Three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lake, preparation method and application

Abstract

The application discloses a three-dimensional interpenetrating network structure lithium iron phosphate active material for extracting lithium from salt lakes, a preparation method and application, wherein the three-dimensional interpenetrating network structure lithium iron phosphate active material comprises a three-dimensional material and lithium iron phosphate loaded on the three-dimensional material. The three-dimensional interpenetrating network structure lithium iron phosphate active material for extracting lithium from salt lakes has a three-dimensional interpenetrating network structure on a macro scale, has a large specific surface area and super-high conductivity of the three-dimensional material, and the lithium iron phosphate loaded on the three-dimensional material successfully reduces the disorder accumulation stress, thereby ensuring the stability of the material structure. The three-dimensional conductive network electrode constructed by the three-dimensional interpenetrating network structure lithium iron phosphate active material has a "micro-crack-micro-pore" composite structure, greatly improves the Li + The diffusion rate in the pole, reduces the charge-discharge polarization degree, enhances the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency, the lithium extraction efficiency,

Description

Technical Field

[0001] This invention relates to the field of lithium extraction technology from salt lakes, and more specifically, to a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes, its preparation method, and its application. Background Technology

[0002] With the accelerated industrialization of new energy electric vehicles and energy storage equipment, global demand for lithium resources is growing exponentially. The efficient development and utilization of lithium resources has become a core issue of common concern to the international academic and industrial communities. Currently, approximately 80% of the world's lithium resources are found in salt lake brines. Compared to other extraction methods, brine lithium extraction has significant advantages in terms of sustainability, economy, and environmental friendliness. However, traditional brine lithium extraction technologies (including precipitation, adsorption-membrane separation, and solvent extraction) generally suffer from technical bottlenecks such as long extraction cycles, low lithium recovery rates, and environmental risks, severely restricting the efficient development and utilization of lithium resources. In contrast, electrochemical deintercalation / intercalation methods, due to their excellent selectivity, low energy consumption, and green environmental characteristics, have become the most promising lithium extraction technology.

[0003] The efficiency of electrochemical lithium extraction is mainly constrained by the following key factors: First, the inherent high ion concentration (rich in Na+) of salt lake brine. + K + The presence of competing cations and high viscosity can easily lead to a series of problems such as decreased cycle stability of electrode materials and impeded lithium-ion mass transfer. Secondly, increased electrode coating thickness can cause local accumulation of lithium-ion concentration gradients, resulting in increased ion / electron transport impedance, ultimately leading to a decrease in lithium extraction efficiency due to concentration polarization and electrochemical polarization effects. Furthermore, the internal stress generated by uneven temperature field distribution during electrode drying may cause problems such as electrode structure cracking and peeling of active material from current collector, which in turn significantly affects lithium adsorption efficiency.

[0004] To address the aforementioned issues, the key scientific problem that current research urgently needs to solve is: how to effectively suppress the reduction in lithium extraction efficiency caused by the polarization effect induced by the high ion concentration / high viscosity brine system and the thick-coated electrode. Summary of the Invention

[0005] The purpose of this invention is to provide a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes, its preparation method and application, which is beneficial to improving lithium extraction efficiency.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes, comprising a three-dimensional material and lithium iron phosphate loaded on the three-dimensional material, wherein the three-dimensional material is selected from at least one of graphene, carbon nanotubes and hollow carbon fibers, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material is 50wt%-55wt%.

[0007] Secondly, the present invention provides a method for preparing the three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes as described in the foregoing embodiments, comprising: Preparation of solutions: Prepare liquid a and liquid b, wherein liquid a includes ferrous sulfate and a reducing agent, and liquid b includes lithium hydroxide, phosphoric acid, a dispersant and a three-dimensional material; Precursor preparation: Under a protective atmosphere, liquid b is injected into liquid a and then subjected to a first solid-liquid separation, hydrothermal reaction, a second solid-liquid separation, washing and drying to obtain the precursor; Calcination: The precursor is calcined under a protective atmosphere to obtain the three-dimensional interpenetrating network structure lithium iron phosphate active material.

[0008] In an optional embodiment, the molar ratio of lithium hydroxide and phosphoric acid in liquid b to ferrous sulfate in liquid a is (2-4):(0.9-1.1):1; And / or, the rate at which liquid b is injected into liquid a is 15 mL / min to 25 mL / min.

