Composite ion-sieve with three-layer core-shell structure, selective electrode and electrochemical redox selective lithium extraction method from lithium-containing acidic solutions

Abstract

The application discloses a three-layer core-shell structure composite ion sieve, a selective lithium extraction electrode and a preparation method thereof, wherein the three-layer core-shell structure composite ion sieve is characterized in that the inner layer is a carbon material, the middle layer is a lithium manganese oxide, and the outer layer is a lithium iron phosphate.The acid leaching solution is obtained by heating and stirring the lithium aluminum silicon glass powder in an acid solution, which can greatly reduce the reaction time and temperature of the leaching process, thereby reducing the energy consumption and realizing the economic and efficient recovery of lithium resources; compared with the traditional lithium manganese oxide selective electrode, the carbon material is used as the inner layer, so that the diffusion path of lithium ions in the electrode is greatly shortened; the lithium iron phosphate is used as the outer coating layer, the stability of the lithium iron phosphate under the acidic condition is utilized, the lithium iron phosphate has better acid resistance, and the lithium can be effectively extracted from the acid leaching solution with high efficiency and high lithium adsorption capacity is achieved.

Description

Technical Field

[0001] This invention relates to the field of resource recycling technology, specifically to a three-layer core-shell composite ion sieve, a selective electrode, and a method for electrochemical oxidation-reduction extraction of lithium from lithium-containing acidic solutions. Background Technology

[0002] Lithium, known as "white oil," is one of China's 24 strategic mineral resources. In recent years, lithium compounds have been widely used in various traditional industrial fields such as lithium batteries, glass ceramics, and aerospace. With the rapid development of new energy vehicles and energy storage equipment, the demand for lithium products is increasing daily.

[0003] Lithium compounds are primarily produced from two primary resources: minerals and lithium-containing brines. Mineral resources are mainly located in Australia and China, while brines are primarily found in South America (Argentina, Bolivia, and Chile). With the rapid development of the new energy industry, the demand for lithium is constantly increasing. Lithium-containing waste materials, as valuable secondary resources, are also being used to produce lithium salt products. Currently, the global lithium recovery rate is extremely low, less than 1%, necessitating the recovery of more secondary resources to meet the growing demand for lithium compounds from the new energy industry. The glass and ceramics industry is the second largest application area for lithium. Lithium aluminum silicate (LAS) microcrystalline glass is a polycrystalline glass produced through controlled crystallization. Its main components are Li-Al-Si-O, with a Li2O content of 3%–6%, and it has high recycling value. The pressure boiling method and limestone roasting method for recovering LAS microcrystalline glass have simple process flows, but they require high temperature and pressure, resulting in high alkali consumption, long processing time, and complex post-processing impurity removal, which restricts its industrial application. Electrochemical oxidation-reduction technology is the most efficient and selective method for lithium extraction. The most important aspects of electrochemical redox lithium extraction technology are the preparation of selective electrodes and the solution to the problem of lithium-ion transport difficulties. Lithium iron phosphate (LFP), lithium manganese oxide (LMO), and lithium titanate (LTO) are the most commonly used electrochemical active materials. Lithium titanate cannot be widely used due to its complex preparation process; lithium manganese oxide has the advantages of high adsorption capacity and high selectivity, but it is thermodynamically unstable under acidic conditions, easily suffers manganese dissolution, and changes in electrode structure lead to insufficient utilization of electrode materials, resulting in capacity decay in long-cycle experiments; lithium iron phosphate has the advantages of thermodynamic stability and good economy under acidic conditions, but its poor selectivity and low actual adsorption capacity will lead to a low overall lithium recovery rate, which is not conducive to large-scale industrial applications.

[0004] Chinese patent application CN116710400A discloses an electrode material for lithium extraction from salt lakes using an electrochemical intercalation-deintercalation method. This patent application uses vanadium dioxide to coat lithium iron phosphate with a coating thickness of 1–10 nm, which can improve electrode conductivity and increase current density, thereby accelerating the extraction of intercalated lithium ions into the electrolyte and improving lithium extraction efficiency. However, due to the poor selectivity and low actual adsorption capacity of lithium iron phosphate, the overall lithium recovery rate is low when extracting lithium under acidic conditions.

[0005] Chinese patent application CN116723997A discloses a lithium iron phosphate cathode material for lithium extraction from salt lakes using an electrochemical intercalation-deintercalation method. This patent application employs alumina coating on lithium iron phosphate to modify the surface of the lithium iron phosphate particles, accelerating the wetting process of brine within the material and further diffusing it to the particle surface. However, due to the poor selectivity of lithium iron phosphate and its low actual adsorption capacity, the overall lithium recovery rate is low under acidic conditions.

[0006] Chinese patent application CN104253270A discloses a lithium iron phosphate-coated lithium manganese oxide composite electrode material. In this patent application, lithium iron phosphate, lithium manganese oxide, and glucose are blended to uniformly coat the surface of spinel-type lithium manganese oxide with lithium iron phosphate. The resulting composite electrode material exhibits good electrochemical temperature characteristics and overcharge resistance. However, this patent application uses lithium iron phosphate-coated lithium manganese oxide as a composite electrode material, not as a lithium extraction material.

[0007] Chinese patent application CN116724425A discloses an electrode material that uses mesoporous silica as the core and grows lithium iron phosphate on the surface. This patent application utilizes the porosity of mesoporous silica to improve mass transfer efficiency, as both lithium-ion adsorption and desorption processes occur within the inner layer of the lithium iron phosphate, thus improving adsorption and deintercalation efficiency. However, due to the poor selectivity of lithium iron phosphate, the actual adsorption capacity is low, resulting in a low overall lithium recovery rate under acidic conditions. Summary of the Invention

[0008] The technical problem to be solved by this invention is to provide a three-layer core-shell composite ion sieve, a selective lithium extraction electrode, and a method for efficiently extracting lithium from lithium aluminum silicon glass leaching solutions using this electrode. Compared with traditional lithium extraction methods from lithium aluminum silicon glass, the method of this invention can greatly reduce the reaction time and temperature of the leaching process, thereby reducing energy consumption and achieving economical and efficient lithium resource recovery. Furthermore, the synthesized three-layer core-shell selective lithium extraction electrode, while maintaining the original advantages of lithium manganese oxide, has better acid resistance and a larger lithium ion diffusion coefficient, achieving efficient lithium extraction and high lithium adsorption capacity in acidic leaching solutions.

[0009] Specifically, the first aspect of the present invention provides a composite ion sieve with a three-layer core-shell structure, wherein the innermost layer is a carbon material, the middle layer is lithium manganese oxide, and the outermost layer is lithium iron phosphate.

[0010] The inventors discovered in their research that during the electrochemical redox lithium extraction process, the inner layer material of the core-shell structure has a large resistance to lithium ion transport and a small diffusion coefficient, which leads to a reduction in the adsorption capacity of the core-shell structure selective electrode during the electrochemical redox lithium extraction experiment. In long-cycle experiments, a significant capacity decay occurs.

[0011] Furthermore, the thermodynamic stability of lithium manganese oxide and lithium iron phosphate is highly dependent on the pH of the solution. The thermodynamic stability range of manganese-based ion sieves is pH > 5. In alkaline solutions, after electrochemical oxidation, manganese-based ion sieves exist as stable solid MnO2, thus exhibiting excellent cycling stability and selectivity in strongly alkaline environments. However, at pH 3–5, the electrochemically active material, lithium manganese oxide, in manganese-based ion sieves undergoes a disproportionation reaction, converting into Mn(OH)2, which cannot adsorb lithium. 2+ This leads to the dissolution of Mn, significantly reducing the cycling stability of manganese-based ion sieves and resulting in poor electrochemical reversibility of the electrode. In long-cycle experiments, a substantial capacity decay occurs. Therefore, manganese-based ion sieves are not suitable for electrochemical redox lithium extraction under acidic environments.

[0012] Unlike manganese-based ion sieves, lithium iron phosphate (LFP) exhibits thermodynamic stability within a pH range of 3–5. Within this range, LFP exists as a stable solid FePO4 after electrochemical oxidation, thus demonstrating excellent cycling stability and selectivity in acidic environments. However, when pH > 5, the thermodynamic properties of LFP become unstable. The electrochemically active FePO4 transforms into Fe(OH)3, which cannot adsorb lithium, resulting in a significant decrease in adsorption / desorption capacity. This structural change makes it difficult to fully utilize the electrode material, and the electrochemical reversibility of the electrode deteriorates, leading to capacity decay in long-cycle experiments.

[0013] Based on the above research findings, the inventors used carbon material as the innermost layer, synthesized lithium manganese oxide with high adsorption capacity as the middle layer on its surface, and coated it with lithium iron phosphate material stable under acidic conditions on the outer layer, forming a three-layer core-shell composite ion sieve. This solved the defects of low lithium-ion diffusion coefficient, high transport resistance, and poor acid resistance of manganese-based ion sieves, and improved the stability and electrochemical performance of lithium extraction from lithium manganese oxide in acidic solutions. At the same time, this composite ion sieve also has the advantages of high selectivity and high adsorption capacity.

[0014] It should be noted that "lithium iron phosphate" in this invention refers to LiFePO4, and "lithium manganese oxide" includes one or more of various lithium manganese compounds, such as LiMn2O4 and Li4Mn5O4. 12 Li 1.6 Mn 1.6 O4, etc.

[0015] In some embodiments of the present invention, the particle size of the innermost carbon material in the composite ion sieve is ≤1μm, more preferably 0.5 to 1μm, for example, it can be 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, etc.

[0016] In some embodiments of the present invention, the thickness of the intermediate layer material lithium manganese oxide in the composite ion sieve is preferably ≤5μm, more preferably 1 to 5μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, etc., but is not limited to the listed values, other unlisted values ​​or ranges within this range are also applicable.

[0017] In some embodiments of the present invention, the thickness of the outer layer material lithium iron phosphate in the composite ion sieve is preferably ≥1μm, more preferably 1 to 5μm, for example, it can be 1μm, 2μm, 3μm, 4μm, 5μm, etc.

