Modified lithium-ion sieves, their preparation methods, and their applications in electrochemical lithium extraction.

Abstract

This disclosure discloses a modified lithium-ion sieve, its preparation method, and its application in electrochemical lithium extraction. The modified lithium-ion sieve comprises alternately stacked matrix material nanosheets and reduced graphene oxide nanosheets, wherein the matrix material nanosheets are MnO2 nanosheets. This modified lithium-ion sieve can be applied to electrochemical lithium extraction from salt lakes. The modified lithium-ion sieve of this disclosure can effectively increase the lithium extraction rate, greatly enhance the application value of MnO2-based lithium-ion sieves, and significantly reduce the cost of use, thereby improving production efficiency.

Description

Technical Field

[0001] This disclosure relates to the field of metallurgical technology, and more specifically, to modified lithium-ion sieves, their preparation methods, and their application in electrochemical lithium extraction. Background Technology

[0002] Lithium resources have wide applications in lithium-ion batteries and related fields. With the rapid development of the lithium-ion battery industry, the demand for lithium resources in industrial production is growing faster and faster, and in recent years there has even been a situation where the supply of lithium raw materials cannot meet the demand.

[0003] Lithium resources are abundant in some high-altitude areas, such as the salt lakes of the Qinghai-Tibet Plateau in China. Therefore, how to efficiently and quickly extract lithium from these salt lakes has been a long-standing scientific problem. Salt lakes typically have low lithium content but high levels of other metals like magnesium. Due to the similar properties of magnesium and lithium, selectively extracting lithium from salt lakes is challenging. In the past, methods for lithium extraction from salt lakes included precipitation, calcination leaching, carbonization, nanofiltration, solvent extraction, and adsorption. Among these, adsorption, which uses lithium-ion sieves to adsorb lithium ions, is considered a promising method due to its high adsorption capacity and selectivity. MnO2-based ion sieves show good adsorption performance for lithium and have certain industrial benefits, thus they are increasingly being used in the field of lithium extraction from salt lakes. However, traditional MnO2-based ion sieves require cyclic acid dissolution during use, leading to rapid structural collapse and a short cycle life.

[0004] Combining electrochemical methods can typically ensure cycle life without sacrificing the adsorption capacity of MnO2-based ion sieves. However, single MnO2-based ion sieves have a small specific surface area and low lithium extraction efficiency. Therefore, structural modification of MnO2-based ion sieves is necessary to efficiently and selectively enrich lithium resources from brine for industrial-scale lithium extraction from salt lakes.

[0005] In view of this, this disclosure is hereby made. Summary of the Invention

[0006] The purpose of this disclosure is to provide a modified lithium-ion sieve, its preparation method, and its application in electrochemical lithium extraction.

[0007] This disclosure is implemented as follows: In a first aspect, this disclosure provides a modified lithium-ion sieve comprising alternately stacked matrix material nanosheets and reduced graphene oxide nanosheets, wherein the matrix material nanosheets are MnO2 nanosheets.

[0008] In an optional embodiment, the matrix material nanosheet is a three-dimensional layered framework structure of MnO2 nanosheet.

[0009] In an optional embodiment, the reduced graphene oxide nanosheets are positively charged reduced graphene oxide nanosheets.

[0010] In an optional embodiment, the positive charge is provided by ammonium ions and / or ammonium ion derivatives.

[0011] In an optional embodiment, the mass ratio of the matrix material nanosheets to the reduced graphene oxide nanosheets is (2~6):1.

[0012] In an optional embodiment, the gap between adjacent MnO2 nanosheets and reduced graphene oxide nanosheets is 2-6 nm.

[0013] In an optional embodiment, the modified lithium-ion sieve has a specific surface area greater than 119 m². 2 / g.

[0014] Secondly, this disclosure provides a method for preparing the modified lithium-ion sieve according to any one of the foregoing embodiments, comprising mixing the matrix material nanosheets and the reduced graphene oxide nanosheets in a solution system to obtain a lower layer of flocculent material, which is the modified lithium-ion sieve.

[0015] In an optional embodiment, the preparation of the reduced graphene oxide nanosheets includes a hydrothermal reaction of a mixture of graphene oxide, a cationic modifier, and a reducing agent.

[0016] In an optional embodiment, the cationic modifier is at least one of polydiallyldimethylammonium chloride, polyvinylpropyldimethylammonium chloride, polydimethyldiallyldimethylammonium chloride, and polyacrylamide.

[0017] In an optional embodiment, the reducing agent is at least one of hydrazine hydrate and sodium borohydride.

[0018] In an optional embodiment, the initial concentration of graphene oxide in the hydrothermal reaction step is 0.01~10 g / L.

[0019] In an optional embodiment, the initial concentration of graphene oxide is 1~2.8 g / L.

[0020] In an optional embodiment, in the hydrothermal reaction step, the mass ratio of graphene oxide to cationic modifier is 1: (0.01~100).

