An electrochemical lithium extraction method

Abstract

The present invention relates to an electrochemical lithium extraction method, which applies pulsed electric field control for a certain period of time to a lithium-containing raw material solution in an electrochemical lithium extraction electrode system. The lithium extraction electrochemical system of the present invention has obvious advantages in lithium extraction cycle stability, long-term selectivity and low unit lithium extraction energy consumption under the optimal process parameters of the pulsed-reverse pulsed electric field combination mode.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical lithium extraction, and particularly relates to an electrochemical lithium extraction method. Background Art

[0002] The methods for extracting and recovering lithium resources from salt lake brine include electrodialysis, evaporation crystallization, solvent extraction, precipitation, ion exchange, and adsorption. Among them, the adsorption method has been widely used due to its low cost and high efficiency. However, pickling is required during the ion exchange adsorption process, generating secondary waste. In addition, the poor permeability and solubility of the adsorbent severely limit its industrial application. The solvent extraction method has high selectivity, high yield, simple operation, and is easy to scale up industrially, making it an ideal separation method for lithium extraction from salt lakes with a high magnesium-lithium ratio. However, this method uses a large amount of organic solvents, resulting in environmental pollution and equipment corrosion. Traditional lithium extraction methods have disadvantages such as high cost, high energy consumption, and low separation efficiency. Electrochemical technology is considered a promising technology for recovering lithium from salt lake brine and seawater.

[0003] Chinese Patent CN112645362A discloses a method for directly preparing lithium carbonate by electrochemical lithium extraction from chloride-type lithium-containing brine. Using chloride-type lithium-containing brine as the electrolyte, a lithium ion sieve electrode and a chloride ion capture electrode are used as the positive and negative electrodes respectively to form a primary battery, and the primary battery discharges to embed lithium ions in the brine into the lithium ion sieve. Chinese Patent CN109440132A also discloses a continuous electrochemical lithium extraction system. This method uses polyaniline (PANI) as the negative electrode of the lithium extraction battery system, and a highly Li + selective λ-MnO2 material as the positive electrode of the battery, and realizes lithium extraction through a two-step flow system. First, the lithium-containing solution is passed through the system. During discharge, anions are embedded in the PANI, and Li + is captured by the highly Li + selective λ-MnO2 electrode. After discharge is completed, a recovery solution is added for charging, and anions are removed from the negative electrode PANI, while Li +Released from the positive electrode. Through multiple repeated cycles, the separation of lithium ions from other cations in the lithium-containing solution and the enrichment of lithium ions in the recovery solution can be achieved. This is an electrochemical lithium extraction method with high efficiency, low energy consumption, high selectivity, simple process, easy control and no pollution. Chinese Patent CN110643831A discloses a diaphragm-free continuous electrochemical lithium extraction system and its lithium extraction method. The system mainly consists of an electrolytic cell, a washing tank, a power supply, a series of lithium absorption and desorption electrodes and an electronic balance electrode. Among them, the electrolytic cell is divided into a raw material pool and a recovery pool with alternating positions by a series of partition plates, and different raw material pools and recovery pools are connected in series through connecting pipes respectively. The raw material to be extracted with lithium and the recovery solution are respectively introduced into the raw material pool and the recovery pool, and the separation of lithium from the raw material and its enrichment in the recovery solution are realized by switching the electrodes between the raw material pool and the recovery pool. Two remarkable features of this system are its high selectivity for lithium ions compared with other cations and very low energy consumption. Patent CN108560019A addresses the concern about the continuity of lithium extraction operation and discloses a continuous flow-controlled asymmetric lithium-ion capacitor lithium extraction device and its lithium extraction method. The device includes a cavity surrounded by two parallel and spaced conductive current collectors and side plates. A lithium-containing solution inlet, a recovery solution inlet, a de-lithiated solution outlet and a lithium-rich recovery solution outlet are made on the side wall of the solution flow cavity. On the premise of improving the cation selectivity, the negative electrode uses an electric double layer capacitor electrode represented by two-dimensional long-range ordered materials such as activated carbon, graphene, and polypyrrole instead of the negative electrode of a rocking chair battery, which has the characteristics of strong cycle stability, no need to repeatedly take out and immerse the electrode, only need to switch the inlet and outlet fluids, and high operation continuity. Patent CN109487081B addresses the electrode morphology and operation mode and discloses a lithium extraction unit and an extended device using a flow electrode and a continuous operation method. This method solves the problems of cumbersome operation of switching electrodes or fluids during the regeneration process using fixed electrodes and uneven mass transfer and electric field distribution during the large-scale amplification process. It uses standard-size modules and can be flexibly scaled up by simply extending the number of standard modules without magnification effects.

