Electrode with high specific surface area and high loading capacity for electric control lithium extraction and preparation method thereof

Abstract

The invention discloses a high-specific-surface-area and high-loading-capacity electrode for electric control lithium extraction and a preparation method of the electrode. The preparation method comprises the following steps: 1) mixing and crushing a lithium adsorbent, a conductive agent, a binder and a pore forming agent, and mixing with an organic solvent to obtain a uniform mixed solution; (2) coating the surface of a base material with the mixed solution obtained in the step (1), drying, cooling after drying, and then introducing hot air again for heat treatment; and (3) after the pore-forming agent is removed, spraying an activated carbon layer on the surface of the electrode to obtain the electrode for electric control lithium extraction. The electrode for lithium extraction has a relatively high specific surface area due to rich pore structures and surface cracks, overcomes the problem of mass transfer blocking caused by too high film thickness of a high-load electrode, and is suitable for various salt lake raw brine, underground brine and oilfield brine; and a new technical scheme is provided for extracting lithium from brine by an electric control ion exchange technology.

Description

Technical Field:

[0001] The present invention belongs to the technical field of lithium extraction, and particularly relates to a preparation method of an electrode for electro-controlled lithium extraction with a high specific surface area and a high loading amount. Background Art:

[0002] With the rapid development of new energy vehicles, the market demand for lithium resources is increasing day by day. Nearly 60% of the global lithium resources are concentrated in salt lake brines. Therefore, lithium extraction from salt lake brines is crucial and imperative.

[0003] The methods for lithium extraction from salt lake brines mainly include precipitation method, solvent extraction method, electrodialysis method, adsorption method, etc. The precipitation method has a simple and mature process, but it is mainly applicable to salt lake brines with a low magnesium-lithium ratio and is not suitable for the high magnesium-lithium ratio salt lakes in China. The extraction method has the advantages of strong continuity, high efficiency, and low fixed cost investment. However, at present, there are still problems such as serious equipment corrosion, easy degradation and deterioration of the extractant, and serious solvent entrainment loss. The advantage of the electrodialysis technology lies in its high separation coefficient, low energy consumption, and no pollution. However, the production cost of the key materials, the monovalent and polyvalent ion selective permeable membranes, is high, resulting in an increase in production cost and many instabilities. The advantage of the adsorption method lies in its high lithium recovery rate, high selectivity, simple desorption process, and low cost. The disadvantage is that most of the adsorbents are in powder form and need to be preformed before large-scale industrial application. Among them, the aluminum-based adsorbents have a low adsorption capacity, while the ion sieve-type adsorbents have a high dissolution loss.

[0004] Kang Jin et al. proposed in "Research Progress of Ionic Liquids for Lithium Extraction from Salt Lake Brines" to use ionic liquids to replace the traditional combination of DBP and FeCl3 to avoid problems such as equipment corrosion and environmental pollution caused by traditional methods. However, the use of ionic liquids still does not change the problems of too high production cost and extractant loss of the extraction method. Yu Liangliang used LiMn2O4 as an adsorbent in "Preparation and Performance Study of Spinel-Type Manganese-Based Lithium Ion Sieve" and used the adsorption method for lithium extraction from salt lakes. However, the dissolution loss of the adsorbent is extremely high and the cycle stability is poor under this method. In view of the deficiencies of the existing lithium extraction technologies, scholars have gradually started to study a new type of lithium extraction technology from salt lakes, that is, the electro-controlled ion exchange technology. This technology is a new type of ion separation technology that combines electrochemistry and ion exchange. By electrochemically controlling the reduction / oxidation state of the membrane, the ion intercalation and deintercalation are realized. It can not only improve the ion exchange efficiency and achieve precise control of the ion exchange process, but also the ion separation does not require chemical regeneration, avoiding secondary pollution caused by chemical regenerants. However, the total amount of lithium extraction by this technology is severely restricted by the electrode loading amount, that is, the membrane thickness. When the membrane thickness is too large, the internal diffusion resistance is serious, the mass transfer is blocked, and the efficiency and the effective reaction area decrease. Therefore, there is an urgent need to develop a preparation method that can make the high membrane thickness electrode have a high specific surface area. Summary of the Invention:

[0005] The object of the present invention is to provide a preparation method of an electrode for electro-controlled lithium extraction with a high specific surface area and a high loading amount, so as to overcome the problem of mass transfer obstruction caused by the high film thickness mentioned above, and thus improve the total amount of lithium extraction.

