Hierarchical porous lithium ion sieve, and preparation method and application thereof

Abstract

This invention provides a hierarchical porous lithium-ion sieve, its preparation method, and its application, belonging to the field of lithium extraction technology. The invention uses needle-like γ-MnOOH as a stabilizer and an aqueous polymerization reaction solution as the liquid phase for foaming. The foamed material is then subjected to ultraviolet light curing to obtain a porous material with γ-MnOOH as the framework. This porous material is further immersed in a lithium hydroxide solution containing an oxidant for a hydrothermal reaction. After the hydrothermal reaction, the product is calcined to obtain hierarchical porous LiMn2O4. Finally, the obtained hierarchical porous LiMn2O4 is impregnated and cured, thereby preparing a hierarchical porous lithium-ion sieve with excellent adsorption rate, adsorption capacity, and cycle stability. Furthermore, the preparation method provided by this invention is simple to operate and beneficial for practical production.

Description

Technical Field

[0001] This invention belongs to the field of lithium extraction technology, and particularly relates to a graded porous lithium-ion sieve, its preparation method and application. Background Technology

[0002] With the widespread adoption of electric vehicles and portable electronic devices, the lithium battery market has grown significantly, and it is projected to consume one-third of the world's current exploitable lithium reserves over the next 30 years. 90% of the world's proven lithium deposits are liquid deposits, and 80% of China's proven lithium deposits are also liquid deposits. Adsorption is considered one of the most promising methods for lithium extraction from salt lakes.

[0003] Lithium adsorbent materials can be classified as inorganic, organic, or a combination of both. As adsorbent materials, a high specific surface area porous material is generally desired to enhance the adsorption capacity of Li. + The diffusion of these molecules enhances the adsorption performance. There are many strategies for preparing porous lithium-ion adsorbent materials, such as loading lithium-ion sieves or lithium-ion imprinted materials with natural or synthetic porous materials, or preparing nanofiber mats by electrospinning. However, these methods can only produce porous materials with a single pore size, and most of them are mesoporous materials (pore size < 50 nm). When the material wettability is low, the exchange of substances inside the material is greatly limited. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a hierarchical porous lithium ion sieve with excellent lithium ion adsorption rate, lithium ion adsorption capacity and cycle stability, as well as its preparation method and application.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a hierarchical porous lithium-ion sieve, the method comprising the following steps:

[0006] (1) Disperse needle-shaped γ-MnOOH in a polymerization reaction aqueous solution containing reactive monomers, crosslinking agents and photoinitiators, then add foaming agent and stir to foam. After foaming, take the upper foam and perform ultraviolet light curing reaction. After the light curing reaction is completed, dry to obtain γ-MnOOH porous material.

[0007] (2) After immersing the γ-MnOOH porous material in an aqueous lithium hydroxide solution, an oxidant was added and mixed. Then, a hydrothermal reaction was carried out. After the reaction was completed, the solid was collected and calcined to obtain fractional porous LiMn2O4.

[0008] (3) The graded porous LiMn2O4 was immersed in a DMF solution of sulfonated polyethersulfone, and then ultrasonicated, filtered, and acid-washed to obtain a graded porous lithium ion sieve.

[0009] In the method for preparing a hierarchical porous lithium-ion sieve provided by this invention, needle-like γ-MnOOH is used as a stabilizer, and an aqueous polymerization reaction solution is used as the liquid phase for foaming. The foamed material is then subjected to ultraviolet light curing to obtain a porous material with γ-MnOOH as the framework. This porous material is further immersed in a lithium hydroxide solution containing an oxidant for hydrothermal reaction. After the hydrothermal reaction, the product is calcined to obtain hierarchical porous LiMn2O4. Subsequently, the obtained hierarchical porous LiMn2O4 is impregnated and cured, thereby preparing a hierarchical porous lithium-ion sieve with excellent adsorption rate, adsorption capacity, and cycle stability. Specifically, the prepared LiMn2O4 inherits the needle-like structure of γ-MnOOH, enabling it to achieve a hierarchical porous spatial structure when used as a framework for porous materials, including micropores, mesopores, and macropores simultaneously. Among them, the micropores and mesopores are formed by the pores between the overlapping needle-like LiMn2O4, while the macropores are formed by the cavities inside the foam, giving the material both a large specific surface area and surface wettability. Further impregnation and curing can stably prepare lithium-ion sieves, thereby ensuring that the obtained product has both improved lithium-ion diffusion and cycle stability.