[0018] During their research, the inventors discovered that lithium iron phosphate adsorbs H₂ under acidic conditions. + In long-cycle adsorption-desorption experiments, a significant capacity decay occurs. If the thickness of the outer lithium iron phosphate layer is less than 1 μm, the protective effect of lithium iron phosphate on the lithium manganese oxide intermediate layer is poor. As a result, during the long-cycle electrochemical redox lithium extraction process of the composite ion sieve, the hydrogen ions adsorbed by lithium iron phosphate will destroy the lithium manganese oxide intermediate layer, causing the electrochemically active substances in the lithium manganese oxide to undergo a disproportionation reaction and be converted into Mn(OH) that cannot adsorb lithium. 2+ This leads to Mn dissolution, significantly reducing the cycling stability of the composite ion sieve and resulting in poor electrochemical reversibility of the electrode. In long-cycle experiments, this causes a substantial capacity decay. Therefore, the thickness of the outer layer material must be ≥1μm.

[0019] In some embodiments of the present invention, the mass ratio of the outer layer material lithium iron phosphate to the intermediate layer material lithium manganese oxide is (0.2-5):1, for example, it can be 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 2:1, 3:1, 4:1, 5:1, etc. However, it is not limited to the listed values; other unlisted values ​​or ranges within this range are also applicable. When the mass ratio of the outer layer material lithium iron phosphate to the intermediate layer material lithium manganese oxide is within the above range, it not only ensures that lithium iron phosphate can form a complete coating layer with the surface of lithium manganese oxide, thus giving the composite ion sieve good acid resistance, but also provides high economic efficiency, meeting the requirements of industrial applications.

[0020] Furthermore, in some embodiments of the present invention, the preparation method of the above-mentioned core-shell structured composite ion sieve includes the following steps:

[0021] After the carbon material-lithium manganese oxide, phosphorus source and iron source are mixed evenly in the solution, a hydrothermal reaction is carried out to obtain the composite ion sieve precursor carbon material-lithium manganese oxide-iron phosphate.

[0022] The composite ion sieve precursor and lithium source are mixed and calcined in a reducing atmosphere to obtain a three-layer core-shell structured composite ion sieve carbon material-lithium manganese oxide-lithium iron phosphate.

[0023] In this invention, lithium manganese oxide can be obtained either by purchase or by synthesis. The synthesis method is not limited; it can be either solid-phase synthesis or liquid-phase synthesis (co-precipitation, sol-gel method, hydrothermal synthesis, etc.).

[0024] In an illustrative embodiment, lithium manganese oxide with carbon as the inner layer material can be synthesized by hydrothermal method. The specific steps may include: mixing carbon material, manganese source and alkaline solution, reacting completely to obtain C-Mn(OH)2; after filtration, washing and drying, calcining in air to obtain C-MnOOH precursor; then mixing C-MnOOH precursor with lithium source solution to hydrothermally synthesize carbon material-lithium manganese oxide.

[0025] In some embodiments of the present invention, the carbon material includes one of carbon black, acetylene black, graphite, carbon fiber, carbon nanotubes, graphene, Ketjen black, or any combination thereof.

[0026] In some embodiments of the present invention, when synthesizing Mn(OH)2 on the surface of carbon materials, the manganese source can be various soluble manganese-containing compounds, including but not limited to one of manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate, or any combination thereof. The aforementioned manganese chloride, manganese sulfate, manganese nitrate, and manganese acetate can all be obtained through conventional methods in the art.

[0027] In some embodiments of the present invention, when synthesizing Mn(OH)2 on the surface of carbon materials, the alkaline solution may include, but is not limited to, one of sodium hydroxide solution, potassium hydroxide solution, or a mixture thereof; the concentration of the alkaline solution may be 0.01 to 10 mol / L, preferably 1 to 5 mol / L, for example, 0.01, 0.02, 0.04, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 mol / L, etc., but is not limited to the listed values, and other unlisted values ​​or ranges within this range are also applicable.

[0028] In some embodiments of the present invention, when synthesizing the MnOOH precursor on the surface of carbon materials, the calcination temperature is preferably controlled to be 100℃ to 1000℃, for example, 100℃, 200℃, 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, etc., but is not limited to the listed values, and other unlisted values ​​or ranges within this range are also applicable.

[0029] In some embodiments of the present invention, when synthesizing the MnOOH precursor on the surface of carbon materials, the calcination time is preferably controlled to be 2 to 72 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, 24 hours, 30 hours, 32 hours, 36 hours, 40 hours, 45 hours, 48 ​​hours, 50 hours, 56 hours, 60 hours, 64 hours, 70 hours, 72 hours, etc., but is not limited to the listed values, and other unlisted values ​​or ranges within this range are also applicable.

[0030] In some embodiments of the present invention, when synthesizing carbon material lithium manganese oxide via a hydrothermal method, the lithium source solution can be a lithium-containing compound commonly used in the art, including but not limited to inorganic acid salts, organic acid salts, or bases of lithium; for example, it can include one or any combination of lithium carbonate, lithium hydroxide, lithium chloride, lithium bromide, lithium fluoride, lithium nitrate, lithium acetate, lithium oxalate, lithium sulfate, lithium acetate, and lithium formate; preferably, the lithium source is lithium chloride, lithium hydroxide, or lithium carbonate. The aforementioned lithium carbonate, lithium hydroxide, lithium chloride, lithium bromide, lithium fluoride, lithium nitrate, lithium acetate, lithium oxalate, lithium sulfate, lithium acetate, and lithium formate can all be obtained through conventional methods in the art. The concentration of the lithium source solution can be 1 to 10 mol / L, for example, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0 mol / L, etc., but it is not limited to the listed values. Other unlisted values ​​or ranges within this range are also applicable.

[0031] In some embodiments of the present invention, when synthesizing carbon material - lithium manganese oxide by hydrothermal method, the pH value of the solution in the reaction vessel is preferably controlled to be 5.0 to 14.0 during the hydrothermal reaction. For example, it can be 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0, 13.0, 14.0, etc., but it is not limited to the listed values. Other unlisted values ​​or ranges within this range are also applicable.

[0032] In some embodiments of the present invention, when synthesizing carbon material - lithium manganese oxide by hydrothermal method, the temperature of the hydrothermal reaction is preferably 100℃ to 300℃, for example, it can be 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc., but is not limited to the listed values, other unlisted values ​​or ranges within this range are also applicable.

[0033] In some embodiments of the present invention, when synthesizing carbon material - lithium manganese oxide by hydrothermal method, the hydrothermal reaction time is controlled to be 2 to 48 hours, preferably 12 to 36 hours. For example, it can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 25 hours, 30 hours, 32 hours, 36 hours, 40 hours, 45 hours, 48 ​​hours, etc., but is not limited to the listed values. Other unlisted values ​​or ranges within this range are also applicable.

[0034] In some embodiments of the present invention, after purchasing or synthesizing carbon material - lithium manganese oxide, it is preferably thoroughly ground to control the D50 particle size ≤ 6 μm, which is beneficial to the subsequent hydrothermal coating of lithium iron phosphate reaction.

[0035] When coating the surface of carbon material-lithium manganese oxide particles with lithium iron phosphate, various methods can be used, including but not limited to solid-phase coating methods (mechanical mixing, solid-phase reaction, etc.) and liquid-phase coating methods (hydrothermal method, sol-gel method, precipitation method, etc.). Hydrothermal coating is preferred because, compared to other methods, it not only has simpler process steps but also forms a more uniform and complete lithium iron phosphate coating layer on the surface of the carbon material-lithium manganese oxide particles.

[0036] In some embodiments of the present invention, when synthesizing lithium iron phosphate by hydrothermal method, the phosphorus source can be a phosphorus-containing compound commonly used in the art, including but not limited to one of sodium phosphate, potassium phosphate, sodium dihydrogen phosphate, ammonium phosphate, and phosphoric acid, or any combination thereof; preferably, the phosphorus source is phosphoric acid. The aforementioned sodium phosphate, potassium phosphate, sodium dihydrogen phosphate, ammonium phosphate, and phosphoric acid can be obtained through conventional methods in the art.

[0037] In some embodiments of the present invention, when synthesizing lithium iron phosphate by hydrothermal method, the iron source can be one or more iron-containing compounds commonly used in the art, including but not limited to ferric chloride, ferrous chloride, ferric sulfate, ferric sulfate, ferrous sulfate, ferrous nitrate, ferrous nitrate, ferric acetate, ferrous acetate, and their various hydrates (e.g., FeSO4·7H2O, FeCl3·6H2O, etc.); preferably, the iron source is ferric chloride or ferric sulfate. The aforementioned ferric chloride, ferrous chloride, ferric sulfate, ferric sulfate, ferrous sulfate, ferrous nitrate, ferrous nitrate, ferric acetate, ferrous acetate, and their various hydrates can be obtained through conventional methods in the art.

[0038] In some embodiments of the present invention, when synthesizing lithium iron phosphate by hydrothermal method, the pH of the reaction solution needs to be controlled within the range of 3.0 to 5.0, for example, 3.0, 3.5, 4.0, 4.5, 5.0, etc., but is not limited to the listed values; other unlisted values ​​or ranges within this range are also applicable. If the pH is <3.0 or >5.0, it will be difficult to synthesize lithium iron phosphate on the surface of manganese-based ion sieves.

[0039] In some embodiments of the present invention, when synthesizing lithium iron phosphate by hydrothermal method, the temperature of the hydrothermal reaction needs to be controlled at 100℃~300℃, preferably 150℃~250℃. For example, it can be 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, etc., but is not limited to the listed values. Other unlisted values ​​or ranges within this range are also applicable.

[0040] In some embodiments of the present invention, when synthesizing lithium iron phosphate by hydrothermal method, the hydrothermal reaction time is controlled to be 2 to 72 hours, preferably 12 to 36 hours. For example, it can be 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 25 hours, 28 hours, 30 hours, 32 hours, 35 hours, 36 hours, 48 ​​hours, 72 hours, etc., but is not limited to the listed values. Other unlisted values ​​or ranges within this range are also applicable.

