An electrode for lithium extraction, its preparation method and application

Abstract

This invention provides a lithium extraction electrode, its preparation method, and its application. The preparation method includes the following steps: mixing an electrode active material, a conductive agent, a binder, and a solvent to obtain a slurry; then coating the slurry onto a current collector and drying it to obtain a lithium extraction electrode; wherein the coating thickness of the slurry is ≥2 mm; mixing the lithium extraction electrode with a weak oxidant solution to carry out a lithium extraction reaction to obtain a lithium extraction electrode after lithium extraction. This invention uses a chemical method for lithium extraction, solving the problems of increased resistance, capacity decay, and reduced electrode lifespan due to polarization caused by increasing the coating thickness to ≥2 mm, while ensuring the lithium extraction amount of the lithium extraction electrode. Based on this method, the lithium extraction electrode prepared has different amounts of lithium extraction on the inner and outer sides, with more lithium extraction on the outer side and less on the inner side. This effectively balances the phenomenon of increased lithium ion vacancies and decreased ion selectivity, improves the material structure stability of the lithium extraction electrode, and exhibits excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of lithium extraction from salt lakes, and particularly relates to an electrode for lithium extraction and a preparation method and application thereof. BACKGROUND

[0002] The electrode material usually has lithium iron phosphate and lithium manganate in the electrochemical method for lithium extraction from salt lakes, and the thinner the coating of the electrode plate, the smaller the resistance, the smaller the mass transfer resistance, and the better the theoretical capacity. + Therefore, the coating thickness is usually about 1mm at present, but the thin coating thickness results in large equipment volume, high investment, and low lithium extraction efficiency. + The thicker the coating, the longer the diffusion and electron path, the greater the mass transfer resistance, and the worse the ion selectivity. + In the electrochemical deintercalation process, with the increase of lithium vacancies in lithium iron phosphate, the ion selectivity becomes poor, too many adsorbed impurity ions will damage the structure of the electrode material, and the electrode material loses its original electrochemical activity, so the adsorption capacity is significantly reduced.

[0003] Therefore, it is urgent to provide a preparation method of an electrode for lithium extraction to solve the problems of increased resistance, capacity attenuation, and reduced service life of the electrode caused by the increase of the coating thickness. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide an electrode for lithium extraction and a preparation method and application thereof. The present application adopts a chemical deintercalation method to solve the problems of increased resistance, capacity attenuation, and reduced service life of the electrode caused by the increase of the coating thickness to ≥2mm, and can ensure the lithium extraction amount of the electrode for lithium extraction while increasing the service life of the electrode. The deintercalation amount of the electrode for lithium extraction prepared by the method is different on the inside and outside, the outside is deintercalated more and the inside is deintercalated less, which can effectively balance the increase of lithium ion vacancies and the decrease of ion selectivity, improve the material structure stability of the electrode for lithium extraction, and exhibit excellent electrochemical performance.

[0005] To achieve the purpose of the present application, the following technical solutions are adopted:

[0006] In a first aspect, the present application provides a preparation method of an electrode for lithium extraction, which comprises the following steps:

[0007] (1) mixing an electrode active material, a conductive agent, a binder, and a solvent to obtain a slurry, then coating the slurry on a current collector, and drying to obtain a to-be-deintercalated electrode;

[0008] The coating thickness of the slurry is ≥2mm.

[0009] (2) The electrode to be delithiated is mixed with a weak oxidant solution to carry out a delithiation reaction, and a lithium extraction electrode after delithiation is obtained.

[0010] This invention employs a chemical delithiation method, solving the problems of increased resistance, capacity decay, and reduced electrode lifespan caused by polarization when the coating thickness is increased to ≥2mm. Furthermore, it maintains the lithium extraction yield of the electrode while extending its lifespan. The lithium extraction electrode prepared by this method exhibits different delithiation amounts on its inner and outer sides—more on the outer side and less on the inner side—effectively balancing the increase in lithium-ion vacancies and decreased ion selectivity. This improves the material structure stability of the lithium extraction electrode, resulting in excellent electrochemical performance and extended electrode lifespan.

