Method and device for extracting lithium ions with low impurities by electrochemical method

Abstract

This application discloses a method and apparatus for electrochemical extraction to obtain low-impurity lithium ions, relating to the field of capacitive deionization technology. The apparatus includes a positive current collector and a negative current collector with a working surface coated with mesoporous activated carbon material and a chemically de-intercalated lithium ion sieve. A lithium-ion-containing solution circulates between the working surfaces of the positive and negative current collectors. A voltage is applied to insert lithium ions into the chemically de-intercalated lithium ion sieve. After the power is turned off, the cations adsorbed by the mesoporous activated carbon material are re-desorbed. The resulting lithium-ion-intercalated sieve electrode is placed in an electrolyte solution and a voltage is applied to remove lithium. This application uses mesoporous activated carbon material as the negative electrode to adsorb impurity cations in the salt solution. The impurity cations are enriched on the surface of the activated carbon and do not accumulate on the surface of the ion sieve, hindering the absorption of lithium. + By placing the lithium ion extraction device closer to the chemical deintercalation sieve, the content of impurity cations intercalating into the sieve lattice can be reduced, thereby improving the lithium extraction efficiency and purity of the sieve.

Description

Technical Field

[0001] This application relates to the field of capacitive deionization technology, and in particular to a method and apparatus for electrochemical extraction to obtain low-impurity lithium ions. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices and new energy electric vehicles, leading to a rapid increase in market demand for lithium resources. There is an urgent need to develop lithium resources to provide high-quality, low-cost lithium raw materials for lithium-ion batteries. Lithium in nature is abundant in mineral deposits such as ores, salt lake brines, geothermal water, and seawater. Among these, salt lake brines are particularly rich in lithium resources and have relatively high lithium content. Therefore, efficient lithium extraction from salt lake brines has become a major research direction in the development and utilization of lithium resources.

[0003] Researchers have developed various lithium extraction processes to address the characteristics of different types of brine. Current main extraction methods include concentration precipitation crystallization, adsorption, electrodialysis, extraction, membrane separation, electrolysis, and calcination leaching. Among these, capacitive deionization (CDI) is an electro-adsorption desalination technology based on the electrochemical double-layer capacitance theory. The electrode material is primarily carbon. When a certain voltage is applied across a porous electrode, ions in the brine move towards the electrode with the opposite charge under the influence of the electric field and are adsorbed onto the electrode surface. Once the porous electrode is saturated, short-circuiting the electrode releases the adsorbed cations and anions back into the water, thus regenerating the electrode. Existing patent CN102382984A discloses a method and apparatus for separating and enriching lithium from magnesium in salt lake brine. This method utilizes an electrodialysis device isolated by anion exchange membranes and an iron phosphate sieve to separate lithium from other ions, simultaneously obtaining a lithium-rich solution.

[0004] However, both the aforementioned capacitor deionization lithium extraction method and the technology disclosed in existing patent CN102382984A involve the adsorption of Mg during the extraction of lithium ions from the solution. 2+ Due to issues with other impurity cations, lithium extraction efficiency is not high enough. Therefore, there is an urgent need to find a lithium extraction method that reduces the adsorption of impurity cations and is highly efficient. Summary of the Invention

[0005] This application provides a method and apparatus for electrochemical extraction to obtain low-impurity lithium ions. It utilizes activated carbon to adsorb impurity cations, reducing the probability of impurity cations entering the chemical deintercalation lithium ion sieve, thereby improving the efficiency and purity of selective lithium extraction by the chemical deintercalation lithium ion sieve.

[0006] To address the aforementioned technical problems, one objective of this application is to provide an apparatus for electrochemical extraction of low-impurity lithium ions, comprising a positive current collector and a negative current collector respectively connected to a power source;

[0007] The positive electrode current collector is an activated carbon electrode material;

[0008] The working surface of the negative electrode current collector is coated with a cation adsorption coating, which includes mesoporous activated carbon material and a chemically inserted / extracted lithium ion sieve.

