Method for preparing lithium extraction electrode and application thereof

Abstract

The present disclosure belongs to the technical field of lithium extraction from salt lake, and discloses a preparation method of lithium extraction electrode and application thereof, wherein a lithium source, an iron source, a phosphorus source and a polymer are uniformly mixed in a solvent, the obtained mixture is dried, the obtained dry material is firstly calcined under a protective atmosphere, and then is subjected to secondary calcination by introducing carbon dioxide or water vapor to obtain lithium iron phosphate, which is soaked in an ammonium bicarbonate solution, the soaked lithium iron phosphate is mixed with a conductive agent, a binder and N-methyl pyrrolidone to prepare a slurry, which is coated on a current collector and is heated and dried to obtain the lithium extraction electrode.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of lithium extraction from salt lake, and particularly relates to a preparation method of a lithium extraction electrode and application thereof. BACKGROUND

[0002] Lithium is widely used in the field of lithium batteries. With the rapid development of the new energy field, the market demand for lithium resources is rapidly increasing, and the development of low-cost and efficient lithium resources has become an important guarantee for enterprises to participate in market competition. The proven lithium resources in nature mainly exist in salt lake brine, seawater and ores, of which the salt lake lithium resources account for about 70%. Due to the high cost and great difficulty of lithium ore mining, and with the increasing depletion and exhaustion of lithium resources, the extraction of lithium from salt lake brine has become a trend in the development of lithium resources.

[0003] At present, the methods for extracting lithium from brine at home and abroad mainly include precipitation method, solvent extraction method, evaporation crystallization method, electrodialysis method, ion exchange adsorption method, etc. The precipitation method, as a mature lithium extraction technology, has the disadvantages of high energy consumption, complex process flow, high cost, and low lithium recovery rate. The extraction method has a fast lithium extraction rate, but the extraction agent dissolved in the brine can easily cause environmental pollution; the adsorption method has the problems of low adsorption capacity, adsorbent dissolution and large water consumption. In recent years, many researchers at home and abroad have carried out extensive exploration and research on new lithium extraction processes, and the electrochemical lithium extraction technology has good use value and application prospect.

[0004] The principle of electrochemical lithium extraction is to charge the working electrode to remove lithium ions to form a lithium ion sieve, and to discharge in the salt water to make the lithium ions selectively enter the lithium ion sieve, so as to realize the enrichment of lithium through the charging and discharging process. However, due to the low lithium concentration in the brine and the presence of a large amount of impurity elements such as magnesium and sodium, the viscosity of the brine is large, which leads to slow mass transfer of the solution inside the electrode, and the efficiency of electrochemical lithium extraction is low. Therefore, it is of great significance to improve the ion transmission rate of the electrode.

[0005] Generally, the conductivity and cycle stability of the electrode are improved by coating a layer of carbon on the surface of the electrode active material. However, the ordinary carbon coating layer is dense or has small pores, and when used for salt lake lithium extraction, it cannot form a uniform mass transfer channel, which leads to slow solution transmission and reduces the lithium extraction efficiency. SUMMARY

[0006] The present disclosure aims to at least solve one of the technical problems existing in the prior art. To this end, the present disclosure proposes a preparation method of a lithium extraction electrode and its application. First, the synthesis raw materials of lithium iron phosphate are dispersed in a polymer network, and the lithium iron phosphate is generated by high-temperature calcination while the polymer is carbonized into a carbon conductive network. Then, a porous carbon network is formed by cooperating with CO2 high-temperature treatment. Finally, the pore-forming agent is uniformly adsorbed on the conductive carbon by mixing with the pore-forming agent, and the pore-forming agent volatilizes to form a uniform mass transfer channel during electrode drying, thereby improving the lithium extraction efficiency.

[0007] According to one aspect of the present disclosure, a preparation method of a lithium extraction electrode is proposed, comprising the following steps:

[0008] S1: mixing a lithium source, an iron source, a phosphorus source and a polymer in a solvent, drying the obtained mixture to obtain a dry material;

[0009] S2: first calcining the dry material at a temperature of 600-900°C in a protective atmosphere, and then second calcining by introducing carbon dioxide or water vapor at a temperature of 750-900°C to obtain lithium iron phosphate;

[0010] S3: soaking the lithium iron phosphate in an ammonium bicarbonate solution, and solid-liquid separation to obtain a solid material;

[0011] S4: mixing the solid material, a conductive agent, a binder and N-methyl pyrrolidone to prepare a slurry, coating the slurry on a current collector, and heating and drying to obtain the lithium extraction electrode.

