Recycling method of lithium battery positive electrode material based on redox medium

Abstract

The invention discloses a lithium battery positive electrode material recovery method based on a redox medium, which comprises the following steps: (1) reduction leaching of a high-potential positive electrode material: mixing the redox medium in a reduction state with the high-potential positive electrode material in an acid solution, and carrying out reduction leaching at normal temperature under the action of the high-potential positive electrode material to obtain the high-potential positive electrode material; the oxidation-reduction medium in the reduction state is oxidized into an oxidation state, and meanwhile, high-valence metal ions in the positive electrode material are reduced into low-valence metal ions which are easily dissolved in acid, so that lithium ions and the metal ions are jointly leached; (2) oxidizing and leaching the low-potential positive electrode material and regenerating a medium: adding the low-potential positive electrode material into the solution obtained in the step (1) at normal temperature; under the action of the residual acid in the solution and the oxidation-state medium, low-valence metal ions in the positive electrode material are oxidized into high-valence ions, meanwhile, ions such as iron and lithium are dissolved out and enter the solution, and the oxidation-state medium is reduced into a reduction state.

Description

Technical Field

[0001] This invention relates to a method for recycling lithium battery cathode materials based on redox media. Background Technology

[0002] With the advancement of global energy transition strategies, lithium-ion batteries have been widely adopted in key areas such as new energy vehicles and large-scale energy storage. At the same time, the volume of retired lithium-ion batteries is growing at an unprecedented rate, and the associated risks of resource waste and environmental pollution have become a core bottleneck restricting the sustainable development of the new energy industry.

[0003] Currently, hydrometallurgy is the mainstream technology for recycling cathode materials from spent lithium-ion batteries in industry. Typical traditional hydrometallurgical processes rely on a "strong acid + strong oxidant / reducing agent" system, such as using hydrogen peroxide to reduce and leach lithium cobalt oxide under acidic conditions. While this method achieves high metal leaching rates with large amounts of acid added, it suffers from several significant drawbacks: First, reagent costs are high, as strong acids and chemical oxidants / reducing agents are disposable consumables requiring continuous and substantial input; second, it places a heavy environmental burden, inevitably generating large amounts of acidic wastewater containing heavy metals; third, energy consumption is enormous, as the reaction typically requires high temperatures (e.g., 80-90°C) to achieve ideal leaching kinetics, resulting in significant heat energy consumption; and fourth, the leaching reaction time is long, generally requiring more than ten hours, leading to low leaching efficiency.

[0004] To circumvent the drawbacks of traditional wet processes, existing technologies have explored recovery methods based on electrochemical principles. Specifically, this involves introducing a redox mediator to construct a "mediated electrolysis" system. In this system, the redox mediator undergoes electrochemical regeneration on the electrode surface driven by an external electric field, subsequently reacting chemically with the cathode material in solution to leach the target metal. While this method reduces the net consumption of chemicals (acid) through media recycling, it still has fundamental limitations: the system operation relies on external electrical energy input and a complete set of electrochemical devices (including electrodes, diaphragms, and power supplies). This not only implies continuous energy consumption but also leads to higher equipment investment and maintenance costs. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a method for recycling lithium battery cathode materials that can significantly reduce recycling costs and has low energy consumption.

[0006] Technical solution: The method for recycling lithium battery cathode materials according to the present invention specifically comprises: (1) Reduction leaching of high potential cathode material: The reduced redox medium is mixed with the high potential cathode material in an acidic solution. After the reaction at room temperature, under the action of the high potential cathode material, the reduced redox medium is oxidized to the oxidized state. At the same time, the high-valence metal ions in the cathode material are reduced to low-valence metal ions that are easily soluble in acid, so that lithium ions and the metal ions are leached out together. (2) Oxidative leaching of low-potential cathode material and regeneration of medium: At room temperature, the low-potential cathode material is added to the solution obtained in step (1). Utilizing the remaining acid in the solution and the effect of the oxidized medium, the low-valence metal ions in the cathode material are oxidized to high-valence ions, while iron, lithium, and other ions dissolve into the solution, and the oxidized medium is reduced to a reduced state.

