Electrode Material for Lithium Extraction from Salt Lakes by Electrochemical Intercalation / Deintercalation Method, Preparation Method Thereof and Application Thereof

Abstract

The present application discloses an electrode material for extracting lithium from salt lakes by an electrochemical insertion / extraction method, a preparation method thereof, and an application thereof. The electrode material includes a core and a shell layer coated on the surface of the core. The core includes lithium iron phosphate, and the shell layer includes vanadium dioxide. By coating vanadium dioxide on the surface of the lithium iron phosphate material in the present application, after performing the lithium extraction operation, the electrolyte is heated to 68 - 90 °C and then the de-lithiation step is carried out, which can improve the conductivity of the electrode, increase its current density, so that the embedded lithium ions are accelerated to escape into the electrolyte, and the lithium extraction efficiency is improved.

Description

Technical Field

[0001] The present application relates to the technical field of electrode materials, and more specifically, to an electrode material for extracting lithium from salt lakes by an electrochemical deintercalation method, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium is an important strategic metal and is widely used in many fields such as energy, chemical industry, electronics, metallurgy, and medicine, and is known as the "new energy metal of the 21st century". In recent years, with the rapid development of the new energy vehicle field and the energy storage industry, the demand for lithium has increased sharply. At present, lithium extraction from ores and salt lakes is the main source. Among them, the lithium resource reserves in salt lake brines account for 65% of the global total. Most of the lithium raw materials required for the production of global lithium salt products come from salt lakes, and with the development of high-quality salt lake resources, the quality of salt lakes has decreased year by year. Salt lake lithium resources in plateau areas (such as the Qinghai-Tibet Plateau) are rich, but most are high-magnesium-to-lithium ratio salt lakes, and the utilization of lithium resources is relatively difficult. Due to the redox properties of transition metals and the reversible cyclic deintercalation characteristics of lithium in lithium-ion battery materials, and their strong adaptability to salt lakes, they are increasingly used for lithium extraction from salt lakes. Therefore, in order to achieve the green and efficient extraction of lithium in salt lake brines, it is particularly necessary to develop an electrode material with excellent conductivity to improve the lithium extraction efficiency.

[0003] In view of this, the present application is specifically proposed. Summary of the Invention

[0004] The purpose of the present application is to provide an electrode material for extracting lithium from salt lakes by an electrochemical deintercalation method, a preparation method thereof, and an application thereof, to overcome the problem of low de-lithiation efficiency when the existing lithium iron phosphate electrode material is applied to lithium extraction from salt lakes.

[0005] The present application is implemented as follows:

[0006] In a first aspect, the present application provides an electrode material, including a core and a shell layer coated on the surface of the core, the core includes lithium iron phosphate, and the shell layer includes vanadium dioxide.

[0007] In an optional embodiment, the content of vanadium dioxide is 0.5 wt% - 3 wt%.

[0008] In an optional embodiment, the shell layer further includes carbon, and the mass ratio of vanadium dioxide to carbon is 1:2.1 - 5.5.

[0009] In an optional embodiment, the particle size of the electrode material is 100 - 800 nm.

[0010] In an optional embodiment, the thickness of the shell layer is 1 - 10 nm.

[0011] Second aspect, the present application provides a method for preparing the electrode material described in the foregoing embodiments, including coating a shell layer containing vanadium dioxide on the surface of lithium iron phosphate.

[0012] In an optional embodiment, it includes calcining a mixture of lithium iron phosphate, vanadium pentoxide, and a carbon source to obtain a lithium iron phosphate material with a vanadium dioxide-coated surface.

[0013] In an optional embodiment, the calcination is carried out in an inert gas atmosphere.

[0014] In an optional embodiment, the carbon source is at least one of elemental carbon or organic carbon.

[0015] In an optional embodiment, the carbon source is graphene.

[0016] In an optional embodiment, the calcination time is 4 - 6 h, and after calcination, it is kept warm for 1.5 - 2.5 h.

[0017] In an optional embodiment, the calcination temperature is 700 - 800 °C.

[0018] Third aspect, the present application provides an electrode, including a conductive agent, a binder, and the electrode material described in any one of the foregoing embodiments.

