Electrode systems, preparation methods and applications for electrochemical lithium extraction

Abstract

This disclosure presents an electrode system, preparation method, and application for electrochemical lithium extraction. The obtained electrode system uses symmetrical electrodes to simultaneously prepare lithium-rich and lithium-poor electrodes, with the lithium-rich electrode having the same amount of lithium insertion and the lithium-poor electrode having the same amount of lithium removal. This greatly reduces the problem of mismatch between lithium insertion and removal capacity caused by the use of asymmetrical electrodes in existing "rocking chair" type electrochemical lithium extraction electrode systems. The electrochemical lithium extraction electrode system only requires the synthesis of one material and the preparation of one electrode sheet, reducing the electrode preparation process and lowering costs.

Description

Technical Field

[0001] This disclosure relates to the field of lithium extraction technology from salt lakes, and more specifically, to electrode systems, preparation methods and applications for electrochemical lithium extraction. Background Technology

[0002] In recent years, with the vigorous development of the new energy vehicle industry, the demand for upstream lithium resources has increased dramatically. Some lithium resources exist in salt lakes at high altitudes, and some of these salt lakes have poor resource endowments and high magnesium content, such as the high lithium-magnesium ratio in salt lakes in high-altitude areas of China. This high ratio limits the industrial application of lithium salts obtained from their processing. To alleviate the current upstream raw material supply problem and ensure the supply security of the new energy industry chain, how to effectively extract lithium from salt lakes has become a current research hotspot.

[0003] Currently, lithium extraction methods from salt lakes, such as evaporation precipitation, ion sieve adsorption, electrodialysis, and extraction, all have different problems. For example, evaporation precipitation is time-consuming, electrodialysis is costly, and adsorption and extraction methods use large amounts of acid washing agents or organic solvents, which can have adverse effects on the ecological environment.

[0004] Electrochemical lithium extraction, characterized by low energy consumption and high selectivity, is a newly emerging method for lithium extraction. It can be mainly divided into two systems: First, ion-sieve adsorbents such as LiFePO4 and λ-MnO2 are used with Pt, Ag, Zn, and AC (activated carbon) to form the working and counter electrodes, respectively, for lithium extraction. This system requires stepwise lithium insertion and extraction. Second, it uses a "rocking chair" electrode system, such as LiFePO4||FePO4 or LiMn2O4||Li 1-x Mn₂O₄. This system operates at low voltage with low energy consumption, but the lithium extraction capacity decreases significantly with increasing cycle number, and also declines at low temperatures. Therefore, optimizing the existing system process and developing an electrochemical lithium extraction method with high cycle life is of great significance. Summary of the Invention

[0005] The purpose of this disclosure is to provide an electrode system, preparation method and application for electrochemical lithium extraction, avoiding the problem of mismatch between lithium insertion capacity and deintercalation capacity caused by the use of asymmetric electrodes in the existing "rocking chair" type electrochemical lithium extraction electrode system.

[0006] This disclosure is implemented as follows:

[0007] In a first aspect, this disclosure provides a method for preparing an electrode system for electrochemical lithium extraction, comprising inserting two electrodes of the symmetrical electrode into a lithium salt solution and connecting them to the positive and negative terminals of a power source, respectively; inserting lithium into the electrode connected to the negative terminal of the power source to obtain a lithium-rich electrode; and delithiating the electrode connected to the positive terminal of the power source to obtain a lithium-poor electrode, wherein the molar amount of lithium inserted in the lithium-rich electrode is equal to the molar amount of lithium ions extracted from the lithium-poor electrode.

[0008] In some embodiments, the symmetrical electrode comprises two electrodes with identical electrode active material structures and compositions, wherein the electrode active material is an electrode active material for electrochemical lithium extraction.

[0009] In some embodiments, the symmetrical electrode is Li x FePO4||Li x FePO4, Li x FePO4@λ-MnO2||Li x FePO4@λ-MnO2, Li x Mn₂O₄||Li x Mn2O4, Li x V2O5||Li x V2O5, Li x NiO2||Li x NiO2, Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 ||Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of the following, wherein 0.05 ≤ x ≤ 0.45 or 0.55 ≤ x ≤ 0.95; wherein, the Li x FePO4@λ-MnO2 includes a composition of Li x The FePO4 core and the coating layer on the core, which is composed of λ-MnO2.

[0010] In some embodiments, the electrode is obtained by coating a slurry containing the powder of the electrode active material, a conductive agent, a binder, and an organic solvent onto a current collector and then drying it.

[0011] In some embodiments, the conductive agent is at least one of activated carbon, carbon nanotubes, conductive carbon black, and graphene, and the mass ratio of the conductive agent to the powder of the electrode active material is 1:5 to 1:15.

[0012] In some embodiments, the binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, and polystyrene-butadiene copolymer, and the mass ratio of the binder to the powder of the electrode active material is 1:10 to 1:40.

[0013] In some embodiments, the organic solvent is at least one of NMP, ethanol, and distilled water, and the mass ratio of the organic solvent to the powder of the electrode active material is 1:1 to 5:1.

[0014] In some embodiments, a foaming agent is also included, wherein the foaming agent is at least one selected from NaCl, KCl, and NH3HCO3, and the mass fraction of the foaming agent in the slurry is 0.025 to 0.5.

