HIGH-SELECTIVITY HYDROPHILIC ELECTRODE FOR EXTRACTING LITHIUM AND PREPARATION METHOD THEREOF

Abstract

The present disclosure relates to a high-selectivity hydrophilic electrode for electrochemically extracting lithium and a preparation method thereof. The preparation method includes the step of carrying out surface coating modification on an electrode active material by using polydopamine. The interception of impurity ions is achieved by utilizing the advantages, which polydopamine has, of preferentially accumulating and transporting lithium ions, thereby improving the selectivity of the electrode active material on lithium. In the pulping process of an electrode adsorption material, a hydroxyl-containing polar hydrophilic organic polymer compound is introduced to perform blending modification, thereby improving the hydrophilicity of a binder polyvinylidene fluoride (PVDF). In addition, pore formation via inorganic salts is combined with a drying mode of low temperature-high temperature so that the porous-microcrack morphology is formed on the electrode, thereby improving the mass transfer effect of the solution inside the electrode. The preparation method of the electrode disclosed by the present disclosure has the characteristics of simplicity, practicability, environmental friendliness, low cost and the like, and is easy for industrial production.

Claims

1. A preparation method of a high-selectivity hydrophilic electrode for extracting lithium, comprising the following steps: (1) putting an electrode active material into a 0.5-5 g/L polydopamine salt solution in a solid-to-liquid mass ratio of 1:5, adjusting the pH value of the solution to 8-9.5, stirring and reacting for 10-12 hours at room temperature; after the reaction is ended, filtering and washing, and drying filter residues at the temperature of 80-120? C. to obtain a polydopamine modified electrode powder material; (2) adding a polymer compound and a binder polyvinylidene fluoride (PVDF) into an N-methyl pyrrolidone solvent, mechanically stirring in vacuum until the above materials are completely dissolved, so as to obtain a mixed glue solution; (3) adding the modified electrode powder material obtained in step (1), a conductive agent acetylene black, a pore forming agent and short-carbon fibers into the mixed glue solution obtained in step (2) in a proportion, and then mechanically stirring for 4-8 hours in vacuum to obtain an electrode slurry, wherein the short-carbon fiber has a particle size of 0.5-3 mm; and (4) coating the electrode slurry obtained in step (3) on a current collector, and then performing segmented drying and water leaching treatment on the coated electrode in turn, so as to obtain a finished product electrode.

2. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1, wherein the electrode active material in step (1) is a lithium ion electrode material, preferably one of LiFePO4, LiMn2O4, LiNixCoyMn(1-x-y)O2 (0<x, y<1, 0<x+y<1) and doped derivatives thereof.

3. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1, wherein the polymer compound in step (2) is a hydroxyl-containing organic matter, preferably a mixture of one or more of polyethylene glycol, polyvinyl alcohol, chitosan and polypropylene glycol.

4. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1, wherein the pore forming agent is a mixture of one or more of soluble inorganic salt solids such as NaCl, KCl, Na2SO4, K2SO4, Na2CO3 and K2CO3.

5. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1 or 4, wherein the particle size distribution of the pore forming agent is as follows: 50-100 meshes of the pore forming agent accounts for 20-30% of the weight of total salts, 100-200 meshes of the pore forming agent accounts for 20-30% of the weight of the total salts, and more than 200 meshes of the pore forming agent accounts for 40-20% of the weight of the total salts.

6. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1, wherein the addition amounts of the polymer compound, the PVDF, the acetylene black, the pore forming agent, the short-carbon fibers and the N-methyl pyrrolidone in the electrode slurry are 0.5-5%, 8-15%, 10-15%, 10-30%, 1-5% and 150-200% of the weight of the electrode powder, respectively.

7. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1, wherein the current collector is a carbon fiber cloth, a carbon fiber felt, a porous carbon-based material, a titanium plate and a titanium mesh.

8. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1, wherein the coating density of the slurry in step (4) is 0.2-5 kg/m2.

9. The preparation method of the high-selectivity hydrophilic electrode for extracting lithium according to claim 1, wherein the segmented drying in step (4) specifically comprises: pre-drying for 3-6 hours at a low temperature of 60-80? C., and then drying for 5-10 hours at a high temperature of 80-120? C.

10. A high-selectivity hydrophilic electrode for extracting lithium prepared by using the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0066] FIG. 1 is a curve of change in concentration of lithium in an anode solution with lithium extraction time in example 1 of the present disclosure.

[0067] FIG. 2 shows circulation performance of an electrode in example 1 of the present disclosure.

[0068] FIG. 3 shows changes in concentrations of lithium in anode solutions of electrodes prepared in example 3 and comparative example 2 of the present disclosure during the extraction of lithium with time.

[0069] FIG. 4 shows changes in concentrations of lithium in anode solutions of electrodes prepared in example 4 and comparative example 3 of the present disclosure during the extraction of lithium with time.

[0070] FIG. 5 is an optical morphology graph of an electrode in example 1 of the present disclosure.

[0071] FIG. 6 is a curve of concentration of lithium ions in an anode solution and current density with time.

[0072] FIG. 7 shows change in concentration of lithium in a lithium-enriched solution with cycle times and cycle performance of an electrode in example 6 of the present disclosure.

[0073] FIG. 8 is a lithium extraction performance comparative graph of electrodes respectively prepared without acrylic acid, polyaniline, nano oxides and pore forming agents under the condition that other preparation process are unchanged and a contrast electrode in example 7 of the present disclosure.

[0074] FIG. 9 is a morphology graph of a lithium manganate electrode in example 7 of the present disclosure.

[0075] FIG. 10 is a morphology graph of an electrode prepared without short-carbon fibers and a pore forming agent and with other conditions identical to those in example 7.

[0076] FIG. 11 shows change in concentrations of lithium in an anode solution in the process of extracting lithium from an electrode in example 9 and comparative examples 7-11.

[0077] FIG. 12 shows cycle performances of electrodes prepared in example 9 and comparative examples 7-11.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0078] Next, specific embodiments of the present disclosure will be further described in detail in combination with examples. The following examples are used for illustrating the present disclosure but not limiting the scope of the present disclosure.

Example 1

[0079] Preparation of lithium ferric phosphate electrode: (1) a lithium ferric phosphate active material was put into a 5 g/L polydopamine salt solution in a solid-to-liquid mass ratio of 1:5 while a reaction temperature was controlled at 20? C. and the pH value of the solution was adjusted to 8.5, the above solution was stirred to react for 15 h, the obtained reaction product was filtered and washed after the reaction was ended, and then filter residue was dried at 100? C.;

[0080] (2) polyethylene glycol and PVDF were added into an N-methyl pyrrolidone solvent, and the above materials were mechanically stirred in vacuum until being completely dissolved;

[0081] (3) polydopamine modified lithium ferric phosphate powders, acetylene black, a pore forming agent solid NaCl and short-carbon fibers having a length of 2 mm were added into an N-methyl pyrrolidone glue solution in a proportion, and then the above materials were mechanically stirred in vacuum for 6 hours to obtain an evenly dispersed electrode slurry;

[0082] (4) the obtained electrode slurry was evenly coated on a titanium mesh having a thickness of 1 mm and an area of 40 cm?50 cm, and the coating density of the lithium ferric phosphate active material after drying was controlled to 2 kg/m, and

[0083] (5) the coated lithium ferric phosphate electrode was dried for 6 hours at 60? C. and then for 6 hours at 100? C. in a blast drying oven, the dried electrode plate was soaked in tap water until NaCl was completely dissolved, and a finished product electrode was obtained by drying in air, wherein the addition amounts of polyethylene glycol, PVDF, acetylene black, KCl, short-carbon fibers and N-methyl pyrrolidone were successively 5%, 10%, 8%, 20%, 3% and 150% of the weight of the electrode powders; the particle size mass distribution of solid NaCl was as follows: 50-100 meshes of the solid NaCl accounted for 25%, 100-200 meshes of the solid NaCl accounted for 40%, and more than 200 meshes of the solid NaCl accounted for 35%.