[0010] In one embodiment, the needle-like γ-MnOOH is prepared by dissolving potassium permanganate in deionized water, then adding ethanol dropwise and stirring until homogeneous, and reacting at 100-200℃ for 18-22h. After the reaction is completed, the mixture is filtered, the filter residue is collected, washed, and dried to obtain needle-like γ-MnOOH.

[0011] In one embodiment, the ratio of potassium permanganate, deionized water, and ethanol is 4.5g:100mL:8mL.

[0012] This invention has found that when the above reaction is used for preparation, the target needle-like γ-MnOOH product can be obtained. When this product is applied to the preparation of hierarchical porous lithium-ion sieves, it can help realize the hierarchical porous structure of lithium-ion sieves as a framework of porous materials, thereby improving the lithium extraction rate and lithium extraction capacity of the prepared product.

[0013] In one embodiment, at least one of the following (a)-(d) is satisfied:

[0014] (a) The reactant monomers include at least one of acrylamide, maleic acid, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, vinylpyrrolidone, vinylimidazole, and allylimidazole;

[0015] (b) The crosslinking agent includes at least one of ethylene glycol dimethacrylate and N,N'-methylenebisacrylamide;

[0016] (c) The photoinitiator includes at least one of Irgacure2959, Irgacure500, and Darocur 1173;

[0017] (d) The foaming agent includes anionic surfactants.

[0018] In one embodiment, the foaming agent includes at least one of sodium dodecyl sulfate (SDS), sodium octyl sulfonate, and sodium dodecylbenzene sulfonate.

[0019] This invention has found that when the reactant, crosslinking agent, photoinitiator, and foaming agent are further selected as substances of the above types, it can help to achieve a hierarchical porous structure of lithium ion sieves, and can further improve the adsorption rate and adsorption capacity of lithium ions of the prepared hierarchical porous lithium ion sieves.

[0020] In one embodiment, at least one of the following (e)-(h) is satisfied:

[0021] (e) The feeding ratio of the needle-like γ-MnOOH, the foaming agent, and the polymerization reaction aqueous solution is (1-3)g:(0.01-0.05)g:100mL;

[0022] (f) The molar ratio of the reactant monomer to the crosslinking agent is (3-7):1;

[0023] (g) The photoinitiator has a mass percentage of 3%-5% based on the sum of the masses of the reactive monomer and the crosslinking agent;

[0024] (h) The total mass percentage of the reactants and crosslinking agents is 2%-5% based on the mass of the aqueous solution used in the polymerization reaction.

[0025] The present invention has found that when the relationship between the raw materials in the crosslinking reaction in step (1) is within the above range, the overall performance of the prepared hierarchical porous lithium ion sieve is better.

[0026] In one embodiment, the stirring speed for foaming is 1800-2200 rpm and the time is 12-18 min.

[0027] In one embodiment, the stirring speed for foaming is 2000 rpm and the time is 15 min.

[0028] This invention has found that when the stirring speed and time for foaming are further selected within the above-mentioned range, sufficient foaming can be achieved while saving reaction time, thus improving foaming efficiency; and macroporous structures can be effectively formed during the foaming process, helping to realize the hierarchical porous structure of lithium ion sieves.

[0029] In one embodiment, the UV curing time is 55-65 minutes.

[0030] In one embodiment, the UV curing time is 60 minutes.

[0031] In one embodiment, after foaming is completed, the material is filtered and the upper wet foam layer is collected.

[0032] The present invention has found that after foaming, the collected foam layer is cured by ultraviolet light. Under the action of photoinitiator, good photocuring results can be achieved in 55-65 minutes.

[0033] In one embodiment, in step (2), the temperature of the hydrothermal reaction is 120-160°C and the time of the hydrothermal reaction is 92-100h.

[0034] This invention has found that immersing the γ-MnOOH porous material prepared by photocuring in an aqueous solution of lithium hydroxide containing an oxidant for hydrothermal reaction can ensure that γ-MnOOH and lithium ions are fully and uniformly mixed, thereby forming a lithium manganese oxide material with complete crystals and uniform elemental dispersion; especially when the temperature and time of the hydrothermal reaction are within the range given in this invention, the overall effect of the obtained product is even better.

[0035] In one embodiment, in step (2), the calcination temperature is 450-550°C and the calcination time is 10-14h.

[0036] This invention has found that when the hydrothermal reaction is completed, further calcination within the temperature and time range specified in this invention can yield lithium manganese oxide material with high crystallinity.