[0009] The inventors of this application discovered in their research that, during the operation of the chemical lithium-ion intercalation / deintercalation sieve, in addition to adsorbing Li... + In addition, it will also accumulate Ca. 2+ Mg 2+ K + Na + Impurity cations, which aggregate on the surface of the chemical lithium-ion intercalation / deintercalation sieve, can hinder the formation of the target cation Li with the same charge. + While approaching chemical deintercalation lithium-ion sieves, these impurity cations may enter the crystal structure of the sieve, resulting in impurities in the product. In capacitive deionization technology, mesoporous activated carbon electrodes, as cathodes, more readily adsorb high-valence cations and cations with small hydration radii, thus enhancing their ability to adsorb Ca2+. 2 + Mg 2+ K + Na + The adsorption capacity is greater than that for Li + The adsorption capacity was assessed by using mesoporous activated carbon as the negative electrode to adsorb impurity cations in the salt solution, and by employing a chemical lithium-ion intercalation / deintercalation sieve to adsorb Li. + ions, realizing Li + Separation from other impurity cations improves lithium extraction efficiency and purity.

[0010] Furthermore, there is a gap between the working surfaces of the positive current collector and the negative current collector, which can be used to allow the lithium-ion-containing solution to flow and can connect the working surfaces of the positive current collector and the negative current collector.

[0011] Furthermore, the pore size of the mesoporous activated carbon material is 40% to 80%.

[0012] By adopting the above scheme, since the hydration radius of high-valence ions is smaller than that of low-valence ions, it is necessary to ensure that the pores of the activated carbon material are larger than the hydration radius of high-valence ions, so that high- and low-valence ions can easily enter the activated carbon material. When the valence of the two ions is the same, the activated carbon material tends to adsorb ions with smaller hydration radii, such as sodium and potassium, whose hydration radii are smaller than those of lithium. The inventors of this application selected a pore occupancy rate within this pore size range to achieve a better adsorption effect on impurity cations while reducing the adsorption effect on lithium ions. A lower pore occupancy rate will lead to a decrease in the adsorption effect of mesoporous activated carbon on impurity anions and cations, affecting the lithium extraction efficiency and purity, while a higher pore occupancy rate will lead to excessively high preparation costs.

[0013] Furthermore, the raw materials for preparing the cation adsorption coating include a mesoporous activated carbon material slurry and a chemically extracted lithium ion sieve slurry;

[0014] The mesoporous activated carbon material slurry comprises mesoporous activated carbon material, a first binder, a first dispersant, and a first conductive agent; the chemically deintercalated lithium ion sieve slurry comprises a chemically deintercalated lithium ion sieve, a second binder, a second dispersant, and a second conductive agent.

[0015] Furthermore, the chemically extracted lithium-ion sieve slurry and the mesoporous activated carbon material slurry are alternately coated along the working surface of the negative electrode current collector at a width ratio of 1:(1-5) to form a cation adsorption coating. Using this method, impurity cations and lithium ions can be better separated, and controlling the width ratio can prevent the large adsorption area of ​​the mesoporous activated carbon material from affecting the adsorption capacity of the chemically extracted lithium-ion sieve, or the small adsorption area from affecting the purity of lithium extraction. Alternatively, the chemically extracted lithium-ion sieve slurry and the mesoporous activated carbon material slurry can be mixed at a mass ratio of 1:(1-70) and coated onto the working surface of the negative electrode current collector to form a cation adsorption coating. This method is relatively simple, and the mixing amount can prevent the large adsorption amount of the mesoporous activated carbon material from affecting the adsorption capacity of the chemically extracted lithium-ion sieve, or the small adsorption amount from affecting the purity of lithium extraction. However, the mixed coating results in a closer distance between the impurity cations and lithium ions, leading to limited improvement in separation quality.

[0016] Furthermore, the chemically extracted lithium-ion screen slurry and the mesoporous activated carbon material slurry are mixed at a mass ratio of 1:(10-15) and coated onto the working surface of the negative electrode current collector to form a cation adsorption coating.

[0017] Furthermore, when the chemically extracted lithium-ion screen slurry and the mesoporous activated carbon material slurry are alternately coated along the parallel direction of the negative electrode current collector working surface to form a cation adsorption coating at a width ratio of 1:(1~5), the unit of the width ratio is centimeters.

[0018] Furthermore, after the chemically extracted lithium-ion sieve slurry and the mesoporous activated carbon material slurry are coated on the working surface of the negative electrode current collector, they are vacuum dried at 100-140°C for 550-700 min to form a cation adsorption coating.

