Preparation, application and recovery method of high-hydrophilicity lithium extraction electrode

Abstract

The invention belongs to the field of lithium resource recovery, and particularly relates to preparation, application and a recovery method of a high-hydrophilicity lithium extraction electrode. The preparation method of the lithium extraction electrode comprises the following steps: sequentially adding a hydrophilic polymer and a cross-linking agent into a solvent, heating and stirring to a homogeneous phase to obtain a binder solution, adding a conductive agent and a lithium extraction active material into the binder solution, uniformly stirring to obtain lithium extraction slurry, coating a current collector with the prepared lithium extraction slurry, and drying to obtain the lithium extraction electrode. And drying to obtain the high-hydrophilicity lithium extraction electrode. The hydrophilic polymer is used for directly bonding the electrode material, so that the electrode is wholly hydrophilic from inside to outside, the prepared electrode material greatly improves the hydrophilicity of the lithium extraction electrode and accelerates the lithium extraction reaction rate, and the electrode material has the characteristics of simple preparation method, low cost, high lithium extraction efficiency, easiness in recovery and environmental protection; and efficient selective lithium extraction can be realized in various lithium-containing solutions.

Description

Technical Field

[0001] The present invention belongs to the field of lithium resource extraction, and in particular relates to a preparation method of a highly hydrophilic lithium extraction electrode and its application and recovery method. Background Art

[0002] With the continuous growth of demand for lithium batteries in the new energy sector, lithium extraction from brine and seawater has become a hot area. The characteristics of low lithium but high sodium, magnesium, potassium, etc. make the separation and extraction technology of lithium resources in salt lake brine face great challenges. In view of the shortcomings of lithium extraction technologies such as salting out, precipitation, extraction, membrane separation and adsorption in terms of recovery rate, environmental pollution, cost, performance, etc., some new green separation technologies have been gradually introduced into the field of lithium resource extraction. With the help of lithium-ion battery active materials to Li under electric field conditions, + The electrochemical lithium extraction technology of specific intercalation / deintercalation has the advantages of high lithium selectivity, fast rate, low material loss, low energy consumption, low pollution and strong applicability, and has attracted much attention in recent years.

[0003] So far, LiFePO 4、 LiMn2O4, LiCoO2, LiV2O5, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. can be used as active materials for lithium extraction electrodes and have been widely studied. The production of electrochemical lithium extraction electrodes requires the use of suitable polymers to bond active materials and conductive agents to form a stable electrode structure. Traditional lithium extraction electrodes are prepared with polyvinylidene fluoride (PVDF) as a binder. This is because PVDF has strong corrosion resistance and excellent electrochemical stability. Rocking chair LiFePO4 / LiFePO4 and rocking chair LiMn2O4 / Li with PVDF as a binder are 1-x Electrode systems such as Mn2O4, LiFePO4 / Ag, LiMn2O4 / AC, and FePO4 / K2NiFe(CN)6 all achieve efficient lithium extraction. However, PVDF has a low surface energy and is hydrophobic, making PVDF-bonded electrodes less hydrophilic and dense. This makes it difficult for the active materials within them to effectively contact the aqueous solution. During operation, the electrodes are prone to overpotential due to concentration polarization, which severely impacts their lifespan and stability. This adverse effect is exacerbated by the increased electrode loading. Furthermore, the difficulty in regenerating and recycling PVDF-bonded electrodes is a major factor hindering their industrial application. Summary of the Invention

[0004] To address these issues, the present invention aims to provide a method for preparing a highly hydrophilic lithium-extraction electrode, as well as its application and recovery, to overcome the problems of PVDF-based lithium-extraction electrodes, such as poor hydrophilicity, slow lithium extraction rates, poor cyclic stability, low loading capacity, and difficulty in recycling. The electrode of the present invention has a simple preparation process, is amenable to industrial production, and enables efficient and selective lithium extraction, easy recycling, and a low-carbon and environmentally friendly process.