[0021] In an optional embodiment, the mass ratio of graphene oxide to cationic modifier is 1: (0.5~5).

[0022] In an optional embodiment, the mass ratio of graphene oxide to reducing agent in the hydrothermal reaction step is 1:(0.01~100).

[0023] In an optional embodiment, the mass ratio of graphene oxide to reducing agent is 1:(0.1~1).

[0024] In an optional embodiment, the temperature of the hydrothermal reaction step is 30~100 ℃ and the time is 0.1~10 h.

[0025] In an optional embodiment, the temperature of the hydrothermal reaction step is 70~90 ℃ and the time is 3~8 h.

[0026] In an optional embodiment, the mixing in the reduced graphene oxide nanosheet preparation step is ultrasonic mixing or mechanical stirring.

[0027] In an optional embodiment, the mixing time in the reduced graphene oxide nanosheet preparation step is 1 to 60 minutes.

[0028] In an optional embodiment, the mixing time in the reduced graphene oxide nanosheet preparation step is 6 to 20 minutes.

[0029] In an optional embodiment, the lower layer of flocculents is separated by centrifugation after mixing in the preparation step of the reduced graphene oxide nanosheets. The centrifugation speed is 6000~30000 rpm and the time is 1~60 minutes.

[0030] In an optional embodiment, the lower layer of flocculents is separated by centrifugation after mixing in the preparation step of the reduced graphene oxide nanosheets. The centrifugation speed is 10,000 to 20,000 rpm and the time is 8 to 20 minutes. In an optional embodiment, the separated lower layer flocculents are dried in the reduced graphene oxide nanosheet preparation step to obtain a dried modified lithium-ion sieve. The drying step is performed at a temperature of 65-85°C for 1-18 hours.

[0031] Thirdly, this disclosure provides a modified lithium-ion sieve electrode, which is obtained by coating a mixture of the modified lithium-ion sieve, conductive agent and binder described in any one of the foregoing embodiments onto a current collector and then drying it.

[0032] In an optional embodiment, the conductive agent is at least one of acetylene black, conductive carbon black, graphene, and carbon nanotubes.

[0033] In an optional embodiment, the adhesive is at least one of polyvinylidene fluoride, carboxymethyl cellulose, and polytetrafluoroethylene.

[0034] In an optional embodiment, the mass ratio of the modified lithium-ion sieve, conductive agent, and binder is 8:(0.5~1.5):(0.8~9).

[0035] In an optional embodiment, the modified lithium-ion sieve is dried at a temperature of 50~100℃ for 1~12 h.

[0036] In an optional embodiment, the modified lithium-ion sieve electrode is placed in the brine chamber, and the inert electrode is placed in the lithium salt chamber as the counter electrode. Then, the lithium ions in the brine chamber are inserted into the ion sieve by an external potential to obtain the modified lithium-ion sieve electrode in the lithium-intercalated state.

[0037] Fourthly, this disclosure provides an application of the modified lithium-ion sieve described in any of the foregoing embodiments in the extraction of lithium.

[0038] Fifthly, this disclosure provides an apparatus for electrochemical lithium extraction from salt lakes using a modified lithium-ion sieve electrode as described in any of the foregoing embodiments, comprising: Electrodes, including modified lithium-ion sieve electrodes as cathode electrodes and lithium-intercalated modified lithium-ion sieve electrodes as anode electrodes; The lithium salt chamber, wherein the anode electrode is disposed within the lithium salt chamber; The cathode electrode is disposed within the brine chamber. Anion exchange membrane: used to separate the lithium salt chamber and the brine chamber.

[0039] Sixthly, this disclosure provides a method for electrochemical lithium extraction from salt lakes using the apparatus described in any of the foregoing embodiments, wherein an external potential is applied between the cathode electrode and the anode electrode to drive the Li in the brine chamber. + Lithium-intercalated ion sieves formed within ion sieves, and lithium-intercalated ion sieves within lithium salt chambers. + It is extracted into the lithium salt chamber to obtain lithium salt.

[0040] The modified lithium-ion sieve disclosed herein is composed of alternating stacks of MnO2 nanosheets and graphene, which has an increased specific surface area, more lithium intercalation sites, and a stable framework structure, effectively improving the specific surface area compared to the unmodified lithium-ion sieve.

[0041] Electrochemical lithium extraction utilizes an external electric field to insert and extract lithium ions from brine into an ion sieve, without involving acid dissolution for lithium removal. Therefore, the ion sieve has a long lifespan. By combining it with an electrochemical device for lithium extraction, this invention can effectively increase the lithium extraction rate, greatly enhance the use value of MnO2-based lithium ion sieves, and significantly reduce usage costs, thereby improving production efficiency. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of the electrochemical lithium extraction device involved in this disclosure; Figure 2 This is the SEM image of the modified lithium-ion sieve synthesized in Example 1; Figure 3 This is the SEM image of the lithium-ion sieve synthesized in Comparative Example 1. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0045] This embodiment provides a modified lithium-ion sieve, comprising alternately stacked matrix material nanosheets and reduced graphene oxide nanosheets, wherein the matrix material nanosheets are MnO2 nanosheets.

