Electrode for extracting lithium from salt lake and preparation method thereof

Abstract

An electrode for extracting lithium from a salt lake and a preparation method thereof, belonging to the field of electrode technology, comprising a current collector and a coating distributed on at least one surface of the current collector. The coating comprises n regions arranged along the same center point and formed in sequence from the inside to the outside, the region closest to the center point of the coating is the first region (101), the region farthest from the center point of the coating is the nth region, wherein, the average porosity of the coating decreases from the first region (101) to the nth region, and the average porosity difference between any two adjacent regions is 1% to 20%. The electrode can effectively improve the purity of recovered lithium.

Description

Electrode for lithium extraction from salt lake and preparation method thereof Technical Field

[0001] This article relates to the field of electrode technology, and specifically to an electrode for lithium extraction from salt lakes and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of new energy vehicles and chemical energy storage, the demand for lithium has surged. Salt lake brines contain vast lithium resources (accounting for approximately 70% of global lithium reserves), leading to increasing interest in lithium extraction from salt lakes.

[0003] In order to develop lithium resources in salt lakes, a variety of processes have been invented, such as evaporation concentration, adsorption, extraction and membrane separation. Evaporation concentration is only suitable for extracting lithium from low magnesium-lithium ratio solutions (Mg / Li<6). Membrane separation is difficult to extract lithium from lithium salt lakes. + and Na + / K + Separation requires the Na + and K + Pre-removal results in a large amount of lithium loss. For the extraction method, the organic extractant has a certain solubility in the brine, which brings potential pollution to the environment.

[0004] In response to the difficulties in extracting lithium from salt lakes, the electrochemical deintercalation method has become an emerging lithium extraction method with great development potential due to its environmental friendliness and high selectivity for lithium. The specific steps are: use an anion exchange membrane to separate the electrodialysis device into two areas, the lithium salt chamber and the brine chamber, fill the brine chamber with salt lake brine, and fill the lithium salt chamber with a supporting electrolyte solution free of impurities; place a conductive substrate coated with an ion sieve in the brine chamber as a cathode; place a conductive substrate coated with a lithium-intercalated ion sieve in the lithium salt chamber as an anode; driven by an external potential, the Li+ in the brine in the brine chamber is intercalated into the ion sieve to form a lithium-intercalated ion sieve, and the lithium-intercalated ion sieve in the lithium salt chamber releases Li+ into the conductive solution and returns to an ion sieve; the lithium-intercalated liquid in the brine chamber is discharged, and salt lake brine is added again, the electrodes of the two chambers are exchanged and placed, and the cycle operation is repeated. This method has good selectivity and enrichment ability for lithium. However, in the actual production process, due to the Li in the brine, + The low concentration (0.1-1 g / L) results in a low lithium extraction rate using the electrochemical deintercalation method. Furthermore, in order to reduce the effect of sodium on lithium intercalation, the cell voltage during the electrolysis process needs to be strictly controlled. A reduction in the cell voltage will also significantly slow the rate of the lithium extraction reaction. Furthermore, the high mineralization and viscosity of the brine hinder the mass transfer of the brine within the electrode, leading to significant polarization when operating at high current densities. This results in a large amount of sodium being embedded within the electrode material, reducing the material's selectivity and cycle performance.

[0005] In order to reduce the polarization during the electrochemical deintercalation and lithium extraction process, the electrode is usually pore-formed to increase the transmission path of the solution, which can improve the overall permeability of the electrode plate and enhance the mass transfer effect of the solution within the electrode. CN113293290A and CN113265538A disclose adding a pore-forming agent during the preparation of the electrode slurry and removing the pore-forming agent by drying or water immersion to make the electrode porous. However, the increase in pores formed on the electrode using this method can easily lead to a decrease in the structural stability and strength of the electrode, thereby affecting the efficiency and cycle life of the lithium extraction electrode.