[0019] In an optional embodiment, the mass ratio of the conductive agent, the binder, and the electrode material is 0.5 - 1.5:0.5 - 1.5:8.

[0020] In an optional embodiment, the conductive agent is at least one of acetylene black, conductive carbon black, graphene, and carbon nanotubes.

[0021] In an optional embodiment, the binder is at least one of polyvinylidene fluoride and polytetrafluoroethylene.

[0022] Fourth aspect, the present application provides a method for preparing an electrode, including coating a slurry containing a conductive agent, a binder, and the electrode material described in any one of the foregoing embodiments on a current collector, and drying to obtain a lithium iron phosphate electrode.

[0023] In an optional embodiment, a solvent, a conductive agent, a binder, and the electrode material are mixed, ground, and slurried, then coated on a current collector and vacuum dried to obtain a lithium iron phosphate electrode.

[0024] In an optional embodiment, using the lithium iron phosphate electrode as the anode, nickel foam as the cathode, and NaCl as the supporting electrolyte, deintercalation of lithium is carried out by electrolysis to obtain a lithium-deficient lithium iron phosphate electrode.

[0025] Fifth aspect, the present application provides an application of the electrode described in the foregoing embodiments in lithium extraction from brine.

[0026] In a sixth aspect, the present application provides an electrochemical lithium extraction device with the electrode described in the foregoing embodiment, including:

[0027] An electrode, including the lithium-deficient lithium iron phosphate electrode described in the foregoing embodiment as a cathode electrode, and / or the lithium iron phosphate electrode described in the foregoing embodiment as an anode electrode;

[0028] An anode chamber for containing a lithium-depleted electrolyte;

[0029] A cathode chamber for containing a lithium-rich electrolyte;

[0030] An anion membrane: used to separate the anode chamber and the cathode chamber.

[0031] In a seventh aspect, the present application provides an electrochemical lithium extraction method, including lithium extraction and / or de-lithiation:

[0032] For lithium extraction, a voltage is applied between the cathode and the anode of the electrochemical lithium extraction device described in the foregoing embodiment, so that lithium ions in the brine are embedded into the lithium-deficient lithium iron phosphate electrode;

[0033] And / or for de-lithiation, a voltage is applied between the cathode and the anode of the electrochemical lithium extraction device described in the foregoing embodiment and the lithium-depleted electrolyte is heated to 68 - 90 °C, so that the embedded lithium ions in the lithium iron phosphate electrode are removed.

[0034] The present application has the following beneficial effects:

[0035] The present application utilizes the property that vanadium dioxide is an excellent electrical conductor when the temperature is greater than 68 °C. By coating vanadium dioxide on the surface of the lithium iron phosphate material, after the lithium extraction operation, the electrolyte is heated to above 68 °C and then the de-lithiation step is carried out, which can improve the electrode conductivity, increase its current density, so that the embedded lithium ions are accelerated to escape into the electrolyte, thereby improving the lithium extraction efficiency. Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required to be used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0037] Figure 1 For the change in the Li + concentration in the anode solution during desorption in Experimental Example 1, Experimental Example 8, and Comparative Experimental Example 1. Detailed Embodiments

[0038] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be described clearly and completely below. For those not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments without indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0039] Some embodiments of this application provide an electrode material, including a core and a shell layer coated on the surface of the core. The core includes lithium iron phosphate, and the shell layer includes vanadium dioxide.

[0040] The method of this application coats vanadium dioxide on the surface of the lithium iron phosphate material. After performing a conventional lithium extraction operation, the electrolyte is heated to above 68 °C and then the delithiation step is carried out, which can improve the electrode conductivity, increase its current density, so that the embedded lithium ions are accelerated to escape into the electrolyte, and the lithium extraction efficiency is improved.

[0041] In some alternative embodiments, the content of vanadium dioxide is 0.5 wt% - 3 wt%, specifically it can be 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, or any value within 0.5 wt% - 3 wt%. Although vanadium dioxide has excellent conductivity above 68 °C, since its conductivity is poor at lower temperatures, its content should not be added too much.