[0046] The modified lithium-ion sieve is composed of alternating stacks of MnO2 nanosheets and graphene, which has a larger specific surface area and more lithium intercalation sites, increasing the specific surface area by more than 40% compared to the unmodified lithium-ion sieve; the stable framework structure helps to extend the service life of the modified lithium-ion sieve.

[0047] In some optional embodiments, the matrix material nanosheets are MnO2 nanosheets with a three-dimensional layered framework structure. For reference, MnO2 nanosheets disclosed in the prior art can be selected, such as the MnO2 nanosheets with a three-dimensional layered framework structure disclosed in patent CN115594223A (unless otherwise specified in the following embodiments, the preparation method of MnO2 nanosheets refers to patent CN115594223A). It has a large specific surface area, and the specific surface area can be further increased after the introduction of reduced graphene oxide nanosheets.

[0048] In some optional embodiments, the mass ratio of the matrix material nanosheets to the reduced graphene oxide nanosheets is 2-6:1; in other optional embodiments, the mass ratio is 3-4:1. If the content of reduced graphene oxide nanosheets is too high, it will reduce the proportion of matrix material nanosheets, thereby reducing the adsorption capacity for lithium ions. If the content of reduced graphene oxide nanosheets is too low, the improvement effect on the lithium-ion capacity is weak, making its effect on improving lithium-ion capacity insignificant. Therefore, the mass of the reduced graphene oxide nanosheets needs to be set appropriately.

[0049] In some optional embodiments, the gap between adjacent MnO2 nanosheets and reduced graphene oxide nanosheets is 2-6 nm. Specifically, it can be any value among 2 nm, 3 nm, 4 nm, 5 nm, 6 nm or 2-6 nm. If the gap is too small, the space for accommodating lithium is reduced, which will reduce the lithium-ion capacity. If the gap is too large, it will easily lead to a decrease in the stability of the structure, thereby causing the structure to collapse.

[0050] In some optional embodiments, the modified lithium-ion sieve has a specific surface area greater than 119 m². 2 / g.

[0051] Another embodiment of this disclosure provides a method for preparing the modified lithium-ion sieve according to any one of the foregoing embodiments, comprising mixing the matrix material nanosheets and the reduced graphene oxide nanosheets in a solution system to obtain a lower layer flocculant, which is the modified lithium-ion sieve.

[0052] In some alternative embodiments, the preparation of the reduced graphene oxide nanosheets includes a hydrothermal reaction of a mixture of graphene oxide, a cationic modifier, and a reducing agent.

[0053] Stacking reduced graphene oxide nanosheets directly with MnO2 nanosheets is quite difficult. The applicant discovered that MnO2 nanosheets with a three-dimensional layered framework structure, such as those disclosed in patent CN115594223A, carry a negative charge. Therefore, this embodiment uses a cationic modifier to modify the surface of graphene oxide, so that the surface of graphene oxide carries a positive charge, thereby enabling the interaction of positive and negative charges between graphene nanosheets and MnO2 nanosheets, improving the conductivity and stability of the structure. Preferably, the positive charge is provided by ammonium ions and / or ammonium ion derivatives, and its positive charge density is relatively high.

[0054] In addition, the surface of graphene oxide has a large number of oxygen-containing functional groups, making it more reactive. Reducing graphene oxide with a reducing agent can also help improve the stability of the modified lithium-ion sieve structure.

[0055] In some embodiments, the cationic modifier is at least one of polydiallyldimethylammonium chloride (PDDA), polyvinylpropyldimethylammonium chloride (PDADMAC), polydimethyldiallyldimethylammonium chloride (PDM), and polyacrylamide (PAM); preferably, the cationic modifier is polydiallyldimethylammonium chloride.

[0056] In some embodiments, the reducing agent is at least one of hydrazine hydrate and sodium borohydride, both of which have strong reducing properties; preferably, the reducing agent is hydrazine hydrate.

[0057] In some embodiments, the initial concentration of graphene oxide in the hydrothermal reaction step is 0.01~10 g / L; in some optional embodiments, the initial concentration of graphene oxide is 1~2.8 g / L. Since the surface of the generated reduced graphene oxide carries a positive charge, too high a concentration is not conducive to the uniform distribution of the positively charged modified reduced graphene oxide nanosheets in the solution, while too low a concentration is not conducive to improving production efficiency. Therefore, it is necessary to reasonably set the initial concentration of graphene oxide.

