A solid electrolyte layer-coated electrode active material and its preparation method and application

Abstract

The present disclosure provides an electrode active material coated with a solid electrolyte layer, and its preparation method and application, relating to the technical field of lithium extraction from salt lakes. The structure of the electrode active material coated with a solid electrolyte layer disclosed in the present disclosure is a core-shell structure, wherein the core structure is composed of the electrode active material, and the shell structure is composed of the solid electrolyte layer; the solid electrolyte layer is composed of polyethylene oxide doped with inorganic nanoparticles and a lithium salt complex, and has good lithium ion conductivity. The electrode active material coated with the solid electrolyte layer is used to prepare an electrode for lithium extraction from salt lakes, and the resulting salt lake lithium extraction electrode has better lithium extraction efficiency, cycle stability and lithium extraction capacity.

Description

Technical Field

[0001] The present disclosure relates to the technical field of lithium extraction from salt lakes, and in particular to an electrode active material coated with a solid electrolyte layer, and a preparation method and application thereof. Background Art

[0002] In recent years, with the rapid development of new energy vehicles and chemical energy storage, global demand for lithium resources has continued to increase, making lithium a key strategic resource. Natural lithium resources are primarily found in salt lake brine, seawater, and ores, with salt lake lithium resources accounting for approximately 70%. Consequently, extracting lithium from salt lake brine is gaining increasing attention.

[0003] Salt lake brine contains elements such as lithium, sodium, potassium, and magnesium. Methods for extracting lithium from salt lakes primarily include precipitation, solvent extraction, evaporative crystallization, electrodialysis, and ion exchange adsorption. However, these methods all have drawbacks, such as the high cost of electrodialysis and membrane separation, and the environmental pollution caused by solvent extraction agents. In recent years, researchers both domestically and internationally have conducted extensive research and exploration into new lithium extraction processes, with electrochemical lithium extraction technology showing promising potential.

[0004] The principle of electrochemical lithium extraction is to charge the working electrode in the electrolyte solution to release lithium ions to form a lithium-depleted electrode. The lithium-rich electrode and the lithium-depleted electrode are used as the anode and cathode respectively. Lithium salt solution is added to the anode and salt lake brine is added to the cathode. Driven by the external potential, Li in the brine is selectively embedded in the lithium-depleted electrode. At the same time, the lithium-rich electrode releases Li into the solution to form a lithium-depleted electrode. Through electrode exchange and cyclic operation, selective enrichment of lithium is achieved.

[0005] While electrochemical deintercalation holds promise for lithium extraction from salt lakes, it still faces challenges such as low lithium exchange capacity and poor electrode cycling stability. The PVDF binder used in the electrode slurry preparation is non-conductive. When the electrode active material binds to the binder, lithium ion transport is hindered, limiting the electrode's lithium extraction capacity.

[0006] Patent CN113265538B provides a method for preparing highly conductive porous electrodes for lithium extraction from salt lakes. By using inorganic nanoparticles and polar hydrophilic polymer organic matter, the binder in the electrode preparation process is blended and modified to improve the hydrophilicity of the binder. Finally, the prepared electrode material is subjected to surface chemical modification in a conductive polymer monomer solution to improve the overall conductivity of the electrode. The increase in hydrophilicity can promote the wetting of the electrode with brine, but it cannot improve the transmission of lithium ions and increase the electrode exchange capacity. The conductive polymer coating modification mainly increases the electronic conductivity of the electrode surface, but cannot increase the ionic conductivity of the interface between the active material and the binder inside the electrode. Summary of the Invention

[0007] The present invention aims to overcome the shortcomings of the prior art by providing a solid electrolyte layer-coated electrode active material, its preparation method, and its application. The solid electrolyte layer-coated electrode active material disclosed herein is used to prepare a salt lake lithium extraction electrode. During lithium extraction, the salt lake lithium extraction electrode can promote the migration of lithium ions, thereby increasing the electrode's lithium extraction capacity and efficiency.

[0008] To achieve the above objectives, the technical solutions adopted by this disclosure are:

[0009] In a first aspect, a method for preparing an electrode active material coated with a solid electrolyte layer is provided, comprising the following steps:

[0010] After the electrode active material, ethylene oxide, catalyst, inorganic nanoparticles, lithium source and solvent are uniformly mixed, a cross-linking agent is added and a polymerization reaction is carried out at 50-80° C. for 18-30 hours. After the reaction is completed, an electrode active material coated with a solid electrolyte layer is obtained;

[0011] The mass of ethylene oxide is 5-20% of the mass of the electrode active material;

[0012] The mass of the catalyst is 0.1-1% of the mass of ethylene oxide, the mass of the inorganic nanoparticles is 5-25% of the mass of ethylene oxide, the mass of the lithium source is 5-15% of the mass of ethylene oxide, and the mass of the crosslinking agent is 0.1-1% of the mass of ethylene oxide.