[0084] Experiment for extracting lithium: the prepared lithium ferric phosphate electrode serving as an anode and foamed nickel serving as a cathode were placed into a 20 g/L NaCl solution, 1.0 V of voltage was applied to two ends of the electrode until a current density was lower than 0.5 A/m.sup.2, so as to prepare an under-lithium Li.sub.1-xFePO.sub.4 electrode. An electrolysis device was divided into a cathode chamber and an anode chamber by using an anionic membrane, and the prepared lithium ferric phosphate electrode and under-lithium Li.sub.1-xFePO.sub.4 electrode were respectively placed into the anode chamber and the cathode chamber. 24 L of to-be-treated brine comprising components as shown in Table 1 was injected into the cathode chamber and 4 L of 5 g/L NaCl solution serving as a support electrolyte was injected to the anode chamber. 0.3 V of voltage was applied to the cathode and the anode. After electrolysis for 5 hours at 5? C., the concentration of lithium in the brine was reduced to 0.08 g/L; the concentration of lithium in the anode lithium-enriched solution was increased to 2.82 g/L, the adsorption capacity of the electrode was 28.4 mg(Li)/g (LiFePO.sub.4), and the average current density of the electrode was 43.7 A/m.sup.2.

TABLE-US-00001 TABLE 1 Components of brine Li Na Mg K B SO.sub.4.sup.2? Concentration (g/L) 0.55 55.30 28.30 4.87 1.85 15.24

[0085] The cathode and the anode after extraction of lithium were exchanged, brine and NaCl were injected again into the cathode and the anode, then lithium was extracted after electrifying, and all the conditions were maintained to be unchanged. After continuous electrolysis for 5 h, the concentration of lithium in the brine was reduced to 0.079 g/L, the concentration of lithium in the anode lithium-enriched solution was increased to 2.83 g/L, the adsorption capacity of the electrode was 28.5 mg(Li)/g (LiFePO.sub.4), and the average current density of the electrode was 43.8 A/m.sup.2. The changes in concentrations of lithium in the brine and the lithium-enriched solution before and after extraction of lithium are seen in Table 2 below. It can be seen from the electrodes can well intercept other impurity ions in the process of extracting lithium, with an interception rate being basically maintained to more than 98%, exhibiting good selectivity.

TABLE-US-00002 TABLE 2 Elements (g/L) Li Na Mg K B.sub.2O.sub.3 SO.sub.4.sup.2? Brine after 0.08 55.25 28.27 4.86 1.84 15.23 extraction of lithium Anode solution 2.84 3.11 0.59 0.10 0.04 0.27

[0086] FIG. 1 is a curve of change in concentration of lithium in an anode solution with electrolysis time, FIG. 2 shows circulation performance of an electrode in the process of extracting lithium under the same conditions after the cathode and the anode were exchanged after each lithium extraction process is ended and then brine and NaCl support electrolyte are injected again. It can be seen that the lithium ferric phosphate electrode prepared in this example has good cycle performance. FIG. 5 is an optical morphology graph of an electrode in example 1.

[0087] The brine with a low lithium concentration was treated by adopting the same conditions and process parameters as those above. 50 L of to-be-treated brine was injected into the cathode chamber and 4 L of 5 g/L NaCl solution serving as a support electrolyte was injected to the anode chamber. 0.2 V of voltage was applied to the cathode and the anode, and then continuous electrolysis was performed for 8 hours at 5? C. Changes of concentrations of lithium in the brine and the anode solution before and after extraction of lithium are seen in Table 3. It can be from the table that after 8 h, the concentration of lithium in the brine was reduced from 0.25 g/L to 0.06 g/L, the concentration of lithium in the anode lithium-enriched solution was increased to 2.36 g/L, the adsorption capacity of the electrode was 23.6 mg(Li)/g (LiFePO.sub.4), and the average current density of the electrode was 22.7 A/m.sup.2.

TABLE-US-00003 TABLE 3 Components in brine Li Na Mg K B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 0.25 33.20 37.90 5.43 2.03 11.24 Brine after 0.06 33.15 37.84 5.42 2.03 11.22 extraction of lithium Anode solution 2.36 2.66 0.80 0.11 0.04 0.20

Comparative Example 1

[0088] LiFePO.sub.4, acetylene black and PVDF were added into an N-methyl pyrrolidone organic solvent in a weight ratio of 8:1:1 to be evenly mixed, the obtained mixture was grinded to form a pulp, the pulp was coated on a titanium mesh current collector used in example 1 (a coating thickness was the same), an electrode was dried for 12 hours in a vacuum oven at 110? C., subsequently, a lithium ferric phosphate contrast electrode was obtained after cooling, and a group of under-lithium electrodes were prepared from this electrode using the same method.

[0089] Similar to the experiment conditions in example 1, 50 L of 0.25 g/L brine was injected to the cathode chamber; 4 L of 5 g/L NaCl solution serving as a support electrolyte was injected into the anode. 0.2 V of voltage was applied to the cathode and the anode to perform continuous electrolysis for 15 hours at 5? C. Changes in components in the solution before and after extraction of lithium are seen in Table 4. It can be seen that by extracting lithium with the contrast electrode, the concentration of lithium in the brine was reduced from 0.25 g/L to 0.14 g/L, the adsorption capacity of the electrode was 15.1 mg(Li)/g (LiFePO.sub.4), and the average current density of the electrode was 7.18 A/m.sup.2 which is lower than that of the same brine treated in example 1.

[0090] In addition, it can be seen by comparing the concentrations of impurity ions that the concentrations of the impurity ions in the obtained lithium-enriched solution prepared in example 1 are lower, indicating that coating of polydopamine on the surface of the electrode takes the effect of preferentially transmitting lithium.

TABLE-US-00004 TABLE 4 Components in brine Li Na Mg K B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 0.25 33.20 37.90 5.43 2.03 11.24 Brine after 0.14 33.07 37.73 5.41 2.02 11.22 extraction of lithium Anode solution 1.40 3.66 2.12 0.29 0.13 0.26

Example 2

[0091] Preparation of lithium ferric phosphate electrode: (1) a lithium ferric phosphate active material was put into a 2 g/L polydopamine salt solution in a solid-to-liquid mass ratio of 1:5 while a reaction temperature was controlled at 25? C. and the pH value of the solution was adjusted to 9, the above solution was stirred to react for 20 h, the obtained reaction product was filtered and washed after the reaction was ended, and then filter residue was dried at 100? C.;

[0092] (2) polyethylene glycol, chitosan and PVDF were added into an N-methyl pyrrolidone solvent, and the above materials were mechanically stirred until being completely dissolved;

[0093] (3) polydopamine modified lithium ferric phosphate powders, a conducive agent acetylene black, a pore forming agent solid KCl and short-carbon fibers having a length of 1 mm were added into an N-methyl pyrrolidone glue solution in a proportion, and then the above materials were mechanically stirred in vacuum for 6 hours to obtain an evenly dispersed electrode slurry;

