A lithium extraction electrode, its preparation method and application

Abstract

This invention belongs to the field of electrode material technology, and relates to a lithium extraction electrode, its preparation method, and its application. The preparation method of the lithium extraction electrode is as follows: A mixture of LiMn2O4 and C powder is added to a micro-suspension system composed of an oil phase and an aqueous solution containing a stabilizer. Free radical-initiated polymerization is then carried out to obtain LiMn2O4-based porous active microparticles with a core-shell structure and surface-anchored hydrophilic macromolecules. The oil phase consists of vinyl monomers, a solvent, and a surfactant. Using the LiMn2O4-based porous active microparticles as the electroactive material, they are mixed and cured with a conductive agent, a hydrophilic binder, and a crosslinking agent to obtain the lithium extraction electrode. This lithium extraction electrode has a stable structure, high water permeability, and uniform internal and external electric fields. It can significantly improve the lithium ion transport rate and electrode lifetime during electrochemical lithium extraction, and has broad application prospects in electrochemical lithium extraction.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, and relates to a lithium extraction electrode, its preparation method and application. Background Technology

[0002] Electrochemical lithium extraction technology has attracted widespread attention in the fields of lithium extraction from salt lake brine and seawater due to its advantages such as high lithium selectivity, fast rate, and low energy consumption. The core of this technology lies in electrode materials with lithium-ion screening function. Among them, spinel-type lithium manganese oxide (LiMn2O4) is an ideal electroactive material due to its unique crystal structure, excellent memory effect and selectivity for lithium ions, high theoretical capacity, and environmental friendliness.

[0003] However, LiMn2O4 faces challenges in practical applications. In aqueous electrolytes, some Mn on the surface of LiMn2O4... 3+ It readily undergoes a disproportionation reaction to form soluble Mn. 2+ This leads to the dissolution of active materials and capacity decay. Moreover, the Jahn-Teller effect of crystalline LiMn2O4 causes lattice distortion, affecting the stability of the electrode structure.

[0004] To improve the electrochemical performance of LiMn2O4, existing technologies employ hydrophilic binder systems and surface coating modifications to address manganese leaching and structural instability issues in aqueous environments. For example, carbon coating technology can be used to improve the electronic conductivity and interfacial stability of LiMn2O4: Reference 1: https: / / doi.org / 10.5229 / JECST.2016.7.2.139. Reference 1 discloses a method using polydopamine as a carbon source, forming a polydopamine layer on the LiMn2O4 surface through spontaneous oxidative polymerization of dopamine, followed by carbonization to obtain carbon-coated LiMn2O4 nanoparticles. This method utilizes the strong adhesion of polydopamine to achieve uniform coating, and the carbon layer effectively suppresses side reactions between the active material and the electrolyte, improving rate performance and cycle stability.

[0005] Reference 2: https: / / doi.org / 10.1002 / smtd.202401972. Reference 2 reports a lithium-ion (Li-Nafion) coating strategy, constructing an approximately 3.5 nm thick Li-Nafion coating on the surface of LiMn2O4 via a simple impregnation method. This coating significantly enhances the hydrophilicity of the LiMn2O4 surface, constructs a rapid lithium-ion transport channel, and effectively suppresses manganese dissolution.

[0006] Reference 3: https: / / doi.org / 10.1016 / j.psep.2024.08.113. Reference 3 reports a method for constructing a stable three-dimensional network structure thin-film electrode through in-situ crosslinking. This study uses LiMn2O4 / C as the active material and polyvinyl alcohol (PVA) and lithium carboxymethyl cellulose (CMCLi) as water-soluble binders to prepare a LiMn2O4 / C / PVA-c-CMCLi thin-film electrode through covalent crosslinking. Compared with traditional PVDF-bonded electrodes, this electrode exhibits a superior adsorption capacity (25.53 mg·g⁻¹). -1 The faster adsorption equilibrium time (2 hours) is attributed to the improved electrolyte wettability and enhanced adhesion strength of the cross-linked three-dimensional network structure, which, through the -COOLi groups in CMCLi, promotes the adsorption of Li. + transmission.

[0007] Reference 4: https: / / doi.org / 10.1016 / j.seppur.2023.123777. Reference 4 reports a physically blended polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA) composite binder for preparing LiMn2O4 / C / PVDF-b-PAA thin film coated electrodes. This composite binder system endows the electrode with excellent mechanical properties, hydrophilicity, and electrochemical performance. When treating simulated brine (Mg / Li ratio approximately 500), Li... + The embedding capacity is approximately 15.1 mg g. -1 After two electrochemical intercalation tests, the total lithium extraction efficiency reached 62.8%. These modification methods reduced the water contact angle of the electrode to some extent, thereby increasing the lithium extraction rate.

[0008] Reference 5: https: / / doi.org / 10.1016 / j.seppur.2025.134074. Reference 5 reports a method for preparing LiFe2PO4 electrodes (LFA) using hydrophilic macromolecular PVA as a binder and urea as a crosslinking agent, and its lithium extraction application.

[0009] However, the aforementioned research on surface coating and hydrophilic binders still has significant shortcomings: carbon coating technology is mainly aimed at organic electrolyte systems; although Li-Nafion surface coating improves the hydrophilicity and stability of the material, the coating uniformity is not easy to control, and subsequent electrode preparation still requires blending with hydrophobic or hydrophilic binders, failing to fundamentally solve the dispersion problem of LiMn2O4 powder in hydrophilic binder systems. Although the hydrophilic binder systems of PVDF-b-PAA and PVA-c-CMCLi improve the overall hydrophilicity of the electrode, when LiFe2PO4 powder is directly blended with high-concentration hydrophilic polymers, it is still easy to cause binder flocculation or active material sedimentation, resulting in poor slurry dispersion and uneven internal electrode structure. Summary of the Invention

[0010] To overcome the problems of flocculation, sedimentation and uneven dispersion caused by the high polarity and high density of LiMn2O4 in hydrophilic binder systems in existing modification methods, which in turn leads to uneven electrode structure and unstable electrochemical performance, this invention provides a lithium extraction electrode, its preparation method and application.