[0005] To achieve the above objectives, the present invention provides a method for preparing a highly hydrophilic lithium extraction electrode, and its application and recovery, comprising the following steps: S1: adding a hydrophilic polymer and a cross-linking agent to a solvent in sequence, raising the temperature and stirring until a homogeneous phase is obtained to obtain a binder solution, wherein the amount of solvent added is 1500-4000% of the mass of the hydrophilic polymer, and the amount of cross-linking agent added is 0-50% of the mass of the hydrophilic polymer. The temperature range of the stirring process is 30-100°C; S2: adding a conductive agent and a lithium extraction active material to the binder solution and stirring uniformly to obtain a lithium extraction electrode slurry, wherein the amount of the conductive agent added is 5-12.5% of the mass of the lithium extraction active material, and the amount of the binder solution added is 250-500% of the mass of the lithium extraction active material; S3: The prepared lithium extraction electrode slurry is coated on the current collector, and the current collector is placed in an oven and dried at a temperature of 20-60° C. to obtain a highly hydrophilic lithium extraction electrode.

[0006] The hydrophilic polymer in step S1 is one or more of polyvinyl alcohol, polyvinyl butyral, cellulose acetate, polyvinyl acetate, polylactic acid, gelatin, starch, chitosan, carboxymethyl cellulose, and polyacrylamide.

[0007] In step S1, the solvent is one of water, anhydrous ethanol, and acetone, and the cross-linking agent is one of urea, glycerol, adipic acid, maleic anhydride, and glutaraldehyde.

[0008] The conductive agent in step S2 is one or more of acetylene black, Super P, graphite, Ketjen black, carbon nanotubes, carbon fibers, and graphene.

[0009] The lithium active material in step S2 is LiFePO 4、 LiMn2O4, LiCoO2, LiV2O5, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 One of O2.

[0010] The current collector in step S3 is one of a graphite plate, a titanium plate, and a carbon fiber cloth.

[0011] A method for applying a highly hydrophilic lithium extraction electrode is disclosed, using the highly hydrophilic lithium extraction electrode prepared as described above. The specific process is as follows: the prepared highly hydrophilic lithium extraction electrode and the corresponding counter electrode are used as the anode and cathode, placed in an electrolytic cell, and a lithium-containing solution is added for selective lithium extraction.

[0012] The corresponding counter electrode is a lithium-poor electrode of a highly hydrophilic lithium extraction electrode after delithiation or other ion-selective deintercalation electrodes prepared with one or more of Ag, Zn, Pb, PPy, activated carbon, and Prussian blue analogs as active materials. The lithium-containing solution is a lithium-containing solution such as salt lake brine, electrode material leachate, lithium precipitation mother liquor, etc. + of aqueous solution.

[0013] A method for recovering a highly hydrophilic lithium-extraction electrode, which recovers the highly hydrophilic lithium-extraction electrode used as described above, comprises the following steps: cleaning and drying the used and invalid highly hydrophilic lithium-extraction electrode, and physically stripping the current collector and the active material coating; placing the active material coating in a beaker, adding a recovery solvent, and increasing the temperature to dissolve the coating to obtain an active material recovery liquid; centrifuging and filtering the active material recovery liquid to remove most of the polymer and obtain waste active material powder.

[0014] The recovery solvent is one of water, anhydrous ethanol and acetone. After the lithium electrode is dissolved, centrifuged and filtered, the solvent can be reused by evaporation, condensation and reflux, and the electrode active material can be regenerated by chemical method.

[0015] Beneficial effects of the present invention: (1) The present invention uses easily degradable and non-toxic hydrophilic polymers and low-boiling-point water, ethanol and other green solvents. The dissolution and evaporation drying processes do not require high temperatures, the electrode preparation process consumes little energy, and is green and environmentally friendly.

[0016] (2) The present invention uses a hydrophilic polymer as a binder, which ensures consistent water permeability inside and on the surface of the electrode material, facilitates the rapid penetration and exchange of lithium ions in the electrode material with the aqueous solution, and effectively improves the lithium extraction rate and efficiency.

[0017] (3) Due to the use of a water-soluble hydrophilic binder, the lithium-extraction electrode prepared in the present invention can be subjected to steps such as heating, dissolution, centrifugation, and filtration to achieve preliminary recovery of the solvent and active material. This effectively reduces the three wastes in the industrial process and lowers the production and environmental costs of the industry.