[0094] (4) the obtained electrode slurry was evenly coated on a carbon fiber cloth having a thickness of 1 mm and an area of 40 cm?50 cm, and the coating density of the lithium ferric phosphate active material after drying was controlled to 2.8 kg/m.sup.2; and

[0095] (5) the coated lithium ferric phosphate electrode was dried for 6 hours at 70? C. and then for 10 hours at 90? C. in a blast drying oven, the dried electrode plate was soaked in tap water until KCl was completely dissolved, and a finished product electrode was obtained by removing and drying in air, wherein the addition amounts of polyethylene glycol, chitosan, PVDF, acetylene black, KCl, short-carbon fibers and N-methyl pyrrolidone were successively 4.5%, 12%, 10%, 30%, 2.5% and 180% of the weight of the electrode powders; the particle size mass distribution of solid KCl was as follows: 50-100 meshes of the solid KCl accounts for 25% of the weight of the total pore forming agent, 100-200 meshes of the solid KCl accounts for 50% of the weight of the total pore forming agent, and more than 200 meshes of the solid KCl accounts for 25% of the weight of the total pore forming agent.

[0096] Preparation of an under-lithium Li.sub.1-xFePO.sub.4 electrode was the same as that in example 1. The prepared lithium ferric phosphate electrode with the carbon fiber cloth as a current collector and the under-lithium Li.sub.1-xFePO.sub.4 electrode were respectively placed in an anode chamber and a cathode chamber. 24 L of to-be-treated brine was injected into the cathode chamber and 4 L of 5 g/L NaCl solution serving as a support electrolyte was injected to the anode chamber. 0.2 V of voltage was applied to the cathode and the anode, and then lithium was continuously extracted at 10? C. After continuous electrolysis for 8 h, the concentration of lithium in the brine was reduced to 0.11 g/L, the concentration of lithium in the anode lithium-enriched solution was increased to 4.51 g/L, the adsorption capacity of the electrode was 32.2 mg(Li)/g (LiFePO.sub.4), and the average current density of the electrode was 43.35 A/m.sup.2. The change in concentrations of the solution after and before extraction of lithium is seen in Table 5.

TABLE-US-00005 TABLE 5 Components of brine Li Na Mg K B SO.sub.4.sup.2? Brine 0.84 33.20 84.50 5.43 0.85 9.34 Brine after 0.11 33.09 84.21 5.41 0.84 9.31 extraction of lithium Anode solution 4.51 2.66 1.77 0.11 0.02 0.17

Example 3

[0097] Preparation of lithium manganate electrode: (1) a lithium manganate phosphate active material was put into a 4 g/L polydopamine salt solution in a solid-to-liquid mass ratio of 1:5 while a reaction temperature was controlled at 20? C. and the pH value of the solution was adjusted to 9.5, the above solution was stirred to react for 10 h, the obtained reaction product was filtered and washed after the reaction was ended, and then filter residue was dried at 100? C.;

[0098] (2) polyethylene glycol, polyvinyl alcohol and PVDF were added into an N-methyl pyrrolidone solvent, and the above materials were mechanically stirred until being completely dissolved;

[0099] (3) polydopamine modified lithium manganate powders, acetylene black, a pore forming agent solid NaCl and short-carbon fibers having a length of 2.5 mm were added into an N-methyl pyrrolidone glue solution in a proportion, and then the above materials were mechanically stirred in vacuum for 8 hours to obtain an evenly dispersed electrode slurry;

[0100] (4) the obtained electrode slurry was evenly coated on a carbon fiber cloth having a thickness of 1 mm and an area of 40 cm?50 cm, and the coating density of the lithium ferric phosphate active material after drying was controlled to 3 kg/m.sup.2; and

[0101] (5) the coated lithium manganate electrode was dried for 5 hours at 60? C. and then for 8 hours at 100? C. in a blast drying oven, the dried electrode plate was soaked in tap water until NaCl was completely dissolved, and a finished product electrode was obtained by drying in air, wherein the addition amounts of polyvinyl alcohol (50%), polyethylene glycol (50%), PVDF, acetylene black, KCl, short-carbon fibers and N-methyl pyrrolidone were successively 3%, 8%, 13%, 30%, 25%, 1% and 180% of the weight of the electrode powders; the particle size mass distribution of the solid KCl was as follows: 50-100 meshes of the solid KCl accounts for 20% of the weight of the total pore forming agent, 100-200 meshes of the solid KCl accounts for 40% of the weight of the total pore forming agent, and more than 200 meshes of the solid KCl accounts for 40% of the weight of the total pore forming agent.

[0102] Preparation of an under-lithium Li.sub.1-xMn.sub.2O.sub.4 electrode was the same as that in example 1. The prepared lithium manganate electrode and the under-lithium Li.sub.1-xMn.sub.2O.sub.4 electrode were respectively placed in an anode chamber and a cathode chamber. 7 L of to-be-treated brine was injected into the cathode chamber and 2 L of 5 g/L NaCl solution was injected to the anode chamber. 0.6 V of voltage was applied to the cathode and the anode. After continuous electrolysis for 5 hours at 20? C., the concentration of lithium in the brine was reduced from 1.84 g/L to 0.13 g/L, the concentration of lithium in the anode lithium-enriched solution was increased to 6.15 g/L, the adsorption capacity of the electrode was 20.5 mg(Li)/g (LiMn.sub.2O.sub.4), and the average current density of the electrode was 59.1 A/m.sup.2. The change in concentrations of the solution after and before extraction of lithium is seen in Table 6. It can be seen that the electrode of the present disclosure has a good magnesium and lithium separation effect.

TABLE-US-00006 TABLE 6 Components of brine Li Na Mg K B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 1.84 1.42 114.50 0.52 11.30 28.50 Brine after 0.13 1.41 114.18 0.52 11.23 28.36 extraction of lithium Anode solution 6.15 2.03 1.15 0.01 0.24 0.51

Comparative Example 2

[0103] Lithium manganate, acetylene black and PVDF were added into an N-methyl pyrrolidone organic solvent in a weight ratio of 8:1:1 to be evenly mixed, the obtained mixture was grinded to form a pulp, the pulp was coated on a ruthenium-coated titanium mesh current collector used in example 3 (a coating thickness was the same), an electrode was dried for 12 hours in a vacuum oven at 110? C., subsequently, a lithium manganate contrast electrode was obtained after cooling, and a group of under-lithium electrodes were prepared from this electrode using the same method.

[0104] 1.84 g/L brine in example 3 was treated based on the same technical parameters. 7 L of brine was injected to the cathode chamber; 2 L of 5 g/L NaCl solution serving as a support electrolyte was injected into the anode. 0.6 V of voltage was applied to the cathode and the anode. After continuous electrolysis for 9 hours at 20? C., the concentration of lithium in the brine was reduced from 1.84 g/L to 0.24 g/L, the adsorption capacity of the electrode was 18.2 mg(Li)/g (LiMn.sub.2O.sub.4), and the average current density of the electrode was 23.33 A/m.sup.2; the concentrations of Mg, K, B.sub.2O.sub.3 and SO.sub.4.sup.2? in the anode solution were 3.54 g/L, 0.08 g/L, 0.36 g/L and 1.21 g/L, respectively. FIG. 3 shows changes in concentrations of lithium in anode solutions of electrodes prepared in example 3 and comparative example 2 of the present disclosure during the extraction of lithium with time. It can be seen from data of example 2 and comparative example 2 that when 1.84 g/L brine having a high magnesium-lithium ratio is treated similarly, the current density in this example is only 40% that in example 3, and the interception rate of impurity ions is also reduced.

