Method for electrochemical synergic leaching of lithium cobaltate and lithium iron phosphate and selective lithium separation

Abstract

The application provides a method for electrochemically synergistic leaching and selective separation of lithium from lithium cobalt oxide and lithium iron phosphate. The application provides a synergistic leaching method based on a fluid electrode device, which utilizes the redox potential difference between Co 3+ / Co 2+ and Fe 3+ / Fe 2+ in the retired lithium cobalt oxide (LCO) and lithium iron phosphate (LFP) to realize the synchronous leaching of the two under the assistance of an applied electric field. When a three-chamber configuration of a monovalent cation exchange membrane plus an anion exchange membrane is adopted, the lithium ion selective migration rate is relatively high. The method operates under normal temperature and near neutral conditions, without the need of adding acid, alkali or reducing agent, and the leaching solution can be directly used for synthesizing a positive electrode material precursor, and the residue is iron phosphate, which can be recycled and utilized, thereby providing a new way for green recycling of waste batteries.

Description

Technical Field

[0001] This invention relates to the field of battery material separation and recycling technology, and in particular to a method for electrochemical co-leaching of lithium cobalt oxide and lithium iron phosphate and selective separation of lithium. Background Technology

[0002] With the rapid development of portable electronic devices and electric vehicles, the amount of lithium-ion batteries being scrapped is surging year by year. Lithium cobalt oxide (LiCoO2, LCO) dominates the consumer electronics market due to its high energy density, while lithium iron phosphate (LiFePO4, LFP) is widely used in the power battery field due to its safety and long cycle life. If these two types of batteries are not disposed of properly after retirement, it will not only waste resources such as cobalt and lithium, but also cause environmental risks such as heavy metal pollution and phosphorus pollution.

[0003] Among existing recycling technologies, pyrometallurgy is energy-intensive and difficult to treat waste gas; hydrometallurgy, although capable of leaching valuable metals, relies on large amounts of inorganic acids, alkalis, and reducing agents, resulting in high wastewater treatment costs. In recent years, electrochemical recycling methods have attracted attention due to their low reagent consumption and mild reaction conditions; however, traditional electrolytic cells typically utilize only a single electrode reaction, and side reactions such as hydrogen evolution or oxygen evolution often occur at the opposite electrode, resulting in low energy efficiency. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for the electrochemical synergistic leaching of lithium cobalt oxide and lithium iron phosphate, along with selective lithium separation. This invention systematically investigates the effects of the LCO / LFP molar ratio and the type of conductive agent on leaching efficiency. Results show that when the LCO / LFP molar ratio is 1:1, the leaching rates of both lithium and cobalt are optimal; activated carbon (AC) exhibits the best electron conduction promoting effect as a conductive agent. When using a three-chamber configuration of a monovalent cation exchange membrane + anion exchange membrane, the selective migration rate of lithium ions is high. This method operates under near-neutral conditions at room temperature, requiring no external acid, alkali, or reducing agent. The leachate can be directly used for the synthesis of cathode material precursors, and the residue, iron phosphate, can be recycled, providing a new approach for the green recycling of waste batteries.

[0005] The purpose of this invention is to provide a method for electrochemical synergistic leaching of lithium cobalt oxide and lithium iron phosphate and selective separation of lithium, comprising the following steps: A three-chamber fluid electrode device is provided; the fluid electrode device includes an anode chamber, a cathode chamber, an intermediate flow channel, an anion exchange membrane, and a monovalent cation exchange membrane; the anion exchange membrane is disposed between the anode chamber and the intermediate flow channel, and the monovalent cation exchange membrane is disposed between the cathode chamber and the intermediate flow channel; The anode chamber contains an aqueous solution of LCO / LFP mixed black powder and a conductive agent; the cathode chamber contains an electrolyte. Under constant current density electric field conditions, the LCO / LFP mixed black powder is stirred and leached, releasing lithium ions and cobalt ions. The lithium ions pass through the monovalent cation exchange membrane into the cathode chamber under the drive of the electric field, while the divalent cobalt ions are blocked by the monovalent cation exchange membrane and remain in the anode chamber. The lithium ions pass through the monovalent cation exchange membrane in the form of lithium ions and enter the intermediate channel, where they exist in the solution. The cobalt ions remain in the black powder solution in the leached anode chamber in the form of cobalt ions.