[0041] In some embodiments of the present invention, when the composite ion sieve precursor is calcined with a lithium source, the molar ratio of the composite ion sieve precursor to the lithium source is preferably 1:(1-2), for example, 1:1, 1:1.2, 1:1.5, 1:1.6, 1:1.8, 1:2, etc., but is not limited to the listed values; other unlisted values ​​or ranges within this range are also applicable. The lithium source can be a lithium-containing compound commonly used in the art.

[0042] In some embodiments of the present invention, when the composite ion sieve precursor is calcined with a lithium source, the reducing atmosphere includes, but is not limited to, hydrogen, or a mixture of hydrogen and an inert gas.

[0043] In some embodiments of the present invention, when the composite ion sieve precursor and the lithium source are calcined, the calcination temperature is preferably 500℃ to 800℃, for example, 500℃, 550℃, 600℃, 650℃, 70℃, 750℃, 800℃, etc., but is not limited to the listed values; other unlisted values ​​or ranges within this range are also applicable. The calcination time is preferably 1 to 12 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, etc., but is not limited to the listed values; other unlisted values ​​or ranges within this range are also applicable.

[0044] Furthermore, in some embodiments of the present invention, the method for preparing the core-shell structured selective lithium extraction electrode includes the following steps:

[0045] A precursor solution is obtained by mixing a three-layer core-shell composite ion sieve, a binder, a conductive agent, and an organic solvent.

[0046] An organic pore-forming agent is added to the precursor solution to obtain a precursor solution containing the organic pore-forming agent.

[0047] The precursor solution containing the organic pore-forming agent is coated onto the electrode substrate material, and the organic pore-forming agent is removed after film formation.

[0048] In some embodiments of the present invention, the adhesive includes at least one of polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene, and aqueous polystyrene ester.

[0049] In some embodiments of the present invention, the conductive agent includes at least one of carbon black, acetylene black, graphite, carbon fiber, carbon nanotubes, graphene, Ketjen black, and composite conductive paste.

[0050] In some embodiments of the present invention, the organic solvent includes at least one of N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, dimethylformamide, and dimethylacetamide.

[0051] In some embodiments of the present invention, the electrode substrate material may be an inert metal and / or a non-metallic conductive material; wherein the inert metal may include gold, silver, platinum, palladium, rhodium, iridium, etc. In some embodiments, the electrode substrate material may include at least one of graphite sheet, titanium sheet, carbon cloth, and carbon felt.

[0052] In some embodiments of the present invention, the organic pore-forming agent is at least one selected from polystyrene, polyethylene glycol, polyvinyl chloride, polyoxymethylene, epoxy resin, polyglycolic acid, lignin, cellulose, and hemicellulose.

[0053] In some embodiments of the present invention, the weight ratio of the core-shell composite ion sieve, organic solvent, binder, conductive agent, and organic pore-forming agent is preferably 8:1 to 10:1 to 10:1 to 10:1 to 10:1 to 3; for example, it can be 8:1 to 10:1 to 10:1 to 10:2, or 8:1 to 10:1 to 10:5:1 to 3, or 8:1 to 10:5:1 to 10:1 to 3, or 8:5:1 to 10:1 to 10:1 to 3, etc.

[0054] In some embodiments of the present invention, organic solvents in the membrane can be removed by low-temperature drying. The temperature of the low-temperature drying is preferably 40°C to 120°C, for example, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, etc.

[0055] In some embodiments of the present invention, after film formation, the organic pore-forming agent in the film is further removed by high-temperature drying. The high-temperature drying temperature is greater than or equal to the volatilization / decomposition temperature of the organic pore-forming agent, causing it to volatilize or decompose. The resulting gas diffuses from the substrate material to the surface of the selective lithium extraction electrode and eventually enters the atmosphere, creating uniform pores that penetrate the selective lithium extraction electrode. The preferred high-temperature drying temperature is 150℃ to 250℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc. The preferred high-temperature drying time is 2 to 24 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 8 hours, 10 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, etc.

[0056] Secondly, the present invention provides a method for electrochemical oxidation-reduction extraction of lithium from an acidic lithium-containing solution, comprising the following steps:

[0057] An electrochemical system is provided, comprising an anode chamber, a cathode chamber, and a diaphragm; the anode chamber contains an anolyte, and the cathode chamber contains a catholyte, wherein the catholyte is an acidic lithium-containing solution; the anode chamber and the cathode chamber are separated by the diaphragm.

[0058] The selective lithium extraction electrode with the above-mentioned three-layer core-shell structure is placed in the anolyte as the anode;

[0059] After the above-mentioned three-layer core-shell structure selective lithium extraction electrode is activated, it is placed in the cathodic solution as a cathode.

[0060] The anode and cathode are connected to a power source to extract lithium.

[0061] In some embodiments of the present invention, the cathode solution is a lithium-containing solution with pH = 3.5 to 4, or an acid leaching solution of lithium aluminum silicon glass.

[0062] Currently, waste lithium aluminum silicon glass is mainly processed using methods such as high-temperature calcination-water leaching, high-temperature calcination-alkali leaching, limestone calcination-water leaching, limestone + CaCl2 doping calcination-water leaching, and pressure boiling. While these methods have simple processes, most require high temperatures and pressures, resulting in high alkali consumption, long processing times, and complex post-processing impurity removal, thus hindering their industrial application. This invention uses acid leaching instead of traditional methods, effectively reducing the reaction temperature and shortening the leaching time. It also produces a lower impurity content in the leachate, avoids the traditional calcination and crystallization process, solves the environmental problems associated with high-temperature calcination, and reduces energy consumption, making it more conducive to low-energy, clean industrial applications.

[0063] In some embodiments of the present invention, the acid leaching solution of the lithium aluminum silicon glass is obtained by grinding the lithium aluminum silicon glass into powder and leaching it in an acidic solution with heating and stirring. After leaching, the solid-liquid mixture is separated to obtain a leaching solution and a leaching residue. The solid-liquid separation operation employs conventional separation methods, such as centrifugation, hydrocyclone separation, or filtration, for subsequent selective lithium extraction.

[0064] In some embodiments of the present invention, the acidic solution may be a commonly used inorganic acid, including but not limited to one or more of HCl, HNO3, and H2SO4. The concentration of the acidic solution may be 0.01–10 mol / L, for example 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L, etc.

[0065] In some embodiments of the present invention, the stirring rate can be 10–2000 rpm, for example, 10 rpm, 100 rpm, 200 rpm, 400 rpm, 500 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, etc. The heating temperature can be 0–250°C, for example, 0°C, 10°C, 30°C, 50°C, 80°C, 100°C, 120°C, 150°C, 180°C, 200°C, 220°C, 250°C, etc.

[0066] In this invention, the anolyte is preferably a lithium-containing solution with a pH of 3-5. In some embodiments of this invention, the anolyte can be one or more lithium-containing solutions selected from lithium chloride solution, lithium bromide solution, lithium fluoride solution, lithium nitrate solution, lithium acetate solution, lithium oxalate solution, lithium sulfate solution, lithium acetate solution, lithium formate solution, etc.; the concentration of the anolyte can be 0.01-1M, for example 0.01M, 0.1M, 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, etc.

[0067] In this invention, the diaphragm is an anion exchange membrane.

[0068] In some optional embodiments, the electrochemical system may include one or more anode chambers, one or more cathode chambers, and one or more membranes. The number of anode chambers, cathode chambers, and membranes corresponds one-to-one; that is, one anode chamber and one cathode chamber constitute a chamber combination. The electrochemical system includes one or more such chamber combinations, and the anode chambers and cathode chambers are separated by membranes. This allows for scaling up electrochemical redox lithium extraction, improving its efficiency, and facilitating industrialization.

[0069] In some embodiments of the present invention, the electrochemical redox lithium extraction method further includes the following steps:

[0070] After lithium extraction is completed, the anode and cathode are removed, cleaned, and the electrodes are exchanged to continue lithium extraction.

[0071] Repeat the above steps to cycle and extract lithium until the lithium content in the cathode solution is below 10 ppm.

[0072] Lithium is recovered from the anolyte.

[0073] In the aforementioned electrochemical redox lithium extraction process, lithium ions in the cathode solution are selectively adsorbed by the core-shell composite ion sieve in the cathode until adsorption equilibrium is reached. Then, after exchanging the cathode and anode, when electrochemical redox lithium extraction continues, the lithium ions adsorbed by the composite ion sieve in the cathode desorb and enter the anolyte. By repeating the above lithium extraction steps, lithium ions in the cathode solution are separated and enriched in the anolyte.

[0074] In some embodiments of the present invention, the lithium extraction voltage can be 0.3 to 1.2V, for example 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1.0V, 1.1V, 1.2V, etc.; the lithium extraction time can be 1 to 100 hours, for example 1 hour, 5 hours, 10 hours, 20 hours, 30 hours, 40 hours, 50 hours, 60 hours, 70 hours, 80 hours, 90 hours, 100 hours, etc.

[0075] The number of cycles for lithium extraction is determined based on factors such as the lithium concentration in the cathode solution. In some embodiments of the present invention, the number of cycles can be 3 to 500.

[0076] In some embodiments of the present invention, a method for recovering lithium from the anolyte includes: concentrating the anolyte to obtain crude water and crude lithium salt. Further, Na₂CO₃ may be added to the concentrated anolyte to obtain crude lithium carbonate.

[0077] In some embodiments of the present invention, the activation includes the following steps:

[0078] An activation device is provided, the activation device comprising an anode chamber, a cathode chamber and a diaphragm; wherein, a salt solution is disposed in the anode chamber, and a conductive electrode and an oxidant solution are disposed in the cathode chamber;

[0079] The electrode to be activated is placed into the salt solution in the anode chamber;

[0080] The electrode to be activated is connected to the positive terminal of the power supply, and the conductive electrode in the cathode cavity serves as the counter electrode and is connected to the negative terminal of the power supply. A constant current is applied to the electrode to be activated for electro-activation.

