A functional grafted ultra-thin nanocellulose separator and a preparation method and application thereof

Abstract

This invention discloses a functionally grafted ultrathin nanocellulose membrane, its preparation method, and its applications. The preparation method includes: uniformly dispersing cellulose nanofibers or oxidized cellulose nanofibers in water to obtain a cellulose aqueous suspension; uniformly dispersing or dissolving functional molecules in the cellulose aqueous suspension to obtain a mixture; subjecting the mixture to a chemical grafting reaction under heating, hydrothermal, or room temperature conditions to obtain a dispersion of surface-functionalized cellulose nanofibers; forming a wet film on a corresponding film-forming substrate using a film-forming process; drying at room temperature; and then peeling off the substrate. This invention utilizes the multiple synergistic effects of the grafted molecules to effectively regulate zinc ion transport, homogenize the deposition interface, and suppress side reactions, thereby significantly inhibiting zinc dendrite growth and improving the cycle life and safety of aqueous zinc-based energy storage systems. This method is simple, operates under mild conditions, and has good prospects for large-scale application.

Description

Technical Field

[0001] This invention belongs to the field of new energy battery materials technology, specifically relating to a functional grafted ultrathin nanocellulose separator, its preparation method and application. Background Technology

[0002] With the rapid development of portable electronic devices and electric vehicles, the demand for energy storage systems with high energy density and high safety is increasing. Aqueous zinc-ion batteries have attracted much attention due to their high theoretical specific capacity, low cost, and intrinsic safety. However, in practical applications, one of the main problems faced by aqueous zinc-based energy storage systems is zinc dendrite growth. The uneven nucleation and growth of zinc ions during deposition easily leads to the formation of zinc dendrites. Continuous dendrite growth can easily puncture the separator, causing short circuits and severely limiting the battery's cycle life and safety. Traditional polyolefin separators suffer from poor electrolyte wettability, low thermal stability, and a lack of control over metal ion deposition. Cellulose nanofibers possess high Young's modulus, excellent thermal stability, and abundant hydrophilic groups, making them ideal separator substrates. However, unmodified nanocellulose has limited ability to control ions. Current modification methods are mostly limited to physical coating, and the coating layer is prone to peeling or swelling during electrolyte immersion. Summary of the Invention

[0003] To address the shortcomings of existing aqueous zinc-based energy storage systems, such as large membrane material thickness, unstable functional layer structure, and limited ion regulation mechanism, the primary objective of this invention is to provide a method for preparing a functionally grafted ultrathin nanocellulose membrane.

[0004] This invention selects TEMPO oxidized cellulose nanofibers rich in carboxyl groups or cellulose nanofibers rich in hydroxyl groups as the membrane matrix material, and selectively introduces specific functional molecules or structural units to construct a functionalized membrane with ion regulation capability and excellent interfacial stability, thereby effectively inhibiting zinc dendrite growth and improving the cycle stability of zinc metal anode.

[0005] Another object of the present invention is to provide a functional grafted ultrathin nanocellulose membrane.

[0006] Another objective of this invention is to provide an application of the above-mentioned functional grafted ultrathin nanocellulose membrane, specifically for aqueous zinc-based energy storage systems.

[0007] The objective of this invention is achieved through the following solution:

[0008] A method for preparing a functional grafted ultrathin nanofiber cellulose membrane includes the following steps:

[0009] (1) Disperse cellulose nanofibers or oxidized cellulose nanofibers uniformly in water to obtain an aqueous cellulose suspension;

[0010] (2) Disperse or dissolve the functional molecules uniformly in an aqueous cellulose suspension to obtain a mixture;

[0011] (3) The mixture obtained in step (2) is subjected to chemical grafting reaction under heating, hydrothermal or room temperature conditions to obtain a dispersion of surface functionalized modified cellulose nanofibers; the dispersion is used to form a wet film on the corresponding film-forming substrate through a film-forming process, and after drying at room temperature, the substrate is peeled off to obtain a functionally grafted ultrathin nanocellulose membrane.

[0012] Preferably, the cellulose nanofibers in step (1) are rich in hydroxyl functional groups on their surface; the oxidized cellulose nanofibers are rich in carboxyl functional groups on their surface; the diameter of both the cellulose nanofibers and the oxidized cellulose nanofibers is 1-50 nm and the length is 0.5-30 µm.