[0011] In this invention, the coating thickness of the slurry is ≥2mm, for example, it can be 2mm, 4mm, 6mm, 8mm or 10mm, etc. This coating thickness is beneficial to improving lithium extraction efficiency and reducing industrial operating costs.

[0012] Preferably, the electrode active material in step (1) is a positive electrode active material, which includes any one or a combination of at least two of lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0013] Preferably, the conductive agent in step (1) includes any one or a combination of at least two of acetylene black, Ketjen black, conductive graphite powder KS-6, or carbon nanotubes.

[0014] Preferably, the current collector in step (1) includes any one or a combination of at least two of titanium, copper, or aluminum.

[0015] Preferably, based on the mass of the electrode active material described in step (1), the content of the conductive agent is 4-10%, for example, it can be 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.; the content of the binder is 4-8%, for example, it can be 4%, 5%, 6%, 7% or 8%, etc.; and the content of the solvent is 100-150%, for example, it can be 100%, 110%, 120%, 130%, 140% or 150%, etc.

[0016] In this invention, by limiting the mass relationship between the conductive agent, binder, solvent, and electrode active material, it is beneficial to obtain a high-performance, long-life electrode.

[0017] Preferably, a pore-forming agent and a reinforcing agent are also added during the mixing process in step (1).

[0018] In this invention, adding a pore-forming agent during the pulping process helps to reduce Li. + Adding a reinforcing agent to enhance the diffusion resistance during the insertion / extraction process helps strengthen the structural strength of the electrode.

[0019] Preferably, the pore-forming agent comprises any one or a combination of at least two of sodium chloride, ammonium bicarbonate, or ammonium carbonate.

[0020] In this invention, the use of the above-mentioned pore-forming agents helps to achieve good pore-forming effects and can significantly reduce Li + Diffusion resistance during the insertion / extraction process.

[0021] Preferably, the reinforcing agent comprises any one or a combination of at least two of short carbon fibers, lignin fibers, glass fibers, polypropylene fibers, or cellulose fibers.

[0022] In this invention, the use of the above-mentioned reinforcing agents can more efficiently increase electrode strength.

[0023] Preferably, based on the mass of the electrode active material described in step (1), the content of the pore-forming agent is 0-40%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, etc., and the content of the reinforcing agent is 1-3%, for example, it can be 1%, 1.5%, 2%, 2.5% or 3%, etc.

[0024] In this invention, if the content of the pore-forming agent is too high, the electrode strength will be reduced; if the content of the reinforcing agent is too high, the slurry will agglomerate and cause pore blockage.

[0025] Preferably, the coating thickness of the slurry in step (1) is 2-5 mm, for example, it can be 2 mm, 3 mm, 4 mm or 5 mm.

[0026] In this invention, if the coating thickness of the slurry is too small, the lithium extraction efficiency will be low; if the coating thickness of the slurry is too thick, it will easily cause an increase in mass transfer resistance and a rise in voltage plateau.

[0027] Preferably, the drying temperature in step (1) is 50-90℃, for example, 50℃, 60℃, 70℃, 80℃ or 90℃, and the drying time is 5-12h, for example, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0028] In this invention, drying within the above-mentioned temperature range can form porous-microcrack solution mass transfer channels on and inside the electrode surface, which is beneficial for obtaining a lithium-free electrode.

[0029] Preferably, the drying method in step (1) is multi-temperature drying, which includes a first-stage drying and a second-stage drying.

[0030] Preferably, the temperature of the drying stage is 50-70℃, for example, 50℃, 60℃ or 70℃, and the time is 6-10h, for example, 6h, 7h, 8h, 9h or 10h.

[0031] Preferably, the temperature of the two-stage drying is 70-90℃, for example, 70℃, 80℃ or 90℃, and the time is 2-6h, for example, 2h, 3h, 4h, 5h or 6h.