[0013] The schematic structural diagram of the electrode active material coated with the solid electrolyte layer of the present disclosure is as follows: Figure 1 As shown, the structure of the electrode active material coated with a solid electrolyte layer is a core-shell structure, wherein the core structure is composed of the electrode active material and the shell structure is composed of the solid electrolyte layer. During the preparation process of the electrode active material coated with the solid electrolyte layer, an in-situ polymerization method is used to coat a solid electrolyte layer on the surface of the electrode active material. The solid electrolyte layer is composed of polyethylene oxide doped with inorganic nanoparticles and a lithium salt complex, and has good lithium ion conductivity. The present disclosure adjusts the preparation parameters of the electrode active material coated with the solid electrolyte layer to obtain solid electrolyte layers of different thicknesses; for example, when other preparation parameters remain unchanged, the thickness of the solid electrolyte layer can be increased by increasing the content of ethylene oxide. The content of the lithium source will affect the lithium ion conductivity of the electrode active material coated with the solid electrolyte layer. If the lithium source content is too little or too much, the lithium ion conductivity will decrease. The present disclosure selects the mass of the lithium source to be 8-12% of the mass of ethylene oxide to obtain an electrode active material coated with a solid electrolyte layer with better lithium ion conductivity.

[0014] Specifically, the temperature and time of the polymerization reaction will affect the mechanical properties and lithium ion conductivity of the electrode active material coated with the solid electrolyte layer. If the temperature of the polymerization reaction is too low or the time is too short, ethylene oxide cannot fully undergo polymerization reaction, resulting in a loose structure of the solid electrolyte layer, thereby causing the mechanical properties and lithium ion conductivity of the electrode active material coated with the solid electrolyte layer to decrease; if the polymerization reaction time is too long or the temperature is too high, the thickness of the solid electrolyte layer is too thick, and the mechanical properties and lithium ion conductivity of the electrode active material coated with the solid electrolyte layer will not be significantly improved.

[0015] In one embodiment, the mass of the inorganic nanoparticles is 10-20% of the mass of ethylene oxide.

[0016] In the present disclosure, the mass of the inorganic nanoparticles can be 5%, 8%, 10%, 12%, 15%, 17%, 20%, 23%, or 25% of the mass of ethylene oxide, or a range consisting of any two of the above values. Specifically, the inorganic nanoparticles can, on the one hand, reduce the erosion of the solution on the electrode active material coated with the solid electrolyte layer, thereby increasing the mechanical strength of the electrode active material coated with the solid electrolyte layer. On the other hand, the hydroxyl groups on the surface of the inorganic nanoparticles can increase the activity of the solid electrolyte layer, thereby increasing the lithium ion conductivity of the electrode active material coated with the solid electrolyte layer. The present disclosure selects the mass of the inorganic nanoparticles to be 10-20% of the mass of ethylene oxide, thereby improving the performance of the electrode active material coated with the solid electrolyte layer.

[0017] In one embodiment, the electrode active material is at least one of lithium iron phosphate and lithium manganese iron phosphate;

[0018] and / or, the average particle size of the electrode active material is 0.5-5 μm;

[0019] And / or, the catalyst is a quaternary ammonium base; specifically one or more of tetramethylammonium hydroxide, tetraethoxyammonium hydroxide, methyltriethylammonium hydroxide and tetrapropylammonium hydroxide;

[0020] and / or, the inorganic nanoparticles are at least one of SiO2 nanoparticles, ZnO nanoparticles, Al2O3 nanoparticles, HBO2 nanoparticles, and TiO2 nanoparticles;

[0021] and / or, the average particle size of the inorganic nanoparticles is 1-50 nm;

[0022] and / or, the cross-linking agent is ethylene glycol dimethacrylate;

[0023] And / or, the lithium source is at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium bis(trifluoromethylsulfonyl)imide.

[0024] In one embodiment, the electrode active material is first added to the solvent, and then ethylene oxide is added. After stirring evenly, the catalyst, inorganic nanoparticles and lithium source are added and ultrasonically mixed. The ultrasonic mixing time is 15-30 minutes.

[0025] It is understood that those skilled in the art can select an appropriate mixing method according to actual needs, such as stirring, ball milling, sand milling, ultrasound, etc., and the specific mixing time can be as long as the components are mixed evenly. In the present invention, ultrasound is selected for 15-30 minutes to obtain a mixed solution with better mixing effect.