[0004] The above solutions have been designed and optimized from the perspectives of element doping, structure, morphology of the lithium extraction electrode material, operation mode, etc. The electric field control all adopts a simple constant current or constant voltage mode. In the face of a system with a low lithium-sodium ratio, it is difficult to overcome the low selectivity of lithium ion intercalation caused by high-concentration sodium ions. The existing electrochemical lithium extraction process is relatively late in the whole process of extracting lithium from brine. Before this, steps such as sodium evaporation, potassium evaporation and lithium enrichment are required, and there is a large loss of lithium in these steps, resulting in a low overall lithium recovery rate. Therefore, advancing the lithium extraction process will be beneficial to the efficient utilization of lithium resources in salt lakes. However, the Li / Na concentration ratio of the original brine in salt lakes faced by advancing the lithium extraction process is between 0.0016 and 0.06. The Li / Na concentration ratio in seawater is even between 1.69×10 -5 to 5.3×10-5 Therefore, for the direct electrochemical lithium extraction process from seawater and the original brine of salt lakes, there is a problem of lithium-sodium selectivity. Because when the Li / Na ratio is low to a certain extent, thermodynamically, it is more favorable for sodium to be inserted into the cathode material rather than for low-concentration lithium to be inserted. Therefore, in a solution with a low Li / Na ratio, the defects of high energy consumption and low selectivity in lithium extraction limit the application of the electrochemical lithium extraction field to a certain extent. Summary of the Invention

[0005] The object of the present invention is to address the problems of high energy consumption, low selectivity, and low recovery rate in lithium extraction in the current electrochemical brine lithium extraction technology when facing a low Li / Na concentration ratio system, such as seawater and the original brine of salt lakes. From the perspective of optimizing the insertion / extraction kinetics, a control method and combination optimization of pulsed electric fields are proposed to enhance the insertion kinetics advantage of lithium ions relative to sodium ions and improve the selectivity of lithium extraction. At the same time, the diffusion efficiency of lithium ions in the electrode bulk phase is increased, the lithium insertion sites are fully utilized, and the lithium extraction capacity is increased.

[0006] The technical solution for achieving the object of the present invention is as follows:

[0007] An electrochemical lithium extraction method, in which a pulsed electric field control is applied to the lithium-containing raw liquid for a certain period of time. Compared with constant current, it can effectively optimize the distribution of lithium ions in the electrode space scale and the time scale during the lithium extraction process, fully utilize more lithium insertion sites, reduce the concentration polarization effect, and increase the insertion and diffusion kinetics advantage of lithium ions over sodium ions.

[0008] The pulsed control includes but is not limited to the following modes:

[0009] The first type: only a positive pulse is applied for 1 - 50 s. Preferably 10 - 30 s.

[0010] The second type: positive pulse + rest, the positive pulse time is 1 - 50 s, and the rest time is 1 - 20 s. Preferably, the positive pulse time is 10 - 30 s, and the rest time is 2 - 10 s.

[0011] Further preferably, the positive pulse and rest periods are 10 s and 2 s (P10r2); the positive pulse and rest periods are 12 s and 2 s (P12r2); the positive pulse and rest periods are 10 s and 10 s (P10r10);

[0012] The third type: positive pulse + rest + negative pulse, the positive pulse time is 1 - 50 s, the rest time is 1 - 20 s, and the negative pulse time is 1 - 15 s. Preferably, the positive pulse time is 10 - 30 s, the rest time is 2 - 10 s, and the negative pulse time is 1 - 5 s.

[0013] Fourth, positive pulse + rest + negative pulse + rest, the positive pulse time is 1 to 40 s, the rest time is 1 to 20 s, the negative pulse time is 1 to 15 s, and the rest time is 1 to 20 s. Preferably, the positive pulse time is 5 to 15 s, the rest time is 1 to 10 s, the negative pulse time is 2 to 25 s, and the rest time is 2 to 15 s.

