An electrode material, its preparation method, and its application in direct lithium extraction from salt lakes via electrochemical intercalation / deintercalation.

Abstract

This application relates to an electrode material, its preparation method, and its application in direct lithium extraction from salt lakes via electrochemical intercalation / deintercalation. The preparation method includes the following steps: (1) mixing mesoporous silica, a lithium source, an iron source, a phosphorus source, and a solvent, and performing a solvothermal reaction to obtain a mixture; (2) heating the obtained mixture to obtain a lithium iron phosphate composite; (3) mixing a coating material and the obtained lithium iron phosphate composite, and calcining to obtain the electrode material. The porous lithium iron phosphate ion sieve based on silica utilizes mesoporous silica as its core, which, compared to the difficult-to-form porous lithium iron phosphate core, possesses abundant pores, improving the porosity of the ion sieve and further enhancing mass transfer efficiency.

Description

Technical Field

[0001] This application belongs to the field of ion sieve manufacturing technology, and relates to an electrode material, preparation method and its application in direct lithium extraction from salt lakes by electrochemical deintercalation method. Background Technology

[0002] With the depletion of fossil fuels and the increasing severity of environmental problems, lithium, as a crucial strategic resource, has gained greater attention. Lithium-ion batteries, due to their advantages such as high output power, high voltage, fast charging and discharging speed, good cycle performance, and long lifespan, have demonstrated significant economic benefits and application prospects in many fields. However, with the increasing depletion of lithium ore resources, the proportion of lithium salts extracted from salt lakes has now risen to over 90%. The low proportion of lithium in salt lakes, coupled with the presence of large amounts of magnesium and potassium, hinders the lithium extraction process. Therefore, effectively extracting lithium resources from lithium-containing salt lake brines has become a research focus for many researchers.

[0003] The earliest and most technologically mature method is carbonate precipitation. However, this method requires a long period of natural evaporation and is affected by uncontrollable factors in the natural environment.

[0004] CN 112473616A discloses a porous C-MnO x / Sn-Al-H2TiO3 ion sieve, its preparation method and application. The preparation method includes: reacting Mn source, 4,5-imidazolium dicarboxylic acid, alkaline substance and solvent to generate Mn-MOF compound, followed by calcination to obtain porous C-MnO3. x Compound; reacting tetrabutyl titanate, water, acidic substances, and ammonium hexafluorotitanate to generate nano-titanium dioxide; making the porous C-MnO x The compound, nano-titanium dioxide, lithium hydroxide, and water are reacted, and then Sn and Al sources are added and mixed before calcination to obtain a composite ion sieve precursor. This precursor is then acidified to obtain porous C-MnO. x / Sn-Al-H2TiO3 ion sieve.

[0005] Ion exchange and adsorption are currently the most studied methods. However, the process of lithium extraction using ion sieves involves the use of strong acids for desorption, which can easily cause corrosion to the equipment and environmental pollution.

[0006] CN 115663180A discloses an electrochemical lithium extraction technology for using salt lakes to achieve in-situ regeneration of spent lithium iron phosphate batteries from a comprehensive utilization perspective. The method utilizes spent lithium iron phosphate cathode material as the cathode, normal lithium iron phosphate as the anode, and salt lake water as the electrolyte. Because of the lithium "vacancies" in the spent lithium iron phosphate, lithium from the brine can be inserted into the spent lithium iron phosphate at the cathode, enabling in-situ regeneration. This achieves the dual benefit of in-situ regeneration of spent lithium iron phosphate cathode material and lithium extraction from brine.

[0007] Based on this, researchers proposed using electrochemical methods for lithium ion adsorption and desorption. This method avoids the use of strong acids, but suffers from low lithium extraction efficiency. Lithium iron phosphate (LFP) materials exhibit good electrochemical reversibility in aqueous solutions, but their lithium intercalation efficiency is low. This is because during adsorption, iron phosphate is converted to lithium iron phosphate from the outside in. Since the external diffusion rate is greater than the internal diffusion rate, the inner layer of iron phosphate is difficult to convert to lithium iron phosphate, and the desorption process also requires more time. The long desorption time can be addressed by reducing the adsorption time, but reducing the adsorption time leads to the presence of unreacted nuclei (iron phosphate), which increases the material cost.

