Lithium iron phosphate active material with three-dimensional interpenetrating network structure for extracting lithium from salt lake, and preparation method and application of lithium iron phosphate active material

Abstract

The invention discloses a three-dimensional interpenetrating network structure lithium iron phosphate active material for salt lake lithium extraction, a preparation method and application. 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 lithium iron phosphate active material with the three-dimensional interpenetrating network structure for extracting lithium from the salt lake has the three-dimensional interpenetrating network structure on a macroscopic scale, and has a large specific surface area and ultrahigh conductivity of a three-dimensional material, and disordered stacking stress of the lithium iron phosphate active material is successfully reduced by the lithium iron phosphate loaded on the three-dimensional material, so that the stability of the material structure is ensured. A three-dimensional conductive network electrode constructed by the lithium iron phosphate active material with the three-dimensional interpenetrating network structure has a'microcrack-micropore 'composite structure, so that the diffusion rate of Li < + > in brine in the pole plate is greatly improved, the charge-discharge polarization degree is reduced, and the cycling stability, the lithium adsorption capacity and the lithium extraction efficiency of the electric de-intercalation lithium extraction pole plate are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium extraction from salt lakes, and in particular to a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes, a preparation method and applications. Background Art

[0002] With the acceleration of the industrialization process of new energy electric vehicles and energy storage equipment, the global demand for lithium resources has shown an exponential growth trend. The efficient development and utilization of lithium resources has become a core issue of common concern to the international academic and industrial communities. Currently, about 80% of the world's lithium resources are found in salt lake brine. Compared with other extraction methods, the brine lithium extraction process has significant advantages in sustainability, economy and environmental friendliness. However, traditional brine lithium extraction technologies (including precipitation, adsorption-membrane separation and solvent extraction) generally have technical bottlenecks such as long extraction cycles, low lithium recovery rates and environmental risks, which seriously restrict the efficient development and utilization of lithium resources. In contrast, the electrochemical deintercalation method has become the most promising lithium extraction technology due to its excellent selectivity, low energy consumption and green environmental protection characteristics.

[0003] The efficiency of electrochemical lithium extraction is mainly restricted by the following key factors: First, the inherent high ion concentration of salt lake brine (rich in Na + , K + The high viscosity of the electrode material can easily lead to a series of problems such as the attenuation of the cycle stability of the electrode material and the obstruction of lithium ion mass transfer; secondly, the increase in the thickness of the electrode coating will cause the accumulation of local lithium ion concentration gradients, resulting in an increase in the ion / electron transfer impedance, and ultimately a decrease in the lithium extraction efficiency due to concentration polarization and electrochemical polarization effects; thirdly, the internal stress generated by the uneven temperature field distribution during the thermal drying of the plate may cause problems such as cracking of the electrode structure and separation of the active material and the current collector, which in turn significantly affects the lithium adsorption efficiency.

[0004] In response to the above problems, the key scientific issue that needs to be urgently addressed in current research is: how to effectively suppress the problem of reduced lithium extraction efficiency caused by the polarization effect caused by the high ion concentration / high viscosity brine system and the thick coated electrode. Summary of the Invention

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

[0006] The present invention is achieved in that:

[0007] In the 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%.

[0008] In a second aspect, 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 aforementioned embodiment, comprising:

[0009] Liquid preparation: preparing liquid a and liquid b, wherein liquid a comprises ferrous sulfate and a reducing agent, and liquid b comprises lithium hydroxide, phosphoric acid, a dispersant, and a three-dimensional material;

[0010] Precursor preparation: Under a protective atmosphere, liquid b is injected into liquid a, followed by a primary solid-liquid separation, a hydrothermal reaction, a secondary solid-liquid separation, washing, and drying to obtain the precursor;

[0011] Calcination: calcining the precursor under a protective atmosphere to obtain the three-dimensional interpenetrating network structure lithium iron phosphate active material.

[0012] In an optional embodiment, the molar ratio of lithium hydroxide and phosphoric acid in the liquid b to ferrous sulfate in the liquid a is (2-4):(0.9-1.1):1;

[0013] And / or, the rate of injection of liquid b into liquid a is 15 mL / min-25 mL / min.