[0014] Further preferably, the positive pulse and rest periods are 12 s and 2 s respectively, and the negative pulse and rest periods with the same amplitude are both 2 s (P12r2R2); the positive pulse and rest periods are 10 s and 2 s respectively, and the negative pulse and rest periods with the same amplitude are both 5 s (P10r2R5); the positive pulse and rest periods are both 10 s, and the negative pulse and rest periods with the same amplitude are both 10 s (P10r10R10).

[0015] It also includes other electric field combination modes that are easily conceivable by practitioners in any other professional field according to this solution and are controlled by current and voltage with different time allocation combinations.

[0016] Further, the intercalation / deintercalation lithium active material can be LiMn2O4 (LMO) or LiFePO4 LFP or LiFePO4 / MXene or LiNi 0.6 Co 0.2 Mn 0.2 O2 / MXene or LiMn2O4 / MXene or LiFePO4 / rGO or LiFePO4 / carbon nanotubes or lithium iron manganese phosphate LMFP or any other material that can be used as an intercalation lithium material or an intercalation lithium composite material.

[0017] Further, the negative electrode is activated carbon, a silver sheet, a bismuth sheet or the deintercalated state corresponding to the above intercalation / deintercalation lithium active material.

[0018] Further, the lithium-containing raw material liquid includes lithium-containing solution systems such as seawater, salt lake raw brine, oilfield brine, and underground brine.

[0019] An implementation manner of the method of the present invention includes the following steps:

[0020] (1) Apply a positive pulse electric field control for a certain time to the two-electrode system composed of the intercalation / deintercalation lithium active material / / AC in the lithium-containing raw material liquid. Due to the electric field effect, the ions in the solution move in opposite directions, the lithium ions move to the positive electrode and are embedded in the lattice of the positive electrode active electrode material, and the chloride ions move to the negative electrode direction and are adsorbed on the negative electrode. Or in the two-electrode system composed of the intercalation lithium active material / / deintercalated lithium active material, the two electrodes are respectively placed in the recovery liquid and the lithium-containing raw material liquid, and a pulse electric field control is applied for a certain time. The lithium ions in the lithium-containing raw material liquid move to the deintercalated electrode and are embedded, and the lithium ions in the intercalated lithium electrode are deintercalated and move to the recovery liquid.

[0021] (2) Implement an electric field rest for a certain period of time on the system. Inserting a short rest time during the lithium intercalation process can provide more time for the lithium ions aggregated on the electrode surface to further diffuse into the bulk phase, ensuring a more uniform distribution of lithium ions within the electrode. Therefore, it can improve the utilization rate of lithium intercalation sites of the active material; meanwhile, effectively reduce the lithium intercalation resistance on the electrode surface.

[0022] (3) Apply a reverse pulse electric field control on the system for a certain period of time. Due to the action of the reverse electric field, the ions in the solution move in the opposite direction, which is beneficial to eliminating the concentration polarization caused by the slow diffusion rate. At the same time, the reverse pulse can help sodium to be removed from the electrode, which is beneficial to increasing the proportion of lithium ions embedded in the bulk phase of the electrode, thereby enhancing the structural stability and lithium ion selectivity of the electrode material.

[0023] (4) Implement an electric field rest for a certain period of time on the system. The rest after the reverse pulse provides time for the sodium ions ejected from the electrode interface to diffuse into the solution, increasing the apparent lithium ion concentration at the electrode interface during the next positive pulse lithium intercalation process, which is beneficial to improving the lithium intercalation selectivity.

[0024] (5) After lithium extraction under the combined electric field of pulse - rest - reverse pulse - rest, drain the lithium - deficient lithium - containing raw material liquid after lithium extraction, and collect it for waiting to be discharged or recycled for reuse. Switch the fluid source to deionized water, input it into the electrolytic cell to wash the electrode assembly, and then drain the washing liquid.

[0025] (6) For the lithium - intercalated active material / / negative electrode system, after lithium extraction, switch the fluid to the recycled liquid for de - lithiumation. The positive and negative poles of the power supply connected to the two electrodes are interchanged. During the de - lithiumation stage, a pulse combined electric field is applied to the system, and lithium ions and chloride ions are released from the electrode and move towards the recycled liquid under the control of the pulse electric field.

