A Janus membrane electrode, construction method, continuous electrochemical lithium extraction system and method

Abstract

The present application relates to the technical field of electrolysis, in particular to a Janus membrane electrode, a construction method, a continuous electrochemical lithium extraction system and method. The Janus membrane electrode comprises a current collector, an active layer arranged on the surface of the current collector, a first functional interface layer arranged on the surface of one side of the active layer, and a second functional interface layer arranged on the surface of the other side of the active layer; the first functional interface layer can realize reversible insertion of metal ions, and the second functional interface layer can realize stripping of metal ions. The present application further provides a construction method of the Janus membrane electrode, a continuous electrochemical lithium extraction system and method. The present application solves the problems of insufficient mechanical stability of the membrane electrode and uncontrollable ion transport path in the electrochemical ion pump lithium extraction technology.

Description

Technical Field

[0001] This invention relates to the field of electrolysis technology, specifically to a Janus membrane electrode, its construction method, and a continuous electrochemical lithium extraction system and method. Background Technology

[0002] With the rapid development of industries such as new energy vehicles and energy storage batteries, the demand for lithium resources continues to grow. Salt lake brine, lithium-containing solutions generated during lithium resource development, and other lithium-containing resource liquids are gradually becoming important sources for lithium resource recycling due to their significant lithium recovery potential. However, in actual lithium resource development processes, lithium-containing solutions are usually accompanied by large amounts of magnesium ions (Mg). 2+ It also contains some sodium ions (Na) + ), potassium ions (K) + ), calcium ions (Ca 2+ ) and other coexisting ions, including Mg 2+ With Li + Having similar hydration properties and migration behavior, leading to Li + With Mg 2+ Selective separation between lithium and magnesium is quite challenging. Therefore, developing highly selective, low-energy-consumption, environmentally friendly, and continuously operating lithium-magnesium separation technologies is of great significance for improving the utilization efficiency of lithium resources.

[0003] Currently, methods for lithium resource recovery in lithium- and magnesium-containing systems mainly include precipitation, solvent extraction, adsorption, and membrane separation. Precipitation typically requires the addition of large amounts of chemical reagents to achieve separation by forming lithium or magnesium salt precipitates; however, this method suffers from high reagent consumption, complex processes, and byproduct generation. Solvent extraction utilizes organic extractants to selectively extract lithium ions, but it suffers from high organic solvent consumption, demanding equipment requirements, and significant environmental impact. Adsorption utilizes lithium-ion sieve materials to target lithium ions... + Selective adsorption offers good selectivity, but it is typically limited by factors such as limited adsorption capacity, complex regeneration processes, and insufficient continuous operation capability. Therefore, there is still a need to develop more efficient and energy-saving lithium-magnesium separation technologies.

[0004] In recent years, electrochemical lithium extraction technologies based on lithium-ion intercalation / deintercalation reactions have attracted widespread attention. This type of technology utilizes lithium-ion sieve electrode materials to extract lithium... + The reversible insertion and extraction properties of Li can be used to realize Li under an applied electric field. + Selective enrichment and release. Compared with traditional chemical separation methods, electrochemical lithium extraction technology has advantages such as simple process, low chemical reagent consumption, easy automation control, and environmental friendliness, and has good application prospects in the field of lithium resource recovery.

[0005] Currently, electrochemical lithium extraction technology mainly includes two technical routes. One route uses a continuous flow electrochemical system, which combines lithium-ion intercalation electrodes with capacitive electrodes to cycle between lithium-containing solutions and recovery solutions, thereby achieving lithium-ion enrichment and recovery. The other route uses a dual lithium-ion electrode alternating operation method, which changes the electrode operating state so that the electrodes respectively undertake the functions of lithium adsorption and lithium desorption, thereby achieving a continuous lithium extraction process.

[0006] However, existing electrochemical lithium extraction technologies still have the following shortcomings: (1) In existing continuous flow electrochemical systems, the working electrode needs to withstand the Li for a long time. + The insertion and extraction processes can easily lead to concentration polarization and accumulation of ion transport resistance during continuous operation, affecting lithium-ion transport efficiency and long-term operational stability. (2) The dual lithium-ion electrode alternating working system requires two working electrodes with lithium-ion storage capacity, and the lithium absorption and delithiation processes are controlled by complex circuits, resulting in a complex device structure and cumbersome control process, which is not conducive to equipment integration. (3) Existing lithium-ion sieve electrodes are usually prepared using ordinary coating methods. These electrodes have many open pores, which can easily lead to non-selective ion migration and solution permeation during long-term operation, reducing the efficiency of Li-ion sieves. + / Mg 2+ Separation performance; (4) Existing electrochemical lithium extraction systems mainly focus on the lithium-ion intercalation performance of the electrode material itself, but lack effective control over the ion transport behavior at the interface between the two sides of the electrode, making it difficult to achieve high-selectivity lithium-ion migration, low ion leakage and long-term stable operation at the same time.

[0007] Therefore, for Li in magnesium- and lithium-containing systems + With Mg 2+ Problems such as difficulty in selective separation, uncontrollable electrode interface transport behavior, and insufficient stability during continuous operation still necessitate the development of a novel electrochemical lithium extraction method and system with asymmetric interface control capabilities, high selective lithium-ion transport capabilities, and continuous operation performance. Summary of the Invention

[0008] In view of this, one objective of the present invention is to provide a Janus membrane electrode and its construction method to solve the problems of insufficient mechanical stability of membrane electrodes and uncontrollable ion transport paths in existing electrochemical ion pump lithium extraction technology. Another objective of the present invention is to provide a continuous electrochemical lithium extraction system and method to solve the problems of frequent switching or replacement of working electrodes, poor system stability during continuous operation, and limited lithium-magnesium separation efficiency in existing electrochemical ion pump lithium extraction technology.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A Janus membrane electrode includes a current collector, an active layer disposed on both sides of the current collector, a first functional interface layer disposed on the surface of one side of the active layer, and a second functional interface layer disposed on the surface of the other side of the active layer. The first functional interface layer enables the reversible insertion of metal ions, and the second functional interface layer enables the extraction of metal ions.

[0010] By employing an integrated structure of "current collector - double-sided active layer - asymmetric functional interface," the problems of mechanical stability and ion transport controllability are simultaneously solved: Mechanically, the current collector acts as a rigid framework supporting the double-sided active layer and the interface layer, dispersing the volume expansion / contraction stress during ion pump operation to the symmetric structure, preventing detachment or cracking of the single-sided interface layer, and significantly improving cycle stability; In terms of ion transport, the first functional interface layer only allows metal ions (such as Li) to pass through. + The second functional interface layer specifically promotes the extraction (de-extraction) of metal ions. Utilizing the Janus asymmetric chemical potential gradient, ions migrate across the membrane along a directional path: "first interface → active layer → current collector → other active layer → second interface." This avoids the increased energy consumption and decreased separation efficiency caused by random ion diffusion or backmixing in traditional membranes, thus achieving a low-resistance, highly selective, and controllable ion pumping process. This effectively solves the problems of insufficient membrane electrode mechanical stability and uncontrollable ion transport paths in existing electrochemical ion pump lithium extraction technologies.

[0011] Preferably, the material of the first functional interface layer is selected from polyethyleneimine (PEI); The material of the second functional interface layer is selected from sodium dodecyl sulfate (SDS); The material of the current collector is selected from at least one of titanium mesh, nickel mesh, and stainless steel mesh; The active layer is made of electrode active materials with reversible lithium insertion and delithiation capabilities, conductive agents, and binders.

[0012] The current collector is a conductive current collector used to support the active layer and collect electrons.

[0013] Preferably, the electrode active material is selected from one or two of lithium manganese oxide (LMO) and aluminum-fluorine co-doped lithium manganese oxide (LMO-Al-F); The conductive agent is selected from conductive carbon black; Preferably, the conductive carbon black is selected from one or both of acetylene black and Super P (superconducting carbon black).

[0014] Preferably, the conductive agent may also be selected from at least one of carbon microspheres, mesoporous carbon, and activated carbon.

[0015] The adhesive is selected from polyvinylidene fluoride (PVDF). The binder is used to achieve bonding between electrode particles and between the electrode and the conductive current collector, thereby improving the overall structural stability of the membrane electrode.

[0016] The mass ratio of the electrode active material, conductive agent, and binder is 8:1:1; The thickness of the active layer is 50~300μm; The thickness of the current collector is 10~200μm; The thickness of the first functional interface layer is 30~40μm; The thickness of the second functional interface layer is 15~25μm.

[0017] The wet film thickness of the active layer on one side is 100~300μm, and after drying and hot pressing, the thickness of the active layer on one side is 50~150μm.

[0018] Preferably, after drying and hot pressing, the thickness of the active layer on one side is 100 μm, the thickness of the current collector is 200 μm, the thickness of the first functional interface layer is 35 μm, and the thickness of the second functional interface layer is 20 μm.

[0019] The present invention also provides a method for constructing a Janus membrane electrode, comprising the following steps: The active layer materials are mixed and then an organic solvent is added to prepare an active layer slurry; The active layer slurry is coated onto the two surfaces of the current collector, and then hot-pressed to obtain the initial membrane electrode. One side of the active layer surface of the initial membrane electrode is immersed in a polyethyleneimine (PEI) solution to construct a first functional interface layer, and the other side of the active layer surface is immersed in a sodium dodecyl sulfate (SDS) solution to construct a second functional interface layer, thus obtaining the Janus membrane electrode.

[0020] Preferably, the polyethyleneimine solution is an aqueous solution of polyethyleneimine; the sodium dodecyl sulfate solution is an aqueous solution of sodium dodecyl sulfate.

[0021] Preferably, the hot pressing temperature is 110~150℃, the hot pressing pressure is 5~20MPa, and the hot pressing time is 1~20min; Preferably, the hot pressing temperature is 130°C, the hot pressing pressure is 10 MPa, and the hot pressing time is 5 min.

[0022] Preferably, the polyethyleneimine solution contains 1% polyethyleneimine by mass. The sodium dodecyl sulfate solution contains 0.5% sodium dodecyl sulfate by mass.

[0023] The present invention also provides a continuous electrochemical lithium extraction system, comprising a first terminal electrode, a first electrolyte flow chamber, a first anion exchange membrane, a raw solution flow chamber, the Janus membrane electrode described in the present invention, a lithium adsorption solution flow chamber, a second anion exchange membrane, a second electrolyte flow chamber, and a second terminal electrode arranged in sequence. The first functional interface layer of the Janus membrane electrode is located on one side of the original liquid flow chamber, and the second functional interface layer is located on one side of the lithium adsorption liquid flow chamber. By adding electrolyte to the first electrolyte flow chamber, lithium-containing stock solution to the stock solution flow chamber, and lithium-ion receiving solution to the lithium absorption solution flow chamber, and using the first terminal electrode as the anode and the Janus membrane electrode as the cathode, lithium ions in the lithium-containing stock solution migrate to the Janus membrane electrode, achieving lithium ion intercalation. Then, by adding electrolyte to the second electrolyte flow chamber, and using the Janus membrane electrode as the anode and the second terminal electrode as the cathode, lithium ions intercalated in the Janus membrane electrode migrate to the lithium-ion receiving solution, achieving lithium ion deintercalation, thereby extracting lithium from the lithium-containing stock solution.