[0032] Preferably, the concentration of the weak oxidant solution in step (2) is 0.25-5 wt%, for example, it can be 0.25 wt%, 0.5 wt%, 0.75 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%.

[0033] In this invention, if the concentration of the weak oxidant solution is too low, the amount of lithium removal will not meet the design requirements; if the concentration of the weak oxidant solution is too high, the amount of lithium removal on the inner and outer sides will be basically the same.

[0034] Preferably, the weak oxidizing agent in the weak oxidizing agent solution in step (2) includes a combination of oxygen and carbon dioxide or any one or a combination of at least two of acetic acid.

[0035] In this invention, the use of the aforementioned weak oxidants can achieve different amounts of lithium removal on the inner and outer sides of the lithium extraction electrode. The outer side of the lithium extraction electrode can achieve a full reaction, resulting in a higher amount of lithium removal, while the inner side of the lithium extraction electrode does not react sufficiently, resulting in a lower amount of lithium removal.

[0036] Preferably, the temperature of the delithiation reaction in step (2) is 20-60℃, for example, 20℃, 30℃, 40℃, 50℃ or 60℃, and the time is 2-12h, for example, 2h, 4h, 6h, 8h, 10h or 12h.

[0037] In this invention, if the temperature of the delithiation reaction is too low, the amount of delithiation will not meet the design requirements; if the temperature of the delithiation reaction is too high, the electrode material structure will be damaged, and the amount of delithiation on the inner and outer sides will differ greatly.

[0038] Preferably, the theoretical delithiation amount of the electrode to be delithiated in step (2) is 10-60 wt%, for example, it can be 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt% or 60 wt%, etc.

[0039] In this invention, the theoretical delithiation amount of the electrode to be delithiated is 10-60 wt%, which is beneficial to increase the electrode lifespan while ensuring the lithium extraction amount.

[0040] Preferably, the preparation method includes the following steps:

[0041] (1) Add the binder to the solvent and stir to dissolve it. Then add the conductive agent, positive electrode active material, reinforcing agent and pore-forming agent in sequence, stir and mix evenly to obtain a slurry. Then coat the slurry onto the current collector and dry it at 50-90℃ for 5-12h to obtain the lithium-free electrode.

[0042] Wherein, based on the mass of the electrode active material, the content of the conductive agent is 4-10%, the content of the binder is 4-8%, the content of the solvent is 100-150%, the content of the pore-forming agent is 0-40%, the content of the reinforcing agent is 1-3%, and the coating thickness of the slurry is ≥2mm;

[0043] (2) Prepare a weak oxidant solution with a concentration of 0.25-5wt% according to the theoretical delithiation amount of 10-60wt% of the electrode to be delithiated, then add the electrode to be delithiated, and carry out the delithiation reaction at 20-60℃ for 2-12h to obtain the delithiated lithium extraction electrode.

[0044] In a second aspect, the present invention provides a lithium extraction electrode prepared by the preparation method described in the first aspect, wherein the amount of lithium removed from the inner side of the lithium extraction electrode is less than the amount of lithium removed from the outer side.

[0045] The lithium extraction electrode prepared by this invention has different amounts of delithiation on the inner and outer sides, with more delithiation on the outer side and less on the inner side. This can effectively balance the phenomenon of increased lithium ion vacancies and decreased ion selectivity, improve the material structure stability of the lithium extraction electrode, and exhibit excellent electrochemical performance.

[0046] For example, the chemical formula of the electrode used for lithium extraction is Li. 1-x FePO4, where 0 < x < 1, for example, can be 0.2, 0.4, 0.6 or 0.8, etc.

[0047] Thirdly, the present invention provides an application of the lithium extraction electrode as described in the second aspect in the field of lithium extraction from salt lakes.