[0026] Or, for the lithium - intercalated active material / / de - lithiumated active material system, after lithium extraction, its lithium - intercalated and de - lithiumated states and their positions in the recycled liquid and lithium - containing raw material liquid are interchanged, and the positive and negative poles of the power supply connected to the two electrodes are also interchanged. Apply a pulse combined electric field, and the lithium ions in the lithium - intercalated state are released into the recycled liquid to further enrich lithium ions. The lithium ions in the lithium - containing raw material liquid diffuse and are intercalated into the de - lithiumated state, and are further extracted.

[0027] (7) Implement an electric field rest for a certain period of time on the system. Inserting a short rest time during the de - lithiumation process can effectively reduce the rapid collapse of the volume of the active material during the process of the electrode ejecting ions, thereby reducing the local pressure of the electrode.

[0028] (8) Apply a reverse pulse electric field control on the system for a certain period of time. The addition of the reverse pulse provides a more uniform concentration for the ion diffusion during the de - lithiumation process of the system, effectively eliminating the concentration polarization.

[0029] (9) Apply an electric field rest to the system for a certain period of time. During this period without electric field control, all lithium and sodium particles in the electrode redistribute within the electrode lattice, improving the structural stability of the active material.

[0030] (10) Under the control of a pulse-rest-reverse pulse-rest combined electric field, lithium ions are enriched in the recycling solution.

[0031] (11) Repeat the operations of the above steps (1 - 10). During the process, the raw material solution and the recycling solution introduced can be recycled, or they can be mixed with fresh lithium-containing raw material solution and then enter the lithium extraction system. The lithium ion concentration in the recycling solution increases gradually with the number of cycles. This continues until the lithium ion concentration in the original brine drops to a certain value, or until it reaches a steady state after mixing with fresh original brine (judged comprehensively considering factors such as energy consumption, operation, and economy).

[0032] Advantages and beneficial effects of the present invention:

[0033] The lithium extraction electrochemical system of the present invention has obvious advantages in lithium extraction cycle stability, long-term selectivity, and low unit lithium extraction energy consumption under the optimal process parameters of the pulse-reverse pulse electric field mode. Pulse charging including the stop time and discharge time is beneficial to eliminating concentration polarization caused by slow diffusion speed, reducing the charging time, improving the utilization rate of the active material, and obtaining a longer cycle life. The same strategy is expected to enhance the diffusion kinetic advantage of lithium ions relative to sodium ions and the actual utilization rate of active sites during the lithium extraction process, thereby enhancing ion selectivity, actual lithium extraction capacity, and cycle stability. After optimizing the electric field combination, the energy utilization rate in real Atacama brine can be as low as 2.2 Wh / mol Li. After 15 cycles, the purity retention rate of lithium ions in the receiving solution is as high as 96.55%, and the lithium-sodium separation coefficient can reach 1020, realizing the efficient separation of lithium resources. Its high selectivity for lithium ions in low lithium-sodium ratio solutions provides feasibility for directly extracting lithium from seawater; it provides the possibility for pre-positioning the lithium extraction process from salt lake brine, and is expected to greatly reduce the lithium loss rate in the lithium extraction process from salt lake brine. Description of the Drawings

[0034] Figure 1 XRD pattern of the MXene composite LMO electrode material prepared in Example 1.

[0035] Figure 2 Microscopic morphologies of LMO and LMO / MXene prepared in Example 1, where a is LMO and b is LMO / MXene.

[0036] Figure 3 Potential / current vs. time curve under a constant current CC electric field.

[0037] Figure 4 Potential / current vs. time curve under a P10r2 electric field.

[0038] Figure 5 Potential / current vs. time curve under the P10r10 electric field.

[0039] Figure 6 Potential / current vs. time curve under the P12r2R2 electric field.

[0040] Figure 7 Cyclic voltammetry test chart of MXene / LMO in simulated lithium-containing brine and simulated lithium-free brine. Detailed implementation mode

[0041] Example 1:

[0042] An electrochemical lithium extraction method, with the set electrochemical parameters being that both the positive pulse and the rest period are 10 s (P10r10). Using Atacama simulated brine (21.6 mM Li + , 39.5 mM Mg 2+ , 330.06 mM Na + , 47.3 mM K + and 0.8 mM Ca 2+ ) as the feed liquid, 10 mM LiCl solution as the recovery liquid, using LMO / MXene as the lithium insertion / extraction cathode material, and activated carbon as the counter electrode, performing cyclic lithium extraction for 15 cycles, obtaining a lithium extraction purity of 0.94 and a unit energy consumption of 2.79 Wh / mol.