[0011] This invention designates a mixture of LiMn2O4 and C as LiMn2O4 / C. This invention utilizes the physical isolation mechanism of LiMn2O4 / C in a micro-suspension system. Specifically, LiMn2O4 / C is added as a functional component to a micro-suspension system composed of an oil phase and an aqueous solution containing a low concentration of hydrophilic macromolecular stabilizer. The oil phase consists of polar functionalized vinyl monomers, a solvent, and a surfactant. During the polymerization reaction, LiMn2O4 / C adsorbs onto the surface of the oil phase droplets and is firmly bonded by the generated polymer through in-situ polymerization of the monomers in the oil phase, thereby forming a hydrophilic LiMn2O4-based porous active microparticle with a core-shell structure. This microparticle has a polar polymer core and a loosely structured, porous LiMn2O4 / C outer shell. Simultaneously, during this process, the low concentration of hydrophilic polymers acting as stabilizers in the aqueous solution is anchored to the surface of the formed LiMn2O4-based porous active microparticles. These surface-anchored hydrophilic macromolecular chains provide abundant reactive functional groups for the subsequent chemical cross-linking reaction when preparing lithium extraction electrodes using PVA as a binder. This enables the LiMn2O4-based porous active microparticles to be effectively cross-linked and fixed with the electrode matrix, thereby ensuring that both the microparticles and the final lithium extraction electrode have good mechanical properties and structural stability.

[0012] This invention provides a method for preparing a lithium extraction electrode, comprising the following steps: A polar functional group-substituted vinyl monomer, solvent, and surfactant are mixed to obtain an oil phase; the oil phase is mixed with an aqueous solution containing a stabilizer to obtain a micro-suspension; a mixture of LiMn2O4 and C powder is added to the micro-suspension, and a free radical-initiated polymerization reaction is carried out under the action of an initiator to form LiMn2O4-based porous active microparticles with a core-shell structure, consisting of a polar polymer core and LiMn2O4 and C shells; the stabilizer is at least one of polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol; the LiMn2O4-based porous active microparticles, conductive agent, binder, and crosslinking agent are mixed and cured to obtain a lithium-extracting electrode.

[0013] Preferably, the mass ratio of the mixture of LiMn2O4 and C to the vinyl monomer substituted with polar functional groups is 1:0.04-0.06; the mass ratio of LiMn2O4 to C is 20:1. This ratio determines the relative content of the polar polymer core and the active material shell in the core-shell structure. When the amount of vinyl monomer substituted with polar functional groups is too low, the formed polar polymer core is too small and cannot effectively bond the LiMn2O4 / C particles, resulting in a loose particle structure and an incomplete shell. When the amount of vinyl monomer substituted with polar functional groups is too high, the formed polar polymer core is too large, the LiMn2O4 / C shell is too thin, the content of active material decreases, and the lithium extraction capacity and rate of the electrode are affected.

[0014] Preferably, the volume ratio of the oil phase to the aqueous solution containing the stabilizer is 1:4.3–5.5; the concentration of the stabilizer in the aqueous solution is 0.5wt%–2wt%. This ratio affects the stability of the microsuspension system and the particle size distribution. When the aqueous phase ratio is too low or the stabilizer concentration is insufficient, droplets are prone to aggregation, resulting in uneven particle size and severe agglomeration; when the aqueous phase ratio is too high or the stabilizer concentration is too high, the particle size is too small, and there are too many hydrophilic macromolecules anchored on the surface, hindering lithium-ion transport.

[0015] Preferably, the vinyl monomer with substituted polar functional groups is at least one selected from acrylamide, acrylic acid, methyl acrylate, and ethyl acrylate; the solvent is C8-C4. 12 At least one of the long-chain fatty alcohols; the surfactant is at least one of sodium dodecyl sulfate or sodium dodecyl sulfonate.

[0016] Preferably, the solvent is at least one of n-octanol, n-pentanol, and lauryl alcohol.

[0017] Preferably, the concentration of the stabilizer in the aqueous solution is 0.5wt% to 2wt%.

[0018] Preferably, the degree of hydrolysis of polyvinyl alcohol in the stabilizer is 60% to 90% and the molecular weight is 80,000 to 120,000; the molecular weight of polyethylene glycol is below 20,000 and the molecular weight of polyvinylpyrrolidone is 30,000 to 90,000.

[0019] More preferably, the molecular weight of polyethylene glycol is 8000 to 2000.

[0020] Preferably, the temperature for the free radical-initiated polymerization reaction is 75℃~90℃, and the time is 2 hours~4 hours.

[0021] Preferably, the initiator is azobisisobutyronitrile, benzoyl peroxide, or potassium persulfate; the mass of the initiator is 0.5% to 1% of the mass of the vinyl monomer substituted with polar functional groups.

[0022] This invention provides a LiMn2O4-based porous active microparticle, which is prepared by the above-described preparation method.

[0023] Preferably, the particle size of the LiMn2O4-based porous active microparticles is 1 μm to 10 μm.

[0024] Preferably, the method for preparing the lithium extraction electrode includes the following steps: LiMn2O4-based porous active microparticles, conductive agent, binder and solvent are mixed to obtain a slurry; when the slurry is cooled to 50°C, a crosslinking agent is added and stirred evenly, and then coated onto a current collector; after curing, it is immersed in an alkaline solution for treatment, and after curing, a lithium-extracting electrode is obtained.

[0025] Preferably, the mass ratio of LiMn2O4-based porous active microparticles, conductive agent, and binder is 10:1:1.

[0026] Preferably, the binder is a mixture of any one of polyethylene glycol and polyvinylpyrrolidone and polyvinyl alcohol, wherein the mass ratio of any one of polyethylene glycol and polyvinylpyrrolidone to polyvinyl alcohol is less than 10%; the degree of hydrolysis of polyvinyl alcohol in the binder is more than 90%, and the degree of polymerization is 1700 to 1800.