[0019] Furthermore, at least one of the following conditions must be met:

[0020] (a) The mass ratio of each raw material in the preparation of the mesoporous activated carbon slurry is: mesoporous activated carbon material: first conductive agent: first binder = (5~10):1:1;

[0021] (b) The mass ratio of each raw material in the preparation of the chemically deintercalated lithium-ion sieve slurry is: chemically deintercalated lithium-ion sieve: second conductive agent: second binder = (12~17):1:1;

[0022] (c) The raw materials for preparing the mesoporous activated carbon slurry also include a first dispersant;

[0023] (d) The raw materials for preparing the chemically deintercalated lithium ion sieve slurry also include a second dispersant.

[0024] Furthermore, the first conductive agent and the second conductive agent are each independently selected from at least one of conductive carbon black, conductive graphite, carbon nanotubes and graphene.

[0025] Furthermore, the first dispersant and the second dispersant are each independently selected from at least one of N-methylpyrrolidone, ethanol, tetrachloroethane, toluene, xylene, anisole, dimethylformamide, dimethylacetamide, dibutyl phthalate, and dimethyl sulfoxide.

[0026] Furthermore, the first adhesive and the second adhesive are each independently selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, and polyimide.

[0027] Furthermore, the chemical deintercalation / intercalation lithium ion screening is selected from at least one of the following: iron phosphate ion sieve, lithium manganese ion sieve, and lithium titanate ion sieve.

[0028] Furthermore, the amount of slurry coating on the working surface of the negative electrode current collector is 100–300 g / cm³. 2 .

[0029] Further, the mesoporous activated carbon material is prepared by the following method: activated carbon and alkali metal are mixed and heated to 250-550°C under the protection of inert gas for 2-5 hours, then heated to 750-950°C, and activated gases water vapor and carbon dioxide are introduced and held for 1-2 hours to obtain activated activated carbon; the activated activated carbon is impregnated with hydrochloric acid, and water vapor is introduced to make it boil, filtered while hot, washed until neutral, and dried to obtain the mesoporous activated carbon material.

[0030] Furthermore, the mass ratio of the activated carbon to the alkali metal is 1:(1-2).

[0031] Furthermore, the alkali metal is sodium hydroxide and / or potassium hydroxide.

[0032] Further, in the preparation step of mesoporous activated carbon material, the activated carbon is impregnated with 5-10 wt% hydrochloric acid, and then boiled by passing in 0.3-0.6 MPa water vapor. It is then filtered while hot, washed until neutral, and dried to obtain mesoporous activated carbon material.

[0033] Furthermore, the volume ratio of water vapor to carbon dioxide in the activating gas is (1-4):2.

[0034] Furthermore, the chemically inserted / extracted lithium ion sieve is prepared by the following method: lithium iron phosphate is placed in a conductive solution, and the potential is adjusted to oxidize ferrous iron to ferric iron and allow lithium ions to enter the conductive solution. The solid phase is then filtered, washed, and dried to obtain the lithium iron phosphate ion sieve.

[0035] Furthermore, in the preparation step of the chemically inserted / extracted lithium ion sieve, the potential is adjusted to 1V to 1.2V.

[0036] Furthermore, in the preparation step of the chemical deintercalation lithium ion sieve, the conductive solution is a sodium chloride solution of 25-30 g / L.

[0037] To address the aforementioned technical problems, a second objective of this application is to provide a method for electrochemical extraction to obtain low-impurity lithium ions, comprising the following steps:

[0038] The lithium-ion-containing solution is circulated through the gap between the positive and negative electrode current collector working surfaces of the device. A voltage is applied for the first time to insert lithium ions into the chemically inserted lithium-ion sieve. After the power is turned off, the circulation allows the cations adsorbed by the mesoporous activated carbon material to re-enter the lithium-ion-containing solution, thus obtaining the lithium-ion-intercalated sieve electrode.

[0039] The lithium-ion intercalation sieve electrode is placed in an electrolyte solution, and a voltage is applied a second time to deintercalate the lithium ions in the lithium-ion intercalation sieve electrode, resulting in a lithium-ion-enriched solution.

[0040] Furthermore, when the voltage is applied for the first time, the flow rate of the lithium-ion solution between the working surfaces of the two parallel electrodes of the device is 10-40 mL / min, and the cycle is repeated 3-5 times.

[0041] Furthermore, after power is cut off, the circulating flow for 2-5 minutes allows the cations adsorbed by the mesoporous activated carbon material to re-enter the lithium-ion-containing solution.

[0042] Furthermore, the lithium-ion-containing solution is a chloride salt solution, which can be one of salt lake brine or its evaporated concentrate, seawater or its evaporated concentrate, or industrial waste brine containing LiCl.