[0015] In some embodiments, the two electrodes are delithiated and lithium-intercalated under constant current conditions to a voltage of 0.2V to 1.0V.

[0016] In some embodiments, the two electrodes are subjected to delithiation and lithium insertion under constant voltage conditions until the current is 0.1 mA to 5 mA.

[0017] In some embodiments, the lithium ion concentration in the lithium salt solution is 0.2 mol / L to 1 mol / L, and the lithium salt solution is a lithium chloride or lithium sulfate solution.

[0018] In some embodiments, the temperature at which lithium is embedded in the lithium-rich electrode and extracted from the lithium-poor electrode is 5°C to 50°C.

[0019] Secondly, this disclosure provides an electrode system for electrochemical lithium extraction obtained by the method described in any of the foregoing embodiments.

[0020] In some embodiments, the electrode system for electrochemical lithium extraction is Li x+y FePO4||Li x-y FePO4, Li x+ y FePO4@λ-MnO2||Li x-y FePO4@λ-MnO2, Li x+y Mn₂O₄||Li x-y Mn2O4, Li x+y V2O5||Li x-y V2O5, Li x+y NiO2||Li x-y NiO2, Li x+y Ni 1 / 3 Co 1 / 3 Mn 1 / 3 ||Li x-y Ni 1 / 3 Co1 / 3 Mn 1 / 3 At least one of the following, wherein 0.05≤x≤0.45 or 0.55≤x≤0.95, xy>0, and x+y<1.

[0021] Thirdly, this disclosure provides an electrochemical lithium extraction apparatus including the electrode system described in the foregoing embodiments, comprising an anode chamber for holding a recovery liquid, a cathode chamber for holding a lithium extraction solution, and a diaphragm separating the cathode chamber and the anode chamber; the lithium-rich electrode in the electrochemical lithium extraction electrode system is inserted into the recovery liquid and connected to the positive terminal of a power supply, and the lithium-poor electrode in the electrochemical lithium extraction electrode system is inserted into the lithium extraction solution and connected to the negative terminal of a power supply.

[0022] In some embodiments, the recovered solution is a NaCl solution with a concentration of 0.1 mol / L to 1 mol / L.

[0023] In some embodiments, the lithium extraction solution includes LiCl, NaCl, MgCl2 and CaCl2, wherein the concentration of LiCl is 0.03 g / L to 2 g / L, the concentration of NaCl is 30 g / L to 100 g / L, the concentration of MgCl2 is 10 g / L to 80 g / L, and the concentration of CaCl2 is 5 g / L to 40 g / L.

[0024] In some embodiments, the lithium extraction solution is brine.

[0025] In some embodiments, the membrane is an anion exchange membrane.

[0026] Fourthly, this disclosure provides an electrochemical lithium extraction method, comprising:

[0027] When the power supply of the electrochemical lithium extraction device described in any of the preceding embodiments is turned on, the lithium-rich electrode is delithiated and the lithium-poor electrode is lithium-intercalated to a specified degree, the positions of the lithium-rich electrode and the lithium-poor electrode are exchanged so that the lithium-rich electrode after delithiation is inserted into the lithium extraction solution and connected to the negative terminal of the power supply, and the lithium-poor electrode after lithium intercalation is inserted into the recovery liquid and connected to the positive terminal of the power supply.

[0028] Repeat the above steps to transfer lithium from the lithium extraction solution to the recovery solution, thereby achieving lithium extraction.

[0029] In some embodiments, after the electrochemical lithium extraction device operates at a constant current to the cutoff potential or at a constant voltage to the cutoff current, the positions of the lithium-rich electrode and the lithium-poor electrode are exchanged.

[0030] In some embodiments, the electrochemical lithium extraction device operates at a constant current until the voltage reaches 0.2V to 0.8V, at which point the positions of the two electrodes are exchanged.

[0031] In some embodiments, after the electrochemical lithium extraction device operates at a constant voltage until the current is 0.1mA to 5mA, the positions of the two electrodes are exchanged.

[0032] In this embodiment, by setting a constant current cutoff voltage and limiting the lithium content in the symmetrical electrode, the "complete de-intercalation" or "complete insertion" of lithium in the electrode can be avoided. The voltage in this embodiment can be any value between 0V and 1V, depending on the selection of the current collector material.

[0033] In some embodiments, the temperature for delithiation of the lithium-rich electrode and lithium insertion of the lithium-poor electrode is 5°C to 50°C.

[0034] This disclosure has the following beneficial effects:

[0035] The electrode system obtained by the method described in this disclosure uses symmetrical electrodes to simultaneously prepare lithium-rich and lithium-poor electrodes, and the lithium-rich electrode has the same amount of lithium insertion and the lithium-poor electrode has the same amount of lithium removal. This greatly reduces the problem of mismatch between lithium insertion and removal capacity caused by the use of asymmetrical electrodes in the existing "rocking chair" type electrochemical lithium extraction electrode system, thereby improving the stability of the system.

[0036] Existing "rocking chair" type electrochemical lithium extraction electrode systems require the synthesis of two electrode active materials and the preparation of two types of electrode sheets. The electrode system provided in this embodiment only requires the synthesis of one material and the preparation of one type of electrode sheet, which reduces the process flow of electrode preparation and lowers costs. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the preparation of lithium-rich and lithium-poor electrodes in Examples 1 and 2 of this disclosure, as well as the experimental apparatus and principle diagram for electrochemical lithium extraction.