[0058] In some embodiments, in the hydrothermal reaction step, the mass ratio of graphene oxide to cationic modifier is 1:(0.01~100), specifically, it can be 1:0.01, 1:0.1, 1:1, 1:10 or 1:100; preferably, the mass ratio of graphene oxide to cationic modifier is 1:0.5-5, for example, it can be 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5 or 1:5, so that the amount of positive charge on graphene oxide and the amount of negative charge on MnO2 nanosheets are matched. In some embodiments, in the hydrothermal reaction step, the mass ratio of graphene oxide to reducing agent is 1:(0.01~100), specifically, it can be 1:0.01, 1:0.1, 1:1, 1:10 or 1:100; preferably, the mass ratio of graphene oxide to reducing agent is 1:(0.1-1), for example, it can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, so that the amount of reducing agent reacts fully with the oxygen-containing functional groups on the graphene oxide.

[0059] In some embodiments, the temperature of the hydrothermal reaction step is 30~100 ℃ and the time is 0.1~10 h; in some optional embodiments, the temperature of the hydrothermal reaction step is 70~90 ℃, for example, 70 ℃, 75 ℃, 80 ℃, 85 ℃ and 90 ℃, and the time is 3~8 h, for example, 3 h, 4 h, 5 h, 6 h, 7 h and 8 h.

[0060] In some optional embodiments, the mixing step is ultrasonic mixing or mechanical stirring, preferably ultrasonic mixing; In some optional embodiments, the mixing step takes 1 to 60 minutes, preferably 6 to 20 minutes; In some optional embodiments, the lower layer of flocculents is separated by centrifugation, wherein the centrifugation step is performed at a speed of 6,000 to 30,000 rpm for 1 to 60 minutes; in some optional embodiments, the speed is performed at 10,000 to 20,000 rpm for 8 to 20 minutes, until the mass of the solid phase no longer increases or almost no longer increases. In some optional embodiments, the separated lower layer flocculents are further dried after the mixing step to obtain a dried modified lithium-ion sieve. The drying temperature is 65~85°C. Too high a temperature may damage the product structure, while too low a temperature will result in slow drying efficiency. The drying time is 1~18 hours, and drying is stopped when the weight hardly changes.

[0061] Another embodiment of this disclosure provides a modified lithium-ion sieve electrode, which is obtained by coating a mixture of a modified lithium-ion sieve, a conductive agent, and a binder onto a current collector and then drying it.

[0062] In some optional embodiments, the conductive agent is at least one of acetylene black, conductive carbon black, graphene, and carbon nanotubes; preferably, the conductive agent is conductive carbon black or carbon nanotubes.

[0063] In some alternative embodiments, the adhesive is at least one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), and polytetrafluoroethylene (PTFE); preferably, the adhesive is polyvinylidene fluoride.

[0064] In some optional embodiments, the mass ratio of the modified lithium-ion sieve, conductive agent, and binder is 8:(0.5~1.5):(0.8~9); preferably, the ratio of the modified lithium-ion sieve, conductive agent, and binder is 8:1:1. The conductive agent can improve the conductivity of the electrode, but too much conductive agent will reduce the proportion of the modified lithium-ion sieve, thereby reducing the lithium extraction effect; too little binder will reduce the bonding effect, preventing the modified lithium-ion sieve from effectively agglomerating. Similarly, too much binder will also reduce the proportion of the modified lithium-ion sieve, thereby reducing the lithium extraction effect.

[0065] In some optional embodiments, the modified lithium-ion sieve is dried at a temperature of 50~100℃ for 1~12h. Too high a temperature may damage the product structure, while too low a temperature will result in slow drying efficiency. In some optional embodiments, during the initial operation of the device, the modified lithium-ion sieve electrode can be placed in the brine chamber, and the inert electrode, serving as the counter electrode, can be placed in the lithium salt chamber. Then, the lithium ions in the brine chamber are driven by an external potential to embed into the ion sieve, resulting in a modified lithium-ion sieve electrode in the lithium-intercalated state. The external potential can be between 0.1 and 1.5 V, preferably between 0.6 and 1 V. The external potential is kept constant until the current drops below 0.1 mA, at which point the reaction stops.

[0066] The inert electrode is one of graphite electrode, platinum metal sheet, carbon fiber, etc., preferably graphite electrode; the inert electrode and the working electrode should have approximately equal area, be in the same position, and face each other.

[0067] Another embodiment of this disclosure provides the application of the modified lithium-ion sieve described in any of the foregoing embodiments in the extraction of lithium.

[0068] Another embodiment of this disclosure provides an apparatus for electrochemical lithium extraction from salt lakes, such as... Figure 1 As shown, it includes: Electrodes, including modified lithium-ion sieve electrodes as cathode electrodes and lithium-intercalated modified lithium-ion sieve electrodes as anode electrodes; The lithium salt chamber, wherein the anode electrode is disposed within the lithium salt chamber; The cathode electrode is disposed within the brine chamber. Anion exchange membrane: used to separate the lithium salt chamber and the brine chamber.

[0069] Electrochemical lithium extraction utilizes an external electric field to insert and extract lithium ions from brine into an ion sieve, without involving acid dissolution for lithium removal. Therefore, the ion sieve has a long lifespan. When combined with the electrochemical device in this embodiment, the lithium extraction rate can be increased by more than 80%, which greatly improves the use value of MnO2-based lithium ion sieves and significantly reduces the cost of use, thereby improving production efficiency.