[0081] In some embodiments of the present invention, the oxidant solution includes Fe 2+ Fe 3+ Cu 2+ Cu + I2, I 3- Sn 4+ Cr 3+ Cd 2+ Pb 2+ PO4 3- V 3+ Sn 2+ HCOOH, HCHO, CH3OH, SbO + VO 2+ H2MoO4, MnO 4- 、Tl 3+ Ag + A solution of at least one of the following. The concentration of the oxidant solution can be 0.001 to 10 mol / L, for example 0.001, 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2, 3, 4, 5, 6, 7, 8, 9, 10 mol / L, etc.

[0082] In some embodiments of the present invention, the salt solution includes solutions containing Cl. - SO4 2- SO3 2- NO 3- NO 2- PO4 3- CO3 2- A solution of at least one of the soluble salts of chlorate and perchlorate. The concentration of the salt solution can be 0.1 to 10 mol / L, for example 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2, 3, 4, 5, 6, 7, 8, 9, 10 mol / L, etc.

[0083] In some embodiments of the present invention, the conductive electrode is an inert conductive electrode; further, the conductive electrode includes at least one of carbon electrode, graphite electrode, carbon cloth electrode, titanium electrode, glassy carbon electrode, carbon felt electrode, platinum electrode, gold electrode, stainless steel electrode, copper electrode, silver electrode, aluminum electrode, and metal alloy electrode.

[0084] In some embodiments of the present invention, the activation voltage can be 0.3 to 1V, for example 0.3V, 0.4V, 0.5V, 0.6V, 0.7V, 0.8V, 0.9V, 1.0V, etc.; the activation time can be 0.1 to 100h, for example 0.1h, 1h, 5h, 10h, 20h, 30h, 40h, 50h, 60h, 70h, 80h, 90h, 100h, etc.

[0085] In addition, the detailed processes for pore formation and activation are already described in patent application 202210656925.6 filed with the State Intellectual Property Office on June 10, 2022 (publication date: August 2, 2022) and patent application 202211254215.7 filed with the State Intellectual Property Office on October 13, 2022 (publication date: December 27, 2022), which are hereby incorporated herein by reference.

[0086] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0087] 1. Compared with traditional methods such as high-temperature roasting-water leaching, high-temperature roasting-alkali leaching, limestone roasting-water leaching, limestone + CaCl2 doped roasting-water leaching, and pressure cooking, the acid leaching method provided by this invention can effectively reduce the reaction temperature, shorten the leaching time, and produce a lower impurity content in the leaching solution. It avoids the traditional calcination and crystallization process, solves the environmental problems of high-temperature roasting, has lower energy consumption, and is more conducive to achieving low-energy clean industrial applications.

[0088] 2. The selective lithium extraction electrode with a three-layer core-shell structure provided by the present invention, with carbon material as the inner layer, can effectively solve the problems of large lithium ion transport resistance and small diffusion coefficient in the electrochemical redox lithium extraction process, and greatly shorten the diffusion path of lithium ions in the electrode.

[0089] 3. The selective lithium extraction electrode with a three-layer core-shell structure provided by the present invention uses lithium iron phosphate as the outer layer material for coating. By utilizing the stability of lithium iron phosphate under acidic conditions, the defect of lithium manganese oxide being intolerant to acid is solved, and the stability and electrochemical performance of lithium manganese oxide in acidic solution are improved. It can realize efficient lithium extraction using lithium manganese oxide with high lithium adsorption capacity under acidic conditions.

[0090] 4. The selective lithium extraction electrode electrochemical oxidation-reduction lithium extraction technology with a three-layer core-shell structure provided by this invention can be effectively applied to the acid leaching system of lithium aluminum silicon glass. By adjusting the current and voltage of the system, selective adsorption / desorption of lithium can be achieved, and a cyclic process of adsorption / desorption can be realized, which greatly reduces energy consumption and process flow and is easy to industrialize. Attached Figure Description

[0091] Figure 1 This is a process flow diagram of one embodiment of the present invention;

[0092] Figure 2 The leaching rates of Li and Al elements under different acid concentrations (a), different solid-liquid ratios (b), and different stirring rates (c) in Example 1 are shown.

[0093] Figure 3 XRD patterns of alkaline leaching residue and pH-adjusted precipitate from Comparative Example 1;

[0094] Figure 4 Fe after electrochemical oxidation of lithium iron phosphate and lithium manganese oxide 3+ Mn 3+ Species distribution map as a function of pH;

[0095] Figure 5 The selective lithium extraction cyclic adsorption-desorption capacity and manganese dissolution rate of the three-layer core-shell composite ion sieve in Example 2 are shown.

[0096] Figure 6 To compare the selective lithium extraction cyclic adsorption-desorption capacity and manganese dissolution rate of the three-layer core-shell composite ion sieve in Example 2;

[0097] Figure 7 SEM image of the C-LiMn2O4-FePO4 composite ion sieve precursor synthesized in Comparative Example 3;

[0098] Figure 8 The selective lithium extraction cyclic adsorption-desorption capacity and manganese dissolution rate of the composite ion sieve synthesized in Comparative Example 4 were compared.

[0099] Figure 9 The selective lithium extraction cycle adsorption / desorption capacity and manganese dissolution rate of C-LiMn2O4 in Comparative Example 5 were measured.

[0100] Figure 10 To compare the selective lithium extraction cyclic adsorption / desorption capacity and iron dissolution rate of the C-LiFePO4 ion sieve in Example 6;

[0101] Figure 11 To compare the selective lithium extraction cyclic adsorption-desorption capacity and manganese dissolution rate of the core-shell structured composite ion sieve in Example 7;

[0102] Figure 12To measure the selective lithium extraction cyclic adsorption-desorption capacity and manganese dissolution rate of the lithium manganese oxide ion screen purchased for Comparative Example 8;

[0103] Figure 13 The selective lithium extraction cyclic adsorption-desorption capacity and iron loss rate of the lithium iron phosphate ion screen purchased for Comparative Example 9 were determined. Detailed Implementation

[0104] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0105] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0106] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0107] Example 1

[0108] After thorough grinding, the lithium aluminum silicon glass was calcined in a muffle furnace at 110°C for 2 hours to remove surface oil and moisture. The dried lithium aluminum silicon glass powder was then placed in a flask for leaching. Leaching was performed in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The resulting solid-liquid mixture was separated to obtain leachate and leaching residue. The pH of the leachate was measured to be 3.74.

[0109] The concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates was analyzed by ICP. The results are as follows: Figure 2 As shown. From Figure 2 It can be seen from the data that under the conditions of 0.75M HCl, 30g / L, and 250rpm, Li + And Al 3 + The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0110] Comparative Example 1

[0111] After thorough grinding, lithium aluminum silicate glass was calcined in a muffle furnace at 110℃ for 2 hours to remove surface oil and moisture. The dried lithium aluminum silicate glass powder was then leached. Leaching was performed in a hydrothermal reactor at 8M NaOH, 5 g / L, 500 rpm, and 250℃ for 12 hours. The resulting solid-liquid mixture was separated to obtain leachate and leaching residue. The concentration of metal ions in the leachate was analyzed using ICP, and the final Li... + And Al 3+ The leaching rates were >88.58% and >94.89%, respectively.

[0112] CO2 was introduced to adjust the pH of the leaching solution to 10 to precipitate Si, Al, and Li elements. After standing for 5 minutes, the solid-liquid mixture was separated to obtain the precipitate, which was dried in an oven at 50°C for 6 hours. The precipitate was then redissolved using 0.5M HF, and the concentration of metal ions in the precipitate was analyzed by ICP. The results showed that the Na element impurity content accounted for 20.79%, and the purity of the precipitate was less than 78.41%.

[0113] Figure 3 The XRD patterns of the alkaline leaching residue and pH-adjusted precipitate from Comparative Example 1 are shown. Observation of the XRD patterns reveals that the Si dissolved after the reaction of lithium-aluminum-silicon waste glass with NaOH... 4+ And Al 3+ With high concentrations of Na + This will form a complex, resulting in excessively high Na impurity content in the subsequent precipitate.

[0114] Example 2

[0115] This embodiment provides a method for preparing a core-shell structured selective lithium extraction electrode, specifically including the following steps:

[0116] (1) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of MnCl2, dissolve them together in 1M NaOH solution, mix thoroughly to obtain C-Mn(OH)2, filter, wash, dry and calcine in air at 550℃ for 36 h to obtain C-MnOOH. Mix C-MnOOH with 3.5M LiCl solution, adjust the pH of the solution to 8, seal and hydrothermally heat at 170℃ for 12 h to synthesize C-LiMn2O4, wash and filter, grind thoroughly to a particle size of 6 μm, i.e., the thickness of the intermediate layer is 5 μm.

[0117] (2) The C-LiMn2O4 synthesized in step (1) was dissolved in deionized water with sodium phosphate and ferric chloride. The pH of the solution was adjusted to 4. After sealing, the solution was hydrothermally synthesized at 200℃ for 24h to obtain a spherical three-layer core-shell structure (C-LiMn2O4-FePO4) composite ion sieve precursor. Finally, the composite ion sieve precursor was dried and then mixed with lithium chloride and calcined at 650℃ for 10h in a reducing atmosphere to obtain a C-LiMn2O4-LiFePO4 composite ion sieve. The sieve was then fully ground to a particle size of 9μm, i.e., an outer layer thickness of 3μm.

[0118] (3) The three-layer core-shell structured solid powder synthesized in step (2) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is coated on two titanium meshes with a thickness of 2mm and dried at 80°C to remove the organic solvent. Then, the temperature is raised to 160°C to dry and remove the organic pore-forming agent, thus obtaining porous selective lithium extraction electrodes A and B with core-shell structure.

[0119] (4) Using electrode A as the anode, the solution in the anode cavity is a 0.01M LiCl solution with pH=3.5, the cathode is a titanium plate, and the solution in the cathode cavity is a 0.5M CuCl2 solution; constant current at 50mA for 10h to obtain the activated electrode A.