[0006] On the one hand, the present invention provides a preparation method of an electrode for electro-controlled lithium extraction with a high specific surface area and a high loading amount, comprising the following steps:

[0007] (1) Mix and pulverize a lithium adsorbent, a conductive agent, a binder, and a pore-forming agent, and mix them with an organic solvent to obtain a homogeneous mixture;

[0008] (2) Coat the mixture obtained in step (1) on the surface of a substrate material and then dry it. After drying is completed, perform a cooling treatment, and then introduce hot air again for heat treatment;

[0009] (3) After removing the pore-forming agent, spray an activated carbon layer on the surface of the electrode to obtain an electrode for electro-controlled lithium extraction.

[0010] In the present invention, the lithium adsorbent is selected from one or more of LiMn2O4, Li4Mn5O 12 , Li 1.6 Mn 1.6 O4, LiFePO4; preferably, one or more of LiMn2O4, Li4Mn5O 12 , Li 1.6 Mn 1.6 O4 are used as the lithium adsorbent. The adsorption capacity of the manganese-based ion sieve is higher, and the problem of manganese dissolution loss existing in the manganese-based ion sieve itself can be solved by an electro-controlled method.

[0011] In the present invention, the conductive agent is selected from one or more of C65 carbon black, acetylene black, Ketjen black, Super P, graphene, carbon nanotubes, activated carbon for capacitors.

[0012] In the present invention, the binder is selected from one or more of polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polystyrene, chlorinated polyvinyl chloride, polymethyl methacrylate, polycarbonate; preferably, the weight-average molecular weight of the binder is between 500,000 and 1,000,000.

[0013] In the present invention, the pore-forming agent is selected from one or more of NaCl, KCl, Na2SO4, K2SO4, Na2CO3, K2CO3, NH4Cl, NH4HCO3, (NH4)2CO3, PEG-6000, Al2O3; when the electrode is subjected to alternating hot and cold treatment, the pore-forming agent needs to be removed by soaking in water or heating. In particular, only when Al2O3 is used as the pore-forming agent, hydrochloric acid soaking is required to remove the pore-forming agent.

[0014] In the present invention, the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; preferably, the organic solvent is N-methylpyrrolidone.

[0015] In the present invention, the mass ratio of the lithium adsorbent: conductive agent: binder: pore-forming agent: organic solvent is 7-10: 0.5-2: 0.5-5: 0.5-2: 28-40.

[0016] In the present invention, the particle size of the mixed powder after mixing and pulverizing the lithium adsorbent, conductive agent, binder, and pore-forming agent is greater than 10 microns and less than 40 microns.

[0017] In the present invention, the matrix material used is selected from one of carbon fiber cloth, carbon fiber felt, graphite plate, titanium plate, and titanium mesh, and preferably a graphite plate.

[0018] In the present invention, the thickness of the electrode coating is 1500μm - 2000μm.

[0019] In the present invention, the drying temperature is 80 - 150°C, and the duration is 12 - 24h. The air flow rate is 0.5 - 10mL / min.

[0020] In the present invention, the temperature of the cooling treatment is -10°C - 0°C, and the duration is 1 - 2h.

[0021] In the present invention, the temperature of the heat treatment is 80 - 150°C, and the duration is 12 - 24h. The air flow rate condition is 0.5 - 10mL / min.

[0022] In the present invention, the carbon spraying uses a carbon spraying instrument to spray the activated carbon in the carbon tank onto the electrode surface under pressure, and the thickness of the activated carbon layer is 15nm - 50nm.

[0023] The beneficial effects of the present invention are as follows:

[0024] The Al2O3 pore-forming agent used in this patent can be removed by using an acid. In particular, when using this pore-forming agent and this removal method, the activation of the manganese-based ion sieve electrode can be completed simultaneously, obtaining the counter electrode required for the subsequent electro-controlled ion exchange process, which simplifies the overall experimental process.

[0025] In addition to using the method of alternating low-temperature cooling and high-temperature evaporation at a certain air flow rate, the present invention causes cracks to naturally occur on the electrode surface. The advantage is that the cracks are naturally generated due to stress changes caused by the alternation of cold and heat, and have minimal impact on the structural stability of the electrode itself. In addition, compressed air is used to assist the solvent evaporation process of the electrode coating, making the evaporation process artificially controllable, avoiding both the low efficiency problem caused by too slow evaporation rate and the problem of unstable coating structure caused by too fast evaporation rate.

