Electrode for electrochemical lithium extraction and preparation method thereof

Abstract

The invention relates to the technical field of lithium resource development and utilization, in particular to an electrode for electrochemical lithium extraction and a preparation method thereof.The preparation method comprises the steps that an aromatic modifier with a conjugated structure is added to conduct graft modification on chitosan; preparing slurry from the grafted and modified chitosan, an active material and a conductive agent, coating a current collector with the slurry, and drying to obtain an electrode preform; adding a thermosetting cross-linking agent into the coating layer of the electrode preform, and curing to obtain an electrode finished product; the cycling stability of the electrode in high-flow-speed brine lithium extraction is remarkably improved, meanwhile, the average current density, the lithium intercalation capacity and the average current efficiency are remarkably improved, and the problems that in the prior art, electrode active substances fall off at the high flow speed, and the lithium ion transmission resistance is large are solved.

Description

Technical Field

[0001] This invention relates to the field of lithium resource development and utilization technology, and in particular to an electrode for electrochemical lithium extraction and its preparation method. Background Technology

[0002] With the continued growth in demand for lithium batteries in the new energy sector, lithium extraction from brine and seawater has become an important research direction. Salt lake brines have low lithium content but high concentrations of impurity ions such as sodium, magnesium, and potassium, posing a greater challenge to the separation and extraction of lithium resources. Existing lithium extraction technologies (such as salting out, precipitation, extraction, membrane separation, and adsorption) have significant limitations in terms of lithium recovery rate, environmental impact, cost control, and performance stability.

[0003] Against this backdrop, based on the active materials such as LiMn2O4 and LiFePO4, the effect of Li on Li under an applied potential + Electrochemical lithium extraction technology, which involves specific extraction / intercalation, is widely used due to its high lithium selectivity, fast rate, low material loss, low energy consumption, low pollution, and wide applicability. This technology simultaneously produces enriched solutions with lithium concentrations greater than 5 g / L, and the electrode materials exhibit good cycle stability. These significant advantages make it a widely recognized large-scale lithium extraction solution in academia and industry, particularly for the high magnesium-to-lithium ratio saline lake resources of the Qinghai-Tibet Plateau in my country, where the electrochemical extraction / intercalation method combines high efficiency with environmental friendliness.

[0004] For the electrochemical lithium extraction process, the stability of the electrode material is crucial to the frequency of electrode replacement, which in turn affects production efficiency and cost. Currently, PVDF is used as the electrode binder in electrochemical lithium extraction. It possesses excellent chemical stability, can withstand various chemicals in complex electrolyte systems such as brine, and is not easily corroded or degraded by chemical reactions. However, in electrochemical lithium extraction, to enhance mass transfer, the electrolyte flow rate is high. PVDF relies on van der Waals forces to form a bonding network, which is a weak interaction. This results in low bonding strength between the conductive substrate and the active material, insufficient adhesion, and easy detachment from the current collector at high flow rates. Furthermore, PVDF is hydrophobic, while brine is an aqueous solution, leading to poor interfacial wettability between the electrode and the electrolyte. This increases the resistance to lithium ion transport at the electrode / electrolyte interface, thus affecting the lithium extraction kinetics and reducing lithium extraction efficiency.

[0005] Therefore, developing an electrode with strong adhesion, high bonding strength, and a certain degree of hydrophilicity is of great significance for improving the performance of electrochemical lithium extraction. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide an electrode for electrochemical lithium extraction and its preparation method, which solves at least one of the problems existing in the prior art, such as electrode active material shedding at high flow rates and high lithium-ion transport resistance.

[0007] The objective of this invention is mainly achieved through the following technical solutions:

[0008] A method for preparing an electrode for electrochemical lithium extraction, comprising:

[0009] Step (1): Add an aromatic modifier with a conjugated structure to graft and modify chitosan;

[0010] Step (2): Prepare a slurry by combining the grafted and modified chitosan with active materials and conductive agents. Coat the slurry onto the current collector and dry it to obtain the electrode preform.

[0011] Step (3): Add a thermosetting crosslinking agent to the coating layer of the electrode preform, and obtain the finished electrode after curing.

[0012] Preferably, step (1) includes:

[0013] S101: Dissolve chitosan powder in a weakly acidic aqueous solution to form a homogeneous chitosan solution;

[0014] S102: Add an aromatic modifier with a conjugated structure to the chitosan solution;

[0015] S103: Adjust the pH of the reaction system to neutral;

[0016] S104: Filter the product after the reaction to remove unreacted modifiers and byproducts, and then dry it to obtain grafted modified chitosan.

[0017] Preferably, the weak acid in step S101 is an organic acid.

[0018] Preferably, the weak acid in step S101 is one or more of formic acid, acetic acid, and malonic acid.

[0019] Preferably, the aromatic modifier is an aromatic compound having active hydrogen and / or nitrogen-sulfur heterocycles.

[0020] Preferably, the aromatic modifier is one or more of pyrrole, aniline, thiophene, pyrrole formaldehyde, benzaldehyde, and thiophene formaldehyde.

[0021] Preferably, the mass ratio of aromatic modifier to chitosan in step (2) is 0.2 to 0.8.

[0022] Preferably, in step (2), the mass ratio of active material, conductive agent, and modified chitosan is 7-9:1-2:1-2.

[0023] Preferably, in step (2), a dispersant is also added, and the mass ratio of the conductive agent to the dispersant is 1-2:1.5-3.

[0024] Preferably, the thermosetting crosslinking agent is an aldehyde crosslinking agent, a carboxylic acid crosslinking agent, an epoxy crosslinking agent, or an isocyanate crosslinking agent.

[0025] Preferably, the thermosetting crosslinking agent is one or more of the following: glutaraldehyde, citric acid, epichlorohydrin, polyethylene glycol diglycidyl ether, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and dicyclohexanediisocyanate.

[0026] An electrochemical lithium extraction electrode is prepared by the above-described method for preparing an electrochemical lithium extraction electrode, comprising a current collector and a modified layer coated on the surface of the current collector.