[0024] Preferably, the first electrolyte flow chamber and the second electrolyte flow chamber are connected through a first electrolyte flow channel, and the first electrolyte flow chamber and the second electrolyte flow chamber are connected to an electrolyte storage tank through a second electrolyte flow channel, so that the electrolyte circulates between the first electrolyte flow chamber, the second electrolyte flow chamber and the electrolyte storage tank. During the electrochemical lithium extraction process, the first terminal electrode and the second terminal electrode continuously undergo electrochemical reactions in the electrolyte, providing electron transfer for the system and maintaining the overall charge balance. The raw liquid flow chamber is connected to the raw liquid storage tank through the raw liquid flow channel, so that the lithium-containing raw liquid circulates between the raw liquid flow chamber and the raw liquid storage tank. The lithium-absorbing liquid flow chamber is connected to the lithium-absorbing liquid storage tank through the lithium-absorbing liquid flow channel, so that the lithium-ion receiving liquid circulates between the lithium-absorbing liquid flow chamber and the lithium-absorbing liquid storage tank.

[0025] The continuous electrochemical lithium extraction system of the present invention includes four fluid chambers with different functions (a first electrolyte flow chamber, a second electrolyte flow chamber, a raw liquid flow chamber, and a lithium absorption liquid flow chamber), each fluid chamber playing a different role during continuous operation.

[0026] The electrolyte in the first electrolyte flow chamber comes into contact with the first terminal electrode, and a terminal electrochemical reaction occurs during the adsorption stage, providing an electron transfer channel for the hot-pressed Janus membrane electrode and maintaining the system charge balance.

[0027] The feed solution flow chamber is located between the first anion exchange membrane and the hot-pressed Janus membrane electrode, and is used to continuously feed high magnesium-to-lithium ratio brine or other lithium-containing feed solutions to be treated. Lithium ions migrate from the feed solution side to the hot-pressed Janus membrane electrode under the drive of the electric field, and selectively insert into the active material lattice of the hot-pressed Janus membrane electrode; magnesium ions and other high-valence ions are difficult to enter the hot-pressed Janus membrane electrode due to the selectivity and interface regulation of the hot-pressed Janus membrane electrode, and are thus retained on the feed solution side.

[0028] The lithium absorption liquid flow chamber is located between the hot-pressed Janus membrane electrode and the second anion exchange membrane. It is used to continuously receive lithium ions released from the hot-pressed Janus membrane electrode and form a lithium-rich lithium ion receiving liquid output.

[0029] The electrolyte in the second electrolyte flow chamber comes into contact with the second terminal electrode, and a terminal electrochemical reaction occurs during the desorption stage. Together with the first electrolyte flow chamber, they form an electrolyte circulation system, which maintains the electronic and ion balance required for the continuous operation of the entire continuous electrochemical lithium extraction system through water decomposition reaction.

[0030] Therefore, the four chambers are not only used to isolate different liquids, but also to perform functions such as terminal electrochemical reaction, raw liquid treatment, lithium ion enrichment and electronic balance maintenance during continuous operation, and together they constitute a continuously operating four-functional chamber reaction system.

[0031] The first electrolyte flow chamber, the second electrolyte flow chamber, and the electrolyte storage tank constitute an electrolyte circulation system; the raw liquid flow chamber and the raw liquid storage tank constitute a raw liquid circulation system; and the lithium-absorbing liquid flow chamber and the lithium-absorbing liquid storage tank constitute a lithium-ion receiving liquid circulation system. The three circulation systems operate independently of each other, and the liquids do not mix. Ion migration and charge compensation are achieved only through membrane electrodes and anion exchange membranes.

[0032] The electrolyte circulation system is used to maintain the system's electron conservation, charge balance, and terminal ion (mainly sulfate ions) migration. Its electrolyte does not enter the original solution flow chamber or the lithium adsorption solution flow chamber, and does not participate in the lithium ion enrichment process.

[0033] Preferably, the electrolyte is selected from sodium sulfate solution, potassium sulfate solution, or other conductive electrolytes that do not participate in lithium ion intercalation / deintercalation reactions.

[0034] This invention also provides a continuous electrochemical lithium extraction method based on a continuous electrochemical lithium extraction system, comprising the following steps: Electrolyte is added to the first electrolyte flow chamber, lithium-containing stock solution is added to the stock solution flow chamber, and lithium-ion receiving solution is added to the lithium absorption solution flow chamber, so that the first terminal electrode is in contact with the electrolyte and the Janus membrane electrode is in contact with the lithium-containing stock solution. Using the first terminal electrode as the anode and the Janus membrane electrode as the cathode, an electric current is applied to the first terminal electrode and the Janus membrane electrode to form a first working circuit, which allows lithium ions in the lithium-containing raw solution to migrate to the Janus membrane electrode and realize the intercalation of lithium ions; that is, in the adsorption stage, the first terminal electrode participates in the electrochemical reaction of the terminal water (i.e., electrolyte) to provide an electron source for the hot-pressed Janus membrane electrode.

[0035] Electrolyte is added to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; The first working circuit is disconnected, and the Janus membrane electrode is used as the anode and the second terminal electrode as the cathode. The Janus membrane electrode and the second terminal electrode are energized to form a second working circuit, which allows the lithium ions embedded in the Janus membrane electrode to migrate to the lithium ion receiving liquid, thereby realizing the deintercalation of lithium ions and the extraction of lithium from the lithium-containing raw solution. That is, in the desorption stage, the second terminal electrode participates in the terminal hydrochemical reaction and forms a new closed circuit with the hot-pressed Janus membrane electrode.

[0036] The second working circuit is disconnected and the first working circuit is closed to achieve continuous electrochemical lithium extraction.

[0037] Preferably, the first working circuit and the second working circuit are not simultaneously conducting, and the control module controls the first working circuit and the second working circuit to conduct alternately according to a preset time program.

[0038] Preferably, the electrolyte comprises sodium sulfate solution and / or potassium sulfate solution; The lithium-containing stock solution is an aqueous solution containing lithium and magnesium, and the aqueous solution containing lithium and magnesium includes Li. + and Mg 2+ Li + The concentration is 10~1000 mg / L, Mg 2+ The concentration is 0.1~100g / L, Mg 2+ With Li + The mass concentration ratio is 1~100; The initial component of the lithium-ion receiving liquid is a sodium sulfate solution.

[0039] The operating current of the first and second working circuits is 1~2mA, and the upper limit of the operating voltage is 2V; The working time of the first working circuit is 10~120s, and the working time of the second working circuit is 5~60s.

[0040] Preferably, the working time of the first working circuit is 30s, and the working time of the second working circuit is 15s.

[0041] Preferably, the lithium and magnesium-containing aqueous solution contains Li + The concentration is 50~500 mg / L, Mg 2+ The concentration is 0.5~10 g / L, Mg 2+ With Li + The mass concentration ratio is 5~50; The aqueous solution containing lithium and magnesium also includes Na. + K + and Ca 2+ At least one cation in it; The aqueous solution containing lithium and magnesium also includes Cl. - and SO4 2- One or two anions in it.

[0042] Preferably, the sodium sulfate solution is an aqueous sodium sulfate solution, and the potassium sulfate solution is an aqueous potassium sulfate solution.

[0043] Preferably, the initial component of the lithium ion receiving liquid is an aqueous solution of sodium sulfate with a sodium sulfate concentration of 200 ppm.

[0044] The Janus membrane electrode is located at the center of the entire membrane stack structure, separating the lithium-containing feed solution from the lithium-ion receiving solution. The first terminal electrode is in contact with the electrolyte in the first electrolyte flow chamber, and the second terminal electrode is in contact with the electrolyte in the second electrolyte flow chamber. The first terminal electrode, the Janus membrane electrode, and the second terminal electrode are electrically connected to the control module.

[0045] Preferably, the control module includes a circuit switching unit, a timing control unit, and a DC power supply unit, wherein the circuit switching unit is used to control the switching between the first working circuit and the second working circuit, the timing control unit is used to control the working time of the first working circuit and the second working circuit, and the DC power supply unit is used to supply power to the first working circuit and the second working circuit.

[0046] The electrochemical lithium extraction system of this invention, used in an electrochemical lithium extraction method, allows for lithium ion adsorption and release under continuous flow conditions without the need for disassembly, switching, or movement of the working electrode between different workstations. Simultaneously, by optimizing the system structure, membrane electrode interface, and circuit control, the system improves the transmembrane migration efficiency of lithium ions, operational stability, and long-term continuous lithium extraction capability, meeting the practical application requirements for continuous lithium extraction from high magnesium-to-lithium ratio brines. This effectively solves the problems of existing electrochemical ion pump lithium extraction technologies, such as the need for frequent switching or replacement of the working electrode during continuous operation, poor system stability during continuous operation, and limited lithium-magnesium separation efficiency.

[0047] The working principle of the electrochemical lithium extraction system of the present invention for electrochemical lithium extraction method is as follows: 1) System operating principle The continuous electrochemical lithium extraction system of the present invention uses a hot-pressed Janus membrane electrode as the sole lithium-ion intercalation / deintercalation working electrode, and sets a raw solution flow chamber and a lithium absorption solution flow chamber on both sides of the electrode. Two terminal electrodes and two electrolyte flow chambers are set on the outside of the system. The raw solution system, electrolyte system and lithium-ion receiving solution system are isolated from each other by two anion exchange membranes.

[0048] The first electrolyte flow chamber and the second electrolyte flow chamber are connected through the first electrolyte flow channel to form an independent terminal electrolyte circulation loop. The original solution flow chamber and the lithium adsorption solution flow chamber each form an independent processing solution circulation loop. The liquids in each loop do not mix with each other. Ion migration is achieved only through the anion exchange membrane and the hot-pressed Janus membrane electrode, and electron transfer is achieved through external wires.

[0049] Throughout the system, the hot-pressed Janus film electrode is always installed in the center of the system and does not participate in position switching. It does not require multiple lithium-ion sieve working electrodes. Instead, by controlling the conduction state of the external circuit, the same working electrode alternately completes the insertion and extraction of lithium ions.

[0050] Compared with existing continuous lithium extraction systems that use multiple working electrodes in rotation, this invention concentrates the adsorption and desorption processes of lithium ions within the same hot-pressed film electrode, while the terminal electrode only serves to maintain the current loop and the terminal electrochemical reaction, thereby achieving functional separation between the working electrode and the terminal reaction unit.

[0051] 2) Adsorption operation process During the adsorption stage, the control module activates the first working circuit while simultaneously deactivating the second working circuit. At this time, the first terminal electrode and the hot-pressed Janus membrane electrode form a closed circuit. The hot-pressed Janus membrane electrode acts as the cathode, where a lithium-ion intercalation reaction occurs, and the first terminal electrode acts as the anode, where a terminal hydrochemical reaction occurs.

[0052] The lithium-containing feed solution continuously flows through the feed solution flow chamber. Under the influence of an electric field, lithium ions migrate to the surface of the hot-pressed Janus membrane electrode and further embed into the lattice of the lithium ion sieve active material. Magnesium ions and other high-valence ions, due to lattice size limitations, interfacial charge regulation, and differences in migration energy barriers, have difficulty entering the interior of the active material and therefore mainly remain in the lithium-containing feed solution and flow out with it. Simultaneously, a terminal water electrochemical reaction occurs in the first electrolyte flow chamber where the first terminal electrode is located, providing an electron source for the hot-pressed Janus membrane electrode. The second terminal electrode is in an open state and does not participate in the electrochemical reaction. Throughout the adsorption stage, the lithium-containing feed solution continues to flow, the lithium ion receiving solution continues to circulate, and the electrolyte continues to circulate; none of the liquid paths need to be stopped.