[0026] In one embodiment, after the reaction is completed, the obtained reaction product needs to be centrifuged, washed, and dried to obtain an electrode active material coated with a solid electrolyte layer.

[0027] It is understandable that after the polymerization reaction is completed, the resulting reactant is a mixed liquid containing a solvent and some components that have not completely reacted. In order to obtain a higher purity solid electrolyte layer-coated electrode active material, the resulting reactant needs to be post-processed after the polymerization reaction is completed, such as centrifugation, washing and drying.

[0028] In one embodiment, the drying temperature is 80-100° C.; and / or the drying time is 10-15 hours.

[0029] It is understandable that those skilled in the art can select appropriate temperature and time for drying to obtain an electrode active material coated with a solid electrolyte layer. In the present disclosure, drying at a temperature of 80-100° C. for 10-15 hours is selected.

[0030] In a second aspect, a solid electrolyte layer-coated electrode active material is provided, wherein the solid electrolyte layer-coated electrode active material is prepared by the above-mentioned method for preparing the solid electrolyte layer-coated electrode active material.

[0031] In one embodiment, the solid electrolyte layer has a thickness of 10-100 nm.

[0032] In the present disclosure, the thickness of the solid electrolyte layer can be 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm; it can also be a range consisting of any two of the above values. It is understandable that the thickness of the solid electrolyte layer has an impact on the performance of the electrode for lithium extraction from salt lakes. On the one hand, the lithium ion diffusion channel formed by the solid electrolyte layer with a thickness of less than 10nm is small, and it cannot effectively serve as a solution mass transfer channel; on the other hand, when the thickness of the solid electrolyte layer is greater than 100nm, the performance of the electrode for lithium extraction from salt lakes does not increase significantly. The present disclosure selects a solid electrolyte layer with a thickness of 30-70nm to obtain an electrode for lithium extraction from salt lakes with better performance.

[0033] In a third aspect, the invention provides an application of the electrode active material coated with the solid electrolyte layer in the preparation of an electrode for lithium extraction from a salt lake.

[0034] In a fourth aspect, an electrode for lithium extraction from salt lakes is provided, characterized in that the electrode for lithium extraction from salt lakes comprises the electrode active material coated with the above-mentioned solid electrolyte layer.

[0035] In one embodiment, the porosity of the electrode for lithium extraction from salt lakes is 20-40%; the electrode for lithium extraction from salt lakes includes the following components: an electrode active material coated with a solid electrolyte layer, a binder, and a conductive agent; based on 100 parts by weight of the electrode active material coated with the solid electrolyte layer, the mass content of each component is: 15-25 parts of the binder and 5-15 parts of the conductive agent.

[0036] The schematic structural diagram of the electrode for lithium extraction from salt lakes obtained in the present disclosure is as follows: Figure 1As shown, the surface of the electrode active material is coated with a dense solid electrolyte layer; the present disclosure uses the electrode active material coated with the solid electrolyte layer, a binder, and a conductive agent to prepare an electrode for lithium extraction from salt lakes with a porosity of 20-40%. On the one hand, the solid electrolyte layer can form a lithium ion diffusion channel between the electrode active material and the binder, providing a transmission path for lithium ions. During the lithium extraction process from the salt lake, lithium ions enter and exit the diffusion channel formed by the solid electrolyte layer, promoting the migration of lithium ions and increasing the lithium extraction capacity and efficiency of the electrode for lithium extraction from the salt lake. On the other hand, brine acts as a lithium ion transmission medium, and the solid electrolyte layer can reduce the corrosion of the brine on the electrode active material, increase the mechanical strength of the electrode active material, and improve the cycle stability of the electrode. At the same time, the solid electrolyte has excellent lithium ion conductivity, and increasing the thickness of the solid electrolyte layer will not reduce the conductivity of the electrode. In addition, the present disclosure uses 15-25 parts by weight of a binder to improve the bonding strength of the electrode for lithium extraction from salt lakes. While improving the mechanical strength of the electrode, the binder cooperates with other components, and the lithium extraction efficiency of the electrode for lithium extraction from salt lakes will not be reduced due to the use of the binder.

[0037] In one embodiment, the porosity of the electrode for lithium extraction from salt lakes is 25-35%.