[0007] In step (1), the redox medium is a NO radical-containing compound, such as TEMPOL (2,2,6,6-tetramethylpiperidine-1-oxy) and its derivatives; or a phenolic / quinone compound, such as dopamine, N-hydroxyimide compounds; or ferrocene and its derivatives; or potassium ferricyanide; or a halide ion or a mixture thereof, such as iodide ions. These redox media have efficient electron transfer capabilities and redox reversibility, and their redox reaction potential is 0.2V~0.9V vs. Ag / AgCl. This invention uses the inherent electrochemical potential difference between different waste cathode materials as the sole driving force for the redox reaction.

[0008] In step (1), the high-potential positive electrode material is an electrode material with a voltage of not less than 0.2V vs. Ag / AgCl, specifically lithium cobalt oxide (LCO, LiCoO2) or lithium nickel manganese cobalt oxide (NCM, LiNi). x Co y Mn 1-x-y O2; Low potential cathode materials are electrode materials with a voltage not higher than 0.9 V vs. Ag / AgCl, specifically lithium iron phosphate (LFP, LiFePO4) or lithium manganese oxide (LMO, LiMn2O4).

[0009] In step (1), the acidic solution refers to an aqueous solution of an inorganic acid or an organic acid, wherein the inorganic acid is selected from at least one of sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid; and the organic acid is selected from at least one of oxalic acid, citric acid, ascorbic acid or acetic acid.

[0010] In step (1), the redox medium, lithium battery cathode material and acidic solution are mixed in the following proportions to form a reaction system: the concentration of the redox medium is 0.05~0.25mol / L; the concentration of the acidic solution is 0.1~0.8mol / L; and the solid-liquid ratio of the cathode material to the acidic solution is 4~25g / L.

[0011] The mixture was stirred at room temperature (20-30°C) to carry out the leaching reaction; the reaction time for both the reduction leaching of the high-potential cathode material and the oxidation leaching of the low-potential cathode material did not exceed 3 hours. During the reaction, the redox medium reacted with the cathode material in a redox reaction, and lithium ions and other metal ions were gradually released into the solution.

[0012] The method of this invention is used for the recycling of cathode materials from waste lithium-ion batteries. The redox media such as TEMPO and PD used in this method have excellent reversibility and efficient electron transfer capabilities, enabling rapid metal leaching at room temperature. Furthermore, the recycling of the redox media avoids the need for strong oxidants and external energy input, significantly reducing recycling costs.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) This invention breaks through the dependence of traditional hydrometallurgy on high temperature and strong oxidant. It can achieve rapid and efficient leaching of metals at room temperature (20~30℃). The leaching rate of lithium and cobalt in lithium cobalt oxide (LCO) reaches more than 90%, and the leaching rate of lithium and iron in lithium iron phosphate (LFP) reaches 95%. The reaction time is only 6 hours. This process does not require external energy input, thereby greatly reducing energy consumption, avoiding the complex equipment requirements of high temperature process, and significantly improving the economy and operability of recycling process.

[0014] (2) The redox medium used in the method of the present invention has excellent reversibility and stability, and can be recycled multiple times in the reaction system. Experiments show that 4-OH-TEMPO can maintain high activity in the reaction system and support at least 50 cycles of leaching. During the recycling process, the leaching efficiency does not decrease significantly. This greatly reduces reagent consumption, and the recovery rate of the redox medium is nearly 90% in the subsequent recovery process. This recycling method significantly improves resource utilization efficiency, reduces recycling costs, and reduces the amount of waste liquid generated. It also avoids the direct use of strong oxidants in traditional hydrometallurgy (reducing the generation of waste liquid). Therefore, the method of the present invention has the advantages of low energy consumption and low cost while having high leaching rate and leaching efficiency. Attached Figure Description