[0048] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) This invention employs a chemical method for lithium removal, which solves the problems of increased resistance, capacity decay, and reduced electrode lifespan caused by polarization when the coating thickness is increased to ≥2mm. Furthermore, it ensures the lithium extraction yield of the lithium extraction electrode while increasing the electrode lifespan. Based on the fact that the lithium extraction electrode prepared by this method has different amounts of lithium removal on the inner and outer sides, with more lithium removal on the outer side and less on the inner side, it can effectively balance the phenomenon of increased lithium ion vacancies and decreased ion selectivity, improve the material structure stability of the lithium extraction electrode, and exhibit excellent electrochemical performance.

[0051] (2) The preparation method provided by the present invention is simple, easy to implement, efficient and environmentally friendly. Attached Figure Description

[0052] Figure 1 The cycling curves are those of the lithium extraction electrodes prepared in Examples 1-2 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0053] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0054] Example 1

[0055] This embodiment provides a method for preparing an electrode for lithium extraction, the method comprising the following steps:

[0056] (1) Polyvinylidene fluoride was added to N-methylpyrrolidone and mechanically stirred until completely dissolved to obtain a mixed adhesive solution. Then, acetylene black, lithium iron phosphate, short carbon fibers and sodium chloride were added in sequence and mechanically stirred for 4 hours to obtain a slurry. The slurry was then coated on a current collector titanium mesh and dried in a 50°C oven for 8 hours and then dried at 90°C for 4 hours to obtain the electrode to be delithiated.

[0057] Based on the mass of the lithium iron phosphate, the content of acetylene black is 4%, the content of polyvinylidene fluoride is 6%, the content of N-methylpyrrolidone is 150%, the content of sodium chloride is 10%, the content of short carbon fibers is 2%, the coating thickness of the slurry is 2 mm, and the coating area is 18 cm × 23 cm.

[0058] (2) Prepare a 2wt% acetic acid solution according to 60wt% of the lithium removal amount of the electrode to be delithiated, heat to 40℃, add the electrode to be delithiated, and carry out the delithiation reaction for 16 hours under stirring to obtain a lithium extraction electrode after delithiation, the chemical formula of which is Li. 0.4 FePO4.

[0059] First, the lithium extraction electrode prepared in this embodiment is divided into two uniform parts, inner and outer, to detect the actual amount of lithium removed from the inner and outer parts. The detection results are shown in Table 1.

[0060] Table 1

[0061] Li (wt%) Inner side 24 Outer side 36

[0062] Secondly, the present invention conducts lithium extraction experiments on the lithium extraction electrode prepared in this embodiment, and the specific steps include:

[0063] 1) The lithium extraction device is divided into a cathode chamber and an anode chamber using an anion exchange membrane, and the prepared lithium extraction electrodes are placed in the anode chamber and cathode chamber respectively;

[0064] 2) Add 5L of brine to the cathode chamber, the composition of which is shown in Table 2 below. Add 3L of 5g / L NaCl solution to the anode chamber. Apply a 0.2C current to the anode and cathode. Stop electrolysis when the voltage is greater than 0.3V, and then charge at a constant voltage of 0.3V. When the current is lower than 0.5A / m... 2 Electrolysis was terminated at the designated time. The composition of the brine and lithium-rich anode solution after lithium extraction is shown in Table 2.

[0065] Table 2

[0066] Concentration (g / L) Li Na K Ca Mg SO4 2- ]] B Brine 0.45 98.48 21.79 0.31 14.66 27.89 0.73 Brine after lithium extraction 0.04 98.40 21.77 0.30 14.65 27.85 0.73 Lithium-rich anode solution 0.67 2.09 0.03 0.01 0.05 0.07 0.01

[0067] As shown in Table 2, the lithium concentration in the brine decreased from 0.45 g / L to 0.04 g / L, while the lithium concentration in the lithium-rich anode solution increased to 0.67 g / L, with an adsorption capacity of 24.4 mg / g.

[0068] In addition, after conducting the above lithium extraction experiment, the anode and cathode were reversed. 3L of a 5g / L NaCl solution was injected into the anode chamber, and 5L of fresh brine was injected into the cathode chamber for long-term circulation. The circulation curve is shown below. Figure 1 As shown in the curve of Example 1, it can be seen that the lithium extraction electrode prepared by the preparation method provided by the present invention has a long cycle life, and the lithium extraction capacity retention rate is still above 90% after 600 cycles.