[0037] In one embodiment, at least one of the following (i)-(l) is satisfied:

[0038] (i) The oxidant includes any one of hydrogen peroxide, hypochlorous acid and its salts, and permanganic acid and its salts;

[0039] (j) The concentration of the lithium hydroxide aqueous solution is (0.15-0.2) g / mL;

[0040] (k) The molar ratio of γ-MnOOH to lithium hydroxide is Li:Mn = 0.7;

[0041] (l) The molar ratio of the oxidant to lithium hydroxide is 1:1.

[0042] The present invention has found that when the parameters for preparing hierarchical porous LiMn2O4 are further selected within the above-mentioned range, a product with a higher lithium ion adsorption rate and a larger lithium ion adsorption capacity can be obtained.

[0043] In one embodiment, the ultrasound time in step (3) is 55-65 minutes.

[0044] In one embodiment, the mass ratio of the hierarchical porous LiMn2O4 to the DMF solution of sulfonated polyethersulfone is 1:(48-52).

[0045] In one embodiment, the pickling is performed by pickling in a hydrochloric acid solution with a mass concentration of (0.2-0.5) mol / L for 22-26 hours.

[0046] In one embodiment, the sulfonated polyethersulfone in the DMF solution contains 30% by mass of sulfonated polyethersulfone.

[0047] The present invention has found that when the prepared hierarchical porous LiMn2O4 is further processed within the above-mentioned conditions, the prepared hierarchical porous LiMn2O4 can be effectively solidified, avoiding the phenomenon that it easily turns into powder and affects the overall effect.

[0048] In a second aspect, the present invention provides a graded porous lithium-ion sieve, wherein the graded porous lithium-ion sieve is prepared by the preparation method described in the present invention.

[0049] The hierarchical porous lithium-ion sieve provided by this invention has a rich pore structure, including micropores (pore diameter < 2 nm), mesopores (pore diameter 2-50 nm), and macropores (pore diameter > 50 nm), and also contains submicron and micron-sized macropores. The presence of the hierarchical porous structure endows the lithium-ion sieve with high water wettability, thus exhibiting a fast lithium extraction rate and a large lithium extraction capacity. At the same time, the hierarchical porous lithium-ion sieve provided by this invention also has excellent stability and excellent cycling performance, maintaining a high lithium extraction rate even after multiple cycles.

[0050] In a third aspect, the present invention provides the application of the graded porous lithium-ion sieve in lithium extraction from salt lakes.

[0051] The graded porous lithium-ion sieve provided by this invention has excellent lithium extraction rate and capacity, and also has good cycle stability. The lithium extraction rate does not decrease significantly after multiple cycles. Therefore, it can be effectively applied to lithium extraction from salt lakes.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] The method for preparing a hierarchical porous lithium-ion sieve provided by this invention uses needle-like γ-MnOOH as a stabilizer and an aqueous polymerization reaction solution as the liquid phase for foaming. The foamed material is then subjected to ultraviolet light curing to obtain a porous material with γ-MnOOH as the framework. This porous material is further immersed in a lithium hydroxide solution containing an oxidant for a hydrothermal reaction. After the hydrothermal reaction, the product is calcined to obtain hierarchical porous LiMn2O4. Finally, the obtained hierarchical porous LiMn2O4 is impregnated and cured, thereby preparing a hierarchical porous lithium-ion sieve with excellent adsorption rate, adsorption capacity, and cycle stability. Furthermore, the preparation method provided by this invention is simple to operate and beneficial for practical production. Attached Figure Description

[0054] Figure 1 SEM image of the hierarchical porous lithium-ion sieve prepared in Example 1;

[0055] Figure 2 XRD comparison images of the hierarchical porous lithium-ion sieves prepared in Example 1 and Comparative Example 1;

[0056] Figure 3 This is a comparison diagram of the pore size distribution of the hierarchical porous lithium-ion sieves prepared in Example 1 and Comparative Example 2. Detailed Implementation

[0057] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0058] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in the field.

[0059] Example 1

[0060] This invention provides a graded porous lithium-ion sieve, the preparation method of which includes the following steps:

[0061] (1) Preparation of needle-shaped γ-MnOOH: Potassium permanganate was dissolved in deionized water, and then ethanol was added dropwise. After stirring evenly, the mixture was transferred to a hydrothermal reactor, sealed, and reacted at 150℃ for 20h. After the reaction was completed, the reaction solution was filtered, the filter residue was collected, and the filter residue was washed with water and ethanol in sequence. After washing, the residue was dried under vacuum at 80℃ to obtain needle-shaped γ-MnOOH (the average cross-sectional diameter of needle-shaped γ-MnOOH was 305nm, and the average aspect ratio was 22.4).