[0015] Figure 1 The figures are cyclic voltammetry (CV) curves for redox media; a is the CV of potassium ferricyanide; b is the CV of N-hydroxyphthalimide (NHPI); c is the CV of dopamine (PD); d is the CV of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy (4-OH-TEMPO). Figure 2The leaching rates of LFP and LCO by 4-OH-TEMPO are shown in the diagram. Figure 3 The leaching rates of 4-OH-TEMPO for LFP and LCO after 50 cycles are shown in the diagram. Figure 4 The leaching rates of PD for LCO and LFP are shown in the diagram. Figure 5 The leaching rates of NHPI for LCO and LFP are shown in the diagram. Figure 6 Photographs and XRD patterns of the final separated lithium carbonate precipitate; Figure 7 This is a leaching rate diagram of LCO using the traditional electrolysis method; Figure 8 The cyclic voltammetry (CV) curves for AQDS and the leaching rates for LCO and LFP are shown. Detailed Implementation

[0016] Example 1 The present invention provides a method for recycling lithium battery cathode materials, comprising the following steps: (1) Prepare a 0.2 mol / L solution of 4-OH-TEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxy) (as a redox medium) in a 0.8 mol / L sulfuric acid solution, and take 100 mL; add 2 g of waste lithium-ion battery cathode material powder (lithium cobalt oxide (LCO)) to the above reaction solution, with a solid-liquid ratio of 20 g / L; place the reaction system at room temperature (25 °C) and stir for 3 hours; the redox medium is oxidized to the oxidized state, and at the same time, the Co in LCO is removed. 3+ Reduced to Co, which is readily soluble in acid 2+ This allows lithium ions and cobalt ions to leach out together. LCO(s) + 2H + + Red (medium) → Li + (aq) + Co 2+ (aq) + SO4 2- (aq) + H₂O + Ox (medium)

[0017] (2) Add 2g of lithium iron phosphate powder (LFP, LiFePO4) to the solution after the reaction, and stir at room temperature for 3 hours; the oxidizing medium (Ox) will oxidize the Fe in LFP. 2+ Oxidized to Fe 3+ At the same time with Li + They enter the solution together, and at the same time, the redox medium itself is reduced and regenerated into a reduced state (Red). After adding acid, it can be reused in the first step of the cycle. LFP(s) + Ox (medium) → Fe 3+ (aq) + Li + (aq) + PO4 3- (aq) + SO4 2- (aq) + Red (medium) .

[0018] After the reaction, the concentrations of lithium ions, cobalt ions, and iron ions in the solution were detected using ICP-OES (inductively coupled plasma optical emission spectrometry), and the leaching rate was calculated. Experimental results: After 6 hours of reaction, the leaching rate of lithium ions in LCO reached 90%, and the leaching rate of cobalt ions reached 91%; the leaching rate of iron ions in LFP reached 95%, and the leaching rate of lithium ions reached 96%. Figure 2 As shown.

[0019] Compared with existing hydrometallurgical processes, the system of Example 1 achieves the same effect as Example 1: the leaching rate of lithium and cobalt in lithium cobalt oxide (LCO) reaches more than 90%, and the leaching rate of lithium in lithium iron phosphate (LFP) reaches 95%. Existing hydrometallurgical processes require a reaction at 90 degrees Celsius for 2 hours, and at room temperature, the existing hydrometallurgical processes require a reaction for 25 hours to achieve a lithium leaching rate of 85% in LCO.

[0020] The system of Example 1 was compared with the traditional electrolysis method: 2g of waste lithium cobalt oxide powder, 0.25g of conductive carbon black, and 0.2g of polytetrafluoroethylene (PVDF) were mixed in N-methylpyrrolidone (NMP), and the mixture was drop-coated onto carbon cloth to prepare an electrode sheet. This electrode sheet was placed in an hcell, forming a three-electrode system, and a reduction voltage of 0.62V vs. Ag / AgCl was applied. Figure 7 As shown, when a voltage of 0.6V is applied and electrolysis is carried out for 3 hours, 69% of lithium and 42% of cobalt are leached, which is far lower than the effect of LCO reduction leaching driven by 4-OH-TEMPO.