[0006] Summary of the Invention

[0007] The purpose of this article is to overcome the shortcomings of the existing technology and provide an electrode for lithium extraction from salt lakes and a preparation method thereof, wherein the electrode can effectively improve the purity of recovered lithium.

[0008] To achieve the above objectives, the technical solutions adopted in this paper are:

[0009] An electrode for lithium extraction from a salt lake, comprising a current collector and a coating distributed on at least one surface of the current collector;

[0010] The coating comprises n regions formed sequentially from the inside to the outside and arranged along the same center point, the region closest to the center point of the coating being the first region, and the region farthest from the center point of the coating being the nth region;

[0011] The average porosity of the coating decreases from the first region to the nth region, and the difference in average porosity between any two adjacent regions is 1% to 20%;

[0012] Where n is a positive integer ≥ 2.

[0013] Due to the certain distance between the anode and cathode, the higher density of electric lines at the edge of the cathode leads to a larger current passing through the edge of the electrode, and the rate of lithium ion insertion into the electrode is greater than that at the center of the electrode.

[0014] The electrode creatively provided in this article has different porosities in the length direction and / or width direction, and the porosity decreases from the center to the edge. The stable electrode skeleton formed by the undecomposed pore-forming agent at the edge of the electrode increases the structural stability of the electrode while ensuring the porosity of the electrode, without affecting the overall lithium extraction electrode efficiency.

[0015] In the electrodes of this paper, the flow rate of the electrolyte at the electrode edge is higher, and the contact area between the electrode edge and the electrolyte is larger, resulting in a higher concentration of active substances at the electrode edge. Therefore, the coexisting impurity cations in the salt lake brine are more easily embedded from the electrode edge, reducing the purity of lithium. This paper forms smaller pores at the electrode edge to reduce the infiltration of the electrolyte, which can make the current distribution uniform throughout the electrode and make the embedding rate of lithium ions on the electrode the same, thereby reducing the embedding of impurity ions at the electrode edge and improving the purity of the recovered lithium.

[0016] In one embodiment, the difference in average porosity between any two adjacent regions is 1% to 5%.

[0017] In one embodiment, the coating is rectangular, square or circular.

[0018] In one embodiment, the area ratio of the nth region to the n-1th region is (n+1):(n-1).

[0019] In one embodiment, the average porosity of the first region is 8-20%.

[0020] In one embodiment, the current collector includes one of a titanium plate, a titanium mesh, and a carbon fiber cloth.

[0021] This article also provides a method for preparing an electrode for lithium extraction from a salt lake, comprising the following steps:

[0022] The electrode slurry is applied to the surface of the current collector and dried to form a coating. The coating is heated at different temperatures according to the designated areas to obtain an electrode for lithium extraction from salt lakes.

[0023] The heating temperature decreases from the first region to the n-1th region;

[0024] The electrode slurry includes an electrode active material, a conductive agent, a binder, a first pore-forming agent, a second pore-forming agent and a solvent;

[0025] The decomposition temperature of the first pore-forming agent is greater than the decomposition temperature of the second pore-forming agent;

[0026] The heating temperature of the n-1th region is greater than the decomposition temperature of the second pore-forming agent.

[0027] This article uses two pore-forming agents with different decomposition temperatures. During drying, relatively uniform pores can be formed on the electrode. Then, the heating temperatures at the edge and center of the electrode plate are controlled differently. The decomposition rate of the high-temperature pore-forming agent is different. The heating temperature near the edge of the electrode is low, the decomposition rate of the pore-forming agent is low, and the pores are also fewer. The closer to the center of the electrode, the higher the heating temperature, the greater the decomposition rate of the pore-forming agent, and the more pores are formed, thus forming a difference in porosity.

[0028] In one embodiment, the heating temperature of the first zone does not exceed 250°C.

[0029] In one embodiment, the heating temperature difference between any two adjacent regions is 10-60° C. When the heating temperature difference between adjacent regions is within this range, it is beneficial to form coating regions with different porosities.

