A method for preparing a self-assembled cellulose membrane, the membrane prepared therefrom, and its applications.

Abstract

This application discloses a method for preparing a self-assembled cellulose separator, the resulting membrane, and its applications. A solvent solution containing cellulose and zinc salt is mixed with a solvent solution containing microporous material, followed by ultrasonic disruption to form a film, thus obtaining the self-assembled cellulose separator. The cellulose is selected from cellulose nanofibers and / or cellulose nanofilaments. After the cellulose and microporous material are uniformly dispersed in the solution, no binder needs to be added during the film-forming process to form the film-forming base solution for the self-assembled separator, exhibiting excellent film-forming performance. This composite separator provides effective channels, promoting the transport of zinc ions in the battery. It has lower internal resistance than traditional separators, high electrolyte retention, and a thinner thickness than traditional separators, thereby improving the battery's energy density and cycle performance. The preparation process of this separator is simple, the reaction conditions are mild, and the production cycle is short, making it suitable for large-scale industrial production and commercial applications.

Description

Technical Field

[0001] This application relates to a method for preparing a self-assembled cellulose membrane, the membrane prepared therefrom, and its application, belonging to the field of electrochemistry. Background Technology

[0002] In recent years, the increasing prominence of energy shortages and the scarcity of lithium resources, coupled with the growing problems of poor safety and high price of lithium-ion batteries, has driven the rapid development of non-lithium chemical power sources in large-scale energy storage fields such as electric vehicles and energy storage grids. Compared to lithium-ion batteries, non-lithium chemical power sources have advantages such as high safety, low price, and environmental friendliness, thus attracting much attention in large-scale energy storage equipment and new energy vehicles. The search for non-lithium chemical power sources has become an important research topic for researchers to meet the sustainable development of future energy needs.

[0003] Zinc is a material with excellent electrochemical activity, abundant reserves, and low cost, making it a highly promising candidate for secondary battery energy storage. Zinc-ion batteries, assembled with zinc metal as the negative electrode, possess advantages such as high discharge capacity, good cycle performance, rapid charge / discharge capability, low cost, environmental friendliness, and high safety, showing great potential for development in portable electronic devices and large-scale energy storage. However, during the charge / discharge process of zinc-ion batteries, the repeated uneven deposition and extraction of zinc ions on the zinc electrode surface leads to the formation of dendritic deposits, eventually forming zinc dendrites. These dendrites can pierce the separator, causing direct contact between the positive and negative electrodes and resulting in a short circuit. Therefore, overcoming the growth of zinc dendrites has become one of the most important research topics in zinc-ion batteries. In conclusion, zinc-ion batteries, as a substitute for lithium-ion batteries, have broad application prospects, but further research is needed to address their existing problems.

[0004] The separator is crucial for aqueous zinc-ion batteries, but current research in this area is relatively limited. A qualified aqueous zinc-ion battery separator must possess several excellent properties, such as good hydrophilicity, high porosity, uniform pore size distribution, good mechanical properties, high ionic conductivity, and high zinc ion transference number. Currently, commonly used separator materials include glass fiber and filter paper, but each has its limitations. While glass fiber has good hydrophilicity, its large pore size makes it susceptible to being pierced by zinc dendrites on the negative electrode, leading to short circuits. Its brittleness also limits its application in flexible batteries. Filter paper, on the other hand, has an irregular pore structure and uneven distribution, resulting in varying electrolyte wetting levels and promoting the growth of zinc dendrites. These two types of separators only serve as skeletal support materials, acting as a barrier between the positive and negative electrodes to prevent short circuits. Therefore, additional zinc salts need to be added during battery assembly, which increases costs. Furthermore, the free movement of positive and negative ions in the zinc salt reduces the overall zinc ion transference number of the battery system, thus affecting the electrochemical performance of the zinc-ion battery. Some researchers have attempted to use Nafion membranes to replace traditional separators because they are rich in sulfonic acid groups, which can be replaced with zinc ions and used as single-ion conductors, thereby improving the electrochemical performance of aqueous zinc-ion batteries. However, Nafion membranes are expensive and environmentally unfriendly, making them unsuitable for large-scale applications. Summary of the Invention

[0005] One of the objectives of this invention is to overcome the shortcomings of the prior art and provide a separator for zinc-ion batteries and a method for preparing the separator thereon, which has advantages such as high safety, puncture resistance, high liquid retention capacity and high porosity.

