A method for selectively recovering lithium iron phosphate batteries in an ozone atmosphere

Abstract

The application discloses a method for selectively recovering lithium iron phosphate batteries in an ozone atmosphere, and belongs to the field of hydrometallurgy. The method uses waste lithium battery positive active material lithium iron phosphate as raw material, and a deep eutectic solvent composed of choline chloride and ethylene glycol as leaching system to obtain a leaching solution containing only lithium in an ozone atmosphere. The deep eutectic solvent is a reaction medium, and the ozone atmosphere is an oxidant. First, the deep eutectic solvent is obtained by mixing and heating choline chloride and ethylene glycol. Then, the lithium iron phosphate powder is mixed and stirred with the deep eutectic solvent under water bath condition, and ozone atmosphere is introduced to realize efficient and selective leaching of lithium. The method uses the deep eutectic solvent as leaching medium and ozone as oxidant to realize efficient and selective leaching of lithium in one step. The leaching efficiency of lithium is more than 90%, and the leaching efficiency of iron is less than 2%. The method has simple and efficient process flow, and has great economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgy, specifically relating to a method for recovering lithium iron phosphate. Background Technology

[0002] Driven by the pursuit of convenient living and energy conservation and emission reduction, the production of new energy vehicles has been increasing year by year. In 2020, global electric vehicle production reached 10 million units, and it is projected to reach 225 million units by 2030 (GDTian, ​​G. Yuan, A. Aleksandrov, et al. Fathollahi-Fard, M. Ivanov, Sustainable Energy Technologies and Assessments, 53, 102447.). Currently, rechargeable lithium batteries, characterized by high energy density, high operating voltage, high charge and discharge efficiency, and long service life, dominate the high-end market for new energy vehicles. In China, as the world's largest producer of new energy vehicles, the installed capacity of low-cost and safe lithium iron phosphate batteries surpassed that of ternary lithium batteries for the first time in 2021, accounting for 51.7%. Considering that the average lifespan of lithium batteries is only 5 to 8 years, China's automotive power batteries began to enter a period of large-scale retirement starting in 2020, and it is estimated that by 2025, the amount of waste lithium batteries will exceed 730,000 tons (Wang Yunke, Yan Wei, Wan Banglong, et al., Yunnan Chemical Industry, 2022, 49(6)). However, to date, more than 50% of waste lithium batteries have not been recycled, which has led to serious environmental pollution and resource waste. In addition, as the world's largest producer of lithium batteries, China's lithium reserves account for only 5.9% of the world's total reserves. Recycling waste lithium batteries can greatly alleviate my country's lithium resource shortage (Zhiyan Consulting data - 2019).

[0003] For the recycling of lithium iron phosphate batteries, pyrometallurgical recycling is often only used as a means of separating active materials. It needs to be combined with solid-phase regeneration or wet leaching processes to achieve metal recycling and reuse. Moreover, this process has high energy consumption and causes serious dust pollution (Wang Yunke, Yan Wei, Wan Banglong, et al., Yunnan Chemical Industry, 2022, 49(6)). In contrast, the wet recycling process using acidic media (sulfuric acid, nitric acid, acetic acid, etc.) can achieve selective leaching of lithium by adding oxidants (hydrogen peroxide, sodium persulfate, sodium hypochlorite, etc.). This process is simple, has low energy consumption, and can obtain pure lithium-containing leachate and iron phosphate. However, it also consumes a large amount of strong acid, strong alkali and high-cost oxidants, and inevitably generates a large amount of recalcitrant wastewater (J. Kumar, R.R. Neiber, J. Park, et al. Chemical Engineering Journal, 2022, 431.).