[0053] 3) Desorption process After the preset adsorption time is completed, the control module disconnects the first working circuit and connects the second working circuit. At this time, the hot-pressed Janus membrane electrode becomes the anode, and the second terminal electrode becomes the cathode. Lithium ions embedded in the lattice of the hot-pressed Janus membrane electrode are deintercalated under the action of the electric field and released into the lithium adsorption liquid flow chamber to form a lithium-rich lithium ion receiving liquid.

[0054] The second terminal electrode, located in the second electrolyte flow chamber, undergoes a terminal hydrochemical reaction, forming a new closed loop together with the hot-pressed Janus membrane electrode; the first terminal electrode remains disconnected and does not participate in the reaction. Because the lithium-containing feed solution, lithium-ion receiving solution, and electrolyte are continuously circulated, the adsorption, release, and enrichment of lithium ions can proceed continuously without stopping the supply, disassembling the membrane electrode, or switching the working electrode position.

[0055] 4) Continuous circulation mechanism The control module periodically switches between the first working circuit and the second working circuit according to a preset program.

[0056] Throughout the entire cycle: the hot-pressed Janus membrane electrode remains centrally mounted in the system; the feed solution circulation system continuously delivers the lithium-containing solution; the lithium-ion receiving solution circulation system continuously receives desorbed lithium ions; the electrolyte circulation system continuously maintains the electrochemical reaction and charge balance; the two terminal electrodes alternately participate in the terminal water electrochemical reaction; and the two working loops are never simultaneously activated. Through this coordinated operation, the hot-pressed Janus membrane electrode repeatedly performs lithium ion adsorption and desorption under continuous flow conditions, achieving continuous enrichment of lithium ions in high magnesium-to-lithium ratio solutions.

[0057] 5) Ion-isolated structure This invention uses two anion exchange membranes to divide the entire system into four independent liquid chambers. The first anion exchange membrane is positioned between the first electrolyte flow chamber and the feed solution flow chamber. The second anion exchange membrane is positioned between the lithium adsorbent flow chamber and the second electrolyte flow chamber. The two anion exchange membranes isolate the electrolyte circulation system from the processing solution circulation system, preventing electrolyte from entering the feed solution flow chamber and the lithium adsorbent flow chamber, while simultaneously ensuring charge balance and the establishment of ion migration pathways within the reaction system. In this invention, the main function of the two anion exchange membranes is to maintain liquid isolation and electrochemical balance between the different circulation systems, while the selective enrichment of lithium ions is primarily achieved by hot-pressing a Janus membrane electrode.

[0058] 6) Janus membrane electrode working mechanism The Janus membrane electrode comprises: a conductive current collector, a dense active layer, a first functional interface layer on the lithium-containing feed solution side, and a second functional interface layer on the lithium-adsorbing solution side. The first functional interface layer on the lithium-containing feed solution side has a first surface charge characteristic. The second functional interface layer on the lithium-adsorbing solution side has a second surface charge characteristic. The first surface charge characteristic and the second surface charge characteristic are different. Therefore, a directional interface environment is formed on both sides of the Janus membrane electrode.

[0059] During the adsorption stage, lithium ions in the lithium-containing feed solution first reach the first functional interface layer on the lithium-containing feed solution side, and then enter the dense active layer to complete the lithium intercalation process. During the desorption stage, lithium ions are released from the dense active layer and enter the lithium ion receiving solution via the second functional interface layer on the lithium adsorption side. Due to the different interface environments on both sides, the interfacial mass transfer resistance can be reduced, improving the continuous operation stability of the membrane electrode.

[0060] 7) System control methods The process includes: S1, starting three circulation systems: electrolyte system, raw solution system, and lithium ion receiving solution system; S2, the control module controls the first working circuit to be turned on, and the hot-pressed Janus membrane electrode completes lithium ion adsorption; S3, after reaching the preset time, the control module controls the first working circuit to be turned off and the second working circuit to be turned on, and the hot-pressed Janus membrane electrode completes lithium ion desorption; S4, repeating S2 and S3 to complete continuous lithium extraction.

[0061] 8) System collaborative operation mechanism The continuous electrochemical ion pump lithium extraction system of the present invention is composed of a working electrode unit (Janus membrane electrode), a terminal electrode unit (first terminal electrode and second terminal electrode), a membrane separation unit (first anion exchange membrane, second anion exchange membrane and Janus membrane electrode), a circulating supply unit (electrolyte circulation system, raw solution circulation system and lithium ion receiving solution circulation system) and a circuit control unit (control module).

[0062] In this system, the individual components do not function independently, but rather form a continuously operating overall reaction system through structural coupling and operational coordination. The hot-pressed Janus membrane electrode, as the only working electrode in the system responsible for the reversible lithium-ion insertion and extraction reaction, is responsible for the selective adsorption and release of lithium ions. The first and second terminal electrodes are respectively located at both ends of the reaction system, only responsible for the terminal electrochemical reaction and the establishment of electronic circuits, and do not perform lithium-ion insertion / extraction functions. The first and second electrolyte flow chambers form an independent electrolyte circulation system through the first electrolyte flow channel, used to maintain the terminal electrochemical reaction and the system's charge balance. The raw solution circulation system continuously delivers lithium-containing raw solution to the raw solution flow chamber. The lithium-ion receiving solution circulation system continuously delivers the desorbed solution and receives lithium ions released from the hot-pressed Janus membrane electrode. The control module alternately activates the first and second working circuits according to a preset program, enabling the hot-pressed Janus membrane electrode to complete the transition between the adsorption and desorption states while maintaining its spatial position. The above-mentioned components together constitute a continuous operating system, enabling lithium-ion migration, charge compensation, electron transfer and terminal electrochemical reactions to proceed simultaneously, thereby achieving continuous enrichment of lithium ions in lithium-containing solutions with a high magnesium-to-lithium ratio.

[0063] The beneficial effects of this invention are: The Janus membrane electrode of this invention integrates the "intercalation" and "extraction" functions of metal ions into independent interface layers on both sides of the current collector. The first and second functional interface layers respectively bear the "intercalation" and "extraction" strains, so that the compressive and tensile stresses generated by volume changes form mechanical symmetry compensation and physical isolation on both sides of the current collector, effectively suppressing the cracking and peeling of the active layer and significantly improving the structural robustness of long-term operation. At the ion transport level, the difference in chemical potential between the two interface layers for the "absorption" and "release" of metal ions forces the construction of a unique transmembrane directional driving force from the first interface layer through the active layer to the second interface layer, completely avoiding the bypass random migration caused by disordered convection or concentration gradients in the solution, making the ion transport path strictly perpendicular to the membrane surface and significantly shortening the solid-phase diffusion distance. This solves the problems of mechanical stability and transport controllability, fundamentally improving the cycle life and energy efficiency of the electrochemical lithium extraction system.

[0064] The continuous electrochemical lithium extraction system of this invention decouples lithium ion capture (in the original electrolyte flow chamber) and release (in the lithium adsorption liquid flow chamber) to both sides of the Janus membrane electrode. Utilizing continuous charge compensation from the terminal electrochemical reactions in the first and second electrolyte flow chambers, the system achieves continuous steady-state operation under a constant electric field, enabling simultaneous adsorption and desorption. This fundamentally eliminates the mechanical disturbances, voltage interruptions, and intermittent relaxation of active materials caused by frequent electrode switching or replacement, significantly enhancing the structural fatigue resistance and operational continuity during long-term operation. The independent and continuous flow of the feed solution and the lithium-ion receiving solution not only utilizes continuous liquid-phase mass transfer to promptly flush the interface, thereby weakening concentration polarization and maintaining a high driving force field across the membrane, but also creates a synergistic barrier effect with the Janus membrane electrode's interfacial size repulsion of high-valence ions and selective lattice insertion of lithium ions. This effectively prevents impurities such as magnesium ions from accumulating, penetrating, or competing for insertion on the membrane surface. Thus, while ensuring the directional and rapid migration of lithium ions into the lithium-ion receiving solution, it significantly improves the lithium-magnesium separation factor, providing a solid theoretical foundation for the transition of electrochemical lithium extraction from intermittent to industrial continuous production. It has significant application value in the field of electrolysis technology. Attached Figure Description

[0065] Figure 1 A flowchart illustrating the preparation method of aluminum-fluorine co-doped lithium manganese oxide; Figure 2 A flowchart illustrating the construction method of the Janus membrane electrode; Figure 3 Comparison of static water contact angle tests on the surface of Janus membrane electrodes before and after PEI modification; Figure 4 This is an infrared spectrum; Figure 5 This is a schematic diagram of a continuous electrochemical lithium extraction system; Figure 6 A schematic diagram of the circuit switching and ion migration mechanism of a three-electrode-four-chamber continuous electrochemical lithium extraction system; Figure 7 The chromatogram of the test sample solution obtained by diluting the sample solution drawn from the lithium-containing liquid flow chamber after 60 minutes of continuous operation at a working current of 1.50mA in Example 4 is shown. Figure 8 For Li + Standard curve plot; Figure 9 Mg 2+ Standard curve plot; Figure 10 for Na + Standard curve plot; Figure 11This is the chromatogram of the sample solution to be tested, prepared by diluting the sample solution drawn from the lithium-containing flow chamber after 60 minutes of continuous operation at a flow rate of 3 mL / min in Example 5. Figure 12 The chromatogram of the sample solution to be tested, which was obtained by continuously running for 60 minutes after the switching mode of the first working loop working time being 30s and the second working loop working time being 15s, was obtained by taking the sample solution from the lithium liquid flow chamber and diluting it. Figure 13 This is the chromatogram of the sample solution to be tested, which was diluted from the lithium-containing liquid flow chamber at 0 min of operation in Example 7. Figure 14 The chromatogram of the test sample solution obtained by diluting the sample solution drawn from the lithium-containing liquid flow chamber after running for 660 min in Example 7 is shown. Figure 15 The graph shows the changes in the concentrations of lithium ions and magnesium ions in the lithium ion receiving solution over time during 660 minutes of continuous operation of the continuous electrochemical lithium extraction system in Example 7. Figure 16 The graph shows the changes in the concentrations of lithium ions and magnesium ions in the lithium ion receiving solution over time after continuous operation of a continuous electrochemical lithium extraction system constructed from an unmodified initial membrane electrode. Figure 17 The current-voltage response curve of the continuous electrochemical lithium extraction system of this invention between 0 and 2500 s under the high-frequency asymmetric dynamic operation strategy of "30s constant current adsorption / 15s constant voltage desorption" is shown. Figure 18 The current-voltage response curve of the continuous electrochemical lithium extraction system of this invention between 0 and 250 s under the high-frequency asymmetric dynamic operation strategy of "30 s constant current adsorption / 15 s constant voltage desorption" is shown. Wherein, 1-first terminal electrode, 2-first electrolyte flow chamber, 3-first anion exchange membrane, 4-raw solution flow chamber, 5-Janus membrane electrode, 6-lithium adsorbent flow chamber, 7-second anion exchange membrane, 8-second electrolyte flow chamber, 9-second terminal electrode, 10-first electrolyte flow channel, 11-second electrolyte flow channel, 12-raw solution flow channel, 13-lithium adsorbent flow channel, 14-blind plate. Detailed Implementation

[0066] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0067] Example 1

[0068] A method for constructing a Janus membrane electrode includes the following steps: Preparation of electrode active materials: Lithium hydroxide (LiOH) and manganese acetate [Mn(CH3COO)2] were weighed according to a Li:Mn molar ratio of 1:1.95, added to 10 mL of anhydrous ethanol and mixed. The mixture was continuously magnetically stirred at 60 °C to ensure that the components were fully mixed and dispersed. The mixture was then heated until the ethanol was completely evaporated to obtain a uniformly mixed precursor powder. The precursor powder was dried in an oven at 110°C to remove residual solvent and obtain the dried precursor. The dried precursor was placed in a muffle furnace and pre-calcined at 500°C in air for 7 hours. Then the temperature was raised to 750°C and calcined in air for 10 hours. After natural cooling to room temperature, lithium manganese oxide (LMO) was obtained.