[0027] The modified layer is composed of uniformly dispersed chitosan, active materials, conductive agents, and crosslinking agents;

[0028] When the electrode used for electrochemical lithium extraction is used as the cathode, the average current density is ≥13.3 A / m. 2 The lithium intercalation capacity is ≥34.3mg / g, the current efficiency is ≥91.8%, and the capacity retention rate is still above 83% after 120 cycles.

[0029] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0030] (1) This invention uses modified grafted chitosan as a binder and combines it with a chemical cross-linking process, which significantly improves the bonding strength between the active material of the electrode and the current collector. This strong adhesion enables the electrode to effectively prevent the active material from falling off in a long-term high-flow-rate brine environment, thus extending the service life of the electrode. Compared with traditional electrodes using PVDF, the electrode of this invention exhibits significantly improved cycle stability in lithium extraction from high-flow-rate brine.

[0031] (2) This invention utilizes chitosan and its modified grafted products, which possess abundant polar groups (such as hydroxyl and amino groups), significantly improving the hydrophilicity of the electrode. This hydrophilicity enhances the wettability between the electrode and the electrolyte, reducing the transport resistance of lithium ions at the electrode / electrolyte interface. The electrode of this invention exhibits excellent hydrophilicity in contact angle tests; brine can completely wet and penetrate the electrode within 1 second, while the hydrophilicity of traditional PVDF electrodes is poor. The grafted and modified chitosan significantly improves the average current density, lithium intercalation capacity, and average current efficiency, solving the problem of high lithium ion transport resistance.

[0032] (3) This invention utilizes chitosan grafted with conjugated structures and conductive polymers at active centers. These conductive polymers provide a denser electron distribution, promoting electron transfer. The improved hydrophilicity and conductivity of the electrode allow for faster diffusion and transfer of lithium ions and electrons within the electrode, thereby enhancing the lithium extraction rate and current efficiency.

[0033] (4) The present invention uses water as a solvent, which replaces the expensive and toxic NMP solvent used in traditional PVDF adhesives, making it more environmentally friendly; chitosan and its modified graft products are inexpensive and readily available, the preparation process is simple, and it is easy to realize industrial application, thus reducing production costs.

[0034] (5) The binder used in this invention is suitable for a variety of lithium electrode active materials, such as LiFePO4, LiMn2O4 and their doped and modified derivatives, and has wide applicability. By adding dispersants (such as polyethylene glycol, polyvinylpyrrolidone, etc.), the active materials and conductive agents in the electrode slurry can be more uniformly dispersed, improving the bonding stability between the various components of the electrode, while retaining a suitable pore structure, further improving the lithium extraction performance.

[0035] (6) The three-dimensional structure formed by the cross-linking process of the present invention significantly improves the mechanical strength and anti-swelling ability of the electrode, so that the electrode maintains good structural integrity during long-term cycling and reduces adhesion failure caused by material deformation or dissolution.

[0036] Other features and advantages of the invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the embodiments described and the accompanying drawings. Attached Figure Description

[0037] Figure 1 The graph shows the cycling performance of the electrodes in electrochemical lithium extraction for Examples 1, 2, and Comparative Example 1 of this invention.

[0038] Figure 2 These are nano-scratch test images of electrode adhesion force in Example 1 and Comparative Example 1 of this invention;

[0039] Figure 3 This is a comparison diagram of the contact angles between the electrode and the water droplet in Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0040] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the present invention.

[0041] On one hand, this invention discloses a method for preparing an electrode for electrochemical lithium extraction, such as... Figure 1 As shown, it includes:

[0042] Step (1): Add an aromatic modifier with a conjugated structure to graft and modify chitosan;

[0043] Step (2): Prepare a slurry by combining the grafted and modified chitosan with active materials and conductive agents. Coat the slurry onto the current collector and dry it to obtain the electrode preform.

[0044] Step (3): Disperse a thermosetting crosslinking agent into the coating layer of the electrode preform, and obtain the finished electrode product after curing.

[0045] In practice, in step (1), the grafted chitosan is introduced with an aromatic modifier having a conjugated structure. These modifiers are covalently linked to the main chain of chitosan, changing the chemical structure of chitosan. The conjugated structure of the aromatic modifier significantly improves the conductivity of chitosan, transforming it from an insulator to a semiconductor or even a conductor. The polar groups (such as amino and hydroxyl groups) in the modifier enhance the hydrophilicity of chitosan and improve its contact performance with the electrolyte. The grafted chitosan is more firmly bonded to the active material and the conductive agent, which helps to improve the mechanical stability and cycle performance of the electrode.

[0046] Step (2) involves preparing a uniform slurry by mixing the grafted and modified chitosan with the active material and conductive agent. The uniformity of the slurry directly affects the quality of the electrode preform. The coating and drying process forms a uniform electrode layer, ensuring the uniform distribution of the active material, conductive agent, and binder.

[0047] In step (3), the cross-linking treatment forms a three-dimensional network structure, which significantly improves the mechanical strength and anti-swelling ability of the electrode. The cross-linked electrode has better chemical stability and can withstand complex electrolyte environments, reducing the dissolution or degradation of electrode materials. The cross-linking treatment further optimizes the conductivity and hydrophilicity of the electrode, improves the overall performance of the electrode, and makes it exhibit higher efficiency and stability in electrochemical applications.

[0048] Compared with existing technologies, this invention uses modified grafted chitosan as a binder and combines it with a chemical cross-linking process, significantly improving the bonding strength between the active material of the electrode and the current collector. This strong adhesion effectively prevents the active material from detaching from the electrode in long-term high-flow-rate brine environments, extending the electrode's service life. Compared with traditional electrodes using PVDF, the electrode of this invention exhibits significantly improved cycling stability in high-flow-rate brine. For example, the electrode retains over 83% capacity after 120 cycles, while the electrode of Comparative Example 1 using PVDF almost completely detaches after 30 cycles.