[0014] In an optional embodiment, the concentration of phosphoric acid in the liquid b is 10 wt%-20 wt%;

[0015] and / or, the concentration of the dispersant is 1 wt%-3 wt%;

[0016] and / or, the dispersant is selected from at least one of sodium dodecyl sulfonate, lauryl sulfate and sodium diisopropylnaphthalene sulfonate;

[0017] and / or, the concentration of ferrous sulfate in the liquid a is 5wt%-10wt%;

[0018] and / or, the concentration of the reducing agent is 15wt%-25wt%;

[0019] And / or, the reducing agent is selected from at least one of sodium bisulfite, sodium sulfite and sodium ascorbate.

[0020] In an optional embodiment, the hydrothermal reaction temperature is 150°C-250°C, and the time is 5h-15h;

[0021] And / or, the solid content of the reaction liquid of the hydrothermal reaction is 15wt%-25wt%;

[0022] And / or, washing comprises water washing and alcohol washing performed sequentially, wherein the water washing agent is water and the alcohol washing agent is anhydrous ethanol;

[0023] And / or, the drying temperature is 50°C-70°C.

[0024] In an optional embodiment, the calcination temperature is 500° C.-900° C., and the calcination time is 4 h-8 h;

[0025] And / or, the heating rate of the calcining step is 1° C. / min-10° C. / min.

[0026] In a third aspect, the present invention provides an electrode active material layer for extracting lithium from salt lakes, comprising the three-dimensional interpenetrating network structure lithium iron phosphate active material described in the aforementioned embodiment.

[0027] In an optional embodiment, the composition further comprises 5wt%-10wt% of a binder, 4wt%-8wt% of a conductive agent, 4wt%-8wt% of a hydrophilic agent, 1wt%-3wt% of a reinforcing agent, and 0wt%-20wt% of a pore-forming agent;

[0028] And / or, in the electrode active material layer, the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material is 70 wt % to 80 wt %.

[0029] In a fourth aspect, the present invention provides an electrode for extracting lithium from salt lakes, comprising a titanium mesh and the electrode active material layer for extracting lithium from salt lakes described in the aforementioned embodiment arranged on at least one side of the titanium mesh.

[0030] In a fifth aspect, the present invention provides a method for preparing an electrode for extracting lithium from a salt lake as described in the aforementioned embodiment, comprising: coating an electrode slurry comprising a three-dimensional interpenetrating network structure of lithium iron phosphate active material on a titanium mesh and then drying the resulting electrode slurry.

[0031] The present invention has the following beneficial effects:

[0032] The three-dimensional interpenetrating network structure lithium iron phosphate active material used in this application for lithium extraction from salt lakes has a three-dimensional interpenetrating network structure on a macroscopic scale. It has a large specific surface area and ultra-high conductivity of the three-dimensional material. The lithium iron phosphate loaded on the three-dimensional material successfully reduces its disordered stacking 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 "microcrack-micropore" composite structure, which greatly improves the Li +The diffusion rate within the electrode plate reduces the degree of charge and discharge polarization, enhances the cycle stability, lithium adsorption capacity and lithium extraction efficiency of the electrode plate during electro-deintercalation and lithium extraction. Therefore, the electrode used for lithium extraction from salt lakes in this application can achieve green and economical recovery of lithium resources from brine. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0034] Figure 1 This is a SEM image of the three-dimensional interpenetrating network structure lithium iron phosphate active material prepared in Example 1;

[0035] Figure 2 This is the XRD pattern of the three-dimensional interpenetrating network structure lithium iron phosphate active material prepared in Example 1;

[0036] Figure 3 2 is a cross-sectional view of the three-dimensional conductive network structure electrode plate prepared in Example 2;

[0037] Figure 4 The normal temperature cycle curve (0.1°C) of Example 1 and Comparative Example 1;

[0038] Figure 5 The charge and discharge curves (0.1C) of Example 2 and Comparative Example 2 are shown. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0040] An embodiment of 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%.