[0009] In an optional embodiment, the concentration of phosphoric acid in liquid b is 10wt%-20wt%; And / or, the concentration of the dispersant is 1wt%-3wt%; And / or, the dispersant is selected from at least one of sodium dodecyl sulfonate, lauryl sulfate, and sodium diisopropylnaphthalene sulfonate; And / or, the concentration of ferrous sulfate in liquid a is 5wt%-10wt%; And / or, the concentration of the reducing agent is 15wt%-25wt%; And / or, the reducing agent is selected from at least one of sodium bisulfite, sodium sulfite, and sodium ascorbate.

[0010] In an optional embodiment, the hydrothermal reaction temperature is 150℃-250℃, and the time is 5h-15h; And / or, the solid content in the reaction solution of the hydrothermal reaction is 15wt%-25wt%; And / or, the washing includes sequential water washing and alcohol washing, wherein the detergent for water washing is water and the detergent for alcohol washing is anhydrous ethanol; And / or, the drying temperature is 50℃-70℃.

[0011] In an optional embodiment, the calcination temperature is 500℃-900℃, and the calcination time is 4h-8h; And / or, the heating rate of the calcination step is 1℃ / min-10℃ / min.

[0012] Thirdly, the present invention provides an electrode active material layer for lithium extraction from salt lakes, comprising the three-dimensional interpenetrating network structure lithium iron phosphate active material described in the foregoing embodiments.

[0013] In optional embodiments, the mixture further includes 5wt%-10wt% of adhesive, 4wt%-8wt% of conductive agent, 4wt%-8wt% of hydrophilic agent, 1wt%-3wt% of reinforcing agent, and 0wt%-20wt% of pore-forming agent; And / or, in the electrode active material layer, the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material is 70wt%-80wt%.

[0014] Fourthly, the present invention provides an electrode for lithium extraction from salt lakes, comprising a titanium mesh and an electrode active material layer for lithium extraction from salt lakes as described in the foregoing embodiments disposed on at least one side of the titanium mesh.

[0015] Fifthly, the present invention provides a method for preparing an electrode for lithium extraction from salt lakes as described in the foregoing embodiments, comprising: coating an electrode slurry comprising a three-dimensional interpenetrating network structure lithium iron phosphate active material onto a titanium mesh and then drying it.

[0016] The present invention has the following beneficial effects: This application presents a three-dimensional interpenetrating network (IPN) lithium iron phosphate (LFP) active material for lithium extraction from salt lakes. This material possesses a macroscopic three-dimensional IPN structure, exhibiting a large specific surface area and ultra-high conductivity characteristic of three-dimensional materials. The LFP loaded onto this three-dimensional material successfully mitigates its disordered stacking stress, thereby ensuring the stability of the material structure. The three-dimensional conductive network electrode constructed from the IPN active material possesses a "microcrack-micropore" composite structure, which significantly improves the conductivity of Li in the brine. + The diffusion rate within the electrode plate reduces the polarization during charge and discharge, thereby enhancing the cycle stability, lithium adsorption capacity, and lithium extraction efficiency of the electrode plate used for lithium extraction from salt lakes. Therefore, the electrode described in this application for lithium extraction from salt lakes can achieve a green and economical recovery of lithium resources from brine. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The image shows a SEM image of the three-dimensional interpenetrating network structure lithium iron phosphate active material prepared in Example 1. Figure 2 The image shows the XRD pattern of the three-dimensional interpenetrating network structure lithium iron phosphate active material prepared in Example 1. Figure 3 This is a cross-sectional view of the three-dimensional conductive network structure electrode plate prepared in Example 2; Figure 4 The room temperature cycling curves (0.1C) for Example 1 and Comparative Example 1 are shown. Figure 5 The charge-discharge curves (0.1C) for Example 2 and Comparative Example 2 are shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention 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.

[0020] This invention provides a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes, comprising a three-dimensional material and lithium iron phosphate loaded on the three-dimensional material. The three-dimensional material is selected from at least one of graphene, carbon nanotubes and hollow carbon fibers, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material is 50wt%-55wt%.