[0070] Another embodiment of this disclosure provides a method for electrochemical lithium extraction from salt lakes using the apparatus described in any of the foregoing embodiments, wherein an external potential is applied between the cathode electrode and the anode electrode to drive the Li in the brine chamber. + Lithium-intercalated ion sieves formed within ion sieves, and lithium-intercalated ion sieves within lithium salt chambers. + The lithium salt is extracted into the lithium salt chamber. The external potential can be between 0.1 and 1.5V, preferably between 0.6 and 1V. The external potential is kept constant until the current drops below 0.1mA, at which point the reaction stops.

[0071] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0072] Example 1: This embodiment provides a method for electrochemical lithium extraction from salt lakes, including the following steps: S1. Dissolve 5g of graphene oxide (GO) material in 2L of deionized water, add 2.5g of PDDA modifier and 0.5g of hydrazine hydrate, mix and react at 80℃ for 6h to obtain a positively charged modified rGO nanosheet solution. S2. Take 15g of MnO2 nanosheet material and mix it with the positively charged rGO solution in step S2, and then mechanically stir it at 1000r / min for 20min. S3. The product obtained in step 2 is centrifuged at 10000 r / min for 8 min, the bottom solid product is collected, and then dried at 65℃ for 8 h to prepare a positively charged rGO-MnO2 modified lithium ion sieve. S4. Dissolve 16g of modified lithium-ion sieve, 2g of conductive carbon black, and 2g of PVDF in 10ml of NMP solvent and mix evenly to form a slurry. Then coat the slurry to a depth of 100cm. 2 Electrode 1 was prepared on a current collector and dried at 70°C for 6 hours. S5. Place the prepared electrode 1 as the cathode in the brine chamber at a depth of 100 cm. 2 An inert electrode is placed in the lithium salt chamber as the counter electrode. An external potential of 0.6V drives the lithium ions in the brine chamber to intercalate into the ion sieve to obtain the lithium-intercalated electrode 2. S6. Place electrode 1 obtained in step S4 in the brine chamber as the cathode, and place electrode 2 obtained in step S5 in the lithium salt chamber as the anode. Driven by a potential of 0.6V, Li in the brine chamber... + Lithium-intercalated ion sieves are formed by embedding ion sieves, and the Lithium-intercalated ion sieves in the lithium salt chamber contain lithium. + It is extracted into the lithium salt chamber to obtain lithium salt.

[0073] Example 2: This embodiment provides a method for electrochemical lithium extraction from salt lakes, including the following steps: S1. Dissolve 2.8g of graphene oxide (GO) material in 1L of deionized water, add 1.4g of PDM modifier and 0.56g of sodium borohydride, mix and react at 70℃ for 3h to obtain a positively charged modified rGO nanosheet solution. S2. Take 9g of MnO2 nanosheet material and mix it with the positively charged rGO solution in step S1, and then perform ultrasonic treatment for 12min. S3. The product obtained in step S2 is centrifuged at 12000 r / min for 20 min, the bottom solid product is collected, and then dried at 80℃ for 7 h to prepare a positively charged rGO-MnO2 modified lithium ion sieve. S4. Dissolve 8g of modified lithium-ion sieve, 1g of carbon nanotubes, and 1g of PVDF in 5ml of NMP solvent and mix evenly to form a slurry. Then coat the slurry to a depth of 100cm. 2 Electrode 1 was prepared on a graphite plate and dried at 65°C for 9 hours. S5. Place the prepared electrode 1 as the cathode in the brine chamber at a depth of 100 cm. 2 A graphite plate is placed in the lithium salt chamber as the counter electrode. An external potential of 0.8V drives the lithium ions in the brine chamber to embed into the ion sieve to obtain the lithium-intercalated electrode 2. S6. Place electrode 1 obtained in step S4 in the brine chamber as the cathode, and place electrode 2 obtained in step S5 in the lithium salt chamber as the anode. Driven by a potential of 0.8V, Li in the brine chamber... + Lithium-intercalated ion sieves are formed by embedding ion sieves, and the Lithium-intercalated ion sieves in the lithium salt chamber contain lithium. + It is extracted into the lithium salt chamber to obtain lithium salt.