[0027] Preferably, the crosslinking agent is epichlorohydrin; the conductive agent is activated carbon.

[0028] Preferably, the mixing temperature is 80℃~95℃.

[0029] This invention provides an application of a lithium extraction electrode in lithium extraction from brine.

[0030] Preferred, specific application method: The lithium-extracting electrode is used as the anode and placed in the anode chamber containing electrolyte; the lithium-depleted electrode is used as the cathode and placed in the cathode chamber containing brine; an anion exchange membrane is used to separate the anode and cathode chambers; a current density of 5 A / m is applied. 2 ~25A / m 2 Constant current charging is performed, and once the voltage rises to 0.8V, it switches to constant voltage charging until the current density drops to 2A / m.2 The following steps complete the lithium extraction; the brine is lithium-containing salt lake brine or simulated lithium-containing brine, and the electrolyte is sodium chloride solution.

[0031] Compared with the prior art, the present invention has the following technical effects: 1. This invention involves adding LiMn2O4 / C powder as a physical isolating agent to a micro-suspension system composed of an oil phase and an aqueous solution containing a low concentration of hydrophilic macromolecular stabilizer. The oil phase consists of vinyl monomers substituted with polar functional groups, a solvent, and a surfactant. Through free radical-initiated polymerization, hydrophilic LiMn2O4-based porous active microparticles with a core-shell structure—a polar polymer core and porous LiMn2O4 / C shell—were successfully prepared. Due to the removal of surfactants and long-chain fatty alcohols during the preparation process, a rich pore structure is formed inside and in the shell of the microparticles. Furthermore, hydrophilic macromolecular chains derived from the aqueous stabilizer are anchored on the surface of the microparticles, thus endowing them with high specific surface area, high hydrophilicity, and excellent ion exchange performance. Lithium extraction electrodes were prepared using hydrophilic LiMn2O4-based porous active microparticles. Due to the hydrophilic and porous nature of the microparticle surface, the large specific surface area and low density effectively improved the dispersibility of LiMn2O4 powder in the hydrophilic macromolecular binder system. It also solved the flocculation and sedimentation problems of hydrophilic binders such as PVA caused by the high polarity and high density of LiMn2O4, thus ensuring the uniformity of the internal and external structure of the lithium extraction electrode.

[0032] 2. In the lithium extraction electrode preparation process, this invention uses epichlorohydrin as a crosslinking agent, which reacts with the hydroxyl groups of the binder PVA under alkaline conditions to form a stable three-dimensional network structure. More importantly, because the surface of the particles is anchored with long PVA chains, these particles can simultaneously participate in crosslinking as network nodes and form chemical bonds with the surface of the graphite current collector, which is also rich in hydroxyl groups. This multiple chemical crosslinking effect firmly binds the active particles, binder network, and current collector into one, significantly improving the mechanical strength and structural stability of the electrode, effectively inhibiting the dissolution and shedding of the active material, and extending the cycle life of the electrode.

[0033] 3. This invention utilizes a highly hydrophilic, porous structure co-constructed from LiMn2O4-based electroactive microparticles and an electrode substrate. This provides a smooth channel for the rapid diffusion of lithium ions from the electrolyte to the active sites, reducing concentration polarization and thus ensuring a high electrochemical reaction rate. Furthermore, the pre-dispersion and fixation of LiMn2O4 within the porous shell on the polymer core surface provides constraint and buffering for the volume changes of LiMn2O4 during lithium insertion / extraction, helping to alleviate structural stress caused by the Jahn-Teller effect. Combined with the aforementioned excellent electrode structural stability, this significantly reduces the dissolution rate of Mn and substantially extends the electrode's cycle life. Attached Figure Description

[0034] Figure 1 SEM images of the LiMn2O4-based porous active microparticles prepared in Examples 1 to 5 are shown below. Specifically, (a) is the SEM image of the LiMn2O4-based porous active microparticles obtained in Example 1; (b) is the SEM image of the LiMnO4-based porous active microparticles obtained in Example 2; (c) is the SEM image of the LiMn2O4-based porous active microparticles obtained in Example 3; (d) is the SEM image of the LiMn2O4-based porous active microparticles obtained in Example 4; and (e) is the SEM image of the LiMnO2O4-based porous active microparticles obtained in Example 5.

[0035] Figure 2 The hydrophilic contact angles are those of the lithium extraction electrode surface prepared in Example 1. Among them, (a) is the hydrophilic contact angle of the lithium extraction electrode surface prepared in Example 1 at 0.4s; (b) is the hydrophilic contact angle of the lithium extraction electrode surface prepared in Example 1 at 0.8s; and (c) is the hydrophilic contact angle of the lithium extraction electrode surface prepared in Example 1 at 1.2s.

[0036] Figure 3 The lithium extraction and deintercalation performance of the lithium extraction electrodes prepared in Example 1 and Comparative Examples 1 to 2 is shown. Among them, (a) is the current-time curve of the lithium extraction electrodes prepared in Example 1 and Comparative Examples 1 to 2 during the constant current charging stage, and (b) is the lithium extraction rate of the lithium extraction electrodes prepared in Example 1 and Comparative Examples 1 to 2 at different current densities.