[0043] Furthermore, the concentration of lithium ions in the lithium-ion-containing solution is below 500 mg / L, and the concentration of impurity cations is above 1000 mg / L.

[0044] Furthermore, the first applied voltage is 0.5V to 2.1V; the second applied voltage is 0.5V to 1.5V.

[0045] Furthermore, the electrolyte solution is a sodium chloride solution of 25–30 g / L.

[0046] Compared with the prior art, this application has the following beneficial effects:

[0047] 1. This application employs mesoporous activated carbon material as the negative electrode to adsorb impurity cations in a salt solution. The cations in the brine are simultaneously adsorbed by both the chemical lithium-ion intercalation / deintercalation sieve and the mesoporous activated carbon material. Due to the selectivity of the mesoporous activated carbon material, the impurity cations accumulate on the surface of the mesoporous activated carbon material and do not aggregate on the surface of the chemical lithium-ion intercalation / deintercalation sieve. Meanwhile, Li... + Embedded within the lattice of a chemically intercalated / deintercalated lithium-ion sieve, preventing impurity cations from hindering Li. + Placing lithium near the chemical lithium-ion deintercalation sieve can improve its lithium extraction efficiency, reduce the amount of impurity cations intercalating into the sieve's lattice, and enhance its ability to extract lithium (Li). + The adsorption efficiency and purity are improved by utilizing the easy adsorption and desorption properties of mesoporous activated carbon materials. After the power is turned off, the impurity cations adsorbed by the mesoporous activated carbon materials are completely desorbed, thereby removing Li... + and Mg 2+ Impurity cations are separated from each other.

[0048] 2. The mesoporous activated carbon material prepared in this application is not only readily resistant to impurity cations Ca... 2+ Mg 2+ K + Na +The adsorption process is simple and easy to implement. When coated on the surface of the current collector simultaneously with a chemically deintercalated lithium ion sieve, it can also greatly enhance the conductivity of the electrode. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of a lithium extraction apparatus for an electrochemical method to obtain low-impurity lithium ions, as described in Examples 1-2 of this application.

[0050] Figure 2 This is a schematic diagram of a lithium extraction apparatus for an electrochemical method to obtain low-impurity lithium ions, as described in Examples 3-4 of this application. Detailed Implementation

[0051] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0052] Example 1

[0053] An electrochemical method for extracting low-impurity lithium ions includes the following steps:

[0054] (1) Preparation of ferric phosphate ion sieve slurry:

[0055] a. Place the lithium iron phosphate cathode material (FePO4 / C) in a conductive solution, which is a 25 g / L sodium chloride solution. Adjust the system potential to 1.2 V to reduce the Fe content in the lithium iron phosphate cathode material. 2+ Oxidized into Fe 3+ At the same time, it makes the Li in the lithium iron phosphate cathode material + After entering the solution, the solid phase is filtered, washed, and dried to obtain an iron phosphate ion sieve.

[0056] b. Mix the ferric phosphate ion sieve, conductive agent and binder in a mass ratio of 15:1:1. Add the mixed powder to the dispersant and grind it into a slurry. The conductive agent is acetylene black, the binder is polyvinylidene fluoride and the dispersant is N-methylpyrrolidone.

[0057] (2) Preparation of mesoporous activated carbon material slurry:

[0058] a. Mix activated carbon raw material with sodium hydroxide at a mass ratio of 1:2, heat under inert gas protection for 4 hours at a heating temperature of 450℃ to obtain pretreated activated carbon, continue heating to 900℃, introduce activation gases water vapor and carbon dioxide at a volume ratio of 1:1, heat for 1.5 hours to obtain activated activated carbon.

[0059] b. The obtained activated carbon is impregnated with 8wt% hydrochloric acid solution, and 0.5MPa water vapor is introduced to make it boil. It is filtered while hot, washed repeatedly three times, and then washed with deionized water until neutral. After drying, mesoporous activated carbon material is obtained, with 60% of the pore size controlled between 0.5 and 10 nm.

[0060] c. Mix the mesoporous activated carbon material, conductive agent, and binder in a mass ratio of 8:1:1 until uniform. Add the mixed powder dropwise to the dispersant and grind it into a slurry. The conductive agent is acetylene black, the binder is polyvinylidene fluoride, and the dispersant is N-methylpyrrolidone.