[0074] Example 3: This embodiment provides a method for electrochemical lithium extraction from salt lakes, including the following steps: S1. Dissolve 2g of graphene oxide (GO) material in 1L of deionized water, add 2g of PAM modifier and 2g of hydrazine hydrate, mix and react at 90℃ for 8h to obtain a positively charged modified rGO nanosheet solution. S2. Take 7g of MnO2 nanosheet material and mix it with the positively charged rGO solution in step S1, and then mechanically stir it at 1000r / min for 16min. S3. The product obtained in step S2 is centrifuged at 16000 r / min for 12 min, the bottom solid product is collected, and then dried at 70℃ for 6 h to prepare a positively charged rGO-MnO2 modified lithium ion sieve. S4. Dissolve 6.4g of modified lithium-ion sieve, 0.8g of conductive carbon black, and 0.8g of PVDF in 5ml of NMP solvent and mix evenly to form a slurry. Then coat the slurry to a depth of 100cm. 2 Electrode 1 was prepared on a current collector and dried at 70°C for 6 hours. S5. Place the prepared electrode 1 as the cathode in the brine chamber at a depth of 100 cm. 2 An inert electrode is placed in the lithium salt chamber as the counter electrode. An external potential of 0.7V drives the lithium ions in the brine chamber to intercalate into the ion sieve to obtain the lithium-intercalated electrode 2. S6. Place electrode 1 obtained in step S4 in the brine chamber as the cathode, and place electrode 2 obtained in step S5 in the lithium salt chamber as the anode. Driven by a potential of 0.7V, Li in the brine chamber... + Lithium-intercalated ion sieves are formed by embedding ion sieves, and the Lithium-intercalated ion sieves in the lithium salt chamber contain lithium. +It is extracted into the lithium salt chamber to obtain lithium salt.

[0075] Example 4: This embodiment provides a method for electrochemical lithium extraction from salt lakes, including the following steps: S1. Dissolve 5g of graphene oxide (GO) material in 5L of deionized water, add 25g of PDADMAC modifier and 2.5g of sodium borohydride, mix and react at 75℃ for 6h to obtain a positively charged modified rGO nanosheet solution. S2. Take 20g of MnO2 nanosheet material and mix it with the positively charged rGO solution in step S1, and then sonicate for 20min. S3. The product obtained in step S2 is centrifuged at 13000 r / min for 16 min, the bottom solid product is collected, and then dried at 85℃ for 6 h to prepare a positively charged rGO-MnO2 modified lithium ion sieve. S4. Dissolve 20g of modified lithium-ion sieve, 2.5g of carbon nanotubes, and 2.5g of PVDF in 12ml of NMP solvent and mix evenly to form a slurry. Then coat the slurry to a depth of 100cm. 2 Electrode 1 was prepared on a current collector and dried at 65°C for 8 hours. S5. Place the prepared electrode 1 as the cathode in the brine chamber at a depth of 100 cm. 2 An inert electrode is placed in the lithium salt chamber as the counter electrode. An external potential of 0.6V drives the lithium ions in the brine chamber to intercalate into the ion sieve to obtain the lithium-intercalated electrode 2. S6. Place electrode 1 obtained in step S4 in the brine chamber as the cathode, and place electrode 2 obtained in step S5 in the lithium salt chamber as the anode. Driven by a potential of 0.6V, Li in the brine chamber... + Lithium-intercalated ion sieves are formed by embedding ion sieves, and the Lithium-intercalated ion sieves in the lithium salt chamber contain lithium. + It is extracted into the lithium salt chamber to obtain lithium salt.

[0076] Example 5: This embodiment provides a method for electrochemical lithium extraction from salt lakes, including the following steps: S1. Dissolve 3g of graphene oxide (GO) material in 2L of deionized water, add 9g of PDDA modifier and 2.4g of hydrazine hydrate, mix and react at 85℃ for 5h to obtain a positively charged modified rGO nanosheet solution. S2. Take 10.8g of MnO2 nanosheet material and mix it with the positively charged rGO solution in step S1, and then mechanically stir it at 800r / min for 6min. S3. The product obtained in step S2 is centrifuged at 20000 r / min for 10 min, the bottom solid product is collected, and then dried at 70℃ for 9 h to prepare a positively charged rGO-MnO2 modified lithium ion sieve. S4. Dissolve 12g of modified lithium-ion sieve, 1.5g of carbon nanotubes, and 1.5g of PVDF in 6ml of NMP solvent and mix evenly to form a slurry. Then coat the slurry to a depth of 100cm. 2 Electrode 1 was prepared on a current collector and dried at 80°C for 7 hours. S5. Place the prepared electrode 1 as the cathode in the brine chamber at a depth of 100 cm. 2 An inert electrode is placed in the lithium salt chamber as the counter electrode. An external potential of 0.8V drives the lithium ions in the brine chamber to intercalate into the ion sieve to obtain the lithium-intercalated electrode 2. S6. Place electrode 1 obtained in step S4 in the brine chamber as the cathode, and place the electrode obtained in step S5 in the lithium salt chamber as the anode. Driven by a potential of 0.8V, Li in the brine chamber... + Lithium-intercalated ion sieves are formed by embedding ion sieves, and the Lithium-intercalated ion sieves in the lithium salt chamber contain lithium. + It is extracted into the lithium salt chamber to obtain lithium salt.

[0077] Example 6 The difference from Example 1 is that step S2 replaces mechanical stirring with ultrasonic treatment.

[0078] Example 7: The difference from Example 1 is that the amount of PDDA added in step S1 is 50g.

[0079] Example 8: The difference from Example 1 is that the amount of hydrazine hydrate added in step S1 is 10g.