[0062] The ratio of potassium permanganate, deionized water and ethanol is 4.5g:100mL:8mL.

[0063] (2) Preparation of γ-MnOOH porous material: The reactive monomer (a mixture of acrylamide and acrylic acid in a molar ratio of 0.5:1), crosslinking agent (N,N'-methylenebisacrylamide) and photoinitiator (Darocur1173) were dissolved in water to obtain a polymerization reaction aqueous solution. Then, needle-shaped γ-MnOOH was ultrasonically dispersed in the polymerization reaction aqueous solution. After dispersion, foaming agent (SDS) was added and stirred at 2000 rpm for 15 min. After stirring, the mixture was filtered, the upper foam was taken, and the foam was transferred to ultraviolet light for ultraviolet curing reaction for 60 min. After the reaction, the mixture was rinsed 5 times with ethanol. After rinsing, the mixture was dried under vacuum at 80℃ to obtain γ-MnOOH porous material.

[0064] The molar ratio of the reactant monomer to the crosslinking agent is 5:1; the amount of photoinitiator added is 4% of the total mass of the reactant monomer and the crosslinking agent; the total mass percentage concentration of the reactant monomer and the crosslinking agent in the polymerization reaction aqueous solution is 4%; the feeding ratio of needle-like γ-MnOOH, foaming agent and polymerization reaction aqueous solution is 2g:0.03g:100mL.

[0065] (3) Preparation of graded porous LiMn2O4: γ-MnOOH porous material was impregnated in a lithium hydroxide aqueous solution with a mass concentration of 0.18 g / mL, and then an oxidant (hydrogen peroxide) was added. After stirring and mixing evenly, the mixture was transferred to a hydrothermal reactor and reacted at 140℃ for 4 days. After the solvent evaporated from the reaction solution, a solid was obtained and then calcined at 500℃ for 12 h to obtain graded porous LiMn2O4.

[0066] The γ-MnOOH porous material and lithium hydroxide were fed in a molar ratio of Li to Mn = 0.7; the molar ratio of oxidant to lithium hydroxide was 1:1.

[0067] (4) Preparation of graded porous lithium ion sieve: Graded porous LiMn2O4 was immersed in a DMF solution of sulfonated polyethersulfone with a mass percentage of 30%, sonicated for 1 h, filtered under normal pressure, dried, and then acid-washed with 0.3 mol / L hydrochloric acid for 24 h. After acid washing, it was taken out and graded porous lithium ion sieve was obtained.

[0068] The mass ratio of hierarchical porous LiMn2O4 to sulfonated polyethersulfone DMF solution is 1:50.

[0069] The microstructure of the material was observed using a JEOL JSM-6490LV scanning electron microscope. The SEM image of the hierarchical porous lithium-ion sieve is shown below. Figure 1 As shown, from Figure 1 As can be seen from the data, the prepared hierarchical porous lithium-ion sieve has a distinct porous structure.

[0070] Example 2

[0071] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (3), the oxidant is replaced with hypochlorous acid and the hydrothermal reaction temperature is 120°C.

[0072] Example 3

[0073] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (3), the oxidant is changed to potassium permanganate and the hydrothermal reaction temperature is 160°C.

[0074] Example 4

[0075] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (3), the reaction is carried out at 120°C for 4 days.

[0076] Example 5

[0077] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (3), the reaction is carried out at 160°C for 4 days.

[0078] Example 6

[0079] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (3), the mass concentration of lithium hydroxide is 0.15 g / mL.

[0080] Example 7

[0081] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (3), the mass concentration of lithium hydroxide is 0.2 g / mL.

[0082] Example 8

[0083] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (2), the feeding ratio of needle-shaped γ-MnOOH, foaming agent and polymerization reaction aqueous solution is 1g:0.05g:100mL.

[0084] Example 9

[0085] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (2), the feeding ratio of needle-shaped γ-MnOOH, foaming agent and polymerization reaction aqueous solution is 3g:0.01g:100mL.

[0086] Example 10

[0087] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (2), the molar ratio of the reactant monomer to the crosslinking agent is 3:1.

[0088] Example 11

[0089] This invention provides a graded porous lithium-ion sieve. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is that in step (2), the molar ratio of the reactant monomer to the crosslinking agent is 7:1.