[0069] S2. Preparation of the active layer slurry: Lithium manganese oxide (LMO), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed and ground in a mass ratio of 8:1:1. Then, 5 mL of N-methylpyrrolidone (NMP) was added, and the mixture was mechanically stirred and ultrasonically dispersed to obtain a uniform active layer slurry.

[0070] S3. Preparation of the initial membrane electrode: Using a 1000-mesh stainless steel mesh with a thickness of 200μm as the current collector, the active layer slurry was coated on both sides of the current collector. Then, it was placed in a vacuum drying oven at 80℃ for 12h and then placed in a hot pressing device. It was hot-pressed for 5min at 130℃ and 10MPa to further densify the active layer, resulting in a hot-pressed and dense initial film electrode with an active layer thickness of 100μm on one side. The edges of the initial membrane electrode, which is hot-pressed and dense, are encapsulated with silicone rubber, retaining only the preset effective working area to prevent liquid circumference and edge leakage during operation, thus obtaining the initial membrane electrode.

[0071] Construction of S4 Janus film electrode: One side of the active layer surface of the initial membrane electrode was immersed in a circulating aqueous solution of polyethyleneimine with a PEI mass percentage of 1% at a flow rate of 3 mL / min for 12 h to construct the first functional interface layer. The other side of the active layer surface was immersed in a circulating aqueous solution of sodium dodecyl sulfate with a SDS mass percentage of 0.5% at a flow rate of 3 mL / min for 12 h to construct the second functional interface layer. The electrode was then removed and dried in a vacuum drying oven at 90 °C for 20 min to obtain a Janus membrane electrode with a first functional interface layer thickness of 35 μm and a second functional interface layer thickness of 20 μm.

[0072] Example 2

[0073] like Figure 1 and Figure 2 As shown, a method for constructing a Janus membrane electrode includes the following steps: S1. Preparation of electrode active materials: Lithium hydroxide (LiOH), manganese acetate [(CH3COO)2Mn], and aluminum hydroxide [Al(OH)3] were weighed according to the molar ratio of Li:Mn:Al of 1:1.95:0.05. They were added to 10 mL of anhydrous ethanol and mixed. The mixture was continuously stirred magnetically at 60 °C to ensure that the components were fully mixed and dispersed. The mixture was then heated until the ethanol was completely evaporated to obtain a uniformly mixed precursor powder. The precursor powder was dried in an oven at 110°C to remove residual solvent and obtain the dried precursor. The dried precursor was placed in a muffle furnace and pre-calcined at 500°C in air for 7 hours. Then the temperature was raised to 750°C and calcined in air for 10 hours. After natural cooling to room temperature, aluminum-doped lithium manganese oxide (LMO-Al) was obtained. Aluminum-doped lithium manganese oxide (LMO-Al) and ammonium fluoride (NH4F) were thoroughly mixed and ground at a mass ratio of 70:1, and then calcined at 400℃ for 2 hours and naturally cooled to room temperature to obtain aluminum-fluorine co-doped lithium manganese oxide (LMO-Al-F).

[0074] S2. Preparation of the active layer slurry: Aluminum-fluorine co-doped lithium manganese oxide (LMO-Al-F), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed and ground in a mass ratio of 8:1:1. Then, 5 mL of N-methylpyrrolidone (NMP) was added, and the mixture was mechanically stirred and ultrasonically dispersed to obtain a uniform active layer slurry.

[0075] S3. Preparation of the initial membrane electrode: Using a 1000-mesh stainless steel mesh with a thickness of 200μm as the current collector, the active layer slurry was coated on both sides of the current collector. Then, it was placed in a vacuum drying oven at 60℃ and dried for 12h. Subsequently, it was placed in a hot pressing device and hot-pressed for 5min at 130℃ and 10MPa to further densify the active layer, resulting in a hot-pressed and dense initial film electrode with an active layer thickness of 100μm on one side. The edges of the initial membrane electrode, which is hot-pressed and dense, are encapsulated with silicone rubber, retaining only the preset effective working area to prevent liquid circumference and edge leakage during operation, thus obtaining the initial membrane electrode.

[0076] Construction of S4 Janus film electrode: One side of the active layer surface of the initial membrane electrode was immersed in a circulating aqueous solution of polyethyleneimine with a PEI mass percentage of 1% at a flow rate of 3 mL / min for 12 h to construct the first functional interface layer. The other side of the active layer surface was immersed in a circulating aqueous solution of sodium dodecyl sulfate with a SDS mass percentage of 0.5% at a flow rate of 3 mL / min for 12 h to construct the second functional interface layer. The electrode was then removed and dried in a vacuum drying oven at 90 °C for 20 min to obtain a Janus membrane electrode with a first functional interface layer thickness of 35 μm and a second functional interface layer thickness of 20 μm.

[0077] Static water contact angle test Static water contact angle tests were performed on one side of the active layer surface of the initial membrane electrode before and after immersion in a polyethyleneimine (PEI) aqueous solution. The results are as follows: Figure 3 As shown. From Figure 3 Analysis shows that the static water contact angle of the initial membrane electrode after modification with polyethyleneimine (PEI) changed from greater than 90° to less than 90°, indicating that the initial membrane electrode modified with PEI changed from hydrophobic to hydrophilic. This is beneficial for improving the wettability and contact area of ​​the original solution on the membrane electrode surface, and promoting the Li + Mass transfer to the membrane electrode surface is improved and interfacial mass transfer resistance is reduced, thereby helping to improve lithium-ion adsorption efficiency and interfacial stability during continuous lithium extraction.

[0078] Infrared spectroscopy analysis Infrared spectroscopy was used to analyze the infrared spectra of one side of the initial membrane electrode and the first and second functional interface layers on both sides of the Janus membrane electrode. The results are as follows: Figure 4 As shown.

[0079] Figure 4In the diagram, the black curve represents the infrared spectrum of one side surface of the initial membrane electrode, the blue curve represents the infrared spectrum of the surface of the first functional interface layer (PEI modified layer) of the Janus membrane electrode, and the orange curve represents the infrared spectrum of the surface of the second functional interface layer (SDS modified layer) of the Janus membrane electrode.

[0080] from Figure 4 Analysis revealed that the infrared spectrum of the initial membrane electrode without PEI and SDS modification remained largely flat, exhibiting only the characteristic absorption peaks of the substrate material. After PEI modification (the first functional interface layer of the Janus membrane electrode), the infrared spectrum at 2918 cm⁻¹... -1 and 2850cm -1 A distinct absorption peak appears nearby, corresponding to the characteristic peak of the -CH2- stretching vibration in the PEI molecule, indicating that PEI has been successfully introduced into the surface of the initial membrane electrode. After SDS modification (the second functional interface layer of the Janus membrane electrode), an absorption peak appears at approximately 1630 cm⁻¹. -1 The characteristic absorption peak of -CO-NH- appears nearby, at approximately 1210 cm⁻¹. -1 A characteristic peak of the S=O stretching vibration appears nearby, corresponding to the characteristic absorption peak of the functional groups contained in SDS. The above results indicate that the PEI functional layer (first functional interface layer) and the SDS functional layer (second functional interface layer) have been successfully fixed on different surfaces of the initial membrane electrode, proving that the in-situ cyclic modification method of the present invention can form Janus interfaces with different chemical compositions on both sides of the initial membrane electrode.

[0081] In the actual construction of the Janus membrane electrode, a polyethyleneimine (PEI) aqueous solution is loaded into the feed solution flow chamber of the continuous electrochemical lithium extraction system, and a sodium dodecyl sulfate (SDS) aqueous solution is loaded into the lithium adsorption solution flow chamber. The PEI solution and SDS solution are driven to circulate in the feed solution flow chamber and the lithium adsorption solution flow chamber respectively by the feed solution circulation pump and the lithium adsorption solution circulation pump, respectively, at a flow rate of 3 ml / min and a circulation time of 12 h. This ensures that the two sides of the initial membrane electrode are in continuous contact with different solutions. Since the two chambers are independent of each other, the PEI solution and SDS solution will not mix directly. Therefore, different functional interface layers can be formed on the two sides of the initial membrane electrode. After completion, the solutions on both sides are drained, and the feed solution flow chamber and the lithium adsorption solution flow chamber are rinsed with deionized water to remove unbound solution. The membrane electrode is then taken out and dried in a vacuum drying oven at 90°C for 20 min to obtain the Janus membrane electrode.

[0082] Example 3

[0083] like Figure 5As shown, a continuous electrochemical lithium extraction system includes a first terminal electrode 1, a first electrolyte flow chamber 2, a first anion exchange membrane 3, a raw liquid flow chamber 4, a Janus membrane electrode 5 prepared in Example 2, a lithium adsorption liquid flow chamber 6, a second anion exchange membrane 7, a second electrolyte flow chamber 8, and a second terminal electrode 9, which are stacked sequentially. The first functional interface layer of the Janus membrane electrode 5 is located on one side of the original liquid flow chamber 4, and the second functional interface layer is located on one side of the lithium adsorption liquid flow chamber 6. The first electrolyte flow chamber 2 and the second electrolyte flow chamber 8 are connected through the first electrolyte flow channel 10, and the first electrolyte flow chamber 2 and the second electrolyte flow chamber 8 are connected to the electrolyte storage tank through the second electrolyte flow channel 11. Figure 5 (not shown in the diagram) allows the electrolyte to circulate between the first electrolyte flow chamber 2, the second electrolyte flow chamber 8, and the electrolyte storage tank. A circulation pump is installed on the first electrolyte flow channel 10 to form a closed electrolyte circulation system. The first terminal electrode 1 is in contact with the electrode liquid in the first electrolyte flow chamber 2, and the second terminal electrode 9 is in contact with the electrolyte in the second electrolyte flow chamber 8. An electrochemical reaction occurs during system operation, providing an electron transport pathway for the entire continuous lithium extraction process and maintaining charge balance. The original liquid flow chamber 4 is connected to the original liquid storage tank through the original liquid flow channel 12. Figure 5 (not shown in the figure), so that the lithium-containing raw liquid circulates between the raw liquid flow chamber 4 and the raw liquid storage tank, and a raw liquid circulation system is formed by setting a circulation pump on the raw liquid flow channel; The lithium absorption fluid flow chamber 6 is connected to the lithium absorption fluid storage tank via the lithium absorption fluid flow channel 13. Figure 5 (not shown in the image), so that the lithium-ion receiving liquid circulates between the lithium-absorbing liquid flow chamber 6 and the lithium-absorbing liquid storage tank, and a lithium-ion receiving liquid circulation system is formed by setting a circulation pump on the lithium-absorbing liquid flow channel 13. The electrolyte closed circulation system, the raw liquid circulation system and the lithium-ion receiving liquid circulation system are independent of each other, and the liquids do not mix during operation; Both the first terminal electrode 1 and the second terminal electrode 9 are made of corrosion-resistant conductive carbon electrodes; Blind plates 14 are provided on the outer sides of both the first terminal electrode 1 and the second terminal electrode 9.