[0021] The lithium iron phosphate active material for lithium extraction from salt lakes presented in this application has a three-dimensional interpenetrating network structure on a macroscopic scale, possessing a large specific surface area (45.7 m²) characteristic of three-dimensional materials. 2 With high conductivity (above 5.1 Ω·cm) and ultra-high permeability (below 5.1 Ω·cm), lithium iron phosphate loaded on a three-dimensional material successfully alleviates its disordered stacking stress, thus ensuring the stability of the material structure. The three-dimensional conductive network electrode constructed from lithium iron phosphate active material with a three-dimensional interpenetrating network structure possesses a "microcrack-micropore" composite structure, which greatly enhances the conductivity of Li in brine. +The diffusion rate within the electrode plate reduces the polarization during charge and discharge, thereby enhancing the cycle stability, lithium adsorption capacity, and lithium extraction efficiency of the electrode plate used for lithium extraction from salt lakes. Therefore, the electrode described in this application for lithium extraction from salt lakes can achieve a green and economical recovery of lithium resources from brine.

[0022] Specifically, the mass fraction of the three-dimensional material in the described three-dimensional interpenetrating network structure lithium iron phosphate active material is 50wt%-55wt%, for example, 50wt%, 51wt%, 52wt%, 53wt%, 54wt%, and 55wt%. If the mass fraction of the three-dimensional material is too high, it will result in too low a proportion of lithium iron phosphate, which is not conducive to improving the lithium adsorption capacity. Conversely, if the mass fraction of the three-dimensional material is too low, it will be not conducive to improving the structural stability and lithium extraction efficiency.

[0023] The present invention also provides a method for preparing the three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes as described in the foregoing embodiments, comprising: Preparation of solutions: Prepare liquid a and liquid b, wherein liquid a includes ferrous sulfate and a reducing agent, and liquid b includes lithium hydroxide, phosphoric acid, a dispersant and a three-dimensional material; Precursor preparation: Under a protective atmosphere, liquid b is injected into liquid a and then subjected to a first solid-liquid separation, hydrothermal reaction, a second solid-liquid separation, washing and drying to obtain the precursor; Calcination: The precursor is calcined under a protective atmosphere to obtain the three-dimensional interpenetrating network structure lithium iron phosphate active material.

[0024] This invention employs a hydrothermal method to synthesize lithium iron phosphate in situ and load it onto the surface of a three-dimensional material, thereby preparing an active material with a three-dimensional interpenetrating network structure on a macroscopic scale.

[0025] In an optional embodiment, the molar ratio of lithium hydroxide, phosphoric acid in liquid b, and ferrous sulfate in liquid a is (2-4):(0.9-1.1):1, for example, 2:0.9:1, 2.2:0.92:1, 2.4:0.94:1, 2.6:0.96:1, 2.8:0.98:1, 3:1:1, 3.2:1.02:1, 3.4:1.04:1, 3.6:1.06:1, 3.8:1.08:1, 4:1.1:1; wherein, excess lithium hydroxide can compensate for lithium loss during subsequent sintering, which is beneficial to avoid capacity decay caused by lithium defects. At the same time, lithium hydroxide is alkaline and can promote Fe²⁺… + With PO4³ - Uniform precipitation is achieved to avoid Fe²⁺ precipitating due to excessive acidity. + Oxidation or incomplete crystallization of lithium iron phosphate.

[0026] In an optional embodiment, the injection rate of liquid b into liquid a is 15 mL / min-25 mL / min, for example, 15 mL / min, 16 mL / min, 17 mL / min, 18 mL / min, 19 mL / min, 20 mL / min, 21 mL / min, 22 mL / min, 23 mL / min, 24 mL / min, or 25 mL / min. Slowly injecting liquid b into liquid a allows Fe²⁺ to… + With PO4³ - Li + The reaction is uniform, generating a nanoscale, well-dispersed LiFePO4 precursor, avoiding rapid precipitation of ferric hydroxide and the formation of a precursor with coarse particles and uneven composition.