[0120] Electrochemical redox lithium extraction was performed using the core-shell structured selective lithium extraction electrode prepared in this embodiment, as detailed below:

[0121] (1) After the lithium aluminum silicon glass was thoroughly ground, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The resulting solid-liquid mixture was separated to obtain the leachate and the leaching residue. The pH of the leaching solution was measured to be 3.74.

[0122] ICP analysis was used to analyze the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0123] (2) Using electrode A as the cathode, the solution in the cathode chamber as the leachate, and the unactivated electrode B as the anode, the anolyte was a 0.01M LiCl solution. Lithium extraction was performed under a constant current of 50mA until the voltage reached 0.8V, followed by selective lithium extraction under a constant voltage of 0.68V for 20 hours. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was placed as the cathode and electrode A as the anode in the anode-cathode chamber for secondary lithium extraction, with the same operating conditions as the initial extraction, for a total of 10 cycles. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0124] Figure 4 The thermodynamic stability curves of lithium manganese oxide and lithium iron phosphate as a function of pH are shown. The graphs reveal that the selective lithium extraction of both lithium iron phosphate and lithium manganese oxide is highly dependent on the pH of the solution. The thermodynamic stability range of lithium manganese oxide is pH > 5; in acidic solutions, the electrochemically active material will convert into Mn(OH)₂, which cannot absorb lithium. 2+ This significantly reduces the cycling stability of lithium manganese oxide, leading to poor electrochemical reversibility of the electrode and a substantial capacity decay in long-cycle experiments. In contrast, lithium iron phosphate exhibits excellent thermodynamic stability within a pH range of 3–5. In LAS microcrystalline glass leaching solution at pH 3.74, lithium iron phosphate demonstrates good thermodynamic stability and exists as a stable solid FePO4 after electrochemical oxidation. Therefore, the three-layer core-shell composite ion sieve of this invention exhibits excellent cycling stability and selectivity under acidic conditions.

[0125] Figure 5 The figure illustrates the selective lithium extraction cyclic adsorption / desorption capacity and manganese dissolution rate of the three-layer core-shell composite ion sieve in Example 2. As can be seen from the figure, the three-layer core-shell selective lithium extraction electrode prepared in this example exhibits excellent selective lithium extraction capacity for Li... + The adsorption capacity is approximately 30.862 mg / g, and the Mn dissolution rate is approximately 0.191%.

[0126] Comparative Example 2

[0127] This comparative example provides a method for preparing a core-shell structured selective lithium extraction electrode, specifically including the following steps:

[0128] (1) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of MnCl2, dissolve them together in 1M NaOH solution, and mix thoroughly to obtain C-Mn(OH)2 precipitate; after filtration, washing, and drying, calcine in air at 550℃ for 36 h to obtain C-MnOOH. Mix C-MnOOH with 3.5M LiCl solution, adjust the pH of the solution to 8, seal and hydrothermally heat at 170℃ for 12 h to synthesize C-LiMn2O4; after washing and filtration, grind thoroughly to a particle size of 6 μm, i.e., an intermediate layer thickness of 5 μm.

[0129] (2) The C-LiMn2O4 synthesized in step (1) was dissolved in deionized water with sodium phosphate and ferric chloride. The pH of the solution was adjusted to 4. After sealing, the solution was hydrothermally synthesized at 200℃ for 24h to obtain a spherical core-shell structure (C-LiMn2O4-FePO4) composite ion sieve precursor. Finally, the core-shell structure composite ion sieve precursor was dried and then mixed with lithium chloride and calcined at 650℃ for 10h in a reducing atmosphere to obtain C-LiMn2O4-LiFePO4. The precursor was then fully ground to a particle size of 6.5μm, i.e., an outer layer thickness of 0.5μm.

[0130] (3) The three-layer core-shell structured solid powder synthesized in step (2) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is coated on two titanium meshes with a thickness of 2mm and dried at 80°C to remove the organic solvent. Then, the temperature is raised to 160°C to dry and remove the organic pore-forming agent, thus obtaining porous selective lithium extraction electrodes A and B with core-shell structure.

[0131] (4) Using electrode A as the anode, the solution in the anode cavity is a 0.01M LiCl solution with pH 3.5, the cathode is a titanium plate, and the solution in the cathode cavity is a 0.5M CuCl2 solution; constant current at 50mA for 10h to obtain the activated electrode A.

[0132] Electrochemical redox lithium extraction was performed using the core-shell structured selective lithium extraction electrode prepared in this comparative example, as detailed below:

[0133] (1) After the lithium aluminum silicon glass was thoroughly ground, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The resulting solid-liquid mixture was separated to obtain the leachate and the leaching residue. The pH of the leaching solution was measured to be 3.74.

[0134] ICP analysis was used to determine the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0135] (2) Using electrode A as the cathode, the solution in the cathode chamber as the leachate, and the unactivated electrode B as the anode, the anolyte was a 0.01M LiCl solution. Lithium extraction was performed under a constant current of 50mA until the voltage reached 0.8V, followed by selective lithium extraction under a constant voltage of 0.68V for 20 hours. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was placed as the cathode and electrode A as the anode in the anode-cathode chamber for secondary lithium extraction, with the same operating conditions as the initial extraction, for a total of 10 cycles. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0136] Figure 6 The figure shows the selective lithium extraction cyclic adsorption / desorption capacity and manganese dissolution rate of the three-layer core-shell composite ion sieve of Comparative Example 2. As can be seen from the figure, the core-shell composite ion sieve synthesized in this comparative example exhibits high selective lithium extraction capacity for Li. + The adsorption capacity is approximately 24.927 mg / g, and the manganese dissolution rate is approximately 1.667%.

[0137] While lithium iron phosphate (LFP) ion sieves, used as an outer coating, can address the dissolution problem of manganese-based ion sieves in acidic systems, the insufficient thickness of the LFP coating (only 0.5 μm) in this comparative example results in inadequate protection of the intermediate lithium manganese oxide layer. Consequently, during long-cycle cyclic electrochemical redox lithium extraction, the hydrogen ions adsorbed by the LFP ion sieve damage the intermediate lithium manganese oxide layer, leading to disproportionation and conversion into non-lithium-adsorbing Mn(OH)₂. 2+ This causes Mn dissolution, significantly reducing the cyclic stability of the composite ion sieve. Consequently, the electrode reversibility is poor during long-cycle cyclic electrochemical redox lithium extraction, resulting in substantial capacity decay and ultimately leading to Li... + The overall recovery rate is low.

[0138] Comparative Example 3

[0139] This comparative example provides a method for preparing a core-shell structured selective lithium extraction electrode, specifically including the following steps:

[0140] (1) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of MnCl2, dissolve them together in 1M NaOH solution, and mix thoroughly to obtain C-Mn(OH)2 precipitate; after filtration, washing, and drying, calcine in air at 550℃ for 36 h to obtain C-MnOOH. Mix C-MnOOH with 3.5M LiCl solution, adjust the pH of the solution to 8, seal and hydrothermally heat at 170℃ for 12 h to synthesize C-LiMn2O4, wash and filter, and grind thoroughly to a particle size of 6 μm, i.e., an intermediate layer thickness of 5 μm.

[0141] (2) The C-LiMn2O4 synthesized in step (1) was dissolved in deionized water with sodium phosphate and ferric chloride. The pH of the solution was adjusted to 1. After sealing, the mixture was hydrothermally synthesized at 200℃ for 24 h. After the reaction was complete, the mixture was filtered and dried. The precursor was then characterized by SEM.

[0142] Figure 7 SEM images and elemental mappings of the C-LiMn2O4-FePO4 composite ion sieve precursor material are shown. Characterization results indicate that it is difficult to synthesize coated iron phosphate material on the C-LiMn2O4 surface under pH=1 conditions. Iron phosphate is thermodynamically stable in the pH range of 3-5; iron dissolution occurs under other pH conditions. Therefore, it is even more difficult to synthesize coated lithium iron phosphate by co-firing and calcining with a lithium source on the C-LiMn2O4 surface under pH=1 conditions.

[0143] Comparative Example 4

[0144] This comparative example provides a method for preparing a composite ion sieve selective lithium extraction electrode, specifically including the following steps:

[0145] (1) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of MnCl2, dissolve them together in 1M NaOH solution, mix thoroughly to obtain C-Mn(OH)2 precipitate, filter, wash, dry and calcine in air at 550℃ for 36 h to obtain C-MnOOH. Mix C-MnOOH with 3.5M LiCl solution, adjust the pH of the solution to 8, seal and hydrothermally heat at 170℃ for 12 h to synthesize C-LiMn2O4, wash and filter, grind thoroughly to a particle size of 6 μm, i.e., the thickness of the intermediate layer is 5 μm.

[0146] (2) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of sodium phosphate and ferric chloride, dissolve them in deionized water, adjust the pH of the solution to 4, seal and then perform hydrothermal synthesis at 200℃ for 24 h to obtain spherical C-FePO4. After drying, mix with lithium chloride and calcine at 650℃ for 10 h in a reducing atmosphere to obtain C-LiFePO4 ion sieve, and grind it thoroughly to a particle size of 3 μm.

[0147] (3) Weigh a certain amount of C-FePO4 lithium and add it to a glucose aqueous solution. Stir for 30 minutes at a temperature of 60℃ and a power of 1500W / L to obtain a C-LiFePO4 suspension. Then add C-LiMn2O4 (the mass ratio of C-LiFePO4 to C-LiMn2O4 is 1:2) to the C-LiFePO4 suspension and stir mechanically for 60 minutes. After filtration, dry the filter cake at 100℃ for 12 hours to obtain a composite ion sieve.

[0148] (4) The composite ion sieve solid powder from step (3) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP, and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is weighed and coated onto two titanium meshes with a thickness of 2mm. The organic solvent is removed by drying at 80°C. Then, the temperature is raised to 160°C and dried to remove the organic pore-forming agent, thus obtaining porous selective lithium extraction electrodes A and B with a core-shell structure.