Example 4

[0105] Preparation of LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 electrode: (1) a LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 ternary active material was put into a 4 g/L polydopamine salt solution in a solid-to-liquid mass ratio of 1:5 while a reaction temperature was controlled at 15? C. and the pH value of the solution was adjusted to 9-10, the above solution was stirred to react for 10 h, the obtained reaction product was filtered and washed after the reaction was ended, and then filter residue was dried at 100? C.;

[0106] (2) chitosan and PVDF were added into an N-methyl pyrrolidone solvent, and the above materials were mechanically stirred until being completely dissolved;

[0107] (3) polydopamine modified LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 powders, acetylene black, a pore forming agent solid Na.sub.2SO.sub.4 and short-carbon fibers having a length of 2 mm were added into an N-methyl pyrrolidone glue solution in a proportion, and then the above materials were mechanically stirred in vacuum for 7 hours to obtain an evenly dispersed electrode slurry;

[0108] (4) the obtained electrode slurry was evenly coated on a carbon fiber felt having a thickness of 1 mm and an area of 40 cm?50 cm, and the coating density of the ternary active material after drying was controlled to 1.5 kg/m.sup.2; and

[0109] (5) the coated ternary electrode was dried for 5 hours at 60? C. and then for 8 hours at 80? C. in a blast drying oven, the dried electrode plate was soaked in tap water until Na.sub.2SO.sub.4 was completely dissolved, and a finished product electrode was obtained by removing and drying in air, wherein the addition amounts of chitosan, PVDF, acetylene black, Na.sub.2SO.sub.4, short-carbon fibers and N-methyl pyrrolidone were successively 5%, 10%, 10%, 20%, 1.5% and 200% of the weight of the electrode powders; the particle size mass distribution of the solid Na.sub.2SO.sub.4 was as follows: 50-100 meshes of the solid Na.sub.2SO.sub.4 accounts for 30% of the weight of the total pore forming agent, 100-200 meshes of the solid Na.sub.2SO.sub.4 accounts for 40% of the weight of the total pore forming agent, and more than 200 meshes of the solid Na.sub.2SO.sub.4 accounts for 30% of the weight of the total pore forming agent.

[0110] Preparation of an under-lithium Li.sub.1-xNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 electrode is the same as that in example 1. The prepared Li.sub.1-xNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 electrode and the under-lithium Li.sub.1-xNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 electrode were respectively placed into an anode chamber and a cathode chamber. 8 L of to-be-treated brine was injected into the cathode chamber and 2 L of 5 g/L NaCl solution was injected to the anode chamber. 1.0 V of voltage was applied to the cathode and the anode. After continuous electrolysis for 3 hours at 5? C., the concentration of lithium in the brine was reduced from 0.67 g/L to 0.11 g/L, the concentration of lithium in the anode lithium-enriched solution was increased to 2.33 g/L, the adsorption capacity of the electrode was 15.5 mg(Li)/g (Li.sub.1-xNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2), and the average current density of the electrode was 29.81 A/m.sup.2. The change in concentrations of the solution after and before extraction of lithium is seen in Table 7.

TABLE-US-00007 TABLE 7 Components of brine Li Na K CO.sub.3.sup.2? B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 0.67 97.20 15.30 21.80 4.50 10.30 Brine after 0.11 96.73 15.21 21.68 4.47 10.24 extraction of lithium Anode solution 2.33 3.94 0.32 0.46 0.09 0.19

Comparative Example 3

[0111] Electrodes for extracting lithium were respectively prepared without polydopamine coating, addition of chitosan, hydrophilic modification and addition of pore forming agents under the conditions that other conditions unchanged by using preparation processes and experimental methods in example 4. FIG. 4 shows changes in concentrations of lithium in anode solutions of electrodes prepared in example 4 and comparative example 3 of the present disclosure during the extraction of lithium with time. By comparing data in FIG. 4, it can be seen that the preparation method of the present disclosure has the significant advantage of extracting lithium, and promotion of this advantage is obtained by modification from many aspects.

[0112] The specific examples of the preparation method of the high-conductivity porous electrode for extracting lithium in the salt lake of the present disclosure are as follows:

Example 5

[0113] Preparation of lithium ferric phosphate: (1) silicon dioxide having a particle size of 20-80 nm, polyacrylic acid and PVDF were added into an N-methyl pyrrolidone (NMP) solvent and then be mechanically stirred for 6 hours in vacuum to obtain a doped blending modified glue solution, wherein the addition amount of silicon dioxide was 1% of the weight of PVDF, and the addition amount of polyacrylic acid is 15% of the weight of PVDF;

[0114] (2) lithium ferric phosphate, acetylene black, carbon nano tubes, short-carbon fibers and a pore forming agent ammonium carbonate were added into the glue solution and then the above materials were mechanically stirred for 8 hours in vacuum to obtain an electrode slurry, wherein in the slurry, the addition amounts of the PVDF, the acetylene black, the carbon nano tubes, the short-carbon fibers, the pore forming agent and the N-methyl pyrrolidone were successively 10%, 10%, 0.5%, 2%, 40% and 200% of the weight of lithium ferric phosphate; the particle size distribution of ammonium carbonate is as follows: 50-100 meshes of ammonium carbonate accounts for 30% of the weight of the total pore forming agent, 100-200 meshes of ammonium carbonate accounts for 50% of the weight of the total pore forming agent, and more than 200 meshes of ammonium carbonate accounts for 20% of the weight of the total pore forming agent;

[0115] (3) the electrode slurry obtained in step (2) was evenly coated on a titanium mesh with an area of 30 cm?50 cm, and the coating density was controlled to 1.5 kg/m.sup.2, and then the coated electrode was pre-dried for 6 hours at a low temperature of 70? C. followed by drying for 5 hours at a high temperature of 100? C.; and

[0116] (4) the electrode dried in step (3) was put into a mixed solution containing 0.15 mol/L sodium dodecyl benzene sulfonate and a pyrrole monomer to be soaked for 3 h, then a 0.1 mol/L FeCl.sub.3 solution was added at 5? C. to react for 8 h, wherein a molar ratio of electrode active material to sodium dodecyl benzene sulfonate to ferric trichloride to pyrrole monomer was 5:1.5:1.5:1. After the reaction was ended, the electrode plate was taken out and then washed with water until the washing water was neutral, so as to obtain a polypyrrole modified porous electrode.

[0117] Lithium extraction experiment: the prepared lithium ferric phosphate electrode serving as an anode and foamed nickel serving as a cathode were placed into a 20 g/L NaCl solution, 1.0 V of voltage was applied to two ends of the electrodes until the current density was lower than 0.5 A/m.sup.2, so as to prepare a delithiated Li.sub.1-xFePO.sub.4 electrode.