[0008] Therefore, how to improve ion sieve materials, increase the lithium intercalation efficiency of lithium iron phosphate, and reduce the cost of materials are technical problems that urgently need to be solved. Summary of the Invention

[0009] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0010] In view of the problems existing in the prior art, this application provides an electrode material, a preparation method and its application in direct lithium extraction from salt lakes by electrochemical intercalation-deintercalation method. The porous lithium iron phosphate ion sieve with silica as the substrate utilizes mesoporous silica as the core. Compared with the porous lithium iron phosphate core that is difficult to form, it has abundant pores, which improves the porosity of the ion sieve and further improves the mass transfer efficiency.

[0011] To achieve this objective, the following technical solution is adopted in this application:

[0012] In a first aspect, this application provides a method for preparing an electrode material, the method comprising the following steps:

[0013] (1) Mix mesoporous silica, lithium source, iron source, phosphorus source and solvent, and carry out a solvothermal reaction to obtain a mixture;

[0014] (2) The resulting mixture was heated to obtain a lithium iron phosphate complex;

[0015] (3) Mix the coating material and the obtained lithium iron phosphate composite, and calcine them to obtain the electrode material.

[0016] The porous lithium iron phosphate ion sieve based on silica in this application utilizes mesoporous silica as its core. Compared with the porous lithium iron phosphate core that is difficult to form, it has abundant pores, which improves the porosity of the ion sieve and further enhances the mass transfer efficiency.

[0017] The preparation method of this application uses mesoporous silica as the core and lithium iron phosphate is grown on its surface, so that the ion sieve core does not participate in the lithium ion adsorption and desorption reaction, but can improve the mass transfer efficiency. The lithium ion adsorption and desorption processes both occur in the inner layer of lithium iron phosphate, which improves the adsorption and deintercalation efficiency.

[0018] Optionally, the mesoporous silica, lithium source, iron source, phosphorus source and solvent described in step (1) are mixed to obtain a mixed solution.

[0019] Optionally, the content of mesoporous silica in the mixed solution is 0.02 to 0.1 g / mL, for example, it can be 0.02 g / mL, 0.04 g / mL, 0.06 g / mL, 0.08 g / mL or 0.1 g / mL, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Optionally, the concentration of the lithium source in the mixed solution is 0.1 to 2 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L or 2 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0021] Optionally, the molar ratio of the lithium source, iron source and phosphorus source in step (1) satisfies the molar ratio of LiFePO4.

[0022] Optionally, the particle size range of the mesoporous silica in step (1) is 0.5 to 1 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Optionally, the pore size of the mesoporous silica in step (1) is 10 to 50 nm, for example, it can be 10 nm, 20 nm, 30 nm, 40 nm or 50 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In the mixed solution described in step (1), mesoporous silica exists in solid form. Silica has a mesopore size of 10–50 nm. If the pore size of silica is too large, it will reduce the mechanical strength of the material, and the pores will be blocked during the growth of lithium iron phosphate, reducing the mass transfer effect. If the pore size of silica is too small, the mass transfer effect will be poor.

[0025] Optionally, the lithium source in step (1) includes any one or a combination of at least two of lithium chloride, lithium hydroxide, lithium carbonate, lithium nitrate, or lithium acetate. Typical but non-limiting combinations include combinations of lithium chloride and lithium hydroxide, combinations of lithium hydroxide and lithium carbonate, combinations of lithium carbonate and lithium nitrate, combinations of lithium nitrate and lithium acetate, combinations of lithium chloride, lithium hydroxide, and lithium carbonate, combinations of lithium hydroxide, lithium carbonate, and lithium nitrate, and combinations of lithium carbonate, lithium nitrate, and lithium acetate.

[0026] Optionally, the iron source in step (1) includes any one or a combination of at least two of ferrous oxalate, ferrous chloride, or ferrous sulfate. Typical but non-limiting combinations include combinations of ferrous oxalate and ferrous chloride, combinations of ferrous chloride and ferrous sulfate, combinations of ferrous oxalate and ferrous sulfate, and combinations of ferrous oxalate, ferrous chloride, and ferrous sulfate.

[0027] Optionally, the phosphorus source in step (1) includes ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate.

[0028] Optionally, the mixing in step (1) may further include mixing the pore-forming agent and the alkali solution.