[0038] In the present disclosure, the porosity of the electrode for lithium extraction from salt lakes can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%; the porosity of the electrode for lithium extraction from salt lakes can also be a range consisting of any two of the above values. Specifically, when the porosity of the electrode for lithium extraction from salt lakes is 20-40%, on the one hand, it can ensure the mechanical strength of the electrode, and on the other hand, it can provide a good channel for the diffusion and mass transfer of brine inside the electrode, effectively improving the mass transfer of the solution inside the electrode; on the basis of the above porosity, when the porosity of the electrode for lithium extraction from salt lakes is 25-35%, the lithium extraction effect and cycle stability of the electrode for lithium extraction from salt lakes are better.

[0039] In one embodiment, the binder has an amount of 18-22 parts by weight.

[0040] In electrodes for lithium extraction from salt lakes, the binder is non-conductive. When the binder binds to the electrode active material, the transport of lithium ions is hindered, thereby limiting the lithium extraction capacity of the electrodes for lithium extraction from salt lakes. It is understood that when the binder content is less than 15 parts, the lithium extraction capacity of the electrodes for lithium extraction from salt lakes increases, but the mechanical strength and cycle stability of the electrodes for lithium extraction from salt lakes are low. The present disclosure selects 18-22 parts by weight of the binder to obtain electrodes for lithium extraction from salt lakes with improved mechanical strength, cycle stability, and lithium extraction performance.

[0041] In one embodiment, the binder is polyvinylidene fluoride; and / or the conductive agent is at least one of acetylene black and Ketjen black.

[0042] In this disclosure, polyvinylidene fluoride is abbreviated as PVDF.

[0043] In a fifth aspect, the present disclosure further provides a method for preparing a lithium extraction electrode for salt lakes, comprising the following steps:

[0044] The binder is dissolved in an organic solvent to obtain a binder solution; the electrode active material coated with the solid electrolyte layer, a pore-forming agent, and a conductive agent are added to the binder solution and stirred evenly; the obtained slurry is coated on a current collector and dried to obtain a lithium extraction electrode for salt lakes.

[0045] In one embodiment, the organic solvent is N-methylpyrrolidone; and / or, the mass of the organic solvent is 120-150% of the mass of the electrode active material coated with the solid electrolyte layer; the pore-forming agent is at least one of (NH4)2CO3, NH4HCO3, NaCl, and KCl; and / or, the mass of the pore-forming agent is 10-20% of the mass of the electrode active material coated with the solid electrolyte layer.

[0046] In the present disclosure, during the preparation of the electrode slurry, a certain proportion of easily pyrolyzed solid salts is added. These solid salts will be evenly dispersed on the surface and inside of the electrode. During the drying process, the solid salts are thermally decomposed, which can allow the original position of the solid salt to be retained inside the salt lake lithium extraction electrode and present a porous form. The present disclosure obtains electrodes for salt lake lithium extraction with different porosities by adjusting the amount of solid salt added.

[0047] In one embodiment, the stirring is vacuum stirring; and or, the stirring time is 0.5-2h.

[0048] In one embodiment, the drying temperature is 100-200° C.; and / or the drying time is 10-20 h.

[0049] In a sixth aspect, the present disclosure provides the application of the electrode for lithium extraction from salt lakes in lithium extraction from salt lakes.

[0050] Compared with the prior art, the beneficial effects of the present disclosure are as follows: the present disclosure uses a solid electrolyte layer-coated electrode active material, a binder, and a conductive agent to prepare an electrode for lithium extraction from salt lakes with a porosity of 20-40%. On the one hand, the solid electrolyte layer can form a lithium ion diffusion channel between the electrode active material and the binder, providing a transmission path for lithium ions. During the lithium extraction process from salt lakes, lithium ions enter and exit the diffusion channel formed by the solid electrolyte layer, promoting the migration of lithium ions and increasing the lithium extraction capacity and efficiency of the electrode for lithium extraction from salt lakes; on the other hand, brine acts as a lithium ion transmission medium, and the solid electrolyte layer can reduce the erosion of brine on the electrode active material, increase the mechanical strength of the electrode active material, and improve the cycle stability of the electrode; at the same time, the solid electrolyte has excellent lithium ion conductivity, and increasing the thickness of the solid electrolyte layer will not reduce the conductivity of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a schematic diagram of the electrode structure for lithium extraction from salt lakes disclosed in the present invention, wherein 1 is the electrode active material, 2 is the solid electrolyte layer, and 3 is the current collector. DETAILED DESCRIPTION

[0052] In order to better illustrate the purpose, technical solutions and advantages of the present disclosure, the present disclosure will be further described below in conjunction with specific embodiments and comparative examples. Its purpose is to understand the content of the present disclosure in detail, rather than to limit the present disclosure. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present disclosure. Unless otherwise specified, the experimental reagents and instruments involved in the implementation of the present disclosure are all commonly used ordinary reagents and instruments.