[0061] (3) Preparation of electrode coated with mesoporous activated carbon and ferric phosphate sieve: The ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are mixed evenly at a ratio of 1:15 and coated onto the working section surface of the negative electrode current collector with a coating amount of 200 g / cm³. 2 After vacuum drying at 125°C for 650 min, a negative electrode with a coating of mesoporous activated carbon and iron phosphate ion sieve is obtained. The positive electrode current collector is a conventional activated carbon electrode material. After electrically connecting the positive and negative electrodes to the battery, a lithium extraction device is obtained.

[0062] (4) Lithium separation:

[0063] a. such as Figures 1-2 As shown in Table 1, 1L of brine from a salt lake is flowed through the gap between the positive and negative electrode current collectors of a lithium extraction device. The composition and content of the brine are shown in Table 1 below. The flow rate is 25mL / min, a voltage of 1.0V is applied, and the process is repeated 3 times to increase the Li content in the brine. + It is embedded in the ferric phosphate ion sieve, while the activated carbon portion preferentially adsorbs Ca. 2+ Mg 2+ K + Na + Reduce Ca 2+ Mg 2+ The probability of impurity cations entering the ion sieve;

[0064] b. After the power is cut off, the impurity cations adsorbed by the activated carbon re-enter the brine, while Li + Embedded in the ion sieve lattice, it is not easy to desorb. After 5 minutes of cycling, the impurity cations are removed, resulting in a lithium-intercalated ion sieve electrode, which realizes the separation of lithium.

[0065] (5) Lithium extraction: The lithium-intercalated ion-sieve electrode is removed and placed in a Ca-free environment. 2+ Mg 2+In the electrolyte salt solution, the electrolyte salt solution is a 25 g / L sodium chloride solution. A voltage of 1 V is applied to cause the lithium ions embedded in the ion sieve coating to be de-intercalated, thereby obtaining a lithium-enriched solution and realizing the extraction of lithium.

[0066] Table 1 - Composition and Content of Salt Lake Brine

[0067] Element Concentration (mg / L) <![CDATA[Li + ]]> 200 <![CDATA[Na + ]]> 1800 <![CDATA[Mg 2+ ]]> 900 <![CDATA[K + ]]> 700 <![CDATA[Ca 2+ ]]> 300

[0068] In Embodiment 1 of this application, after the salt lake brine was circulated three times in the lithium extraction device, it was tested and found that the ferric phosphate ion sieve showed a high Li... + The adsorption capacity was 40.3 mg / g, accounting for 98% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.12 mg / g, for Mg 2+ The adsorption capacity was 0.15 mg / g for K+, 0.25 mg / g for K+, and 0.32 mg / g for Na+. Because mesoporous activated carbon electrodes, when used as cathodes, more readily adsorb high-valence cations and cations with small hydration radii, such as Ca2+, they are more effective at adsorbing these cations. 2+ Mg 2+ K + Na + Adsorption capacity for Li > + Due to its adsorption capacity, mesoporous activated carbon materials at the cathode can be used to adsorb Ca from salt lake brine. 2+ Mg 2+ K + Na + Impurity cations are effectively reduced, thus minimizing their aggregation on the surface of the ferric phosphate ion sieve. This reduces the likelihood of impurity cations blocking the target cation Li, which has the same charge. + This increases the chance of accessing the ferric phosphate ion sieve, and on the other hand, reduces the entry of these impurity cations into the lattice structure of the ferric phosphate ion sieve, thereby improving the purity of the extracted lithium. Simultaneously, because the impurity cations adsorbed by the mesoporous activated carbon material are easily detached after power is turned off, and Li... + It is difficult for the ions embedded in the lattice of the iron phosphate ion sieve to detach, thus realizing Li + Separation from impurity cations.

[0069] Example 2

[0070] An electrochemical method for extracting low-impurity lithium ions is disclosed. All steps, reagents, and process parameters used in each step are the same as in Example 1. The difference lies in step (3): the ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are mixed uniformly at a ratio of 1:10 and coated onto the working section surface of the negative electrode current collector with a coating amount of 200 g / cm³. 2 .

[0071] In Embodiment 2 of this application, after the salt lake brine was circulated three times in the lithium extraction device, it was tested and found that the ferric phosphate sieve was effective against Li. + The adsorption capacity was 39.8 mg / g, accounting for 97.3% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.16 mg / g, for Mg 2+ The adsorption capacity was 0.21 mg / g, the adsorption capacity for K+ was 0.30 mg / g, and the adsorption capacity for Na+ was 0.42 mg / g.