[0084] Example 4

[0085] like Figure 6 As shown, a method for continuous electrochemical lithium extraction using the continuous electrochemical lithium extraction system in Example 3 includes the following steps: S1. Add electrolyte to the first electrolyte flow chamber, add simulated lithium-containing stock solution to the stock solution flow chamber, and add lithium ion receiving solution to the lithium absorption solution flow chamber, so that the first terminal electrode is in contact with the electrolyte and the Janus membrane electrode is in contact with the simulated lithium-containing stock solution. In this study, a sodium sulfate aqueous solution of 200 ppm was used as the electrolyte, a mixed aqueous solution containing 200 ppm lithium sulfate and 200 ppm magnesium chloride was used as the simulated lithium-containing stock solution, and a sodium sulfate aqueous solution of 200 ppm was used as the lithium ion receiving solution. Carbon paper is used as the first terminal electrode 1 and the second terminal electrode 9. Commercial ASTOM NEOSEPTA type anion exchange membranes were used as the first anion exchange membrane 3 and the second anion exchange membrane 7. S2. Using the first terminal electrode as the anode and the Janus film electrode as the cathode, energize the first terminal electrode and the Janus film electrode to form a first working circuit (see...). Figure 6 (See the left figure in the image), which simulates the migration of lithium ions in the lithium-containing feed solution to the Janus membrane electrode, achieving lithium ion intercalation; that is, during the adsorption stage, the power converter turns on circuit 1 (turns off circuit 2). The first terminal electrode acts as the anode, where the oxygen evolution reaction occurs, and the Janus membrane electrode acts as the cathode; under the drive of the electric field, the lithium in the simulated lithium-containing feed solution... + LMO lattice selectively penetrates the positive charge barrier (first functional interface layer) and embeds into the Janus film electrode, while multivalent Mg 2+ Then, due to the Donnan effect, it is strongly electrostatically repelled and trapped (purple zigzag arrow). Simultaneously, it simulates the anions (Cl-) in the lithium-containing stock solution. - SO4 2- It migrates through the AEM (first anion exchange membrane) to the first electrolyte flow chamber to maintain the balance charge during the adsorption phase; S3. Add electrolyte to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; Disconnect the first working circuit, and energize the Janus membrane electrode as the anode and the second terminal electrode as the cathode to form a second working circuit (see...). Figure 6 (See the right figure in the image), allowing lithium ions embedded in the Janus membrane electrode to migrate to the lithium ion receiving solution, thus achieving lithium ion deintercalation; that is, during the desorption stage, the power converter switches the conduction circuit 2 on (disconnects circuit 1). The Janus membrane electrode becomes the anode, and the second terminal electrode becomes the cathode, where the hydrogen evolution reaction occurs; the Li in the LMO lattice embedded in the Janus membrane electrode... + Under the synergistic attraction of the reverse electric field and the negative charge at the interface, the lithium ion is accelerated to enter the lithium-ion receiving liquid to achieve efficient enrichment, thereby realizing a complete cycle of continuous lithium extraction. The control system operates in constant current mode, with the operating currents of the first and second working circuits set to 1.0mA, 1.25mA, 1.50mA, 1.75mA and 2.00mA respectively, and the upper limit of the operating voltage set to 2.0V. The working time of the first working circuit is 30s, and the working time of the second working circuit is 15s. The flow rate of the solution in the closed electrolyte circulation system, the raw solution circulation system, and the lithium ion receiving solution circulation system is 3 mL / min.

[0086] Continuous lithium extraction experiments were conducted under different operating current conditions. Samples were drawn from the stock solution flow chamber and the lithium-containing solution flow chamber every 15 minutes, with each sample volume being 1 mL. The sample solution was filtered through a 0.22 μm filter membrane and then diluted with 2 mL of deionized water to prepare the test sample solution. The single injection volume was [missing data]. The chromatograms of the test sample solution were obtained using a Metrohm ion chromatograph. The chromatogram of the test sample solution diluted from the lithium-containing flow chamber after 60 minutes of continuous operation at a working current of 1.50 mA is shown below. Figure 7 As shown, based on the chromatogram and Li + Standard curve, Mg 2+ The standard curve was used to calculate the Li in the sample solution. + and Mg 2+ Concentration, and converted to Li in simulated lithium-containing stock solution and lithium-ion receiving solution. + and Mg 2+ The concentration was determined, and the Li / Mg separation coefficient was calculated.

[0087] Among them, Li + Mg 2+ and Na + The establishment of the standard curve includes the following steps: Lithium-containing aqueous solutions with lithium ion concentrations of 1 ppm, 2 ppm, 5 ppm, 10 ppm, 20 ppm, and 30 ppm were prepared sequentially using the lithium ion standard solution of national standard sample GSB 04-1734-2004. Ion chromatography analysis was then performed on the lithium-containing aqueous solutions of different concentrations, with a single injection volume of [missing value]. Then, Li in a lithium-containing aqueous solution + Using the concentration of Li as the x-axis and the corresponding peak area as the y-axis, a standard curve was established through linear fitting to obtain the Li... + Standard curves such as Figure 8 As shown.

[0088] Magnesium-containing aqueous solutions with magnesium ion concentrations of 1 ppm, 2 ppm, 5 ppm, 10 ppm, 20 ppm, and 30 ppm were prepared sequentially using the magnesium ion standard solution of national standard sample GSB 04-1735-2004. Ion chromatography analysis was then performed on the magnesium-containing aqueous solutions of different concentrations, with a single injection volume of [missing value]. Then, Mg in a magnesium-containing aqueous solution 2+ Using the concentration of Mg as the x-axis and the corresponding peak area as the y-axis, a standard curve was established through linear fitting to obtain the Mg concentration. 2+ Standard curves such as Figure 9 As shown.

[0089] Sodium-containing aqueous solutions with sodium ion concentrations of 1 ppm, 2 ppm, 5 ppm, 10 ppm, 20 ppm, and 30 ppm were prepared sequentially using the national standard sample GSB 04-1738-2004. Ion chromatography analysis was then performed on the sodium-containing aqueous solutions of different concentrations, with a single injection volume of [volume missing]. Then, using sodium-containing aqueous solution Na + Using the concentration of Na as the x-axis and the corresponding peak area as the y-axis, a standard curve was established through linear fitting to obtain the Na... + Standard curves such as Figure 10 As shown.

[0090] The formula for calculating the Li / Mg separation coefficient is: (I) In formula (I), Indicates the Li / Mg separation coefficient. Indicates the presence of Li in the lithium-ion receiving solution + / Mg 2+ concentration ratio, Indicating the presence of Li in the simulated lithium-containing stock solution + / Mg 2+ The initial concentration ratio, in this embodiment, simulates the Li in the lithium-containing stock solution. + / Mg 2+ The initial concentration ratio is 1.

[0091] Experimental results show that the Li / Mg separation coefficient is optimal when the operating current is 1.50mA, proving that the overall system performance is optimal. Therefore, 1.50mA is determined to be the preferred operating current.

[0092] Example 5

[0093] like Figure 6 As shown, a method for continuous electrochemical lithium extraction using the continuous electrochemical lithium extraction system in Example 3 includes the following steps: S1. Add electrolyte to the first electrolyte flow chamber, add simulated lithium-containing stock solution to the stock solution flow chamber, and add lithium ion receiving solution to the lithium absorption solution flow chamber, so that the first terminal electrode is in contact with the electrolyte and the Janus membrane electrode is in contact with the simulated lithium-containing stock solution. In this study, a sodium sulfate aqueous solution of 200 ppm was used as the electrolyte, a mixed aqueous solution containing 200 ppm lithium sulfate and 200 ppm magnesium chloride was used as the simulated lithium-containing stock solution, and a sodium sulfate aqueous solution of 200 ppm was used as the lithium ion receiving solution. S2. Using the first terminal electrode as the anode and the Janus film electrode as the cathode, energize the first terminal electrode and the Janus film electrode to form a first working circuit (see...). Figure 6 (See the left figure in the image), which simulates the migration of lithium ions in the lithium-containing feed solution to the Janus membrane electrode, achieving lithium ion intercalation; that is, during the adsorption stage, the power converter turns on circuit 1 (turns off circuit 2). The first terminal electrode acts as the anode, where the oxygen evolution reaction occurs, and the Janus membrane electrode acts as the cathode; under the drive of the electric field, the lithium in the simulated lithium-containing feed solution... + LMO lattice selectively penetrates the positive charge barrier (first functional interface layer) and embeds into the Janus film electrode, while multivalent Mg 2+ Then, due to the Donnan effect, it is strongly electrostatically repelled and trapped (purple zigzag arrow). Simultaneously, it simulates the anions (Cl-) in the lithium-containing stock solution. - SO4 2- It migrates to the left through the AEM (first anion exchange membrane) to balance the charge; S3. Add electrolyte to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; Disconnect the first working circuit, and energize the Janus membrane electrode as the anode and the second terminal electrode as the cathode to form a second working circuit (see...). Figure 6 (See the right figure in the image), allowing lithium ions embedded in the Janus membrane electrode to migrate to the lithium ion receiving solution, thus achieving lithium ion deintercalation; that is, during the desorption stage, the power converter switches the conduction circuit 2 on (disconnects circuit 1). The Janus membrane electrode becomes the anode, and the second terminal electrode becomes the cathode, where the hydrogen evolution reaction occurs; the Li in the LMO lattice embedded in the Janus membrane electrode... + Under the synergistic attraction of the reverse electric field and the negative charge at the interface, the lithium ion is accelerated to enter the lithium-ion receiving liquid to achieve efficient enrichment, thereby realizing a complete cycle of continuous lithium extraction. The control system operates in constant current mode, with the operating current of the first working circuit and the second working circuit both set to 1.50mA, the upper limit of the operating voltage set to 2.0V, the operating time of the first working circuit being 30s, and the operating time of the second working circuit being 15s. The flow rates of the solutions in the closed electrolyte circulation system, the stock solution circulation system, and the lithium ion receiving solution circulation system were set to 1 mL / min, 2 mL / min, 3 mL / min, and 4 mL / min, respectively.