[0029] Optionally, the pore-forming agent includes any one or a combination of at least two of chitosan, CTAB (hexadecyltrimethylammonium bromide), SDS (sodium dodecyl sulfate), P123 (polyoxyethylene-polyoxypropylene-polyoxyethylene triblock polyether), or F127 (EO-PO type polyether). Typical but non-limiting combinations include combinations of chitosan and CTAB, combinations of CTAB and SDS, combinations of SDS and P123, combinations of P123 and F127, combinations of chitosan, CTAB, and SDS, combinations of CTAB, SDS, and P123, combinations of SDS, P123, and F127, combinations of chitosan, CTAB, SDS, and P123, combinations of CTAB, SDS, P123, and F127, and combinations of chitosan, CTAB, SDS, P123, and F127.

[0030] Optionally, the mass of the pore-forming agent is 2 to 8 wt% of the mass of LiFePO4 in the mixture, for example, it can be 2 wt%, 4 wt%, 5 wt%, 6 wt% or 8 wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Optionally, the pH of the mixed alkaline solution is controlled to be 6 to 8, for example, 6, 6.5, 7, 7.5 or 8, but not limited to the listed values. Other unlisted values ​​within the range are also applicable, with 7 being the preferred value.

[0032] Optionally, the solvothermal reaction in step (1) is mixed and stirred for 0.5 to 2 hours beforehand. For example, it can be 0.5 hours, 1 hour, 1.5 hours, 1.8 hours or 2 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Optionally, the temperature of the solvothermal reaction in step (1) is 100 to 150°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Optionally, the time for the solvothermal reaction in step (1) is 6 to 12 hours, for example, 6 hours, 8 hours, 9 hours, 10 hours or 12 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Optionally, after the solvothermal reaction in step (1), a suspension is obtained, which is then filtered and washed to obtain a mixture.

[0036] Optionally, the heating in step (2) is carried out in an inert gas atmosphere.

[0037] Optionally, the heating temperature in step (2) is 400 to 600°C, for example, 400°C, 450°C, 500°C, 550°C or 600°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Optionally, the heating time in step (2) is 6 to 20 hours, for example, 6 hours, 10 hours, 15 hours, 18 hours or 20 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Optionally, the pore size of the lithium iron phosphate composite in step (2) is 50 to 300 nm, for example, it can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm or 300 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Optionally, the particle size of the lithium iron phosphate composite in step (2) is 1 to 10 μm, for example, it can be 1 μm, 3 μm, 5 μm, 7 μm, 9 μm or 10 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Optionally, the particle size of the coating material in step (3) is in the nanometer range.

[0042] Optionally, the coating material in step (3) includes titanium dioxide.

[0043] This application employs nano-titanium dioxide to coat the outer layer of lithium iron phosphate material, which improves the mechanical strength of the ion screen, increases the service life of the lithium ion screen, and helps to reduce costs.

[0044] Optionally, the mass ratio of the coating material to the obtained lithium iron phosphate complex in step (3) is 0.5 to 2:100, for example, it can be 0.5:100, 1:100, 1.2:100, 1.8:100 or 2:100, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Optionally, the mixing in step (3) includes stirring.

[0046] Optionally, the stirring speed is 8000 to 20000 rpm, for example, it can be 8000 rpm, 10000 rpm, 12000 rpm, 15000 rpm or 20000 rpm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] Optionally, the calcination in step (3) is carried out in an inert gas atmosphere.

[0048] Optionally, the roasting temperature in step (3) is 600 to 800°C, for example, 600°C, 650°C, 700°C, 750°C or 800°C, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] Optionally, the roasting time in step (3) is 3 to 5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] As a preferred embodiment of the preparation method described in the first aspect of this application, the preparation method includes the following steps:

[0051] (1) Mix mesoporous silica, lithium source, iron source, phosphorus source, pore-forming agent, alkaline solution and solvent to obtain a mixed solution. The content of mesoporous silica in the mixed solution is 0.02-0.1 g / mL, the concentration of lithium source is 0.1-2 mol / L, the molar ratio of lithium source, iron source and phosphorus source satisfies the molar ratio of LiFePO4, the pH of the mixed solution is controlled to be 6-8, stirred for 0.5-2 h and then subjected to a solvothermal reaction at 100-150℃ for 6-12 h to obtain a suspension. After filtration and washing, a mixture is obtained.