[0118] An electrolysis device was divided into a cathode chamber and an anode chamber by using an anionic membrane, and then the prepared lithium ferric phosphate electrode and the delithiated lithium ferric phosphate electrode were respectively placed into the anode chamber and the cathode chamber. 15 L of to-be-treated brine was injected into the cathode chamber and 2 L of 5 g/L NaCl solution serving as a support electrolyte was injected to the anode chamber. 0.3 V of voltage was applied to the cathode and the anode to perform electrolysis for 4 hours at 20? C. Components in the brine and the anode lithium-enriched solution before and after extraction of lithium are seen in Table 8. FIG. 6 is a curve of concentration of lithium ions in an anode solution and current density with time. It can be seen that the concentration of lithium in the brine is reduced from 0.54 g/L to 0.09 g/L; the concentration of lithium in the anode lithium-enriched solution is increased to 3.4 g/L, and a magnesium-to-lithium ratio is reduced from 97 in the brine to 0.26 in the lithium-enriched solution. After the electrolysis is ended, the adsorption capacity of the electrode is 30.2 mg (Li)/g(LiFePO.sub.4), and the average current density in the above process is 43.6 A/m.sup.2.

TABLE-US-00008 TABLE 8 Concentration (g/L) Li Na Mg K B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 0.54 53.70 52.40 4.05 2.67 10.67 Brine after 0.09 53.56 52.28 4.04 2.66 10.64 extraction of lithium Anode lithium- 3.40 3.07 0.89 0.09 0.06 0.19 enriched solution

Example 6

[0119] Preparation of lithium ferric phosphate: (1) silicon dioxide having a particle size of 20-50 nm, polymethylacrylic acid and PVDF were added into an N-methyl pyrrolidone (NMP) solvent, wherein the addition amount of titanium dioxide was 2% the weight of PVDF, the addition amount of polymethylacrylic acid was 15% the weight of PVDF, and then the above materials were mechanically stirred for 5 hours in vacuum to obtain a doped blending modified glue solution;

[0120] (2) lithium ferric phosphate, acetylene black, carbon nano tubes, short-carbon fibers and ammonium bicarbonate were added into the glue solution and then mechanically stirred for 8 hours in vacuum at 20-30? C. to obtain an electrode slurry, wherein in the slurry, the addition amounts of the PVDF, the acetylene black, the carbon nano tubes, the short-carbon fibers, the pore forming agent and the N-methyl pyrrolidone were successively 9%, 12%, 1%, 3%, 35% and 150% of the weight of lithium ferric phosphate; the particle size distribution of ammonium bicarbonate is as follows: 50-100 meshes of ammonium carbonate accounts for 30% of the weight of the total pore forming agent, 100-200 meshes of ammonium carbonate accounts for 40% of the weight of the total pore forming agent, and more than 200 meshes of ammonium carbonate accounts for 30% of the weight of the total pore forming agent;

[0121] (3) the electrode slurry obtained in step (2) was evenly coated on a titanium mesh with an area of 30 cm?50 cm, and the coating density was controlled to 1.0 kg/m.sup.2, and then the coated electrode was pre-dried for 5 hours at a low temperature of 80? C. followed by drying for 5 hours at a high temperature of 110? C.;

[0122] (4) the electrode dried in step (3) was put into a mixed solution containing 0.15 mol/L sodium dodecyl benzene sulfonate and a thiophene monomer to be soaked for 2 h, then a 0.1 mol/L FeCl.sub.3 solution was added at 5? C. to react for 8 h, wherein a molar ratio of electrode active material to sodium dodecyl benzene sulfonate to ferric trichloride to thiophene monomer was 5:1.5:2:1. After the reaction was ended, the electrode plate was taken out and then washed with water until the washing water was neutral, so as to obtain a conductive thiophene modified porous electrode.

[0123] Lithium extraction experiment: a delithiated Li.sub.1-xFePO.sub.4 electrode was prepared by the method in example 5. An electrolysis device was divided into a cathode chamber and an anode chamber by using an anionic membrane, and the prepared lithium ferric phosphate electrode and the delithiated Li.sub.1-xFePO.sub.4 electrode were respectively placed into the anode chamber and the cathode chamber. 40 L of to-be-treated brine was injected into the cathode chamber, and 2 L of 5 g/L NaCl solution serving as a support electrolyte was injected into the anode chamber. 0.2 V of voltage was applied to the cathode and the anode to perform electrolysis for 5 hours at 5? C. Components in the brine and the lithium-enriched solution before and after extraction of lithium are seen in Table 9. It can be seen that the concentration of lithium in the brine is reduced from 0.17 g/L to 0.08 g/L; the concentration of lithium in the anode lithium-enriched solution is increased to 1.85 g/L, and a magnesium-to-lithium ratio is reduced from 221.2 in the brine to 0.2 in the lithium-enriched solution. After the electrolysis is ended, the adsorption capacity of the electrode is 24.7 mg (Li)/g(LiFePO.sub.4), and the average current density in the above process is 19 A/m.sup.2.

TABLE-US-00009 TABLE 9 Concentration (g/L) Li Na Mg K B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 0.17 97.40 37.60 6.34 4.3 8.47 Brine after 0.08 97.38 37.58 6.33 4.3 8.47 extraction of lithium Anode lithium- 1.85 2.49 0.38 0.06 0.04 0.08 enriched solution

[0124] After the above extraction of lithium was ended, the cathode and the anode were exchanged, 10 L of 5 g/L NaCl solution serving as a support electrolyte was injected into the anode, 20 L of the above fresh brine was injected into the cathode, and then 0.2 V of voltage was applied to the cathode and the anode to perform electrolysis at 5? C. After each electrolysis period was ended, the cathode and the anode were exchanged, the lithium-containing anode solution in the previous period was continued to serve as an anode solution in the next period, 20 L of fresh brine was changed for the cathode solution each time, and then lithium was extracted under the same conditions. The cycle performance and the lithium enrichment effect of the electrode were investigated. Change in concentrations of lithium in a lithium-enriched solution with cycle times and cycle performance of an electrode in this example are as shown in FIG. 7. It can be seen from FIG. 7 that the lithium ferric phosphate electrode prepared in this example has a good cycle performance, and lithium is enriched in the anode solution during the cycle.

Example 7

[0125] Preparation of lithium manganate electrode: (1) zirconium dioxide having a particle size of 80-100 nm, polymethylacrylic acid and PVDF were added into an N-methyl pyrrolidone (NMP) solvent, wherein the addition amount of nano oxides was 2% of the weight of PVDF, the addition amount of polymethylacrylic acid was 15% of the weight of PVDF, then the above materials were mechanically stirred for 5 hours at 40-50? C. to obtain a doped blending modified glue solution;

[0126] (2) lithium manganate, acetylene black, carbon nano tubes, short-carbon fibers and a pore forming agent ammonium oxalate were added into the glue solution and then mechanically stirred for 8 hours in vacuum to obtain an electrode slurry, wherein in the slurry, the addition amounts of the PVDF, the acetylene black, the carbon nano tubes, the short-carbon fibers, the pore forming agent and the N-methyl pyrrolidone were successively 15%, 15%, 1.5%, 2.5%, 30% and 190% of the weight of lithium manganate; the particle size distribution of ammonium oxalate is as follows: 50-100 meshes of ammonium oxalate accounts for 25% the weight of the total pore forming agent, 100-200 meshes of ammonium oxalate accounts for 50% the weight of the total pore forming agent, and more than 200 meshes of ammonium oxalate accounts for 25% the weight of the total pore forming agent;

[0127] (3) the electrode slurry obtained in step (2) was evenly coated on a carbon fiber cloth with an area of 30 cm?40 cm, and the coating density was controlled to 2.5 kg/m.sup.2, and then the coated electrode was pre-dried for 7 hours at a low temperature of 85? C. followed by drying for 8 hours at a high temperature of 120? C.; and

[0128] (4) the electrode dried in step (3) was put into a mixed solution containing 0.15 mol/L sodium dodecyl benzene sulfonate and a phenylamine monomer to be soaked for 10 h, then a 0.1 mol/L FeCl.sub.3 solution was added at 3? C. to react for 10 h, wherein a molar ratio of electrode active material to sodium dodecyl benzene sulfonate to ferric trichloride to phenylamine monomer was 5:2:2:2. After the reaction was ended, the electrode plate was taken out and then washed with water until the washing water was neutral, so as to obtain a polyphenylamine modified porous electrode.