[0004] As a novel green solvent, deep eutectic solvents, composed of green components such as hydrogen bond donors (carboxylic acids, amides, organic alcohols) and hydrogen bond acceptors (quaternary ammonium salts, organic alcohols, etc.), possess the ability to dissolve various metal oxides. Furthermore, they avoid the use of strong acids and bases and the discharge of wastewater, and are widely used for the efficient extraction of metals from various resources (AP Abbott, G. Capper, DLDavies, et al. J. Chem. Eng. Data, 2006, 51(1280-1282).). In 2019, Tran et al. utilized Cl in choline chloride... - Leaching lithium cobalt oxide (LCO) was first achieved using a deep eutectic solvent (1 mol choline chloride: 2 mol ethylene glycol) to leach the active material of lithium-ion batteries using the coordination ability of LCO and the reducing environment provided by ethylene glycol. After reacting at 220°C for 24 hours, more than 90% of the lithium and cobalt were leached out. In the following years, many researchers investigated the leaching effects of different types of deep eutectic solvents (1 mol choline chloride: 2 urea, 1 mol choline chloride: 2 p-toluenesulfonic acid, 1 mol choline chloride: 1 oxalic acid, etc.) on the active materials of lithium-ion batteries such as LCO, LCO, and LCO (ZJWang, S.Li, TBLi, et al. Mining, Metallurgy & Exploration, 2022.). However, for lithium iron phosphate batteries, which account for more than 50% of the automotive power battery market, most current research is still at the stage of selective leaching of lithium using non-green systems (inorganic acid plus oxidant), which has problems with the discharge of toxic waste gas and acidic wastewater. Furthermore, since the components commonly used in deep eutectic solvents (organic acids, alcohols, amides, quaternary ammonium salts, etc.) all exhibit reducing properties, they are unable to provide the oxidation environment required for the selective leaching of lithium iron phosphate. This is also the reason why deep eutectic solvents are not currently used for the selective recovery of lithium resources from lithium iron phosphate. Therefore, developing a green leaching system based on deep eutectic solvents to achieve efficient and selective recovery of lithium iron phosphate is of great significance for solving the problems of toxic waste gas and acidic wastewater emissions caused by the wet recycling process of waste lithium batteries, and for achieving the goal of efficient and selective recovery of lithium elements, with significant economic and environmental benefits. Summary of the Invention

[0005] This invention proposes a method for selectively recovering lithium iron phosphate batteries under an ozone atmosphere. The method uses a deep eutectic solvent composed of choline chloride and ethylene glycol as the leaching medium and an ozone atmosphere obtained by an ozone generator and air as the oxidant. This method achieves efficient and selective leaching of lithium in lithium iron phosphate, the positive electrode active material of lithium batteries, in one step, resulting in a leaching solution containing only lithium.

[0006] The method for selectively recycling waste lithium iron phosphate batteries under an ozone atmosphere proposed in this invention comprises the following specific process steps:

[0007] (1) Under water bath conditions, choline chloride and ethylene glycol with a molar ratio of 1:2-1:8 are mixed and stirred to obtain a clear and transparent deep eutectic solvent.

[0008] (2) The deep eutectic solvent obtained in step (1) and lithium iron phosphate powder are mixed at a solid-liquid ratio of 5-60 g / L. An ozone atmosphere is introduced into the mixed solution, and the mixture is reacted for 5-8 h under a water bath at 40-60℃. Then, solid-liquid separation is performed to obtain lithium-containing filtrate and iron phosphate solid product.

[0009] Furthermore, the water bath temperature in step (1) is 30-60℃.

[0010] Furthermore, the mixing time in step (1) is 5-30 min.

[0011] Preferably, the deep eutectic solvent and lithium iron phosphate powder in step (2) are mixed at a solid-liquid ratio of 20-30 g / L.

[0012] Furthermore, the lithium iron phosphate powder used in step (2) is the positive electrode active material from the waste lithium battery LFP18650E-150.

[0013] Furthermore, the ozone atmosphere used in step (2) is prepared by an air source ozone generator with an ozone yield of 2 g / h and a flow rate of 16 L / min.

[0014] Furthermore, the deep eutectic solvent used in step (2) is the leaching reaction medium, and the ozone atmosphere is the oxidant.

[0015] Furthermore, in step (2), the leaching efficiency of lithium exceeds 90%, while the leaching efficiency of iron is less than 2%.

[0016] In this invention, a deep eutectic solvent composed of choline chloride and ethylene glycol is used as the leaching system. The positive electrode active material powder is mixed with the deep eutectic solvent, and an ozone atmosphere is simultaneously introduced as an oxidant to obtain a leaching solution containing only lithium, thereby achieving efficient and selective leaching of lithium.

[0017] In the efficient recycling process of lithium iron phosphate, the positive electrode active material of lithium batteries, choline chloride and ethylene glycol are used as leaching media, and ozone atmosphere is used as oxidant. The leaching mechanism is shown in equation (1). As the reaction proceeds, the hydroxyl groups in choline chloride and ethylene glycol are oxidized by ozone to generate carboxyl groups, producing a large amount of H+. + H + It enhanced the oxidizing power of O3 (E(O3 / O2) = 2.076, E(O2 / H2O) = 1.229). In H... + Under the influence of O3, LiFePO4 undergoes a delithiation oxidation reaction, and the Li in LiFePO4 is oxidized. + The delithiation reaction and Fe2+ The oxidation reaction occurs simultaneously, yielding a lithium-containing leaching solution and FePO4.