[0052] The mesoporous silica has a particle size range of 0.5–1 μm; the mesoporous silica has a pore size of 10–50 nm; the pore-forming agent includes any one or a combination of at least two of chitosan, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock polyether or EO-PO type polyether.

[0053] (2) The mixture was heated at 400-600℃ for 6-20h under an inert gas atmosphere to obtain a lithium iron phosphate composite with a pore size of 50-300nm and a particle size of 1-10μm.

[0054] (3) Mix nano-titanium dioxide and the obtained lithium iron phosphate composite at a mass ratio of 0.5 to 2:100, stir uniformly at a speed of 8000 to 20000 rpm, and calcine at 600 to 800°C for 3 to 5 hours in an inert gas atmosphere to obtain the electrode material.

[0055] Secondly, this application provides an electrode material, which is obtained by the preparation method described in the first aspect.

[0056] Thirdly, this application provides an application of the electrode material described in the second aspect, said electrode material being used for direct lithium extraction from salt lakes via an electrochemical deintercalation / intercalation method.

[0057] Based on the above technical solutions, the beneficial effects of this application are as follows:

[0058] (1) The porous lithium iron phosphate ion sieve based on silica in this application utilizes mesoporous silica as the core. Compared with the porous lithium iron phosphate core that is difficult to form, it has abundant pores, which improves the porosity of the ion sieve and further improves the mass transfer efficiency.

[0059] (2) The preparation method of this application uses mesoporous silica as the core and lithium iron phosphate is grown on its surface, so that the core of the ion sieve does not participate in the lithium ion adsorption and desorption reaction, but can improve the mass transfer efficiency. The lithium ion adsorption and desorption processes both occur in the inner layer of lithium iron phosphate, which improves the adsorption and deintercalation efficiency.

[0060] (3) The coating of nano-titanium dioxide on the outer layer of lithium iron phosphate material improves the mechanical strength of the ion screen, increases the service life of the lithium ion screen, and helps to reduce costs.

[0061] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0062] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0063] Figure 1 This is a SEM image of the electrode material described in Example 1.

[0064] Figure 2 These are XRD patterns of the electrode material described in Example 1 before and after adsorption-desorption cycles. Detailed Implementation

[0065] The technical solution of this application will be further described below with reference to the accompanying drawings and specific embodiments. However, the examples below are merely simplified examples of this application and do not represent or limit the scope of protection of this application. The scope of protection of this application shall be determined by the claims.

[0066] Example 1

[0067] This embodiment provides a method for preparing an electrode material, the method comprising the following steps:

[0068] (1) Mix 3g of mesoporous silica, 0.05mol of lithium hydroxide, 0.05mol of ferrous oxalate, 0.05mol of ammonium dihydrogen phosphate, 0.4g of chitosan, ammonia and water to obtain a mixed solution. The content of mesoporous silica in the mixed solution is 0.03g / mL. The pH of the mixed solution is controlled at 7. Stir for 1h and then carry out a solvothermal reaction at 120℃ for 8h to obtain a suspension. Filter and wash to obtain a mixture.

[0069] The mesoporous silica has a particle size range of 0.8 μm; the pore size of the mesoporous silica is 10–50 nm.

[0070] (2) Under an inert gas atmosphere, the mixture was heated at 500°C for 10 h at a heating rate of 5°C / min to obtain a lithium iron phosphate composite with a pore size of 150 nm and a particle size of 5 μm.

[0071] (3) Nano-titanium dioxide and the obtained lithium iron phosphate composite were mixed at a mass ratio of 1:100, stirred uniformly at 10000 rpm, and calcined at 750°C for 4 hours in an inert gas atmosphere to obtain the electrode material. The SEM image of the electrode material is shown below. Figure 1 As shown.

[0072] Example 2

[0073] This embodiment provides a method for preparing an electrode material, the method comprising the following steps:

[0074] (1) Mix mesoporous silica, lithium chloride, ferrous chloride, diammonium hydrogen phosphate, CTAB, ammonia solution and water to obtain a mixed solution. The content of mesoporous silica in the mixed solution is 0.02 g / mL, the concentration of lithium chloride is 0.1 mol / L, and the molar ratio of lithium chloride, ferrous chloride and diammonium hydrogen phosphate satisfies the molar ratio of LiFePO4. The pH of the mixed solution is controlled to be 6. After stirring for 2 h, a solvothermal reaction is carried out at 100℃ for 12 h to obtain a suspension. After filtration and washing, a mixture is obtained.