[0006] According to one aspect of this application, a method for preparing a self-assembled cellulose membrane is provided, comprising mixing a solvent solution containing cellulose and zinc salt with a solvent solution containing microporous material, ultrasonically breaking down the mixture, and forming a film to obtain the self-assembled cellulose membrane;

[0007] The cellulose is selected from cellulose nanofibers and / or cellulose nanofilaments;

[0008] The film formation is selected from one of the following methods: vacuum filtration, phase inversion, calendering, and casting.

[0009] The cellulose can be modified;

[0010] The modified cellulose contains at least one of COOH, COONa, SO3H, SO3Na, and quaternary ammonium cations.

[0011] The zinc salt is selected from at least one of zinc sulfate, zinc trifluoromethanesulfonate, zinc chloride, zinc perchlorate, zinc nitrate, zinc tetrafluoroborate, and zinc acetate.

[0012] In the solvent solution containing cellulose and zinc salt, the content of cellulose is 0.5 mg / ml;

[0013] In the solvent solution containing cellulose and zinc salt, the content of zinc salt is 0.01 to 10 M.

[0014] The solvent is selected from at least one of deionized water, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), methanol, ethanol, and acetone.

[0015] The microporous material is selected from at least one of UiO-66, UiO-66-COOH, UiO-66-NO2, UiO-66-NH2, NaX zeolite, ZSM-5 zeolite, ZSM-11 zeolite, ZiF-7, ZiF-8, and Mil-88.

[0016] In the solvent solution containing the microporous material, the mass ratio of the microporous material to the cellulose in the solvent solution containing cellulose and zinc salt is 0.01 to 1:1.

[0017] Specifically,

[0018] (1) 100 mg of modified / unmodified cellulose nanofibers were dispersed in 200 ml of a solvent containing zinc salt and then ultrasonically crushed to obtain a uniform dispersion.

[0019] (2) The microporous material used is manually ground or ball-milled to obtain a fine powder, which is then added to the homogeneous dispersion obtained in step 1) above. The mixture is stirred while being added to obtain a dispersion of cellulose nanofiber / microporous material composite.

[0020] (3) The dispersion of cellulose / microporous material composite was ultrasonically crushed at a certain temperature to obtain a uniform cellulose nanofiber / microporous material dispersion; the ultrasonic crushing temperature was 20-50℃ and the crushing time was 10-60 minutes.

[0021] (4) Film formation is then performed to obtain a separator for zinc-ion batteries.

[0022] According to another aspect of this application, a self-assembled cellulose membrane is provided, which is prepared by the above-described preparation method.

[0023] According to another aspect of this application, an application of the above-described self-assembled cellulose membrane is provided for use in an aqueous zinc-ion battery.

[0024] The advantages of this application are:

[0025] After the cellulose and microporous material are uniformly dispersed in the solution, no binder needs to be added during the film-forming process to form a self-assembling membrane base solution with excellent film-forming effect. This composite membrane provides effective channels to promote the transport of zinc ions in the battery, has lower internal resistance than traditional membranes, high electrolyte retention rate, and a thinner thickness than traditional membranes, thus improving the battery's energy density and cycle performance. The preparation process of this membrane is simple, the reaction conditions are mild, and the production cycle is short, making it suitable for large-scale industrial production and commercial applications. Attached Figure Description

[0026] Figure 1 Cycle count curve of the separator prepared in Example 1 applied to a coin cell Zn||Zn half-cell.

[0027] Figure 2 The cycle life curve of the glass fiber separator used in Comparative Example 1 applied to a button-type Zn||Zn half-cell. Detailed Implementation

[0028] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0029] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0030] Example 1:

[0031] 100 mg of neutral cellulose nanofibers were dissolved in an aqueous solution containing 200 ml of 2 M ZnSO4 zinc salt, and the solution was ultrasonically broken down to obtain a homogeneous dispersion.

[0032] 1 mg of UiO-66-COOH material was manually ground to obtain a fine powder, which was then added to a homogeneous dispersion while stirring to obtain a dispersion of aramid cellulose nanofibers / UiO-66-COOH composite.

[0033] The dispersion of neutral cellulose nanofibers / UiO-66-COOH composite was ultrasonically broken at 50 degrees Celsius for 30 min to obtain a uniform dispersion of neutral cellulose nanofibers / microporous materials.

[0034] The resulting dispersion was vacuum filtered to obtain a neutral cellulose nanofiber / UiO-66-COOH multidimensional self-assembled membrane.

[0035] Symmetrical cells were assembled using the multi-dimensional self-assembly separator of Example 1, with a 1 mA cm 2 The current density cycling performance is shown in the attached figure. Figure 1 As shown.