[0027] In an optional embodiment, the concentration of phosphoric acid in liquid b is 10wt%-20wt%, for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, or 20wt%. And / or, the concentration of the dispersant is 1wt%-3wt%, for example 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%; which is beneficial for the dispersion of three-dimensional materials in liquids; And / or, the dispersant is selected from at least one of sodium dodecyl sulfonate, lauryl sulfate, and sodium diisopropylnaphthalene sulfonate; And / or, the concentration of ferrous sulfate in liquid a is 5wt%-10wt%, for example 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%; And / or, the concentration of the reducing agent is 15wt%-25wt%, for example 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%; And / or, the reducing agent is selected from at least one of sodium bisulfite, sodium sulfite, and sodium ascorbate.

[0028] The concentrations of each component in liquids a and b need to be appropriate. If the concentration is too high, it will accelerate the precipitation rate and may form large, unevenly composed precursors. If the concentration is too low, it will not be conducive to improving production efficiency.

[0029] After liquid b is injected into liquid a, a precipitate is formed. After the injection of liquid b is completed, the reaction solution can be separated into solid and liquid, and the separated solid can be mixed with water to obtain a solid-liquid mixture. The solid-liquid mixture is then placed in a hydrothermal reactor for hydrothermal reaction.

[0030] In an optional embodiment, the hydrothermal reaction temperature is 150℃-250℃, for example 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, and the time is 5h-15h, for example 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h. Appropriately increasing the hydrothermal reaction temperature can make the crystal growth rate moderate, which is conducive to the full nucleation and growth of crystals, forming nanoscale particles with uniform particle size. If the temperature is too high, it may lead to the formation of coarse and unevenly composed precursors and may cause lithium iron phosphate lattice distortion. If the temperature is too low, it is not conducive to improving production efficiency.

[0031] In an optional embodiment, the solid content in the hydrothermal reaction solution is 15wt%-25wt%, for example, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, or 25wt%. This allows for a moderate crystal growth rate. If the solid content is too high, it may result in coarse crystals with uneven composition and a large number of impurity ions. If the solid content is too low, it will be detrimental to improving production efficiency.

[0032] In an optional embodiment, the washing process includes sequential water washing and alcohol washing, wherein the detergent for water washing is water and the detergent for alcohol washing is anhydrous ethanol; water washing mainly removes impurity ions from the lithium iron phosphate precursor, while alcohol washing can remove organic matter therein.

[0033] In an optional embodiment, the drying temperature is 50℃-70℃, for example 50℃, 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃, or 70℃.

[0034] In an optional embodiment, the calcination temperature is 500℃-900℃, for example 500℃, 540℃, 580℃, 620℃, 660℃, 700℃, 740℃, 780℃, 820℃, 860℃, 900℃, and the calcination time is 4h-8h, for example 4h, 4.4h, 4.8h, 5.2h, 5.6h, 6h, 6.4h, 6.8h, 7.2h, 7.6h, 8h; And / or, the heating rate of the calcination step is 1℃ / min-10℃ / min, for example 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, 10℃ / min.

[0035] Under the above conditions, calcination will not affect the three-dimensional material structure, and at the same time, it is beneficial to obtain fine and uniform lithium iron phosphate crystals.

[0036] The present invention also provides an electrode active material layer for lithium extraction from salt lakes, comprising the three-dimensional interpenetrating network structure lithium iron phosphate active material described in the foregoing embodiments.

[0037] In optional embodiments, the mixture further includes 5wt%-10wt% of adhesive, 4wt%-8wt% of conductive agent, 4wt%-8wt% of hydrophilic agent, 1wt%-3wt% of reinforcing agent, and 0wt%-20wt% of pore-forming agent; The mass fraction of the binder in the electrode active material layer is 5wt%-10wt%, for example, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, 10wt%, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylonitrile (PAN); The conductive agent in the electrode active material layer has a mass fraction of 4wt%-8wt%, for example, 4wt%, 4.4wt%, 4.8wt%, 5.2wt%, 5.6wt%, 6wt%, 6.4wt%, 6.8wt%, 7.2wt%, 7.6wt%, or 8wt%; the conductive agent is selected from at least one of conductive carbon (SP), Ketjen black, and acetylene black. The mass fraction of the hydrophilic agent in the electrode active material layer is 4wt%-8wt%, for example, 4wt%, 4.4wt%, 4.8wt%, 5.2wt%, 5.6wt%, 6wt%, 6.4wt%, 6.8wt%, 7.2wt%, 7.6wt%, 8wt%; the hydrophilic agent is selected from at least one of polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polyethylene glycol (PEG); The mass fraction of the reinforcing agent in the electrode active material layer is 1wt%-3wt%, for example, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.6wt%, 2.8wt%, or 3wt%; the reinforcing agent is selected from at least one of carbon fiber and graphite fiber. The mass fraction of the pore-forming agent in the electrode active material layer is 0wt%-20wt%, for example, 0wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt%, 12wt%, 14wt%, 16wt%, 18wt%, 20wt%; the pore-forming agent is selected from at least one of ammonium carbonate ((NH4)2CO3), ammonium bicarbonate (NH4HCO3), sodium chloride (NaCl), and sodium bicarbonate (NaHCO3).