[0041] The three-dimensional interpenetrating network structure lithium iron phosphate active material used in the present application for lithium extraction from salt lakes has a three-dimensional interpenetrating network structure on a macro scale, which has a large specific surface area (45.7m 2 / g or more) and ultra-high conductivity (below 5.1Ω·cm), the lithium iron phosphate loaded on the three-dimensional material successfully reduces its disordered stacking 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 "microcrack-micropore" composite structure, which greatly improves the Li + The diffusion rate within the electrode plate reduces the degree of charge and discharge polarization, enhances the cycle stability, lithium adsorption capacity and lithium extraction efficiency of the electrode plate during electro-deintercalation and lithium extraction. Therefore, the electrode used for lithium extraction from salt lakes in this application can achieve green and economical recovery of lithium resources from brine.

[0042] Specifically, the mass fraction of the three-dimensional material in the 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, the lithium iron phosphate ratio will be too low, 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 detrimental to improving the structural stability and lithium extraction efficiency.

[0043] An embodiment of the present invention further 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 aforementioned embodiment, comprising:

[0044] Liquid preparation: preparing liquid a and liquid b, wherein liquid a comprises ferrous sulfate and a reducing agent, and liquid b comprises lithium hydroxide, phosphoric acid, a dispersant, and a three-dimensional material;

[0045] Precursor preparation: Under a protective atmosphere, liquid b is injected into liquid a, followed by a primary solid-liquid separation, a hydrothermal reaction, a secondary solid-liquid separation, washing, and drying to obtain the precursor;

[0046] Calcination: calcining the precursor under a protective atmosphere to obtain the three-dimensional interpenetrating network structure lithium iron phosphate active material.

[0047] The present invention adopts a hydrothermal method to synthesize lithium iron phosphate in situ and load it on the surface of a three-dimensional material, thereby preparing an active material with a three-dimensional interpenetrating network structure on a macro scale.

[0048] In an optional embodiment, the molar ratio of lithium hydroxide and phosphoric acid in the liquid b to ferrous sulfate in the 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 the excess lithium hydroxide can make up for the lithium loss in the subsequent sintering process, which is beneficial to avoid the capacity decay caused by lithium defects, and lithium hydroxide has alkalinity, which can promote Fe 2+ With PO4 3 - uniform precipitation, avoiding the Fe 2+ Oxidation or incomplete crystallization of lithium iron phosphate.

[0049] In an optional embodiment, the rate of injecting liquid b into liquid a is 15mL / min-25mL / min, such as 15mL / min, 16mL / min, 17mL / min, 18mL / min, 19mL / min, 20mL / min, 21mL / min, 22mL / min, 23mL / min, 24mL / min, 25mL / min. Liquid b is slowly injected into liquid a to make Fe 2+ With PO4 3 -、Li + The reaction is uniform to generate a nano-scale, well-dispersed LiFePO4 precursor, avoiding the rapid precipitation of iron hydroxide to form a precursor with coarse particles and uneven composition.

[0050] In an optional embodiment, the concentration of phosphoric acid in the liquid b is 10 wt%-20 wt%, for example, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%;

[0051] And / or, the concentration of the dispersant is 1 wt%-3 wt%, for example 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%; which is conducive to the dispersion of the three-dimensional material in the liquid;

[0052] and / or, the dispersant is selected from at least one of sodium dodecyl sulfonate, lauryl sulfate and sodium diisopropylnaphthalene sulfonate;

[0053] and / or, the concentration of ferrous sulfate in the liquid a is 5 wt%-10 wt%, for example, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%;

[0054] and / or, the concentration of the reducing agent is 15 wt%-25 wt%, for example, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%;

[0055] And / or, the reducing agent is selected from at least one of sodium bisulfite, sodium sulfite and sodium ascorbate.

[0056] The concentration of each component in liquid a and liquid b needs to be appropriate. Too high a concentration will accelerate the precipitation rate and may form a coarse precursor with uneven composition. Too low a concentration is not conducive to improving production efficiency.

[0057] After the liquid b is injected into the liquid a, a precipitate is generated. After the injection of the liquid b is completed, the reaction liquid can be subjected to solid-liquid separation, and the separated solid is mixed with water to obtain a solid-liquid mixture, which is then placed in a hydrothermal kettle for a hydrothermal reaction.

[0058] In an optional embodiment, the hydrothermal reaction temperature is 150°C-250°C, for example, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 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 sufficient nucleation and growth of crystals to form nano-scale particles with uniform particle size; too high a temperature may lead to the formation of coarse, unevenly composed precursors and may cause lattice distortion of lithium iron phosphate; too low a temperature is not conducive to improving production efficiency.