[0037] Figure 4 The cycling stability of the lithium extraction electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 2 is shown. Specifically, (a) shows the Li-values ​​of the lithium extraction electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 2 at different cycling cycles. + (a) Capacity; (b) The average lithium extraction rate and Mn dissolution rate of the lithium extraction electrodes prepared in Examples 1 to 5 and Comparative Examples 1 to 2 under 100 cycles. Detailed Implementation

[0038] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0039] In the description of the present invention, unless otherwise specified, the reagents used are commercially available and of analytical grade, and the methods used are conventional techniques in the art. Among them: lithium iron phosphate was purchased from Jiangsu Leneng Battery Co., Ltd.; N-methyl-2-pyrrolidone was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd.; acetylene black was purchased from Cyber Electrochemical Materials Network; polyvinylidene fluoride, polyvinyl alcohol, polyethylene glycol, and poly-N-vinylpyrrolidone were all purchased from Arkema Co., Ltd., purchased from Tianjin Fuyu Fine Chemical Co., Ltd., graphite plate Cyber Electrochemical Materials Network; epichlorohydrin was purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. Polyvinylidene fluoride is abbreviated as PVDF, polyvinylidene fluoride is abbreviated as PVDF, polyvinyl alcohol is abbreviated as PVA, polyethylene glycol is abbreviated as PEG, poly-N-vinylpyrrolidone is abbreviated as PVP, benzoyl peroxide is abbreviated as BPO, and epichlorohydrin is abbreviated as ECH; sodium dodecyl sulfate is abbreviated as SDS. Figure 3 The Chinese name of Time in Figure 3 is time, and the Chinese name of Current is current; the Chinese name of Current density is current density, Li + The Chinese name of extraction rate is lithium extraction rate; Figure 4 The Chinese name of Number of cycle in Figure 4 is cycle period, and the Chinese name of Capacity is capacity; the Chinese name of Mn loss Capacity is Mn loss amount.

[0040] Example 1 A method for preparing a lithium extraction electrode includes the following steps: Take 0.05 g of acrylamide and dissolve it in a mixture of 10 mL of n-octanol and 3 g of SDS to obtain an oil phase. Mix the oil phase with 30 mL of a 0.5 wt% PVA (the hydrolysis degree of PVA is 90% and the molecular weight is 120,000) aqueous solution, and stir at a speed of 300 revolutions per minute to form a stable micro-suspension.

[0041] Add 1 g of a mixture of LiMn2O4 and C powder (where the mass ratio of LiMn2O4 to C is 10:1) to the micro-suspension, and continue to stir and disperse evenly. Then add 5 mg of BPO as an initiator, stir and slowly heat up to 80 °C, and keep the temperature for reaction for 2 hours. Stop the reaction, filter the reaction product, and wash it alternately with deionized water and ethanol for multiple times, and dry it to obtain 1.032 g of LiMn2O4-based porous active particles, denoted as PA@LiMn2O4 / C1.

[0042] PA@LiMn2O4 / C, acetylene black, and binder (a mixture of PVA and PVP, with PVP comprising 10% of the PVA mass) were mixed at a mass ratio of 10:1:1 to obtain a mixture. The mixture was then dispersed in water, with the water mass being twice the mixture volume, and stirred at 90°C for 12 hours to obtain a homogeneous slurry. The PVA had a degree of hydrolysis of 90% and a degree of polymerization of 1750; the PVP had a molecular weight of 90,000.

[0043] The slurry was cooled to 50°C, and 0.5 mL of ECH was slowly added dropwise as a crosslinking agent while stirring, and the mixture was stirred until homogeneous. The resulting slurry was then uniformly coated onto a graphite current collector measuring 13 cm × 5 cm × 0.3 cm, with a coating area of ​​5 cm × 5 cm and a coating amount of 0.5 g / cm². 2 Let it cure at room temperature.

[0044] The cured electrode plate was immersed in a 3wt% NaOH solution for 30 minutes, then removed and placed in a constant temperature drying oven. The temperature was raised to 80℃ and maintained for 4 hours to allow the electrode to dry and cure completely, resulting in a highly hydrophilic lithium manganese oxide lithium extraction electrode, denoted as PA@LM1.

[0045] Example 2 A method for preparing a lithium extraction electrode is basically the same as the method in Example 1, except that: The vinyl monomer used is 0.06g of acrylamide; the stabilizers are PVA, PEG and PVP; among them, PVA has a degree of hydrolysis of 90% and a molecular weight of 120,000; PVP has a molecular weight of 90,000; and PEG has a molecular weight of 8,000.

[0046] 0.06 g of acrylamide was dissolved in a mixture of 10 mL of n-octanol and 3 g of SDS to obtain the oil phase. The oil phase was mixed with 30 mL of an aqueous solution containing 1 wt% PVA, 0.1% PEG, and 0.1% PVP; wherein PVA has a degree of hydrolysis of 90% and a molecular weight of 120,000, PVP has a molecular weight of 90,000, and PEG has a molecular weight of 8,000. The mixture was stirred at 300 rpm to form a stable microsuspension.

[0047] Add 1g of a mixture of LiMn2O4 and C powder (with a mass ratio of LiMn2O4 to C of 10:1) to the micro-suspension and continue stirring to disperse evenly. Then add 5mg of BPO as an initiator, stir, and slowly heat to 80℃, and react at this temperature for 2 hours. Stop the reaction, filter the reaction product, wash it several times alternately with deionized water and ethanol, and dry it to obtain 1.102g of LiMn2O4-based porous active microparticles, denoted as PA@LiMn2O4 / C2.

[0048] PA@LiMn2O4 / C2, acetylene black, and binder (a mixture of PVA and PVP, with PVP comprising 10% of the PVA mass) were mixed at a mass ratio of 10:1:1 to obtain a mixture. The mixture was then dispersed in water, with the water mass being twice the volume of the mixture, and stirred at 90°C for 12 hours until a homogeneous slurry was obtained. The PVA had a degree of hydrolysis of 90% and a degree of polymerization of 1750; the PVP had a molecular weight of 90,000.

[0049] The slurry was cooled to 50°C, and 0.5 mL of ECH was slowly added dropwise as a crosslinking agent while stirring, with continued stirring until homogeneous. Subsequently, the resulting slurry was uniformly coated onto a graphite current collector measuring 13 cm × 5 cm × 0.3 cm, with a coating area of ​​5 cm × 5 cm and a coating amount of 0.5 g / cm². 2 Let it cure at room temperature.