[0018] (4) The lithium extraction electrode preparation method provided by the present invention has strong compatibility and can be applied to the preparation of lithium extraction electrodes of various active materials, and can be widely applied to the extraction of lithium resources from various lithium-containing solutions.

[0019] (5) Since the electrode provided by the present invention has high hydrophilicity, the lithium extraction rate is fast, the lithium extraction efficiency is high, and the production process is simple, so the industrialization investment is small, the process is short, and the effect is faster. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the infrared spectrum of the highly hydrophilic lithium-extraction electrode prepared in Example 2 of the present invention; Figure 2 This is a water contact angle diagram of the highly hydrophilic lithium extraction electrode prepared in Example 3 of the present invention; Figure 3 This is a morphology diagram of the electrode prepared in Example 5 of the present invention. DETAILED DESCRIPTION

[0021] In order to make the content, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below based on specific embodiments of the present invention, wherein: Example 1

[0022] A method for preparing a highly hydrophilic lithium-extraction electrode comprises the following steps: S1: adding a hydrophilic polymer and a cross-linking agent to a solvent in sequence, raising the temperature and stirring until a homogeneous phase is obtained to obtain a binder solution, wherein the amount of solvent added is 1500-4000% of the mass of the hydrophilic polymer, and the amount of cross-linking agent added is 0-50% of the mass of the hydrophilic polymer. The temperature range of the stirring process is 30-100°C; S2: adding a conductive agent and a lithium extraction active material to the binder solution and stirring uniformly to obtain a lithium extraction electrode slurry, wherein the amount of the conductive agent added is 5-12.5% of the mass of the lithium extraction active material, and the amount of the binder solution added is 250-500% of the mass of the lithium extraction active material; S3: The prepared lithium extraction electrode slurry is coated on the current collector, and the current collector is placed in an oven and dried at a temperature of 20-60° C. to obtain a highly hydrophilic lithium extraction electrode.

[0023] The hydrophilic polymer in step S1 is one or more of polyvinyl alcohol, polyvinyl butyral, cellulose acetate, polyvinyl acetate, polylactic acid, gelatin, starch, chitosan, carboxymethyl cellulose, and polyacrylamide.

[0024] In actual use, hydrophilic polymers are used as binders to replace PVDF, which can make the electrode hydrophilic from the inside out. Most of the hydrophilic polymers contain hydroxyl groups, carboxyl groups, ether bonds, etc., which can form hydrogen bonds or chemical bonds with the hydroxyl groups and oxygen-containing functional groups on the surface of the lithium-extracting active materials and conductive agents, and can form a contact hydrophilic network on the surface of the lithium-extracting active materials to the maximum extent. +In addition, hydrophilic polymers contain only C, H, O, and N elements and are more easily degraded than PVDF.

[0025] In step S1, the solvent is one of water, anhydrous ethanol, and acetone, and the cross-linking agent is one of urea, glycerol, adipic acid, maleic anhydride, and glutaraldehyde.

[0026] In actual use, the cross-linking agent can undergo physical or chemical cross-linking with the groups in the hydrophilic polymer to solve the swelling and dissolution behavior of the water-soluble polymer or some hydrophilic polymers during the lithium extraction process and electrode rinsing, thereby avoiding the disintegration and shedding of the electrode material.

[0027] The conductive agent in step S2 is one or more of acetylene black, Super P, graphite, Ketjen black, carbon nanotubes, carbon fibers, and graphene.

[0028] The lithium active material in step S2 is LiFePO 4、 LiMn2O4, LiCoO2, LiV2O5, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 One of O2.

[0029] The current collector in step S3 is one of a graphite plate, a titanium plate, and a carbon fiber cloth.

[0030] When the present invention is actually used, the prepared lithium-extraction electrode slurry is coated on the current collector and placed in an oven to be dried at a temperature of 20-60°C. A low-boiling-point, low-surface-tension solvent is used to dissolve the hydrophilic polymer. A low-temperature drying method is selected to effectively slow down the solvent volatilization rate, so that the electrode can be dried more slowly from bottom to top and from outside to inside, avoiding the occurrence of undesirable phenomena such as peeling and cracking.