[0043] The preparation method of LMO / MXene is as follows: including the following steps:

[0044] Step 1: LiMn2O4 (LMO) was synthesized by solid-state reaction. Li2CO3 and MnO2 were mixed according to the molar ratio of Li to Mn of 1 / 1, heated in a muffle furnace at 550 °C with a heating rate of 5 °C / min for 6 h and then cooled to room temperature to obtain LMO.

[0045] Step 2: Ti3C2-MXene was synthesized by solvothermal method. LiF and hydrochloric acid with a concentration of 12 mol / L were mixed evenly in a molar ratio of 1 / 1, and then Ti3AlC2 was added in portions slowly with stirring. Subsequently, it was stirred at a constant temperature of 40 °C for 24 hours. The reaction product was added with deionized water and centrifuged at 3500 rpm for 10 min until the pH of the supernatant was 6 / 7. The solid at the bottom of the centrifuge tube was collected, dissolved in deionized water, and ultrasonically treated for 2 hours under the conditions of an argon atmosphere and an ice bath. Finally, the upper dark green liquid was collected by centrifugation and freeze-dried, and the obtained product was Ti3C2-MXene.

[0046] Step 3: Prepare the LMO / MXene composite material through an electrostatic self-assembly process. Add LMO particles to an aqueous solution (1.2 mg / mL) of CTAB in a glass bottle and stir continuously for 30 min. Then, drop the above solution into a beaker containing a layered Ti3C2-MXene suspension and continue stirring for 30 minutes. Subsequently, wash with deionized water until the residual CTAB is removed, and dry in vacuum at 70 °C to obtain the LMO / MXene composite material.

[0047] Table 1 shows the lithium extraction purity and energy consumption of LMO / MXene, LMO, LiFePO4 / MXene, LiFePO4, LiNi 0.6 Co 0.2 Mn 0.2 O2 electrode materials in Atacama simulated brine (21.6 mM Li + , 39.5 mM Mg 2+ , 33.06 mM Na + , 47.3 mM K + and 0.8 mM Ca 2+ ).

[0048] Table 1

[0049]

[0050] Example 2:

[0051] The difference from Example 1 is that the electrochemical parameters are set on the electrochemical workstation as a forward pulse and a stationary period of 10 s and 2 s (P10r2) respectively, and lithium extraction is cycled 15 times to obtain a lithium extraction purity of 0.903 and a unit energy consumption of 3.378 Wh / mol.

[0052] Example 3:

[0053] The difference from Example 1 is that the electrochemical parameters are set on the electrochemical workstation as a forward pulse and a rest period of 12 s and 2 s respectively, and a co-amplitude reverse pulse and a rest period of 2 s (P12r2R2), and lithium extraction is cycled 15 times to obtain a lithium extraction purity of 0.972 and a unit energy consumption of 2.159 Wh / mol

[0054] Example 4:

[0055] The difference from Example 3 is that the positive electrode material is LMO. The obtained lithium extraction purity is 0.921 and the unit energy consumption is 2.972 Wh / mol.

[0056] Example 5:

[0057] The difference from Example 3 is that the positive electrode material is LiFePO4 / MXene material, the lithium extraction purity is 0.932, and the unit energy consumption is 2.921Wh / mol.

[0058] The preparation method of LiFePO4 / MXene composite material comprises the following steps:

[0059] Step 1: LiFePO4 is synthesized using a high-temperature solid-phase method. Ferrous oxalate (FeC2O4), diammonium hydrogen phosphate ((NH4)2HPO4), and lithium carbonate (Li2CO) are mixed thoroughly in a stoichiometric ratio, pre-decomposed at a relatively low temperature in an inert atmosphere, and then calcined at a high temperature and ground into powder.