[0006] In some embodiments of the present invention, an intermediate flow channel is provided between the anode chamber and the cathode chamber of the fluid electrode device, and the intermediate flow channel contains deionized water.

[0007] In some embodiments of the present invention, the solid content of the LCO / LFP mixed black powder aqueous solution is 0.05 wt%.

[0008] In some embodiments of the present invention, the molar ratio of LCO to LFP in the LCO / LFP mixed black powder aqueous solution is 1:2-2:1. Exemplarily, it can be 1:2, 1:1, or 2:1, and more preferably 1:1. When the molar ratio is 1:1, the leaching rates of Li and Co are significantly higher than in other ratios. When LFP is in excess, the leaching rates of both lithium and cobalt decrease because some LFP particles fail to form effective contact with LCO and cannot participate in cooperative electron transfer.

[0009] In some embodiments of the present invention, the amount of the conductive agent is 0.05-2 wt% of the mass of the LCO / LFP mixed black powder.

[0010] In some embodiments of the present invention, the conductive agent is selected from one or more of CB carbon black, CNT carbon nanotubes, AB acetylene black, and AC activated carbon. The present invention found that the lithium and cobalt leaching rates of the system with added AC are superior to those of AB, CNT, and CB. Without the conductive agent, the leaching rates of Li and Co are both low. The high specific surface area and abundant microporous structure of AC are beneficial for constructing a three-dimensional conductive network, while its surface oxygen-containing functional groups can promote interfacial charge transfer and reduce contact resistance. Furthermore, the capacitive properties of AC activated carbon can buffer local charge fluctuations and maintain a stable microcouple effect. Therefore, activated carbon is the optimal conductive agent for this system. The present invention improves the conductivity of the fluid electrode and the distribution of potential and current density by adding the conductive agent, forming more conductive pathways between LFP / LCO particles. This effectively improves electron transfer between LCO and LFP, thereby promoting the leaching of Li and Co from LFP and LCO, while simultaneously alleviating local acid enrichment.

[0011] In some embodiments of the present invention, the electrolyte comprises a Na2SO4 solution, and the concentration of the electrolyte is 0.05-1.0 mol / L.

[0012] In some embodiments of the present invention, the constant current density condition is: the constant current value is 1-10mA.

[0013] In some embodiments of the present invention, the leaching time is 120-300 min.

[0014] Chamber reaction formula: Leaching: LiFePO4 + 4H + +LiCoO2=FePO4+2Li + +2H2O+Co 2+ ; Anode: 2H₂O - 4e - =4H + +O2; Cathode: 2H₂O + 2e⁻ - =H2+2OH - ; The technical solution of the present invention has the following advantages over the prior art: This invention utilizes the complementary redox properties of LCO and LFP: Co in LCO 3+ Can be reduced to Co 2+ (Standard potential +1.92 V vs. SHE), while Fe in LFP 2+ It can be oxidized to Fe 3+ (Standard potential approximately +0.771 vs. SHE). If the two are mixed and placed in an external electric field, they may form a spontaneous microcouple system, achieving electron supply and demand matching, thereby avoiding the need for external oxidants or reductants. Based on this, this invention designs a fluid electrode device that separates the anode chamber, intermediate channel (optional), and cathode chamber through an ion exchange membrane. A mixed LCO / LFP black powder is placed in the anode chamber, and the cathode chamber contains a sodium sulfate-supported electrolyte. A constant current density electric field is applied to drive lithium ion migration across the membrane, simultaneously promoting the reductive leaching of LCO and the oxidative delithiation of LFP. This invention systematically investigates the impact of key process parameters and compares the performance differences between the two membrane stack configurations, aiming to provide technical support for the green and efficient recycling of retired lithium batteries. Attached Figure Description

[0015] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein... Figure 1 This is a schematic diagram of the three chambers of the present invention.