[0039] Figure 2 The XRD pattern of the lithium-poor electrode prepared in Example 1 of this disclosure;

[0040] Figure 3 The diagram shows the lithium extraction capacity and cycle life of the electrodes in Embodiment 1 and Comparative Example 1 of this disclosure.

[0041] Figure 4 The diagram shows the lithium extraction capacity cycle life of the electrodes in Embodiment 2 and Comparative Example 2 of this disclosure. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0043] This disclosure provides a method for preparing an electrode system for electrochemical lithium extraction, comprising inserting two electrodes of the symmetrical electrode into a lithium salt solution and connecting them to the positive and negative terminals of a power source, respectively; inserting lithium into the electrode connected to the negative terminal of the power source to obtain a lithium-rich electrode; and delithiating the electrode connected to the positive terminal of the power source to obtain a lithium-poor electrode, wherein the molar amount of lithium inserted in the lithium-rich electrode is equal to the molar amount of lithium ions extracted from the lithium-poor electrode.

[0044] In this embodiment, symmetrical electrodes are inserted into a lithium salt solution and connected to a power source, so that one electrode is lithium-intercalated and the other electrode is delithiated. Since symmetrical electrodes are used to prepare lithium-rich and delithiated electrodes, the amount of lithium intercalated at the cathode is equal to the amount of lithium delithiated at the anode.

[0045] The electrode system obtained by the method described in this embodiment uses a symmetrical electrode to simultaneously prepare lithium-rich and lithium-poor electrodes through lithium insertion and delithiation. The lithium insertion amount of the lithium-rich electrode and the lithium delithiation amount of the lithium-poor electrode are equal, which greatly reduces the problem of mismatch between lithium insertion capacity and delithiation capacity caused by the use of asymmetrical electrodes in the existing "rocking chair" type electrochemical lithium extraction electrode system, thereby improving the stability of the system.

[0046] Existing "rocking chair" type electrochemical lithium extraction electrode systems require the synthesis of two electrode active materials and the preparation of two types of electrode sheets. The symmetrical electrode system provided in this embodiment only requires the synthesis of one material and the preparation of one type of electrode sheet, which reduces the process flow of electrode preparation and lowers costs.

[0047] In some embodiments, the symmetrical electrode comprises two electrodes with identical electrode active material structures and compositions. The electrode active material is an electrode active material used for electrochemical lithium extraction. Specifically, the symmetrical electrode may be Li... x FePO4||Li x FePO4, Li x FePO4@λ-MnO2||Li x FePO4@λ-MnO2, Li x Mn₂O₄||Li x Mn2O4, Li x V2O5||Li x V2O5, Li x NiO2||Li xNiO2, Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 ||Li x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of the following, wherein 0.05 ≤ x ≤ 0.45 or 0.55 ≤ x ≤ 0.95; wherein, the Li x FePO4@λ-MnO2 includes a composition of Li x The FePO4 core and the coating layer on the core, which is composed of λ-MnO2.

[0048] In this embodiment, by limiting the lithium content in the electrode active material of the symmetrical electrode, the composition of the electrochemical lithium extraction electrode system prepared from it is adjusted. Combined with the control of the molar amount of lithium embedded in the lithium-rich electrode and lithium ions extracted from the lithium-poor electrode, "complete deintercalation" or "complete insertion" of lithium in the electrode can be avoided. Although this sacrifices some of the amount of lithium that can be intercalated or extracted, avoiding "complete deintercalation" or "complete insertion" of lithium effectively reduces the damage to the electrode structure during lithium extraction, thereby improving cycle stability. This results in a significantly lower lithium extraction capacity reduction after multiple cycles compared to existing "rocking chair" electrochemical lithium extraction electrode systems, effectively mitigating the capacity decay problem of the electrode active material even at a low temperature of 5°C. Furthermore, the application of the lithium-rich and lithium-poor electrode system based on the symmetrical electrode to electrochemical lithium extraction also helps improve lithium extraction efficiency. Specifically, compared to 0.05≤x≤0.45, 0.55≤x≤0.95 is more conducive to improving the stability of the electrode system.

[0049] In some embodiments, the electrode is obtained by coating a slurry containing the powder of the electrode active material, a conductive agent, a binder, and an organic solvent onto a current collector and then drying it. Specifically, the conductive agent can be at least one of activated carbon, carbon nanotubes, conductive carbon black, and graphene, and the mass ratio of the conductive agent to the powder of the electrode active material is 1:5 to 1:15; the binder can be at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, and polystyrene-butadiene copolymer, and the mass ratio of the binder to the powder of the electrode active material is 1:10 to 1:40; the organic solvent can be at least one of NMP, ethanol, and distilled water, and the mass ratio of the organic solvent to the powder of the electrode active material is 1:1 to 5:1; a foaming agent is also included, which can be at least one of NaCl, KCl, and NH3HCO3, and the mass fraction of the foaming agent in the slurry is 0.025 to 0.5.