[0036] Example 2:

[0037] 100 mg of carboxylated cellulose nanofibers were dissolved in an aqueous solution containing 200 ml of 2 M Zn(OTF)2 zinc salt, and the solution was ultrasonically broken down to obtain a homogeneous dispersion.

[0038] 100 mg of NaX zeolite material was manually ground for 30 minutes to obtain a fine powder, which was then added to a homogeneous dispersion while stirring to obtain a dispersion of carboxylated cellulose nanofibers / NaX zeolite composite.

[0039] The dispersion of cellulose / NaX zeolite composite was ultrasonically broken at 25 degrees Celsius for 30 min to obtain a homogeneous cellulose / NaX zeolite dispersion.

[0040] The obtained material was vacuum filtered to obtain a carboxylated cellulose nanofiber / NaX zeolite multidimensional self-assembled membrane.

[0041] Example 3:

[0042] 100 mg of sulfonated cellulose nanofibers were dissolved in a DMAc solution containing 200 ml of 3 M Zn(OTF)2 zinc salt, and the solution was ultrasonically broken down to obtain a uniform dispersion.

[0043] 100 mg of ZiF-8 material was manually ground for 30 minutes to obtain a fine powder, which was then added to a uniform dispersion while stirring to obtain a dispersion of sulfonated cellulose nanofibers / ZiF-8 zeolite composite.

[0044] The dispersion of sulfonated cellulose / ZiF-8 composite was ultrasonically broken at 40 degrees Celsius for 30 min to obtain a uniform sulfonated cellulose nanofiber / ZiF-8 dispersion.

[0045] The obtained dispersion was adjusted to a thickness of 100 μm using a doctor blade and then uniformly coated onto a glass plate. After drying, a sulfonated cellulose / ZiF-8 multidimensional self-assembled membrane was obtained.

[0046] Comparative Example 1:

[0047] Symmetrical cells are assembled using commercially available glass fiber separators, with a 1 mA cm⁻¹. 2 The current density cycling performance is shown in the attached figure. Figure 2 As shown.

[0048] As shown in the figure, the multi-dimensional self-assembled separator prepared in Example 1, when used as a separator for an aqueous zinc-ion battery, significantly improves the cycle performance of the symmetrical battery, enabling it to operate stably for over 1100 hours. In contrast, the commercially available glass fiber separator used in Comparative Example 1 fails after only 300 hours of battery operation. This demonstrates that the multi-layer separator for zinc-ion batteries prepared in this invention gives the zinc-ion battery superior electrochemical performance.

[0049] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing a self-assembled cellulose separator for aqueous zinc-ion batteries, characterized in that, A solvent solution containing cellulose and zinc salts is mixed with a solvent solution containing microporous material, and the mixture is ultrasonically broken up to form a film, thereby obtaining the self-assembled cellulose membrane. The cellulose is selected from cellulose nanofibers and / or cellulose nanofilaments; The film formation method is selected from one of vacuum filtration, phase inversion, calendering, and casting. The microporous material is selected from at least one of UiO-66, UiO-66-COOH, UiO-66-NO2, UiO-66-NH2, NaX zeolite, ZSM-5 zeolite, ZSM-11 zeolite, ZiF-7, ZiF-8, and Mil-88.

2. The preparation method according to claim 1, characterized in that, The cellulose has been modified; The modified cellulose contains at least one of the following: -COOH, -COONa, -SO3H, -SO3Na, and quaternary ammonium cations.

3. The preparation method according to claim 1, characterized in that, The zinc salt is selected from at least one of zinc sulfate, zinc trifluoromethanesulfonate, zinc chloride, zinc perchlorate, zinc nitrate, zinc tetrafluoroborate, and zinc acetate.

4. The preparation method according to claim 1, characterized in that, In the solvent solution containing cellulose and zinc salt, the content of cellulose is 0.5 mg / ml; In the solvent solution containing cellulose and zinc salt, the content of zinc salt is 0.01~10M.

5. The preparation method according to claim 1, characterized in that, The solvent is selected from at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide, methanol, ethanol, and acetone.

6. The preparation method according to claim 1, characterized in that, In the solvent solution containing the microporous material, the mass ratio of the microporous material to the cellulose in the solvent solution containing cellulose and zinc salt is 0.01~1:

1.

7. A self-assembled cellulose membrane, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. An application of the self-assembled cellulose membrane according to claim 7, characterized in that, Used in aqueous zinc-ion batteries.

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