[0021] Cyclic Experiment: In the above reaction system, the experimental steps were repeated. 1 mol of LCO consumes 4 mol of protons, so 2 mol of sulfuric acid was added. Based on the input amount, 0.04 mol of sulfuric acid needs to be added to the system during the cycle. The results show that the reaction system can stably support 50 cycles, 4-OH-TEMPO maintains high activity, and the leaching rate does not decrease significantly. The results are as follows. Figure 3 As shown, after 50 cycles, the leaching rate of lithium ions in LCO still reached over 91%, and the leaching rate of cobalt ions reached 90%; the leaching rate of iron ions in LFP reached 92%, and the leaching rate of lithium ions reached 93%.

[0022] Valuable metals in LCO and LFP can be rapidly and efficiently leached at room temperature through the redox-mediated action of 4-OH-TEMPO, and the system exhibits good cycling stability, significantly reducing reagent consumption and energy requirements.

[0023] Example 2 The present invention provides a method for recycling lithium battery cathode materials, comprising the following steps: (1) Prepare a 0.05 mol / L PD (dopamine) solution in a 0.1 mol / L sulfuric acid solution, and take 100 mL; first take 0.4894 g of waste lithium-ion battery cathode material powder (lithium cobalt oxide (LCO)) and add it to the above solution, with a solid-liquid ratio of 4.894 g / L; place the reaction system at room temperature (25℃) and stir for 3 hours; the redox medium is oxidized to the oxidized state, and at the same time, the Co in LCO is removed. 3+ Reduced to Co, which is readily soluble in acid 2+ This allows lithium ions and cobalt ions to leach out together. LCO(s) + 2H + + Red (medium) → Li + (aq) + Co 2+ (aq) + SO4 2- (aq) + H₂O + Ox (medium) (2) Add 2g of lithium iron phosphate powder (LFP, LiFePO4) to the solution after the reaction, and stir at room temperature for 3 hours; the oxidizing medium (Ox) will oxidize the Fe in LFP. 2+ Oxidized to Fe 3+ At the same time with Li + When they enter the solution together, the redox medium itself is reduced and regenerated into a reduced state (Red). After adding acid, it can be reused in the first step of the cycle. LFP(s) + Ox (medium) → Fe 3+ (aq) + Li + (aq) + PO4 3- (aq) + SO4 2- (aq) + Red(medium).

[0024] After the reaction, the concentrations of lithium, cobalt, and iron ions in the solution were detected using ICP-OES (inductively coupled plasma optical emission spectrometry), and the leaching rates were calculated. Experimental results: After 6 hours of reaction, the leaching rate of lithium ions in LCO reached 93%, and the leaching rate of cobalt ions reached 90%; the leaching rate of iron ions in LFP reached 94%, and the leaching rate of lithium ions reached 95%. Figure 4 As shown.

[0025] Example 3 The present invention provides a method for recycling lithium battery cathode materials, comprising the following steps: (1) Prepare a 0.25 mol / L NHPI (N-hydroxyphthalimide) solution in a 0.5 mol / L sulfuric acid solution, and take 100 mL; first take 2.4468 g of waste lithium-ion battery cathode material powder (lithium cobalt oxide (LCO)) and add it to the above solution, with a solid-liquid ratio of 24.468 g / L; place the reaction system at room temperature (25℃) and stir for 3 hours; the redox medium is oxidized to the oxidized state, and at the same time, the Co in LCO is removed. 3+ Reduced to Co, which is readily soluble in acid 2+ This allows lithium ions and cobalt ions to leach out together. LCO(s) + 2H + + Red (medium) → Li + (aq) + Co 2+ (aq) + SO4 2- (aq) + H₂O + Ox (medium)

[0026] (2) Add 2g of lithium iron phosphate powder (LFP, LiFePO4) to the solution after the reaction, and stir at room temperature for 3 hours; the oxidizing medium (Ox) will oxidize the Fe in LFP. 2+ Oxidized to Fe 3+ At the same time with Li + They enter the solution together, and at the same time, the redox medium itself is reduced and regenerated into a reduced state (Red). After adding acid, it can be reused in the first step of the cycle. LFP(s) + Ox (medium) → Fe 3+ (aq) + Li + (aq) + PO4 3- (aq) + SO4 2- (aq) + Red (medium) .