[0059] In an optional embodiment, the solid content of the reaction liquid of the hydrothermal reaction is 15wt%-25wt%, for example 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%; the crystal growth rate can be moderate; if the solid content is too high, it may lead to the formation of coarse, uneven composition, and more impurity ions; if the solid content is too low, it is not conducive to improving production efficiency.

[0060] In an optional embodiment, washing includes water washing and alcohol washing performed in sequence, the water washing agent is water, and the alcohol washing agent is anhydrous ethanol; water washing mainly removes impurity ions in the lithium iron phosphate precursor, and alcohol washing can remove organic matter therein.

[0061] In an optional embodiment, the drying temperature is 50°C-70°C, for example, 50°C, 52°C, 54°C, 56°C, 58°C, 60°C, 62°C, 64°C, 66°C, 68°C, or 70°C.

[0062] In an optional embodiment, the calcination temperature is 500° C.-900° C., for example, 500° C., 540° C., 580° C., 620° C., 660° C., 700° C., 740° C., 780° C., 820° C., 860° C., 900° C., and the calcination time is 4 h-8 h, for example, 4 h, 4.4 h, 4.8 h, 5.2 h, 5.6 h, 6 h, 6.4 h, 6.8 h, 7.2 h, 7.6 h, 8 h;

[0063] And / or, the heating rate of the calcining step is 1°C / min-10°C / min, for example, 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min.

[0064] Calcination under the above conditions will not affect the three-dimensional material structure, and is conducive to obtaining fine and uniform lithium iron phosphate crystals.

[0065] An embodiment of the present invention further provides an electrode active material layer for extracting lithium from salt lakes, comprising the three-dimensional interpenetrating network structure lithium iron phosphate active material described in the above embodiment.

[0066] In an optional embodiment, the composition further comprises 5wt%-10wt% of a binder, 4wt%-8wt% of a conductive agent, 4wt%-8wt% of a hydrophilic agent, 1wt%-3wt% of a reinforcing agent, and 0wt%-20wt% of a pore-forming agent;

[0067] The mass fraction of the binder in the electrode active material layer is 5 wt%-10 wt%, for example, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, 10 wt%, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyacrylonitrile (PAN);

[0068] The mass fraction of the conductive agent in the electrode active material layer is 4 wt%-8 wt%, for example, 4 wt%, 4.4 wt%, 4.8 wt%, 5.2 wt%, 5.6 wt%, 6 wt%, 6.4 wt%, 6.8 wt%, 7.2 wt%, 7.6 wt%, and 8 wt%; the conductive agent is selected from at least one of conductive carbon (SP), Ketjen black, and acetylene black;

[0069] The mass fraction of the hydrophilic agent in the electrode active material layer is 4 wt%-8 wt%, for example, 4 wt%, 4.4 wt%, 4.8 wt%, 5.2 wt%, 5.6 wt%, 6 wt%, 6.4 wt%, 6.8 wt%, 7.2 wt%, 7.6 wt%, and 8 wt%; the hydrophilic agent is selected from at least one of polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polyethylene glycol (PEG);

[0070] The mass fraction of the reinforcing agent in the electrode active material layer is 1 wt%-3 wt%, for example, 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%; the reinforcing agent is selected from at least one of carbon fiber and graphite fiber;

[0071] 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).

[0072] In an optional embodiment, in the electrode active material layer, the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material is 70wt%-80wt%, for example, 70wt%, 71wt%, 72wt%, 73wt%, 74wt%, 75wt%, 76wt%, 77wt%, 78wt%, 79wt%, 80wt%.

[0073] If the mass fraction of the three-dimensional interpenetrating network structure lithium iron phosphate active material is too high, although the lithium adsorption capacity is improved, the binder / conductive agent content is insufficient, which will lead to poor contact between particles and is not conducive to increasing the lithium ion mobility 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.

[0074] An embodiment of the present invention further provides an electrode for extracting lithium from salt lakes, comprising a titanium mesh and the electrode active material layer for extracting lithium from salt lakes described in the above embodiment arranged on at least one side of the titanium mesh.