[0042] In some alternative embodiments, the shell layer further includes carbon, and the mass ratio of vanadium dioxide to carbon is 1:2.1 - 5.5, specifically it can be 1:2.1, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, or any value within 1:2.1 - 5.5. Although vanadium dioxide has excellent conductivity above 68 °C, since its conductivity is poor at lower temperatures, carbon can also be included in the coating layer to improve the conductivity of the shell layer, especially the conductivity at lower temperatures.

[0043] In some alternative embodiments, the particle size of the electrode material is 100 - 800 nm.

[0044] In some alternative embodiments, the thickness of the shell layer is 1 - 10 nm. If the shell layer thickness is too small, the vanadium dioxide coating amount is relatively low, and the improvement of the conductive performance is limited; if the shell layer thickness is too large, the lithium ion insertion / extraction path is too long, which may increase the difficulty of lithium ion insertion / extraction.

[0045] Another embodiment of this application provides a preparation method of the electrode material described in the foregoing embodiment, including coating a shell layer containing vanadium dioxide on the surface of lithium iron phosphate.

[0046] In some optional embodiments, a mixture of lithium iron phosphate, vanadium pentoxide and a carbon source is calcined to obtain a lithium iron phosphate material with vanadium dioxide coated on the surface.

[0047] Since vanadium dioxide has a high melting point and needs to be melted at nearly two thousand degrees Celsius, it is difficult to calcine. Therefore, in this application, vanadium dioxide is not directly used to coat the lithium iron phosphate. Instead, vanadium pentoxide and a carbon source are used as raw materials, and carbon is used to reduce the vanadium pentoxide to vanadium dioxide at a higher temperature and generate carbon oxides.

[0048] Among them, lithium iron phosphate can be prepared in a conventional manner, for example, by a solid phase method, a liquid phase method, etc., wherein a phosphorus source, an iron source, a lithium source and a carbon source are uniformly mixed in proportion, the mixture slurry is placed in a blast furnace to dry, and then calcined under the protection of an inert gas.

[0049] The mixing in this embodiment can be a conventional mixing method, such as ball milling, or some special methods, such as using a solvent to prepare a suspension, so that the lithium iron phosphate, vanadium pentoxide and carbon source are mixed more fully.

[0050] In some optional embodiments, the calcination is performed under an inert gas atmosphere to prevent the material from being oxidized.

[0051] In some optional embodiments, the carbon source is at least one of elemental carbon or organic carbon, for example, graphite, graphene, glucose, etc., preferably graphene.

[0052] In some optional embodiments, the calcination temperature is 700-800°C, specifically 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, or any value between 700 and 800°C. If the calcination temperature is too high, it may cause problems such as structural collapse.

[0053] In some optional embodiments, the calcination time is 4-6 hours, specifically 4 hours, 5 hours, 6 hours or any value in the range of 4-6 hours, preferably 5 hours, and the heat preservation after calcination is 1.5-2.5 hours, preferably 2 hours. If the calcination time is too long, problems such as structural collapse may occur, and heat preservation is conducive to the stability of the material structure.

[0054] Another embodiment of the present application provides an electrode, comprising a conductive agent, a binder, and the electrode material described in any one of the aforementioned embodiments.

[0055] In some embodiments, the mass ratio of the conductive agent, the binder and the electrode material is 0.5-1.5:0.5-1.5:8, preferably 1:1:8.

[0056] In some embodiments, the conductive agent is at least one of acetylene black, conductive carbon black, graphene, and carbon nanotubes;

[0057] In some embodiments, the binder is at least one of polyvinylidene fluoride and polytetrafluoroethylene.

[0058] Another embodiment of the present application provides a method for preparing an electrode, which includes coating a slurry containing a conductive agent, a binder, and the electrode material according to any one of the foregoing embodiments on a current collector, and drying to obtain a lithium iron phosphate electrode.

[0059] In some alternative embodiments, a solvent, a conductive agent, a binder, and the electrode material are mixed, ground, and slurried, then coated on a current collector, and vacuum dried to obtain a lithium iron phosphate electrode embodiment, wherein the solvent can be N-methylpyrrolidone.

[0060] In some alternative embodiments, using the lithium iron phosphate electrode as the anode, nickel foam as the cathode, and NaCl as the supporting electrolyte, lithium is removed by electrolysis to obtain a lithium-deficient lithium iron phosphate electrode. Specifically, a DC voltage of 1.0 V can be applied between the cathode and the anode for electrolytic lithium removal.