[0049] Compared with existing technologies, this invention utilizes chitosan grafted with conjugated structures and conductive polymers at active centers. These conductive polymers provide a denser electron distribution, promoting electron transfer. The improved hydrophilicity and conductivity of the electrode allow for faster diffusion and transfer of lithium ions and electrons within the electrode, thereby increasing the lithium extraction rate and current efficiency. Experimental results show that the electrode of this invention achieves an average current density of 13.3 A / m during lithium extraction. 2 The lithium intercalation capacity reaches 34.3 mg / g, and the current efficiency reaches 91.8%, which is significantly better than that of traditional PVDF electrodes (current density 9.9 A / m). 2 (Lithium intercalation capacity 25.6 mg / g, current efficiency 77.6%).

[0050] Specifically, step (1) includes the following steps:

[0051] S101: Dissolve chitosan powder in a weakly acidic aqueous solution to form a homogeneous chitosan solution;

[0052] S102: Add an aromatic modifier with a conjugated structure to the chitosan solution;

[0053] S103: Adjust the pH of the reaction system to neutral;

[0054] S104: Filter the product after the reaction to remove unreacted modifiers and byproducts, and then dry it to obtain grafted modified chitosan.

[0055] Specifically, the weak acid mentioned in step S101 is an organic acid, which may be one or more of formic acid, acetic acid, and malonic acid.

[0056] It should be noted that weak organic acids (such as acetic acid and formic acid) are relatively weak, providing a mild acidic environment without excessively damaging the structure of chitosan. Furthermore, these weak organic acids can protonate the amino groups of chitosan (forming -NH3). + This improves its solubility, allowing chitosan to dissolve at room temperature; in addition, the weak organic acid can avoid excessive protonation and avoid side reactions that may be caused by strong acids.

[0057] Specifically, aromatic modifiers can be aromatic compounds with active hydrogen and / or nitrogen-sulfur heterocycles.

[0058] Preferably, the aromatic modifier can be one or more of pyrrole, aniline, thiophene, pyrrole formaldehyde, benzaldehyde, and thiophene formaldehyde.

[0059] During implementation, aromatic modifiers can achieve grafting reactions by nucleophilic substitution or free radical substitution of chitosan with active hydrogen or aldehyde groups.

[0060] Compared with existing technologies, this invention utilizes chitosan and its modified grafted products, which possess abundant polar groups (such as hydroxyl and amino groups), significantly improving the hydrophilicity of the electrode. This hydrophilicity enhances the interfacial compatibility between the electrode and the aqueous electrolyte, reducing the transport resistance of lithium ions at the electrode / electrolyte interface. The electrode of this invention exhibits excellent hydrophilicity in contact angle tests; brine can completely wet and penetrate the electrode within 1 second, while traditional PVDF electrodes show poor hydrophilicity. The grafted and modified chitosan significantly improves the average current density, lithium intercalation capacity, and average current efficiency (%), solving the problem of high lithium ion transport resistance.

[0061] Specifically, the mass ratio of aromatic modifier to chitosan is 0.2 to 0.8, which can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8.

[0062] It should be noted that the above range is because if the ratio is too low, the grafting rate will be low and raw materials will be wasted, while if it is too high, the grafting will be excessive and not conducive to subsequent cross-linking.

[0063] Specifically, the initiator of the grafting reaction in step (1) can be one or more of hydrogen peroxide, ferric chloride, ammonium persulfate, and azobisisobutyronitrile.

[0064] Specifically, the reaction temperature of the grafting reaction in step (1) is 25℃~60℃, which can be 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃; the reaction time of the grafting reaction in step (1) is 3h~8h, which can be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h.

[0065] It should be noted that selecting the above temperature and reaction time can ensure that the desired product is obtained, and that higher temperatures or longer reaction times will cause the molecular structure to be destroyed and the adhesion properties to be lost.

[0066] Specifically, in step (2), the mass ratio of active material, conductive agent, and modified chitosan is 7-9:1-2:1-2.

[0067] It should be noted that within this range, the slurry has a certain viscosity, which is suitable for coating; below this range, the slurry is too thin, and the electrode is prone to cracking; too high a viscosity is not conducive to coating.

[0068] It should be noted that the active material, as a key component, provides lithium-ion-specific adsorption sites in electrochemical lithium extraction, selectively capturing Li+ in solution and repelling Na+ through electrochemical reactions. + K +Impurity ions are eliminated to ensure lithium extraction purity. Simultaneously, as an electron transfer medium, they undergo redox reactions under an electric field, driving Li+ ions to rapidly insert into the material lattice or desorb and release, thus increasing the lithium extraction rate.

[0069] Specifically, in step (2), the conductive agent is at least one of acetylene black, superP, Ketjen black, and carbon nanotubes.

[0070] Specifically, in step (2), the current collector can be at least one of titanium-based materials, conductive polymer-based materials, etc.

[0071] Preferably, in step (2), a dispersant is also added, and the mass ratio of the conductive agent to the dispersant is 1-2:1.5-3.

[0072] The dispersant is at least one of polyvinylpyrrolidone (PVP), polyethylene glycol, polyvinyl alcohol, or sodium carboxymethyl cellulose (CMC).

[0073] Specifically, in step (2), the coating density of the slurry is 50 mg / cm³. 2 ~120mg / cm 2 It can be 50mg / cm 2 55mg / cm 2 60mg / cm 2 65mg / cm 2 70mg / cm 2 75mg / cm 2 80mg / cm 2 85mg / cm 2 90mg / cm 2 95mg / cm 2 100mg / cm 2 105mg / cm 2 110mg / cm 2 115mg / cm 2 Or 120mg / cm 2 The drying temperature is 40℃~90℃, which can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃ or 90℃, and the drying time is 8h~20h, which can be 8h, 10h, 12h, 14h, 16h, 18h or 20h.

[0074] It should be noted that if the coating density is too low, the overall adsorption capacity of the electrode will be low; if the coating density is too high, it will be detrimental to the mass transfer of ions in the solution inside the electrode; if the drying temperature is too low, the drying time will be long; if the drying temperature is too high, the electrode will be prone to cracking.