[0060] Step 2: Ti3C2-MXene was synthesized using a solvothermal method. LiF and 12 mol / L hydrochloric acid were mixed in a 1 / 1 molar ratio. Ti3AlC2 was then slowly added in portions while stirring. The mixture was then stirred at a constant temperature of 40°C for 24 hours. The reaction product was added to deionized water and centrifuged at 3500 rpm for 10 minutes until the supernatant reached a pH of 6 / 7. The solid at the bottom of the centrifuge tube was collected and dissolved in deionized water. The mixture was sonicated for 2 hours under an argon atmosphere in an ice bath. Finally, the dark green liquid above was collected by centrifugation and freeze-dried to obtain Ti3C2-MXene.

[0061] Step 3: Prepare the LiFePO4 / MXene composite material through an electrostatic self-assembly process. LiFePO4 particles were added to a glass bottle containing a CTAB aqueous solution (1.2 mg / mL) under continuous stirring for 30 minutes. The above solution was then added dropwise to the layered Ti3C2-MXene suspension in a beaker and stirred for 30 minutes. Subsequently, the particles were washed with deionized water to remove the residual CTAB and dried in a vacuum at 70°C to obtain the LiFePO4 / MXene composite material.

[0062] Example 6:

[0063] The difference from Example 5 is that the positive electrode material is LiFePO4, the extracted lithium purity is 0.911, and the specific energy consumption is 3.022Wh / mol.

[0064] Example 7:

[0065] The difference from Example 6 is that the positive electrode material is LiNi 0.6 Co 0.2 Mn 0.2 O2 material, the lithium extraction purity was 0.952, and the unit energy consumption was 2.443Wh / mol.

[0066] LiNi 0.6 Co0.2 Mn 0.2 The preparation method of O2 material is as follows:

[0067] Solvothermal synthesis of LiNi 0.6 Co 0.2 Mn 0.2 O2: According to the ratio of Ni:Co:Mn=6:2:2, a certain amount of Ni(CH3COO)2·4H2O, Co(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O were weighed and dissolved, and an appropriate amount of NaOH was weighed and dissolved as a precipitant. Concentrated NH3·H2O was diluted to a certain concentration as a complexing agent, and the metal cation solution was continuously pumped in at a certain rate. After the reaction was complete, the precursor product was filtered, washed, and dried to obtain the precursor product. The precursor product was mixed evenly with LiOH·H2O in a ratio of 1:2 and then transferred to a muffle furnace, heated to 750℃ and calcined for 12h to obtain LiNi 0.6 Co 0.2 Mn 0.2 O2.

[0068] Comparative Example 1:

[0069] The difference from Example 4 is that the electric field mode of the electrochemical workstation is set to constant current (CC), the lithium extraction purity is 0.845, and the unit energy consumption is 4.971Wh / mol.

[0070] Comparative Example 2:

[0071] The difference from Example 1 is that the electric field mode of the electrochemical workstation is set to constant current (CC), the lithium extraction purity is 0.881, and the unit energy consumption is 4.410Wh / mol.

[0072] Comparative Example 3:

[0073] The difference from Example 6 is that the electric field mode of the electrochemical workstation is set to constant current (CC), and the lithium extraction cycle is performed for 15 cycles, resulting in a lithium extraction purity of 0.853 and a unit energy consumption of 5.124 Wh / mol.

[0074] Table 2 shows the LMO / MXene electrode materials prepared in Example 1, the P12r2R2 electric field mode, and the results of the experiments in Atacama simulated brine (21.6 mM Li + , 39.5 mM Mg 2+ , 330.6mM Na + , 47.3 mM K + and 0.8 mM Ca 2+ ) The purity and energy consumption of lithium extraction are analyzed after 15 cycles.

[0075] Table 2

[0076] Number of turns 1st 5th 10th 15th Purity 0.972 0.963 0.954 0.938 Energy consumption (Wh / mol) 2.2 4.5 5.8 8.7