[0038] In an optional embodiment, the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material in the electrode active material layer is 70wt%-80wt%, for example, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, or 80wt%.

[0039] If the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material is too high, although the lithium adsorption capacity will be improved, the content of binder / conductive agent will be insufficient, which will lead to poor contact between particles and will not be conducive to increasing the lithium ion migration rate. Conversely, if the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material is too low, there will be too many additives such as conductive agent, the active material loading will decrease, and the lithium adsorption capacity will decrease.

[0040] The present invention also provides an electrode for lithium extraction from salt lakes, comprising a titanium mesh and an electrode active material layer for lithium extraction from salt lakes as described in the foregoing embodiments disposed on at least one side of the titanium mesh.

[0041] The present invention also provides a method for preparing the electrode for lithium extraction from salt lakes as described in the foregoing embodiments, comprising: coating an electrode slurry comprising a three-dimensional interpenetrating network structure lithium iron phosphate active material onto a titanium mesh and then drying it, wherein the coating method is selected from one of blade coating, dip coating and extrusion coating.

[0042] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0043] Example 1 This embodiment provides a method for preparing an electrode for lithium extraction from salt lakes, including the following steps: Liquid a, comprising ferrous sulfate and sodium ascorbate, and liquid b, comprising lithium hydroxide, phosphoric acid, sodium dodecyl sulfate, and carbon nanotubes, were prepared. Liquid a contained 8 wt% ferrous sulfate (FeSO4) and 20 wt% sodium ascorbate (C6H7O6Na); liquid b contained 20 wt% sodium dodecyl sulfate (C6H7O6Na) and 8 wt% phosphoric acid. 12 H 25 The concentration of SO4Na is 2.5wt%. The molar ratio of lithium hydroxide, phosphoric acid and ferrous sulfate in liquid b to that in liquid a is 3:1:1. Under N2 protection, 200mL of liquid b is slowly injected into 400mL of liquid a at a rate of 20mL / min to generate a precipitate. The reaction solution is subjected to a first solid-liquid separation to separate the precipitate. Water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20wt%. A hydrothermal reaction is carried out, followed by a second solid-liquid separation. The mixture is then washed with deionized water and anhydrous ethanol in sequence and dried to obtain the precursor. The hydrothermal reaction temperature is 200℃, the time is 10h, and the drying temperature is 60℃. The obtained precursor was calcined in an N2 atmosphere to obtain a three-dimensional interpenetrating network structure lithium iron phosphate active material. SEM images are shown below. Figure 1 As shown, the XRD pattern is as follows Figure 2 As shown, the calcination temperature is 700℃, the calcination time is 6h, the heating rate of the calcination step is 5℃ / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material is 52wt%.

[0044] A three-dimensional interpenetrating network (IPN) lithium iron phosphate (LFP) active material (80 wt%, PVDF 5 wt%, SP 8 wt%, PEG 4 wt%, and carbon fiber 3 wt%) was uniformly dispersed in NMP to obtain an LFP electrode slurry. The LFP slurry was then coated onto a titanium mesh using a blade coating method. After drying, a three-dimensional conductive network structure electrode plate was obtained, as shown in the cross-sectional view below. Figure 3 As shown.