[0094] Continuous lithium extraction experiments were conducted under different flow rate conditions. Samples were drawn from the stock solution flow chamber and the lithium-containing solution flow chamber every 15 minutes, with each sample volume being 1 mL. The sample solution was filtered through a 0.22 μm filter membrane and then diluted with 2 mL of deionized water to prepare the test sample solution. The single injection volume was [missing data]. The chromatograms of the test sample solution were obtained using a Metrohm ion chromatograph. The chromatogram of the test sample solution diluted from the lithium-containing flow chamber after 60 minutes of continuous operation at a flow rate of 3 mL / min is shown below. Figure 11 As shown, based on the chromatogram and Li + Standard curve, Mg 2+ The standard curve was used to calculate the Li in the sample solution. + and Mg 2+ Concentration, and converted to Li in simulated lithium-containing stock solution and lithium-ion receiving solution. + and Mg 2+ The concentration was determined, and the Li / Mg separation coefficient was calculated according to formula (I).

[0095] Experimental results show that the Li / Mg separation coefficient is optimal when the flow rate is 3 mL / min, proving that the overall system performance is optimal. Therefore, 3 mL / min is determined to be the preferred circulation flow rate.

[0096] Example 6

[0097] like Figure 6 As shown, a method for continuous electrochemical lithium extraction using the continuous electrochemical lithium extraction system in Example 3 includes the following steps: S1. Add electrolyte to the first electrolyte flow chamber, add simulated lithium-containing stock solution to the stock solution flow chamber, and add lithium ion receiving solution to the lithium absorption solution flow chamber, so that the first terminal electrode is in contact with the electrolyte and the Janus membrane electrode is in contact with the simulated lithium-containing stock solution. In this study, a sodium sulfate aqueous solution of 200 ppm was used as the electrolyte, a mixed aqueous solution containing 200 ppm lithium sulfate and 200 ppm magnesium chloride was used as the simulated lithium-containing stock solution, and a sodium sulfate aqueous solution of 200 ppm was used as the lithium ion receiving solution. S2. Using the first terminal electrode as the anode and the Janus film electrode as the cathode, energize the first terminal electrode and the Janus film electrode to form a first working circuit (see...). Figure 6(See the left figure in the image), which simulates the migration of lithium ions in the lithium-containing feed solution to the Janus membrane electrode, achieving lithium ion intercalation; that is, during the adsorption stage, the power converter turns on circuit 1 (turns off circuit 2). The first terminal electrode acts as the anode, where the oxygen evolution reaction occurs, and the Janus membrane electrode acts as the cathode; under the drive of the electric field, the lithium in the simulated lithium-containing feed solution... + LMO lattice selectively penetrates the positive charge barrier (first functional interface layer) and embeds into the Janus film electrode, while multivalent Mg 2+ Then, due to the Donnan effect, it is strongly electrostatically repelled and trapped (purple zigzag arrow). Simultaneously, it simulates the anions (Cl-) in the lithium-containing stock solution. - SO4 2- It migrates to the left through the AEM (first anion exchange membrane) to balance the charge; S3. Add electrolyte to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; Disconnect the first working circuit, and energize the Janus membrane electrode as the anode and the second terminal electrode as the cathode to form a second working circuit (see...). Figure 6 (See the right figure in the image), allowing lithium ions embedded in the Janus membrane electrode to migrate to the lithium ion receiving solution, thus achieving lithium ion deintercalation; that is, during the desorption stage, the power converter switches the conduction circuit 2 on (disconnects circuit 1). The Janus membrane electrode becomes the anode, and the second terminal electrode becomes the cathode, where the hydrogen evolution reaction occurs; the Li in the LMO lattice embedded in the Janus membrane electrode... + Under the synergistic attraction of the reverse electric field and the negative charge at the interface, the lithium ion is accelerated to enter the lithium-ion receiving liquid to achieve efficient enrichment, thereby realizing a complete cycle of continuous lithium extraction. The control system operates in constant current mode, with the operating current of the first and second working circuits both set to 1.50mA and the upper limit of the operating voltage set to 2.0V. The working times of the first working circuit and the second working circuit are set to 30s and 15s, 30s and 30s, and 30s and 60s, respectively. The flow rate of the solutions in the closed electrolyte circulation system, the raw solution circulation system, and the lithium ion receiving solution circulation system was all set to 3 mL / min.

[0098] Continuous lithium extraction experiments were conducted under different operating time conditions. Samples were drawn from the stock solution flow chamber and the lithium-containing solution flow chamber every 15 minutes, with each sample volume being 1 mL. The sample solution was filtered through a 0.22 μm filter membrane and then diluted with 2 mL of deionized water to prepare the test sample solution. The single injection volume was [missing data]. The chromatogram of the test sample solution was obtained using a Metrohm ion chromatograph. Specifically, when switching between a first working loop operating time of 30 s and a second working loop operating time of 15 s, the chromatogram of the test sample solution diluted from the lithium-containing flow chamber after 60 minutes of continuous operation is shown below. Figure 12 As shown, based on the chromatogram and Li + Standard curve, Mg 2+ The standard curve was used to calculate the Li in the sample solution. + and Mg 2+ Concentration, and converted to Li in simulated lithium-containing stock solution and lithium-ion receiving solution. + and Mg 2+ The concentration was determined, and the Li / Mg separation coefficient was calculated according to formula (I).

[0099] Experimental results show that the Li / Mg separation coefficient is optimal when the switching mode of the first working loop working time is 30s and the second working loop working time is 15s is adopted, proving that the system has the best continuous operation performance. Therefore, the working time of the first working loop is determined to be 30s and the working time of the second working loop is determined to be 15s as the preferred operating mode.

[0100] Example 7

[0101] like Figure 6 As shown, a method for continuous electrochemical lithium extraction using the continuous electrochemical lithium extraction system in Example 3 includes the following steps: S1. Add electrolyte to the first electrolyte flow chamber, add the lithium-containing stock solution to be tested to the stock solution flow chamber, and add lithium ion receiving liquid to the lithium absorption liquid flow chamber, so that the first terminal electrode is in contact with the electrolyte and the Janus membrane electrode is in contact with the lithium-containing stock solution to be treated. The electrolyte was a 200ppm Na2SO4 aqueous solution. Li in the lithium-containing stock solution to be tested + The concentration was 200 ppm, Mg 2+ The concentration was 2000 ppm, and the lithium-containing stock solution to be tested also contained Na. + K + Cl - SO4 2- Water.

[0102] A 200 ppm Na2SO4 aqueous solution was used as the lithium ion receiving solution; S2. Using the first terminal electrode as the anode and the Janus film electrode as the cathode, energize the first terminal electrode and the Janus film electrode to form a first working circuit (see...). Figure 6(See the left figure in the image), allowing lithium ions in the lithium-containing feed solution to migrate to the Janus membrane electrode, achieving lithium ion intercalation; that is, during the adsorption stage, the power converter turns on circuit 1 (turns off circuit 2). The first terminal electrode acts as the anode, where the oxygen evolution reaction occurs, and the Janus membrane electrode acts as the cathode; under the drive of the electric field, the Li in the desalinated water... + LMO lattice selectively penetrates the positive charge barrier (first functional interface layer) and embeds into the Janus film electrode, while multivalent Mg 2+ Then, due to the Donnan effect, it is strongly electrostatically repelled and retained (purple returning arrow). Simultaneously, the anions (Cl-) in the lithium-containing stock solution being tested... - SO4 2- It migrates to the left through the AEM (first anion exchange membrane) to balance the charge; The control system operates in constant current mode, with the first working circuit set to 1.50mA, the upper limit of the working voltage set to 2.0V, and the working time of the first working circuit set to 30s; the second working circuit is in the open state. The flow rate of the solution in the closed electrolyte circulation system, the raw solution circulation system, and the lithium ion receiving solution circulation system is set to 3 mL / min; Li in the lithium-containing stock solution to be tested + Mg is embedded in the lattice of the hot-pressed Janus membrane electrode active material under electric field driving. 2+ Because it is difficult to embed into the crystal lattice, it remains in the lithium-containing raw solution to be tested; S3. Add electrolyte to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; Disconnect the first working circuit, and energize the Janus membrane electrode as the anode and the second terminal electrode as the cathode to form a second working circuit (see...). Figure 6 (See the right figure in the image), allowing lithium ions embedded in the Janus membrane electrode to migrate to the lithium ion receiving solution, thus achieving lithium ion deintercalation; that is, during the desorption stage, the power converter switches the conduction circuit 2 on (disconnects circuit 1). The Janus membrane electrode becomes the anode, and the second terminal electrode becomes the cathode, where the hydrogen evolution reaction occurs; the Li in the LMO lattice embedded in the Janus membrane electrode... + Under the synergistic attraction of the reverse electric field and the negative charge at the interface, the lithium ion is accelerated to enter the lithium-ion receiving liquid to achieve efficient enrichment, thereby realizing a complete cycle of continuous lithium extraction. The control system operates in constant current mode, with the operating current of the second working circuit set to 1.50mA and the upper limit of the operating voltage set to 2.0V; the operating time of the second working circuit is set to 15s. The flow rate of the solution in the closed electrolyte circulation system, the raw solution circulation system, and the lithium ion receiving solution circulation system is set to 3 mL / min; Li embedded in Janus film electrode + The lithium ions are deintercalated and released into the lithium-ion receiving liquid, thereby achieving the directional migration and enrichment of lithium ions; Disconnect the second working circuit, close the first working circuit, and repeat S2 and S3 to achieve continuous electrochemical lithium extraction.

[0103] During continuous operation, sample solutions were drawn from the stock solution flow chamber and the lithium-containing solution flow chamber every 60 minutes, with each sample volume being 1 mL. After filtration through a 0.22 μm filter membrane, the sample solution was diluted with 2 mL of deionized water to prepare the test sample solution. The single injection volume was [missing data]. The chromatograms of the test sample solution were obtained using a Metrohm ion chromatograph. The chromatogram of the test sample solution diluted from the lithium-containing flow chamber at 0 min of operation is shown below. Figure 13 As shown, after 660 minutes of continuous operation, the chromatogram of the test sample solution diluted from the lithium-containing liquid flow chamber is as follows. Figure 14 As shown, based on the chromatogram and Li + Standard curve, Mg 2+ The standard curve was used to calculate the Li in the sample solution. + and Mg 2+ Concentration, and converted to Li in simulated lithium-containing stock solution and lithium-ion receiving solution. + and Mg 2+ Concentration of Li in lithium-ion receiving solution + and Mg 2+ The results of the concentration change over time are as follows Figure 15 As shown.

[0104] from Figure 15 Analysis shows that as the continuous operating time increases, the Li in the lithium-ion receiving solution decreases. + The concentration continued to rise, gradually increasing from the initial value to approximately 68 ppm, showing an overall approximately linear growth trend. In contrast, Mg... 2+ The concentration remained consistently low, increasing only from the initial value to approximately 8 ppm, indicating that the system of this invention can effectively suppress Mg. 2+ Migration, to achieve Li + Preferential enrichment. After continuous operation for approximately 660 minutes (about 11 hours), Li + The concentration continued to increase, and no obvious plateau or sudden decay was observed, indicating that the continuous electrochemical ion pump lithium extraction system described in this invention has good continuous operation stability.