[0030] In one embodiment, the decomposition temperature of the first pore-forming agent minus the decomposition temperature of the second pore-forming agent = (20-100)° C. In particular, when the decomposition temperatures of the two pore-forming agents are within this range, it is beneficial to form coating regions with different porosities.

[0031] In one embodiment, the first pore-forming agent includes at least one of ammonium chloride and ammonium nitrate.

[0032] In one embodiment, the second pore-forming agent comprises at least one of ammonium bicarbonate, sodium bicarbonate, and ammonium carbonate. Using these two types of pore-forming agents, the second pore-forming agent (with a lower decomposition temperature) can simultaneously form pores during the electrode drying process. The first pore-forming agent (with a higher decomposition temperature) has a different decomposition temperature than the second pore-forming agent, and the decomposition temperature range is relatively wide. This facilitates the formation of multiple porosity gradients from the edge to the center of the electrode at different heating temperatures.

[0033] In one embodiment, the mass ratio of the electrode active material, the conductive agent, the binder, the first pore-forming agent, the second pore-forming agent, and the solvent is 100:(10-15):(8-15):(10-20):(4-8):(150-200).

[0034] In one embodiment, the electrode active material includes LiMn2O4, LiFePO4, LiNi x Co y Mn 1-x-y At least one of O2;

[0035] Among them, 0<x<1, 0<y<1.

[0036] In one embodiment, the conductive agent includes at least one of acetylene black, carbon black, carbon nanotubes, and carbon nanofibers; and / or

[0037] The binder comprises polyvinylidene fluoride; and / or

[0038] The solvent includes N-methylpyrrolidone.

[0039] In one embodiment, the coating amount of the electrode slurry is 0.2-5 kg / m 2 .

[0040] In one embodiment, the drying temperature is 55-70°C.

[0041] The beneficial effects of this article are as follows: (1) The electrode of this article has different porosities in the length direction and / or width direction, and the porosity decreases from the center to the edge direction. The stable electrode skeleton formed by the undecomposed pore-forming agent at the electrode edge increases the structural stability of the electrode while ensuring the porosity of the electrode, and does not affect the overall lithium extraction electrode efficiency. (2) The electrode of this article has a higher flow rate of the electrolyte at the electrode edge, and the contact area between the electrode edge and the electrolyte is larger, resulting in a higher concentration of active substances at the electrode edge. Therefore, the coexisting impurity cations in the salt lake brine are more likely to be embedded from the electrode edge, reducing the purity of lithium. The smaller pores formed at the electrode edge of this article reduce the infiltration of the electrolyte, which can make the current distribution uniform across the electrode and make the lithium ion embedding rate on the electrode the same, thereby reducing the embedding of impurity ions at the electrode edge and improving the purity of the recovered lithium. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG1 is a regional distribution diagram of the coatings of Examples 1 to 3 and Comparative Examples 1 to 2;

[0043] FIG2 is a regional distribution diagram of the coating of Example 4;

[0044] FIG3 is a regional distribution diagram of the coating of Example 5;

[0045] FIG4 is a regional distribution diagram of the coating of Example 6;

[0046] FIG5 is a regional distribution diagram of the coating of Example 7;

[0047] FIG7 is a regional distribution diagram of the coating of Example 8;

[0048] Markings in the figure: 101, first area; 102, second area; 103, third area; 104, fourth area; 105, fifth area. DETAILED DESCRIPTION

[0049] In order to better illustrate the purpose, technical solutions and advantages of this article, this article will be further described below in conjunction with specific embodiments and comparative examples. The purpose is to understand the content of this article in detail, rather than to limit this article.

[0050] Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this article are commonly used reagents and instruments.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description herein, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0052] Example 1

[0053] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0054] (1) LiMn2O4 powder, PVDF, acetylene black, sodium bicarbonate, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0055] The addition amounts of acetylene black, PVDF, sodium bicarbonate, ammonium nitrate and N-methylpyrrolidone are 10%, 8%, 6%, 15% and 150% of the mass of the LiMn2O4 powder, respectively.