[0050] The cured electrode plate was immersed in a 3wt% NaOH solution for 30 minutes, then removed and placed in a constant temperature drying oven. The temperature was raised to 80℃ and maintained for 4 hours to allow the electrode to dry and cure completely, resulting in a highly hydrophilic lithium manganese oxide lithium extraction electrode, denoted as PA@LM2.

[0051] Example 3 A method for preparing a lithium extraction electrode is basically the same as the method in Example 1, except that: The vinyl monomer used was a blend of 0.05g acrylamide and 0.01g acrylic acid; the mass of the mixture of LiMn2O4 and C powder was 1.1g.

[0052] 0.05 g of acrylamide and 0.01 g of acrylic acid were dissolved together in a mixture of 10 mL of n-octanol and 3 g of SDS to obtain the oil phase. The oil phase was mixed with 30 mL of an aqueous solution containing 1 wt% PVA (PVA has a degree of hydrolysis of 90% and a molecular weight of 120,000) and stirred at 300 rpm to form a stable micro-suspension.

[0053] A mixture of 1.1 g of LiMn2O4 and C powder (with a mass ratio of LiMn2O4 to C of 10:1) was added to the micro-suspension, and the mixture was stirred and dispersed evenly. Then, 5 mg of BPO was added as an initiator, and the mixture was stirred and slowly heated to 80 °C, and reacted at this temperature for 2 hours. The reaction was stopped, the reaction product was filtered, and washed several times alternately with deionized water and ethanol, and dried to obtain 1.233 g of LiMn2O4-based porous active microparticles, denoted as PA@LiMn2O4 / C3.

[0054] PA@LiMn2O4 / C3, acetylene black, and binder (a mixture of PVA and PVP, where PVP accounts for 10% of the mass of PVA) were mixed at a mass ratio of 10:1:1 to obtain a mixture. The mixture was then dispersed in water, with the water mass being twice the volume of the mixture, and stirred at 90°C for 12 hours until a homogeneous slurry was obtained. The PVA had a degree of hydrolysis of 90% and a degree of polymerization of 1750; the PVP had a molecular weight of 90,000.

[0055] The slurry was cooled to 50°C, and 0.5 mL of ECH was slowly added dropwise as a crosslinking agent while stirring, with continued stirring until homogeneous. Subsequently, the resulting slurry was uniformly coated onto a graphite current collector measuring 13 cm × 5 cm × 0.3 cm, with a coating area of ​​5 cm × 5 cm and a coating amount of 0.5 g / cm². 2 Let it cure at room temperature.

[0056] The cured electrode plate was immersed in a 3wt% NaOH solution for 30 minutes, then removed and placed in a constant temperature drying oven. The temperature was raised to 80℃ and maintained for 4 hours to allow the electrode to dry and cure completely, resulting in a highly hydrophilic lithium manganese oxide lithium extraction electrode, denoted as PA@LM3.

[0057] Example 4 A method for preparing a lithium extraction electrode is basically the same as the method in Example 1, except that: The vinyl monomer used was a blend of 0.05g acrylamide and 0.01g methyl acrylate; the mass of the mixture of LiMn2O4 and C powder was 1.2g.

[0058] 0.05 g of acrylamide and 0.01 g of methyl acrylate were dissolved together in a mixture of 10 mL of n-octanol and 3 g of SDS to obtain the oil phase. The oil phase was mixed with 30 mL of an aqueous solution containing 1 wt% polyvinyl alcohol (PVA) (90% degree of hydrolysis, molecular weight 120,000) and stirred at 300 rpm to form a stable micro-suspension.

[0059] A mixture of 1.2 g of LiMn2O4 and C powder (with a mass ratio of LiMn2O4 to C of 10:1) was added to the micro-suspension, and the mixture was stirred until evenly dispersed. Then, 5 mg of benzoyl peroxide (BPO) was added as an initiator, and the mixture was stirred and slowly heated to 80 °C, and reacted at this temperature for 2 hours. The reaction was stopped, the reaction product was filtered, and washed several times alternately with deionized water and ethanol, and dried to obtain 1.355 g of LiMn2O4-based porous active microparticles, denoted as PA@LiMn2O4 / C4.

[0060] PA@LiMn2O4 / C4, acetylene black, and binder (a mixture of PVA and PVP, where PVP accounts for 10% of the mass of PVA) were mixed at a mass ratio of 10:1:1 to obtain a mixture. The mixture was then dispersed in water, with the water mass being twice the volume of the mixture, and stirred at 90°C for 12 hours until a homogeneous slurry was obtained. The PVA had a degree of hydrolysis of 90% and a degree of polymerization of 1750; the PVP had a molecular weight of 90,000.

[0061] The slurry was cooled to 50°C, and 0.5 mL of ECH was slowly added dropwise as a crosslinking agent while stirring, with continued stirring until homogeneous. Subsequently, the resulting slurry was uniformly coated onto a graphite current collector measuring 13 cm × 5 cm × 0.3 cm, with a coating area of ​​5 cm × 5 cm and a coating amount of 0.5 g / cm². 2 Let it cure at room temperature.

[0062] The cured electrode plate was immersed in a 3wt% NaOH solution for 30 minutes, then removed and placed in a constant temperature drying oven. The temperature was raised to 80℃ and maintained for 4 hours to allow the electrode to dry and cure completely, resulting in a highly hydrophilic lithium manganese oxide lithium extraction electrode, denoted as PA@LM4.

[0063] Example 5 A method for preparing a lithium extraction electrode is basically the same as the method in Example 1, except that: The stabilizers used are PVA, PEG and PVP; among them, PVA has a degree of hydrolysis of 90% and a molecular weight of 120,000; PVE has a molecular weight of 90,000; and PEG has a molecular weight of 8,000.