[0053] In the embodiments and comparative examples disclosed herein, the average particle size of lithium iron phosphate is 3 μm; the average particle size of SiO 2 nanospheres is 25 nm.

[0054] Example 1

[0055] The preparation of the electrode active material coated with the solid electrolyte layer of this embodiment includes the following steps:

[0056] (1) Weigh 50 g of lithium iron phosphate and place it in a three-necked flask. Add 500 mL of acetonitrile, dissolve 5 g of ethylene oxide in the acetonitrile, and stir to obtain a mixture. Then add 50 mg of tetramethylammonium hydroxide as a catalyst, 250 mg of SiO2 nanospheres, and 250 mg of lithium perchlorate. Ultrasonicate for 15 min, then add 50 mg of ethylene glycol dimethacrylate as a crosslinker. Polymerize at 80°C with stirring for 18 h.

[0057] (2) The product obtained by the polymerization reaction was centrifuged, washed, and dried at 80° C. for 15 h to obtain lithium iron phosphate coated with a solid electrolyte layer. The thickness of the solid electrolyte layer was 50 nm.

[0058] Example 2

[0059] The preparation of the electrode active material coated with the solid electrolyte layer of this embodiment includes the following steps:

[0060] (1) Weigh 50 g of lithium iron phosphate and place it in a three-necked flask. Add 500 mL of acetonitrile, dissolve 10 g of ethylene oxide in the acetonitrile, and stir to obtain a mixture. Then add 100 mg of tetramethylammonium hydroxide catalyst, 1 g of SiO2 nanospheres, and 1.5 g of lithium perchlorate. Ultrasonicate for 20 min, then add 75 mg of ethylene glycol dimethacrylate as a crosslinker, and perform polymerization at 65°C with stirring for 24 h.

[0061] (2) The product obtained by the polymerization reaction was centrifuged, washed, and dried at 100° C. for 10 h to obtain lithium iron phosphate coated with a solid electrolyte layer. The thickness of the solid electrolyte layer was 100 nm.

[0062] Example 3

[0063] (1) Weigh 50 g of lithium iron phosphate and place it in a three-necked flask. Add 500 mL of acetonitrile, dissolve 2.5 g of ethylene oxide in the acetonitrile, and stir to obtain a mixture. Then, add 25 mg of tetramethylammonium hydroxide as a catalyst, 250 mg of SiO2 nanospheres, and 200 mg of lithium perchlorate. Ultrasonicate for 30 min, and then add 25 mg of ethylene glycol dimethacrylate as a crosslinker. Stir and perform polymerization at 50°C for 30 h.

[0064] (2) The product obtained by the polymerization reaction was centrifuged, washed, and dried at 90° C. for 12 h to obtain lithium iron phosphate coated with a solid electrolyte layer. The thickness of the solid electrolyte layer was 15 nm.

[0065] Example 4

[0066] The preparation of the electrode active material coated with the solid electrolyte layer in this embodiment is different from that in Example 1 only in that the mass of silicon dioxide in step (1) is 0.5 g.

[0067] Example 5

[0068] The preparation of the electrode active material coated with the solid electrolyte layer in this embodiment is different from that in Example 1 only in that the mass of silicon dioxide in step (1) is 0.75 g.

[0069] Example 6

[0070] The preparation of the electrode active material coated with the solid electrolyte layer in this embodiment is different from that in Example 1 only in that the mass of silicon dioxide in step (1) is 1 g.

[0071] Example 7

[0072] The preparation of the electrode active material coated with the solid electrolyte layer in this embodiment is different from that in Example 1 only in that the mass of lithium perchlorate in step (1) is 0.4 g.

[0073] Example 8

[0074] The preparation of the electrode active material coated with the solid electrolyte layer in this embodiment is different from that in Example 1 only in that the mass of lithium perchlorate in step (1) is 0.6 g.

[0075] Example 9

[0076] The preparation of the solid electrolyte layer-coated electrode active material in this embodiment differs from that in Example 1 only in that the mass of ethylene oxide in step (1) is 4 g, and the thickness of the solid electrolyte layer in the obtained solid electrolyte layer-coated electrode active material is 30 nm.

[0077] Example 10

[0078] The preparation of the solid electrolyte layer-coated electrode active material in this embodiment differs from that in Example 1 only in that the mass of ethylene oxide in step (1) is 7.5 g, and the thickness of the solid electrolyte layer in the obtained solid electrolyte layer-coated electrode active material is 70 nm.