[0149] (5) Using electrode A as the anode, the solution in the anode cavity is a 0.01M LiCl solution with pH=3.5, the cathode is a titanium plate, and the solution in the cathode cavity is a 0.5M CuCl2 solution; constant current at 50mA for 10h to obtain the activated electrode A.

[0150] Electrochemical redox lithium extraction was performed using the core-shell structured selective lithium extraction electrode prepared in this comparative example, as detailed below:

[0151] (1) After the lithium aluminum silicon glass was thoroughly ground, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The resulting solid-liquid mixture was separated to obtain the leachate and the leaching residue. The pH of the leaching solution was measured to be 3.74.

[0152] ICP analysis was used to analyze the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0153] (2) Using electrode A as the cathode, the solution in the cathode chamber as the leachate, and the unactivated electrode B as the anode, the anolyte was a 0.01M LiCl solution. Lithium extraction was performed under a constant current of 50mA until the voltage reached 0.8V, followed by selective lithium extraction under a constant voltage of 0.68V for 20 hours. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was placed as the cathode and electrode A as the anode in the anode-cathode chamber for secondary lithium extraction, with the same operating conditions as the initial extraction, for a total of 10 cycles. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0154] Figure 8 The figure shows the selective lithium extraction cyclic adsorption / desorption capacity and manganese dissolution rate of the composite ion sieve in Comparative Example 4. As can be seen from the figure, the selective lithium extraction electrode prepared in this comparative example exhibits good performance for Li... +The adsorption capacity is approximately 17.72 mg / g, and the Mn dissolution rate is approximately 2.384%. This method can only prepare composite ion sieve electrodes, lacking a distinct core-shell structure and failing to achieve complete coating, leading to structural damage during long-term experiments. Furthermore, the composite lithium iron phosphate adsorbs H+ during cyclic adsorption-desorption experiments. + This leads to a gradual increase in the manganese solubility of manganese-based ion sieves during long-term cyclic electrochemical oxidation lithium extraction, resulting in a gradual decrease in adsorption capacity and ultimately causing Li... + The overall recovery rate is low.

[0155] Comparative Example 5

[0156] This comparative example provides a method for preparing a selective lithium extraction electrode from lithium manganese oxide, specifically including the following steps:

[0157] (1) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of MnCl2 and dissolve them together in 1M NaOH solution. After thorough mixing, C-Mn(OH)2 precipitate is obtained. After filtration, washing and drying, the dried product is calcined in air at 550℃ for 36h to obtain C-MnOOH. Then, C-MnOOH is mixed with 3.5M LiCl solution, the pH of the solution is adjusted to 8, sealed and hydrothermally heated at 170℃ for 12h to synthesize C-LiMn2O4. After washing and filtration, it is thoroughly ground to a particle size of 6 μm, that is, the thickness of the intermediate layer is 5 μm.

[0158] (2) The C-LiMn2O4 powder synthesized in step (1) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is weighed and coated on two titanium meshes with a thickness of 2mm. The organic solvent is removed by drying at 80°C. Then, the temperature is raised to 160°C and dried to remove the pore-forming agent, thus obtaining lithium manganese oxide selective lithium extraction electrodes A and B.

[0159] (3) Electrode A was used as the anode, and the solution in the anode cavity was a 0.01M LiCl solution with pH 3.5; the cathode was a titanium plate, and the solution in the cathode cavity was a 0.5M CuCl2 solution; the constant current was maintained at 50mA for 10h to obtain the activated electrode A.

[0160] Electrochemical redox lithium extraction was performed using the lithium manganese oxide selective lithium extraction electrode prepared in this comparative example, as follows:

[0161] (1) After grinding the lithium aluminum silicon glass thoroughly, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface; then the dried lithium aluminum silicon glass powder was put into a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The solid-liquid mixture obtained from the reaction was separated to obtain the leachate and the leach residue. The pH of the leachate was measured to be 3.74.

[0162] ICP analysis was used to determine the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0163] (2) Electrode A was used as the cathode, and the solution in the cathode chamber was the leachate; the unactivated electrode B was used as the anode, and the anolyte was a 0.01M LiCl solution; lithium extraction was performed at a constant current of 50mA until the voltage reached 0.8V, and then selective lithium extraction was performed at a constant voltage of 0.68V for 20h. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was used as the cathode and electrode A as the anode, and the two electrodes were placed in the anode-cathode chamber for secondary lithium extraction. The lithium extraction conditions were the same as the initial lithium extraction, and the cycle was repeated 10 times. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0164] Figure 9 The adsorption / desorption capacity and manganese dissolution rate of the selective lithium extraction cycle of C-LiMn2O4 in Comparative Example 5 are shown. As can be seen from the figure, C-LiMn2O4 exhibits high efficiency in lithium extraction. + The adsorption capacity is approximately 21.788 mg / g, and the Mn dissolution rate is approximately 2.439%. C-LiMn₂O₄ exhibits a high lithium adsorption capacity, but the significant manganese dissolution rate in acidic systems severely impacts the efficiency of selective lithium extraction, ultimately affecting the Li₂ adsorption capacity. + The overall recovery rate.

[0165] Comparative Example 6

[0166] This comparative example provides a method for preparing a lithium iron phosphate ion sieve selective lithium extraction electrode, specifically including the following steps:

[0167] (1) Take a certain amount of carbon black with a particle size of 1 μm and a certain amount of sodium phosphate and ferric chloride solution, adjust the pH of the solution to 4, seal it and hydrothermally synthesize it at 200℃ for 24 h to obtain spherical C-FePO4; filter, dry and mix it with lithium chloride, and calcine it at 650℃ for 10 h in a reducing atmosphere to obtain C-LiFePO4 ion sieve.

[0168] (2) The C-LiFePO4 solid powder synthesized in step (1) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is weighed and coated on two titanium meshes with a thickness of 2mm. The organic solvent is removed by drying at 80°C. Then, the temperature is raised to 160°C and dried to remove the pore-forming agent, thus obtaining porous selective lithium extraction electrodes A and B with lithium iron phosphate.

[0169] (3) Electrode A was used as the anode, and the solution in the anode cavity was a 0.01M LiCl solution with pH 3.5; the cathode was a titanium plate, and the solution in the cathode cavity was a 0.5M CuCl2 solution; the constant current was maintained at 50mA for 10h to obtain the activated electrode A.

[0170] Electrochemical redox lithium extraction was performed using the C-LiFePO4 ion sieve selective lithium extraction electrode prepared in this comparative example, as detailed below:

[0171] (1) After grinding the lithium aluminum silicon glass thoroughly, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The solid-liquid mixture obtained from the reaction was separated to obtain the leachate and the leach residue. The pH of the leachate was measured to be 3.74.

[0172] ICP analysis was used to determine the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0173] (2) Electrode A was used as the cathode, and the solution in the cathode chamber was the leachate; the unactivated electrode B was used as the anode, and the anolyte was a 0.01M LiCl solution; lithium extraction was performed at a constant current of 50mA until the voltage reached 0.8V, and then selective lithium extraction was performed at a constant voltage of 0.68V for 20h. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was used as the cathode and electrode A as the anode, and the two electrodes were placed in the anode-cathode chamber for secondary lithium extraction. The lithium extraction operation conditions were the same as the initial lithium extraction, and the cycle was repeated 10 times.

[0174] Figure 10 The figure shows the adsorption / desorption capacity and iron loss rate of the C-LiFePO4 ion sieve in the selective lithium extraction cycle of Comparative Example 6. As can be seen from the figure, the C-LiFePO4 ion sieve exhibits high efficiency in selective lithium extraction of Li... +The adsorption capacity is approximately 18.65 mg / g, and the iron dissolution rate is approximately 0.127%. Although the C-LiFePO4 ion sieve can solve the dissolution problem in acidic systems, its adsorption capacity is not high, and it adsorbs H+ during cyclic adsorption-desorption experiments. + This leads to a gradual decrease in adsorption capacity during long-term cyclic electrochemical oxidation lithium extraction, ultimately resulting in the degradation of Li. + The overall recovery rate is low.

[0175] Comparative Example 7

[0176] This comparative example provides a method for preparing a selective lithium extraction electrode, specifically including the following steps:

[0177] (1) The purchased lithium manganese oxide was ground to a particle size of 5 μm. Then, sodium phosphate and ferric chloride were added to the ion sieve solution to adjust the pH of the solution to 4. After sealing, the solution was hydrothermally synthesized at 200℃ for 24 h to obtain a spherical core-shell structure (lithium manganese oxide-ferric phosphate) composite ion sieve. Finally, the core-shell structure composite ion sieve was dried and mixed with lithium chloride. It was then calcined at 650℃ for 10 h in a reducing atmosphere to obtain a lithium manganese oxide-lithium iron phosphate composite ion sieve.

[0178] (2) The core-shell structured solid powder synthesized in step (1) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is weighed and coated on two titanium meshes with a thickness of 2mm. The organic solvent is removed by drying at 80°C. Then, the temperature is raised to 160°C and dried to remove the pore-forming agent, thus obtaining porous selective lithium extraction electrodes A and B with core-shell structure.

[0179] (3) Electrode A was used as the anode, and the solution in the anode cavity was a 0.01M LiCl solution with pH 3.5; the cathode was a titanium plate, and the solution in the cathode cavity was a 0.5M CuCl2 solution; the constant current was maintained at 50mA for 10h to obtain the activated electrode A.

[0180] Electrochemical redox lithium extraction was performed using the core-shell structured selective lithium extraction electrode prepared in this embodiment, as detailed below:

[0181] (1) After grinding the lithium aluminum silicon glass thoroughly, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The solid-liquid mixture obtained from the reaction was separated to obtain the leachate and the leach residue. The pH of the leachate was measured to be 3.74.