[0064] 0.05 g of acrylamide was dissolved in a mixture of 10 mL of n-octanol and 3 g of SDS to obtain the oil phase. The oil phase was mixed with 30 mL of an aqueous solution containing 1 wt% PVA, 0.1% PEG, and 0.1% PVP; wherein the degree of hydrolysis of PVA was 90% and the molecular weight was 120,000; the molecular weight of PVP was 90,000 and the molecular weight of PEG was 8,000. The mixture was stirred at 300 rpm to form a stable microsuspension.

[0065] A mixture of 1.0 g of LiMn2O4 and C powder (with a mass ratio of LiMn2O4 to C of 10:1) was added to the micro-suspension, and the mixture was stirred and dispersed evenly. Then, 5 mg of BPO was added as an initiator, and the mixture was stirred and slowly heated to 80 °C, and reacted at this temperature for 2 hours. The reaction was stopped, the reaction product was filtered, and washed several times alternately with deionized water and ethanol, and dried to obtain 1.233 g of LiMn2O4-based porous active microparticles PA@LiMn2O4 / C5.

[0066] PA@LiMn2O4 / C5, acetylene black, and binder (PVA containing 10% PEG) were mixed at a mass ratio of 10:1:1 to obtain a mixture. The mixture was then dispersed in water, with the water volume being twice the mixture volume, and stirred at 90°C for 12 hours until a homogeneous slurry was obtained. The PVA had a degree of hydrolysis of 90% and a degree of polymerization of 1750; the PVP had a molecular weight of 90,000.

[0067] The slurry was cooled to 50°C, and 0.5 mL of ECH was slowly added dropwise as a crosslinking agent while stirring, with continued stirring until homogeneous. Subsequently, the resulting slurry was uniformly coated onto a graphite current collector measuring 13 cm × 5 cm × 0.3 cm, with a coating area of ​​5 cm × 5 cm and a coating amount of 0.5 g / cm². 2 Let it cure at room temperature.

[0068] The cured electrode plate was immersed in a 3wt% NaOH solution for 30 minutes, then removed and placed in a constant temperature drying oven. The temperature was raised to 80℃ and maintained for 4 hours to allow the electrode to dry and cure completely, resulting in a highly hydrophilic lithium manganese oxide lithium extraction electrode, denoted as PA@LM5.

[0069] Comparative Example 1 The preparation method of LiMn2O4 / PVDF electrode includes the following steps: LiMn₂O₄ / C powder, acetylene black, and PVDF were mixed in a mass ratio of 8:1:1, and an appropriate amount of NMP was added to grind them into a uniform slurry. The slurry was then coated evenly onto a graphite current collector measuring 13cm × 5cm × 0.3cm, with a coating area of ​​5cm × 5cm and a coating amount of 0.5g / cm². 2 The LiMn2O4 / PVDF electrode, denoted as LMO-F, was obtained by vacuum drying at 120℃ for 12 h.

[0070] Comparative Example 2 The preparation method of LiMn2O4 / PVA electrode includes the following steps: LiMn2O4 / C powder, acetylene black, and PVA (PVA with a hydrolysis degree of 90% and a polymerization degree of 1750) were mixed at a mass ratio of 8:1:1 and dispersed in water. The mixture was heated and stirred at 90°C for 12 hours. Subsequent crosslinking, coating, curing, alkali treatment, and drying steps were the same as in Example 1; a LiMn2O4 / PVA electrode, denoted as LMO-A, was obtained.

[0071] Experimental test: 1. Surface morphology test.

[0072] The morphology of the electrode prepared in Example 1 was characterized using a scanning electron microscope (GeminiSEM500, Zeiss).

[0073] like Figure 1As shown, in Examples 1 to 3, the obtained microparticles had small particle sizes, all below 2 μm, due to the suitable monomer and PVA content in the aqueous phase of the micro-suspension system. In Example 4, however, the higher monomer content resulted in larger particle sizes and uneven particle size distribution. In Example 5, the higher PVA content in the aqueous phase led to significant particle aggregation. The LiMn₂O₄-based porous active microparticles prepared in Examples 1 to 5 all effectively improved the uniformity and overall performance of the lithium electrode.

[0074] 2. Wettability test.

[0075] The contact angle of the test electrode was measured using a water contact angle meter (Datap hysic OCA20, Germany, lying drop method, deionized water).

[0076] like Figure 2 As shown, the contact angle of the PA@LiMn2O4 / C / PVA electrode is 9.3°, indicating that the electrode is hydrophilic.

[0077] 3. Electrochemical lithium extraction test.

[0078] Lithium extraction performance was tested using an electrolytic cell separated by anion exchange membranes, with both the cathode and anode chambers having a volume of 160 mL. The anion exchange membrane was (ATG-10, Hangzhou Lanran Technology Co., Ltd.). Voltage and current were monitored using a LanDian battery testing system (CT3002A, Wuhan LanDian Instrument Co., Ltd.).

[0079] Lithium extraction process: The lithium extraction electrode prepared in Example 1 was used as the anode and placed in an anode chamber containing NaCl solution; the delithiated Li... 1-x A Mn₂O₄ electrode was used as the cathode, placed in a cathode chamber containing simulated lithium-containing brine. The simulated lithium-containing brine consisted of a mixture of 1 g / L LiCl, 20 g / L NaCl, 20 g / L MgCl₂, and 5 g / L KCl. The current density was set to 20 A / m. 2 Constant current charging is performed. Once the voltage rises to 0.8V, it switches to constant voltage charging at 0.8V until the current density drops to 2 A / m. 2 Next, remove the electrode and thoroughly rinse it with deionized water until the conductivity of the cleaning solution is <50 μS / cm. Then, exchange the electrode positions and repeat the above steps.

[0080] Lithium de-intercalation / extraction performance evaluation: The cathode chamber is filled with a lithium-poor electrode (Li) after lithium de-intercalation. 1-x Mn₂O₄ was prepared with 2 g / L LiCl solution added; a lithium-rich electrode, LiMn₂O₄, was placed in the anode chamber with 2 g / L LiCl solution added. The current density was set to 5 A / m. 2 10A / m 2 15A / m 220A / m 2 and 25A / m 2 Charge at a constant current until the voltage rises to 0.8V, then charge at a constant voltage of 0.8V until the current density is less than 2A / m. 2 .