[0027] After the reaction, the concentrations of lithium ions, cobalt ions, and iron ions in the solution were detected using ICP-OES (inductively coupled plasma optical emission spectrometry), and the leaching rate was calculated. Experimental results: After 6 hours of reaction, the leaching rate of lithium ions in LCO reached 92%, and the leaching rate of cobalt ions reached 91%; the leaching rate of iron ions in LFP reached 95%, and the leaching rate of lithium ions reached 96%. Figure 5 As shown.

[0028] Comparative Example 1 A method for recycling lithium battery cathode material includes the following steps: (1) Take 100 mL of sulfuric acid solution with a concentration of 0.5 mol / L; take 2 g of waste lithium-ion battery cathode material powder (lithium cobalt oxide (LCO)) and add it to the above solution, with a solid-liquid ratio of 20 g / L; place the reaction system at room temperature (25°C) and stir for 3 hours; (2) Add 2g of lithium iron phosphate powder (LFP, LiFePO4) to the solution after the reaction and stir at room temperature for 3 hours.

[0029] After the reaction was completed, the concentrations of lithium ions, cobalt ions, and iron ions in the solution were detected using ICP-OES (inductively coupled plasma optical emission spectrometry) to calculate the leaching rate. After 4 hours of reaction, the leaching rate of lithium ions in LCO was only 10%, and the leaching rate of cobalt ions was only 5%. The leaching rates of lithium ions and iron ions in LFP were 40%, respectively. This is because the olivine structure of LFP can be destroyed by acid, but due to the slow kinetics and the formation of the FePO4 passivation layer, the dissolution of LFP will stop quickly.

[0030] As shown in Comparative Example 1, efficient leaching of metal ions cannot be achieved using sulfuric acid solution alone. The addition of a redox medium to the acid solution in this invention significantly improves the metal leaching rate. The redox media (4-OH-TEMPOL, PD, NHPI) of this invention can achieve rapid and efficient leaching of lithium and cobalt from waste lithium-ion battery cathode materials at room temperature, and the redox media exhibits good cycle stability, supporting multiple cycles. The introduction of the redox media not only improves leaching efficiency but also reduces reagent consumption and waste liquid generation.

[0031] Comparative Example 2 Sodium anthraquinone-2,6-disulfonate (AQDS) was used as the redox medium to mediate the leaching of LCO and LFP, specifically as follows: (1) Prepare a 0.2 mol / L AQDS (Red) solution in a 0.8 mol / L sulfuric acid solution, and take 100 mL; add 2 g of waste lithium-ion battery cathode material powder (lithium cobalt oxide (LCO)) to the above reaction solution, with a solid-liquid ratio of 20 g / L; place the reaction system at room temperature (25℃) and stir for 3 hours; AQDS (Red) is oxidized to the oxidized state, and at the same time, the Co in LCO is oxidized. 3+ Reduced to Co, which is readily soluble in acid 2+ This allows lithium ions and cobalt ions to leach out together, as shown in the ICP results. Figure 8 As shown; (2) 2g of lithium iron phosphate powder (LFP, LiFePO4) was added to the solution after the reaction, and stirred at room temperature for 3 hours; however, since the reduction potential of AQDS is lower than the oxidation potential of LFP, this reaction cannot occur, and the ICP test results are as follows. Figure 8As shown, only a small amount of lithium iron was detected, which is due to residual sulfuric acid.