[0077] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for electrochemically extracting lithium in a low Li / Na concentration ratio system, characterized in that, The specific steps are as follows: (1) Apply a positive pulse electric field control to the two - electrode system composed of the intercalation - deintercalation lithium - active material / / AC in the lithium - containing raw liquid for a certain period of time. Due to the electric field effect, the ions in the solution move in the opposite direction. Lithium ions move towards the positive electrode and intercalate into the lattice of the positive - electrode active material, and chloride ions move towards the negative electrode and adsorb onto the negative electrode; or in the two - electrode system composed of the lithium - intercalated active material / / lithium - deintercalated active material, the two electrodes are respectively placed in the recovery liquid and the lithium - containing raw liquid, and a pulse electric field control is applied for a certain period of time. Lithium ions in the lithium - containing raw liquid move towards the lithium - deintercalated electrode and intercalate, and lithium ions in the lithium - intercalated electrode are deintercalated and move into the recovery liquid; (2) Apply an electric - field rest to the system for a certain period of time. Inserting a short rest time during the lithium - intercalation process provides more time for the lithium ions aggregated on the electrode surface to further diffuse into the bulk phase, ensuring a more uniform distribution of lithium ions in the electrode, improving the utilization rate of the lithium - intercalation sites of the active material, and effectively reducing the lithium - intercalation resistance on the electrode surface; (3) Apply a reverse - pulse electric field control to the system for a certain period of time. Due to the reverse - electric - field effect, the ions in the solution move in the opposite direction, which is beneficial to eliminating the concentration polarization caused by the slow diffusion rate. At the same time, the reverse pulse helps sodium to be removed from the electrode, which is beneficial to increasing the proportion of lithium ions intercalated in the electrode bulk phase, and then enhancing the structural stability and lithium - ion selectivity of the electrode material; (4) Apply an electric - field rest to the system for a certain period of time. The rest after the reverse pulse provides time for the sodium ions deintercalated from the electrode interface to diffuse into the solution, increasing the apparent lithium - ion concentration at the electrode interface during the next positive - pulse lithium - intercalation process, which is beneficial to improving the lithium - intercalation selectivity; (5) After lithium extraction under the combined electric field of pulse - rest - reverse - pulse - rest, discharge the lithium - deficient lithium - containing raw liquid after lithium extraction, collect it for waiting to be discharged or recycled for reuse; switch the fluid source to deionized water, input it into the electrolytic cell to wash the electrode assembly, and then discharge the washing liquid; (6) For the lithium - intercalated active material / / negative - electrode system, after lithium extraction, switch the fluid to the recovery liquid for deintercalation. The positive and negative poles of the power supply connected to the two electrodes are interchanged. During the deintercalation stage, a pulse - combined electric field is applied to the system. Lithium ions and chloride ions are released from the electrodes under the control of the pulse electric field and move towards the recovery liquid; Or, for the lithium - intercalated active material / / lithium - deintercalated active material system, after lithium extraction, the intercalation - deintercalation state and its positions in the recovery liquid and the lithium - containing raw liquid are interchanged, and the positive and negative poles of the power supply connected to the two electrodes are also interchanged. Apply a pulse - combined electric field. Lithium ions in the lithium - intercalated state are released into the recovery liquid to further enrich lithium ions, and lithium ions in the lithium - containing raw liquid diffuse and intercalate into the lithium - deintercalated state, and are further extracted; (8) Apply an electric - field rest to the system for a certain period of time. Inserting a short rest time during the deintercalation process effectively reduces the rapid collapse of the volume of the active material during the ion - deintercalation process of the electrode, and then reduces the local pressure of the electrode; (9) Apply a reverse - pulse electric field control to the system for a certain period of time. The addition of the reverse pulse provides a more uniform concentration for the ion diffusion during the deintercalation process of the system, eliminating the concentration polarization; (9) Implement an electric field rest for a certain period of time on the system. During this period without electric field control, all lithium and sodium particles in the electrode redistribute within the electrode lattice, improving the structural stability of the active material; (10) Under the combined electric field control of pulse - rest - reverse pulse - rest, lithium ions are enriched in the recycling liquid; (11) Repeat the operations of the above steps (1 - 10). During the process, the raw material liquid and the recycling liquid introduced can be recycled, or they can be mixed with fresh lithium - containing raw material liquid and then enter the lithium extraction system. The lithium ion concentration in the recycling liquid increases successively with the number of cycles; until the lithium ion concentration in the original brine is reduced to a certain value, or until it reaches a steady state after mixing with fresh original brine; The insertion / extraction lithium active material is one or more of LiMn2O4, LiFePO4, LiFePO4 / MXene, LiNi 0.6 Co 0.2 Mn 0.2 O2 / MXene, LiMn2O4 / MXene, LiFePO4 / rGO, LiFePO4 / carbon nanotubes, lithium iron manganese phosphate; the negative electrode is activated carbon, silver sheet, bismuth sheet or the de-lithiated state corresponding to the above insertion / extraction lithium active material.

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