[0013] Preferably, the concentration of the aqueous cellulose suspension in step (1) is 0.1-10 mg / mL, more preferably 0.5-1 mg / mL, so that the cellulose nanofibers can be fully dispersed.

[0014] Preferably, the functional molecules described in step (2) include, but are not limited to, at least one of the following: thionicotinamide, 4-fluoroaniline, L-arginine, 5-aminoisophthalic acid, p-aminobenzoic acid, polyethyleneimine, ε-polylysine hydrochloride, diethylenetriamine, triethylenetetramine, 2-aminoterephthalic acid, tetraethylenepentamine, gallic acid, citric acid-β-cyclodextrin, L-lysine, tannic acid, N-hydroxymethylacrylamide, pyridoxine, L-histidine, and polyethylene glycolamine.

[0015] Preferably, in step (2), the feeding ratio of functional molecules to cellulose nanofibers rich in hydroxyl groups or oxidized nanocellulose rich in carboxyl groups is controlled within the range of 1:1 to 10:1, where the molar ratio of the active groups (such as amino, phenolic hydroxyl groups, etc.) contained in the functional molecules to the carboxyl groups on the surface of oxidized nanocellulose or the hydroxyl groups on the surface of cellulose nanofibers is controlled within the range of 1:1 to 10:1.

[0016] Preferably, in step (3), the chemical grafting reaction includes, but is not limited to, hydrothermal methods, water bath heating methods, or room temperature reaction methods, that is, the chemical grafting reaction can be carried out under water bath heating, hydrothermal reactor heating, or room temperature conditions. Preferably, it is carried out by hydrothermal methods or water bath heating methods, specifically by hydrothermal reaction at 60-150 °C for 2-48 hours.

[0017] Preferably, the amounts of the cellulose aqueous suspension in step (1) and the dispersion obtained after the chemical grafting reaction in step (3) satisfy the following: the loading of the cellulose nanofibers is 0.5-10 mg / cm³. 2 Preferably 1-6 mg / cm 2The loading of the functional molecules is 0.1-9 mg / cm³. 2 Preferably 0.3-5 mg / cm 2 Loading capacity refers to the amount of material loaded relative to the filter membrane substrate; for example, a cellulose loading capacity of 1 mg / cm³. 2 The diaphragm was used to filter 12.56 mg of cellulose to a loading area of ​​12.56 cm². 2 On the filter membrane.

[0018] Preferably, in step (3), when the functional molecule contains a primary amino molecule, the pH value of the mixture obtained in step (2) is adjusted to 7.5-8.5 before the chemical grafting reaction is carried out; when the functional molecule contains a phenolic hydroxyl molecule, the pH value of the mixture obtained in step (2) is adjusted to 4-5 before the chemical grafting reaction is carried out.

[0019] Preferably, in step (3), the film-forming process includes, but is not limited to, filtration, casting, or coating.

[0020] Preferably, the film-forming substrate in step (3) is a mixed cellulose aqueous filter membrane (suitable for functional molecules using water as a solvent) or a nylon filter membrane (suitable for functional molecules using organic solvents or water or a mixture of both as solvents). The pore size of the film-forming substrate is preferably 0.01-2 µm.

[0021] A functional grafted ultrathin nanocellulose membrane prepared by the above method, wherein the thickness of the functional grafted ultrathin nanocellulose membrane is 3-50 µm, preferably 5-30 µm.

[0022] This invention discloses a functionally grafted ultrathin nanocellulose diaphragm, which uses cellulose nanofibers or oxidized nanocellulose containing functional groups as the diaphragm matrix. It features ultrathinness, puncture resistance, high liquid retention, and high porosity. The cellulose diaphragm is functionally grafted by introducing functional molecules (including but not limited to thionicotinamide, 4-fluoroaniline, L-arginine, 5-aminoisophthalic acid, p-aminobenzoic acid, polyethyleneimine, ε-polylysine hydrochloride, diethylenetriamine, triethylenetetramine, 2-aminoterephthalic acid, tetraethylenepentamine, gallic acid, citric acid-β-cyclodextrin, L-lysine, tannic acid, N-hydroxymethylacrylamide, pyridoxine, L-histidine, and polyethylene glycolamine).

[0023] A water-based zinc-based energy storage system, comprising the aforementioned functionally grafted ultrathin nanocellulose membrane.