[0090] Example 12

[0091] This invention provides a graded porous lithium-ion sieve, the preparation method of which includes the following steps:

[0092] (1) Preparation of nano-needle γ-MnOOH: Potassium permanganate was dissolved in deionized water, and then ethanol was added dropwise. After stirring evenly, the mixture was transferred to a hydrothermal reactor, sealed, and reacted at 150°C for 20 h. The resulting reaction solution was filtered, and the filter residue was washed with water and ethanol in sequence. After drying under vacuum at 80°C, nano-needle γ-MnOOH was obtained (the average cross-sectional diameter of the needle-like γ-MnOOH was 305 nm, and the average aspect ratio was 22.4).

[0093] The reaction feed ratio of potassium permanganate, deionized water, and ethanol is 4.5g:100mL:8mL;

[0094] (2) Preparation of γ-MnOOH porous material: The reaction monomer (a mixture of methacrylic acid, hydroxyethyl methacrylate and allyl imidazole in a ratio of 1:0.2:0.1), crosslinking agent (ethylene glycol dimethacrylate) and photoinitiator (Darocur1173) were dissolved in water to obtain a polymerization reaction aqueous solution. Then, needle-shaped γ-MnOOH was ultrasonically dispersed in the polymerization reaction aqueous solution. After dispersion, foaming agent (sodium dodecylbenzenesulfonate) was added and stirred at 2000 rpm for 15 min. After stirring, the lower aqueous phase was filtered off and the upper wet foam was retained. The wet foam was transferred to ultraviolet light for ultraviolet curing reaction for 60 min. After the reaction, it was rinsed 5 times with ethanol. After rinsing, it was dried under vacuum at 80℃ to obtain γ-MnOOH porous material.

[0095] The molar ratio of the reactant monomer to the crosslinking agent is 3:1; the amount of photoinitiator added is 5% of the total mass of the reactant monomer and the crosslinking agent; the total mass percentage concentration of the reactant monomer and the crosslinking agent in the polymerization reaction aqueous solution is 2%; the feeding ratio of needle-shaped γ-MnOOH, foaming agent and polymerization reaction aqueous solution is 1g:0.05g:100mL.

[0096] (3) Preparation of hierarchical porous LiMn2O4 material: The γ-MnOOH porous material obtained in step (2) was immersed in a lithium hydroxide aqueous solution with a mass concentration of 0.18 g / mL, and an oxidant (hydrogen peroxide) was added. After stirring and mixing evenly, it was transferred to a hydrothermal reactor and reacted at 140°C for 4 days. After the solvent evaporated from the reaction solution, the resulting solid was calcined at 450°C for 12 h to obtain hierarchical porous LiMn2O4 material.

[0097] In this process, the γ-MnOOH porous material and lithium hydroxide are fed together at a Li / Mn molar ratio of 0.7; the molar ratio of oxidant to lithium hydroxide is 1:1.

[0098] (4) The hierarchical porous LiMn2O4 material was immersed in 30wt% sulfonated polyethersulfone DMF solution, sonicated for 1h, filtered under normal pressure, dried, and then acid-washed with 0.3mol / L hydrochloric acid for 24h to obtain the hierarchical porous lithium ion sieve.

[0099] The mass ratio of hierarchical porous LiMn2O4 material to sulfonated polyethersulfone casting solution is 1:50.

[0100] Example 13

[0101] This invention provides a graded porous lithium-ion sieve, the preparation method of which includes the following steps:

[0102] (1) Preparation of nano-needle γ-MnOOH: Potassium permanganate was dissolved in deionized water, and then ethanol was added dropwise. After stirring evenly, the mixture was transferred to a hydrothermal reactor, sealed, and reacted at 150°C for 20 h. The resulting reaction solution was filtered, and the filter residue was washed with water and ethanol in sequence. After drying under vacuum at 80°C, nano-needle γ-MnOOH was obtained (the average cross-sectional diameter of the needle-like γ-MnOOH was 305 nm, and the average aspect ratio was 22.4).

[0103] The reaction feed ratio of potassium permanganate, deionized water, and ethanol is 4.5g:100mL:8mL;

[0104] (2) Preparation of γ-MnOOH porous material: The reaction monomer (a mixture of methacrylic acid, hydroxyethyl methacrylate and allyl imidazole in a ratio of 1:0.2:0.1), crosslinking agent (ethylene glycol dimethacrylate) and photoinitiator (Darocur1173) were dissolved in water to obtain a polymerization reaction aqueous solution. Then, the γ-MnOOH porous material was ultrasonically dispersed in the polymerization reaction aqueous solution, and a foaming agent (sodium octyl sulfonate) was added. The mixture was stirred and foamed at 2000 rpm for 15 min. After foaming, the lower aqueous phase was filtered off and the upper wet foam was retained. The wet foam was transferred to ultraviolet light for ultraviolet curing reaction for 60 min. After the reaction, the mixture was rinsed 5 times with ethanol. After rinsing, the mixture was dried under vacuum at 80℃ to obtain the γ-MnOOH porous material.