[0056] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 2 kg / m 2 .

[0057] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 60°C for 6 hours until the electrode slurry dries to form a coating;

[0058] (4) Dividing the coating (wherein the radius of the coating is R) into three regions arranged along the same center point as shown in FIG1 , namely, a first region 101, a second region 102, and a third region 103, wherein the radius of the first region 101 is 1 / 3R, wherein the second region 102 is an area covered by 1 / 3R to 2 / 3R, and wherein the third region 103 is an area covered by 2 / 3R to R;

[0059] The area ratio of the first region 101, the second region 102, and the third region 103 is 1:3:5;

[0060] (5) Using a carbon dioxide laser beam as a heating source, the second region was heated at 110°C for 10 min, and the first region was heated at 150°C for 15 min, followed by water washing and air drying to obtain an electrode for lithium extraction from salt lakes.

[0061] Example 2

[0062] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0063] (1) LiMn2O4 powder, PVDF, acetylene black, ammonium bicarbonate, and ammonium chloride were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0064] The addition amounts of acetylene black, PVDF, ammonium bicarbonate, ammonium chloride and N-methylpyrrolidone are 15%, 10%, 4%, 20% and 150% of the mass of the LiMn2O4 powder, respectively.

[0065] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 0.2 kg / m 2 .

[0066] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 55°C for 6 hours until the electrode slurry dries to form a coating;

[0067] (4) Dividing the coating (wherein the radius of the coating is R) into three regions arranged along the same center point as shown in FIG1 , namely, a first region 101, a second region 102, and a third region 103, wherein the radius of the first region 101 is 1 / 3R, wherein the second region 102 is an area covered by 1 / 3R to 2 / 3R, and wherein the third region 103 is an area covered by 2 / 3R to R;

[0068] The area ratio of the first region 101, the second region 102, and the third region 103 is 1:3:5;

[0069] (5) Using a carbon dioxide laser beam as a heating source, the second region was heated at 100°C for 10 minutes, and the first region was heated at 140°C for 15 minutes, followed by water washing and drying to obtain an electrode for lithium extraction from salt lakes.

[0070] Example 3

[0071] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0072] (1) LiMn2O4 powder, PVDF, acetylene black, ammonium bicarbonate, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0073] The addition amounts of acetylene black, PVDF, ammonium bicarbonate, ammonium nitrate and N-methylpyrrolidone are 12%, 15%, 8%, 10% and 200% of the mass of the LiMn2O4 powder, respectively.

[0074] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 5 kg / m 2 .

[0075] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 70°C for 6 h until the electrode slurry dries to form a coating;

[0076] (4) Dividing the coating (wherein the radius of the coating is R) into three regions arranged along the same center point as shown in FIG1 , namely, a first region 101, a second region 102, and a third region 103, wherein the radius of the first region 101 is 1 / 3R, wherein the second region 102 is an area covered by 1 / 3R to 2 / 3R, and wherein the third region 103 is an area covered by 2 / 3R to R;

[0077] The area ratio of the first region 101, the second region 102, and the third region 103 is 1:3:5;

[0078] (5) Using a carbon dioxide laser beam as a heating source, the second region was heated at 110°C for 10 min, and the first region was heated at 140°C for 10 min, followed by water washing and drying to obtain an electrode for lithium extraction from salt lakes.

[0079] Example 4

[0080] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0081] (1) LiMn2O4 powder, PVDF, acetylene black, sodium bicarbonate, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0082] The addition amounts of acetylene black, PVDF, sodium bicarbonate, ammonium nitrate and N-methylpyrrolidone are 10%, 8%, 6%, 15% and 150% of the mass of the LiMn2O4 powder, respectively.

[0083] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 2 kg / m 2 .