[0024] The mechanism of this invention is as follows:

[0025] This invention employs a stable chemical bonding (grafting) design to endow nanocellulose with specific "ion-regulating functional groups" at the molecular level. This allows for the regulation of ion flux, stabilization of interfacial chemistry, and effective suppression of side reactions, while ensuring both high mechanical strength and ultrathin thickness of the membrane. The functions of the selected functional molecules in this invention are as follows:

[0026] (1) By grafting functional molecules such as thionicotinamide, 4-fluoroaniline, L-asparagine, and pyridoxine onto the membrane, it is made capable of in-situ modification of the zinc anode interface, forming a dense and dynamically renewed adsorption layer, which effectively blocks the direct contact between free water molecules in the electrolyte and zinc metal, thereby significantly inhibiting side reactions such as hydrogen evolution reaction and electrode corrosion.

[0027] (2) Linear polyelectrolytes such as polyethyleneimine and ε-polylysine hydrochloride, as well as molecules such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and p-phenylenediamine that can construct multiple charge sites are used as electrostatic regulators to construct a stable charge functional layer on and inside the membrane surface. The electrostatic field generated by the fixed charge (positive or negative) carried by it can guide and homogenize zinc ions at the interface and regulate the electric field distribution on the electrode surface.

[0028] (3) Citric acid-β-cyclodextrin, gallic acid, tannic acid, catechin, L-histidine, 5-aminoisophthalic acid, 2-aminoterephthalic acid, N-hydroxymethylacrylamide, etc. are used as ion coordination directing agents. These molecules are rich in carboxyl, amino, phenolic hydroxyl groups or have specific cavity structures, which can introduce uniformly distributed functional coordination sites in the membrane, specifically and reversibly coordinate zinc ions, effectively reduce their desolvation energy barrier and nucleation overpotential, guide zinc ions to preferentially nucleate uniformly at many sites, and achieve a dense and flat zinc deposition layer;

[0029] (4) Using L-arginine, polyethylene glycolamine, L-lysine and other hydrophilic modifiers, the amino or carboxyl groups at their ends are grafted onto the cellulose skeleton, introducing strong hydrophilic segments or groups on the membrane surface, which greatly enhances the wettability and liquid retention capacity of the membrane to aqueous electrolyte.

[0030] From a practical application perspective, this invention designs and prepares a functionally grafted ultrathin nanocellulose membrane for use in aqueous zinc-based energy storage systems, thereby improving the specific energy of these systems and reducing their production costs. By introducing functional molecules from the cellulose membrane and directly grafting these functional molecules with cellulose through chemical reactions, the electric / ionic field and nucleation barrier of zinc ions during the charging and discharging process can be controlled. Ultimately, this achieves the goal of uniformly depositing zinc ions onto the zinc metal surface, inhibiting zinc dendrite growth, and improving the cycle life of the system.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] (1) High stability of functional layer: Unlike physical blending or coating processes, this invention adopts a chemical grafting strategy, which enables functional molecules to be firmly bonded to the cellulose skeleton through covalent bonds. During long-term cycling, no dissolution or migration occurs, ensuring the durability and stability of the functional interface.

[0033] (2) Structural synergistic optimization: Through controlled preparation process and cross-linking design, while achieving ultrathin membrane, excellent mechanical strength and ionic conductivity are also taken into account, giving it good physical barrier and efficient ion transport capability.

[0034] (3) Synergistic effect of multiple mechanisms: The above advantages do not exist in isolation, but are organically combined through chemical grafting, and ultimately show significant synergistic enhancement in inhibiting dendrite growth, stabilizing electrode interface and improving cycle life.

[0035] (4) Simple preparation and excellent comprehensive performance: Compared with the complex modification processes reported, the grafting and film formation method based on the nanocellulose aqueous dispersion system of this invention is simple, mild, and has low raw material cost. The prepared diaphragm integrates ultrathin structure, high mechanical strength, high ionic conductivity and multiple interface regulation functions, which significantly improves the cycle stability of zinc anode and has good potential for large-scale production and practical application. Attached Figure Description

[0036] Figure 1 This is a cross-sectional view of the thickness of the thionicotinamide-functionalized grafted ultrathin cellulose membrane prepared in Example 1;

[0037] Figure 2 The image shows the surface morphology of the thionicotinamide-functionalized ultrathin cellulose membrane prepared in Example 1.