[0050] In some embodiments, the two electrodes are delithiated and lithium-intercalated under constant current conditions to a voltage of 0.2V to 1.0V. Specifically, the voltage can be any value between 0.2V, 0.4V, 0.6V, 0.7V, 1.0V, or 0.2V to 1.0V.

[0051] In this embodiment, by setting a constant current cutoff voltage and limiting the lithium content in the symmetrical electrode, the "complete delithiation" or "complete insertion" of lithium in the electrode can be avoided. In this embodiment, the current density can be any value between 0.1C, 0.2C, 0.5C, or 0.1C to 0.8C. The current density mainly affects the rate of lithium delithiation and insertion, and has little impact on cycle stability and capacity within a certain range. However, if the current density is too high, it will reduce the cycle stability and capacity of the electrode system to a certain extent.

[0052] In some embodiments, the two electrodes are delithiated and lithium-intercalated under constant voltage conditions to a current of 0.1mA to 5mA. Specifically, the current can be any value between 0.1mA, 0.5mA, 1mA, 2mA, 3mA, 4mA, 5mA, or 0.1mA to 5mA.

[0053] In this embodiment, by setting a constant current cutoff voltage and limiting the lithium content in the symmetrical electrode, complete lithium desorption or insertion in the electrode can be avoided. The voltage in this embodiment can be any value between approximately 0V and 1V, depending on the selection of the current collector material. The voltage primarily affects the rate of lithium desorption and insertion; within a certain range, it has little impact on cycle stability and capacity. However, if the voltage is too high, it will reduce the cycle stability and capacity of the electrode system to some extent.

[0054] In some embodiments, the lithium ion concentration in the lithium salt solution is 0.2 mol / L to 1 mol / L, specifically, it can be any value between 0.2 mol / L, 0.4 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, or 0.2 mol / L to 1 mol / L. The lithium salt solution is a lithium chloride or lithium sulfate solution. Typically, salt lakes contain a large amount of chloride ions; therefore, lithium chloride is usually used when preparing the electrode system for electrochemical lithium extraction to match the lithium extraction solution. For salt lakes containing a large amount of sulfate ions, lithium sulfate can also be used.

[0055] In some embodiments, the temperature at which lithium is inserted into the lithium-rich electrode and extracted from the lithium-poor electrode is 5°C to 50°C. Specifically, it can be any value between 10°C, 20°C, 30°C, 40°C, 50°C, or 5°C to 50°C. Good performance can also be achieved at lower temperatures, such as 5°C.

[0056] Secondly, this disclosure provides an electrode system for electrochemical lithium extraction obtained by the method described in any of the foregoing embodiments.

[0057] Thirdly, this disclosure provides an electrochemical lithium extraction electrode system obtained according to the method described in the foregoing embodiments, wherein the electrochemical lithium extraction electrode system is Li x+y FePO4||Li x-y FePO4, Li x+y FePO4@λ-MnO2||Li x-y FePO4@λ-MnO2, Li x+y Mn₂O₄||Li x-y Mn2O4, Li x+y V2O5||Li x-y V2O5, Li x+y NiO2||Li x-y NiO2, Li x+y Ni 1 / 3 Co 1 / 3Mn 1 / 3 ||Li x-y Ni 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of the following, wherein 0.05≤x≤0.45 or 0.55≤x≤0.95, xy>0, and x+y<1.

[0058] In some embodiments, the system includes an anode chamber for holding the recovered liquid, a cathode chamber for holding the lithium extraction solution, and a diaphragm separating the cathode chamber and the anode chamber; the lithium-rich electrode in the electrochemical lithium extraction electrode system is inserted into the recovered liquid and connected to the positive terminal of the power supply, and the lithium-poor electrode in the electrochemical lithium extraction electrode system is inserted into the lithium extraction solution and connected to the negative terminal of the power supply.

[0059] In some embodiments, the recovered solution is a NaCl solution with a concentration of 0.1 mol / L to 1 mol / L. Specifically, it can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 4 mol / L, 6 mol / L, 8 mol / L, 1 mol / L, or any value between 0.1 mol / L and 1 mol / L.

[0060] In some embodiments, the lithium extraction solution includes LiCl, NaCl, MgCl2, and CaCl2. The concentration of LiCl is 0.03 g / L to 2 g / L, the concentration of NaCl is 30 g / L to 100 g / L, the concentration of MgCl2 is 10 g / L to 80 g / L, and the concentration of CaCl2 is 5 g / L to 40 g / L. Specifically, the lithium extraction solution may include 0.03 g / L LiCl, 100 g / L NaCl, 80 g / L MgCl2, and 40 g / L CaCl2, or other components. LiCl, NaCl, MgCl2, and CaCl2 are the main components of brine, and the purpose of the lithium extraction solution in this embodiment is to simulate the composition of brine.

[0061] In some embodiments, the lithium extraction solution is brine.

[0062] In some embodiments, the membrane is an anion exchange membrane from Asahi Kasei Corporation of Japan.

[0063] Fourthly, this disclosure provides an electrochemical lithium extraction method, comprising:

[0064] When the power supply of the electrochemical lithium extraction device described in any of the preceding embodiments is turned on, the lithium-rich electrode is delithiated and the lithium-poor electrode is lithium-intercalated to a specified degree, the positions of the lithium-rich electrode and the lithium-poor electrode are exchanged so that the lithium-rich electrode after delithiation is inserted into the lithium extraction solution and connected to the negative terminal of the power supply, and the lithium-poor electrode after lithium intercalation is inserted into the recovery liquid and connected to the positive terminal of the power supply.