[0016] Figure 2 This is a schematic diagram of the two chambers of the present invention.

[0017] Figure 3This invention relates to the lithium-cobalt leaching efficiency under different structures of three-chamber and two-chamber chambers.

[0018] Figure 4 This invention relates to the lithium leaching efficiency under different black powder compositions in the three chambers.

[0019] Figure 5 This invention relates to the cobalt leaching efficiency under different black powder compositions in the three chambers.

[0020] Figure 6 The leaching rates of lithium and cobalt in the three-chamber 1:1 molar ratio LFP and LCO of this invention are measured with and without AC doping.

[0021] Figure 7 This refers to the pH change during the three-chamber leaching process of this invention.

[0022] Figure 8 It is the conductivity during the leaching process of the intermediate flow channel chamber in the three-chamber system of this invention.

[0023] Figure 9 This invention describes the lithium leaching rate and cobalt leaching rate under different molar ratios of LCO and LFP.

[0024] Figure 10 This refers to the leaching rate of lithium cobalt under different conductive agent ratios according to the present invention.

[0025] Figure 11 This refers to the leaching rate of lithium cobalt under different types of conductive agents according to the present invention.

[0026] Figure 12 This invention relates to XRD and TEM analysis of the solid composition after leaching in the three-chamber anode chamber. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0028] 1. The device used in this invention employs conductive carbon plates as the anode and cathode. Two configurations are designed: a two-chamber configuration and a three-chamber configuration. Figure 1 and Figure 2 ): Structure I (three chambers, CEM+AEM): Cathode chamber | CEM | Intermediate chamber (pure water) | AEM | Anode chamber; Structure II (two chambers, CEM): Cathode chamber | CEM | Anode chamber (no intermediate chamber).

[0029] 2. This invention uses atomic absorption spectrometry to determine the concentrations of Li and Co in the leachate.

[0030] Example 1 This embodiment provides a method for electrochemical synergistic leaching of decommissioned lithium cobalt oxide and lithium iron phosphate, and selective separation of lithium, as detailed below: A three-chamber fluid electrode apparatus was used, consisting of an MCEM (monovalent cation exchange membrane) and an AEM (anion exchange membrane). A mixed aqueous solution of LCO / LFP black powder (1 wt% solids content, LCO to LFP molar ratio 1:1) was injected into the anode chamber, along with 0.5 wt% AC conductive agent (based on the weight of the black powder). The cathode chamber contained a 0.1 mol / L Na₂SO₄ solution, and the intermediate chamber contained deionized water. A constant current of 2 mA was applied, and the mixture was magnetically stirred at room temperature for 120 min. Lithium and cobalt concentrations were measured every 20 min in both the anode and intermediate chambers, and pH was measured during the leaching process.

[0031] Example 2 This embodiment provides a method for electrochemical synergistic leaching and lithium selective separation of decommissioned lithium cobalt oxide and lithium iron phosphate, which is similar to that in Embodiment 1, except that the molar ratio of LCO to LFP is 1:2.

[0032] Example 3 This embodiment provides a method for electrochemical synergistic leaching and lithium selective separation of decommissioned lithium cobalt oxide and lithium iron phosphate, which is similar to that in Embodiment 1, except that the molar ratio of LCO to LFP is 2:1.

[0033] Example 4 This embodiment provides a method for electrochemical synergistic leaching and selective lithium separation of decommissioned lithium cobalt oxide and lithium iron phosphate, which is similar to that in Embodiment 1, except that CB is used as the conductive agent.

[0034] Example 5 This embodiment provides a method for electrochemical synergistic leaching and selective lithium separation of decommissioned lithium cobalt oxide and lithium iron phosphate, which is similar to that in Embodiment 1, except that CNT is used as the conductive agent.

[0035] Example 6 This embodiment provides a method for electrochemical synergistic leaching and selective lithium separation of decommissioned lithium cobalt oxide and lithium iron phosphate, which is similar to that in Embodiment 1, except that AB is used as the conductive agent.