[0018] 6LiFePO4 + O3 + 6H + =6Li + +6FePO4+3H2O (1)

[0019] The lithium and iron content in the leaching solution was measured and calculated, showing that the lithium leaching efficiency exceeded 90%, while the iron leaching efficiency was less than 2%. Analysis of the solid product after washing, drying, and grinding revealed that the product was FePO4, with no LiFePO4 residue found. This demonstrates that the present invention achieves highly efficient and selective lithium leaching in one step by mixing a deep eutectic solvent with the positive electrode active material powder and simultaneously introducing an ozone atmosphere, yielding a leaching solution containing only lithium.

[0020] The advantages of this invention are as follows: For lithium iron phosphate batteries, which currently account for over 50% of the new energy vehicle power battery market, this invention is the first to use a green deep eutectic solvent (a solution composed of choline chloride and ethylene glycol) as the leaching system under an ozone atmosphere. This avoids the use of strong inorganic acids and the discharge of acidic wastewater, achieving highly efficient and selective leaching of lithium from waste lithium-ion battery cathode active materials—lithium iron phosphate—in one step. The lithium leaching efficiency exceeds 90%, yielding a lithium-containing leaching solution, thus achieving efficient recycling of waste lithium battery cathode active materials. The leaching medium used in this invention (a deep eutectic solvent composed of choline chloride and ethylene glycol) has excellent characteristics such as low saturated vapor pressure, low volatility with gas, and low green toxicity. Furthermore, the specific heat capacity of this deep eutectic solvent (2.2 J / (g·K)) is only half that of acidic aqueous solutions (4.2 J / (g·K)), which means that a significant amount of energy can be saved in the actual heating leaching process. The oxidant (ozone atmosphere) is widely available and can be obtained at any time through air and ozone generators, without being limited by geographical environment. This process is simple, environmentally friendly, and low-cost, and can efficiently recover valuable lithium metal from waste lithium batteries (lithium iron phosphate). This greatly alleviates the pressure of my country's lithium resource shortage and reduces the manufacturing cost of lithium batteries. Attached Figure Description

[0021] Figure 1 XRD pattern of the positive electrode active material.

[0022] Figure 2 Flowchart of lithium iron phosphate recovery process using deep eutectic solvent under ozone atmosphere.

[0023] Figure 3 XRD patterns of solid products. Detailed Implementation

[0024] Source of leaching medium

[0025] The leaching medium consists of choline chloride (solid phase) and ethylene glycol (liquid phase), both of which are analytical grade reagents from Sinopharm Reagent Group. They are mixed and heated to obtain a deep eutectic solvent.

[0026] Oxidizing agent source

[0027] The oxidant is ozone atmosphere obtained by ionizing air through an ozone generator. The ozone generator model is QJ-8002 (Guangzhou Quanju Ozone Technology Co., Ltd.), the ozone yield is 2g / h, and the gas flow rate is 16L / min.

[0028] Source of raw materials

[0029] The raw material used (lithium iron phosphate powder) is derived from the positive electrode active material in discarded lithium batteries (LFP18650E-150). Figure 1 The X-ray diffraction (XRD) pattern of the raw material revealed that the diffraction peaks of the positive electrode active material were consistent with the standard card (JCPDS:81-1173) of LiFe(PO4), and the crystal structure was orthorhombic.

[0030] Example 1 (see process) Figure 2 )

[0031] (1) Under the condition of 30℃ water bath, choline chloride and ethylene glycol with a molar ratio of 1:8 were mixed and stirred for 5 min to obtain a clear and transparent deep eutectic solvent.

[0032] (2) The deep eutectic solvent obtained in step (1) and lithium iron phosphate powder are mixed at a solid-liquid ratio of 20 g / L. Ozone atmosphere is introduced into the mixed solution, and after reacting for 7 h in a water bath at 40 °C, solid-liquid separation is performed to obtain lithium-containing filtrate and iron phosphate solid product.

[0033] Example 2 (see process) Figure 2 )

[0034] (1) Under the condition of 50℃ water bath, choline chloride and ethylene glycol with a molar ratio of 1:6 were mixed and stirred for 30 min to obtain a clear and transparent deep eutectic solvent.