[0026] After obtaining the electrode with surface cracks, the present invention adds a step of carbon spraying. Through this operation, the electrode can achieve the purpose of plating a carbon layer from the inside out through the cracks, thereby further enhancing the electrode conductivity and weakening the high resistance problem brought by the high-film-thickness electrode. Specific implementation manner:

[0027] The following specific examples further illustrate the above invention in detail, but the scope of the present invention is not limited to the following examples. Without departing from the above method thinking of the present invention, appropriate substitutions or changes are within the scope of the present invention.

[0028] The main raw material sources used in the examples and comparative examples of the present invention are as follows, and all can be obtained through ordinary commercial channels. LiMn2O4, Li4Mn5O 12 、Li 1.6 Mn 1.6 O4, LiFePO4, organic solvents, the pore-forming agent brand is Aladdin, with a purity greater than 99%; the polyvinylidene fluoride brand is Innochem (A97278) with a weight-average molecular weight of about 1 million, the polyvinyl chloride brand is Aladdin (P434342-1kg) with a weight-average molecular weight of about 1 million, the polyacrylic acid brand is Yuanye (S59107-25g) with a weight-average molecular weight of about 1.25 million, the polycarbonate brand is Adamas (41389BA), with a weight-average molecular weight of about 900,000; the carbon black brand is Alfa (H30253) with a purity greater than 99%, the Ketjen black brand is Kelude (MA-EN-CO-060211) EC-300J, the graphene brand is Apinno (GC112858) with a purity greater than 98%, and the activated carbon for capacitors brand is Xianfeng Nano (100566) SSA: 1800㎡ / g.

[0029] Testing method:

[0030] The ball mill is produced by Changsha Tianchuang Powder Technology Co., Ltd., with the model SQM-0.5. The ball milling conditions are 20 minutes, and the rotation speed of the machine itself is fixed.

[0031] The carbon spraying instrument is produced by Leica of Switzerland, model is Leica EMACE600, the carbon spraying thickness is 15-50nm, the type of carbon spraying is mostly activated carbon for capacitors, the brand of activated carbon for capacitors is Xianfeng Nano (100566), SSA: 1800㎡ / g.

[0032] The test conditions for the electrode adsorption capacity are as follows: the electrode described in this patent and the activated carbon electrode are used as counter electrodes and placed in a 0.5 mol / L lithium chloride solution. The adsorption experiment is carried out using the electrically controlled ion exchange technology in a 1 V constant voltage mode. The time required for the current to decay to a constant value is recorded as the adsorption equilibrium time. The concentration change of the lithium chloride solution before and after the adsorption test is measured to calculate the adsorption capacity.

[0033] Example 1

[0034] (1) Take 10g Li4Mn5O 12 2g of polyvinylidene fluoride, 5g of carbon black and 2g of Al2O3 were added to 40g of N,N-dimethylformamide and fully mixed and dispersed in an ultrasonic oscillator to obtain a casting solution; an automatic film scraping machine was used to prepare an electrode coating with a thickness of 2000 microns on the surface of the carbon fiber cloth.

[0035] (2) Immediately after preparation, Li4Mn5O 12 The electrode was placed in a 150°C oven and kept at a constant temperature for 24 hours in a hot air environment with a flow rate of 10 mL / min; then, the electrode was placed in a refrigerator at a temperature of 0°C to cool for 2 hours; finally, it was put back into the oven at a temperature of 150°C and kept at an air flow rate of 10 mL / min for 24 hours.

[0036] (3) After the electrode is taken out, it is completely immersed in 0.5 mol / L hydrochloric acid for 24 hours. After drying, the activated carbon in the carbon can is sprayed onto the electrode surface under pressure using a Swiss Leica carbon sprayer, thereby spraying a layer of highly conductive 15 nm activated carbon layer for capacitors on the electrode surface, thereby obtaining a high film thickness electrode with uniform cracks.

[0037] Example 2

[0038] (1) 7 g of LiMn2O4, 0.5 g of polyvinyl chloride, 0.5 g of graphene and 0.5 g of KCl were added to 28 g of N,N-dimethylacetamide and fully mixed and dispersed in an ultrasonic oscillator to obtain a casting solution; an automatic film scraping machine was then used to prepare an electrode coating with a thickness of 1500 μm on the surface of the carbon fiber felt.