[0031] A method for applying a highly hydrophilic lithium extraction electrode is disclosed, using the highly hydrophilic lithium extraction electrode prepared as described above. The specific process is as follows: the prepared highly hydrophilic lithium extraction electrode and the corresponding counter electrode are used as the anode and cathode, placed in an electrolytic cell, and a lithium-containing solution is added for selective lithium extraction.

[0032] The corresponding counter electrode is a lithium-poor electrode after delithiation of a highly hydrophilic lithium-extraction electrode or other ion-selective deintercalation electrodes prepared with one or more of Ag, Zn, Pb, PPy, activated carbon, and Prussian blue analogs as active materials. The lithium-poor electrode is made of a lithium-rich electrode, such as LiFePO 4、 LiMn2O4, LiCoO2, LiV2O5, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3The O2 electrode is obtained after lithium is removed. The lithium-poor electrode is the cathode and the lithium-rich electrode is the anode. Applying voltage can complete the process of lithium extraction and lithium removal. Other ion selective deintercalation electrodes have other ions (such as Na + , K + Mg 2+ 、Zn 2+ 、Cl - 、SO4 2- ) reversible intercalation and deintercalation capabilities, generating different half-electrode electrochemical reactions to maintain the conservation of materials and electrons during the lithium extraction process. Lithium extraction is achieved by applying a voltage to the lithium-poor electrode as the cathode and the other ion-selective deintercalation electrode as the anode. After completion, the delithiation process is completed by reversing the current direction.

[0033] The lithium-containing solution is salt lake brine, electrode material leaching solution, lithium precipitation mother solution, etc. + The pH range of the lithium-containing solution is 4-10 to ensure that the active material is not decomposed; Li + The content is >150mg / L, which can make the lithium extraction process more efficient.

[0034] A method for recovering a highly hydrophilic lithium-extraction electrode, which recovers the highly hydrophilic lithium-extraction electrode used as described above, comprises the following steps: cleaning and drying the used and invalid highly hydrophilic lithium-extraction electrode, and physically stripping the current collector and the active material coating; placing the active material coating in a beaker, adding a recovery solvent, and increasing the temperature to dissolve the coating to obtain an active material recovery liquid; centrifuging and filtering the active material recovery liquid to remove most of the polymer and obtain waste active material powder.

[0035] The recovery solvent is one of water, anhydrous ethanol and acetone. After the lithium electrode is dissolved, centrifuged and filtered, the solvent can be reused by evaporation, condensation and reflux, and the electrode active material can be regenerated by chemical method. Example 2

[0036] A polyvinyl alcohol (PVA)-based LiFePO4 electrode was prepared using a method for preparing a highly hydrophilic lithium-extraction electrode as described in Example 1. The specific process is as follows: PVA with a degree of alcoholysis of 99% was added to deionized water, the temperature was raised to 95°C, mechanically stirred for 6 hours, and then urea was added to obtain a uniform binder solution. The amount of water added was 3400% of the mass of the PVA, and the amount of urea added was 40% of the weight of the PVA. Acetylene black and LiFePO4 were added to the binder solution in sequence and mechanically stirred for 4 hours to obtain a lithium-extraction electrode slurry. The amounts of binder solution and acetylene black added to the slurry were 385% and 12.5% of the weight of the lithium iron phosphate, respectively. The slurry was evenly coated on a 40 cm × 30 cm graphite plate, and the coating density was controlled to be 160 mg / cm 2The coated electrode was then dried at 35°C for 4 hours to obtain a PVA-based LiFePO4 electrode. The infrared spectrum of the PVA-based LiFePO4 electrode is shown in FIG. Figure 1 shown.