[0105] The molar ratio of the reactive monomer to the crosslinking agent is 7:1; the amount of photoinitiator added is 3% of the total mass of the reactive monomer and the crosslinking agent; the total mass percentage concentration of the reactive monomer and the crosslinking agent in the polymerization reaction solution is 5%; the feeding ratio of needle-shaped γ-MnOOH, foaming agent and polymerization reaction solution is 3g:0.01g:100mL.

[0106] (3) Preparation of hierarchical porous LiMn2O4 material: The γ-MnOOH porous material obtained in step (2) was immersed in a lithium hydroxide aqueous solution with a mass concentration of 0.18 g / mL, and an oxidant (hydrogen peroxide) was added. After stirring and mixing evenly, it was transferred to a hydrothermal reactor and reacted at 140°C for 4 days. After the solvent evaporated from the reaction solution, the resulting solid was calcined at 550°C for 12 h to obtain hierarchical porous LiMn2O4 material.

[0107] In this process, the γ-MnOOH porous material and lithium hydroxide are fed together at a Li / Mn molar ratio of 0.7; the molar ratio of oxidant to lithium hydroxide is 1:1.

[0108] (4) The hierarchical porous LiMn2O4 material was immersed in 30wt% sulfonated polyethersulfone DMF solution, sonicated for 1h, filtered under normal pressure, dried, and then acid-washed with 0.3mol / L hydrochloric acid for 24h to obtain the hierarchical porous lithium ion sieve.

[0109] The mass ratio of hierarchical porous LiMn2O4 material to sulfonated polyethersulfone casting solution is 1:50.

[0110] Comparative Example 1

[0111] The present invention provides a graded porous lithium-ion sieve as a comparative example. The only difference between the preparation method of the graded porous lithium-ion sieve and that of Example 1 is in step (3). Step (3) of this comparative example is as follows:

[0112] γ-MnOOH porous material was impregnated in a lithium hydroxide aqueous solution with a mass concentration of 0.18 g / mL. After stirring and mixing evenly, the mixture was transferred to a hydrothermal reactor and reacted at 140℃ for 4 days. After the solvent evaporated from the reaction solution, a solid was obtained. The solid was then calcined at 500℃ for 12 h to obtain fractional porous LiMn2O4.

[0113] The γ-MnOOH porous material and lithium hydroxide were fed in a molar ratio of Li:Mn = 0.7.

[0114] Comparative Example 2

[0115] This invention provides a lithium-ion sieve as a comparative example. The lithium-ion sieve provided in this comparative example is prepared using a conventional granulation method. The preparation method of the lithium-ion sieve includes the following steps:

[0116] (1) Mix γ-MnOOH and LiOH·H2O in a mortar with a Li / Mn molar ratio of 0.7, and add 2wt% anhydrous ethanol to grind the above materials. At this time, the mixture becomes a slurry. After grinding for a period of time, the amount of anhydrous ethanol gradually decreases until the mixture becomes dry. Place the obtained dry mixture powder in a muffle furnace at 700℃ and keep it warm for 10h to obtain LiMn2O4 material.

[0117] (2) Mix and grind LiMn2O4 material with PVC in N-methylpyrrolidone to obtain a slurry. Then, drop the slurry into water with an injection agent to form particles. Control the particle diameter to be 2-4 mm. Wash the obtained particles with deionized water and dry them at 80°C for 12 h to obtain the formed ion sieve precursor particles.

[0118] The mass ratio of LiMn2O4, PVC, and N-methylpyrrolidone is 8:1:1.

[0119] (3) The ion sieve precursor particles were soaked in 0.3M hydrochloric acid solution for 24h and dried at 80℃ for 12h to obtain lithium ion sieve.

[0120] Comparative Example 3

[0121] The present invention provides a graded porous lithium ion sieve in a comparative example. The only difference between the preparation method of the graded porous lithium ion sieve and that of Example 1 is that step (4) is omitted.

[0122] Research has shown that without the impregnation and reinforcement step (4), the prepared product is prone to collapse into powder and is not practically applicable. Therefore, the product of this comparative example will not be tested in subsequent effect example tests.