[0061] Another embodiment of the present application provides an application of the electrode material or electrode according to the foregoing embodiments in lithium extraction from brine.

[0062] Another embodiment of the present application provides an electrochemical lithium extraction device with the electrode according to the foregoing embodiments, including:

[0063] An electrode, including the lithium-deficient lithium iron phosphate electrode according to the foregoing embodiments as the cathode electrode, and / or the lithium iron phosphate electrode according to the foregoing embodiments as the anode electrode;

[0064] An anode chamber for accommodating a lithium-deficient electrolyte;

[0065] A cathode chamber for accommodating a lithium-rich electrolyte;

[0066] An anion membrane: used to separate the anode chamber and the cathode chamber.

[0067] Another embodiment of the present application provides an electrochemical lithium extraction method, including lithium extraction and lithium removal;

[0068] Lithium extraction: applying a voltage between the cathode and the anode of the electrochemical lithium extraction device according to the foregoing embodiments to embed lithium ions in the brine into the lithium-deficient lithium iron phosphate electrode;

[0069] Lithium removal: applying a voltage between the cathode and the anode of the electrochemical lithium extraction device according to the foregoing embodiments and heating the lithium-deficient electrolyte to above 68 °C to remove the embedded lithium ions from the lithium iron phosphate electrode.

[0070] When the temperature of the lithium - poor electrolyte is too low, it cannot quickly heat the electrode to above 68 °C, and the conductivity of the electrode is poor. However, when the temperature is too high, it may affect the stability of the electrode structure and has high requirements for the materials used in the silver ion membrane, cathode chamber, and anode chamber. Therefore, the temperature of the lithium - poor electrolyte should not be higher than 90 °C.

[0071] The features and properties of the present application will be further described in detail below in conjunction with the embodiments.

[0072] Example 1:

[0073] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0074] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying. After crushing and grinding, sinter it under nitrogen protection, calcine it at 700 °C for 10 h, and keep the temperature for 6 h. After the sintered material is crushed and sieved, add 3.28 g of vanadium pentoxide and 7.18 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 750 °C for 5 h, and keep the temperature for 2 h.

[0075] Example 2:

[0076] Compared with Example 1, the content of the coated vanadium dioxide is 0.5 wt%.

[0077] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0078] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying. After crushing and grinding, sinter it under nitrogen protection, calcine it at 700 °C for 10 h, and keep the temperature for 6 h. After the sintered material is crushed and sieved, add 1.07 g of vanadium pentoxide and 7.18 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 750 °C for 5 h, and keep the temperature for 2 h.

[0079] Example 3:

[0080] Compared with Example 1, the content of the coated vanadium dioxide is 3 wt%.

[0081] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0082] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying. After pulverizing and grinding, sinter it under nitrogen protection at 700 °C for 10 h with a heat preservation time of 6 h. After pulverizing and sieving the sintered material, add 6.38 g of vanadium pentoxide and 7.18 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 750 °C for 5 h with a heat preservation time of 2 h.

[0083] Example 4:

[0084] Compared with Example 1, the mass ratio of vanadium pentoxide to carbon is 1:2.

[0085] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0086] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying. After pulverizing and grinding, sinter it under nitrogen protection at 700 °C for 10 h with a heat preservation time of 6 h. After pulverizing and sieving the sintered material, add 3.28 g of vanadium pentoxide and 6.56 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 750 °C for 5 h with a heat preservation time of 2 h.

[0087] Example 5:

[0088] Compared with Example 1, the mass ratio of vanadium pentoxide to carbon is 1:5.

[0089] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0090] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying. After pulverizing and grinding, sinter it under nitrogen protection at 700 °C for 10 h with a heat preservation time of 6 h. After pulverizing and sieving the sintered material, add 3.28 g of vanadium pentoxide and 16.4 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 750 °C for 5 h with a heat preservation time of 2 h.

[0091] Example 6:

[0092] Compared with Example 1, the calcination temperature is 700 °C.