[0045] Example 2 This embodiment provides a method for preparing an electrode for lithium extraction from salt lakes, including the following steps: Liquid a, comprising ferrous sulfate and sodium ascorbate, and liquid b, comprising lithium hydroxide, phosphoric acid, sodium dodecyl sulfate, and carbon nanotubes, were prepared. Liquid a contained 8 wt% ferrous sulfate (FeSO4) and 20 wt% sodium ascorbate (C6H7O6Na); liquid b contained 20 wt% sodium dodecyl sulfate (C6H7O6Na) and 8 wt% phosphoric acid. 12 H 25 The concentration of SO4Na is 2.5wt%. The molar ratio of lithium hydroxide, phosphoric acid and ferrous sulfate in liquid b to that in liquid a is 3:1:1. Under N2 protection, 200mL of liquid b is slowly injected into 400mL of liquid a at a rate of 20mL / min to generate a precipitate. The reaction solution is subjected to a first solid-liquid separation to separate the precipitate. Water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20wt%. A hydrothermal reaction is carried out, followed by a second solid-liquid separation. The mixture is then washed with deionized water and anhydrous ethanol in sequence and dried to obtain the precursor. The hydrothermal reaction temperature is 200℃, the time is 10h, and the drying temperature is 60℃. The obtained precursor was calcined in a N2 atmosphere to obtain a three-dimensional interpenetrating network structure lithium iron phosphate active material. The calcination temperature was 700℃, the calcination time was 6h, the heating rate of the calcination step was 5℃ / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material was 52wt%.

[0046] A three-dimensional interpenetrating network structure lithium iron phosphate active material of 71.2 wt%, PVDF 4.4 wt%, SP 7.1 wt%, PEG 3.6 wt%, carbon fiber 2.7 wt%, sodium chloride 8.9 wt%, and ammonium bicarbonate 2.2 wt% was uniformly dispersed in NMP to obtain an LFP electrode slurry. The LFP slurry was coated onto a titanium mesh by a scraping method, and after drying, a three-dimensional conductive network structure electrode plate was obtained.

[0047] Example 3 This embodiment provides a method for preparing an electrode for lithium extraction from salt lakes, including the following steps: Liquid a, comprising ferrous sulfate and sodium ascorbate, and liquid b, comprising lithium hydroxide, phosphoric acid, sodium dodecyl sulfate, and carbon nanotubes, were prepared. Liquid a contained 5 wt% ferrous sulfate (FeSO4) and 15 wt% sodium ascorbate (C6H7O6Na); liquid b contained 15 wt% sodium dodecyl sulfate (C6H7O6Na) and 15 wt% sodium ascorbate (C6H7O6Na). 12 H 25 The concentration of SO4Na is 1 wt%. The molar ratio of lithium hydroxide, phosphoric acid and ferrous sulfate in liquid b to that in liquid a is 3:1:1. Under N2 protection, 200 mL of liquid b is slowly injected into 400 mL of liquid a at a rate of 20 mL / min to generate a precipitate. The reaction solution is subjected to a first solid-liquid separation to separate the precipitate. Water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20 wt%. A hydrothermal reaction is carried out, followed by a second solid-liquid separation. The mixture is then washed with deionized water and anhydrous ethanol in sequence and dried to obtain the precursor. The hydrothermal reaction temperature is 150 °C, the time is 15 h, and the drying temperature is 70 °C. The obtained precursor was calcined in a N2 atmosphere to obtain a three-dimensional interpenetrating network structure lithium iron phosphate active material. The calcination temperature was 900℃, the calcination time was 4h, the heating rate of the calcination step was 10℃ / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material was 55wt%.

[0048] 80wt% of lithium iron phosphate active material with a three-dimensional interpenetrating network structure, 5wt% of PVDF, 8wt% of SP, 4wt% of PEG and 3wt% of carbon fiber were uniformly dispersed in NMP to obtain LFP electrode slurry; the LFP slurry was coated onto a titanium mesh by a scraping method and dried to obtain a three-dimensional conductive network structure electrode plate.

