 and CH3COOH, and the alkali is any one of NaOH, LiOH and KOH.

3. The method of claim 1, wherein: The oxidizing agent is any one of H2O2, KMnO4 and KClO3.

4. The method of claim 1, wherein: The temperature condition of the high-temperature reaction is 600-900℃.

5. Application of the Li3Fe2(PO4)3 material in a lithium ion battery positive electrode material according to claim 1.

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