[0065] Repeat the above steps to transfer lithium from the lithium extraction solution to the recovery solution, thereby achieving lithium extraction.

[0066] In some embodiments, after the electrochemical lithium extraction device operates at a constant current to the cutoff potential or at a constant voltage to the cutoff current, the positions of the lithium-rich electrode and the lithium-poor electrode are exchanged.

[0067] In some embodiments, after the electrochemical lithium extraction device operates at a constant current to a voltage of 0.2V to 0.8V, the positions of the two electrodes are exchanged. Specifically, the cutoff voltage can be any value between 0.2V, 0.4V, 0.6V, 0.8V, or 0.2V to 0.8V.

[0068] In this embodiment, by setting a constant current cutoff voltage, the complete de-intercalation or complete insertion of lithium in the electrode can be avoided. Typically, to maximize the removal of lithium during the lithium extraction process, the selected cutoff voltage is slightly lower than the cutoff voltage used in preparing the electrode system for electrochemical lithium extraction. In this embodiment, the current density can be any value between 0.1C, 0.2C, 0.5C, or 0.1C to 0.8C.

[0069] In some embodiments, after the electrochemical lithium extraction device operates at a constant voltage until the current is 0.1mA to 5mA, the positions of the two electrodes are exchanged. Specifically, the cutoff current can be any value between 0.1mA, 0.5mA, 1mA, 2mA, 3mA, 4mA, 5mA, or 0.1mA to 5mA.

[0070] In this embodiment, by setting a constant current cutoff voltage and limiting the lithium content in the symmetrical electrode, the "complete de-intercalation" or "complete insertion" of lithium in the electrode can be avoided. The voltage in this embodiment can be any value between 0V and 1V, depending on the selection of the current collector material.

[0071] In some embodiments, the temperature for delithiation of the lithium-rich electrode and lithium insertion of the lithium-poor electrode is 5°C to 50°C. Specifically, it can be any value between 5°C, 10°C, 20°C, 30°C, 40°C, 50°C, or 5°C to 50°C.

[0072] Normally, the electrode's cycling structure is more easily damaged at low temperatures, making it more difficult to suppress electrode capacity decay at low temperatures. Compared with the existing "rocking chair" type electrochemical lithium extraction electrode system, the electrode system in this embodiment can still alleviate the problem of electrode capacity decay at 5°C.

[0073] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0074] Example 1

[0075] This embodiment provides an electrochemical lithium extraction method, including the following steps:

[0076] (1) Preparation of symmetrical electrodes:

[0077] Li 0.75 FePO4@λ-MnO2 powder (λ-MnO2 coating weight 2wt%), conductive activated carbon, binder polyvinylidene fluoride, and foaming agent NH4HCO3 are ground evenly in a mass ratio of 7:1:1:1. Then, an appropriate amount of NMP is added and the mixture is ground to a slurry consistency. This slurry is then coated onto a titanium mesh, with a coating area of ​​2×2 cm. 2 The coating weight is 2-4 mg, and it is dried in an oven at 60℃ to obtain symmetrical electrode sheets.

[0078] (2) Preparation of lithium-rich and lithium-poor electrodes:

[0079] Li 0.75 FePO4@λ-MnO2||Li 0.75 The FePO4@λ-MnO2 electrodes are connected to the positive and negative terminals of the power supply, respectively, and placed in the electrolytic cell as follows: Figure 1As shown, a 0.5 mol / L LiCl lithium-containing solution was prepared, and electrochemical lithium intercalation / deintercalation was performed at a constant voltage of 0.5 V until the current reached 2 mA, simultaneously obtaining a lithium-rich electrode and a lithium-poor electrode. The resulting lithium-poor electrode Li 0.75 The XRD results of FePO4@λ-MnO2 are as follows: Figure 2 As shown in the figure, the diffraction peaks of the obtained electrode correspond to those of LiFePO4 and FePO4. The coated λ-MnO2, due to its low content, is not present in the phase. These results indicate that a lithium-poor electrode, LiFePO4, was successfully prepared by electrochemical method. 0.75 FePO4@λ-MnO2.

[0080] (3) Electrochemical lithium extraction:

[0081] The experiment was conducted in an electrolytic cell at 25°C. The electrolytic cell was separated by an anion exchange membrane. The recovery solution used was a 0.5 mol / L NaCl solution, and the lithium extraction solution was a mixed solution with concentrations of LiCl, NaCl, MgCl2, and CaCl2 of 0.6 g / L, 100 g / L, 60 g / L, and 20 g / L, respectively.

[0082] The lithium-rich electrode and the lithium-lean electrode are connected to the positive and negative terminals of the power supply, respectively, and placed in an electrolytic cell. The lithium-rich electrode is placed in the recovery solution, and the lithium-lean electrode is placed in the lithium extraction solution. A constant current is applied at a current density of 0.1C until the cutoff voltage reaches 0.35V. At this point, lithium from the lithium-rich electrode is released into the recovery solution, becoming the lithium-lean electrode, while lithium from the lithium extraction solution is inserted into the lithium-lean electrode, transforming the lithium-lean electrode into a lithium-rich electrode.