[0080] Comparative Example 1: The difference from Example 1 is that S1-S3 are not performed; that is, the MnO2 nanosheets are directly prepared as lithium-ion sieves and lithium is extracted from salt lake brine.

[0081] Comparative Example 2: The difference from Example 1 is that step S1 does not add a positive charge modifier; that is, GO is simply mixed with a reducing agent to obtain an rGO solution, and a lithium ion sieve is prepared.

[0082] Comparative Example 3: The difference from Example 1 is that step S1 does not add a reducing agent; that is, GO is simply mixed with a positive charge modifier to obtain an rGO solution, and a lithium ion sieve is prepared.

[0083] Comparative Example 4: The difference from Example 1 is that in step S1, 5g of graphene oxide (GO) material is dissolved in 0.5L of deionized water.

[0084] Comparative Example 5: The difference from Example 1 is that the temperature of the hydrothermal reaction in step S1 is 120°C.

[0085] Comparative Example 6: The difference from Example 1 is that the amount of MnO2 nanosheets added in step S2 is 5g.

[0086] Comparative Example 7: The difference from Example 1 is that the amount of MnO2 nanosheets added in step S2 is 40g.

[0087] Comparative Example 8: The difference from Example 1 is that the method for preparing MnO2 nanosheets in step S2 is described in CN 111001404 A, specifically including the following steps: S1. Manganese sulfate monohydrate (MnSO4·H2O) was completely dissolved in a pure aqueous solution, and then 40 wt.% sodium permanganate (NaMnO4) solution was added. The molar ratio of manganese sulfate to sodium permanganate was 3:2. After ultrasonic vibration for 5 minutes, the solution was allowed to stand at 25°C for 24 hours. The solution was then filtered, washed until the filtrate was transparent and dried to obtain amorphous manganese oxide. S2. The dried amorphous manganese oxide from step S1 is dispersed in a pure aqueous solution, and then reacted at 80°C for 24 h. After filtration, washing, and drying, γ-MnO2 is obtained. S3. After calcining the γ-MnO2 in step S2 at 350℃ for 3h, β-MnO2 nanosheet catalyst is obtained.

[0088] The modified lithium-ion sieves prepared in each example and comparative example were characterized by SEM. The SEM images of the modified lithium-ion sieves obtained in Example 1 and Comparative Example 1 are shown in the figure below. Figure 2 and Figure 3 ,pass Figure 2 and Figure 3 It can be seen that without modifying graphene oxide with positive charge and reducing agent, the modified ion sieve exhibits more structural collapse and poorer stability. The effectiveness of the electrochemical lithium extraction method from salt lakes in the examples and comparative examples was evaluated. The main elements and concentrations in the salt lake brine used are shown in Table 1, the specific surface area of ​​the modified lithium ion sieve material is shown in Table 2, and the Li- ion sieve concentration after lithium extraction was measured. + The extraction rate and lithium concentration in the remaining brine are shown in Table 3.

[0089] Table 1 Concentration of major elements in salt lake brine

[0090] Table 2. Specific surface area of ​​the modified lithium-ion sieve materials prepared in each embodiment.

[0091] Table 3. Single-batch lithium extraction rate and residual brine lithium concentration for each example and comparative example.

[0092] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0093] Industrial applicability The modified lithium-ion sieve disclosed in this invention is composed of alternating stacks of MnO2 nanosheets and graphene, exhibiting an increased specific surface area, more lithium intercalation sites, and a stable framework structure, effectively improving the specific surface area compared to the unmodified lithium-ion sieve. When this material is applied to an electrochemical lithium extraction device, lithium ions in brine are intercalated and extracted into the sieve using an external electric field, without acid dissolution for lithium extraction. The sieve has a long lifespan and effectively increases the lithium extraction rate, significantly enhancing the usability of MnO2-based lithium-ion sieves and substantially reducing operating costs, thereby improving production efficiency and demonstrating great application potential.

Claims

1. A modified lithium-ion sieve, characterized in that, The modified lithium-ion sieve comprises alternating stacked matrix material nanosheets and reduced graphene oxide nanosheets, wherein the matrix material nanosheets are MnO2 nanosheets, and the reduced graphene oxide nanosheets are positively charged modified reduced graphene oxide nanosheets. The specific surface area of ​​the modified lithium-ion sieve is greater than 119 m². 2 / g.

2. The modified lithium-ion sieve according to claim 1, characterized in that, The matrix material nanosheets are MnO2 nanosheets with a three-dimensional layered framework structure.

3. The modified lithium-ion sieve according to claim 1, characterized in that, The positive charge is provided by ammonium ions and / or ammonium ion derivatives.

4. The modified lithium-ion sieve according to claim 1, characterized in that, The mass ratio of the matrix material nanosheets to the reduced graphene oxide nanosheets is (2~6):

1.

5. The modified lithium-ion sieve according to claim 1, characterized in that, The gap between adjacent MnO2 nanosheets and reduced graphene oxide nanosheets is 2~6 nm.