[0182] ICP analysis was used to determine the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0183] (2) Electrode A was used as the cathode, and the solution in the cathode chamber was the leachate; the unactivated electrode B was used as the anode, and the anolyte was a 0.01M LiCl solution; lithium extraction was performed at a constant current of 50mA until the voltage reached 0.8V, and then selective lithium extraction was performed at a constant voltage of 0.68V for 20h. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was used as the cathode and electrode A as the anode, and the two electrodes were placed in the anode-cathode chamber for secondary lithium extraction. The lithium extraction conditions were the same as the initial lithium extraction, and the cycle was repeated 10 times. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0184] Figure 11 The figure shows the adsorption / desorption capacity and manganese dissolution rate of the core-shell composite ion sieve for selective lithium extraction in Comparative Example 7. As can be seen from the figure, the core-shell selective lithium extraction electrode synthesized from purchased lithium manganese oxide exhibits high efficiency for Li... + The adsorption capacity is approximately 29.084 mg / g, and the Mn dissolution rate is approximately 0.198%. Because there is no carbon black as the innermost layer material, the lithium-ion transport path is long and the resistance is high, resulting in a decrease in the amount of ions adsorbed within the same time frame.

[0185] Comparative Example 8

[0186] This comparative example provides a selective lithium extraction electrode for lithium manganese oxide, and its preparation method is as follows:

[0187] (1) The purchased lithium manganese oxide powder was mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve was weighed and coated on two titanium meshes with a thickness of 2mm. The organic solvent was removed by drying at 80°C. Then, the temperature was raised to 160°C and dried to remove the organic pore-forming agent, thus obtaining lithium selective lithium extraction electrodes A and B with lithium manganese oxide.

[0188] (2) Electrode A was used as the anode, and the solution in the anode cavity was a 0.01M LiCl solution with pH 3.5; the cathode was a titanium plate, and the solution in the cathode cavity was a 0.5M CuCl2 solution; the electrode A was activated by constant current at 50mA for 10h.

[0189] Electrochemical redox lithium extraction was performed using the lithium manganese oxide selective lithium extraction electrode prepared in this comparative example, as follows:

[0190] (1) After grinding the lithium aluminum silicon glass thoroughly, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The solid-liquid mixture obtained from the reaction was separated to obtain the leachate and the leach residue. The pH of the leachate was measured to be 3.74.

[0191] ICP analysis was used to determine the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0192] (2) Electrode A was used as the cathode, and the solution in the cathode chamber was the leachate; the unactivated electrode B was used as the anode, and the anolyte was a 0.01M LiCl solution; lithium extraction was performed at a constant current of 50mA until the voltage reached 0.8V, and then selective lithium extraction was performed at a constant voltage of 0.68V for 20h. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was used as the cathode and electrode A as the anode, and the two electrodes were placed in the anode-cathode chamber for secondary lithium extraction. The lithium extraction conditions were the same as the initial lithium extraction, and the cycle was repeated 10 times. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0193] Figure 12 The figure shows the adsorption / desorption capacity and manganese loss rate of the selective lithium extraction cycle of lithium manganese oxide in Comparative Example 8. As can be seen from the figure, the purchased lithium manganese oxide exhibits high efficiency for lithium extraction. + The adsorption capacity is approximately 19.962 mg / g, and the Mn dissolution rate is approximately 2.528%. However, the purchased lithium manganese oxide exhibits a high manganese dissolution rate in acidic systems, which will severely reduce the efficiency of selective lithium extraction. Furthermore, the absence of carbon black as the innermost layer material results in a long lithium-ion diffusion path, ultimately affecting the Li-ion extraction efficiency. + The overall recovery rate.

[0194] Comparative Example 9

[0195] This comparative example provides a method for preparing a lithium iron phosphate ion sieve selective lithium extraction electrode, specifically including the following steps:

[0196] (1) The purchased lithium iron phosphate powder was mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve was weighed and coated on two titanium meshes with a thickness of 2mm. The organic solvent was removed by drying at 80°C. Then, the temperature was raised to 160°C and dried to remove the pore-forming agent, thus obtaining lithium iron phosphate ion sieve selective lithium extraction electrodes A and B.

[0197] (2) Electrode A was used as the anode, and the solution in the anode cavity was a 0.01M LiCl solution with pH 3.5; the cathode was a titanium plate, and the solution in the cathode cavity was a 0.5M CuCl2 solution; the electrode A was activated by constant current at 50mA for 10h.

[0198] Electrochemical redox lithium extraction was performed using the lithium iron phosphate ion sieve selective lithium extraction electrode prepared in this comparative example, as follows:

[0199] (1) After grinding the lithium aluminum silicon glass thoroughly, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The solid-liquid mixture obtained from the reaction was separated to obtain the leachate and the leach residue. The pH of the leachate was measured to be 3.74.

[0200] ICP analysis was used to determine the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0201] (2) Electrode A was used as the cathode, and the solution in the cathode chamber was the leachate; the unactivated electrode B was used as the anode, and the anolyte was a 0.01M LiCl solution; lithium extraction was performed at a constant current of 50mA until the voltage reached 0.8V, and then selective lithium extraction was performed at a constant voltage of 0.68V for 20h. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was used as the cathode and electrode A as the anode, and the two electrodes were placed in the anode-cathode chamber for secondary lithium extraction. The lithium extraction conditions were the same as the initial lithium extraction, and the cycle was repeated 10 times. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0202] Figure 13 The figure shows the adsorption / desorption capacity and iron loss rate of the lithium iron phosphate ion sieve in the selective lithium extraction cycle of Comparative Example 9. As can be seen from the figure, the purchased lithium iron phosphate ion sieve exhibits high efficiency in lithium extraction. +The adsorption capacity was approximately 17.859 mg / g, and the iron loss rate was approximately 0.126%. While the purchased lithium iron phosphate ion sieve can address the loss issue in acidic systems, its adsorption capacity is not high, and it adsorbs H+ during cyclic adsorption-desorption experiments. + This leads to a gradual decrease in adsorption capacity during long-cycle electrochemical oxidation lithium extraction. Furthermore, the absence of carbon black as the innermost layer material results in a long lithium-ion diffusion path, ultimately leading to... + The overall recovery rate is low.

[0203] Example 3

[0204] This embodiment provides a method for preparing a core-shell structured selective lithium extraction electrode, specifically including the following steps:

[0205] (1) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of MnCl2, dissolve them together in 1M NaOH solution, mix thoroughly to obtain C-Mn(OH)2, filter, wash, dry, and then calcine in air at 550℃ for 36 h to obtain C-MnOOH. Mix C-MnOOH with 3.5M LiCl solution, adjust the pH of the solution to 8, seal, and then hydrothermally heat at 170℃ for 12 h to synthesize C-Li4Mn5O 12 After cleaning and filtration, the particles are thoroughly ground to a particle size of 6μm, i.e., the thickness of the intermediate layer is 5μm.

[0206] (2) Apply the synthesized C-Li4Mn5O from step (1) 12 Sodium phosphate and ferric chloride were dissolved in deionized water, and the pH of the solution was adjusted to 4. After sealing, the mixture was hydrothermally synthesized at 200℃ for 24 hours to obtain a spherical three-layer core-shell structure (C-Li4Mn5O). 12 -FePO4) composite ion sieve; finally, after drying the core-shell structured composite ion sieve precursor, it was mixed with lithium chloride and calcined at 650℃ for 10h in a reducing atmosphere to obtain C-Li4Mn5O 12 -LiFePO4; grind thoroughly until the particle size is 9μm, that is, the outer layer thickness is 3μm.

[0207] (3) The three-layer core-shell structured solid powder synthesized in step (2) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is coated on two titanium meshes with a thickness of 2mm and dried at 80°C to remove the organic solvent. Then, the temperature is raised to 160°C to dry and remove the organic pore-forming agent, thus obtaining porous selective lithium extraction electrodes A and B with core-shell structure.

[0208] (4) Using electrode A as the anode, the solution in the anode cavity is a 0.01M LiCl solution with pH=3.5, the cathode is a titanium plate, and the solution in the cathode cavity is a 0.5M CuCl2 solution; constant current at 50mA for 10h to obtain the activated electrode A.

[0209] Electrochemical redox lithium extraction was performed using the core-shell structured selective lithium extraction electrode prepared in this embodiment, as detailed below:

[0210] (1) After the lithium aluminum silicon glass was thoroughly ground, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The resulting solid-liquid mixture was separated to obtain the leachate and the leaching residue. The pH of the leaching solution was measured to be 3.74.

[0211] ICP analysis was used to analyze the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0212] (2) Using electrode A as the cathode, the solution in the cathode chamber as the leachate, and the unactivated electrode B as the anode, the anolyte was a 0.01M LiCl solution. Lithium extraction was performed under a constant current of 50mA until the voltage reached 0.8V, followed by selective lithium extraction under a constant voltage of 0.68V for 20 hours. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was placed as the cathode and electrode A as the anode in the anode-cathode chamber for secondary lithium extraction, with the same operating conditions as the initial extraction, for a total of 10 cycles. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0213] The three-layer core-shell structured selective lithium extraction electrode prepared in this embodiment is effective for Li-... + The adsorption capacity is approximately 50.534 mg / g, and the Mn dissolution rate is approximately 0.173%.

[0214] Example 4

[0215] This embodiment provides a method for preparing a core-shell structured selective lithium extraction electrode, specifically including the following steps:

[0216] (1) Weigh a certain amount of carbon black with a particle size of 1 μm and a certain amount of MnCl2, dissolve them together in a 1M NaOH solution, mix thoroughly to obtain C-Mn(OH)2, filter, wash, dry, and then calcine in air at 550℃ for 36 h to obtain C-MnOOH. Mix C-MnOOH with a 3.5M LiCl solution, adjust the pH of the solution to 8, seal, and then hydrothermally heat at 170℃ for 12 h to synthesize C-Li 1.6 Mn 1.6 After cleaning and filtering, O4 is thoroughly ground until the particle size is 6μm, that is, the thickness of the intermediate layer is 5μm.

[0217] (2) Apply the C-Li synthesized in step (1) 1.6 Mn 1.6 O4, sodium phosphate, and ferric chloride were dissolved in deionized water, and the pH of the solution was adjusted to 4. After sealing, the mixture was hydrothermally synthesized at 200°C for 24 hours to obtain a spherical three-layer core-shell structure (C-Li). 1.6 Mn 1.6 O4-FePO4) composite ion sieve; finally, after drying the core-shell structured composite ion sieve precursor, it was mixed with lithium chloride and calcined at 650℃ for 10 h in a reducing atmosphere to obtain C-Li 1.6 Mn 1.6 O4-LiFePO4; grind thoroughly until the particle size is 9μm, that is, the outer layer thickness is 3μm.