[0075] Specifically, the active material in step (2) satisfies: Li1-x MePO4, where 0≤x≤1, and Me is Fe, Co, Ni, or Mn;

[0076] Or Li 1-x Mn₂O₄, where 0 ≤ x ≤ 1;

[0077] or LiNi x Co y Mn (1-x-y) O2, 0 <x,y<1,0<x+y<1。

[0078] Compared with existing technologies, the binder used in this invention is suitable for a variety of lithium electrode active materials, such as LiFePO4, LiMn2O4 and their doped and modified derivatives, and has wide applicability. By adding dispersants (such as polyethylene glycol, polyvinylpyrrolidone, etc.), the active materials and conductive agents in the electrode slurry can be more uniformly dispersed, improving the bonding stability between the various components of the electrode, while retaining a suitable pore structure, further improving the lithium extraction performance.

[0079] Specifically, in step (3), the crosslinking agent is isophorone diisocyanate (IPDI), 1,6-hexanediisocyanate (HDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), or dicyclohexane diisocyanate (HDI). 12 One or more of the following: MDI.

[0080] Specifically, the crosslinking agent solvent is at least one of ethyl acetate, butyl acetate, ethylene glycol monobutyl ether, tetrahydrofuran, ethanol, ethylene glycol, and propylene glycol.

[0081] Specifically, in step (3), the curing temperature of the crosslinking agent is 20℃~60℃, which can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, and the reaction time is 0.5h~24h, which can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h. h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, 14.5h, 15h, 15.5h, 16h, 16.5 h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h, 20h, 20.5h, 21h, 21.5h, 22h, 22.5h, 23h, 23.5h or 24h.

[0082] It should be noted that the above temperature and reaction time were selected because if the temperature and reaction time are too low, the cross-linking will not be sufficient, and if the temperature and reaction time are too high, the cross-linking will be excessive, resulting in an overly dense electrode that is not conducive to mass transfer.

[0083] Compared with existing technologies, the three-dimensional structure formed by the cross-linking process of this invention significantly improves the mechanical strength and anti-swelling ability of the electrode, enabling the electrode to maintain good structural integrity during long-term cycling, reducing adhesion failure caused by material deformation or dissolution, and maintaining a capacity retention rate of over 83% after 120 cycles, while traditional PVDF electrodes almost completely detach after 30 cycles.

[0084] On the other hand, the present invention discloses an electrode for electrochemical lithium extraction, which is prepared by the above preparation method and includes a current collector and a modified layer coated on the surface of the current collector;

[0085] The modified layer is composed of uniformly dispersed chitosan, active materials, conductive agents, and crosslinking agents;

[0086] When the electrode used for electrochemical lithium extraction is used as the cathode, the average current density is ≥13.3 A / m. 2 The lithium intercalation capacity is ≥34.3mg / g, the current efficiency is ≥91.8%, and the capacity retention rate is still above 83% after 120 cycles.

[0087] To further illustrate the technical solution of the present invention, the following embodiments and comparative examples are provided:

[0088] Example 1

[0089] This embodiment provides a method for preparing an electrode for electrochemical lithium extraction, including:

[0090] (1) Chitosan was dissolved in 0.1M formic acid solution, and then pyrrole formaldehyde was added. After reacting at 60℃ for 6 hours, pyrrole and ferric chloride initiator were added, and the reaction was carried out at 40℃ for 3 hours. The solution was adjusted to neutral with NaOH, filtered, washed and dried to obtain polypyrrole-grafted chitosan.

[0091] (2) Dissolve polypyrrole-grafted chitosan in a 2% acetic acid aqueous solution to prepare a 3wt% binder solution. Mix LiFePO4, Ketjen Black, polypyrrole-grafted chitosan, and polyethylene glycol at a mass ratio of 8:1:1:1.5 to form a slurry. Then, apply the lithium extraction slurry to a coating density of 50 mg / cm³. 2 The electrode is uniformly coated onto a titanium-based current collector and dried at 40°C for 20 hours to obtain a dry electrode.

[0092] (3) The above electrode was immersed in an ethylene glycol solution of 1,6-hexamethylene diisocyanate and crosslinked at 60°C for 0.5 h, then dried to obtain the high-binding-strength hydrophilic electrode for electrochemical lithium extraction. The 1,6-hexamethylene diisocyanate and ethylene glycol were added at a mass ratio of 1:80.

[0093] Using the prepared lithium iron phosphate electrode as the anode and nickel foam as the cathode, the electrode was placed in a 10 g / L NaCl solution. A voltage was applied across the electrode and the nickel foam until the current density was below 0.5 A / m. 2 That is, to obtain lithium in the lithium-deficient state through electrochemical lithium extraction using Li 1-x FePO4 electrode.

[0094] Lithium extraction experiment: The electrolysis device was divided into a cathode chamber and an anode chamber using an anion exchange membrane. The prepared lithium iron phosphate electrode and the lithium iron phosphate electrode in a lithium-deficient state were placed in the anode chamber and cathode chamber, respectively. 210 mL of the brine to be treated was injected into the cathode chamber; 210 mL of 10 g / L NaCl solution was injected into the anode chamber as the supporting electrolyte.

[0095] At 25℃, a constant current followed by a constant voltage method was adopted, with a current of 30mA (15A / m). 2 The current is constant for electrolysis until the voltage reaches 0.3V, then constant for voltage electrolysis at 0.3V until the current drops to 8mA (4A / m). 2 Electrolysis is complete. The main components (g / L) and pH of the brine are shown in Table 1. The results show that the average current density and average electrode material Li during lithium extraction... + The adsorption capacity and average current efficiency are shown in Table 2.

[0096] Table 1 Main components of brine

[0097] Element Li Na K Mg Ca S pH Concentration (g / L) 0.355 26.87 2.5 2.74 0.234 5.5 7.8

[0098] Cyclic lithium extraction experiment: A diaphragmless electrochemical lithium extraction device was used to conduct a cyclic lithium extraction experiment, with Li... 1-x FePO4 and LiFePO4 electrodes are the cathode and anode, respectively, and are placed in a lithium extraction device to conduct a cyclic lithium extraction experiment.