[0075] An embodiment of the present invention also provides a method for preparing an electrode for lithium extraction from a salt lake as described in the aforementioned embodiment, comprising: coating an electrode slurry comprising a three-dimensional interpenetrating network structure of lithium iron phosphate active material on a titanium mesh and then drying the resulting electrode slurry, wherein the coating method is selected from one of blade coating, dip coating, and extrusion coating.

[0076] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0077] Example 1

[0078] This embodiment provides a method for preparing an electrode for extracting lithium from a salt lake, comprising the following steps:

[0079] Liquid a comprising ferrous sulfate and sodium ascorbate and liquid b comprising lithium hydroxide, phosphoric acid, sodium lauryl sulfate and carbon nanotubes were prepared, wherein the concentration of ferrous sulfate (FeSO4) in liquid a was 8 wt%, and the concentration of sodium ascorbate (C6H7O6Na) was 20 wt%; the concentration of sodium lauryl sulfate (C6H7O6Na) in liquid b was 20 wt%. 12 H 25 SO4Na) concentration is 2.5wt%, the molar ratio of lithium hydroxide and phosphoric acid in the liquid b to ferrous sulfate in the 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 solid-liquid separation, the precipitate is separated, water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20wt%, a hydrothermal reaction is performed, followed by a secondary solid-liquid separation, and then washed with deionized water and anhydrous ethanol in sequence, and dried to obtain a precursor; the hydrothermal reaction temperature is 200°C, the time is 10h, and the drying temperature is 60°C;

[0080] The obtained precursor was calcined in N2 atmosphere to obtain a three-dimensional interpenetrating network structure lithium iron phosphate active material, as shown in the SEM image. Figure 1 As shown, the XRD pattern is Figure 2 As shown, the calcination temperature is 700° C., the calcination time is 6 h, the heating rate of the calcination step is 5° C. / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material is 52 wt %.

[0081] 80wt% of three-dimensional interpenetrating network structure lithium iron phosphate active material, 5wt% of PVDF, 8wt% of SP, 4wt% of PEG and 3wt% of carbon fiber are uniformly dispersed in NMP to obtain LFP electrode slurry; the LFP slurry is coated on a titanium mesh by doctor blade coating, and after drying, a three-dimensional conductive network structure electrode plate is obtained, as shown in the cross-sectional view. Figure 3 shown.

[0082] Example 2

[0083] This embodiment provides a method for preparing an electrode for extracting lithium from a salt lake, comprising the following steps:

[0084] Liquid a comprising ferrous sulfate and sodium ascorbate and liquid b comprising lithium hydroxide, phosphoric acid, sodium lauryl sulfate and carbon nanotubes were prepared, wherein the concentration of ferrous sulfate (FeSO4) in liquid a was 8 wt%, and the concentration of sodium ascorbate (C6H7O6Na) was 20 wt%; the concentration of sodium lauryl sulfate (C6H7O6Na) in liquid b was 20 wt%. 12 H 25 SO4Na) concentration is 2.5wt%, the molar ratio of lithium hydroxide and phosphoric acid in the liquid b to ferrous sulfate in the 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 solid-liquid separation, the precipitate is separated, water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20wt%, a hydrothermal reaction is performed, followed by a secondary solid-liquid separation, and then washed with deionized water and anhydrous ethanol in sequence, and dried to obtain a precursor; the hydrothermal reaction temperature is 200°C, the time is 10h, and the drying temperature is 60°C;

[0085] 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°C, the calcination time was 6 h, the heating rate of the calcination step was 5°C / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material was 52 wt%.

[0086] The three-dimensional interpenetrating network structure lithium iron phosphate active material 71.2wt%, PVDF 4.4wt%, SP 7.1wt%, PEG 3.6wt%, carbon fiber 2.7wt%, sodium chloride 8.9wt% and ammonium bicarbonate 2.2wt% were uniformly dispersed in NMP to obtain LFP electrode slurry; the LFP slurry was coated on a titanium mesh by doctor blade coating and dried to obtain a three-dimensional conductive network structure electrode plate.