[0012] In some embodiments of the present disclosure, in step S1, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium dihydrogen phosphate or lithium acetate.

[0013] In some embodiments of the present disclosure, in step S1, the iron source is at least one of ferrous oxalate, ferric nitrate or ferric phosphate.

[0014] In some embodiments of the present disclosure, in step S1, the phosphorus source is at least one of ammonium dihydrogen phosphate or phosphoric acid.

[0015] In some embodiments of the present disclosure, in step S1, the polymer is at least one of polypyrrole, polyethylene, polypropylene, polystyrene, polycarbonate or polyaniline.

[0016] In some embodiments of the present disclosure, in step S1, the solvent is at least one of ethanol, acetone, methanol or water.

[0017] In some embodiments of the present disclosure, in step S1, the lithium source, the iron source and the phosphorus source are mixed in a molar ratio of Li:Fe:P=(1.2-2):(1-1.1):1.

[0018] In some embodiments of the present disclosure, in step S1, the amount of the polymer added is 1-10% of the mass of the synthesized lithium iron phosphate.

[0019] In some embodiments of the present disclosure, in step S1, the mixing method is ball milling, and the ball milling time is 4-12 h. Ball milling can refine the particles of the raw materials and make the raw materials mix more uniformly.

[0020] In some embodiments of the present disclosure, in step S2, the first calcination time is 12-24 h.

[0021] In some embodiments of the present disclosure, in step S2, the temperature is raised to the first calcination temperature at a temperature raising rate of 5-10 ℃ / min.

[0022] In some embodiments of the present disclosure, in step S2, the flow rate of the carbon dioxide or water vapor introduced is 0.05-0.5 L / min.

[0023] In some embodiments of the present disclosure, in step S2, the second calcination time is 1-4 h.

[0024] In some embodiments of the present disclosure, in step S2, the temperature is raised to the second calcination temperature at a temperature raising rate of 2-8 ℃ / min.

[0025] In some embodiments of the present disclosure, in step S3, the concentration of the ammonium bicarbonate solution is 0.1-1 mol / L, and the solid-liquid ratio of the lithium iron phosphate to the ammonium bicarbonate solution is 1 g / (2-6) mL.

[0026] In some embodiments of the present disclosure, in step S3, the soaking time is 2-6 h.

[0027] In some embodiments of the present disclosure, in step S4, the density of the slurry coating is 150-200 mg / cm 2 .

[0028] In some embodiments of the present disclosure, in step S4, the temperature for the heating and drying is 50-80 ℃, and the time is 4-8 h.

[0029] The present disclosure also provides the use of the lithium extraction electrode prepared by the preparation method in salt lake lithium extraction.

[0030] According to the embodiments of the present disclosure, at least the following beneficial effects are achieved:

[0031] The lithium source, iron source and phosphorus source are mixed and ground with a polymer first, and then calcined at high temperature, while the lithium iron phosphate is generated, the polymer is carbonized to form a carbon conductive network, so that the synthesized lithium iron phosphate is distributed in the carbon conductive network. Then, part of the carbon reacts with CO2 / water vapor to form CO gas at high temperature, forming a porous carbon network. When the lithium iron phosphate embedded with the porous carbon network is mixed with the ammonium bicarbonate solution, the ammonium bicarbonate is easily adsorbed on the porous carbon, so that a large amount of ammonium bicarbonate is uniformly distributed around the lithium iron phosphate particles. During the electrode drying process, the ammonium bicarbonate is decomposed by heat to produce a large amount of gas, forming uniform mass transfer channels between the lithium iron phosphate particles. Therefore, the present disclosure can not only improve the conductivity of the material and accelerate the migration of electrons, but also promote the mass transfer of the solution and improve the lithium extraction efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0032] The present disclosure will be further described below in combination with the drawings and examples, in which:

[0033] Figure 1 The lithium extraction efficiency of the electrodes of the examples and comparative examples of the present disclosure is compared. DETAILED DESCRIPTION

[0034] The concept and technical effects of the present disclosure will be described below in combination with examples to fully understand the purpose, features and effects of the present disclosure.

[0035] Example 1

[0036] An electrochemical deintercalation method salt lake lithium extraction electrode is prepared in this example, and the specific process is as follows:

[0037] (1) 29 g of lithium hydroxide, 144 g of ferrous oxalate, 115 g of ammonium dihydrogen phosphate and 15 g of polyaniline are weighed and placed in a ball mill jar, and anhydrous ethanol is added as a dispersant, and mixed and ball milled for 12 h.