6. A method for preparing the modified lithium-ion sieve according to any one of claims 1-5, characterized in that, The modified lithium-ion sieve is obtained by mixing the matrix material nanosheets and the reduced graphene oxide nanosheets in a solution system to obtain the lower layer flocculent.

7. The method for preparing the modified lithium-ion sieve according to claim 6, characterized in that, The preparation of the reduced graphene oxide nanosheets involves mixing graphene oxide, a cationic modifier, and a reducing agent and then carrying out a hydrothermal reaction.

8. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The cationic modifier is at least one of polydiallyldimethylammonium chloride and polyacrylamide.

9. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The reducing agent is at least one of hydrazine hydrate and sodium borohydride.

10. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, In the hydrothermal reaction step, the initial concentration of graphene oxide is 0.01~10 g / L.

11. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The initial concentration of graphene oxide is 1~2.8 g / L.

12. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, In the hydrothermal reaction step, the mass ratio of graphene oxide to cationic modifier is 1:(0.01~100).

13. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The mass ratio of graphene oxide to cationic modifier is 1:(0.5~5).

14. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, In the hydrothermal reaction step, the mass ratio of graphene oxide to reducing agent is 1:(0.01~100).

15. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The mass ratio of graphene oxide to reducing agent is 1:(0.1~1).

16. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The hydrothermal reaction step is carried out at a temperature of 30~100 ℃ for a time of 0.1~10 h.

17. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The hydrothermal reaction step is carried out at a temperature of 70-90 °C for 3-8 h.

18. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The mixing process in the preparation step of the reduced graphene oxide nanosheets is ultrasonic mixing or mechanical stirring.

19. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The mixing time in the preparation step of the reduced graphene oxide nanosheets is 1 to 60 minutes.

20. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, The mixing time in the preparation step of the reduced graphene oxide nanosheets is 6-20 minutes.

21. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, In the preparation step of the reduced graphene oxide nanosheets, the lower layer of flocculents is separated by centrifugation after mixing. The centrifugation speed is 6000~30000 rpm and the time is 1~60 minutes.

22. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, In the preparation step of the reduced graphene oxide nanosheets, the lower layer of flocculents is separated by centrifugation after mixing. The centrifugation speed is 10,000 to 20,000 rpm and the time is 8 to 20 minutes.

23. The method for preparing the modified lithium-ion sieve according to claim 7, characterized in that, In the preparation step of the reduced graphene oxide nanosheets, the separated lower layer flocculents are dried to obtain a dried modified lithium-ion sieve. The drying step is performed at a temperature of 65~85℃ for 1~18h.

24. A modified lithium-ion sieve electrode, characterized in that, It is obtained by coating a mixture of the modified lithium-ion sieve, conductive agent and binder as described in any one of claims 1-5 onto a current collector and then drying it.

25. The modified lithium-ion sieve electrode according to claim 24, characterized in that, The conductive agent is at least one of acetylene black, conductive carbon black, graphene, and carbon nanotubes.

26. The modified lithium-ion sieve electrode according to claim 24, characterized in that, The adhesive is at least one of polyvinylidene fluoride, carboxymethyl cellulose, and polytetrafluoroethylene.

27. The modified lithium-ion sieve electrode according to claim 24, characterized in that, The mass ratio of the modified lithium-ion sieve, conductive agent, and binder is 8:(0.5~1.5):(0.8~9).

28. The modified lithium-ion sieve electrode according to claim 24, characterized in that, The drying temperature is 50~100℃, and the time is 1~12 h.

29. The modified lithium-ion sieve electrode according to claim 24, characterized in that, The modified lithium-ion sieve electrode is placed in the brine chamber, and the inert electrode is placed in the lithium salt chamber as the counter electrode. Then, the lithium ions in the brine chamber are inserted into the ion sieve by external potential to obtain the modified lithium-ion sieve electrode in the lithium-intercalated state.

30. The application of a modified lithium-ion sieve electrode according to any one of claims 1-5 or any one of claims 24-29 in the extraction of lithium.

31. An apparatus for electrochemical lithium extraction from salt lakes with a modified lithium-ion sieve electrode as described in any one of claims 24-29, characterized in that, include: Electrodes, including modified lithium-ion sieve electrodes as cathode electrodes and lithium-intercalated modified lithium-ion sieve electrodes as anode electrodes; The lithium salt chamber, wherein the anode electrode is disposed within the lithium salt chamber; The cathode electrode is disposed within the brine chamber. Anion exchange membrane: used to separate the lithium salt chamber and the brine chamber.

32. A method for electrochemical lithium extraction from salt lakes using the apparatus of claim 31, characterized in that, An external potential is applied between the cathode and anode electrodes to drive the Li in the brine chamber. + Lithium-intercalated ion sieves formed within ion sieves, and lithium-intercalated ion sieves within lithium salt chambers. + It is extracted into the lithium salt chamber to obtain lithium salt.

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