[0036] Comparative Example 1 This comparative example provides a separation method for electrochemical co-leaching of decommissioned lithium cobalt oxide and lithium iron phosphate, similar to Example 1, except that no conductive agent is added.

[0037] The leaching solutions obtained from the above examples and comparative examples were tested for cobalt and lithium leaching efficiency. The lithium leaching rate was calculated as follows: (lithium ion concentration in the anode chamber × anode chamber solution volume + lithium ions in the intermediate channel × intermediate channel solution volume) / mass of lithium in the mixed black powder; the cobalt leaching rate was calculated as follows: (cobalt ion concentration in the anode chamber × anode chamber solution volume + cobalt ions in the intermediate channel × intermediate channel solution volume) / mass of cobalt in the mixed black powder.

[0038] With the total amount of LCO / LFP black powder fixed at 0.5 wt% of the total mass, the molar ratio of LCO / LFP was varied (1:2, 1:1, 2:1). A constant current of 2 mA was applied in apparatus I, and the reaction was carried out for 2 hours. The experimental results are shown in [Figure Number]. Figure 3 , Figure 4 and Figure 9 .Depend on Figure 9 It was found that when the molar ratio was 1:1, the leaching rates of both Li and Co were significantly higher than at other ratios. When LFP was in excess, the leaching rates of both Li and Co decreased because some LFP particles failed to form effective contact with LCO and could not participate in cooperative electron transfer. Therefore, a 1:1 molar ratio can achieve stoichiometric matching of the electrochemical reactions of the two, and this ratio was used in subsequent experiments.

[0039] Under conditions of a 1:1 molar ratio, Structure I apparatus, and 2 mA, 0.05 wt% of CB, CNT, AB, and AC (by weight of black powder) were added, with no conductive agent added as a control. The results are shown in [Figure number missing]. Figure 5 and Figure 10 . Figure 10 The results showed that the lithium and cobalt leaching rates of the system with added AC were superior to those of AB, CNT, and CB. Figure 5 It is evident that the leaching rates of Li and Co are both low without the addition of a conductive agent. Analysis shows that the high specific surface area and abundant microporous structure of activated carbon (AC) are beneficial for constructing a three-dimensional conductive network. Simultaneously, its surface oxygen-containing functional groups can promote interfacial charge transfer and reduce contact resistance. Furthermore, the capacitive properties of AC can buffer local charge fluctuations and maintain a stable microcouple effect. Therefore, activated carbon is the optimal conductive agent for this system.

[0040] This invention also systematically investigated the leaching behavior of the LFP+LCO system with and without AC doping, including pH changes, Faraday efficiency, and conductivity of the intermediate flow channel chamber during the leaching process. The experimental results are as follows: Figure 6 , Figure 7 and Figure 8 As shown in the figure. The results demonstrate the promoting mechanism of AC on the LCO / LFP synergistic leaching system: the pH of the anode chamber in both systems (AC system and no AC system) decreased from approximately 6.4 to approximately 1.2, and the acidic environment promoted the leaching of Co. 3+Reduction and dissolution; the cathode chamber was maintained at 12~13, and the conductivity peaked at 90 min (approximately 5600 μS / cm), which was earlier and higher than that of the system without AC (approximately 4850 μS / cm at 120 min), indicating that AC accelerated the oxidative delithiation and ion dissolution kinetics of LFP.

[0041] Effect of membrane stack configuration on leaching performance Two apparatus configurations (Structure I and Structure II) were compared under the same operating conditions (1:1 molar ratio, 0.5 wt% AC, 2 mA, 2 h) to examine leaching efficiency and ion selectivity. Structure I (three-chamber, MCEM+AEM) achieved the highest lithium leaching rate of 94.36% at approximately 88 minutes and the highest cobalt leaching rate of 84.31% at 120 minutes. Structure II (two-chamber, MCEM) achieved the highest lithium leaching rate of 92.79% at approximately 120 minutes and the highest cobalt leaching rate of 69.23% at 120 minutes. This indicates that the three-chamber configuration has higher leaching selectivity for lithium and cobalt, and the monovalent cation exchange membrane effectively blocks Fe. 3+ / Fe 2+ Transmembrane migration.