[0038] (2) After the ball milling material of step (1) is dried, it is placed in a tube furnace, heated to 900℃ at a rate of 10℃ / min under a nitrogen atmosphere, calcined for 12 h, and then 0.5 L / min of CO2 gas is introduced, and the temperature is kept at 900℃ for 2 h to make part of the carbon react with CO2 to obtain lithium iron phosphate.

[0039] (3) Ammonium bicarbonate is dissolved in deionized water to prepare a 1 mol / L solution, and the lithium iron phosphate obtained in step (2) is placed in the ammonium bicarbonate solution according to the solid-liquid ratio of 1 g:2 mL, mixed uniformly, and then filtered after standing for 3 h, and naturally air dried to obtain a solid material.

[0040] (4) Take the solid material of step (3), acetylene black and PVDF by mass ratio 8:1:1, add N-methyl pyrrolidone NMP, fully stir to form slurry, uniformly coat the slurry on the titanium mesh current collector, the coating density is 200 mg / cm 2 , 80℃ dry for 5h to obtain a porous electrode.

[0041] Example 2

[0042] In this embodiment, an electrochemical deintercalation method salt lake lithium electrode is prepared, and the specific process is as follows:

[0043] (1) Take 45g lithium carbonate, 242g iron nitrate, 115g ammonium dihydrogen phosphate, 8g polyaniline, and place them in a ball mill tank. Add anhydrous ethanol as a dispersant and mix ball mill for 8h.

[0044] (2) After drying the ball milling material of step (1), place it in a tube furnace, heat to 600℃ at a rate of 5℃ / min under nitrogen atmosphere, calcine for 24h, then pass CO2 gas at a flow rate of 0.1L / min, heat to 800℃ at a rate of 5℃ / min, and keep the temperature for 4h to make part of the carbon react with CO2 to obtain lithium iron phosphate.

[0045] (3) Dissolve ammonium bicarbonate in deionized water to prepare a 0.1mol / L solution. Place the lithium iron phosphate obtained in step (2) in the ammonium bicarbonate solution according to the solid-liquid ratio of 1g:6mL, mix uniformly, stand for 2h, then filter and air dry to obtain a solid material.

[0046] (4) Take the solid material of step (3), acetylene black and PVDF by mass ratio 8:1:1, add N-methyl pyrrolidone NMP, fully stir to form slurry, uniformly coat the slurry on the titanium mesh current collector, the coating density is 200 mg / cm 2 , 80℃ dry for 5h to obtain a porous electrode.

[0047] Example 3

[0048] In this embodiment, an electrochemical deintercalation method salt lake lithium electrode is prepared, and the specific process is as follows:

[0049] (1) Take 45g lithium carbonate, 242g iron nitrate, 115g ammonium dihydrogen phosphate, 8g polyaniline, and place them in a ball mill tank. Add anhydrous ethanol as a dispersant and mix ball mill for 8h.

[0050] (2) After drying the ball milling material of step (1), place it in a tube furnace, heat to 600℃ at a rate of 5℃ / min under nitrogen atmosphere, calcine for 24h, then pass CO2 gas at a flow rate of 0.1L / min, heat to 800℃ at a rate of 5℃ / min, and keep the temperature for 4h to make part of the carbon react with CO2 to obtain lithium iron phosphate.

[0051] (3) Ammonium bicarbonate was dissolved in deionized water to prepare a 0.5 mol / L solution, and the lithium iron phosphate obtained in step (2) was placed in the ammonium bicarbonate solution at a solid-liquid ratio of 1 g:4 mL, uniformly mixed, and then filtered after standing for 4 h, and naturally air-dried to obtain a solid material.

[0052] (4) The solid material of step (3), acetylene black and PVDF were weighed at a mass ratio of 8:1:1, added into N-methyl pyrrolidone (NMP), and fully stirred to form a slurry, which was uniformly coated on a titanium mesh current collector at a coating density of 150 mg / cm 2 , and dried at 60°C for 8 h to obtain a porous electrode.

[0053] Comparative Example 1

[0054] This comparative example prepared an electrochemical deintercalation method salt lake lithium extraction electrode, which differed from Example 1 in that no CO2 gas was introduced for treatment, and the specific process was as follows:

[0055] (1) 29 g of lithium hydroxide, 144 g of ferrous oxalate, 115 g of ammonium dihydrogen phosphate, and 15 g of polyaniline were placed in a ball mill jar, and anhydrous ethanol was added as a dispersant, and the mixture was ball milled for 12 h.

[0056] (2) The ball milled material of step (1) was dried and then placed in a tube furnace, and heated to 900°C at a rate of 10°C / min under a nitrogen atmosphere, and calcined for 12 h to obtain lithium iron phosphate.