[0072] Example 3

[0073] An electrochemical method for extracting low-impurity lithium ions is disclosed. All steps, reagents, and process parameters used in each step are the same as in Example 1. The difference lies in step (3): the ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are mixed uniformly at a ratio of 1:20 and coated onto the working section surface of the negative electrode current collector with a coating amount of 200 g / cm³. 2 .

[0074] In Embodiment 3 of this application, after the salt lake brine was circulated three times on the lithium extraction device, it was tested and found that the ferric phosphate ion sieve showed a high Li... + The adsorption capacity was 36.6 mg / g, accounting for 98.4% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.10 mg / g, for Mg 2+ The adsorption capacity was 0.11 mg / g, the adsorption capacity for K+ was 0.19 mg / g, and the adsorption capacity for Na+ was 0.21 mg / g.

[0075] Example 4

[0076] An electrochemical method for extracting low-impurity lithium ions is disclosed. All steps, reagents, and process parameters used in each step are the same as in Example 1. The difference lies in step (3): the ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are mixed uniformly in a 1:4 ratio and coated onto the working section surface of the negative electrode current collector at a coating amount of 200 g / cm³. 2 .

[0077] In Embodiment 4 of this application, after the salt lake brine was circulated three times in the lithium extraction device, it was tested and found that the ferric phosphate sieve was effective against Li. + The adsorption capacity was 40.5 mg / g, accounting for 96.8% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.28 mg / g, for Mg 2+ The adsorption capacity was 0.31 mg / g, the adsorption capacity for K+ was 0.34 mg / g, and the adsorption capacity for Na+ was 0.42 mg / g.

[0078] Example 5

[0079] An electrochemical method for extracting low-impurity lithium ions is disclosed. All steps, reagents, and process parameters are the same as in Example 1. The difference lies in step (3), where the ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are alternately and uniformly coated along the parallel direction of the negative electrode current collector working section at a width ratio of 1 cm:4 cm, with a coating amount of 200 g / cm. 2 .

[0080] In Example 5 of this application, after the salt lake brine was circulated three times in the lithium extraction device, it was tested and found that the ferric phosphate sieve was effective against Li. + The adsorption capacity was 41.1 mg / g, accounting for 98.6% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.13 mg / g, for Mg 2+ The adsorption capacity was 0.15 mg / g, the adsorption capacity for K+ was 0.13 mg / g, and the adsorption capacity for Na+ was 0.18 mg / g.

[0081] Example 6

[0082] An electrochemical method for extracting low-impurity lithium ions is described. All steps, reagents, and process parameters are the same as in Example 5. The difference lies in step (3), where the ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are alternately and uniformly coated along the parallel direction of the negative electrode current collector working section at a width ratio of 1 cm:7 cm, with a coating amount of 200 g / cm. 2 .

[0083] In Embodiment Six of this application, after the salt lake brine is circulated three times in the lithium extraction device, the ferric phosphate ion sieve is used to screen for Li. + The adsorption capacity was 36.5 mg / g, accounting for 98.9% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.10 mg / g, for Mg 2+ The adsorption capacity was 0.08 mg / g, the adsorption capacity for K+ was 0.10 mg / g, and the adsorption capacity for Na+ was 0.11 mg / g.

[0084] Example 7

[0085] An electrochemical method for extracting low-impurity lithium ions is disclosed. All steps, reagents, and process parameters are the same as in Example 6. The difference lies in step (3), where the ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are alternately and uniformly coated along the parallel direction of the negative electrode current collector working section at a width ratio of 1:2, with a coating amount of 200 g / cm². 2 .

[0086] In Embodiment 7 of this application, after the salt lake brine is circulated three times in the lithium extraction device, the ferric phosphate ion sieve is used to screen for Li. + The adsorption capacity was 41.7 mg / g, accounting for 97.6% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.22 mg / g, for Mg 2+ The adsorption capacity was 0.31 mg / g, the adsorption capacity for K+ was 0.23 mg / g, and the adsorption capacity for Na+ was 0.28 mg / g.

[0087] Example 8

[0088] An electrochemical method for extracting low-impurity lithium ions is disclosed. All steps, reagents, and process parameters are the same as in Example 7. The difference lies in step (3), where the ferric phosphate sieve slurry obtained in step (1) and the mesoporous activated carbon material slurry obtained in step (2) are alternately and uniformly coated along the parallel direction of the negative electrode current collector working section at a width ratio of 2:1, with a coating amount of 200 g / cm². 2 .