[0099] Example 1-1

[0100] The difference between this embodiment and Example 1 is that the synthesis of the modified chitosan binder has been changed; the modifiers are benzaldehyde and aniline, and the initiator is ammonium persulfate. The electrode preparation uses LiMn2O4 as the active material, acetylene black as the conductive agent, titanium-based current collector as the current collector, and a butyl acetate solution of toluene diisocyanate as the crosslinking agent. The specific steps are as follows:

[0101] (1) Chitosan was dissolved in 0.1M acetic acid solution, and benzaldehyde was added. After reacting at 50℃ for 8 hours, aniline and initiator ammonium persulfate were added. After reacting at 25℃ for 6 hours, the solution was adjusted to neutral with NaOH. After filtration, washing and drying, polyaniline-grafted chitosan was obtained.

[0102] (2) Dissolve polyaniline-grafted chitosan in a 2% acetic acid aqueous solution to prepare a 3wt% binder solution. Mix LiMn2O4, acetylene black, polyaniline-grafted chitosan, and polyethylene glycol at a mass ratio of 7:1:1:1.5 to form a slurry. Then, apply the lithium extraction slurry to a coating density of 120 mg / cm³. 2 The electrode was uniformly coated onto a titanium-based current collector and dried at 45°C for 18 hours to obtain a dry electrode.

[0103] (3) The above electrode was immersed in a butyl acetate solution of toluene diisocyanate and crosslinked at 50°C for 6 hours, then dried to obtain the high-bonding-strength hydrophilic electrode for electrochemical lithium extraction. Toluene diisocyanate and butyl acetate were added at a mass ratio of 1:80.

[0104] Furthermore, the electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are largely the same as in Example 1. Lithium extraction was carried out using the same brine and experimental conditions as in Example 1. The results show that the average current density during lithium extraction and the electrode material Li + The adsorption capacity and average current efficiency are shown in Table 2.

[0105] Examples 1-2

[0106] The difference between this embodiment and Example 1 is that the synthesis of modified chitosan has been altered; the modifier is thiophene-formaldehyde and thiophene in a 1:1 mass ratio, and the initiator is hydrogen peroxide. Electrode preparation: the active material is LiNi. x Co y Mn (1-x-y) An ethanol solution containing O2, superP as the conductive agent, titanium-based current collector, and diphenylmethane diisocyanate (MDI) as the crosslinking agent, is prepared. The specific steps are as follows:

[0107] (1) Chitosan was dissolved in 0.1M malonic acid solution, and then thiophene formaldehyde was added. After reacting at 45°C for 8 hours, thiophene and initiator hydrogen peroxide were added, and the reaction was carried out at 25°C for 8 hours. The solution was adjusted to neutral with NaOH, filtered, washed and dried to obtain polythiophene-grafted chitosan.

[0108] (2) Polythiophene-grafted chitosan was dissolved in a 2% aqueous acetic acid solution to prepare a 3wt% binder solution. LiNi x Co y Mn (1-x-y)O2, superP, polythiophene-grafted chitosan, and polyethylene glycol were mixed evenly in a mass ratio of 9:2:2:3 to prepare a slurry. Then, the lithium extraction slurry was coated at a density of 60 mg / cm³. 2 The electrode is uniformly coated onto a titanium-based current collector and dried at 90°C for 8 hours to obtain a dry electrode.

[0109] (3) The above electrode was immersed in an ethanol solution of diphenylmethane diisocyanate (MDI) and crosslinked at 20°C for 24 h. After drying, the high-bonding-strength hydrophilic electrode for electrochemical lithium extraction was obtained. The diphenylmethane diisocyanate and ethanol were added at a mass ratio of 1:80.

[0110] Furthermore, the electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are largely the same as in Example 1. Lithium extraction was carried out using the same brine and experimental conditions as in Example 1. The results show that the average current density during lithium extraction and the electrode material Li + The adsorption capacity and current efficiency are shown in Table 2.

[0111] Examples 1-3

[0112] The difference between this embodiment and Example 1 is that: the initiator is azobisisobutyronitrile; and the electrode preparation uses Li as the active material. 0.5 An ethyl acetate solution containing FePO4, carbon nanotubes as the conductive agent, a conductive polymer-based material as the current collector, and isophorone diisocyanate as the crosslinking agent. The specific steps are as follows:

[0113] (1) Chitosan was dissolved in 0.1M acetic acid solution, and benzaldehyde was added. After reacting at 50℃ for 8 hours, aniline and initiator ammonium persulfate were added. After reacting at 25℃ for 6 hours, the solution was adjusted to neutral with NaOH. After filtration, washing and drying, polyaniline-grafted chitosan was obtained.

[0114] (2) Polyaniline-grafted chitosan was dissolved in a 2% aqueous acetic acid solution to prepare a 3wt% binder solution. 0.5 FePO4, carbon nanotubes, polyaniline-grafted chitosan, and polyethylene glycol were mixed evenly in a mass ratio of 8:1:1:1.5 to form a slurry. The lithium extraction slurry was then coated at a density of 70 mg / cm³. 2 The electrode is uniformly coated onto a conductive polymer current collector and dried at 45°C for 18 hours to obtain a dry electrode.

[0115] (3) The above electrode was immersed in an ethyl acetate solution of isophorone diisocyanate and crosslinked at 30°C for 1.5 h, then dried to obtain the high-binding-strength hydrophilic electrode for electrochemical lithium extraction. Isophorone diisocyanate and ethyl acetate were added at a mass ratio of 1:80.

[0116] Furthermore, the electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are largely the same as in Example 1. Lithium extraction was carried out using the same brine and experimental conditions as in Example 1. The results show that the average current density during lithium extraction and the electrode material Li + The adsorption capacity and average current efficiency are shown in Table 2.