[0079] Example 11

[0080] The preparation of the electrode for lithium extraction from salt lakes in this embodiment includes the following steps:

[0081] Add PVDF to N-methylpyrrolidone and stir until completely dissolved to obtain a mixed glue solution;

[0082] The lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1, NH4HCO3, and acetylene black were added to the mixed glue solution and vacuum stirred for 0.5 h to obtain a mixed slurry; wherein the added amounts of PVDF, NH4HCO3, acetylene black, and N-methylpyrrolidone were 20%, 15%, 5%, and 120% of the mass of the lithium iron phosphate coated with the solid electrolyte layer, respectively;

[0083] The obtained mixed slurry was coated on the titanium mesh with a coating density of 150 mg lithium iron phosphate / cm 2 , and then dried at 120℃ for 10h to obtain an electrode for lithium extraction from salt lakes with a porosity of 30%.

[0084] Example 12

[0085] The preparation of the electrode for lithium extraction from salt lakes in this embodiment includes the following steps:

[0086] Add PVDF to N-methylpyrrolidone and stir until completely dissolved to obtain a mixed glue solution;

[0087] The lithium iron phosphate coated with the solid electrolyte layer obtained in Example 2, NH4HCO3, and Ketjen black were added to the mixed glue solution and stirred under vacuum for 1 hour to obtain a mixed slurry; the amounts of PVDF, NH4HCO3, Ketjen black, and N-methylpyrrolidone added were 15%, 20%, 15%, and 150% of the mass of the lithium iron phosphate coated with the solid electrolyte layer, respectively;

[0088] The obtained mixed slurry was coated on the titanium mesh with a coating density of 200 mg lithium iron phosphate / cm 2 , and then dried at 120℃ for 14h to obtain an electrode for lithium extraction from salt lakes with a porosity of 40%.

[0089] Example 13

[0090] The preparation of the electrode for lithium extraction from salt lakes in this embodiment includes the following steps:

[0091] Add PVDF to N-methylpyrrolidone and stir until completely dissolved to obtain a mixed glue solution;

[0092] The lithium iron phosphate coated with the solid electrolyte layer obtained in Example 3, NH4HCO3, and Ketjen black were added to the mixed glue solution of step (3), and vacuum stirred for 2 hours to obtain a mixed slurry; the amount of PVDF, NH4HCO3, Ketjen black, and N-methylpyrrolidone added was 25%, 10%, 12%, and 135% of the mass of the lithium iron phosphate coated with the solid electrolyte layer, respectively;

[0093] The obtained mixed slurry was coated on the titanium mesh with a coating density of 200 mg lithium iron phosphate / cm 2 , and then dried at 100℃ for 20h to obtain an electrode for lithium extraction from salt lakes with a porosity of 20%.

[0094] Example 14

[0095] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 4 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0096] Example 15

[0097] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 5 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0098] Example 16

[0099] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 6 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0100] Example 17

[0101] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 7 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0102] Example 18

[0103] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 8 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0104] Example 19

[0105] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 9 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0106] Example 20

[0107] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 10 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0108] Example 21

[0109] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of PVDF added is 18% of the mass of the lithium iron phosphate coated with the solid electrolyte layer.

[0110] Example 22

[0111] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of PVDF added is 22% of the mass of the lithium iron phosphate coated with the solid electrolyte layer.

[0112] Example 23

[0113] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of NH4HCO3 added is 12% of the mass of the lithium iron phosphate coated with the solid electrolyte layer; the porosity of the obtained electrode for lithium extraction from salt lakes is 25%.

[0114] Example 24

[0115] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this embodiment and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of NH4HCO3 added is 18% of the mass of the lithium iron phosphate coated with the solid electrolyte layer; the porosity of the obtained electrode for lithium extraction from salt lakes is 35%.

[0116] Comparative Example 1

[0117] The preparation of the electrode active material coated with the solid electrolyte layer in this comparative example is different from that in Example 1 only in that the mass of silicon dioxide in step (1) is 0.2 g.

[0118] Comparative Example 2

[0119] The preparation of the electrode active material coated with the solid electrolyte layer in this comparative example is different from that in Example 1 only in that the mass of silicon dioxide in step (1) is 1.4 g.

[0120] Comparative Example 3

[0121] The preparation of the electrode active material coated with the solid electrolyte layer in this comparative example is different from that in Example 1 only in that the mass of lithium perchlorate in step (1) is 0.2 g.

[0122] Comparative Example 4

[0123] The preparation of the electrode active material coated with the solid electrolyte layer in this comparative example is different from that in Example 1 only in that the mass of lithium perchlorate in step (1) is 0.8 g.