[0129] Lithium extraction experiment: a delithiated Li.sub.1-xMn.sub.2O.sub.4 electrode was prepared by the method in example 5. An electrolysis device was divided into a cathode chamber and an anode chamber by using an anionic membrane, and the prepared lithium manganate electrode and the delithiated Li.sub.1-xMn.sub.2O.sub.4 electrode were respectively placed into the anode chamber and the cathode chamber. 4 L of to-be-treated brine was injected into the cathode chamber, and 1 L of 5 g/L NaCl solution serving as a support electrolyte was injected into the anode chamber. 0.65 V of voltage was applied to the cathode and the anode to perform electrolysis for 4 hours at 15? C. Components in the brine and the anode lithium-enriched solution before and after extraction of lithium are seen in Table 10. It can be seen that the concentration of lithium in the brine is reduced from 1.69 g/L to 0.15 g/L, and the recovery rate of lithium is up to more than 91%; the concentration of lithium in the anode lithium-enriched solution is increased to 6.09 g/L, and a magnesium-to-lithium ratio is reduced from 63.1 in the brine to 0.37 in the lithium-enriched solution. After the electrolysis is ended, the adsorption capacity of the electrode is 20.3 mg (Li)/g(LiMn.sub.2O.sub.4), and the average current density in the above process is 48.8 A/m.sup.2.

TABLE-US-00010 TABLE 10 Concentration (g/L) Li Na Mg K B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 1.69 1.89 106.70 0.67 10.50 24.60 Brine after 0.15 1.88 106.05 0.66 10.44 24.47 extraction of lithium Anode lithium- 5.34 2.04 2.24 0.02 0.22 0.44 enriched solution

[0130] Lithium extraction electrodes were respectively prepared by using the preparation method in example 7 without polyacrylic acid, polyaniline, nano oxides and pore forming agents under the conditions that other preparation process conditions were unchanged, and contrast electrodes were prepared by using a method disclosed in example 1 from Chinese Patent CN107201452B. The coating densities of all the electrodes are 2.5 kg/m.sup.2, the to-be-treated brine is the brine with a high magnesium-to-lithium ratio and a concentration of Li being 1.69 g/L, and comparison of lithium extraction effects is as shown in FIG. 8. It can be seen that addition and modification of nano oxides, polyacrylic acid, polyaniline, pore forming agents and the like are conducive to promotion of electrode materials, especially, the electrode obtained by blending, compounding and coating from many aspects have optimal performance.

[0131] Under the same magnification times, the morphology of the lithium manganate electrode prepared in this example is as shown in FIG. 9; the morphology of the electrode prepared without short-carbon fibers and a pore forming agent under the conditions that other conditions are unchanged is as shown in FIG. 10. It can be seen that many cracks are present on the surface of the electrode as shown in FIG. 9 and evenly distributed. The cracks of the electrode as shown in FIG. 10 are unevenly distributed, and surface cracking and stripping situations are obviously aggravated. It is indicated that change in preparation processes can directly affect the surface morphology of the electrode and then further influence the lithium extraction performance of the electrode.

Example 8

[0132] Preparation of LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 electrode: (1) aluminum oxide having a particle size of 80-100 nm, polymethylacrylic acid and PVDF were added into an N-methyl pyrrolidone (NMP) solvent, wherein the addition amount of nano oxides was 1% of the weight of PVDF, the addition amount of polymethylacrylic acid was 30% of the weight of PVDF, and then the above materials were mechanically stirred for 5 hours in vacuum to obtain a doped blending modified glue solution;

[0133] (2) a LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 ternary electrode material, acetylene black, carbon nano tubes, short-carbon fibers and ammonium carbonate were added into the glue solution, and then the above materials were mechanically stirred for 8 hours in vacuum to obtain an electrode slurry, wherein in the slurry, the addition amounts of the PVDF, the acetylene black, the carbon nano tubes, the short-carbon fibers, the pore forming agent and the N-methyl pyrrolidone were successively 8%, 15%, 2%, 1.5%, 40% and 200% of the weight of ternary electrode material; the particle size distribution of ammonium carbonate is as follows: 50-100 meshes of ammonium carbonate accounts for 20% of the weight of the total pore forming agent, 100-200 meshes of ammonium carbonate accounts for 60% of the weight of the total pore forming agent, and more than 200 meshes of ammonium carbonate accounts for 20% of the weight of the total pore forming agent;

[0134] (3) the electrode slurry obtained in step (2) was evenly coated on a titanium mesh with an area of 30 cm?40 cm, and the coating density was controlled to 2.0 kg/m.sup.2, and then the coated electrode was pre-dried for 5 hours at a low temperature of 80? C. followed by drying for 6 hours at a high temperature of 105? C.;

[0135] (4) the electrode dried in step (3) was put into a mixed solution containing 0.15 mol/L sodium dodecyl benzene sulfonate and an indole monomer to be soaked for 6 h, then a 0.1 mol/L FeCl.sub.3 solution was added at 0? C. to react for 8 h, wherein a molar ratio of electrode active material to sodium dodecyl benzene sulfonate to ferric trichloride to indole monomer was 5:1:1.5:2. After the reaction was ended, the electrode plate was taken out and then washed with water until the washing water was neutral, so as to obtain a polyindole modified porous electrode.

[0136] Lithium extraction experiment: a delithiated Li.sub.1-xNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 electrode was prepared by the method in example 5. An electrolysis device was divided into a cathode chamber and an anode chamber by using an anionic membrane, and the prepared ternary electrode and the delithiated ternary electrode were respectively placed into the anode chamber and the cathode chamber. 10 L of to-be-treated carbonate brine was injected into the cathode chamber, and 2 L of 5 g/L NaCl solution serving as a support electrolyte was injected into the anode chamber. 0.85 V of voltage was applied to the cathode and the anode to perform electrolysis for 3 hours at 15? C. Components in the brine and the anode lithium-enriched solution before and after extraction of lithium are seen in Table 11. It can be seen that the concentration of lithium in the brine is reduced from 0.67 g/L to 0.15 g/L, and the recovery rate of lithium is up to more than 78%; the concentration of lithium in the anode lithium-enriched solution is increased to 2.63 g/L. After the electrolysis is ended, the adsorption capacity of the electrode is 21.0 mg (Li)/g, and the average current density in the above process is 56.1 A/m.sup.2.