[0081] Cyclic stability test: Li is placed in the cathode chamber. 1-x A Mn₂O₄ electrode was used, and a LiMn₂O₄ electrode was placed in the anode chamber. A mixed solution of 1.5 g / L LiCl, 30 g / L MgCl₂, 30 g / L NaCl, and 3 g / L KCl was added. The current density was set to 20 A / m. 2 Constant current charging is applied until the voltage rises to 0.8V, then constant voltage charging is applied at 0.8V until the current density is less than 2A / m. 2 A cyclic experiment of 100 cycles was conducted to investigate the actual capacity, stability, and Mn dissolution of the electrode in a brine environment. After accumulating 100 cycles, the average lithium extraction rate (u) and cumulative Mn dissolution rate (K) of the electrode were calculated.

[0082] Ion concentration test: Samples were taken at regular intervals, and the ion concentration in the solution was detected by inductively coupled plasma atomic emission spectrometry (ICP, Semikron, Germany).

[0083] The lithium extraction rate u is calculated using the following formula: In the formula, C0 is the initial lithium concentration in the brine, in g / L; C i V0 is the lithium concentration in the brine at the time of sampling, in g / L; V0 is the initial brine volume, in L; V0 i S represents the volume of brine at the time of sampling, in liters (L); S represents the coating area of ​​the active material on the electrode, in m². 2 t2-t1 is the interval time during the lithium extraction process, in hours.

[0084] The Mn dissolution rate is calculated using the following formula: In the formula, C m V represents the concentration of Mn ions at the time of sampling, in mg / L; Cm' represents the initial concentration of Mn ions, in mg / L; V represents the volume of the sampling solution, in L; and M represents the manganese content of lithium manganate in the electrode, in mg.

[0085] Comparative example: For LiMn2O4 / PVDF electrodes with the same loading, the average lithium extraction rate u over 100 cycles was 18.53 g / m. 2 / h, the cumulative Mn dissolution rate is 3.3 mg / g.

[0086] like Figure 3As shown, the LMO-F prepared in Comparative Example 1 only achieved a flux of 0.5 A / m 2 Under these conditions, constant current electrolysis can be maintained for a relatively long time, at 1A / m 2 ~2.5A / m 2 Under constant voltage electrolysis conditions, the lithium extraction rate is slow. This is because as the constant current operation time increases, the polarization of LMO-F intensifies, and the overpotential also increases, thus the lithium extraction rate increases slowly in the later stages. The LMO-A prepared in Comparative Example 2 is a PVA-bonded LiMn2O4 electrode, similar to the PA@LM1 prepared in Example 1. Both can achieve lithium extraction at 0.5 A / m 2 ~2.5A / m 2 Maintaining constant current electrolysis for a longer period of time results in a faster lithium extraction rate. Furthermore, as the constant current operation time increases, the lithium extraction rate of both LMO-A and PA@LM1 shows a linear increase. This suggests that, like LMO-A, PA@LM1 also has low polarization and exhibits highly efficient lithium intercalation / deintercalation performance, and its lithium extraction performance is not affected by the microparticle process.

[0087] like Figure 4 As shown, the electrode prepared in Example 1 has an average lithium extraction rate u of 18.53 g / m² after 100 cycles. 2 The cumulative Mn dissolution rate was 3.3 mg / g / h. The average lithium extraction rate u of LMO-F (Comparative Example 1) and LMO (Comparative Example 2) under these conditions was 18.53 g / m³. 2 The cumulative Mn dissolution rate was 3.3 mg / g / h. The PVDF-bonded LiMn2O4 electrode (LMO-P) prepared in Comparative Example 1 had the lowest lithium capacity and average lithium extraction rate in each cycle, but the lowest Mn dissolution rate. This is related to the high hydrophobicity of PVDF, which hinders the permeability of the solution and Li+. PVA-bonded LiMn2O4 electrodes all exhibited relatively high lithium extraction capacity and rate. Among them, the PVA-bonded LiMn2O4 electrode (LMO-A) had the fastest lithium extraction rate, but its lithium capacity in each cycle was only slightly higher than PA@LM1, while its Mn dissolution rate was the highest. This is related to the uneven distribution of LiMn2O4 inside the electrode and the lack of coating on the LiMn2O4 surface, leading to unstable electrode performance and easy degradation. The electrodes prepared in Examples 1 to 5 had higher lithium capacity and lithium extraction rate than LMO-F, and their Mn dissolution rate was significantly lower than that of the LMO-A electrode prepared in Comparative Example 2.

[0088] like Figure 4As shown, in the lithium extraction electrode PA@LM2 prepared in Example 2, compared with Example 1, the polymer mass in the PA@LiMn2O4 / C2 core increased due to the introduction of a macromolecular porogen into the aqueous solution, but the pore size became more abundant. Furthermore, in the prepared lithium extraction electrode PA@LM2, because the LiMn2O4 content in the overall electrode material decreased to some extent and the coating material increased, the lithium extraction rate was slightly lower than in Example 1, and the Mn dissolution rate also decreased.

[0089] In the lithium extraction electrode PA@LM3 prepared in Example 3, compared to Example 1, the introduction of acrylic acid into the vinyl monomer increased the amount of polymer in the PA@LiMn2O4 / C3 core; simultaneously, the total mass of LiMn2O4 / C powder used as a stabilizing separator and functional material was increased. Furthermore, the introduction of macromolecular porogens PEG and PVP into the aqueous solution increased the polymer mass in the PA@LiMn2O4 / C3 core, resulting in a more abundant pore size. Due to the tighter coating of the internal LiMnO4 electrode, the lithium extraction rate of the lithium extraction electrode PA@LM3 was slightly lower than that of Example 1, and the Mn dissolution was reduced.