[0038] Figure 3 In Example 1, at a current density of 2 mA / cm² 2 The cutoff capacity is 1 mAh / cm³. 2 Constant current charge-discharge curves of zinc-zinc symmetric batteries using thionicotinamide functionally grafted ultrathin cellulose separators.

[0039] Figure 4 In Example 1, the current density was 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 Constant current charge-discharge curves of zinc-zinc symmetric batteries using thionicotinamide functionally grafted ultrathin cellulose separators.

[0040] Figure 5 Cross-sectional view of the thickness of the citric acid-β-cyclodextrin-MOF functional grafted ultrathin cellulose membrane prepared in Example 2;

[0041] Figure 6 Surface morphology of the citric acid-β-cyclodextrin-MOF functional grafted ultrathin cellulose membrane prepared in Example 2;

[0042] Figure 7 In Example 2, the current density was 1 mA / cm². 2 The cutoff capacity is 0.5 mAh / cm³. 2 The constant current charge-discharge curves of zinc-zinc symmetric batteries using citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose separators are shown.

[0043] Figure 8 In Example 2, the current density was 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 The constant current charge-discharge curves of zinc-zinc symmetric batteries using citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose separators are shown.

[0044] Figure 9 In Example 3, the current density was 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 Constant current charge-discharge curves of zinc-zinc symmetric batteries using L-arginine functionally grafted ultrathin cellulose membranes.

[0045] Figure 10 In Example 4, the current density was 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 The constant current charge-discharge curves of a zinc-zinc symmetric battery using an ε-polylysine hydrochloride functionally grafted ultrathin cellulose membrane are shown.

[0046] Figure 11 In Example 5, the current density was 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 Constant current charge-discharge curves of zinc-zinc symmetric batteries using tannic acid-functionalized grafted ultrathin cellulose membranes.

[0047] Figure 12 For Comparative Example 1, at a current density of 1 mA / cm 2 The cutoff capacity is 0.5 mAh / cm³. 2 Constant current charge-discharge curves of zinc-zinc symmetric batteries using nonwoven fabric diaphragms;

[0048] Figure 13 For Comparative Example 2, at a current density of 1 mA / cm² 2 The cutoff capacity is 0.5 mAh / cm³. 2The constant current charge-discharge curves of zinc-zinc symmetric batteries using commercial glass fiber diaphragms were obtained.

[0049] Figure 14 For Comparative Example 2, the current density is 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 The constant current charge-discharge curves of zinc-zinc symmetric batteries using commercial glass fiber diaphragms were obtained.

[0050] Figure 15 This is a cross-sectional view of the thickness of the ultrathin cellulose nanofiber membrane prepared in Comparative Example 3;

[0051] Figure 16 The image shows the surface morphology of the ultrathin cellulose nanofiber membrane prepared in Comparative Example 3.

[0052] Figure 17 For Comparative Example 4, the current density is 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 At that time, the loading rates were 1, 3, and 9 mg / cm³. 2 Constant current charge-discharge curves of zinc-zinc symmetric batteries with ultrathin cellulose nanofiber separators;

[0053] Figure 18 In Comparative Example 4, the current density is 5 mA / cm². 2 The cutoff capacity is 2.5 mAh / cm³. 2 The constant current charge-discharge curves of a zinc-zinc symmetric battery using an ultrathin TEMPO oxidized nanocellulose membrane are shown. Detailed Implementation

[0054] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0055] Example 1

[0056] Preparation of thionicotinamide-functionalized grafted ultrathin cellulose membranes

[0057] (1) 37.7 mg of commercial carboxycellulose nanofibers (model TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 10.4 mg of thionicotinamide was added to achieve a molar ratio of amino to carboxyl groups of 2:1, and the dispersion was sonicated again to ensure uniform dispersion. The mixture was subjected to a hydrothermal reaction at 120 °C for 8 hours to induce amidation condensation grafting. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 The thionicotinamide-functionalized grafted ultrathin cellulose membrane has a thickness of approximately 19 μm, and the thickness cross-sectional diagram is shown below. Figure 1 As shown. Figure 2 The loading capacity is 3 mg / cm³ 2 The surface morphology of the thionicotinamide-functionalized grafted ultrathin cellulose membrane is shown in the figure. As can be seen from the figure, the thionicotinamide-functionalized grafted ultrathin cellulose membrane exhibits a very dense morphology.