[0084] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 60°C for 6 hours until the electrode slurry dries to form a coating;

[0085] (4) Dividing the coating (wherein the radius of the coating is R) into two regions arranged along the same center point as shown in FIG2 , namely, a first region 101 and a second region 102, wherein the radius of the first region 101 is 1 / 2R, and the second region 102 is an area covered by 1 / 2R to R;

[0086] The area ratio of the first region 101 to the second region 102 is 1:3;

[0087] (5) Using a carbon dioxide laser beam as a heating source, the first region was heated at 130° C. for 20 min, followed by water washing and drying to obtain an electrode for lithium extraction from salt lakes.

[0088] Example 5

[0089] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0090] (1) LiMn2O4 powder, PVDF, acetylene black, sodium bicarbonate, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0091] The addition amounts of acetylene black, PVDF, sodium bicarbonate, ammonium nitrate and N-methylpyrrolidone are 10%, 8%, 6%, 15% and 150% of the mass of the LiMn2O4 powder, respectively.

[0092] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 2 kg / m 2 .

[0093] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 60°C for 6 hours until the electrode slurry dries to form a coating;

[0094] (4) The coating (wherein the radius of the coating is R) is divided into four regions arranged along the same center point as shown in FIG3 , namely a first region 101, a second region 102, a third region 103, and a fourth region 104, wherein the radius of the first region 101 is 1 / 4R, wherein the second region 102 is an area covered by 1 / 4R to 2 / 4R, wherein the third region 103 is an area covered by 2 / 4R to 3 / 4R, wherein the fourth region 104 is an area covered by 3 / 4R to R,

[0095] The area ratio of the first region 101, the second region 102, the third region 103, and the fourth region 104 is 1:3:5:7;

[0096] (5) Using a carbon dioxide laser beam as a heating source, the third region was heated at 110°C for 10 min, the second region was heated at 130°C for 10 min, and the first region was heated at 160°C for 10 min. The electrodes were then washed with water and dried to obtain an electrode for lithium extraction from a salt lake.

[0097] Example 6

[0098] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0099] (1) LiMn2O4 powder, PVDF, acetylene black, sodium bicarbonate, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0100] The addition amounts of acetylene black, PVDF, sodium bicarbonate, ammonium nitrate and N-methylpyrrolidone are 10%, 8%, 6%, 15% and 150% of the mass of the LiMn2O4 powder, respectively.

[0101] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 2 kg / m 2 .

[0102] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 60°C for 6 hours until the electrode slurry dries to form a coating;

[0103] (4) Dividing the coating (wherein the radius of the coating is R) into five regions arranged along the same center point as shown in FIG4 , namely a first region 101, a second region 102, a third region 103, a fourth region 104, and a fifth region 105, wherein the radius of the first region 101 is 1 / 4R, wherein the second region 102 is a region covered by 1 / 5R to 2 / 5R, wherein the third region 103 is a region covered by 2 / 5R to 3 / 5R, wherein the fourth region 104 is a region covered by 3 / 5R to 4 / 5R, wherein the fifth region 105 is a region covered by 4 / 5R to R;

[0104] The area ratio of the first region 101, the second region 102, the third region 103, the fourth region 104, and the fifth region is 1:3:5:7:9;

[0105] (5) Using a carbon dioxide laser beam as a heating source, the fourth region was heated at 110°C for 10 min, the third region was heated at 120°C for 10 min, the second region was heated at 140°C for 10 min, and the first region was heated at 170°C for 10 min. The electrodes were then washed with water and dried to obtain an electrode for lithium extraction from salt lakes.

[0106] Example 7

[0107] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0108] (1) LiMn2O4 powder, PVDF, acetylene black, ammonium bicarbonate, and ammonium chloride were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0109] The addition amounts of acetylene black, PVDF, ammonium bicarbonate, ammonium chloride and N-methylpyrrolidone are 15%, 10%, 4%, 20% and 150% of the mass of the LiMn2O4 powder, respectively.