[0093] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0094] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying. After pulverizing and grinding, sinter it under nitrogen protection at 700 °C for 10 h with a heat preservation time of 6 h. After pulverizing and sieving the sintered material, add 3.28 g of vanadium pentoxide and 6.56 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 700 °C for 5 h with a heat preservation time of 2 h.

[0095] Example 7:

[0096] Compared with Example 1, the calcination temperature is 800 °C.

[0097] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0098] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying. After pulverizing and grinding, sinter it under nitrogen protection at 800 °C for 5 h with a heat preservation time of 2 h. After pulverizing and sieving the sintered material, add 3.28 g of vanadium pentoxide and 6.56 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 800 °C for 5 h with a heat preservation time of 2 h.

[0099] Comparative Example 1:

[0100] Compared with Example 1, there is no coating of vanadium dioxide.

[0101] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose and mix them by grinding. Place the mixture slurry in a blast furnace for drying, and then after pulverizing and grinding, sinter it under inert gas protection at 700 °C for 12 h with a heat preservation time of 10 h. After pulverizing and sieving the sintered material, add 7.18 g of graphene and mix them evenly. Place it in a tubular furnace, introduce nitrogen, and calcine it at 650 °C for 8 h with a heat preservation time of 2 h.

[0102] Comparative Example 2:

[0103] Compared with Example 1, the content of the coated vanadium dioxide is 0.1 wt%.

[0104] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0105] Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, and mix and grind them. Place the mixture slurry in a blast furnace for drying. After pulverization and grinding, sinter it under nitrogen protection, calcine it at 700 °C for 10 h, and keep the temperature for 6 h. After pulverizing and sieving the sintered material, add 0.22 g of vanadium pentoxide and 7.18 g of graphene, mix them evenly, place them in a tube furnace, introduce nitrogen, and calcine at 750 °C for 5 h, and keep the temperature for 2 h.

[0106] Comparative Example 3:

[0107] Compared with Example 1, the content of vanadium dioxide coating is 5 wt%.

[0108] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0109] Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, and mix and grind them. Place the mixture slurry in a blast furnace for drying. After pulverization and grinding, sinter it under nitrogen protection, calcine it at 700 °C for 10 h, and keep the temperature for 6 h. After pulverizing and sieving the sintered material, add 10.7 g of vanadium pentoxide and 7.18 g of graphene, mix them evenly, place them in a tube furnace, introduce nitrogen, and calcine at 750 °C for 5 h, and keep the temperature for 2 h.

[0110] Comparative Example 4:

[0111] Compared with Example 1, the mass ratio of vanadium pentoxide to carbon is 1:1.

[0112] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0113] Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, and mix and grind them. Place the mixture slurry in a blast furnace for drying. After pulverization and grinding, sinter it under nitrogen protection, calcine it at 700 °C for 10 h, and keep the temperature for 6 h. After pulverizing and sieving the sintered material, add 3.28 g of vanadium pentoxide and 3.28 g of graphene, mix them evenly, place them in a tube furnace, introduce nitrogen, and calcine at 750 °C for 5 h, and keep the temperature for 2 h.

[0114] Comparative Example 5:

[0115] Compared with Example 1, the mass ratio of vanadium pentoxide to carbon is 1:8.

[0116] A preparation method of a lithium iron phosphate electrode material coated with vanadium dioxide includes the following steps:

[0117] Weigh 151.85 g of ferrous phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, and mix and grind them. Place the mixture slurry in a blast furnace for drying. After pulverizing and grinding, sinter it under nitrogen protection, calcine it at 700 °C for 10 h, and keep the temperature for 6 h. After pulverizing and sieving the sintered material, add 3.28 g of vanadium pentoxide and 26.24 g of graphene, mix them evenly, place them in a tubular furnace, introduce nitrogen, and calcine at 750 °C for 5 h, and keep the temperature for 2 h.

[0118] Experimental example:

[0119] Mix the lithium iron phosphate materials, PVDF, and conductive carbon black obtained in the above Examples 1-7 and Comparative Examples 1-5 in a mass ratio of 8:1:1, and use N-methylpyrrolidone as the solvent. After fully grinding and adjusting the slurry, uniformly coat it on the current collector (the slurry coating area is 1 cm × 1 cm), and then dry it in a vacuum drying oven at 90 °C for 12 h. Use the prepared lithium iron phosphate electrode as the anode, nickel foam as the cathode, and 1.0 mol / L NaCl as the supporting electrolyte, and electrolytically delithiate at a DC voltage of 1.0 V until the current is lower than 2 mA / g to obtain the under-lithiated electrode material.