[0123] Example 1

[0124] 1. The lithium-ion sieves prepared in Examples 1-13 and Comparative Example 1 were verified by XRD. Specifically, the crystal phase and crystal structure of the materials were studied using an X-ray powder diffractometer (XRD, Rigaku D / max-2600PC, Japan). Cu Kα rays were used for the test, with a wavelength λ of 0.154056 nm, a voltage of 40 kV, a current of 40 mA, and a scanning range 2θ of 10-80°. The XRD test results were analyzed using Jade 6 software.

[0125] The products prepared in Examples 1-13 conform to JCPDS (35-0782), and the XRD comparison diagrams of the lithium-ion sieves prepared in Example 1 and Comparative Example 1 are shown in the figure. Figure 2 As shown, from Figure 2 It can be seen that the lithium-ion sieves prepared in Example 1 and Comparative Example 1 conform to JCPDS (35-0782), but the product prepared in Comparative Example 1 contains Mn2O3 impurity phase.

[0126] 2. The pore size distribution of the lithium-ion sieves was determined using an automated mercury porosimeter (AutoPore IV 9510) and calculated using N2 adsorption / desorption experiments. The results showed that the lithium-ion sieves prepared in Examples 1-13 all possessed abundant pore structures. Specifically, the pore size distribution comparison diagrams of the lithium-ion sieves prepared in Example 1 and Comparative Example 2 are shown below. Figure 3 As shown, Figure 3 The left half shows the pore size distribution calculated using N2 adsorption / desorption experiments, and the right half shows the pore size distribution obtained using mercury intrusion porosimetry. Figure 3 As can be seen, the product prepared in Example 1 has a rich pore structure, including micropores (<2nm), mesopores (2-50nm) and macropores (>50nm), and there are submicron and micron-sized macropores; the lithium-ion sieve prepared in Comparative Example 2 is obtained by conventional granulation, and the pore size is mainly distributed in the mesopore range, and the pores are relatively simple.

[0127] Example 2

[0128] This example verifies the adsorption capacity and adsorption rate of the lithium-ion sieves prepared in Examples 1-13 and Comparative Examples 1-2, as well as the lithium extraction rate after 100 cycles. The specific process includes the following steps:

[0129] The lithium-ion sieve was immersed in a lithium-containing solution (the concentration of lithium ions in the lithium-containing solution was 0.05 mol / L, and the solid-liquid ratio of the lithium-ion sieve to the lithium-containing solution was 1 g:1000 mL), and shaken at 100 rpm in a constant temperature shaking oven at 25 °C for 24 h to ensure that the adsorption reached equilibrium; the Li content in the solution was determined by ICP-OES. + The content of . Adsorption capacity Q eThe formula for calculating (mg / g) is as follows:

[0130]

[0131] In the formula, C0 (mg / L) represents Li + The initial concentration of C; e (mg / L) is the Li when adsorption equilibrium is reached + The concentration of ; V(L) is the volume of the solution; m(g) is the mass of the lithium ion sieve;

[0132] The adsorption capacity was measured after 30 minutes of adsorption. And calculate the adsorption rate r E The formula for calculating (%) is as follows:

[0133]

[0134] In the formula, Q represents the adsorption capacity calculated after 30 minutes of adsorption. e (mg / g) represents the adsorption capacity calculated after 24 hours of adsorption;

[0135] Lithium extraction was performed using the method described above. The first lithium adsorption was taken as the start of the first cycle, and adsorption-deintercalation constituted one cycle. After 100 cycles, Q was measured. e The delithiation process involves acid washing in 0.3M hydrochloric acid solution for 24 hours and drying at 80℃ for 12 hours.

[0136] The results are shown in Table 1.

[0137] Table 1

[0138]

[0139]

[0140] As can be seen from Table 1, when the preparation method of the present invention is used, the obtained lithium-ion sieve has excellent lithium extraction rate, lithium extraction capacity and cycle stability. Specifically, the initial adsorption capacity of the obtained lithium-ion sieve is above 26.21 mg / g, the lithium extraction rate retention rate is above 95.6% after 100 cycles, and the lithium extraction rate is above 58.2%. Compared with the lithium-ion sieve prepared by conventional granulation method in Comparative Example 2, the lithium-ion sieve prepared by the method of the present invention has significantly improved adsorption rate and adsorption capacity, and the cycle stability is also significantly better. Among them, compared with Comparative Example 2, the adsorption capacity is increased by 5.13%-9.83%, the adsorption rate is increased by 15.02%-36.76%, and the adsorption rate can be increased by 3.94% after 100 cycles.