[0110] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 0.2 kg / m 2 .

[0111] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 55°C for 6 hours until the electrode slurry dries to form a coating;

[0112] (4) The coating (where the side length of the coating is a) is divided into four regions arranged along the same center point as shown in FIG5 , namely, a first region 101, a second region 102, a third region 103, and a fourth region 104, wherein the side length of the first region is 1 / 4a, the side length of the second region is 2 / 4a, the side length of the third region is 3 / 4a, and the side length of the fourth region is a.

[0113] The area ratio of the first region 101, the second region 102, the third region 103, and the fourth region 104 is 1:3:5:7;

[0114] (5) Using a carbon dioxide laser beam as a heating source, the third region was heated at 110°C for 10 min, the second region was heated at 150°C for 10 min, and the first region was heated at 200°C for 10 min. The electrodes were then washed with water and dried to obtain an electrode for lithium extraction from a salt lake.

[0115] Example 8

[0116] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0117] (1) LiMn2O4 powder, PVDF, acetylene black, ammonium bicarbonate, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0118] The addition amounts of acetylene black, PVDF, ammonium bicarbonate, ammonium nitrate and N-methylpyrrolidone are 12%, 15%, 8%, 10% and 200% of the mass of the LiMn2O4 powder, respectively.

[0119] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 5 kg / m 2 .

[0120] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 70°C for 6 h until the electrode slurry dries to form a coating;

[0121] (4) The coating (wherein the length of the coating is b and the width is c) is divided into three regions arranged along the same center point as shown in FIG6 , namely, a first region 101, a second region 102, a third region 103, and a fourth region 104, wherein the length of the first region is 1 / 4b and the width is 1 / 4c, the length of the second region is 2 / 4b and the width is 2 / 4c, the side length of the third region is 3 / 4b and the width is 3 / 4c, the length of the fourth region is b and the width is c,

[0122] The area ratio of the first region 101, the second region 102, the third region 103, and the fourth region 104 is 1:3:5:7;

[0123] (5) Using a carbon dioxide laser beam as a heating source, the third region was heated at 110°C for 10 min, the second region was heated at 170°C for 10 min, and the first region was heated at 230°C for 10 min. The electrodes were then washed with water and dried to obtain an electrode for lithium extraction from salt lakes.

[0124] Comparative Example 1

[0125] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0126] (1) LiMn2O4 powder, PVDF, acetylene black, and sodium bicarbonate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0127] The addition amounts of acetylene black, PVDF, sodium bicarbonate and N-methylpyrrolidone are 10%, 8%, 6% and 150% of the mass of the LiMn2O4 powder, respectively.

[0128] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 2 kg / m 2 .

[0129] (3) The titanium mesh coated with the electrode slurry was dried in a forced air drying oven at 60° C. for 6 h to form a coating (divided into three areas using the same division method as in Example 1), thereby obtaining an electrode for lithium extraction from salt lakes.

[0130] Comparative Example 2

[0131] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0132] (1) LiMn2O4 powder, PVDF, acetylene black, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0133] The addition amounts of acetylene black, PVDF, ammonium nitrate and N-methylpyrrolidone are 10%, 8%, 15% and 150% of the mass of the LiMn2O4 powder, respectively.

[0134] (2) The electrode slurry was evenly coated on the titanium mesh (divided into three areas using the same division method as in Example 1), wherein the coating density of the electrode slurry was 2 kg / m 2 .

[0135] (3) The titanium mesh coated with the electrode slurry was dried in a forced air drying oven at 60° C. for 6 h to form a coating (divided into three areas using the same division method as in Example 1), thereby obtaining an electrode for lithium extraction from salt lakes.