[0049] Example 4 This embodiment provides a method for preparing an electrode for lithium extraction from salt lakes, including the following steps: Liquid a, comprising ferrous sulfate and sodium ascorbate, and liquid b, comprising lithium hydroxide, phosphoric acid, sodium dodecyl sulfate, and carbon nanotubes, were prepared. Liquid a contained 10 wt% ferrous sulfate (FeSO4) and 25 wt% sodium ascorbate (C6H7O6Na); liquid b contained 25 wt% sodium dodecyl sulfate (C6H7O6Na) and 10 wt% phosphate. 12 H 25 The concentration of SO4Na is 3wt%, and the molar ratio of lithium hydroxide, phosphoric acid and ferrous sulfate in liquid b to that in liquid a is 3:1:1. Under N2 protection, 200mL of liquid b is slowly injected into 400mL of liquid a at a rate of 20mL / min to generate a precipitate. The reaction solution is subjected to a first solid-liquid separation to separate the precipitate. Water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20wt%. A hydrothermal reaction is carried out, followed by a second solid-liquid separation. The mixture is then washed with deionized water and anhydrous ethanol in sequence, and dried to obtain the precursor. The hydrothermal reaction temperature is 250℃, the time is 5h, and the drying temperature is 50℃. The obtained precursor was calcined in a N2 atmosphere to obtain a three-dimensional interpenetrating network structure lithium iron phosphate active material. The calcination temperature was 500℃, the calcination time was 8h, the heating rate of the calcination step was 1℃ / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material was 50wt%.

[0050] 80wt% of lithium iron phosphate active material with a three-dimensional interpenetrating network structure, 5wt% of PVDF, 8wt% of SP, 4wt% of PEG and 3wt% of carbon fiber were uniformly dispersed in NMP to obtain LFP electrode slurry; the LFP slurry was coated onto a titanium mesh by a scraping method and dried to obtain a three-dimensional conductive network structure electrode plate.

[0051] Example 5 The only difference between this embodiment and Embodiment 1 is that the carbon nanotubes in the three-dimensional interpenetrating network structure lithium iron phosphate active material are replaced with graphene of equal mass.

[0052] Example 6 The only difference between this embodiment and Embodiment 1 is that the carbon nanotubes in the three-dimensional interpenetrating network structure lithium iron phosphate active material are replaced with hollow carbon fibers of equal mass.

[0053] Comparative Example 1 This comparative example provides a method for preparing an electrode for lithium extraction from salt lakes. The only difference from Example 1 is that no three-dimensional material is added to liquid b.

[0054] Comparative Example 2 The only difference from Example 2 is that no three-dimensional material was added to liquid b.

[0055] Comparative Example 3 The only difference between this embodiment and Embodiment 1 is that the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material is too high at 60wt%, while the mass ratio of other components remains unchanged.

[0056] Comparative Example 4 The only difference between this embodiment and Embodiment 1 is that the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material is less than 40wt%, while the mass ratio of the other components remains unchanged.

[0057] Comparative Example 5 The only difference between this embodiment and Embodiment 1 is that the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material in the three-dimensional conductive network structure electrode is too small, at 65wt%, while the mass ratio of other components remains unchanged.

[0058] Comparative Example 6 The only difference between this embodiment and Embodiment 1 is that the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material in the three-dimensional conductive network structure electrode is too high at 85wt%, while the mass ratio of other components remains unchanged.

[0059] The lithium extraction plates prepared in the above embodiments and comparative examples were used as positive electrodes, and the lithium extraction plates after delithiation by chemical oxidation and anion exchange membranes were assembled into an electrochemical deintercalation / intercalation device. The electrochemical deintercalation / intercalation lithium extraction and electrochemical performance were tested using the Blue Battery Testing System. The test methods and conditions are as follows: Lithium extraction specific capacity: At 25℃, after the lithium extraction device extracts lithium 10 times at 0.1C (5 charge-discharge cycles), the average value of the specific capacity of the 10 charge + discharge cycles is calculated.

[0060] Cycling performance: At 25°C, after the lithium extraction device extracts lithium 600 times at 0.1C (300 charge-discharge cycles), the ratio of the specific capacity of the 600th cycle to the specific capacity of the 1st cycle.

[0061] Lithium extraction efficiency: The ratio of the specific capacity of the second extraction to the specific capacity of the first extraction after the lithium extraction device is initially operated at 0.1C for 2 times (1 charge-discharge cycle) at 25℃.

[0062] Lithium extraction rate (Q): The electrochemical deintercalation device is charged once for lithium extraction, Q = [( C 0 V 0- C 1 V 1)*1000] / M 0; in the formula C 0 represents the initial lithium concentration (g / L) in the brine. C 1 represents the lithium concentration in the brine at the end of lithium extraction (g / L); V 0 represents the initial brine volume (L). V 1 represents the volume of brine at the end of lithium extraction (L);M 0 represents the mass of the three-dimensional interpenetrating network structure lithium iron phosphate (LiFePO4) active material in the lithium extraction electrode.