[0075] The mesoporous silica has a particle size range of 0.5 μm; the pore size of the mesoporous silica is 10–50 nm.

[0076] (2) The mixture was heated at 400°C for 20 h under an inert gas atmosphere to obtain a lithium iron phosphate composite with a pore size of 50 nm and a particle size of 1 μm.

[0077] (3) The nano-titanium dioxide and the obtained lithium iron phosphate composite were mixed at a mass ratio of 0.5:100, stirred uniformly at a speed of 8000 rpm, and calcined at 600°C for 5 h in an inert gas atmosphere to obtain the electrode material.

[0078] Example 3

[0079] This embodiment provides a method for preparing an electrode material, the method comprising the following steps:

[0080] (1) Mix mesoporous silica, lithium carbonate, ferrous sulfate, diammonium hydrogen phosphate, SDS, ammonia solution and water to obtain a mixed solution. The content of mesoporous silica in the mixed solution is 0.1 g / mL, the concentration of lithium carbonate is 2 mol / L, and the molar ratio of lithium carbonate, ferrous sulfate and diammonium hydrogen phosphate satisfies the molar ratio of LiFePO4. The pH of the mixed solution is controlled to be 8. After stirring for 2 h and then performing a solvothermal reaction at 150℃ for 6 h, a suspension is obtained. After filtration and washing, a mixture is obtained.

[0081] The mesoporous silica has a particle size range of 1 μm; the pore size of the mesoporous silica is 10–50 nm.

[0082] (2) The mixture was heated at 600°C for 6 hours under an inert gas atmosphere to obtain a lithium iron phosphate composite with a pore size of 300 nm and a particle size of 10 μm.

[0083] (3) The nano-titanium dioxide and the obtained lithium iron phosphate composite were mixed at a mass ratio of 2:100, stirred uniformly at a speed of 20,000 rpm, and calcined at 800°C for 3 hours in an inert gas atmosphere to obtain the electrode material.

[0084] Example 4

[0085] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the pore size of the mesoporous silica in step (1) is 2-10 nm.

[0086] Example 5

[0087] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the content of mesoporous silica in step (1) is 0.01 g / mL.

[0088] Example 6

[0089] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the content of mesoporous silica in step (1) is 0.2 g / mL.

[0090] Example 7

[0091] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the particle size of the mesoporous silica in step (1) is 0.3 μm.

[0092] Example 8

[0093] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the particle size of the mesoporous silica in step (1) is 1.5 μm.

[0094] Example 9

[0095] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that chitosan is not added in step (1).

[0096] Example 10

[0097] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the mass of chitosan in step (1) is 1 wt% of the mass of LiFePO4 in the mixture.

[0098] Example 11

[0099] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the mass of chitosan in step (1) is 10 wt% of the mass of LiFePO4 in the mixture.

[0100] Example 12

[0101] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the titanium dioxide in step (3) is micron-sized titanium dioxide.

[0102] Example 13

[0103] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the mass ratio of nano-titanium dioxide to the obtained lithium iron phosphate composite in step (3) is 0.1:100.

[0104] Example 14

[0105] This embodiment provides a method for preparing an electrode material, which differs from Embodiment 1 in that the mass ratio of nano-titanium dioxide to the obtained lithium iron phosphate composite in step (3) is 2.5:100.

[0106] Comparative Example 1

[0107] This comparative example provides a method for preparing an electrode material, which differs from Example 1 in that: mesoporous silica is not added in step (1), and nano-titanium dioxide is not added in step (3).

[0108] Comparative Example 2

[0109] This comparative example provides a method for preparing an electrode material, which differs from Example 1 in that mesoporous silica is not added in step (1).

[0110] Comparative Example 3

[0111] This comparative example provides a method for preparing an electrode material, which differs from Comparative Example 1 in that chitosan is not added in step (1).

[0112] Comparative Example 4

[0113] This comparative example provides a method for preparing an electrode material, which differs from Example 1 in that the mesoporous silica in step (1) is replaced with non-porous silica.