[0120] Use simulated brine as the source liquid (the composition is shown in Table 1), use the above material as the positive electrode, a carbon rod as the negative electrode, and perform one adsorption with a voltage range of 1.0 V between the two electrodes. Subsequently, heat the electrolyte to 80 °C, place the lithium iron phosphate electrode saturated with adsorption in the anode chamber of the electrolysis device, and apply a constant current of 1.0 V for one desorption.

[0121] Comparative experimental example:

[0122] Compared with the experimental example, the electrolyte is not heated during delithiation.

[0123] The brine composition before and after treatment in Experimental Example 1, Experimental Example 8 (the experimental example corresponding to Comparative Example 1), and Comparative Experimental Example 1 is shown in Table 1, and the change in the Li + concentration during desorption is as Figure 1 , and the content of the embedded elements in the electrode at 0 h of desorption and the lithium concentration in the anode liquid at 4 h of desorption in each experimental example and comparative experimental example are shown in Table 2.

[0124] Table 1 Brine composition before and after treatment

[0125]

[0126] Table 2 Content of embedded elements in the electrode at 0 h of desorption and lithium concentration in the anode liquid at 4 h of desorption

[0127]

[0128]

[0129] From the above experimental data, it can be seen that the lithium concentration in the anolyte of the experimental examples of Examples 1-7 is higher than that of the experimental examples of Comparative Examples 1-5. This is because the vanadium dioxide coating layer within a specific content range in the experimental examples can generate high conductivity at temperatures above 68 °C, thereby enabling rapid desorption of lithium ions. The sodium ion content in Examples 1-3 is lower than that in Comparative Example 1 because the current during adsorption in Examples 1-3 is smaller, resulting in a lower adsorbed sodium ion content. Compared with Experimental Example 8, Experimental Example 1 has a reduced efficiency of absorbing lithium ions, but at the same time, it also reduces the adsorption of impurity ions.

[0130] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

[0131] Industrial Applicability

[0132] The inventor utilizes the property that vanadium dioxide is an excellent electrical conductor at temperatures above 68 °C. By coating vanadium dioxide on the surface of the lithium iron phosphate material, after the lithium extraction operation, the electrolyte is heated to above 68 °C and then the delithiation step is carried out, which can improve the electrode conductivity, increase its current density, thereby accelerating the extraction of the embedded lithium ions into the electrolyte and enhancing the lithium extraction efficiency.

[0133] In order to overcome the problem of poor conductivity of vanadium dioxide at lower temperatures, carbon is introduced into the coating layer to improve the conductivity of the shell layer, especially at lower temperatures. Moreover, during the preparation of the coating layer, the carbon source can also act as a reducing agent to reduce vanadium pentoxide to vanadium dioxide, overcoming the problem that the melting point of vanadium dioxide is too high and it is difficult to melt and coat on the core, greatly reducing the difficulty and cost of industrial application.

Claims

1. Application of an electrode material in electrochemical lithium extraction, Characterized in that, The electrode material includes a core and a shell layer coated on the surface of the core. The core includes lithium iron phosphate, and the shell layer includes vanadium dioxide; The content of vanadium dioxide is 0.5wt% - 3wt%; Electrochemical lithium extraction includes lithium extraction and de-lithiation: Lithium extraction: Apply a voltage between the cathode and anode of the electrochemical lithium extraction device to embed lithium ions in the brine into the lithium-deficient lithium iron phosphate electrode; De-lithiation: Apply a voltage between the cathode and anode of the electrochemical lithium extraction device and heat the lithium-deficient electrolyte to above 68°C to extract the embedded lithium ions from the lithium iron phosphate electrode.

2. Application of the electrode material according to claim 1 in electrochemical lithium extraction, Characterized in that, The shell layer also includes carbon, and the mass ratio of vanadium dioxide to carbon is 1:2 - 5.