[0035] (2) The deep eutectic solvent obtained in step (1) and lithium iron phosphate powder are mixed at a solid-liquid ratio of 30 g / L. Ozone atmosphere is introduced into the mixed solution, and after reacting for 6 h in a water bath at 50 °C, solid-liquid separation is performed to obtain lithium-containing filtrate and iron phosphate solid product.

[0036] Example 3 (see process) Figure 2 )

[0037] (1) Under the conditions of 60℃ water bath, choline chloride and ethylene glycol with a molar ratio of 1:2 were mixed and stirred for 30 min to obtain a clear and transparent deep eutectic solvent.

[0038] (2) The deep eutectic solvent obtained in step (1) and lithium iron phosphate powder are mixed at a solid-liquid ratio of 20 g / L. Ozone atmosphere is introduced into the mixed solution, and after reacting for 5 h in a water bath at 60 °C, solid-liquid separation is performed to obtain lithium-containing filtrate and iron phosphate solid product.

[0039] Example 4 (see process) Figure 2 )

[0040] (1) Under the conditions of 60℃ water bath, choline chloride and ethylene glycol with a molar ratio of 1:4 were mixed and stirred for 30 min to obtain a clear and transparent deep eutectic solvent.

[0041] (2) The deep eutectic solvent obtained in step (1) and lithium iron phosphate powder are mixed at a solid-liquid ratio of 30 g / L. Ozone atmosphere is introduced into the mixed solution, and after reacting for 6 h in a water bath at 50 °C, solid-liquid separation is performed to obtain lithium-containing filtrate and iron phosphate solid product.

[0042] Specific test results

[0043] The lithium and iron contents in the filtrate were determined by inductively coupled plasma optical emission spectrometry (ICP-OES), and the leaching efficiencies of lithium and iron were calculated by comparing them with those in the lithium iron phosphate powder before the reaction. The calculation results for the four examples are shown in Table 1. It can be observed that the leaching efficiency of lithium is consistently greater than 90%, while the leaching efficiency of iron is less than 2%. Taking Example 1 as an example, the leaching efficiency of lithium is 91.9%, and the leaching efficiency of iron is 1.7%, indicating that approximately 98.3% of the iron remains in the solid product. Figure 3 It is clearly seen that the XRD pattern of the solid product from Example 1 shows diffraction peaks consistent with the orthorhombic (Mn,Fe)PO4 (JCPDS: 37-0478) standard card, with no diffraction peaks for lithium iron phosphate detected. This indicates that most of the lithium in lithium iron phosphate has been removed. Therefore, this invention targets lithium iron phosphate cathode active materials from waste lithium batteries, using a deep eutectic solvent (a solution formed by choline chloride and ethylene glycol) as the leaching medium and an ozone atmosphere as the oxidant, achieving efficient and selective leaching of lithium in one step, yielding a leaching solution containing only lithium.

[0044] Table 1 shows the lithium and iron leaching efficiency in the examples.

[0045]

Claims

1. A method for selectively recovering lithium iron phosphate batteries under an ozone atmosphere, characterized in that, The specific process steps are as follows: (1) Under water bath conditions of 30-60℃, choline chloride and ethylene glycol with a molar ratio of 1:2-1:8 are mixed and stirred for 5-30 minutes to obtain a clear and transparent deep eutectic solvent. (2) The deep eutectic solvent obtained in step (1) and lithium iron phosphate powder are mixed at a solid-liquid ratio of 20-30 g / L. Ozone atmosphere is introduced into the mixed solution and the reaction is carried out under water bath conditions of 40-60℃ for 5-8 hours. Then, solid-liquid separation is carried out to obtain lithium-containing filtrate and iron phosphate solid product. The lithium leaching efficiency is over 90% and the iron leaching efficiency is less than 2%.

2. The method for selectively recovering lithium iron phosphate batteries under an ozone atmosphere as described in claim 1, characterized in that, The lithium iron phosphate powder used in step (2) is the positive electrode active material from the waste lithium battery LFP18650E-150.

3. The method for selectively recovering lithium iron phosphate batteries under an ozone atmosphere as described in claim 1, characterized in that, The ozone atmosphere used in step (2) was prepared by an air source ozone generator with an ozone yield of 2 g / h and a flow rate of 16 L / min.

4. The method for selectively recovering lithium iron phosphate batteries under an ozone atmosphere as described in claim 1, characterized in that, The deep eutectic solvent used in step (2) is the leaching reaction medium, and the ozone atmosphere is the oxidant.

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