[0136] Comparative Example 3

[0137] A method for preparing an electrode for lithium extraction from a salt lake comprises the following steps:

[0138] (1) LiMn2O4 powder, PVDF, acetylene black, sodium bicarbonate, and ammonium nitrate were added to N-methylpyrrolidone in proportion and stirred mechanically under vacuum for 6 h to obtain a uniformly dispersed electrode slurry.

[0139] The addition amounts of acetylene black, PVDF, sodium bicarbonate, ammonium nitrate and N-methylpyrrolidone are 10%, 8%, 6%, 15% and 150% of the mass of the LiMn2O4 powder, respectively.

[0140] (2) The electrode slurry is evenly coated on the titanium mesh, wherein the coating density of the electrode slurry is 2 kg / m 2 .

[0141] (3) Dry the titanium mesh coated with the electrode slurry in a blast drying oven at 60°C for 6 hours until the electrode slurry dries to form a coating;

[0142] (4) Dividing the coating (wherein the radius of the coating is R) into three regions arranged along the same center point as shown in FIG1 , namely, a first region 101, a second region 102, and a third region 103, wherein the radius of the first region 101 is 1 / 3R, wherein the second region 102 is an area covered by 1 / 3R to 2 / 3R, and wherein the third region 103 is an area covered by 2 / 3R to R;

[0143] The area ratio of the first region 101, the second region 102, and the third region 103 is 1:3:5;

[0144] (5) Using a carbon dioxide laser beam as a heating source, the coating was heated at 110°C for 10 min, then washed with water and dried to obtain an electrode for lithium extraction from salt lakes.

[0145] Test Example 1

[0146] The average porosity of the electrode was tested using a true density tester, and the test results are shown in Table 1.

[0147] Table 1

[0148] As can be seen from Table 1, the average porosity of the coating of the electrode prepared herein decreases from the first region to the nth region, and the difference in average porosity between any two adjacent regions is 1% to 20%.

[0149] Test Example 2

[0150] Lithium extraction experiment: The electrolytic cell was divided into an anode chamber and a cathode chamber by an anion membrane. The electrodes for lithium extraction prepared in the above embodiment and comparative example were used as anodes and nickel foam was used as cathodes. The cells were placed in a 20 g / L NaCl solution. A voltage of 1.0 V was applied across the electrodes until the current density was lower than 0.5 A / m 2 , which can produce lithium-deficient state Li 1-x Mn2O4 electrode.

[0151] The electrolysis device is divided into cathode chamber and anode chamber by anion membrane, and the prepared LiMn2O4 electrode and Li 1-x The Mn2O4 electrodes were placed in the anode chamber and the cathode chamber respectively. The brine to be treated was injected into the cathode chamber, and a lithium chloride solution with a concentration of 50 mmol / L was injected into the anode chamber as a supporting electrolyte. A voltage of 0.5 V was applied to the anode and cathode to perform constant voltage electrolysis at 15°C. The electrolysis was terminated when the current was lower than 0.15 A. The anode and cathode after lithium extraction were swapped, and the brine and lithium chloride solution were re-injected and the power was turned on to extract lithium. All conditions were kept unchanged. The electrolysis was terminated when the current was lower than 0.15 A. The lithium ions in the brine were enriched in the anode liquid. The relevant parameters obtained are shown in Table 2.

[0152] Table 2

[0153] As can be seen from Table 2, the electrode with a special porosity distribution prepared in this paper can effectively improve the lithium extraction effect. Among them, the flow rate of the electrolyte at the edge of the electrode is higher, and the contact area between the electrode edge and the electrolyte is larger, resulting in a higher concentration of active substances at the edge of the electrode. Therefore, the coexisting impurity cations in the salt lake brine are more easily embedded from the edge of the electrode, reducing the purity of lithium. In this paper, smaller pores are formed at the edge of the electrode to reduce the infiltration of the electrolyte, which can make the current distribution uniform throughout the electrode and make the embedding rate of lithium ions on the electrode the same, thereby reducing the embedding of impurity ions at the edge of the electrode and improving the purity of the recovered lithium.