[0083] Remove the two electrodes and rinse them with distilled water. Exchange the positions of the two electrodes and maintain a constant current at the same current density until the same cutoff voltage is reached.

[0084] Repeating the above electrode exchange steps, after five cycles of lithium insertion / extraction reactions, the lithium extraction capacity was 23.72 mg / g, and after 100 cycles, the lithium extraction capacity remained above 90%. The results are shown in [Figure number missing]. Figure 3 .

[0085] Comparative Example 1

[0086] This comparative example provides an electrochemical lithium extraction method, which differs from Example 1 in that the electrode system in Example 1 is replaced with a LiFePO4||FePO4 system, while other conditions remain the same. The method includes the following steps:

[0087] This comparative example uses the LiFePO4@λ-MnO2||FePO4@λ-MnO2 system. The prepared LiFePO4@λ-MnO2 and FePO4@λ-MnO2 powders were ground uniformly with electrode powder, conductive activated carbon, binder polyvinylidene fluoride, and foaming agent NH3HCO3 in a mass ratio of 7:1:1:1. An appropriate amount of NMP was added, and the mixture was ground to a slurry consistency. This slurry was then coated onto a titanium mesh, with a coating area of ​​2×2 cm. 2 The coating weight was 2-4 mg, and the coatings were dried in an oven at 60℃ to obtain two types of electrodes: LiFePO4 and FePO4.

[0088] In the electrolytic cell, at 25°C and a current density of 0.1C, a constant current was maintained until the cutoff voltage reached 0.35V. The two electrodes were then removed and rinsed with distilled water. Their positions were then interchanged, and the electrodes were maintained at the same current density until the same cutoff voltage was reached.

[0089] Repeating the above electrode exchange steps, after five cycles of lithium insertion / extraction reactions, the lithium extraction capacity was 32.64 mg / g. After 50 cycles, the lithium extraction capacity only remained at 50% of the original value. See the results below. Figure 3 Compared with Example 1, although the initial lithium extraction capacity was relatively high, the long-term cycle stability was poor.

[0090] Example 2

[0091] This embodiment provides an electrochemical lithium extraction method, including the following steps:

[0092] (1) Preparation of symmetrical electrodes:

[0093] Li 0.75 FePO4 powder, conductive activated carbon, binder polyvinylidene fluoride, and foaming agent KCl are ground evenly in a mass ratio of 7:1:1:1. An appropriate amount of NMP is added and the mixture is ground to a slurry consistency. This slurry is then coated onto a titanium mesh, covering an area of ​​2×2 cm. 2 The coating weight is 2-4 mg, and it is dried in an oven at 60℃ to obtain symmetrical electrode sheets.

[0094] (2) Preparation of lithium-rich and lithium-poor electrodes:

[0095] Li 0.75 FePO4||Li 0.75 The FePO4 electrode is connected to the positive and negative terminals of the power supply, respectively, and placed in an electrolytic cell. A lithium-containing LiCl solution with a concentration of 0.5 mol / L is prepared, and electrochemical lithium intercalation and deintercalation are performed at a constant voltage of 0.5 V until the current reaches 2 mA, thus obtaining both lithium-rich and lithium-poor electrodes.

[0096] (3) Electrochemical lithium extraction:

[0097] The experiment was conducted in an electrolytic cell at 15°C. The electrolytic cell was separated by an anion exchange membrane. The recovery solution used was a 0.5 mol / L NaCl solution, and the lithium extraction solution was a mixed solution with LiCl, NaCl, MgCl2, and CaCl2 concentrations of 0.6 g / L, 100 g / L, 60 g / L, and 20 g / L, respectively.

[0098] The lithium-rich electrode and the lithium-lean electrode are connected to the positive and negative terminals of the power supply, respectively, and placed in an electrolytic cell. The lithium-rich electrode is placed in the recovery solution, and the lithium-lean electrode is placed in the lithium extraction solution. The voltage is kept constant at 0.5V until the cutoff current is 2mA. At this point, lithium from the lithium-rich electrode is released into the recovery solution, becoming the lithium-lean electrode, while lithium from the lithium extraction solution is inserted into the lithium-lean electrode, transforming the lithium-lean electrode into a lithium-rich electrode.

[0099] Remove the two electrodes and rinse them with distilled water. Exchange the positions of the two electrodes and maintain a constant current at the same current density until the same cutoff voltage is reached.

[0100] Repeating the above electrode exchange steps, after five cycles of lithium insertion / extraction reactions, the lithium extraction capacity was 21.15 mg / g, and after 100 cycles, the lithium extraction capacity remained above 85%. The cycling results are shown below. Figure 4 .

[0101] Comparative Example 2

[0102] This comparative example provides an electrochemical lithium extraction method, which differs from Example 2 in that the electrode system in Example 2 is replaced with a LiFePO4||FePO4 system, while other conditions remain the same. The method includes the following steps:

[0103] This comparative example uses the LiFePO4||FePO4 system. Two powders, LiFePO4 and FePO4, were prepared and ground uniformly with electrode powder, conductive activated carbon, binder polyvinylidene fluoride, and foaming agent KCl in a mass ratio of 7:1:1:1. An appropriate amount of NMP was added and the mixture was ground to a slurry consistency. This slurry was then coated onto a titanium mesh, with a coating area of ​​2×2 cm. 2 The coating weight was 2-4 mg, and the coatings were dried in an oven at 60℃ to obtain two types of electrodes: LiFePO4 and FePO4.