[0218] (3) The three-layer core-shell structured solid powder synthesized in step (2) is mixed with binder PVDF, conductive agent acetylene black, solvent NMP and organic pore-forming agent polystyrene in a mass ratio of 8:1:1:15:1.2 and stirred at 60°C for 2 hours. Then, 4g of the uniformly mixed ion sieve is coated on two titanium meshes with a thickness of 2mm and dried at 80°C to remove the organic solvent. Then, the temperature is raised to 160°C to dry and remove the organic pore-forming agent, thus obtaining porous selective lithium extraction electrodes A and B with core-shell structure.

[0219] (4) Using electrode A as the anode, the solution in the anode cavity is a 0.01M LiCl solution with pH=3.5, the cathode is a titanium plate, and the solution in the cathode cavity is a 0.5M CuCl2 solution; constant current at 50mA for 10h to obtain the activated electrode A.

[0220] Electrochemical redox lithium extraction was performed using the core-shell structured selective lithium extraction electrode prepared in this embodiment, as detailed below:

[0221] (1) After the lithium aluminum silicon glass was thoroughly ground, it was calcined in a muffle furnace at 110°C for 2 hours to remove the oily substances and moisture on the surface. Then, the dried lithium aluminum silicon glass powder was placed in a flask for leaching. The leaching was carried out in a jacketed reactor at 80°C for 1 hour in hydrochloric acid solution. The resulting solid-liquid mixture was separated to obtain the leachate and the leaching residue. The pH of the leaching solution was measured to be 3.74.

[0222] ICP analysis was used to analyze the concentration of metal ions in the leachate under different acid concentrations, solid-liquid ratios, and stirring rates. The results showed that under the conditions of 0.75 M HCl, 30 g / L, and 250 rpm, the concentration of Li... + And Al 3+ The leaching rates were >99.02% and >95.54%, respectively, and leaching equilibrium was almost reached after 10 minutes of leaching.

[0223] (2) Using electrode A as the cathode, the solution in the cathode chamber as the leachate, and the unactivated electrode B as the anode, the anolyte was a 0.01M LiCl solution. Lithium extraction was performed under a constant current of 50mA until the voltage reached 0.8V, followed by selective lithium extraction under a constant voltage of 0.68V for 20 hours. After lithium extraction, the surfaces of electrodes A and B were rinsed. Then, electrode B was placed as the cathode and electrode A as the anode in the anode-cathode chamber for secondary lithium extraction, with the same operating conditions as the initial extraction, for a total of 10 cycles. Finally, the delithiated anolyte solution was concentrated multiple times and then Na2CO3 was added to obtain crude lithium carbonate product.

[0224] The three-layer core-shell structured selective lithium extraction electrode prepared in this embodiment is effective for Li-... + The adsorption capacity is approximately 61.316 mg / g, and the Mn dissolution rate is approximately 0.182%.

[0225] The above-described 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. The scope of protection of the present invention is defined by the claims.

Claims

1. A composite ion sieve with a three-layer core-shell structure, characterized in that, The inner layer of the composite ion sieve is made of carbon material, the middle layer is lithium manganese oxide, and the outer layer is lithium iron phosphate.

2. The composite ion sieve with a three-layer core-shell structure according to claim 1, characterized in that, The composite ion sieve satisfies at least one of the following conditions: (i) The thickness of the lithium manganese oxide is ≤5 μm; (ii) The thickness of the lithium iron phosphate is ≥1μm; (iii) The mass ratio of the material of the outer layer to the material of the middle layer is (0.2 to 5):1; (iv) The particle size of the carbon material is ≤1μm.

3. A method for preparing a three-layer core-shell composite ion sieve, characterized in that, Includes the following steps: Carbon material-lithium manganese oxide, phosphorus source and iron source are mixed evenly in solution and then subjected to hydrothermal reaction under pH 3.0-5.0 conditions to obtain a three-layer core-shell structured composite ion sieve precursor. The composite ion sieve precursor and lithium source are mixed and calcined in a reducing atmosphere to obtain a three-layer core-shell structured composite ion sieve.

4. The method for preparing a three-layer core-shell composite ion sieve according to claim 3, characterized in that, The particle size of the carbon material is ≤1μm; and / or, The phosphorus source includes at least one of sodium phosphate, potassium phosphate, sodium dihydrogen phosphate, ammonium phosphate, and phosphoric acid; and / or, The iron source includes at least one of ferric chloride, ferric sulfate, and their various hydrates; and / or, The hydrothermal reaction temperature is 100℃~300℃, and the holding time for the hydrothermal reaction is 2~72h; and / or, The lithium source includes at least one selected from lithium carbonate, lithium hydroxide, lithium chloride, lithium bromide, lithium fluoride, lithium nitrate, lithium acetate, lithium oxalate, lithium sulfate, lithium acetate, and lithium formate; and / or, The molar ratio of the lithium source to the composite ion sieve precursor is 1:(1-2); and / or, The roasting temperature is 500℃~800℃, and the roasting time is 1~12h.

5. A selective lithium extraction electrode with a three-layer core-shell structure, characterized in that, The selective lithium extraction electrode with a three-layer core-shell structure is prepared by fabricating a composite ion sieve with a three-layer core-shell structure as described in claim 1 or 2 into a selective lithium extraction electrode, and then creating pores; the preparation method includes the following steps: A precursor solution is obtained by mixing a three-layer core-shell composite ion sieve, a binder, a conductive agent, and an organic solvent. An organic pore-forming agent is added to the precursor solution to obtain a precursor solution containing the organic pore-forming agent. The precursor solution containing the organic pore-forming agent is coated onto the electrode substrate material to form a selective electrode, and then the organic pore-forming agent is removed. The adhesive comprises at least one of polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene, and waterborne polystyrene ester; and / or, The conductive agent includes at least one of carbon black, acetylene black, graphite, carbon fiber, carbon nanotubes, graphene, Ketjen black, and composite conductive paste; and / or, The organic solvent includes at least one of N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone, dimethylformamide, and dimethylacetamide; and / or, The electrode substrate material is an inert metal and / or a non-metallic conductive material; and / or, The electrode substrate material includes at least one of graphite sheet, titanium sheet, carbon cloth, and carbon felt; and / or, The organic pore-forming agent is at least one selected from polystyrene, polyethylene glycol, polyvinyl chloride, polyoxymethylene, epoxy resin, polyglycolic acid, lignin, cellulose, and hemicellulose; and / or, The weight ratio of the composite ion sieve with the three-layer core-shell structure, organic solvent, binder, conductive agent, and organic pore-forming agent is 8:1–10:1–10:1–10:1–3; and / or, The organic solvent is removed by low-temperature drying, wherein the low-temperature drying temperature is 40°C to 120°C; and / or, The organic pore-forming agent is removed by high-temperature drying, wherein the high-temperature drying temperature is 150℃~250℃ and the high-temperature drying time is 2~24h.

6. A method for extracting lithium from an acidic lithium-containing solution via electrochemical oxidation-reduction, characterized in that, Includes the following steps: An electrochemical system is provided, comprising an anode chamber, a cathode chamber, and a diaphragm; the anode chamber contains an anolyte, and the cathode chamber contains a catholyte, wherein the catholyte is an acidic lithium-containing solution; the anode chamber and the cathode chamber are separated by the diaphragm. The selective lithium extraction electrode with the three-layer core-shell structure described in claim 5 is placed in the anolyte as the anode. After the selective lithium extraction electrode with the three-layer core-shell structure described in claim 5 is activated, it is placed in the catholy solution as a cathode. The anode and cathode are connected to a power source to extract lithium.

7. The method for electrochemical oxidation-reduction extraction of lithium from an acidic lithium-containing solution according to claim 6, characterized in that, The electrochemical system satisfies at least one of the following conditions: (a) The cathode solution comprises an acid leaching solution of lithium aluminosilicate glass; (b) The cathode solution is a lithium-containing solution with a pH of 3.5–4; (c) The anolyte is a lithium-containing solution with a pH of 3 to 5; (d) The anolyte is one or more of the following: lithium chloride solution, lithium bromide solution, lithium fluoride solution, lithium nitrate solution, lithium acetate solution, lithium oxalate solution, lithium sulfate solution, lithium acetate solution, and lithium formate solution, at a concentration of 0.01–1 M. (e) The membrane is an anion exchange membrane.

8. The method for electrochemical oxidation-reduction extraction of lithium from an acidic lithium-containing solution according to claim 6, characterized in that, The cathode solution is an acid leachate obtained by heating and stirring lithium aluminum silicon glass powder in an acidic solution, wherein: The acidic solution includes one or more of HCl, HNO3, and H2SO4; and / or, The concentration of the acidic solution is 0.01–10 mol / L; and / or, The stirring rate is 10–2000 rpm; and / or, The heating temperature is 0–250°C.

9. The method for electrochemical oxidation-reduction extraction of lithium from an acidic lithium-containing solution according to claim 6, characterized in that, It also includes the following steps: After lithium extraction is completed, the anode and cathode are removed, cleaned, and the electrodes are exchanged to continue lithium extraction. Repeat the above steps to cycle and extract lithium until the lithium content in the cathode solution is below 10 ppm. Lithium is recovered from the anolyte.

10. The method for electrochemical oxidation-reduction extraction of lithium from an acidic lithium-containing solution according to claim 9, characterized in that, The lithium extraction voltage is 0.3–1.2V; and / or, The lithium extraction time is 1–100 h; and / or, The number of lithium extraction cycles is 3 to 500; and / or, The method for recovering lithium from the anolyte includes: concentrating the anolyte to obtain crude water and crude lithium salt; or adding Na2CO3 to the concentrated anolyte to obtain crude lithium carbonate.

Images