[0141] As can be seen from Example 1 and Comparative Example 1, during the hydrothermal reaction stage after γ-MnOOH is impregnated in an aqueous lithium hydroxide solution and then mixed with an oxidant, the addition of an oxidant significantly affects the overall performance of the product. When no oxidant was added during the hydrothermal reaction in Comparative Example 1, compared with Example 1, the adsorption capacity decreased by 16.16%, the adsorption rate decreased by 10.89%, and the adsorption rate decreased by 4.16% after 100 cycles.

Claims

1. A method for preparing a hierarchical porous lithium-ion sieve, characterized in that, The preparation method includes the following steps: (1) Disperse needle-shaped γ-MnOOH in a polymerization reaction aqueous solution containing reactive monomers, crosslinking agents and photoinitiators, then add foaming agent and stir to foam. After foaming, take the upper foam and perform ultraviolet light curing reaction. After the light curing reaction is completed, dry to obtain γ-MnOOH porous material. (2) After immersing the γ-MnOOH porous material in an aqueous lithium hydroxide solution, an oxidant was added and mixed. Then, a hydrothermal reaction was carried out. After the reaction was completed, the solid was collected and calcined to obtain fractional porous LiMn2O4. (3) The graded porous LiMn2O4 was immersed in a DMF solution of sulfonated polyethersulfone, and then ultrasonicated, filtered, and acid-washed to obtain a graded porous lithium ion sieve. In step (2), the temperature of the hydrothermal reaction is 120-160℃ and the time of the hydrothermal reaction is 92-100h; the temperature of the calcination is 450-550℃ and the time of the calcination is 10-14h.

2. The preparation method according to claim 1, characterized in that, The method for preparing the needle-like γ-MnOOH is as follows: potassium permanganate is dissolved in deionized water, followed by the addition of ethanol and stirring until homogeneous. The mixture is then reacted at 100-200℃ for 18-22 hours. After the reaction is completed, the mixture is filtered, the filter residue is collected, washed, and dried to obtain needle-like γ-MnOOH.

3. The preparation method according to claim 1, characterized in that, Satisfying at least one of the following (a)-(d): (a) The reactant monomers include at least one of acrylamide, maleic acid, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, 2-acrylamido-2-methylpropanesulfonic acid, itaconic acid, vinylpyrrolidone, vinylimidazole, and allylimidazole; (b) The crosslinking agent includes at least one of ethylene glycol dimethacrylate and N,N'-methylenebisacrylamide; (c) The photoinitiator includes at least one of Irgacure2959, Irgacure500, and Darocur 1173; (d) The foaming agent includes anionic surfactants.

4. The preparation method according to claim 1, characterized in that, Satisfying at least one of the following (e)-(h): (e) The feeding ratio of the needle-like γ-MnOOH, the foaming agent, and the polymerization reaction aqueous solution is (1-3) g: (0.01-0.05) g: 100 mL; (f) The molar ratio of the reactant monomer to the crosslinking agent is (3-7):1; (g) The photoinitiator comprises 3%-5% by mass, based on the sum of the masses of the reactant monomer and the crosslinking agent; (h) The total mass percentage of the monomers and crosslinking agents is 2%-5% based on the mass of the aqueous solution of the polymerization reaction.

5. The preparation method according to claim 1, characterized in that, The stirring speed for foaming is 1800-2200 rpm, and the time is 12-18 min; And / or, the UV curing time is 55-65 min.

6. The preparation method according to claim 1, characterized in that, Satisfying at least one of the following (i)-(l): (i) The oxidizing agent includes any one of hydrogen peroxide, hypochlorous acid and its salts, and potassium permanganate; (j) The concentration of the lithium hydroxide aqueous solution is (0.15-0.2) g / mL; (k) The molar ratio of γ-MnOOH to lithium hydroxide is Li:Mn = 0.7; (l) The molar ratio of the oxidant to lithium hydroxide is 1:

1.

7. The preparation method according to claim 1, characterized in that, In step (3), the ultrasound duration is 55-65 minutes; And / or, the mass ratio of the hierarchical porous LiMn2O4 to the DMF solution of sulfonated polyethersulfone is 1:(48-52). And / or, the pickling is performed by pickling in a hydrochloric acid solution with a mass concentration of (0.2-0.5) mol / L for 22-26 hours.

8. A graded porous lithium-ion sieve, characterized in that, The graded porous lithium-ion sieve is prepared using the preparation method described in any one of claims 1-7.

9. The application of the graded porous lithium-ion sieve as described in claim 8 in lithium extraction from salt lakes.

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