[0037] The lithium extraction experiment was carried out by using a highly hydrophilic lithium extraction electrode as in Example 1. The specific process was as follows: the prepared PVA-based LiFePO4 electrode was used as the anode and the nickel foam was used as the cathode. The electrodes were placed in a 2.5 g / L NaCl solution and a voltage of 1.0 V was applied across the electrodes until the current density was lower than 2 A / m 2 , a FePO4 electrode can be made. A double-chamber electrolytic cell separated by an anion membrane was used for lithium extraction experiments. The prepared PVA-based LiFePO4 electrode and FePO4 electrode were placed in the anode chamber and cathode chamber respectively. 5 L of brine was added to the cathode chamber, and 2 L of 5 g / L NaCl solution was injected into the anode as the enrichment solution. A voltage of 0.35 V was applied to the two electrodes, and electrolysis was carried out at room temperature for 5.7 hours. The changes in the main cation concentrations of the brine and the enrichment solution before and after lithium extraction showed that the lithium concentration in the brine decreased from 2.15 g / L to 0.67 g / L; the lithium concentration in the enrichment solution increased to 3.70 g / L, and its magnesium-lithium ratio decreased from 38.47 in the brine to 1.48. After the electrolysis, the adsorption capacity of the electrode was 38.5 mg (Li) / g (LiFePO4), and the average current density during the lithium extraction process was 52.6 A / m 2 .

[0038] A recycling experiment was conducted using the highly hydrophilic lithium-extraction electrode recovery method described in Example 1. The used PVA-based LiFePO4 electrode was cleaned and dried, and the current collector and active material coating were physically exfoliated. 30g of the active material coating was placed in a beaker, 200mL of deionized water was added, and the temperature was raised to 95°C to dissolve the coating, yielding an active material recovery solution. The recovered active material solution was centrifuged and filtered, and then dried at 50°C for 1 hour to yield 25.6g of spent LiFePO4 / acetylene black powder. Example 3

[0039] A PVB-based LiFePO4 electrode was prepared using a method for preparing a highly hydrophilic lithium-extraction electrode as described in Example 1. The specific process is as follows: polyvinyl butyral (PVB) was added to anhydrous ethanol, the temperature was raised to 60°C, and mechanical stirring was performed for 3 hours to obtain a uniform binder solution. The amount of anhydrous ethanol added was 2700% of the mass of PVB. Super P and LiFePO4 were added to the binder solution in sequence, and mechanical stirring was performed for 4 hours to obtain a lithium-extraction electrode slurry. The amounts of binder solution and Super P added to the slurry were 350% and 12.5% of the weight of lithium iron phosphate, respectively. The slurry was evenly coated on a 30 cm × 25 cm carbon fiber cloth, and the coating density was controlled to be 120 mg / cm 2 The coated electrode was then dried at 25 °C for 6 hours to obtain a PVB-based LiFePO4 electrode. The water contact angle of the PVB-based LiFePO4 electrode is as follows: Figure 2 shown.

[0040] The lithium extraction experiment was carried out by using a highly hydrophilic lithium extraction electrode as in Example 1. The specific process was as follows: the prepared PVB-based LiFePO4 electrode was used as the anode and the nickel foam was used as the cathode. The electrodes were placed in a 2.5 g / L NaCl solution and a voltage of 1.0 V was applied across the electrodes until the current density was lower than 2 A / m 2 , a FePO4 electrode can be made. A double-chamber electrolytic cell separated by an anion membrane was used for lithium extraction experiments. The prepared PVB-based LiFePO4 electrode and FePO4 electrode were placed in the anode chamber and cathode chamber respectively. 5L of lithium precipitation mother liquor was added to the cathode chamber, and 1.5L of 5 g / L NaCl solution was injected into the anode as an enrichment solution. A voltage of 0.35V was applied to the two poles, and electrolysis was carried out at room temperature for 3.3 hours. From the composition of the lithium precipitation mother liquor and the enrichment solution before and after lithium extraction, it can be seen that the lithium concentration in the lithium precipitation mother liquor decreased from 1.15g / L to 0.47g / L; the lithium concentration in the enrichment solution increased to 2.26g / L. After the electrolysis, the adsorption capacity of the electrode was 37.6mg (Li) / g(LiFePO4), and the average current density during the lithium extraction process was 43.5A / m 2 .