[0063] The test results are shown in Table 1, where the room temperature cycling curves (0.1C) of Example 1 and Comparative Example 1 are shown in Table 1. Figure 4 As shown, the charge-discharge curves (0.1C) of Example 2 and Comparative Example 2 are as follows. Figure 5 As shown.

[0064] Table 1

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An electrode active material layer for lithium extraction from salt lakes, characterized in that, The electrode active material layer includes a three-dimensional interpenetrating network structure lithium iron phosphate active material, wherein the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material is 70wt%-80wt%; the three-dimensional interpenetrating network structure lithium iron phosphate active material comprises a three-dimensional material and lithium iron phosphate supported on the three-dimensional material, wherein the three-dimensional material is selected from at least one of graphene, carbon nanotubes, and hollow carbon fibers, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material is 50wt%-55wt%; The electrode active material layer further includes a binder of 5wt%-10wt%, a conductive agent of 4wt%-8wt%, a hydrophilic agent of 4wt%-8wt%, a reinforcing agent of 1wt%-3wt%, and a pore-forming agent of 0wt%-20wt%; the reinforcing agent is selected from at least one of carbon fiber and graphite fiber.

2. The electrode active material layer for lithium extraction from salt lakes according to claim 1, characterized in that, The preparation method of the three-dimensional interpenetrating network structure lithium iron phosphate active material includes: Preparation of solutions: Prepare liquid a and liquid b, wherein liquid a includes ferrous sulfate and a reducing agent, and liquid b includes lithium hydroxide, phosphoric acid, a dispersant and a three-dimensional material; Precursor preparation: Under a protective atmosphere, liquid b is injected into liquid a and then subjected to a first solid-liquid separation, hydrothermal reaction, a second solid-liquid separation, washing and drying to obtain the precursor; Calcination: The precursor is calcined under a protective atmosphere to obtain the three-dimensional interpenetrating network structure lithium iron phosphate active material.

3. The electrode active material layer for lithium extraction from salt lakes according to claim 2, characterized in that, The molar ratio of lithium hydroxide and phosphoric acid in liquid b to ferrous sulfate in liquid a is (2-4):(0.9-1.1):1; And / or, the rate at which liquid b is injected into liquid a is 15 mL / min-25 mL / min.

4. The electrode active material layer for lithium extraction from salt lakes according to claim 2, characterized in that, The concentration of phosphoric acid in liquid b is 10wt%-20wt%; And / or, the concentration of the dispersant is 1wt%-3wt%; And / or, the dispersant is selected from at least one of sodium dodecyl sulfonate, lauryl sulfate, and sodium diisopropylnaphthalene sulfonate; And / or, the concentration of ferrous sulfate in liquid a is 5wt%-10wt%; And / or, the concentration of the reducing agent is 15wt%-25wt%; And / or, the reducing agent is selected from at least one of sodium bisulfite, sodium sulfite, and sodium ascorbate.

5. The electrode active material layer for lithium extraction from salt lakes according to claim 2, characterized in that, The hydrothermal reaction temperature is 150℃-250℃, and the time is 5h-15h. And / or, the solid content in the reaction solution of the hydrothermal reaction is 15wt%-25wt%; And / or, the washing includes sequential water washing and alcohol washing, wherein the detergent for water washing is water and the detergent for alcohol washing is anhydrous ethanol; And / or, the drying temperature is 50℃-70℃.

6. The electrode active material layer for lithium extraction from salt lakes according to claim 2, characterized in that, The calcination temperature is 500℃-900℃, and the calcination time is 4h-8h; And / or, the heating rate of the calcination step is 1℃ / min-10℃ / min.

7. An electrode for lithium extraction from salt lakes, characterized in that, It includes a titanium mesh and an electrode active material layer for lithium extraction from salt lakes as described in any one of claims 1-6 disposed on at least one side of the titanium mesh.

8. A method for preparing an electrode for lithium extraction from salt lakes as described in claim 7, characterized in that, include: The electrode slurry, which includes a three-dimensional interpenetrating network structure of lithium iron phosphate active material, is coated onto a titanium mesh and then dried.

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