[0087] Example 3

[0088] This embodiment provides a method for preparing an electrode for extracting lithium from a salt lake, comprising the following steps:

[0089] Liquid a comprising ferrous sulfate and sodium ascorbate and liquid b comprising lithium hydroxide, phosphoric acid, sodium lauryl sulfate and carbon nanotubes were prepared, wherein the concentration of ferrous sulfate (FeSO4) in liquid a was 5 wt%, and the concentration of sodium ascorbate (C6H7O6Na) was 15 wt%; the concentration of sodium lauryl sulfate (C6H7O6Na) in liquid b was 15 wt%. 12 H 25SO4Na) concentration is 1wt%, the molar ratio of lithium hydroxide and phosphoric acid in the liquid b to ferrous sulfate in the 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 solid-liquid separation, the precipitate is separated, water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20wt%, a hydrothermal reaction is performed, followed by a secondary solid-liquid separation, and then washed with deionized water and anhydrous ethanol in sequence, and dried to obtain a precursor; the hydrothermal reaction temperature is 150°C, the time is 15h, and the drying temperature is 70°C;

[0090] 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°C, the calcination time was 4 hours, the heating rate of the calcination step was 10°C / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material was 55wt%.

[0091] 80wt% of three-dimensional interpenetrating network structure lithium iron phosphate active material, 5wt% of PVDF, 8wt% of SP, 4wt% of PEG and 3wt% of carbon fiber are uniformly dispersed in NMP to obtain LFP electrode slurry; the LFP slurry is coated on a titanium mesh by doctor blade coating and dried to obtain a three-dimensional conductive network structure electrode plate.

[0092] Example 4

[0093] This embodiment provides a method for preparing an electrode for extracting lithium from a salt lake, comprising the following steps:

[0094] Liquid a comprising ferrous sulfate and sodium ascorbate and liquid b comprising lithium hydroxide, phosphoric acid, sodium lauryl sulfate and carbon nanotubes were prepared, wherein the concentration of ferrous sulfate (FeSO4) in liquid a was 10 wt%, and the concentration of sodium ascorbate (C6H7O6Na) was 25 wt%; the concentration of sodium lauryl sulfate (C6H7O6Na) in liquid b was 10 wt%. 12 H 25 SO4Na) concentration is 3wt%, and the molar ratio of lithium hydroxide and phosphoric acid in the liquid b to ferrous sulfate in the 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 solid-liquid separation, the precipitate is separated, water is added to the precipitate to obtain a solid-liquid mixture with a solid content of 20wt%, a hydrothermal reaction is performed, followed by a secondary solid-liquid separation, and then washed with deionized water and anhydrous ethanol in sequence, and dried to obtain a precursor; the hydrothermal reaction temperature is 250°C, the time is 5h, and the drying temperature is 50°C;

[0095] 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°C, the calcination time was 8 hours, the heating rate of the calcination step was 1°C / min, and the mass fraction of the three-dimensional material in the three-dimensional interpenetrating network structure lithium iron phosphate active material was 50wt%.

[0096] 80wt% of three-dimensional interpenetrating network structure lithium iron phosphate active material, 5wt% of PVDF, 8wt% of SP, 4wt% of PEG and 3wt% of carbon fiber are uniformly dispersed in NMP to obtain LFP electrode slurry; the LFP slurry is coated on a titanium mesh by doctor blade coating and dried to obtain a three-dimensional conductive network structure electrode plate.

[0097] Example 5

[0098] 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 by graphene of equal mass.

[0099] Example 6

[0100] 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 by hollow carbon fibers of equal mass.

[0101] Comparative Example 1

[0102] This comparative example provides a method for preparing an electrode for extracting lithium from a salt lake. The only difference from Example 1 is that no three-dimensional material is added to liquid b.

[0103] Comparative Example 2

[0104] The only difference from Example 2 is that no three-dimensional material is added to liquid b.

[0105] Comparative Example 3

[0106] 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 as high as 60 wt %, and the mass ratios of other components remain unchanged.

[0107] Comparative Example 4

[0108] 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 as low as 40 wt %, and the mass ratios of the other components remain unchanged.

[0109] Comparative Example 5

[0110] 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 plate is as low as 65wt%, and the mass ratios of other components remain unchanged.

[0111] Comparative Example 6

[0112] 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 plate is too high, namely 85wt%, and the mass ratios of other components remain unchanged.