[0104] In the electrolytic cell, a constant voltage of 0.5V is maintained at 15°C until the cutoff current reaches 2mA. The two electrodes are then removed and rinsed with distilled water. The positions of the two electrodes are swapped, and a constant current is maintained at the same current density until the same cutoff voltage is reached.

[0105] Repeating the above electrode exchange steps, after five cycles of lithium insertion / extraction reactions, the lithium extraction capacity was 19.35 mg / g. After 50 cycles, the lithium extraction capacity was only 10.20 mg / g. See the results below. Figure 4Compared to Example 2, the initial lithium extraction capacity and long-term cycling stability were both poorer. This indicates that the electrode system used in Example 2 has better stability at low temperatures (15°C) compared to the LiFePO4||FePO4 system.

[0106] Example 3

[0107] The only difference from Example 1 is that the lithium extraction temperature is 5°C.

[0108] In this embodiment, after five lithium insertion / extraction reactions, the lithium extraction capacity of the electrode was 22.45 mg / g, and after 100 cycles, the lithium extraction capacity remained above 80%.

[0109] Comparative Example 3

[0110] The only difference from Comparative Example 1 is that the lithium extraction temperature is 5℃.

[0111] After five cycles of lithium intercalation / deintercalation reaction in this comparative example, the lithium extraction capacity of the electrode was 28.65 mg / g, and after 50 cycles, the lithium extraction capacity remained above 30%.

[0112] Example 4

[0113] The only difference from Example 1 is that the electrode system is replaced with Li. 0.75 Mn₂O₄||Li 0.75 Mn2O4.

[0114] In this embodiment, after five lithium insertion / extraction reactions, the lithium extraction capacity of the electrode was 18.15 mg / g, and after 100 cycles, the lithium extraction capacity remained above 90%.

[0115] Comparative Example 4

[0116] The only difference from Comparative Example 1 is that the electrode system is replaced with LiMn2O4||MnO2.

[0117] After five cycles of lithium intercalation / deintercalation reaction in this comparative example, the lithium extraction capacity of the electrode was 30.22 mg / g, and after 100 cycles, the lithium extraction capacity remained above 60%.

[0118] Industrial applicability

[0119] The electrode system obtained by the method described in this disclosure uses a symmetrical electrode to simultaneously prepare lithium-rich and lithium-poor electrodes through lithium insertion and extraction. The lithium insertion amount of the lithium-rich electrode and the lithium extraction amount of the lithium-poor electrode are equal, which greatly reduces the problem of lithium insertion capacity and extraction capacity mismatch caused by the use of asymmetrical electrodes in the existing "rocking chair" type electrochemical lithium extraction electrode system, thereby improving the stability of the system. The existing "rocking chair" type electrochemical lithium extraction electrode system requires the synthesis of two electrode active materials and the preparation of two electrode sheets. The symmetrical electrode system provided in this embodiment only requires the synthesis of one material and the preparation of one electrode sheet, which reduces the electrode preparation process, lowers the cost, and is more conducive to industrial applications.

Claims

1. A method for preparing an electrode system for electrochemical lithium extraction, characterized in that, The method involves inserting two electrodes of a symmetrical electrode into a lithium salt solution and connecting them to the positive and negative terminals of a power source, respectively. The electrode connected to the negative terminal of the power source is subjected to lithium intercalation to obtain a lithium-rich electrode, and the electrode connected to the positive terminal of the power source is subjected to lithium delithiation to obtain a lithium-poor electrode. The molar amount of lithium intercalated in the lithium-rich electrode is equal to the molar amount of lithium ions delithlated from the lithium-poor electrode. The symmetrical electrode comprises two electrodes with identical electrode active material structures and compositions, wherein the electrode active material is an electrode active material used for electrochemical lithium extraction. The symmetrical electrode is Li x FePO4||Li x FePO4, Li x FePO4@λ-MnO2||Li x FePO4@λ-MnO2, Li x Mn₂O₄||Li x Mn2O4, Li x V2O5||Li x V2O5, Li x NiO2||Li x At least one of NiO2, wherein 0.05 ≤ x ≤ 0.45 or 0.55 ≤ x ≤ 0.95; wherein the Li x FePO4@λ-MnO2 includes a composition of Li x The FePO4 core and the coating layer on the core, which is composed of λ-MnO2.

2. The method for preparing the electrode system for electrochemical lithium extraction according to claim 1, characterized in that, The electrode is obtained by coating a slurry containing the electrode active material powder, conductive agent, binder and organic solvent onto the current collector and then drying it.

3. The method for preparing the electrode system for electrochemical lithium extraction according to claim 2, characterized in that, The conductive agent is at least one of activated carbon, carbon nanotubes, conductive carbon black and graphene, and the mass ratio of the conductive agent to the powder of the electrode active material is 1:5 to 1:

15.