[0114] Comparative Example 5

[0115] This comparative example provides a method for preparing an electrode material, which differs from Example 1 in that: the mesoporous silica in step (1) is replaced with macroporous silica with a pore size of 70-100 nm.

[0116] Using N-methylpyrrolidone as a solvent, the electrode material obtained above, acetylene black, and PVDF were mixed at a mass ratio of 8:1:1, slurryed, and the slurry was uniformly coated onto a 1 cm thick layer. 2 On the carbon sheet, a coating density of 100 mg lithium iron phosphate / cm³ is applied. 2 The sample was dried at 60℃ for 5 hours. Simulated brine (composition shown in Table 1) was used as the source solution, with lithium iron phosphate as the positive electrode and a carbon rod as the negative electrode. The voltage range between the two electrodes was 0.5-2.5 mV / cm. -2 Apply -0.5mA / cm -2 Adsorption was performed once using a constant current, followed by the application of a constant current of 0.5 mA / cm.-2 One desorption and one adsorption-desorption cycle constitutes one lithium extraction experiment. After 50 cycles, the XRD patterns of Example 1 before and after the cycle show that the crystal structure is basically unchanged, indicating that the electrode material has excellent stability. The experimental results are shown in Table 2.

[0117] Table 1

[0118]

[0119] Table 2

[0120]

[0121] The following conclusions can be drawn from Table 2:

[0122] (1) As can be seen from Examples 1-3 and Comparative Examples 1-3, the porous lithium iron phosphate ion sieve based on silica in this application utilizes mesoporous silica as the core. Compared with the porous lithium iron phosphate core that is difficult to form, it has abundant pores, which improves the porosity of the ion sieve and further improves the mass transfer efficiency.

[0123] (2) As can be seen from the comparison of Examples 1, 4 and Comparative Examples 4-5, mesoporous silica as the core can improve the adsorption capacity. When silica is non-porous or the pore size is not within the preferred range provided in this application, the improvement on adsorption capacity and capacity retention rate is not obvious.

[0124] (3) As can be seen from the comparison between Example 1 and Examples 5-8, when the content or particle size of mesoporous silica is not within the preferred range of this application, the improvement on adsorption capacity and capacity retention rate is not obvious.

[0125] (4) As can be seen from the comparison between Example 1 and Examples 9-11, the use of pore-forming agents to prepare lithium iron phosphate can improve the adsorption capacity of the material. When the content of pore-forming agents is not within the preferred range of this application, it is difficult to improve the adsorption capacity and capacity retention rate at the same time.

[0126] (5) As can be seen from the comparison between Example 1 and Examples 12-14, coating with nano-titanium dioxide can improve the capacity retention rate. However, when the mass of nano-titanium dioxide is not within the preferred range of this application, the improvement on the capacity retention rate is not significant.

[0127] This application illustrates its detailed structural features through the above embodiments, but it is not limited to these detailed structural features, meaning that this application does not necessarily rely on them for implementation. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of selected components, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this application.

Claims

1. A method for preparing an electrode material, wherein, The preparation method includes the following steps: (1) Mix mesoporous silica, lithium source, iron source, phosphorus source, pore-forming agent, alkaline solution and solvent to obtain a mixed solution, and carry out a solvothermal reaction to obtain a mixture; The content of mesoporous silica in the mixed solution in step (1) is 0.02-0.1 g / mL; The particle size range of the mesoporous silica in step (1) is 0.5 to 1 μm; the pore size of the mesoporous silica in step (1) is 10 to 50 nm. (2) The resulting mixture was heated to obtain a lithium iron phosphate complex; (3) Mix the coating material and the obtained lithium iron phosphate composite, and calcine them to obtain the electrode material; The coating material in step (3) includes titanium dioxide.

2. The preparation method according to claim 1, wherein, The concentration of lithium source in the mixed solution is 0.1–2 mol / L; The molar ratio of the lithium source, iron source and phosphorus source in step (1) satisfies the molar ratio of LiFePO4.

3. The preparation method according to claim 1 or 2, wherein, The lithium source in step (1) includes any one or a combination of at least two of lithium chloride, lithium hydroxide, lithium carbonate, lithium nitrate, or lithium acetate; The iron source in step (1) includes any one or a combination of at least two of ferrous oxalate, ferrous chloride, or ferrous sulfate; The phosphorus source in step (1) includes ammonium dihydrogen phosphate and / or diammonium hydrogen phosphate.