[0069] Example 2

[0070] This embodiment provides a method for preparing an electrode for lithium extraction, the method comprising the following steps:

[0071] (1) Polyvinylidene fluoride was added to N-methylpyrrolidone and mechanically stirred until completely dissolved to obtain a mixed adhesive solution. Then, acetylene black, lithium iron phosphate, short carbon fibers and sodium chloride were added in sequence and mechanically stirred for 4 hours to obtain a slurry. The slurry was then coated on a current collector titanium mesh and dried in a 50°C oven for 8 hours and then dried at 90°C for 4 hours to obtain the electrode to be delithiated.

[0072] Based on the mass of the lithium iron phosphate, the content of acetylene black is 4%, the content of polyvinylidene fluoride is 6%, the content of N-methylpyrrolidone is 150%, the content of sodium chloride is 10%, the content of short carbon fibers is 2%, the coating thickness of the slurry is 3 mm, and the coating area is 18 cm × 23 cm.

[0073] (2) Prepare a 2wt% acetic acid solution according to 60wt% of the lithium removal amount of the electrode to be delithiated, heat to 40℃, add the electrode to be delithiated, and carry out the delithiation reaction for 16 hours under stirring to obtain a lithium extraction electrode after delithiation, the chemical formula of which is Li. 0.4 FePO4.

[0074] First, the lithium extraction electrode prepared in this embodiment is divided into two uniform parts, inner and outer, to detect the actual amount of lithium removed from the inner and outer parts. The detection results are shown in Table 3.

[0075] Table 3

[0076] Li (wt%) Inner side 21 Outer side 39

[0077] Secondly, the present invention conducts lithium extraction experiments on the lithium extraction electrode prepared in this embodiment, and the specific steps include:

[0078] 1) The lithium extraction device is divided into a cathode chamber and an anode chamber using an anion exchange membrane, and the prepared lithium extraction electrodes are placed in the anode chamber and cathode chamber respectively;

[0079] 2) Add 5L of brine to the cathode chamber, the composition of which is shown in Table 4 below. Add 3L of 5g / L NaCl solution to the anode chamber. Apply a 0.2C current to the anode and cathode. Stop electrolysis when the voltage is greater than 0.3V, and then charge at a constant voltage of 0.3V. When the current is lower than 0.5A / m... 2 Electrolysis was terminated at that time. The composition of the brine and the lithium-rich anode solution after lithium extraction is shown in Table 4.

[0080] Table 4

[0081]

[0082]

[0083] As shown in Table 4, the lithium concentration in the brine decreased from 0.71 g / L to 0.04 g / L, while the lithium concentration in the lithium-rich anode solution increased to 1.1 g / L, with an adsorption capacity of 24.9 mg / g.

[0084] In addition, after conducting the above lithium extraction experiment, the anode and cathode were reversed. 3L of a 5g / L NaCl solution was injected into the anode chamber, and 5L of fresh brine was injected into the cathode chamber for long-term circulation. The circulation curve is shown below. Figure 1As shown in the curve of Example 2, it can be seen that the lithium extraction electrode prepared by the preparation method provided by the present invention has a long cycle life, and the lithium extraction capacity retention rate is still above 90% after 600 cycles.

[0085] Example 3

[0086] The difference between this embodiment and Example 1 is that the concentration of the acetic acid solution is 0.1 wt%.

[0087] The remaining preparation methods and parameters are consistent with those in Example 1.

[0088] Example 4

[0089] The difference between this embodiment and Embodiment 1 is that the concentration of the acetic acid solution is 8 wt%.

[0090] The remaining preparation methods and parameters are consistent with those in Example 1.

[0091] Example 5

[0092] The difference between this embodiment and Embodiment 1 is that the temperature of the delithiation reaction is 10°C.

[0093] The remaining preparation methods and parameters are consistent with those in Example 1.