[0117] Example 2

[0118] This embodiment discloses a method for preparing a high-binding-strength hydrophilic electrode for lithium extraction from a lithium-containing solution, specifically including the following steps:

[0119] (1) Chitosan was dissolved in a 2% acetic acid aqueous solution to prepare a 3wt% binder solution. LiFePO4, acetylene black, chitosan, and polyethylene glycol were mixed evenly in a mass ratio of 8:1:1:1.5 to form a slurry. Then, the lithium extraction slurry was coated at a density of 120 mg / cm³. 2 The electrode is uniformly coated onto a titanium-based current collector and dried at 50°C for 20 hours to obtain a dry electrode.

[0120] (2) The above electrode was immersed in an ethanol solution of toluene diisocyanate and crosslinked at 50°C for 0.5 h, then dried to obtain the high-binding-strength hydrophilic electrode for electrochemical lithium extraction. Toluene diisocyanate and ethanol were added at a mass ratio of 1:80.

[0121] Furthermore, the electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are largely the same as in Example 1. Lithium extraction was carried out using the same brine and experimental conditions as in Example 1. The results show that the average current density during lithium extraction and the electrode material Li + The adsorption capacity and average current efficiency are shown in Table 2.

[0122] Example 2-1

[0123] The difference between this embodiment and Embodiment 2 lies in the electrode preparation: the conductive agent is Ketjen black, the current collector is a titanium-based current collector, and the crosslinking agent is a tetrahydrofuran solution of isophorone diisocyanate. The specific steps are as follows:

[0124] (1) Chitosan was dissolved in a 2% acetic acid aqueous solution to prepare a 3wt% binder solution. LiFePO4, Ketjen Black, chitosan, and polyethylene glycol were mixed evenly at a mass ratio of 8:1:1:1.5 to form a slurry. Then, the lithium extraction slurry was coated at a density of 80 mg / cm³. 2 The electrode is uniformly coated onto a titanium-based current collector and dried at 60°C for 15 hours to obtain a dry electrode.

[0125] (2) The above electrode was immersed in a tetrahydrofuran solution of isophorone diisocyanate and crosslinked at 25°C for 24 h, then dried to obtain the high-binding-strength hydrophilic electrode for electrochemical lithium extraction. Isophorone diisocyanate and tetrahydrofuran were added at a mass ratio of 1:80.

[0126] Furthermore, the electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are largely the same as in Example 1. Lithium extraction was carried out using the same brine and experimental conditions as in Example 1. The results show that the average current density during lithium extraction and the electrode material Li + The adsorption capacity and average current efficiency are shown in Table 2.

[0127] Example 2-2

[0128] The difference between this embodiment and Example 2 is that the electrode preparation uses LiMn2O4 as the active material, SuperP as the conductive agent, a titanium-based current collector, and a propylene glycol solution of 1,6-hexamethylene diisocyanate as the crosslinking agent. The specific steps are as follows:

[0129] (1) Chitosan was dissolved in a 2% acetic acid aqueous solution to prepare a 3wt% binder solution. LiMn2O4, SuperP, chitosan, and polyethylene glycol were mixed evenly in a mass ratio of 7:1:1:1.5 to form a slurry. Then, the lithium extraction slurry was coated at a density of 90 mg / cm³. 2 The electrode was uniformly coated onto a titanium-based current collector and dried at 70°C for 12 hours to obtain a dry electrode.

[0130] (2) The above electrode was immersed in a propylene glycol solution of 1,6-hexamethylene diisocyanate and crosslinked at 45°C for 12 h, then dried to obtain the high-binding-strength hydrophilic electrode for electrochemical lithium extraction. The 1,6-hexamethylene diisocyanate and propylene glycol were added at a mass ratio of 1:80.

[0131] Furthermore, the electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are largely the same as in Example 1. Lithium extraction was carried out using the same brine and experimental conditions as in Example 1. The results show that the average current density during lithium extraction and the electrode material Li + The adsorption capacity and average current efficiency are shown in Table 2.

[0132] Example 2-3

[0133] The difference between this embodiment and Embodiment 2 is that the electrode preparation uses Li as the active material. 0.5 FePO4, carbon nanotubes as the conductive agent, titanium-based current collector as the current collector, and dicyclohexane diisocyanate as the crosslinking agent (H 12 The specific steps for preparing an ethylene glycol monobutyl ether solution of MDI are as follows:

[0134] (1) Dissolve chitosan in a 2% aqueous acetic acid solution to prepare a 3wt% binder solution. Li 0.5 FePO4, carbon nanotubes, chitosan, and polyethylene glycol were mixed evenly in a mass ratio of 8:1:1:1.5 to prepare a slurry. The lithium extraction slurry was then coated at a density of 100 mg / cm³. 2 The electrode is uniformly coated onto a titanium-based current collector and dried at 80°C for 10 hours to obtain a dry electrode.

[0135] (2) The electrode above is immersed in a solution of dicyclohexane diisocyanate and ethylene glycol monobutyl ether, crosslinked at 50°C for 6 hours, and dried to obtain the high-binding-strength hydrophilic electrode for electrochemical lithium extraction, wherein dicyclohexane diisocyanate and ethylene glycol monobutyl ether are added at a mass ratio of 1:80.

[0136] Furthermore, the electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are largely the same as in Example 1. Lithium extraction was carried out using the same brine and experimental conditions as in Example 1. The results show that the average current density during lithium extraction and the electrode material Li + The adsorption capacity and average current efficiency are shown in Table 2.

[0137] Example 3

[0138] The electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are the same as in Example 1, except that the dispersant is polyvinyl alcohol. LiFePO4, acetylene black, grafted chitosan, and polyvinyl alcohol are mixed uniformly at a mass ratio of 8:1:1:3 to form a slurry. Results show that the average current density during lithium extraction, and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0139] Example 4

[0140] The electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are the same as in Example 1, except that the dispersant is polyvinylpyrrolidone (PVP). LiFePO4, acetylene black, grafted chitosan, and PVP were mixed uniformly at a mass ratio of 8:1:1:1.5 to form a slurry. Results showed that the average current density during lithium extraction and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0141] Example 5

[0142] The electrode preparation method and the construction of the electrochemical lithium extraction system in this embodiment are the same as in Example 1, except that the dispersant is sodium carboxymethyl cellulose (CMC). LiFePO4, acetylene black, grafted chitosan, and sodium carboxymethyl cellulose were mixed uniformly at a mass ratio of 8:1:1:1.5 to form a slurry. Results showed that the average current density during lithium extraction and the electrode material Li...+ The adsorption capacity and average current efficiency are shown in Table 2.