[0057] (3) Ammonium bicarbonate was dissolved in deionized water to prepare a 1 mol / L solution, and the lithium iron phosphate obtained in step (2) was placed in the ammonium bicarbonate solution at a solid-liquid ratio of 1 g:2 mL, uniformly mixed, and then filtered after standing for 3 h, and naturally air-dried to obtain a solid material.

[0058] (4) The solid material of step (3), acetylene black and PVDF were weighed at a mass ratio of 8:1:1, added into N-methyl pyrrolidone (NMP), and fully stirred to form a slurry, which was uniformly coated on a titanium mesh current collector at a coating density of 200 mg / cm 2 , and dried at 80°C for 5 h to obtain a porous electrode.

[0059] Comparative Example 2

[0060] This example prepared an electrochemical deintercalation method salt lake lithium extraction electrode, which differed from Example 1 in that no ammonium bicarbonate solution was soaked, and the specific process was as follows:

[0061] (1) 29 g of lithium hydroxide, 144 g of ferrous oxalate, 115 g of ammonium dihydrogen phosphate, and 15 g of polyaniline were placed in a ball mill jar, and anhydrous ethanol was added as a dispersant, and the mixture was ball milled for 12 h.

[0062] (2) The ball-milled material of step (1) was dried and placed in a tube furnace, and heated to 900℃ at a rate of 10℃ / min under nitrogen atmosphere for 12h, then CO2 gas was introduced at a flow rate of 0.5L / min, and the temperature was kept at 900℃ for 2h to make part of the carbon react with CO2 to obtain lithium iron phosphate.

[0063] (3) Lithium iron phosphate, acetylene black and PVDF of step (2) were weighed according to a mass ratio of 8:1:1, added into N-methyl pyrrolidone (NMP), and fully stirred to form a slurry, which was uniformly coated on a titanium mesh current collector at a coating density of 200mg / cm 2 , and dried at 80℃ for 5h to obtain a porous electrode.

[0064] Comparative Example 3

[0065] In this example, a lithium extraction electrode from salt lake by electrochemical deintercalation method was prepared, which was different from Example 1 in that no CO2 gas was introduced for treatment, and no ammonium bicarbonate solution was soaked. The specific process was as follows:

[0066] (1) 29g of lithium hydroxide, 144g of ferrous oxalate, 115g of ammonium dihydrogen phosphate and 15g of polyaniline were weighed and placed in a ball mill tank, and anhydrous ethanol was added as a dispersant, and mixed and ball milled for 12h.

[0067] (2) The ball-milled material of step (1) was dried and placed in a tube furnace, and heated to 900℃ at a rate of 10℃ / min under nitrogen atmosphere for 12h to obtain lithium iron phosphate.

[0068] (3) Lithium iron phosphate, acetylene black and PVDF of step (2) were weighed according to a mass ratio of 8:1:1, added into N-methyl pyrrolidone (NMP), and fully stirred to form a slurry, which was uniformly coated on a titanium mesh current collector at a coating density of 200mg / cm 2 , and dried at 80℃ for 5h to obtain a porous electrode.

[0069] Test Example

[0070] Lithium extraction experiment: The electrodes prepared in the examples and comparative examples were used as positive electrodes, AgCl electrode was used as negative electrode, and 0.05mol / L KCl solution was used as electrolyte. The lithium-rich electrode was deintercalated at a constant voltage of 1.0V to obtain a lithium-poor electrode. The electrolytic device was separated into anode and cathode chambers by an anion exchange membrane. The lithium-rich electrode and the lithium-poor electrode were placed in the anode chamber and the cathode chamber respectively. Brine with a lithium concentration of 1.52g / L was injected into the cathode chamber, and NaCl solution was injected into the anode chamber. A voltage of 0.3V was applied to the anode and cathode to extract lithium.

[0071] The lithium extraction efficiency of the electrodes in the lithium extraction process of the examples and comparative examples was detected as shown in Table 1. Figure 1As shown, the anode lithium concentration and the brine lithium concentration change over time as shown in Table 1.

[0072] Table 1 Anode lithium concentration and brine lithium concentration at different time points for lithium extraction

[0073]

[0074]

[0075] As can be seen from the results of Examples 1-3 in Table 1, the electrodes prepared using the lithium iron phosphate materials provided in Examples 1-3 exhibit high lithium extraction efficiency, because the porous carbon embedded in the lithium iron phosphate material can adsorb a large amount of ammonium bicarbonate molecules, which are easily decomposed to form mass transfer channels during electrode drying, thereby improving the adsorption and desorption efficiency of lithium ions. The adsorption amount of ammonium bicarbonate has a significant effect on the lithium extraction effect of the electrode. When there are more pores in the carbon network and the concentration of the ammonium bicarbonate solution is higher, a large amount of ammonium bicarbonate is easily adsorbed on the porous carbon, and the porosity is large during electrode preparation, so the lithium extraction effect of the electrode is better, the lithium concentration in the brine after lithium extraction is lower, and the lithium concentration in the anode solution is higher.