[0094] Example 6

[0095] The difference between this embodiment and Embodiment 1 is that the delithiation reaction temperature is 70°C.

[0096] The remaining preparation methods and parameters are consistent with those in Example 1.

[0097] In this invention, the lithium extraction electrodes prepared in Examples 1 and 3-6 were divided into two uniform portions, inner and outer, to detect the actual amount of lithium removed from the inner and outer portions. The detection results are shown in Table 5.

[0098] Table 5

[0099]

[0100] analyze:

[0101] As can be seen from Examples 1 and 3-4, if the concentration of the weak oxidant solution is too low, the amount of lithium removed will be too low to meet the design requirements; if the concentration of the weak oxidant solution is too high, the amount of lithium removed on the inner and outer sides will be basically the same.

[0102] As can be seen from Examples 1 and 5-6, if the temperature of the delithiation reaction is too low, the amount of delithiation will not meet the design requirements; if the temperature of the delithiation reaction is too high, the amount of delithiation on the inner and outer sides will differ greatly.

[0103] Comparative Example 1

[0104] This comparative example provides a method for preparing an electrode for lithium extraction, the method comprising the following steps:

[0105] (1) Prepare a 2wt% acetic acid solution according to 60wt% delithiation of lithium iron phosphate material, heat to 40℃, then add lithium iron phosphate powder, and stir for 2 hours to obtain the chemical formula Li 0.4 Lithium iron phosphate material after delithiation of FePO4;

[0106] (2) Polyvinylidene fluoride was added to N-methylpyrrolidone and mechanically stirred until completely dissolved to obtain a mixed adhesive solution. Then, acetylene black, the delithiated lithium iron phosphate material, short carbon fibers and sodium chloride were added in sequence and mechanically stirred for 4 hours to obtain a slurry. The slurry was then coated on a current collector titanium mesh and dried in a 50°C forced-air drying oven for 8 hours and then dried at 90°C for 4 hours to obtain the electrode to be delithiated.

[0107] Based on the mass of the lithium iron phosphate, the content of acetylene black is 4%, the content of polyvinylidene fluoride is 6%, the content of N-methylpyrrolidone is 150%, the content of sodium chloride is 10%, the content of short carbon fibers is 2%, the coating thickness of the slurry is 2 mm, and the coating area is 18 cm × 23 cm.

[0108] First, the lithium extraction electrode prepared in this comparative example is divided into two uniform parts, inner and outer, to detect the actual amount of lithium removed from the inner and outer parts. The detection results are shown in Table 6.

[0109] Table 6

[0110] Li (wt%) Inner side 30 Outer side 30

[0111] Secondly, the present invention conducts lithium extraction experiments on the lithium extraction electrode prepared in this embodiment, and the specific steps include:

[0112] 1) The lithium extraction device is divided into a cathode chamber and an anode chamber using an anion exchange membrane, and the prepared lithium iron phosphate electrode and the delithiated lithium iron phosphate electrode are placed in the anode chamber and the cathode chamber, respectively;

[0113] 2) Add 5L of brine to the cathode chamber, the composition of which is shown in Table 7 below. Add 3L of 5g / L NaCl solution to the anode chamber. Apply a current of 0.2C to the anode and cathode. Stop electrolysis when the voltage is greater than 0.3V, then maintain a constant voltage of 0.3V. When the current is less than 0.5A / m... 2 Electrolysis was terminated at the designated time. The composition of the brine and the lithium-rich anode solution after lithium extraction is shown in Table 7.