[0041] A recovery experiment was conducted using the highly hydrophilic lithium-extraction electrode recovery method described in Example 1. The specific process was as follows: the used PVB-based LiFePO4 electrode was cleaned and dried, and the current collector and active material coating were physically stripped. 20g of the active material coating was placed in a beaker, 150mL of anhydrous ethanol was added, and the temperature was raised to 60°C to dissolve the coating, obtaining an active material recovery solution. The active material recovery solution was centrifuged and filtered, and then dried at 50°C for 1 hour to obtain 17.8g of spent LiFePO4 / Super P powder. Example 4

[0042] A PVB-based LiMn2O4 electrode was prepared by using a method for preparing a highly hydrophilic lithium-extraction electrode as described in Example 1. The specific process is as follows: (1) PVB was added to anhydrous ethanol, the temperature was raised to 60°C, and mechanically stirred for 3 hours to obtain a uniform binder solution. The amount of anhydrous ethanol added was 1350% of the mass of PVB. Acetylene black and LiMn2O4 were added to the binder solution in sequence, and mechanically stirred for 4 hours to obtain a lithium-extraction electrode slurry. The amounts of binder solution and Ketjen black added to the slurry were 350% and 10% of the weight of lithium iron phosphate, respectively. The slurry was evenly coated on a 30 cm × 25 cm graphite plate, and the coating density was controlled to be 120 mg / cm 2 The coated electrode was then dried at 30°C for 6 hours to obtain a PVB-based LiMn2O4 electrode.

[0043] The lithium extraction experiment was carried out by using a highly hydrophilic lithium extraction electrode as described in Example 1. The specific process was as follows: the prepared PVB-based LiMn2O4 electrode was used as the anode and the nickel foam was used as the cathode. The electrodes were placed in a 5 g / L NaSO4 solution and a voltage of 1.0 V was applied across the electrodes until the current density was lower than 2 A / m 2 , can be made into Li 1-x Mn2O4 electrode. A double-chamber electrolytic cell separated by anion membrane was used for lithium extraction experiments. 1-x The Mn2O4 electrodes were placed in the anode chamber and the cathode chamber respectively. 4L of battery material leachate was added to the cathode chamber, and 2L of 2g / L NaSO4 solution was injected into the anode as a supporting electrolyte. A voltage of 0.6V was applied to the two poles, and electrolysis was carried out at room temperature for 2.8 hours. From the composition of the battery material leachate and the enriched solution before and after lithium extraction, it can be seen that the lithium concentration in the battery material leachate decreased from 1.31g / L to 0.66g / L; the lithium concentration in the enriched solution increased to 1.29g / L. After the electrolysis, the adsorption capacity of the electrode was 28.7mg (Li) / g(LiMn2O4), and the average current density in the above process was 36.6A / m 2 .

[0044] A recovery experiment was conducted using the highly hydrophilic lithium-extraction electrode recovery method described in Example 1. The specific process was as follows: the used PVB-based LiMn2O4 electrode was cleaned and dried, and the current collector and active material coating were physically stripped. 15g of the active material coating was placed in a beaker, 100mL of anhydrous ethanol was added, and the temperature was raised to 60°C to dissolve the coating, obtaining an active material recovery solution. The active material recovery solution was centrifuged and filtered, and then dried at 50°C for 1 hour to obtain 11.15g of spent LiMn2O4 / Ketjen Black powder. Example 5

[0045] The preparation method of a highly hydrophilic lithium-extraction electrode as in Example 1 was used to prepare a PVA-based LiFePO4 electrode. The parameters were the same as those in Example 2, but the electrode was coated on a 30 cm × 30 cm graphite plate and the coating density was controlled to be 100 mg / cm 2 .