[0076] As can be seen from the results of Example 1 and Comparative Example 1, the lithium extraction efficiency of the electrode of Comparative Example 1 is lower, because Comparative Example 1 does not remove part of the carbon in the carbon network to form pores, the adsorption amount of ammonium bicarbonate is less, the porosity is lower, and the number of mass transfer channels is less.

[0077] As can be seen from the results of Example 1 and Comparative Example 2, the lithium extraction efficiency of the electrode of Comparative Example 2 is lower, because Comparative Example 2 does not adsorb ammonium bicarbonate on the porous carbon, and cannot further form pores, so the solution only mass transfers through the porous carbon.

[0078] As can be seen from the results of Comparative Examples 1, 2 and 3, the lithium extraction efficiency of the electrode of Comparative Example 3 is the lowest, because Comparative Example 3 neither removes part of the carbon in the carbon network to form pores, nor adsorbs ammonium bicarbonate on the carbon network, so mass transfer channels cannot be formed between the particles, resulting in low lithium extraction efficiency of the electrode.

Claims

1. A method for producing a lithium extraction electrode, characterized by, The method comprises the following steps: S1: mixing a lithium source, an iron source, a phosphorus source and a polymer in a solvent, drying the obtained mixture to obtain a dry material; S2: first calcining the dry material at a temperature of 600-900 DEG C under a protective atmosphere, then introducing carbon dioxide or water vapor to perform second calcination at a temperature of 750-900 DEG C, to obtain lithium iron phosphate; S3: immersing the lithium iron phosphate in an ammonium bicarbonate solution, and performing solid-liquid separation to obtain a solid material; S4: mixing the solid material, a conductive agent, a binder and N-methyl pyrrolidone to prepare a slurry, coating the slurry on a current collector, and heating and drying to obtain the lithium extraction electrode; In step S2, the flow rate of the introduced carbon dioxide or water vapor is 0.05-0.5 L / min, and the second calcination time is 1-4 h.

2. The production method according to claim 1, characterized by, In step S1, the lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium dihydrogen phosphate or lithium acetate.

3. The preparation method according to claim 1, characterized in that, In step S1, the iron source is at least one of ferrous oxalate, iron nitrate or iron phosphate.

4. The method of claim 1, wherein, In step S1, the phosphorus source is at least one of ammonium dihydrogen phosphate or phosphoric acid.

5. The preparation method according to claim 1, characterized in that, In step S1, the polymer is at least one of polypyrrole, polyethylene, polypropylene, polystyrene, polycarbonate or polyaniline.

6. The method of claim 1, wherein, In step S1, the solvent is at least one of ethanol, acetone, methanol or water.

7. The preparation method according to claim 1, characterized in that, In step S1, the lithium source, the iron source and the phosphorus source are mixed in a molar ratio of Li:Fe:P=(1.2-2):(1-1.1):

1.

8. The method of claim 1, wherein, In step S1, the polymer is added in an amount of 1%-10% of the mass of the synthesized lithium iron phosphate.

9. The method of claim 1, wherein, In step S1, the mixing is performed by ball milling, and the ball milling time is 4-12 h.

10. The method of claim 1, wherein, In step S2, the first calcination time is 12-24 h.

11. The method of claim 1, wherein, In step S2, the temperature is raised to the first calcination temperature at a temperature raising rate of 5-10 DEG C / min.

12. The method of claim 1, wherein, In step S2, the temperature is raised to the second calcination temperature at a temperature raising rate of 2-8 DEG C / min.

13. The method of claim 1, wherein, In step S3, the concentration of the ammonium bicarbonate solution is 0.1-1 mol / L, and the solid-liquid ratio of the lithium iron phosphate to the ammonium bicarbonate solution is 1 g / (2-6) mL.

14. The method of claim 1, wherein, In step S3, the immersion time is 2-6 h.

15. The method of claim 1, wherein, In step S4, the density of the slurry coating is 150-200 mg / cm 2 .

16. The method of claim 1, wherein, In step S4, the heating and drying temperature is 50-80 DEG C, and the time is 4-8 h.

17. The lithium extraction electrode prepared by the method of any one of claims 1-16 is applied to lithium extraction in a salt lake.

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