[0114] Table 7

[0115] Concentration (g / L) Li Na K Ca Mg SO4 2- ]]> B Brine 0.45 98.48 21.79 0.31 14.66 27.89 0.73 Brine after lithium extraction 0.04 98.40 21.77 0.30 14.62 27.85 0.73 Lithium-rich anode solution 0.66 2.10 0.03 0.01 0.05 0.07 0.01

[0116] In addition, after conducting the above lithium extraction experiment, the anode and cathode were reversed. 3L of a 5g / L NaCl solution was injected into the anode chamber, and 5L of fresh brine was injected into the cathode chamber for long-term circulation. The circulation curve is shown below. Figure 1 As shown in the curve of Comparative Example 1, it can be seen that the lithium extraction electrode prepared in this comparative example has a thick coating and the same amount of lithium removal on both the inner and outer sides, resulting in the same number of lithium ion vacancies on both the inner and outer sides. + The diffusion and electron pathways are long, Li + The mass transfer resistance is high, and the capacity shows a decreasing trend with the increase of lithium extraction times.

[0117] Comparative Example 2

[0118] This comparative example provides a method for preparing an electrode for lithium extraction, the method comprising the following steps:

[0119] (1) Polyvinylidene fluoride was added to N-methylpyrrolidone and mechanically stirred until completely dissolved to obtain a mixed adhesive solution. Then, acetylene black, lithium iron phosphate, short carbon fibers and sodium chloride were added in sequence and mechanically stirred for 4 hours to obtain a slurry. The slurry was then coated on a current collector titanium mesh and dried in a 50°C oven for 8 hours and then dried at 90°C for 4 hours to obtain the electrode to be delithiated.

[0120] Based on the mass of the lithium iron phosphate, the content of acetylene black is 4%, the content of polyvinylidene fluoride is 6%, the content of N-methylpyrrolidone is 150%, the content of sodium chloride is 10%, the content of short carbon fibers is 2%, the coating thickness of the slurry is 3 mm, and the coating area is 18 cm × 23 cm.

[0121] (2) Prepare a 2wt% sodium persulfate solution according to 60wt% of the lithium removal amount of the electrode to be delithiated, heat to 40℃, add the electrode to be delithiated, and carry out the delithiation reaction for 16 hours under stirring to obtain a lithium extraction electrode after delithiation, the chemical formula of which is Li. 0.4 FePO4.

[0122] First, the lithium extraction electrode prepared in this comparative example is divided into two uniform parts, inner and outer, to detect the actual amount of lithium removed from the inner and outer parts. The detection results are shown in Table 8.

[0123] Table 8

[0124]

[0125]

[0126] Secondly, the present invention conducts lithium extraction experiments on the lithium extraction electrode prepared in this embodiment, and the specific steps include:

[0127] 1) The lithium extraction device is divided into a cathode chamber and an anode chamber using an anion exchange membrane, and the prepared lithium iron phosphate electrode and the delithiated lithium iron phosphate electrode are placed in the anode chamber and the cathode chamber, respectively;

[0128] 2) Add 5L of brine to the cathode chamber, the composition of which is shown in Table 9 below. Add 3L of 5g / L NaCl solution to the anode chamber. Apply a current of 0.2C to the anode and cathode. Stop electrolysis when the voltage is greater than 0.3V, then maintain a constant voltage of 0.3V. When the current is lower than 0.5A / m... 2 Electrolysis was terminated at the designated time. The composition of the brine and lithium-rich anode solution after lithium extraction is shown in Table 9.

[0129] Table 9

[0130] Concentration (g / L) Li Na K Ca Mg SO4 2- ]]> B Brine 0.71 98.48 21.79 0.31 14.66 27.89 0.73 Brine after lithium extraction 0.04 98.40 21.77 0.30 14.62 27.85 0.73 Lithium-rich anode solution 1.09 2.10 0.03 0.01 0.05 0.07 0.01

[0131] In addition, after conducting the above lithium extraction experiment, the anode and cathode were reversed. 3L of a 5g / L NaCl solution was injected into the anode chamber, and 5L of fresh brine was injected into the cathode chamber for long-term circulation. The circulation curve is shown below. Figure 1 Concentration (g / L) Li Na Ca Mg Brine Brine after lithium extraction Lithium-rich anode solution Figure 1 As shown in the curve of Comparative Example 1, it can be seen that the lithium extraction electrode prepared in this comparative example has a thick coating and the same amount of lithium removal on both the inner and outer sides, resulting in the same number of lithium ion vacancies on both the inner and outer sides. + The diffusion and electron pathways are long, Li + The mass transfer resistance is high, and the capacity shows a decreasing trend with the increase of lithium extraction times.