[0039] (2) Immediately after preparation, the LiMn2O4 electrode was placed in an oven at 80°C and kept at a constant temperature for 12 hours in a hot air environment with a flow rate of 0.5 mL / min; then, the electrode was placed in a refrigerator at a temperature of -10°C and cooled for 1 hour; finally, it was returned to the oven at a temperature of 120°C and kept at an air flow rate of 0.5 mL / min for 12 hours.

[0040] (3) After the electrode is taken out, it is completely immersed in pure water for 24 hours. After drying, the activated carbon in the carbon can is sprayed onto the electrode surface under pressure using a Swiss Leica carbon sprayer, thereby spraying a layer of highly conductive 50nm capacitor activated carbon layer on the electrode surface to obtain a high film thickness electrode with uniform cracks.

[0041] Example 3

[0042] (1) 8 g of LiFePO, 3 g of polyacrylic acid, 1 g of Ketjen black and 1 g of Na2SO4 were added to 35 g of N-methylpyrrolidone and fully mixed and dispersed in an ultrasonic oscillator to obtain a casting solution; an automatic film scraping machine was then used to prepare an electrode coating with a thickness of 1800 μm on the surface of a graphite plate.

[0043] (2) Immediately after preparation, the LiFePO4 electrode was placed in a 120°C oven and maintained at a constant temperature for 18 hours in a hot air environment with a flow rate of 5 mL / min; then, the electrode was placed in a refrigerator at a temperature of -5°C and cooled for 1.5 hours; finally, it was returned to the oven at a temperature of 120°C and maintained at an air flow rate of 5 mL / min for 18 hours.

[0044] (3) After the electrode is taken out, it is completely immersed in pure water for 24 hours. After drying, the activated carbon in the carbon can is sprayed onto the electrode surface under pressure using a Swiss Leica carbon sprayer, thereby spraying a layer of highly conductive 35nm capacitor activated carbon layer on the electrode surface, thereby obtaining a high film thickness electrode with uniform cracks.

[0045] Example 4

[0046] (1) Take 9 g Li 1.6 Mn 1.6 O4, 1.5g polycarbonate, 1.5g activated carbon for capacitors and 1.5g NH4HCO3 were added to 30g N-methylpyrrolidone and fully mixed and dispersed in an ultrasonic oscillator to obtain a casting solution; an automatic scraping machine was used to prepare an electrode coating with a thickness of 1700 microns on the surface of the graphite plate.

[0047] (2) Immediately after preparation, Li 1.6 Mn 1.6The O4 electrode was placed in an oven at 100 °C and kept at a constant temperature for 16 h in a hot air environment with a flow rate of 3 mL / min; then, the electrode was placed in a refrigerator at -3 °C and cooled for 2 h; finally, it was put back into the oven at 100 °C and kept for 16 h at an air flow rate of 3 mL / min.

[0048] (3) After the electrode was taken out, it was completely immersed in pure water for 24 h. After drying, a Swiss Leica carbon spraying instrument was used to spray the activated carbon in the carbon tank onto the electrode surface under pressure, so as to spray a 25-nm-thick activated carbon layer with high conductivity for the capacitor on the electrode surface, and a high-film-thickness electrode with uniform cracks could be obtained.

[0049] Comparative Example 1

[0050] (1) 7 g of LiMn2O4, 0.5 g of polyvinyl chloride, 0.5 g of graphene, and 0.5 g of KCl were added to 28 g of N,N-dimethylacetamide and mixed and dispersed thoroughly in an ultrasonic oscillator to obtain a casting solution; then, an automatic film scraping machine was used to prepare an electrode coating with a thickness of 1500 microns on the surface of the carbon fiber felt.

[0051] (2) Immediately after preparation, the LiMn2O4 electrode was placed in an oven at 80 °C and kept at a constant temperature for 12 h.

[0052] (3) After the electrode was taken out, it was completely immersed in pure water for 24 h. After drying, a Swiss Leica carbon spraying instrument was used to spray the activated carbon in the carbon tank onto the electrode surface under pressure, so as to spray a 50-nm-thick activated carbon layer with high conductivity for the capacitor on the electrode surface, and a high-film-thickness electrode with a complete surface and no cracks could be obtained.