5.

3. Application of the electrode material according to claim 1 in electrochemical lithium extraction, Characterized in that, The particle size of the electrode material is 100 - 800nm.

4. Application of the electrode material according to claim 1 in electrochemical lithium extraction, Characterized in that, The thickness of the shell layer is 1 - 10nm.

5. Application of the electrode material according to claim 1 in electrochemical lithium extraction, Characterized in that, The preparation method of the electrode material includes coating a shell layer containing vanadium dioxide on the surface of lithium iron phosphate.

6. Application of the electrode material according to claim 5 in electrochemical lithium extraction, Characterized in that, The preparation method of the electrode material includes calcining a mixture of lithium iron phosphate, vanadium pentoxide and a carbon source to obtain a lithium iron phosphate material with a vanadium dioxide-coated surface.

7. Application of the electrode material according to claim 6 in electrochemical lithium extraction, Characterized in that, The carbon source is at least one of elemental carbon or organic carbon.

8. Application of the electrode material according to claim 6 in electrochemical lithium extraction, Characterized in that, The carbon source is graphene.

9. Application of the electrode material according to claim 6 in electrochemical lithium extraction, Characterized in that, The calcination step is carried out in an inert gas atmosphere.

10. Application of the electrode material according to claim 6 in electrochemical lithium extraction, Characterized in that, The temperature of the calcination step is 700 - 800°C.

11. Application of the electrode material according to claim 6 in electrochemical lithium extraction, Characterized in that, The time of the calcination step is 4 - 6h, and after calcination, it is kept warm for 1.5 - 2.5h.

12. Application of the electrode material according to claim 1 in electrochemical lithium extraction, Characterized in that, The electrodes used in the electrochemical lithium extraction include a conductive agent, a binder and the electrode material described above.

13. Application of the electrode material according to claim 12 in electrochemical lithium extraction, Characterized in that, The mass ratio of the conductive agent, the binder and the electrode material is 0.5 - 1.5:0.5 - 1.5:

8.

14. Application of the electrode material according to claim 12 in electrochemical lithium extraction, Characterized in that, The conductive agent is at least one of acetylene black, conductive carbon black, graphene and carbon nanotubes.

15. Use of the electrode material according to claim 12 in electrochemical lithium extraction, characterized in that, the binder is at least one of polyvinylidene fluoride and polytetrafluoroethylene.

16. Use of the electrode material according to claim 12 in electrochemical lithium extraction, characterized in that, the method for preparing the electrode includes coating a slurry containing a conductive agent, a binder and the electrode material on a current collector, and drying to obtain a lithium iron phosphate electrode.

17. Use of the electrode material according to claim 16 in electrochemical lithium extraction, characterized in that, a solvent, a conductive agent, a binder and the electrode material are mixed, ground, slurried and then coated on a current collector, and vacuum dried to obtain a lithium iron phosphate electrode.

18. Use of the electrode material according to claim 16 in electrochemical lithium extraction, characterized in that, using the lithium iron phosphate electrode as the anode, nickel foam as the cathode, and NaCl as the supporting electrolyte, and applying an electric current to de-lithiate to obtain a lithium-deficient lithium iron phosphate electrode.

19. An electrochemical lithium extraction device, characterized in that, comprising: an electrode, including the lithium-deficient lithium iron phosphate electrode according to claim 18 as the cathode electrode, and / or the lithium iron phosphate electrode according to any one of claims 12-17 as the anode electrode; an anode chamber for accommodating a lithium-deficient electrolyte; a cathode chamber for accommodating a lithium-rich electrolyte; an anion membrane: for separating the anode chamber and the cathode chamber.

20. An electrochemical lithium extraction method, characterized in that, including lithium extraction and / or de-lithiation, lithium extraction, applying a voltage between the cathode and the anode of the electrochemical lithium extraction device according to claim 19 to embed lithium ions in the brine into the lithium-deficient lithium iron phosphate electrode; and / or de-lithiation, applying a voltage between the cathode and the anode of the electrochemical lithium extraction device according to claim 19 and heating the lithium-deficient electrolyte to 68-90 °C to extract the embedded lithium ions from the lithium iron phosphate electrode.

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