[0132] In summary, although Comparative Example 1 and Comparative Example 2 showed good selectivity for lithium during the first lithium extraction, Comparative Example 1 used uniform delithiation of powder, resulting in the same amount of lithium removed from both the inner and outer sides. This led to increased electrode polarization and continuous capacity decay as the number of lithium extractions increased. Comparative Example 2 used sodium persulfate, which has strong oxidizing properties. The excessive oxidizing properties resulted in the same amount of lithium removed from both the inner and outer sides of the electrode. This also led to increased electrode polarization and continuous capacity decay as the number of lithium extractions increased.

[0133] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for producing an electrode for lithium extraction, characterized by, The preparation method comprises the following steps: (1) mixing an electrode active material, a conductive agent, a binder and a solvent to obtain a slurry, and then coating the slurry on a current collector to obtain a to-be-delithiated electrode after drying; wherein the coating thickness of the slurry is ≥2 mm; the content of the conductive agent is 4-10% based on the mass of the electrode active material in step (1); the content of the binder is 4-8%; and the content of the solvent is 100-150%; In the mixing process of step (1), a pore-forming agent and a reinforcing agent are also added; the pore-forming agent comprises any one or a combination of at least two of sodium chloride, ammonium bicarbonate or ammonium carbonate; the reinforcing agent comprises any one or a combination of at least two of short carbon fibers, lignin fibers, glass fibers, polypropylene fibers or cellulose fibers; the content of the pore-forming agent is 0-40% based on the mass of the electrode active material in step (1); and the content of the reinforcing agent is 1-3%; (2) mixing the to-be-delithiated electrode and a weak oxidizing agent solution to perform a delithiation reaction to obtain a delithiated lithium extraction electrode; The concentration of the weak oxidizing agent solution in step (2) is 0.25-5 wt%; the weak oxidizing agent in the weak oxidizing agent solution in step (2) comprises a combination of oxygen and carbon dioxide or any one or a combination of at least two of acetic acid; The temperature of the delithiation reaction in step (2) is 20-60°C, and the time is 2-12 h.

2. The production method according to claim 1, characterized by, The coating thickness of the slurry in step (1) is 2-5 mm.

3. The preparation method according to claim 1, characterized in that, The temperature of the drying in step (1) is 50-90°C, and the drying time is 5-12 h.

4. The production method according to claim 1, characterized by, The theoretical delithiation amount of the to-be-delithiated electrode in step (2) is 10-60 wt%.

5. The method of claim 1, wherein, The preparation method comprises the following steps: (1) adding a binder to a solvent to stir and dissolve, then sequentially adding a conductive agent, a positive electrode active material, a reinforcing agent and a pore-forming agent, stirring and mixing uniformly to obtain a slurry, and then coating the slurry on a current collector to obtain a to-be-delithiated electrode after drying at 50-90°C for 5-12 h; wherein the content of the conductive agent is 4-10% based on the mass of the electrode active material; the content of the binder is 4-8%; the content of the solvent is 100-150%; the content of the pore-forming agent is 0-40%; the content of the reinforcing agent is 1-3%; and the coating thickness of the slurry is ≥2 mm; (2) preparing a weak oxidizing agent solution with a concentration of 0.25-5 wt% according to the theoretical delithiation amount of the to-be-delithiated electrode, then adding the to-be-delithiated electrode, and performing a delithiation reaction at 20-60°C for 2-12 h to obtain a delithiated lithium extraction electrode.

6. A lithium extraction electrode prepared by the method according to any one of claims 1 to 5, characterized in that, The inner delithiation amount of the lithium extraction electrode is less than the outer delithiation amount.

7. Use of the lithium extraction electrode according to claim 6 in the field of lithium extraction from salt lakes.

Images