[0105] Comparative Example 1 A continuous electrochemical lithium extraction method includes the following steps: S1. Preparation of electrode active materials: Lithium hydroxide (LiOH), manganese acetate [Mn(CH3COO)2], and aluminum hydroxide [Al(OH)3] were weighed according to the molar ratio of Li:Mn:Al of 1:1.95:0.05. They were added to 10 mL of anhydrous ethanol and mixed. The mixture was continuously stirred magnetically at 60 °C to ensure that the components were fully mixed and dispersed. The mixture was then heated until the ethanol was completely evaporated to obtain a uniformly mixed precursor powder. The precursor powder was dried in an oven at 110°C to remove residual solvent and obtain the dried precursor. The dried precursor was placed in a muffle furnace and pre-calcined in air at 500°C for 7 hours. Then the temperature was raised to 750°C and calcined in air for 10 hours. After natural cooling to room temperature, aluminum-doped lithium manganese oxide (LMO-Al) was obtained. Aluminum-doped lithium manganese oxide (LMO-Al) and ammonium fluoride were thoroughly mixed and ground at a mass ratio of 70:1, and then calcined at 400℃ for 2 hours and naturally cooled to room temperature to obtain aluminum-fluorine co-doped lithium manganese oxide (LMO-Al-F).

[0106] S2. Preparation of the active layer slurry: Aluminum-fluorine co-doped lithium manganese oxide (LMO-Al-F), conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed and ground in a mass ratio of 8:1:1. Then, 5 mL of N-methylpyrrolidone (NMP) was added, and the mixture was mechanically stirred and ultrasonically dispersed to obtain a uniform active layer slurry.

[0107] S3. Preparation of the initial membrane electrode: Using a 1000-mesh stainless steel mesh with a thickness of 200μm as the current collector, the active layer slurry was coated on both sides of the current collector. Then, it was placed in a vacuum drying oven at 80℃ for 12h and then placed in a hot pressing device. It was hot-pressed for 5min at 130℃ and 10MPa to further densify the active layer, resulting in a hot-pressed and dense initial film electrode with an active layer thickness of 100μm on one side. The edges of the initial membrane electrode, which is hot-pressed and dense, are encapsulated with silicone rubber, retaining only the preset effective working area to prevent liquid circumference and edge leakage during operation, thus obtaining the initial membrane electrode.

[0108] S4. Replace the Janus membrane electrode used in the continuous electrochemical lithium extraction system in Example 5 with the initial membrane electrode prepared in S3. The rest is the same as in Example 5. Then, add electrolyte to the first electrolyte flow chamber, add the lithium-containing stock solution to be tested to the stock solution flow chamber, and add lithium ion receiving liquid to the lithium absorption liquid flow chamber, so that the first terminal electrode is in contact with the electrolyte and the initial membrane electrode is in contact with the simulated lithium-containing stock solution. In this study, a 200 ppm Na2SO4 aqueous solution was used as the electrolyte; a mixed aqueous solution containing 200 ppm lithium sulfate and 200 ppm magnesium chloride was used as the simulated lithium-containing stock solution; and a 200 ppm Na2SO4 aqueous solution was used as the lithium ion receiving solution. S2. Using the first terminal electrode as the anode and the initial membrane electrode as the cathode, energize the first terminal electrode and the initial membrane electrode to form a first working circuit, allowing lithium ions in the simulated lithium-containing raw solution to migrate to the initial membrane electrode, achieving lithium ion intercalation; that is, in the adsorption stage, the first terminal electrode acts as the anode, undergoing the oxygen evolution reaction, and the initial membrane electrode acts as the cathode; under the drive of the electric field, the lithium in the simulated lithium-containing raw solution... + The LMO lattice selectively penetrates the positive charge barrier (first functional interface layer) and embeds into the initial membrane electrode, while the multivalent Mg 2+ Then, due to the Donnan effect, it is strongly electrostatically repelled and retained (purple zigzag arrow). Simultaneously, the anion (Cl...) - SO4 2- It migrates to the left through the AEM (first anion exchange membrane) to balance the charge; The control system operates in constant current mode, with the first working circuit set to 1.50mA, the upper limit of the working voltage set to 2.0V, and the working time of the first working circuit set to 30s; the second working circuit is in the open state. The flow rate of the solution in the closed electrolyte circulation system, the raw solution circulation system, and the lithium ion receiving solution circulation system is set to 3 mL / min; S3. Add electrolyte to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; The first working circuit is disconnected, and the initial membrane electrode is used as the anode, and the second terminal electrode as the cathode. Current is applied to both the initial membrane electrode and the second terminal electrode to form a second working circuit. This allows lithium ions embedded in the initial membrane electrode to migrate to the lithium ion receiving solution, achieving lithium ion deintercalation. In other words, during the desorption stage, the initial membrane electrode becomes the anode, and the second terminal electrode becomes the cathode, resulting in a hydrogen evolution reaction. The Li ions embedded in the LMO lattice of the initial membrane electrode... + Under the synergistic attraction of the reverse electric field and the negative charge at the interface, the lithium ion is accelerated to enter the lithium-ion receiving liquid to achieve efficient enrichment, thereby realizing a complete cycle of continuous lithium extraction. The control system operates in constant current mode, with the operating current of the second working circuit set to 1.50mA and the upper limit of the operating voltage set to 2.0V; the operating time of the second working circuit is set to 15s. The flow rate of the solution in the closed electrolyte circulation system, the raw solution circulation system, and the lithium ion receiving solution circulation system is set to 3 mL / min; Li embedded in the initial membrane electrode +The lithium ions are deintercalated and released into the lithium-ion receiving liquid, thereby achieving the directional migration and enrichment of lithium ions; Disconnect the second working circuit, close the first working circuit, and repeat S2 and S3 to achieve continuous electrochemical lithium extraction.

[0109] During continuous operation, sample solutions were drawn from the stock solution flow chamber and the lithium-containing solution flow chamber every 60 minutes, with each sample volume being 1 mL. After filtration through a 0.22 μm filter membrane, the sample solution was diluted with 2 mL of deionized water to prepare the test sample solution. The single injection volume was [missing data]. The chromatogram of the sample solution was obtained using a Metrohm ion chromatograph. Based on the chromatogram and Li... + Standard curve, Mg 2+ The standard curve was used to calculate the Li in the sample solution. + and Mg 2+ Concentration, and converted to Li in simulated lithium-containing stock solution and lithium-ion receiving solution. + and Mg 2+ Concentration of Li in lithium-ion receiving solution + and Mg 2+ The results of the concentration change over time are as follows Figure 16 As shown.

[0110] from Figure 16 Analysis showed that the magnesium ion concentration in the lithium-ion receiving solution increased significantly after 30 minutes. After 90 minutes of continuous operation, the Li / Mg separation coefficient was approximately 2. Figure 15 Compared to the previous method, after 30 minutes of continuous operation, the magnesium ion concentration in the lithium ion receiving solution did not increase significantly, and the Li / Mg separation coefficient increased significantly with the extension of the operating time, thus proving that the modified hot-pressed Janus membrane electrode has a better Li / Mg separation effect.

[0111] By comparison Figure 16 and Figure 15 It can be seen that the initial membrane electrode without Janus interface showed a decrease in Li / Mg separation performance and continuous operation stability during continuous operation. This indicates that, under the condition of keeping the membrane electrode material composition, device structure and operating parameters consistent, the construction of Janus interface can improve the functional division of the two sides of the membrane electrode, enhance the directional migration ability of lithium ions, and thus improve the lithium extraction performance of continuous electrochemical ion pump.

[0112] Example 8

[0113] like Figure 6 As shown, a method for continuous electrochemical lithium extraction using the continuous electrochemical lithium extraction system in Example 3 includes the following steps: S1. Add electrolyte to the first electrolyte flow chamber, add simulated lithium-containing stock solution to the stock solution flow chamber, and add lithium ion receiving solution to the lithium absorption solution flow chamber, so that the first terminal electrode is in contact with the electrolyte and the Janus membrane electrode is in contact with the simulated lithium-containing stock solution. In this study, a 200ppm Na2SO4 aqueous solution was used as the electrolyte; a simulated lithium-containing stock solution with a lithium sulfate concentration of 200ppm and a magnesium chloride concentration of 200ppm was used; and a 200ppm Na2SO4 aqueous solution was used as the lithium ion receiving solution. S2. Using the first terminal electrode as the anode and the Janus film electrode as the cathode, energize the first terminal electrode and the Janus film electrode to form a first working circuit (see...). Figure 6 (See the left figure in the image), which simulates the migration of lithium ions in the lithium-containing feed solution to the Janus membrane electrode, achieving lithium ion intercalation; that is, during the adsorption stage, the power converter turns on circuit 1 (turns off circuit 2). The first terminal electrode acts as the anode, where the oxygen evolution reaction occurs, and the Janus membrane electrode acts as the cathode; under the drive of the electric field, the lithium in the simulated lithium-containing feed solution... + LMO lattice selectively penetrates the positive charge barrier (first functional interface layer) and embeds into the Janus film electrode, while multivalent Mg 2+ Then, due to the Donnan effect, it is strongly electrostatically repelled and trapped (purple zigzag arrow). Simultaneously, it simulates the anions (Cl-) in the lithium-containing stock solution. - SO4 2- It migrates to the left through the AEM (first anion exchange membrane) to balance the charge; The control system operates in constant current mode, with the first working circuit set to 1.50mA, the upper limit of the working voltage set to 2.0V, and the working time of the first working circuit set to 30s; the second working circuit is in the open state. The flow rates of the solutions in the closed electrolyte circulation system, the stock solution circulation system, and the lithium ion receiving solution circulation system were all set to 3 mL / min. Simulated Li in lithium-containing stock solution + Mg is embedded in the lattice of the hot-pressed Janus membrane electrode active material under electric field driving. 2+ Because it is difficult to embed into the crystal lattice, it remains in the simulated lithium-containing solution; S3. Add electrolyte to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; Disconnect the first working circuit, and energize the Janus membrane electrode as the anode and the second terminal electrode as the cathode to form a second working circuit (see...). Figure 6(See the right figure in the image), allowing lithium ions embedded in the Janus membrane electrode to migrate to the lithium ion receiving solution, thus achieving lithium ion deintercalation; that is, during the desorption stage, the power converter switches the conduction circuit 2 on (disconnects circuit 1). The Janus membrane electrode becomes the anode, and the second terminal electrode becomes the cathode, where the hydrogen evolution reaction occurs; the Li in the LMO lattice embedded in the Janus membrane electrode... + Under the synergistic attraction of the reverse electric field and the negative charge at the interface, the lithium ion is accelerated to enter the lithium-ion receiving liquid to achieve efficient enrichment, thereby realizing a complete cycle of continuous lithium extraction. The control system operates in constant current mode, with the operating current of the second working circuit set to 1.50mA and the upper limit of the operating voltage set to 2.0V; the operating time of the second working circuit is set to 15s. The flow rates of the solutions in the closed electrolyte circulation system, the stock solution circulation system, and the lithium ion receiving solution circulation system were all set to 3 mL / min. Li embedded in Janus film electrode + The lithium ions are deintercalated and released into the lithium-ion receiving liquid, thereby achieving the directional migration and enrichment of lithium ions; Disconnect the second working circuit, close the first working circuit, and repeat S2 and S3 to achieve continuous electrochemical lithium extraction.

[0114] During continuous operation, an electrochemical workstation was used to record the changes in current and voltage in real time. The results are as follows: Figure 17 and Figure 18 As shown.