TABLE-US-00011 TABLE 11 Concentration (g/L) Li Na K CO.sub.3.sup.2? B.sub.2O.sub.3 SO.sub.4.sup.2? Brine 0.67 102.80 14.90 23.40 6.30 7.50 Brine after 0.15 102.60 14.84 23.30 6.27 7.47 extraction of lithium Anode lithium- 2.63 3.03 0.31 0.49 0.13 0.14 enriched solution

Comparative Example 4

[0137] Other conditions are the same as those in example 8, and the difference is that the particle size of the pore forming agent ammonium carbonate is 100-200 meshes. After electrolysis for 3.5 hours at 5? C., the concentration of lithium in the brine is reduced from 0.67 g/L to 0.21 g/L, and the recovery rate of lithium is 67.6%. The concentration of lithium in the anode lithium-enriched solution is increased to 2.32 g/L. After the electrolysis is ended, the adsorption capacity of the electrode is 19.3 mg(Li)/g, and the average current density is 42.4 A/m.sup.2.

Comparative Example 5

[0138] Other conditions are the same as those in example 8, and the difference is that drying is directly performed for 8 hours at a low temperature of 80? C. After electrolysis for 4.2 h, the concentration of lithium in the brine is reduced from 0.67 g/L to 0.23 g/L, and the recovery rate of lithium is 65%. The concentration of lithium in the anode lithium-enriched solution is increased to 2.27 g/L. After the electrolysis is ended, the adsorption capacity of the electrode is 18.9 mg(Li)/g, and the average current density is 34.6 A/m.sup.2.

Comparative Example 6

[0139] Other conditions are the same as those in example 8, and the difference is that drying is directly performed for 6 hours at a high temperature of 105? C. After electrolysis for 3.7 h, the concentration of lithium in the brine is reduced from 0.67 g/L to 0.23 g/L, and the recovery rate of lithium is 65%. The concentration of lithium in the anode lithium-enriched solution is increased to 2.23 g/L. After the electrolysis is ended, the adsorption capacity of the electrode is 19.4 mg(Li)/g, and the average current density is 40.3 A/m.sup.2.

[0140] The specific examples of an preparation method of a composite porous electrode material for extracting lithium in the present disclosure are as follows:

Example 9

[0141] This example provides a preparation method of a composite porous electrode material for extracting lithium, comprising the following steps:

[0142] (1) in a solid-to-liquid mass ratio of 1:5, adding lithium ferric phosphate into a polydopamine solution with a concentration of 0.5 g/L and a pH value of 7.5, stirring and reacting for 20 hours at 40? C., filtering after the reaction, and then drying filter residue at 80? C. to obtain a polydopamine modified lithium ferric phosphate material;

[0143] (2) placing a conductive agent acetylene black into 20 wt. % nitric acid to be acidized for 1 hour at 60? C., after that, washing with 0.1 mol/L sodium hydroxide and pure water in sequence, and then filtering to obtain a modified conductive agent;

[0144] (3) mixing and pulping the modified conductive agent acetylene black, an aqueous binder polyacrylic acid, a structure reinforcing agent polypropylene fiber, a pore forming agent NaCl and water whose addition amounts are 8%, 15%, 5%, 40% and 300% the weight of the polydopamine modified electrode active material; and

[0145] (4) coating mixed slurry on carbon fiber cloth, with a coating density of 200 mgLiFePO.sub.4/m.sup.2 and a coating area of 15?20 cm.sup.2, drying for 4 hours at 60? C. and then drying for 5 hours at 120? C., so as to obtain the composite porous electrode material for an aqueous solution system.

Example 10

[0146] This example provides a preparation method of a composite porous electrode material for extracting lithium, comprising the following steps:

[0147] (1) in a solid-to-liquid ratio of 1:10, adding lithium manganate into a polydopamine solution with a concentration of 5 g/L and a pH value of 10, stirring and reacting for 10 hours at 10? C., filtering after the reaction, and then drying filter residue at 80? C. to obtain a polydopamine modified lithium manganate material;

[0148] (2) placing a conductive agent Ketjen black into 65 wt. % nitric acid to be acidized for 12 hours at 20? C., after that, washing with 0.1 mol/L sodium hydroxide and pure water in sequence, and then filtering to obtain a modified conductive agent;

[0149] (3) mixing and pulping the modified conductive agent Ketjin black, an aqueous binder polyurethane, a structure reinforcing agent lignin fiber, a pore forming agent Na.sub.2CO.sub.3 and water whose addition amounts were 12%, 5%, 0.5%, 20% and 150% of the weight of the polydopamine modified electrode active material; and

[0150] (4) coating the mixed slurry on a carbon fiber cloth, with a coating density of 150 mgLiFeMn.sub.2O.sub.4/m.sup.2 and a coating area of 20?20 cm.sup.2, drying for 3 hours at 80? C. and then drying for 6 hours at 100? C., so as to obtain the composite porous electrode material for the aqueous solution system.

Example 11

[0151] This example provides a preparation method of a composite porous electrode material for extracting lithium, comprising the following steps:

[0152] (1) in a solid-to-liquid ratio of 1:7.5, adding LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 into a polydopamine solution with a concentration of 3 g/L and a pH value of 8, stirring and reacting for 15 hours at 20? C., filtering after the reaction, and then drying filter residue at 80? C. to obtain a polydopamine modified LiNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2 material;

[0153] (2) placing a conductive agent superP into 50 wt. % sulfuric acid to be acidized for 10 hours at 30? C., after that, washing with 1 mol/L sodium hydroxide and pure water in sequence, and then filtering to obtain a modified conductive agent;

[0154] (3) mixing and pulping the modified conductive agent superP, an aqueous binder polymethyl acrylate, a structure reinforcing agent carbon fiber, a pore forming agent KCl and water whose addition amounts are 10%, 10%, 3%, 30% and 200% the weight of the polydopamine modified electrode active material; and

[0155] (4) coating the mixed slurry on a carbon fiber cloth, with a coating density of 100 mg/m.sup.2 and a coating area of 15?20 cm.sup.2, drying for 5 hours at 70? C. and then drying for 6 hours at 90? C., so as to obtain the composite porous electrode material for the aqueous solution system.

Comparative Example 7

[0156] This comparative example differs from example 9 in that hydrophilic modification treatment in step (1) of example 9 is not performed on lithium ferric phosphate, and other steps are the same as those in example 9.

Comparative Example 8

[0157] This comparative example differs from example 9 in that acidization treatment in step (2) of example 9 is not performed on acetylene black, and other steps are the same as those in example 9.

Comparative Example 9

[0158] This comparative example differs from example 9 in that aqueous binder polyacrylic acid in example 9 is changed into hydropholic PVDF, and others are the same as those in example 9.

Comparative Example 10

[0159] This comparative example differs from example 9 in that pore forming treatment in step (3) of example 9 is not performed on lithium ferric phosphate, and others are the same as those in example 9.

Comparative Example 11

[0160] This comparative example differs from example 9 in that any modification treatment is not performed on electrodes, a structure of a traditional lithium ion battery is used: LiFePO.sub.4+C+PVDF mode, and main steps are as follows:

[0161] (1) adding PVDF into NMP (PVDF:NMP=1:15), and stirring to obtain a first mixed homogenate;

[0162] (2) successively adding lithium ferric phosphate and acetylene black into the first mixed homogenate (LiFePO.sub.4: acetylene black: PVDF: NMP=8:1:1), evenly stirring to obtain a second mixed solution, evenly coating the second mixed solution on a carbon fiber cloth, with a coating density of 200 mgLiFePO.sub.4/m.sup.2 and a coating area of 15?20 cm.sup.2, and then drying for 24 hours at 70? C. to obtain a finished product electrode.