4. The preparation method according to claim 1, wherein, The pore-forming agent in step (1) includes any one or a combination of at least two of chitosan, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock polyether or EO-PO type polyether.

5. The preparation method according to claim 1, wherein, The mass of the pore-forming agent is 2-8 wt% of the mass of LiFePO4 in the mixture.

6. The preparation method according to claim 1, wherein, The pH of the mixed solution is controlled to be 6-8 by mixing the alkaline solution.

7. The preparation method according to claim 6, wherein, The pH of the mixed solution is controlled to be 7 by mixing the alkaline solution.

8. The preparation method according to claim 1, wherein, Before the solvothermal reaction in step (1), the mixture is stirred for 0.5 to 2 hours.

9. The preparation method according to claim 1, wherein, The temperature of the solvothermal reaction in step (1) is 100-150℃.

10. The preparation method according to claim 1, wherein, The solvothermal reaction in step (1) takes 6 to 12 hours.

11. The preparation method according to claim 1, wherein, After the solvothermal reaction in step (1), a suspension is obtained, which is then filtered and washed to obtain the mixture.

12. The preparation method according to claim 1, wherein, The heating in step (2) is carried out in an inert gas atmosphere.

13. The preparation method according to claim 1, wherein, The heating temperature in step (2) is 400-600℃.

14. The preparation method according to claim 1, wherein, The heating time in step (2) is 6 to 20 hours.

15. The preparation method according to claim 1, wherein, The pore size of the lithium iron phosphate composite in step (2) is 50-300 nm.

16. The preparation method according to claim 1, wherein, The particle size of the lithium iron phosphate complex in step (2) is 1 to 10 μm.

17. The preparation method according to claim 1, wherein, The particle size of the coating material in step (3) is in the nanometer range.

18. The preparation method according to claim 1, wherein, The mass ratio of the coating material to the obtained lithium iron phosphate complex in step (3) is 0.5 to 2:

100.

19. The preparation method according to claim 1, wherein, The mixing in step (3) includes stirring.

20. The preparation method according to claim 19, wherein, The stirring speed is 8000-20000 rpm.

21. The preparation method according to claim 1, wherein, The calcination in step (3) is carried out in an inert gas atmosphere.

22. The preparation method according to claim 1, wherein, The roasting temperature in step (3) is 600-800℃.

23. The preparation method according to claim 1, wherein, The roasting time in step (3) is 3 to 5 hours.

24. The preparation method according to claim 1, wherein, The preparation method includes the following steps: (1) Mix mesoporous silica, lithium source, iron source, phosphorus source, pore-forming agent, alkaline solution and solvent to obtain a mixed solution. The content of mesoporous silica in the mixed solution is 0.02-0.1 g / mL, the concentration of lithium source is 0.1-2 mol / L, the molar ratio of lithium source, iron source and phosphorus source satisfies the molar ratio of LiFePO4, the pH of the mixed solution is controlled at 6-8, stirred for 0.5-2 h, and then subjected to a solvothermal reaction at 100-150℃ for 6-12 h to obtain a suspension. After filtration and washing, a mixture is obtained. The mesoporous silica has a particle size range of 0.5–1 μm; the mesoporous silica has a pore size of 10–50 nm; the pore-forming agent includes any one or a combination of at least two of chitosan, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock polyether or EO-PO type polyether. (2) The mixture was heated at 400-600℃ for 6-20h under an inert gas atmosphere to obtain a lithium iron phosphate composite with a pore size of 50-300nm and a particle size of 1-10μm. (3) Mix nano-titanium dioxide and the obtained lithium iron phosphate composite at a mass ratio of 0.5 to 2:100, stir uniformly at a speed of 8000 to 20000 rpm, and calcine at 600 to 800°C for 3 to 5 hours in an inert gas atmosphere to obtain the electrode material.

25. An electrode material, wherein, The electrode material is obtained by the preparation method described in any one of claims 1-24.

26. An application of the electrode material according to claim 25, wherein, The electrode material is used for direct lithium extraction from salt lakes via electrochemical deintercalation / intercalation.

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