[0058] (2) Zinc sheets were grafted with a thionicotinamide-functionalized ultrathin cellulose membrane and assembled into a zinc-zinc symmetrical battery using a CR2032 coin cell casing. Electrochemical performance was then tested to investigate the inhibitory effect of the thionicotinamide-grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled battery was allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the thionicotinamide-grafted ultrathin cellulose membrane before electrochemical performance testing.

[0059] (3) At a current density of 2 mA / cm 2 The cutoff capacity is 1 mAh / cm³. 2 Constant current charge-discharge tests were performed under the specified test conditions, and the charge-discharge curves are as follows: Figure 3 As shown; at a current density of 5 mA / cm² 2 Cut-off capacity 2.5 mAh / cm³ 2 Constant current charge-discharge tests were performed under the specified test conditions, and the charge-discharge curves are as follows: Figure 4 As shown in the figure. Tests indicate that the zinc-zinc symmetric battery using a thionicotinamide-grafted ultrathin cellulose membrane did not exhibit short-circuit behavior after 1200 h of charge-discharge behavior at relatively low current density and cutoff capacity, while maintaining relatively high current density and cutoff capacity (5 mA / cm²). 2 Current density, 2.5 mAh / cm 2Even at its cutoff capacity, it could still undergo 700 hours of normal charge-discharge without exhibiting a short circuit. Compared to the unfunctionalized cellulose membrane (Example 2), the thionicotinamide-grafted membrane showed superior cycling stability, indicating that it can effectively induce uniform zinc ion deposition and inhibit dendrite growth.

[0060] Example 2

[0061] Preparation of Citric Acid-β-Cyclodextrin-MOF Functionally Grafted Ultrathin Cellulose Membranes

[0062] (1) 37.7 mg of commercial cellulose nanofibers (CNF-H2) were weighed and dispersed in deionized water to prepare a cellulose nanofiber dispersion, which was then uniformly dispersed by ultrasonication. The hydrothermally synthesized citric acid-β-cyclodextrin-MOF material was then filtered onto a cellulose nanofiber membrane using vacuum filtration. After drying at room temperature, the filter membrane substrate was peeled off, yielding a cellulose nanofiber loading of 3 mg / cm³. 2 The ultrathin cellulose membrane, in which the citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose membrane has a thickness of approximately 24 μm, is shown in the thickness cross-sectional diagram below. Figure 5 As shown. Figure 6 The loading capacity is 3 mg / cm³ 2 The surface morphology of the citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose membrane is shown in the figure. As can be seen from the figure, the citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose membrane is composed of cellulose nanofibers wound together, and exhibits a relatively dense morphology with a few nanopores.

[0063] (2) Zinc sheets were assembled into zinc-zinc symmetrical cells using a CR2032 coin cell casing with a citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose membrane. Electrochemical performance was then tested to investigate the inhibitory effect of the citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose membrane before electrochemical performance testing.

[0064] (3) at 1 mA / cm 2 Current density, 0.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 7 As shown. A loading of 3 mg / cm³ was used. 2The zinc-zinc symmetric battery with a citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose separator can perform normal charge-discharge behavior for 2000 h; while the zinc-zinc symmetric battery in Example 2, assembled with a common commercial glass fiber separator, can only complete normal charge-discharge behavior for 36 h before a short circuit occurs.

[0065] (4) at 5 mA / cm 2 Current density, 2.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 8 As shown, the zinc-zinc symmetric battery using a citric acid-β-cyclodextrin-MOF functionally grafted ultrathin cellulose separator did not exhibit short circuit after 680 h of charge-discharge behavior.

[0066] Example 3

[0067] Preparation of L-arginine-functionalized grafted ultrathin cellulose membranes

[0068] (1) 37.7 mg of commercial carboxycellulose nanofibers (model TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 19.7 mg of L-arginine was added to achieve a molar ratio of amino to carboxyl groups of 2:1, and the dispersion was sonicated again to ensure uniform dispersion. The mixture was subjected to hydrothermal reaction at 100 °C for 8 hours to induce amidation condensation grafting reaction. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 L-arginine functional grafted ultrathin cellulose membrane.