[0032] Metal Separation and Recovery: After multiple leaching processes, the leachate contains a large amount of lithium, cobalt, and iron ions. The target metal salts are separated by adding a precipitant. The specific steps are as follows: The redox medium is first precipitated in the leachate using the salting-out effect, followed by filtration. Then, the pH of the solution is adjusted to 3-4, causing iron ions to precipitate as ferric hydroxide. After filtration, the pH is adjusted to 6-7, and ammonium oxalate is added to generate cobalt oxalate precipitate. This precipitate is then filtered, washed, and dried. Next, sodium carbonate is added to the solution, and the mixture is heated at 80°C for 1 hour. The mixture is then filtered while hot and washed with hot water to obtain lithium carbonate precipitate. This precipitate is then filtered, washed, and dried to obtain the target solid product. The actual product image and XRD pattern are shown below. Figure 6 As shown in the XRD pattern, the XRD pattern of the precipitated lithium carbonate is consistent with that of the standard card, indicating that lithium carbonate was successfully recovered from the waste cathode, thus achieving the recovery of high-purity metal salts.

[0033] Figure 1 The redox potential was determined by testing the cyclic voltammetry curves of the redox media. The test results showed that the redox potentials of the screened redox media were all between 0.2V and 0.9V vs. AgCl / Ag.

Claims

1. A method for recycling a lithium battery cathode material based on a redox mediator, characterized in that, The method comprises the following steps: (1) reducing leaching of high potential cathode material: mixing the reduced redox medium with the high potential cathode material in an acidic solution, and under normal temperature, the reduced redox medium is oxidized to the oxidized state under the action of the high potential cathode material, and the high-valence metal ions in the cathode material are reduced to low-valence metal ions which are easy to dissolve in acid, so that lithium ions and the metal ions are co-leached; (2) oxidizing leaching of low potential cathode material and regenerating the medium: adding the low potential cathode material into the solution obtained in step (1) under normal temperature; under the action of the remaining acid in the solution and the oxidized medium, the low-valence metal ions in the cathode material are oxidized to high-valence ions, and the iron and lithium ions are dissolved into the solution, while the oxidized medium is reduced to the reduced state.

2. The method of claim 1, wherein: In step (1), the redox medium is a N-O free radical compound, or a phenolic / quinoxaline compound, or ferrocene and its derivatives, or potassium ferricyanide, or halogen ions or a mixture thereof.

3. The method for recycling lithium battery cathode material according to claim 2, characterized in that: The redox medium is one of TEMPOL or its derivatives, or dopamine or N-hydroxy imide compounds.

4. The method for recycling lithium battery cathode material according to claim 2, characterized in that: The redox potential of the redox medium is between 0.2 V and 0.9 V vs. Ag / AgCl.

5. The method of claim 1, wherein: In steps (1)-(2), the high potential cathode material is an electrode material with a voltage of not less than 0.2 V vs. Ag / AgCl, and the low potential cathode material is an electrode material with a voltage of not higher than 0.9 V vs. Ag / AgCl.

6. The method for recycling lithium battery cathode material according to claim 5, characterized in that: The high potential cathode material is lithium cobaltate or lithium cobalt-nickel-manganese acid, and the low potential cathode material is lithium iron phosphate or lithium manganate.

7. The method of claim 1, wherein: In step (1), the acidic solution is an aqueous solution of inorganic acid or organic acid.

8. The method for recycling lithium battery cathode material according to claim 7, characterized in that: The inorganic acid is at least one of sulfuric acid, hydrochloric acid, nitric acid or phosphoric acid, and the organic acid is at least one of oxalic acid, citric acid, ascorbic acid or acetic acid. 9.The method of claim 1, wherein: In steps (1)-(2), the concentration of the acidic solution is 0.1-0.8 mol / L, the concentration of the redox medium in the acidic solution is 0.05-0.25 mol / L, the solid-liquid ratio of the high potential cathode material to the acidic solution is 4-25 g / L, and the solid-liquid ratio of the low potential cathode material to the acidic solution is 2-25 g / L.

10. The method of claim 1, wherein: In steps (1)-(2), the reaction time for reducing leaching of the high potential cathode material and oxidizing leaching of the low potential cathode material is not more than 3 h.

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