[0115] from Figure 17 Analysis shows that during the 30s adsorption half-cycle of a single cycle, the system operates in constant current mode (currently set at 1.5mA, with the yellow line remaining horizontal). At this time, the response voltage (green line) shows a gentle linear upward trend (rising from approximately 1.6V to 1.7V), and is far lower than the conventional water splitting potential, indicating that the system has extremely low interfacial transport resistance. During the subsequent 15s desorption half-cycle, the system quickly switches to constant voltage mode (maintained at 2.0V, with the green line remaining horizontal), and the response current (yellow line) shows a rapid exponential decay, indicating that the embedded lithium ions achieve extremely rapid deintercalation and release under the traction of electric field reversal and the asymmetric negative charge interface on the lithium ion receiving liquid side.

[0116] from Figure 17 Analysis shows that during high-frequency continuous cyclic operation lasting over 2000 seconds, the system's current-voltage waveform exhibits high reproducibility and periodic consistency. In the initial stage (approximately 0-500 seconds), the system's baseline voltage and polarization potential undergo a brief adaptive rise before rapidly reaching a stable dynamic equilibrium. No sustained voltage spikes or runaway phenomena were observed throughout the entire long-term operation.

[0117] from Figure 17 and Figure 18 Comprehensive analysis reveals that the high-frequency asymmetric operation strategy (30s / 15s) adopted in this invention achieves the following three key technical conclusions: Conclusion 1: This invention alleviates severe interfacial concentration polarization. Traditional long-period constant-current lithium extraction easily leads to ion depletion on the membrane electrode surface, causing severe concentration polarization. This invention, through high-frequency switching, ensures the electrode always operates in an "unsaturated," semi-infinite diffusion range. Figure 17 The long-term stability of the polarization voltage directly proves that the strategy effectively suppresses concentration polarization and maintains excellent fluid mass transfer conditions.

[0118] Conclusion 2: "Shallow charge and shallow discharge" was achieved, which improved the cycle life of the electrode structure. Figure 18 The short, alternating constant current and constant voltage cycles ensure that ions shuttle at high frequency only within the surface and shallow lattice of the active material. This dynamic operation avoids excessive lattice expansion and contraction caused by deep insertion and extraction, effectively suppressing the Jahn-Teller distortion of lithium manganese oxide materials from an electrical control perspective.

[0119] Conclusion 3: The system's low specific energy consumption (SEC) was ensured. By effectively curbing the rise of polarization overpotential, the system operating voltage was maintained at a low level, avoiding the consumption of electrical energy by non-specific side reactions (such as water splitting to produce gas), thus achieving efficient and low-energy continuous lithium extraction on an engineering macroscale.

[0120] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses LMO-Al-F co-doped lithium ion sieve active material, which improves the structural stability of the active material and the lithium ion intercalation-deintercalation cycle performance, providing a stable electrode basis for continuous lithium extraction.

[0121] (2) The present invention uses hot pressing process to prepare dense membrane electrode, which effectively reduces the porosity of membrane electrode, improves the mechanical stability of membrane electrode, reduces non-selective ion leakage, and is conducive to improving continuous operation life.

[0122] (3) The present invention constructs PEI and SDS functional interfaces on both sides of the membrane electrode to form a hot-pressed Janus membrane electrode with interface anisotropy, which helps to improve the interface environment on both sides of the membrane electrode and improve the directional migration ability and interface stability of lithium ions.

[0123] (4) The present invention constructs a three-electrode four-channel continuous electrochemical ion pump lithium extraction system. The first electrolyte channel and the second electrolyte channel share the terminal electrolyte circulation system. Electrochemical reactions occur continuously on both sides of the terminal electrode to maintain electron transfer and charge balance, so as to realize the continuous and stable operation of the entire system.

[0124] (5) The present invention adopts a dual working loop cycle switching control strategy, which enables the hot-pressed Janus membrane electrode to automatically switch between lithium ion adsorption and desorption states without disassembly, thereby achieving continuous adsorption, continuous desorption and continuous enrichment, and improving the system's automation level and continuous operation capability.

[0125] (6) Examples show that, under the preferred conditions of a working current of 1.5 mA, a maximum working voltage of 2.0 V, a flow rate of 3 mL / min, and an adsorption / desorption time of 30 s / 15 s, the system of the present invention can operate stably and continuously for about 660 min, and the Li ion receiving solution contains Li + The concentration continued to increase, while Mg 2+ The concentration remained at a low level throughout, verifying that the invention has good continuous operation stability and lithium-ion selective migration capability.

[0126] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A Janus film electrode, characterized in that, It includes a current collector, an active layer disposed on both sides of the current collector, a first functional interface layer disposed on the surface of one active layer, and a second functional interface layer disposed on the surface of the other active layer. The first functional interface layer enables the reversible insertion of metal ions, and the second functional interface layer enables the extraction of metal ions. The material of the first functional interface layer is selected from polyethyleneimine; The material of the second functional interface layer is selected from sodium dodecyl sulfate; The active layer is made of electrode active materials with reversible lithium insertion and delithiation capabilities, conductive agents, and binders.

2. The Janus film electrode according to claim 1, characterized in that, The material of the current collector is selected from at least one of titanium mesh, nickel mesh, and stainless steel mesh.

3. The Janus film electrode according to claim 2, characterized in that, The electrode active material is selected from one or two of lithium manganese oxide and aluminum-fluorine co-doped lithium manganese oxide; The conductive agent is selected from conductive carbon black; The adhesive is selected from polyvinylidene fluoride; The mass ratio of the electrode active material, conductive agent, and binder is 8:1:1; The thickness of the active layer is 50~300μm; The thickness of the current collector is 10~200μm; The thickness of the first functional interface layer is 30~40μm; The thickness of the second functional interface layer is 15~25μm.

4. A method for constructing a Janus film electrode as described in any one of claims 1 to 3, characterized in that, Includes the following steps: The active layer materials are mixed and then an organic solvent is added to prepare an active layer slurry; The active layer slurry is coated onto the two surfaces of the current collector, and then hot-pressed to obtain the initial membrane electrode. One side of the active layer surface of the initial membrane electrode is immersed in a polyethyleneimine solution to construct a first functional interface layer, and the other side of the active layer surface is immersed in a sodium dodecyl sulfate solution to construct a second functional interface layer, thus obtaining the Janus membrane electrode.

5. The construction method according to claim 4, characterized in that, The hot pressing temperature is 110~150℃, the hot pressing pressure is 5~20MPa, and the hot pressing time is 1~20min; The polyethyleneimine solution contains 1 wt% polyethyleneimine. The sodium dodecyl sulfate solution contains 0.5 wt% sodium dodecyl sulfate.

6. A continuous electrochemical lithium extraction system, characterized in that, It includes a first terminal electrode, a first electrolyte flow chamber, a first anion exchange membrane, a raw liquid flow chamber, a Janus membrane electrode as described in any one of claims 1 to 3, a lithium adsorbent flow chamber, a second anion exchange membrane, a second electrolyte flow chamber, and a second terminal electrode, which are stacked sequentially. The first functional interface layer of the Janus membrane electrode is located on one side of the original liquid flow chamber, and the second functional interface layer is located on one side of the lithium adsorption liquid flow chamber. By adding electrolyte to the first electrolyte flow chamber, lithium-containing stock solution to the stock solution flow chamber, and lithium-ion receiving solution to the lithium absorption solution flow chamber, and using the first terminal electrode as the anode and the Janus membrane electrode as the cathode, lithium ions in the lithium-containing stock solution migrate to the Janus membrane electrode, achieving lithium ion intercalation. Then, by adding electrolyte to the second electrolyte flow chamber, and using the Janus membrane electrode as the anode and the second terminal electrode as the cathode, lithium ions intercalated in the Janus membrane electrode migrate to the lithium-ion receiving solution, achieving lithium ion deintercalation, thereby achieving lithium extraction from the lithium-containing stock solution to be treated.

7. The continuous electrochemical lithium extraction system according to claim 6, characterized in that, The first electrolyte flow chamber and the second electrolyte flow chamber are connected through the first electrolyte flow channel, and the first electrolyte flow chamber and the second electrolyte flow chamber are connected to the electrolyte storage tank through the second electrolyte flow channel, so that the electrolyte circulates between the first electrolyte flow chamber, the second electrolyte flow chamber and the electrolyte storage tank. The raw liquid flow chamber is connected to the raw liquid storage tank through the raw liquid flow channel, so that the lithium-containing raw liquid circulates between the raw liquid flow chamber and the raw liquid storage tank. The lithium-absorbing liquid flow chamber is connected to the lithium-absorbing liquid storage tank through the lithium-absorbing liquid flow channel, so that the lithium-ion receiving liquid circulates between the lithium-absorbing liquid flow chamber and the lithium-absorbing liquid storage tank.

8. A continuous electrochemical lithium extraction method based on the continuous electrochemical lithium extraction system of claim 6 or claim 7, characterized in that, Includes the following steps: Electrolyte is added to the first electrolyte flow chamber, lithium-containing stock solution to be treated is added to the stock solution flow chamber, and lithium-ion receiving solution is added to the lithium absorption solution flow chamber, so that the first terminal electrode is in contact with the electrolyte and the Janus membrane electrode is in contact with the lithium-containing stock solution. Using the first terminal electrode as the anode and the Janus membrane electrode as the cathode, energize the first terminal electrode and the Janus membrane electrode to form a first working circuit, so that lithium ions in the lithium-containing raw solution migrate to the Janus membrane electrode and realize the intercalation of lithium ions. Electrolyte is added to the second electrolyte flow chamber so that the second terminal electrode comes into contact with the electrolyte; The first working circuit is disconnected, and the Janus membrane electrode is used as the anode and the second terminal electrode is used as the cathode. The Janus membrane electrode and the second terminal electrode are energized to form the second working circuit, so that the lithium ions embedded in the Janus membrane electrode migrate to the lithium ion receiving liquid, thereby realizing the deintercalation of lithium ions and thus realizing the extraction of lithium from the lithium-containing raw solution. The second working circuit is disconnected and the first working circuit is closed to achieve continuous electrochemical lithium extraction.

9. The continuous electrochemical lithium extraction method according to claim 8, characterized in that, The electrolyte comprises sodium sulfate solution and / or potassium sulfate solution; The lithium-containing stock solution is an aqueous solution containing lithium and magnesium, and the aqueous solution containing lithium and magnesium includes Li. + and Mg 2+ Li + The concentration is 10~1000 mg / L, Mg 2+ The concentration is 0.1~100g / L, Mg 2+ With Li + The mass concentration ratio is 1~100; The initial component of the lithium ion receiving liquid is a sodium sulfate solution; The operating current of the first and second working circuits is 1~2mA, and the upper limit of the operating voltage is 2V; The working time of the first working circuit is 10~120s, and the working time of the second working circuit is 5~60s.

10. The continuous electrochemical lithium extraction method according to claim 9, characterized in that, The aqueous solution containing lithium and magnesium contains Li + The concentration is 50~500 mg / L, Mg 2+ The concentration is 0.5~10 g / L, Mg 2+ With Li + The mass concentration ratio is 5~50; The aqueous solution containing lithium and magnesium also includes Na. + K + and Ca 2+ At least one cation in it; The aqueous solution containing lithium and magnesium also includes Cl. - and SO4 2- One or two anions in it.

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