[0143] Example 6

[0144] The electrode preparation method and electrochemical lithium extraction system in this embodiment are the same as in Example 1, except that the crosslinking agent is an ethyl acetate solution of polyethylene glycol diglycidyl ether (PEGDE). The PEGDE and ethyl acetate solution are added at a mass ratio of 1:80. Results show that the average current density during lithium extraction and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0145] Comparative Example 1

[0146] LiFePO4, acetylene black, and PVDF were added to NMP at a mass ratio of 8:1:1 and mixed evenly. The mixture was then ground into a slurry and coated onto a titanium-based current collector (with the same coating density). The electrode was placed in a vacuum drying oven at 110°C for 12 hours and dried. After cooling, a lithium iron phosphate control electrode was obtained. A set of under-lithiated electrodes was then prepared using the same method.

[0147] Lithium extraction was performed under the exact same experimental conditions as in Example 1. The results showed that the average current density during lithium extraction, and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0148] Comparative Example 2

[0149] LiMn2O4, acetylene black, and PVDF were added to NMP organic solvent at a weight ratio of 8:1:1 and mixed evenly. The mixture was then ground into a slurry and coated onto a titanium-based current collector (with the same coating density). The electrode was placed in a vacuum drying oven at 110°C for 12 hours and dried. After cooling, a lithium manganese oxide control electrode was obtained. A set of under-lithiated electrodes was prepared using the same method.

[0150] Lithium extraction was performed under the exact same experimental conditions as in Example 1. The results showed that the average current density during lithium extraction, and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0151] Comparative Example 3

[0152] The electrode for electrochemical lithium extraction in this comparative example is the same as that in Example 1, except that the preparation step (3) in Example 1 is removed, i.e., no crosslinking agent is added.

[0153] Lithium extraction was performed under the exact same experimental conditions as in Example 1. The results showed that the average current density during lithium extraction, and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0154] Comparative Example 4

[0155] The electrode for electrochemical lithium extraction in this comparative example is the same as that in Example 2, except that the preparation step (2) in Example 2 is omitted, i.e., no crosslinking agent is added.

[0156] Lithium extraction was performed under the exact same experimental conditions as in Example 1. The results showed that the average current density during lithium extraction, and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0157] Comparative Example 5

[0158] The electrode used for electrochemical lithium extraction in this comparative example is the same as that in Example 1, except that polyethylene glycol in step (2) of the preparation in Example 1 is removed, that is, polyethylene glycol, the dispersant, is not added.

[0159] Lithium extraction was performed under the exact same experimental conditions as in Example 1. The results showed that the average current density and the electrode material Li... + The adsorption capacity and average current efficiency are shown in Table 2.

[0160] Table 2. Detection data for both examples and comparative examples.

[0161] Group <![CDATA[Average current density (A / m 2 )]]> Lithium intercalation capacity (mg / g) Average current efficiency (%) Example 1 13.3 34.3 91.8 Example 1-1 12.9 28.8 90.15 Examples 1-2 13.2 33.4 90.86 Examples 1-3 13.6 33.1 91.7 Example 2 12.1 30.8 89.1 Example 2-1 11.8 30.2 88.82 Example 2-2 11.5 26.8 88.46 Example 2-3 11.8 30.5 88.79 Example 3 12.5 31.8 89.26 Example 4 12.2 32.3 89.1 Example 5 12.6 31.4 89.65 Example 6 12.8 31.8 89.95 Comparative Example 1 9.9 25.6 77.6 Comparative Example 2 9.4 22.3 76.25 Comparative Example 3 11 29.1 85.7 Comparative Example 4 10.7 28.6 85.1 Comparative Example 5 10.5 28.5 83.4

[0162] The results show:

[0163] Comparing Examples 1-3 (modified chitosan scheme) and Examples 2-3 (using unmodified chitosan scheme), it can be seen that grafted modified chitosan can significantly improve the average current density, lithium intercalation capacity, and average current efficiency (%), by >1 A / m. 2 >3.5 mg / g and >2.7%.

[0164] Compared with Comparative Examples 3 and 4 (without crosslinking agent), Examples 1-2-3 show a significant improvement in the overall electrochemical performance and lithium extraction performance of the electrode after crosslinking. This indicates that the use of crosslinking agent can maintain structural stability, connect the active material and the current collector together to maintain mechanical integrity, and improve the electrode structure density and resistance to electrolyte swelling, preventing the binder from dissolving or excessively swelling in the electrolyte and ensuring the long-term integrity of the electrode structure. The electrode of this invention exhibits an average current density ≥13.3 A / m during lithium extraction. 2 The lithium intercalation capacity is ≥34.3mg / g, and the current efficiency is ≥91.8%.

[0165] As can be seen from Examples 1-3 and Comparative Example 1, the current density, lithium intercalation capacity, and current efficiency during the lithium extraction process in Comparative Example 1, which uses PVDF binder, are all lower than those of the electrodes provided in Examples 1 and 2. A comparison of the contact angle experiments between water droplets and electrodes in Comparative Example 1 and Example 1 reveals that, using the electrode provided by this invention, brine can completely wet and penetrate the electrode within 1 second, achieving a hydrophilic state, as shown in the results. Figure 3 As shown. Simultaneously, the modified chitosan-grafted crosslinked electrode exhibits high current density and current efficiency, enabling high-current-density lithium extraction. The conjugated structure and active centers of the conductive polymer provide a denser electron distribution and promote electron transfer, while retaining the electrode's high hydrophilicity. This synergistic effect significantly enhances Li-… + Diffusion and electron transport. The high current density lithium extraction achieved by this invention is the result of a comprehensive improvement in electrode conductivity and hydrophilicity.