Claims

1. An electrode for extracting lithium from a salt lake, characterized in that: comprising a current collector and a coating distributed on at least one surface of the current collector; The coating includes n regions formed sequentially from the inside to the outside and arranged along the same center point, the region closest to the center point of the coating is the first region, and the region farthest from the center point of the coating is the nth region; The average porosity of the coating decreases from the first region to the nth region, and the difference in average porosity between any two adjacent regions is 1% to 20%; Wherein n is a positive integer ≥2.

2. The electrode for lithium extraction from salt lake according to claim 1, characterized in that: The coating is rectangular, square or circular.

3. The electrode for extracting lithium from salt lake according to claim 1, characterized in that: The area ratio of the nth region to the n-1th region is (n+1):(n-1).

4. The electrode for extracting lithium from salt lake according to claim 1, characterized in that: The average porosity of the first region is 8-20%.

5. The electrode for extracting lithium from salt lake according to claim 1, characterized in that: The current collector includes one of a titanium plate, a titanium mesh, and a carbon fiber cloth.

6. The method for preparing an electrode for extracting lithium from a salt lake according to any one of claims 1 to 5, characterized in that: The following steps are involved: The electrode slurry is applied to the surface of the current collector, and dried to form a coating. The coating is heated at different heating temperatures according to the designated areas to obtain an electrode for lithium extraction from a salt lake; Wherein, the heating temperature decreases from the first region to the n-1th region; The electrode slurry comprises an electrode active material, a conductive agent, a binder, a first pore-forming agent, a second pore-forming agent and a solvent; The decomposition temperature of the first pore-forming agent is greater than the decomposition temperature of the second pore-forming agent; The heating temperature of the n-1th region is greater than the decomposition temperature of the second pore-forming agent.

7. The method for preparing an electrode for lithium extraction from a salt lake according to claim 6, characterized in that: The heating temperature of the first zone does not exceed 250°C.

8. The method for preparing an electrode for extracting lithium from a salt lake according to claim 6, characterized in that: The heating temperature difference between any two adjacent areas is 10 to 60°C.

9. The method for preparing an electrode for extracting lithium from a salt lake according to claim 6, characterized in that: The decomposition temperature of the first pore-forming agent minus the decomposition temperature of the second pore-forming agent=(20-100)°C.

10. The method for preparing an electrode for extracting lithium from a salt lake according to claim 6, characterized in that: The first pore-forming agent includes at least one of ammonium chloride and ammonium nitrate.

11. The method for preparing an electrode for extracting lithium from a salt lake according to claim 6, characterized in that: The second pore-forming agent includes at least one of ammonium bicarbonate, sodium bicarbonate, and ammonium carbonate.

12. The method for preparing an electrode for extracting lithium from a salt lake according to claim 3, characterized in that: The mass ratio of the electrode active material, the conductive agent, the binder, the first pore-forming agent, the second pore-forming agent, and the solvent is 100: (10-15): (8-15): (10-20): (4-8): (150-200).

13. The method for preparing an electrode for lithium extraction from a salt lake according to claim 6, characterized in that: The electrode active material includes LiMn2O4, LiFePO4, LiNi x Co y Mn 1-x-y At least one of O2; Among them, 0<x<1, 0<y<1.

14. The method for preparing an electrode for extracting lithium from a salt lake according to claim 6, characterized in that: The conductive agent comprises at least one of acetylene black, carbon black, carbon nanotubes, and carbon nanofibers; and / or The binder comprises polyvinylidene fluoride; and / or The solvent includes N-methylpyrrolidone.

15. The method for preparing an electrode for extracting lithium from a salt lake according to claim 6, characterized in that: The coating amount of the electrode slurry is 0.2-5 kg / m 2 .

16. The method for preparing an electrode for extracting lithium from a salt lake according to claim 6, characterized in that: The drying temperature is 55-70°C.

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