Experiment Example 1

[0163] Preparation of under-lithium lithium ferric phosphate electrode: an electrolytic cell was divided into an anode chamber and a cathode chamber with an anionic membrane, the lithium ferric phosphate electrodes prepared in example 9, comparative example 7, comparative example 8, comparative example 9 and comparative example 10 were respectively used as anodes, foamed nickel was used as a cathode, and the cathode and the anode were both filled with a 15 g/L KCl solution. In addition, for the cathode, the pH of the solution was adjusted to 2-3 with sulfuric acid. 1.0 V of voltage was applied to two ends of the carbon fiber cloth electrode and foamed nickel until the current density was lower than 0.5 A/m.sup.2, so as to prepare an under-lithium Li.sub.1-xFePO.sub.4 electrode.

[0164] Lithium extraction experiment: an electrolysis device was divided into a cathode chamber and an anode chamber with an anionic membrane. The lithium ferric phosphate electrode and the under-lithium lithium ferric phosphate electrode were respectively placed into the anode chamber and the cathode chamber. 2.0 L of to-be-treated brine was injected into the cathode chamber. The components of the to-be-treated brine are seen in Table 12. 1.0 L of 10 g/L NaCl solution serving as a support electrolyte was injected into the anode. 0.3 V of voltage was applied to the cathode and the anode to perform electrolysis at 5? C., and the electrolysis was ended when a current was lower than 150 mA. Change in concentration of lithium in the anode obtained by extracting lithium is as shown in FIG. 11, and the cycle performance of the electrode is as shown in FIG. 12.

TABLE-US-00012 TABLE 12 Components of brine Elements Li Na Mg K B SO.sub.4.sup.2? Concentration (g/L) 1.50 88.35 12.15 20.38 2.35 19.84

[0165] It can be seen from FIG. 11 and FIG. 12 that compared with comparative example 11 in which any modification treatment is not done, all of comparative example 7, comparative example 8, comparative example 9 and comparative example 10 in which modification treatments are done gain certain effects in the aspects of absorption capacity and lithium release rate, however, results obtained in example 9 in which various modification measures are synthesized are not obvious, which is an effect that other single modification measures do not have.

Experiment Example 2

[0166] Preparation of under-lithium lithium manganate electrode: an electrolytic cell was divided into an anode chamber and a cathode chamber with an anionic membrane, the lithium manganate electrode prepared in example 10 was used as an anode, foamed nickel was used as a cathode, and the cathode and the anode were both filled with a 20 g/L NaCl solution. In addition, for the cathode, the pH of the solution was adjusted to 2-3 with sulfuric acid. 1.2 V of voltage was applied to two ends of the titanium electrode and foamed nickel until the current density was lower than 0.5 A/m.sup.2, so as to prepare an under-lithium Li.sub.1-xMn.sub.2O.sub.4 electrode.

[0167] Lithium extraction experiment: an electrolysis device was divided into a cathode chamber and an anode chamber with an anionic membrane. The lithium manganate electrode and the under-lithium lithium manganate electrode that were prepared in example 9 and experiment example 2 were respectively placed into the anode chamber and the cathode chamber. 1.0 L of to-be-treated brine was injected into the cathode chamber. The components of the to-be-treated brine are seen in Table 13. 1.0 L of 10 g/L NaCl solution serving as a support electrolyte was injected into the anode. 0.65 V of voltage was applied to the cathode and the anode to perform electrolysis at 10? C., and the electrolysis was ended when a current was lower than 150 mA. Changes in concentration of lithium in the brine in the process of extracting lithium and concentration of lithium in the anode lithium-enriched solution are seen Table 14.

TABLE-US-00013 TABLE 13 Components of brine Elements Li Na Mg K B SO.sub.4.sup.2? Concentration (g/L) 1.5 1.5 108.3 1.32 2.18 23.18

TABLE-US-00014 TABLE 14 Changes in concentration of lithium in anode and concentration of lithium in brine after extraction of lithium Elements Li Na Mg K B SO.sub.4.sup.2? Initial 1.5 1.5 108.3 1.32 2.18 23.18 concentration of brine (g/L) Ending 0.27 1.51 106.8 1.25 2.1 22.1 concentration of brine (g/L) Concentration of 1.25 3.95 0.73 0.08 0.05 0.23 anode solution (g/L)

[0168] It can be seen from Table 14 that the lithium manganate electrode prepared in example 9 is used, the recovery rate of lithium after electrolysis for 6 hours is up to 82%, a magnesium-to-lithium ratio of the anode lithium-enriched solution is reduced from 72.2 in initial brine to 0.58 in the anode lithium-enriched solution, and this electrode has a good interception effect on impurities such as Na, K, B and SO.sub.4.sup.2?.

Experiment Example 3

[0169] Preparation of under-lithium Li.sub.1-xNi.sub.0.33Co.sub.0.33Mn.sub.0.33O.sub.2 electrode: an electrolytic cell was divided into an anode chamber and a cathode chamber with an anionic membrane, the lithium nickel cobalt manganate ternary material electrode prepared in example 11 was used as an anode, foamed nickel was used as a cathode, and the cathode and the anode were both filled with a 10 g/L NaCl solution. In addition, for the cathode, the pH of the solution was adjusted to 2-3 with sulfuric acid. 1.3 V of voltage was applied to two ends of the titanium electrode and the foamed nickel until the current density was lower than 0.5 A/m.sup.2, so as to prepare the under-lithium Li.sub.1-xMn.sub.2O.sub.4 electrode.

[0170] Lithium extraction experiment: an electrolysis device was divided into a cathode chamber and an anode chamber with an anionic membrane. The lithium manganate electrode and the under-lithium lithium manganate electrode that were prepared in example 9 and experiment example 2 were respectively placed into the anode chamber and the cathode chamber. 1.0 L of to-be-treated brine was injected into the cathode chamber. The components of the to-be-treated brine are seen in Table 15. 1.0 L of 10 g/L NaCl solution serving as a support electrolyte was injected into the anode. 0.9 V of voltage was applied to the cathode and the anode to perform electrolysis at 5? C., and the electrolysis was ended when a current was lower than 150 mA. Changes in concentration of lithium in the brine in the process of extracting lithium and concentration of lithium in the anode lithium-enriched solution are seen Table 16.

TABLE-US-00015 TABLE 15 Components of brine Elements Li Na Mg K B SO.sub.4.sup.2? Concentration (g/L) 0.83 90.3 0.2 20.5 1.45 21.3

TABLE-US-00016 TABLE 16 Changes in concentration of lithium in anode and concentration of lithium in brine after extraction of lithium Elements Li Na Mg K B SO.sub.4.sup.2? Initial concentration 0.83 90.3 0.2 20.5 1.45 21.3 of brine (g/L) Ending concentration 0.25 88.5 0.19 20.2 1.42 21.8 of brine (g/L) Concentration of 0.63 4.8 0.02 0.1 0.04 0.25 anode solution (g/L)

[0171] It can be seen from Table 16 that although 0.83 g/L brine with a high sodium-to-lithium ratio is treated, the material also exhibits a good selective lithium extraction property. After electrolysis is ended, the recovery rate of lithium is as high as 70%, the interception rate of lithium is up to more than 98%, and the interception rates of other impurity ions are also basically maintained at such the level.

[0172] The above descriptions are only specific embodiments of the present disclosure, but the protective scope of the present disclosure is not limited thereto. With the technical scope disclosed in the present disclosure, those skilled in the art can easily conceive that variations or replacements are all included within the protective scope of the present disclosure. Therefore, the protective scope of the present disclosure should be based on the protective scope of the appended claims.