[0046] Preparation of PVA-based Ag electrode pair: Add PVA with a degree of alcoholysis of 99% to deionized water, raise the temperature to 95°C, and mechanically stir for 6 hours to obtain a uniform binder solution. The amount of water added is 1900% of the mass of PVA. Add acetylene black and Ag powder to the binder solution in turn, and mechanically stir for 4 hours to obtain an electrode slurry. The amount of binder solution and acetylene black added to the slurry is 250% and 8% of the weight of Ag powder, respectively. (3) The electrode slurry obtained in step (2) is evenly coated on a 30 cm × 30 cm graphite plate, and the Ag coating density is controlled to be 110 mg / cm 2 The coated electrode was then dried at 45°C for 6 hours to obtain a PVA-based Ag counter electrode. The morphology of the PVA-based Ag counter electrode is shown in FIG. Figure 3 shown.

[0047] Lithium extraction experiment: The prepared LiFePO4 electrode was used as the anode and nickel foam was used as the cathode. They were placed in a 2.5 g / L NaCl solution and a voltage of 1 V was applied across the electrodes until the current density was lower than 2 A / m 2 , FePO4 electrode can be made. A double electrolytic cell without anion membrane separation was used for lithium extraction experiments. The prepared PVA-based FePO4 electrode and Ag counter electrode were placed in brine tanks respectively. 8 L of brine was added to the brine tank, a voltage of 0.35 V was applied to the two electrodes, and electrolysis was carried out at room temperature for 5.21 hours. After that, the electrode was taken out, placed in a recovery tank, 2 L of 5 g / L NaCl solution was injected, a voltage of 1 V was applied to the two electrodes, and electrolysis was carried out at room temperature until the current density was less than 2 A / m 2 The lithium extraction is completed. The composition of the brine and the enriched solution before and after lithium extraction shows that the lithium concentration in the brine decreased from 0.75g / L to 0.27g / L; the lithium concentration in the enriched solution increased to 1.20g / L, and its magnesium-lithium ratio decreased from 102 in the brine to 6.47. After the electrolysis, the adsorption capacity of the electrode was 36.8mg (Li) / g (LiFePO4), and the average current density during the above process was 28.1A / m 2 .

[0048] Example 6

[0049] A cellulose acetate (CA)-based LiFePO4 electrode was prepared by using a method for preparing a highly hydrophilic lithium-extraction electrode as described in Example 1. The specific process is as follows: CA was added to acetone, the temperature was raised to 45°C, and mechanical stirring was performed for 3 hours to obtain a uniform binder solution. The amount of acetone added was 2700% of the mass of CA. Acetylene black and LiFePO4 were added to the binder solution in sequence, and mechanical stirring was performed for 4 hours to obtain a lithium-extraction electrode slurry. The amount of binder solution and acetylene black added to the slurry was 350% and 12.5% of the weight of lithium iron phosphate, respectively. The slurry was evenly coated on a 30 cm × 25 cm graphite plate, and the coating density was controlled to be 80 mg / cm 2 The coated electrode was then dried at 20°C for 4 hours to obtain a CA-based LiFePO4 electrode.

[0050] The lithium extraction experiment was carried out by using a highly hydrophilic lithium extraction electrode as described in Example 1. The specific process was as follows: the prepared CA-based LiFePO4 electrode was used as the anode and the nickel foam was used as the cathode. The electrodes were placed in a 5 g / L NaCl solution and a voltage of 1.0 V was applied across the electrodes until the current density was lower than 2 A / m 2 , a FePO4 electrode can be made. A double-chamber electrolytic cell separated by an anion membrane was used for lithium extraction experiments. The prepared CA-based LiFePO4 electrode and FePO4 electrode were placed in the anode chamber and cathode chamber respectively. 4L of brine was added to the cathode chamber, and 1.5L of 2 g / L NaCl solution was injected into the anode as a supporting electrolyte. A voltage of 0.35V was applied to the two electrodes, and electrolysis was carried out at room temperature for 2.93 hours. From the composition of the brine and the enriched solution before and after lithium extraction, it can be seen that the lithium concentration in the brine decreased from 1.12g / L to 0.56g / L; the lithium concentration in the enriched solution increased to 1.50g / L, and its magnesium-lithium ratio decreased from 33.4 in the brine to 1.07. After the electrolysis, the adsorption capacity of the electrode was 37.4mg (Li) / g(LiFePO4), and the average current density in the above process was 30.2A / m 2 .