[0090] In Example 4, the lithium extraction electrode PA@LM4 was prepared. Compared to Example 1, methyl acrylate was introduced into the vinyl monomer. This increased the amount of polymer in the core and enhanced the strength of the core binder, thus improving the stability of the LiMn2O4 electrode. Simultaneously, the total mass of the LiMn2O4 / C powder used as a stabilizing separator and functional material was increased. As a result, the lithium extraction electrode PA@LM4, compared to Example 1, exhibited increased internal LiMn2O4 electrode coating strength and density. The LiMnO4 content in the electrode was also relatively increased. The lithium extraction rate was slightly lower than in Example 1, and the Mn dissolution rate also decreased, but the stability was improved.

[0091] In Example 5, when preparing the lithium extraction electrode PA@LM5, compared to Example 1, 10% of PEG with a molecular weight of 20,000 was added to the binder, resulting in an increased overall pore size of the electrode and thus a faster lithium extraction rate than in Example 1. However, because the LiMn2O4 electrode coating inside the particles was looser, the cumulative Mn dissolution during the lithium extraction process increased.

[0092] In summary, the LiMn2O4-based porous active microparticles prepared using a micro-suspension polymerization system provided by this invention are used to prepare lithium extraction electrodes. Because the LiMn2O4 powder is pre-dispersed and bonded to the surface of the polar polymer shell to form hydrophilic porous microparticles with a loose internal and external structure, the problems of flocculation, agglomeration, and sedimentation in the direct preparation of PVA-based lithium extraction electrodes using LiMn2O4 powder are solved, ensuring that the lithium extraction electrode material is uniform, structurally loose, and overall hydrophilic. Furthermore, the cross-linking reaction under alkaline conditions enhances the mechanical properties of the electrode. This significantly improves the water permeability and stability of the LiMn2O4 lithium extraction electrode and increases the electrochemical lithium extraction rate. Simultaneously, by avoiding phenomena such as overpotential, the electrode lifespan is greatly extended.

[0093] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations. The above-described embodiments are merely preferred embodiments for fully illustrating this invention, and their scope of protection is not limited thereto.

Claims

1. A method for preparing a lithium extraction electrode, characterized in that, Includes the following steps: A mixture of a vinyl monomer with substituted polar functional groups, a solvent, and a surfactant is used to obtain an oil phase. The oil phase is mixed with an aqueous solution containing a stabilizer to obtain a micro-suspension; A mixture of LiMn2O4 and C is added to a micro-suspension, and under the action of an initiator, a free radical-initiated polymerization reaction is carried out to form LiMn2O4-based porous active microparticles with a core-shell structure, consisting of a polar polymer core and LiMn2O4 and C shells. The stabilizer is at least one of polyethylene glycol, polyvinylpyrrolidone, and polyvinyl alcohol; A lithium extraction electrode is obtained by mixing and curing LiMn2O4-based porous active microparticles, conductive agent, binder and crosslinking agent.

2. The method for preparing the lithium extraction electrode according to claim 1, characterized in that, The mass ratio of the mixture of LiMn2O4 and C to the vinyl monomer substituted with polar functional groups is 1:0.04 to 0.06; The mass ratio of LiMn2O4 to C is 10:

1.

3. The method for preparing the lithium extraction electrode according to claim 2, characterized in that, The volume ratio of the oil phase to the aqueous phase solution containing the stabilizer is 1:4.3–5.5; The concentration of stabilizer in the aqueous solution is 0.5wt% to 2wt%.

4. The method for preparing the lithium extraction electrode according to claim 3, characterized in that, The vinyl monomer substituted with a polar functional group is at least one of acrylamide, acrylic acid, methyl acrylate and ethyl acrylate; The solvent is C8 to C9. 12 At least one of the long-chain fatty alcohols; The surfactant is at least one of sodium dodecyl sulfate or sodium dodecyl sulfonate.

5. The method for preparing the lithium extraction electrode according to claim 1, characterized in that, The degree of hydrolysis of polyvinyl alcohol in the stabilizer is 60%–90%, and the molecular weight is 80,000–120,000. The molecular weight of polyethylene glycol is below 20,000; The molecular weight of polyvinylpyrrolidone is 30,000 to 90,000.

6. The method for preparing the lithium extraction electrode according to claim 1, characterized in that, The temperature for free radical-initiated polymerization is 75℃~90℃; The initiator is azobisisobutyronitrile, benzoyl peroxide, or potassium persulfate; the mass of the initiator is 0.5% to 1% of the mass of the vinyl monomer substituted with polar functional groups.

7. The method for preparing the lithium extraction electrode according to claim 1, characterized in that, The particle size of LiMn2O4-based porous active microparticles is 0.2 μm to 2 μm.

8. The method for preparing the lithium extraction electrode according to claim 1, characterized in that, The method for preparing LiMn2O4-based lithium electrodes includes the following steps: LiMn2O4-based porous active microparticles, conductive agent, binder and solvent are heated and mixed to obtain a slurry; when the slurry is cooled to 50°C, a crosslinking agent is added and stirred evenly, and then coated onto a current collector; after curing, it is immersed in an alkaline solution to obtain a LiMn2O4-based lithium electrode. The mass ratio of LiMn2O4-based porous active microparticles, conductive agent, and binder is 10:1:1; The adhesive is any one of polyethylene glycol and polyvinylpyrrolidone and a mixture of polyvinyl alcohol; The degree of hydrolysis of polyvinyl alcohol in the adhesive is over 90%, and the degree of polymerization is 1700-1800; The crosslinking agent is epichlorohydrin; The conductive agent is activated carbon.

9. A lithium extraction electrode, characterized in that, The lithium extraction electrode is prepared by the method for preparing a lithium extraction electrode according to any one of claims 1 to 8.

10. An application of a lithium extraction electrode in lithium extraction from brine, characterized in that, The lithium extraction electrode is the lithium extraction electrode according to claim 9.

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