[0124] Comparative Example 5

[0125] The preparation of the electrode for lithium extraction from salt lakes in this comparative example comprises the following steps:

[0126] (1) Add PVDF to N-methylpyrrolidone and stir until completely dissolved to obtain a mixed glue solution;

[0127] (2) Add lithium iron phosphate, NH4HCO3, and acetylene black to the mixed glue solution and stir for 5 hours to obtain a mixed slurry; the added amounts of PVDF, NH4HCO3, acetylene black, and N-methylpyrrolidone are 8%, 15%, 5%, and 120% of the mass of lithium iron phosphate, respectively;

[0128] (3) Coat the mixed slurry on the titanium mesh with a coating density of 150 mg lithium iron phosphate / cm 2, and then dried at 120℃ for 10h to obtain the electrode for lithium extraction from salt lake.

[0129] Comparative Example 6

[0130] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of PVDF added is 10% of the mass of the lithium iron phosphate coated with the solid electrolyte layer.

[0131] Comparative Example 7

[0132] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of PVDF added is 30% of the mass of the lithium iron phosphate coated with the solid electrolyte layer.

[0133] Comparative Example 8

[0134] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of NH4HCO3 added is 8% of the mass of the lithium iron phosphate coated with the solid electrolyte layer; the porosity of the obtained electrode for lithium extraction from salt lakes is 18%.

[0135] Comparative Example 9

[0136] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the amount of NH4HCO3 added is 22% of the mass of the lithium iron phosphate coated with the solid electrolyte layer; the porosity of the obtained electrode for lithium extraction from salt lakes is 43%.

[0137] Comparative Example 10

[0138] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Comparative Example 1 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0139] Comparative Example 11

[0140] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Comparative Example 2 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0141] Comparative Example 12

[0142] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Comparative Example 3 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0143] Comparative Example 13

[0144] The only difference between the preparation of the electrode for lithium extraction from salt lakes in this comparative example and the preparation of the electrode for lithium extraction from salt lakes in Example 11 is that the lithium iron phosphate coated with the solid electrolyte layer obtained in Comparative Example 4 replaces the lithium iron phosphate coated with the solid electrolyte layer obtained in Example 1.

[0145] Lithium extraction test:

[0146] The lithium-extracted salt lake electrode obtained in each embodiment and comparative example is used as the anode, nickel foam is used as the cathode, and 20g / L NaCl solution is used as the electrolyte. A voltage of 1.0V is applied between the two ends of the electrode until the current density is less than 0.5A / m2 to produce a delithiation electrode.

[0147] The electrolysis device is separated into an anode chamber and a cathode chamber by an anion exchange membrane. The electrode for lithium extraction from salt lake obtained in each embodiment and comparative example is used as the anode, and the delithiation state electrode obtained in each embodiment and comparative example is used as the cathode, which are placed in the anode chamber and the cathode chamber respectively. The electrode for lithium extraction from salt lake obtained in each embodiment and the delithiation state electrode are made corresponding to each other. For example, the electrode for lithium extraction from salt lake obtained in Example 1 is used as the anode, and the delithiation state electrode obtained in Example 1 is used as the cathode; brine is injected into the cathode chamber, and NaCl solution is injected into the anode chamber. A voltage of 0.3 V is applied to the anode and the cathode for constant voltage electrolysis for 8 hours.

[0148] The changes in lithium ion concentration of the brine before and after the lithium extraction reaction, the lithium concentration of the anolyte after the completion of lithium extraction, and the capacity retention rate of the electrode after 100 lithium extractions in the examples and comparative examples are shown in Table 1.

[0149] Table 1

[0150]

[0151]

[0152]

[0153] As can be seen from Table 1, the electrode for lithium extraction from salt lakes obtained in the present disclosure has a high lithium extraction efficiency, and the capacity retention rate is above 88% after 100 cycles; this indicates that the electrode active material coated with the solid electrolyte layer disclosed in the present disclosure can produce an electrode for lithium extraction from salt lakes with high lithium extraction efficiency and high capacity retention rate.