[0051] Obviously, the specific implementation methods described above are only part of the embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or replacements that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a highly hydrophilic lithium-extraction electrode, characterized in that: The following steps are involved: S1: adding a hydrophilic polymer and a cross-linking agent to a solvent in sequence, raising the temperature and stirring until a homogeneous phase is obtained to obtain a binder solution, wherein the amount of solvent added is 1500-4000% of the mass of the hydrophilic polymer, and the amount of cross-linking agent added is 0-50% of the mass of the hydrophilic polymer. The temperature range of the stirring process is 30-100°C; S2: adding a conductive agent and a lithium extraction active material to the binder solution and stirring uniformly to obtain a lithium extraction electrode slurry, wherein the amount of the conductive agent added is 5-12.5% of the mass of the lithium extraction active material, and the amount of the binder solution added is 250-500% of the mass of the lithium extraction active material; S3: The prepared lithium extraction electrode slurry is coated on the current collector, and the current collector is placed in an oven and dried at a temperature of 20-60° C. to obtain a highly hydrophilic lithium extraction electrode.

2. The method for preparing a highly hydrophilic lithium-extraction electrode according to claim 1, wherein: The hydrophilic polymer in step S1 is one or more of polyvinyl alcohol, polyvinyl butyral, cellulose acetate, polyvinyl acetate, polylactic acid, gelatin, starch, chitosan, carboxymethyl cellulose, and polyacrylamide.

3. The method for preparing a highly hydrophilic lithium-extraction electrode according to claim 1, wherein: In step S1, the solvent is one of water, anhydrous ethanol, and acetone, and the cross-linking agent is one of urea, glycerol, adipic acid, maleic anhydride, and glutaraldehyde.

4. The method for preparing a highly hydrophilic lithium-extraction electrode according to claim 1, wherein: The conductive agent in step S2 is one or more of acetylene black, Super P, graphite, Ketjen black, carbon nanotubes, carbon fibers, and graphene.

5. The method for preparing a highly hydrophilic lithium-extraction electrode according to claim 1, wherein: The lithium active material in step S2 is LiFePO 4、 LiMn2O4, LiCoO2, LiV2O5, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 One of O2.

6. The method for preparing a highly hydrophilic lithium-extraction electrode according to claim 1, wherein: The current collector in step S3 is one of a graphite plate, a titanium plate, and a carbon fiber cloth.

7. A method for applying a highly hydrophilic lithium extraction electrode, using the highly hydrophilic lithium extraction electrode prepared as claimed in claim 1, characterized in that: The specific process is: the prepared highly hydrophilic lithium-extraction electrode and the corresponding counter electrode are used as the anode and cathode, placed in an electrolytic cell, and a lithium-containing solution is added for selective lithium extraction.

8. The method for applying a highly hydrophilic lithium extraction electrode according to claim 7, characterized in that: The corresponding counter electrode is a lithium-poor electrode of a highly hydrophilic lithium extraction electrode after delithiation or other ion-selective deintercalation electrodes prepared with one or more of Ag, Zn, Pb, PPy, activated carbon, and Prussian blue analogs as active materials. The lithium-containing solution is a lithium-containing solution such as salt lake brine, electrode material leachate, lithium precipitation mother liquor, etc. + of aqueous solution.

9. A method for recovering a highly hydrophilic lithium extraction electrode, comprising recovering the highly hydrophilic lithium extraction electrode as used in claim 7, characterized in that: The specific process is as follows: the used and failed highly hydrophilic lithium-extraction electrode is cleaned and dried, and the current collector and active material coating are physically peeled off; the active material coating is placed in a beaker, a recovery solvent is added and the temperature is increased to dissolve the coating to obtain an active material recovery liquid; the active material recovery liquid is centrifuged and filtered to remove most of the polymer to obtain waste active material powder.

10. The method for recovering a highly hydrophilic lithium-extracting electrode according to claim 9, wherein: The recovery solvent is one of water, anhydrous ethanol and acetone. After the lithium electrode is dissolved, centrifuged and filtered, the solvent can be reused by evaporation, condensation and reflux, and the electrode active material can be regenerated by chemical method.

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