[0053] Comparative Example 2

[0054] (1) 9 g of Li 1.6 Mn 1.6 O4, 1.5 g of polycarbonate, 1.5 g of activated carbon for the capacitor, and 1.5 g of NH4HCO3 were added to 30 g of N-methylpyrrolidone and mixed and dispersed thoroughly in an ultrasonic oscillator to obtain a casting solution; then, an automatic film scraping machine was used to prepare an electrode coating with a thickness of 1700 microns on the surface of the graphite plate.

[0055] (2) Immediately after preparation, the Li 1.6 Mn 1.6 O4 electrode was placed in an oven at 100 °C and kept at a constant temperature for 16 h in a hot air environment with a flow rate of 3 mL / min; then, the electrode was placed in a refrigerator at -3 °C and cooled for 2 h; finally, it was put back into the oven at 100 °C and kept for 16 h at an air flow rate of 3 mL / min.

[0056] (3) After the electrode is taken out, completely immerse the electrode in pure water for 24 h to obtain a high film thickness electrode with uniform cracks.

[0057] Sample Adsorption capacity / (mg / g) Time required to reach equilibrium / min Example 1 16 15 Example 2 14 13 Example 3 12 10 Example 4 16 14 Comparative Example 1 6 30 Comparative Example 2 10 25

[0058] As can be seen from the above table, this patent can effectively enhance the lithium ion mass transfer rate and effect of the high film thickness electrode, enhance the electrode conductivity, so as to achieve the effects of improving the adsorption capacity and reducing the equilibrium time.

Claims

1. A preparation method of an electrode for electrochemically extracting lithium with high specific surface area and high loading capacity, comprising the following steps : (1) Mix and pulverize a lithium adsorbent, a conductive agent, a binder, and a pore-forming agent, and mix with an organic solvent to obtain a uniformly mixed solution; (2) Coat the mixed solution obtained in step (1) on the surface of a substrate material and then dry it. After drying is completed, perform a cooling treatment, and then introduce hot air again for heat treatment; (3) After removing the pore-forming agent, spray an activated carbon layer on the surface of the electrode to obtain an electrode for electrochemically extracting lithium.

2. The preparation method according to claim 1, characterized in that, The lithium adsorbent is selected from LiMn2O4, Li4Mn5O 12 , Li 1.6 Mn 1.6 O4, LiFePO4, or one or more of them; preferably one or more of LiMn2O4, Li4Mn5O 12 , Li 1.6 Mn 1.6 O4.

3. The preparation method according to claim 1 or 2, characterized in that, The conductive agent is selected from one or more of C65 carbon black, acetylene black, Ketjen black, Super P, graphene, carbon nanotubes, and activated carbon for capacitors; and / or, the binder is selected from one or more of polyvinyl chloride, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polystyrene, chlorinated polyvinyl chloride, polymethyl methacrylate, polycarbonate; preferably, the weight-average molecular weight of the binder is between 500,000 and 1,000,000.

4. The preparation method according to any one of claims 1 to 3, characterized in that, The pore-forming agent is selected from NaCl, KCl, Na2SO4, K2SO4, Na2CO3, K2CO3, NH4Cl, NH4HCO3, (NH4)2CO3, PEG-6000, and one or more of Al2O3; and / or, the organic solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

5. The preparation method according to any one of claims 1-4, characterized in that, The lithium adsorbent: The mass ratio of the conductive agent: the binder: the pore-forming agent: the organic solvent is 7-10: 0.5-2: 0.5-5: 0.5-2: 28-40; and / or, the substrate material used is selected from one of carbon fiber cloth, carbon fiber felt, graphite plate, titanium plate, and titanium mesh, preferably a graphite plate.

6. The preparation method according to any one of claims 1-5, characterized in that, The thickness of the electrode coating is 1500μm-2000μm; and / or, the drying temperature is 80-150°C, and the duration is 12-24h; the air flow rate is 0.5-10mL / min.

7. The preparation method according to any one of claims 1-6, characterized in that, The temperature of the cooling treatment is -10°C-0°C, and the duration is 1-2h.

8. The preparation method according to any one of claims 1-7, characterized in that, The temperature of the heat treatment is 80-150°C, and the duration is 12-24h, and the air flow rate condition is 0.5-10mL / min.

9. The preparation method according to any one of claims 1-8, characterized in that, The thickness of the activated carbon layer is 15nm-50nm.

10. An electrode for electrochemically extracting lithium prepared by the preparation method according to any one of claims 1-9.