4. The method for preparing the electrode system for electrochemical lithium extraction according to claim 2, characterized in that, The binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, and polystyrene-butadiene copolymer, and the mass ratio of the binder to the powder of the electrode active material is 1:10 to 1:

40.

5. The method for preparing the electrode system for electrochemical lithium extraction according to claim 2, characterized in that, The organic solvent is at least one of N-methylpyrrolidone, ethanol, and distilled water, and the mass ratio of the organic solvent to the powder of the electrode active material is 1:1 to 5:

1.

6. The method for preparing the electrode system for electrochemical lithium extraction according to claim 2, characterized in that, It also includes a foaming agent, which is at least one of NaCl, KCl and NH3HCO3, and the mass fraction of the foaming agent in the slurry is 0.025~0.5%.

7. The method for preparing the electrode system for electrochemical lithium extraction according to claim 1, characterized in that, The two electrodes are subjected to delithiation and lithium insertion under constant current conditions until the voltage is 0.2V~1.0V.

8. The method for preparing the electrode system for electrochemical lithium extraction according to claim 1, characterized in that, The two electrodes are subjected to delithiation and lithium insertion under constant voltage conditions until the current is 0.1mA~5mA.

9. The method for preparing the electrode system for electrochemical lithium extraction according to claim 1, characterized in that, The lithium ion concentration in the lithium salt solution is 0.2 mol / L to 1 mol / L, and the lithium salt solution is a lithium chloride or lithium sulfate solution.

10. The method for preparing the electrode system for electrochemical lithium extraction according to claim 1, characterized in that, The lithium-rich electrode has a lithium-intercalation temperature of 5°C to 50°C, and the lithium-poor electrode has a lithium-extraction temperature of 5°C to 50°C.

11. An electrode system for electrochemical lithium extraction obtained by the method according to any one of claims 1-10.

12. The electrode system for electrochemical lithium extraction according to claim 11, characterized in that, The electrode system used for electrochemical lithium extraction is Li x+y FePO4||Li x-y FePO4, Li x+y FePO4@λ-MnO2||Li x-y FePO4@λ-MnO2, Li x+y Mn₂O₄||Li x- y Mn2O4, Li x+y V2O5||Li x-y V2O5, Li x+y NiO2||Li x-y At least one of NiO2, wherein 0.05≤x≤0.45 or 0.55≤x≤0.95, xy>0, and x+y<1.

13. An electrochemical lithium extraction apparatus having the electrode system for electrochemical lithium extraction as described in claim 11, characterized in that, The system includes an anode chamber for holding the recovered liquid, a cathode chamber for holding the lithium extraction solution, and a diaphragm separating the cathode chamber and the anode chamber; the lithium-rich electrode in the electrochemical lithium extraction electrode system is inserted into the recovered liquid and connected to the positive terminal of the power supply, and the lithium-poor electrode in the electrochemical lithium extraction electrode system is inserted into the lithium extraction solution and connected to the negative terminal of the power supply.

14. The electrochemical lithium extraction apparatus according to claim 13, characterized in that, The recovered solution is a NaCl solution with a concentration of 0.1 mol / L to 1 mol / L.

15. The electrochemical lithium extraction apparatus according to claim 13, characterized in that, The lithium extraction solution comprises LiCl, NaCl, MgCl2, and CaCl2, wherein the concentration of LiCl is 0.03 g / L to 2 g / L, the concentration of NaCl is 30 g / L to 100 g / L, the concentration of MgCl2 is 10 g / L to 80 g / L, and the concentration of CaCl2 is 5 g / L to 40 g / L.

16. The electrochemical lithium extraction apparatus according to claim 13, characterized in that, The lithium extraction solution is brine.

17. The electrochemical lithium extraction apparatus according to claim 13, characterized in that, The membrane is an anion exchange membrane.

18. An electrochemical lithium extraction method, characterized in that, include: When the power supply of the electrochemical lithium extraction device according to any one of claims 13-17 is turned on, the lithium-rich electrode is delithiated and the lithium-poor electrode is lithium-intercalated to a specified degree, the positions of the lithium-rich electrode and the lithium-poor electrode are exchanged so that the lithium-rich electrode after delithiation is inserted into the lithium extraction solution and connected to the negative terminal of the power supply, and the lithium-poor electrode after lithium intercalation is inserted into the recovery liquid and connected to the positive terminal of the power supply. Repeat the above steps to transfer lithium from the lithium extraction solution to the recovery solution, thereby achieving lithium extraction.

19. The electrochemical lithium extraction method according to claim 18, characterized in that, After the electrochemical lithium extraction device operates at constant current to the cutoff potential or at constant voltage to the cutoff current, the positions of the lithium-rich electrode and the lithium-poor electrode are exchanged.

20. The electrochemical lithium extraction method according to claim 19, characterized in that, After the electrochemical lithium extraction device operates at a constant current until the voltage reaches 0.2V~0.8V, the positions of the two electrodes are exchanged.

21. The electrochemical lithium extraction method according to claim 19, characterized in that, After the electrochemical lithium extraction device operates at constant voltage until the current is 0.1mA~5mA, the positions of the two electrodes are exchanged.

22. The electrochemical lithium extraction method according to claim 18, characterized in that, The temperature for delithiation of the lithium-rich electrode and lithium insertion of the lithium-poor electrode is 5℃~50℃.

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