[0154] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present disclosure rather than to limit the scope of protection of the present disclosure. Although the present disclosure has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present disclosure may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A method for preparing an electrode active material coated with a solid electrolyte layer, characterized in that: The following steps are involved: After the electrode active material, ethylene oxide, catalyst, inorganic nanoparticles, lithium source and solvent are uniformly mixed, a crosslinking agent is added and a polymerization reaction is carried out at 50-80 ° C for 18-30 hours. After the reaction, an electrode active material coated with a solid electrolyte layer is obtained; the electrode active material is at least one of lithium iron phosphate and lithium manganese iron phosphate; The mass of ethylene oxide is 5-20% of the mass of the electrode active material; The mass of the catalyst is 0.1-1% of the mass of ethylene oxide, the mass of the inorganic nanoparticles is 5-25% of the mass of ethylene oxide, the mass of the lithium source is 5-15% of the mass of ethylene oxide, and the mass of the cross-linking agent is 0.1-1% of the mass of ethylene oxide.

2. The preparation method according to claim 1, wherein The mass of the inorganic nanoparticles is 10-20% of the mass of ethylene oxide.

3. The preparation method according to claim 1, wherein The average particle size of the electrode active material is 0.5-5 μm; and / or, the catalyst is a quaternary ammonium base; and / or, the inorganic nanoparticles are at least one of SiO2 nanoparticles, ZnO nanoparticles, Al2O3 nanoparticles, HBO2 nanoparticles, and TiO2 nanoparticles; and / or, the average particle size of the inorganic nanoparticles is 1-50 nm; and / or, the cross-linking agent is ethylene glycol dimethacrylate; And / or, the lithium source is at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluorophosphate, and lithium bis(trifluoromethylsulfonyl)imide.

4. The preparation method according to claim 1, wherein First, the electrode active material is added to the solvent, and then ethylene oxide is added. After stirring evenly, the catalyst, inorganic nanoparticles and lithium source are added and ultrasonically mixed. The ultrasonic mixing time is 15-30 minutes.

5. The preparation method according to claim 1, wherein After the reaction is completed, the obtained reaction product is centrifuged, washed, and dried to obtain an electrode active material coated with a solid electrolyte layer.

6. The preparation method according to claim 5, wherein The drying temperature is 80-100° C.; and / or the drying time is 10-15 hours.

7. An electrode active material coated with a solid electrolyte layer, characterized in that: The solid electrolyte layer-coated electrode active material is prepared by the preparation method of the solid electrolyte layer-coated electrode active material according to any one of claims 1 to 6.

8. The solid electrolyte layer-coated electrode active material according to claim 7, wherein: The thickness of the solid electrolyte layer is 10-100 nm.

9. Use of the electrode active material coated with the solid electrolyte layer as claimed in claim 7 or 8 in preparing an electrode for lithium extraction from salt lakes.

10. An electrode for extracting lithium from salt lakes, characterized in that: The porosity of the electrode for lithium extraction from salt lakes is 20-40%; the electrode for lithium extraction from salt lakes is Includes the following components: The electrode active material, binder, and conductive agent coated with a solid electrolyte layer as described in claim 7 or 8; based on 100 parts by weight of the electrode active material coated with the solid electrolyte layer, the mass content of each component is: 15-25 parts of binder and 5-15 parts of conductive agent.

11. The electrode for lithium extraction from salt lakes according to claim 10, characterized in that: The porosity of the electrode for lithium extraction from salt lakes is 25-35%.

12. The electrode for extracting lithium from salt lakes according to claim 10, wherein: The mass of the binder is 18-22 parts by weight.

13. The electrode for extracting lithium from salt lakes according to claim 10, wherein: The binder is polyvinylidene fluoride; and / or the conductive agent is at least one of acetylene black and Ketjen black.

14. The method for preparing an electrode for lithium extraction from a salt lake according to any one of claims 10 to 13, characterized in that: The following steps are involved: dissolving a binder in an organic solvent to obtain a binder solution; The electrode active material coated with the solid electrolyte layer, the pore-forming agent and the conductive agent are added to the binder solution and stirred evenly. The obtained slurry is coated on the current collector and dried to obtain the lithium extraction electrode for salt lake.

15. The preparation method according to claim 14, wherein The organic solvent is N-methylpyrrolidone; and / or, the mass of the organic solvent is 120-150% of the mass of the electrode active material coated with the solid electrolyte layer; the pore-forming agent is at least one of (NH4)2CO3, NH4HCO3, NaCl, and KCl; and / or, the mass of the pore-forming agent is 10-20% of the mass of the electrode active material coated with the solid electrolyte layer.

16. The preparation method according to claim 14, wherein The stirring is vacuum stirring; and or, the stirring time is 0.5-2h.

17. The preparation method according to claim 14, wherein The drying temperature is 100-200° C.; and / or the drying time is 10-20 hours.

18. Use of the electrode for lithium extraction from salt lakes according to any one of claims 10 to 13 in extracting lithium from salt lakes.

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