[0166] Meanwhile, the chitosan and modified grafted chitosan crosslinking binders provided by this invention have a wide range of applications, including LiMn2O4 and LiNi. x Co y Mn (1-x-y) O2 or LiFePO4 doped derivative electrodes also exhibit good lithium extraction performance. Compared to Comparative Example 5, the addition of a dispersant in Examples 1-6 helps to disperse the electrode active material more uniformly in the slurry, allowing the binder to more evenly coat the active material and conductive agent, thus improving the bonding stability between the electrode components. Simultaneously, the dispersant also participates in the construction of the cross-linking network, inhibiting the structural densification caused by excessive chitosan cross-linking, preserving a suitable porous structure, ensuring lithium-ion migration channels without affecting electron conduction, and improving lithium extraction performance.

[0167] Experimental Example 1

[0168] The electrodes obtained in Examples 1, 2, and 1 (Comparative Example 1) were subjected to lithium extraction cycling experiments at high flow rates, and the capacity retention rate of the electrodes was monitored during the cycling process. The electrodes obtained in Examples 1, 2, and 1 (Comparative Example 1) were placed in the anode and cathode chambers of an electrolytic cell, respectively. 2.5 L of a 10 g / L NaCl solution was added to the anode chamber as a supporting electrolyte, and 2.5 L of the brine solution from Table 1 was added to the cathode chamber. The temperature was room temperature, and the magnetic circulation pump was turned on, with a water flow rate of 10 m / s.

[0169] The change in electrode capacity retention with the number of cycles during lithium extraction is as follows: Figure 1 As shown. By Figure 1It can be seen that for the modified chitosan of Example 1 or the chitosan crosslinked electrode of Example 2, the electrode capacity retention rate remained above 83% after 120 cycles. This indicates that during the cycling process, even in a high-flow-rate underwater environment, the titanium-based current collector did not detach from the electrode and maintained good interaction with the active material, enabling the electrode to maintain a high capacity retention rate after long-term cycling. In contrast, the electrode of Comparative Example 1 showed partial detachment after only 15 cycles on the titanium-based current collector, and almost completely detached after 30 cycles.

[0170] To further investigate the adhesion force between the electrode and the titanium-based current collector, nano-scraping was used to characterize the electrode. The friction coefficient was measured by scratching and peeling the samples from Example 1 and Comparative Example 1. Figure 2 As shown, the adhesion force of Example 1 was more than twice that of Comparative Example 1. This is because the traditional commercial adhesive PVDF has a highly symmetrical molecular structure, resulting in only weak van der Waals forces between it and the active material and current collector. The chitosan and modified grafted chitosan crosslinked electrodes provided by this invention can generate a strong adhesion force with the current collector, exhibiting high bonding strength and resisting detachment and residue during long-term cycling.

[0171] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an electrode for electrochemical lithium extraction, characterized in that, include: Step (1): Add an aromatic modifier with a conjugated structure to graft and modify chitosan; Step (2): Prepare a slurry by combining the grafted and modified chitosan with active materials and conductive agents. Coat the slurry onto the current collector and dry it to obtain the electrode preform. Step (3): Add a thermosetting crosslinking agent to the coating layer of the electrode preform, and obtain the finished electrode after curing.

2. The method for preparing the electrode for electrochemical lithium extraction according to claim 1, characterized in that, Step (1) includes: S101: Dissolve chitosan powder in a weakly acidic aqueous solution to form a homogeneous chitosan solution; S102: Add an aromatic modifier with a conjugated structure to the chitosan solution; S103: Adjust the pH of the reaction system to neutral; S104: Filter the product after the reaction to remove unreacted modifiers and byproducts, and then dry it to obtain grafted modified chitosan.

3. The method for preparing an electrode for electrochemical lithium extraction according to claim 2, characterized in that, In step S101, the weak acid is an organic acid, preferably one or more of formic acid, acetic acid, and malonic acid.

4. The method for preparing an electrode for electrochemical lithium extraction according to claim 1, characterized in that, The aromatic modifier is an aromatic compound having active hydrogen and / or nitrogen-sulfur heterocycles. Preferably, the aromatic modifier is one or more of pyrrole, aniline, thiophene, pyrrole formaldehyde, benzaldehyde, and thiophene formaldehyde.

5. The method for preparing an electrode for electrochemical lithium extraction according to claim 4, characterized in that, In step (2), the mass ratio of aromatic modifier to chitosan is 0.2 to 0.

8.

6. The method for preparing an electrode for electrochemical lithium extraction according to claim 5, characterized in that, In step (2), the mass ratio of active material, conductive agent, and modified chitosan is 7-9:1-2:1-2.

7. The method for preparing an electrode for electrochemical lithium extraction according to claim 6, characterized in that, In step (2), a dispersant also needs to be added. The mass ratio of the conductive agent to the dispersant is 1-2:1.5-3.

8. The method for preparing an electrochemical lithium extraction electrode according to any one of claims 1-7, characterized in that, The thermosetting crosslinking agent is an aldehyde crosslinking agent, a carboxylic acid crosslinking agent, an epoxy crosslinking agent, or an isocyanate crosslinking agent.

9. The method for preparing an electrode for electrochemical lithium extraction according to claim 8, characterized in that, The thermosetting crosslinking agent is one or more of the following: glutaraldehyde, citric acid, epichlorohydrin, polyethylene glycol diglycidyl ether, isophorone diisocyanate, 1,6-hexane diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and dicyclohexane diisocyanate.

10. An electrode for electrochemical lithium extraction, characterized in that, The electrode for electrochemical lithium extraction is prepared by the method of any one of claims 1-9, comprising a current collector and a modified layer coated on the surface of the current collector; The modified layer consists of uniformly dispersed chitosan, active materials, conductive agents, and crosslinking agents.

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