[0089] In Embodiment 8 of this application, after the salt lake brine is circulated three times in the lithium extraction device, the ferric phosphate ion sieve is used to screen for Li. + The adsorption capacity was 32.6 mg / g, accounting for 88% of the total adsorption capacity, for Ca 2+ The adsorption capacity was 0.68 mg / g, for Mg 2+ The adsorption capacity was 0.71 mg / g, the adsorption capacity for K+ was 1.47 mg / g, and the adsorption capacity for Na+ was 1.58 mg / g.

[0090] Comparative Example 1

[0091] An electrochemical method for extracting low-impurity lithium ions is provided. The steps, reagents, and process parameters used in each step are the same as in Example 1. The difference is that in step (3), the iron phosphate sieve slurry obtained in step (1) is uniformly coated on the working section surface of the negative electrode current collector.

[0092] In Comparative Example 1 of this application, after the brine from the salt lake was circulated three times in a lithium extraction device, the ferric phosphate sieve showed the effect on Li... + The adsorption capacity was 28.5 mg / g, for Ca2+ The adsorption capacity was 0.75 mg / g, for Mg 2+ The adsorption capacity for K+ was 0.81 mg / g, for K+ it was 1.64 mg / g, and for Na+ it was 1.72 mg / g. Compared to the examples, the lithium extraction device in Comparative Example 1 did not have a mesoporous activated carbon material coated on the cathode, and therefore could not adsorb impurity cations from the brine to reduce their content in the lattice structure of the ferric phosphate ion sieve, resulting in poor adsorption of Li+. + The adsorption capacity was significantly reduced, and at the same time, a large amount of impurity cations, such as Mg, were also adsorbed. 2+ and Ca 2+ .

[0093] Comparative Example 2

[0094] An electrochemical method for extracting low-impurity lithium ions is provided. The steps and reagents and process parameters used in each step are the same as those in Example 1. The difference is that in step (2)c, the activated carbon material that has not been treated into a mesoporous state, the conductive agent and the binder are mixed evenly in a mass ratio of 8:1:1. The mixed powder is added dropwise to the dispersant and ground into a slurry.

[0095] In Comparative Example 2 of this application, after the salt lake brine was circulated three times in a lithium extraction device, the ferric phosphate sieve showed the effect on Li... + The adsorption capacity was 29.84 mg / g, for Ca 2+ The adsorption capacity was 0.63 mg / g, for Mg 2+ The adsorption capacity was 0.62 mg / g. This indicates that using mesoporous activated carbon materials helps improve the adsorption of impurity cations such as Ca in salt lake brine. 2+ Mg 2+ K + Na + The adsorption and desorption of impurity cations by the iron phosphate sieve reduces the amount of impurity cations embedded in the lithium ion sieve lattice and hinders the approach of Li+ to the lithium ion sieve, thereby improving the adsorption and desorption of Li+ by the iron phosphate sieve. + The extraction purity and content.

[0096] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application for those skilled in the art.

Claims

1. An apparatus for electrochemical extraction of low-impurity lithium ions, characterized in that, This includes a positive current collector and a negative current collector, which are respectively connected to the power source; The positive electrode current collector is an activated carbon electrode material; The working surface of the negative electrode current collector is coated with a cation adsorption coating, which contains mesoporous activated carbon material and a chemical lithium ion deintercalation / intercalation sieve. The raw materials for preparing the cation adsorption coating include mesoporous activated carbon material slurry and chemically extracted lithium ion sieve slurry. The mesoporous activated carbon material slurry comprises mesoporous activated carbon material, a first binder, a first dispersant, and a first conductive agent; the chemically deintercalated lithium-ion sieve slurry comprises a chemically deintercalated lithium-ion sieve, a second binder, a second dispersant, and a second conductive agent. The chemically extracted lithium-ion screen slurry and the mesoporous activated carbon material slurry are alternately coated along the working surface of the negative electrode current collector in a width ratio of 1: (1~5) to form a cation adsorption coating. Alternatively, the chemically extracted lithium-ion screen slurry and the mesoporous activated carbon material slurry are mixed at a mass ratio of 1:(1~70) and coated onto the working surface of the negative electrode current collector to form a cation adsorption coating.

2. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 1, characterized in that, The mesoporous activated carbon material has a pore size of 0.5~10nm accounting for 40%~80% of the pores.

3. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 1, characterized in that, The chemically extracted lithium-ion sieve slurry and the mesoporous activated carbon material slurry are coated on the working surface of the negative electrode current collector and then vacuum dried at 100~140℃ for 550~700 min to form a cation adsorption coating.

4. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 1, characterized in that, At least one of the following must be met: (a) In the raw materials for preparing the mesoporous activated carbon slurry, the mass ratio of each raw material is: mesoporous activated carbon material: first conductive agent: first binder = (5~10): 1: 1; (b) In the preparation of the chemically deintercalated lithium-ion sieve slurry, the mass ratio of each raw material is: chemically deintercalated lithium-ion sieve: second conductive agent: second binder = (12~17): 1: 1; (c) The raw materials for preparing the mesoporous activated carbon slurry further include a first dispersant; (d) The raw materials for preparing the chemically deintercalated lithium ion sieve slurry also include a second dispersant.

5. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 4, characterized in that, The first conductive agent and the second conductive agent are each independently selected from at least one of conductive carbon black, conductive graphite, carbon nanotubes and graphene; The first adhesive and the second adhesive are each independently selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene and polyimide; The first dispersant and the second dispersant are each independently selected from at least one of N-methylpyrrolidone, ethanol, tetrachloroethane, toluene, xylene, anisole, dimethylformamide, dimethylacetamide, dibutyl phthalate, and dimethyl sulfoxide; The chemical deintercalation / intercalation lithium ion screening is selected from at least one of the following: iron phosphate ion sieve, lithium manganese ion sieve, and lithium titanate ion sieve.

6. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 1, characterized in that, The amount of slurry coating on the working surface of the negative electrode current collector is 100~300g / cm³. 2 .

7. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 1, characterized in that, The mesoporous activated carbon material is prepared by the following method: activated carbon and alkali metal are mixed and heated to 250~550℃ under the protection of inert gas for 2~5h, and then heated to 750~950℃ while activating gases water vapor and carbon dioxide are introduced and held for 1~2h to obtain activated activated carbon; the activated activated carbon is impregnated with hydrochloric acid, water vapor is introduced to make it boil, and it is filtered while hot, washed until neutral, and dried to obtain the mesoporous activated carbon material.

8. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 7, characterized in that, The mass ratio of activated carbon to alkali metal is 1:(1~2), and the alkali metal is sodium hydroxide and / or potassium hydroxide.

9. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 1, characterized in that, The chemically inserted / extracted lithium ion sieve is prepared by the following method: lithium iron phosphate is placed in a conductive solution, and the potential is adjusted to oxidize ferrous iron to ferric iron and allow lithium ions to enter the conductive solution. The solid phase is then filtered, washed, and dried to obtain the lithium iron phosphate ion sieve.

10. The apparatus for electrochemical extraction of low-impurity lithium ions as described in claim 9, characterized in that, In the preparation steps of the chemical lithium ion deintercalation sieve, the potential is adjusted to 1V~1.2V, and the conductive solution is a sodium chloride solution of 25~30g / L.

11. A method for extracting low-impurity lithium ions using the apparatus described in any one of claims 1 to 10, characterized in that, Includes the following steps: The lithium-ion-containing solution is circulated through the gap between the positive and negative electrode current collector working surfaces of the device. A voltage is applied for the first time to insert lithium ions into the chemically inserted lithium-ion sieve. After the power is turned off, the circulation allows the cations adsorbed by the mesoporous activated carbon material to re-enter the lithium-ion-containing solution, thus obtaining the lithium-ion-intercalated sieve electrode. The lithium-ion intercalation sieve electrode is placed in an electrolyte solution, and a voltage is applied a second time to deintercalate the lithium ions in the lithium-ion intercalation sieve electrode, resulting in a lithium-ion-enriched solution.

12. The method for obtaining low-impurity lithium ions by electrochemical extraction as described in claim 11, characterized in that, The first applied voltage is 0.5V~2.1V; the second applied voltage is 0.5V~1.5V.

13. The method for obtaining low-impurity lithium ions by electrochemical extraction as described in claim 12, characterized in that, When the voltage is applied for the first time, the flow rate of the lithium-ion solution between the working surfaces of the two parallel electrodes of the device is 10~40 mL / min.

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