[0113] The lithium extraction plate prepared in the above embodiments and comparative examples was used as the positive electrode, and the negative electrode was assembled into an electrochemical deintercalation device using the lithium extraction plate and an anion exchange membrane after delithiation by chemical oxidation. The electrochemical deintercalation and lithium extraction and electrochemical performance tests were performed using a blue battery test system. The test method and conditions are as follows:

[0114] Lithium extraction specific capacity: At 25°C, the lithium extraction device extracts lithium 10 times at 0.1C (5 charge and discharge cycles), and the average value of the 10 charge + discharge specific capacities is calculated.

[0115] Cycling performance: The ratio of the 600th specific capacity to the 1st specific capacity after the lithium extraction device extracts lithium 600 times (300 charge and discharge cycles) at 0.1C at 25°C.

[0116] Lithium extraction efficiency: The ratio of the second specific capacity to the first specific capacity after the lithium extraction device extracts lithium twice (one charge and discharge cycle) at 0.1C at 25°C.

[0117] Lithium extraction amount (Q): The electrochemical deintercalation device is charged once to extract lithium, Q = [(C0V0-C1V1)*1000] / M0; where C0 is the lithium concentration in the initial brine (g / L), C1 is the lithium concentration in the brine at the end of lithium extraction (g / L); V0 is the initial brine volume (L), V1 is the brine volume at the end of lithium extraction (L); M0 is the mass of the three-dimensional interpenetrating network structure lithium iron phosphate (LiFePO4) active material in the lithium extraction electrode.

[0118] The test results are shown in Table 1, wherein the normal temperature cycle curves (0.1C) of Example 1 and Comparative Example 1 are shown in Table 1. Figure 4 As shown, the charge and discharge curves (0.1C) of Example 2 and Comparative Example 2 are as follows Figure 5 shown.

[0119] Table 1

[0120]

[0121] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes, characterized in that: It includes 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%.

2. A method for preparing a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes according to claim 1, characterized in that: include: Prepare liquid: 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, followed by a primary solid-liquid separation, a hydrothermal reaction, a secondary solid-liquid separation, washing, and drying to obtain the precursor; Calcination: calcining the precursor under a protective atmosphere to obtain the three-dimensional interpenetrating network structure lithium iron phosphate active material.

3. The method for preparing a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes according to claim 2, characterized in that: The molar ratio of lithium hydroxide and phosphoric acid in the liquid b to ferrous sulfate in the liquid a is (2-4):(0.9-1.1):1; And / or, the rate of injection of liquid b into liquid a is 15 mL / min-25 mL / min.

4. The method for preparing a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes according to claim 2, characterized in that: The concentration of phosphoric acid in the liquid b is 10wt%-20wt%; and / or, the concentration of the dispersant is 1 wt%-3 wt%; 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 the 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 method for preparing a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes according to claim 2, characterized in that: The hydrothermal reaction temperature is 150°C-250°C and the time is 5h-15h; And / or, the solid content of the reaction liquid of the hydrothermal reaction is 15wt%-25wt%; And / or, washing comprises water washing and alcohol washing performed sequentially, wherein the water washing agent is water and the alcohol washing agent is anhydrous ethanol; And / or, the drying temperature is 50°C-70°C.

6. The method for preparing a three-dimensional interpenetrating network structure lithium iron phosphate active material for lithium extraction from salt lakes according to claim 2, characterized in that: The calcination temperature is 500-900°C, and the calcination time is 4-8 hours; And / or, the heating rate of the calcining step is 1° C. / min-10° C. / min.

7. An electrode active material layer for extracting lithium from salt lakes, characterized in that: The invention comprises the three-dimensional interpenetrating network structure lithium iron phosphate active material according to claim 1.

8. The electrode active material layer for extracting lithium from salt lakes according to claim 7, characterized in that: The invention also comprises 5wt%-10wt% of a binder, 4wt%-8wt% of a conductive agent, 4wt%-8wt% of a hydrophilic agent, 1wt%-3wt% of a reinforcing agent and 0wt%-20wt% of a 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 70 wt % to 80 wt %.

9. An electrode for extracting lithium from salt lakes, characterized in that: The invention comprises a titanium mesh and an electrode active material layer for extracting lithium from a salt lake according to claim 7 or 8, which is arranged on at least one side of the titanium mesh.

10. A method for preparing an electrode for extracting lithium from a salt lake according to claim 9, characterized in that: include: The electrode slurry including lithium iron phosphate active material with a three-dimensional interpenetrating network structure is coated on a titanium mesh and then dried.

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