[0042] in conclusion (1) By utilizing the redox potential difference between retired LCO and LFP, synergistic leaching without the need for external oxidant / reducing agent was achieved in the device. When the molar ratio of LCO / LFP is 1:1, the leaching rates of lithium and cobalt are optimal.

[0043] (2) Activated carbon (AC) is the best conductive agent. Its high specific surface area and conductive network structure significantly promote electron transfer between particles.

[0044] (3) The membrane stack configuration has a significant impact on leaching performance and product purity: the three-chamber MCEM+AEM configuration can obtain the highest lithium selectivity and is suitable for the preparation of high-purity products.

[0045] (4) Under optimal process conditions (1:1 molar ratio, 0.5wt% AC, 2mA, 2 h), the leachate can be directly used for the synthesis of cathode material precursors, and the residue is pure phase FePO4, realizing the full-component resource utilization of retired battery cathode materials. This method provides a feasible technical solution for the green recycling of waste lithium batteries.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for electrochemical synergistic leaching of lithium cobalt oxide and lithium iron phosphate and selective separation of lithium, characterized in that, Includes the following steps: A three-chamber fluid electrode device is provided; the fluid electrode device includes an anode chamber, a cathode chamber, an intermediate flow channel, an anion exchange membrane, and a monovalent cation exchange membrane; the anion exchange membrane is disposed between the anode chamber and the intermediate flow channel, and the monovalent cation exchange membrane is disposed between the cathode chamber and the intermediate flow channel; The anode chamber contains a mixed black powder solution of LCO / LFP and a conductive agent; the cathode chamber contains an electrolyte. Under the condition of constant current density electric field, the LCO / LFP mixed black powder is stirred and leached, releasing lithium ions and cobalt ions. The lithium ions pass through the monovalent cation exchange membrane into the cathode chamber under the drive of the electric field, while the divalent cobalt ions are blocked by the monovalent cation exchange membrane and remain in the anode chamber. The lithium ions pass through the monovalent cation exchange membrane in the form of lithium ions and enter the intermediate channel, where they exist in the solution. The cobalt ions remain in the black powder solution in the leached anode chamber in the form of cobalt ions.

2. The method for electrochemical synergistic leaching and selective lithium separation of lithium cobalt oxide and lithium iron phosphate according to claim 1, characterized in that, The solid content of the LCO / LFP mixed black powder aqueous solution is 0.05-2wt%.

3. The method for electrochemical synergistic leaching and selective lithium separation of lithium cobalt oxide and lithium iron phosphate according to claim 1, characterized in that, The molar ratio of LCO to LFP in the LCO / LFP mixed black powder solution is 1:2-2:

1.

4. The method for electrochemical synergistic leaching and selective lithium separation of lithium cobalt oxide and lithium iron phosphate according to claim 1, characterized in that, The amount of the conductive agent is 0.05-2 wt% of the mass of the LCO / LFP mixed black powder.

5. The method for electrochemical synergistic leaching and selective lithium separation of lithium cobalt oxide and lithium iron phosphate according to claim 1, characterized in that, The conductive agent is selected from one or more of carbon black CB, carbon nanotubes CNT, acetylene black AB, and activated carbon AC.

6. The method for electrochemical synergistic leaching and selective lithium separation of lithium cobalt oxide and lithium iron phosphate according to claim 1, characterized in that, The electrolyte includes a Na2SO4 solution, and the concentration of the electrolyte is 0.05-1.0 mol / L.

7. The method for electrochemical synergistic leaching and selective lithium separation of lithium cobalt oxide and lithium iron phosphate according to claim 1, characterized in that, Conditions for constant current density: The constant current value is 1mA-10mA.

8. The method for electrochemical synergistic leaching and selective lithium separation of lithium cobalt oxide and lithium iron phosphate according to claim 1, characterized in that, The leaching time is 120-300 min.

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