[0069] (2) Zinc sheets and L-arginine-functionalized grafted ultrathin cellulose membranes were assembled into zinc-zinc symmetrical cells using a CR2032 coin cell casing for electrochemical performance testing to investigate the inhibitory effect of the ε-polylysine hydrochloride-functionalized grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the L-arginine-functionalized grafted ultrathin cellulose membrane before electrochemical performance testing.

[0070] (3) At 5 mA / cm 2 Current density, 2.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 9 As shown, the zinc-zinc symmetric battery using an L-arginine-functionalized grafted ultrathin cellulose separator did not exhibit a short circuit after 480 h of charge-discharge behavior.

[0071] Example 4

[0072] Preparation of ε-polylysine hydrochloride functionalized grafted ultrathin cellulose membrane

[0073] (1) 37.7 mg of commercial carboxycellulose nanofibers (model TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 8.87 mg of ε-polylysine hydrochloride was added to achieve a molar ratio of amino to carboxyl groups of 2:1, and the dispersion was sonicated again to ensure uniform dispersion. The mixture was subjected to hydrothermal reaction at 100 °C for 8 hours to induce amidation condensation grafting reaction. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 ε-polylysine hydrochloride functional grafted ultrathin cellulose membrane.

[0074] (2) Zinc sheets were assembled with ε-polylysine hydrochloride-functionalized grafted ultrathin cellulose membranes using CR2032 coin cell casings to form zinc-zinc symmetrical cells for electrochemical performance testing, in order to investigate the inhibitory effect of the ε-polylysine hydrochloride-functionalized grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the ε-polylysine hydrochloride-functionalized grafted ultrathin cellulose membrane before electrochemical performance testing.

[0075] (3) At 5 mA / cm 2 Current density, 2.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 10 As shown, the zinc-zinc symmetric battery using an ε-polylysine hydrochloride functionally grafted ultrathin cellulose separator did not exhibit a short circuit after 520 h of charge-discharge behavior.

[0076] Example 5

[0077] Preparation of tannic acid-functionalized grafted ultrathin cellulose membranes

[0078] (1) 37.7 mg of commercial carboxycellulose nanofibers (TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 64.1 mg of tannic acid was added to make the molar ratio of tannic acid molecules to TOCNF carboxyl groups 1:1. The dispersion was then sonicated again to ensure uniform dispersion, and the pH of the mixture was adjusted to 4-5. The mixture was subjected to hydrothermal reaction at 120 °C for 6 hours, during which esterification and hydrogen bonding reactions mainly occurred. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 Tannic acid functional grafted ultrathin cellulose membrane.

[0079] (2) Zinc sheets and tannic acid-functionalized grafted ultrathin cellulose membranes were assembled into zinc-zinc symmetrical cells using a CR2032 coin cell casing for electrochemical performance testing to investigate the inhibitory effect of the tannic acid-functionalized grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the tannic acid-functionalized grafted ultrathin cellulose membrane before electrochemical performance testing.

[0080] (3) At 5 mA / cm 2 Current density, 2.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 11 As shown, the zinc-zinc symmetric battery using a tannic acid-grafted ultrathin cellulose separator did not exhibit a short circuit after 505 hours of charge-discharge behavior.

[0081] Example 6

[0082] Preparation of polyethyleneimine-functionalized grafted ultrathin cellulose membranes

[0083] (1) 37.7 mg of commercial carboxycellulose nanofibers (model TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 3.3 mg of polyethyleneimine was added to make the molar ratio of amino to carboxyl groups 2:1, and the dispersion was sonicated again to ensure uniform dispersion. The mixture was reacted in a water bath at 100 °C for 6 hours to induce amidation condensation grafting reaction. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 Polyethyleneimine functional grafted ultrathin cellulose diaphragm.

[0084] (2) Zinc sheets and polyethyleneimine-functionalized grafted ultrathin cellulose membranes were assembled into zinc-zinc symmetrical cells using CR2032 coin cell casings for electrochemical performance testing to investigate the inhibitory effect of the polyethyleneimine-functionalized grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the polyethyleneimine-functionalized grafted ultrathin cellulose membrane before electrochemical performance testing.

[0085] Example 7

[0086] Preparation of 4-fluoroaniline functionalized grafted ultrathin cellulose membrane

[0087] (1) 37.7 mg of commercial carboxycellulose nanofibers (model TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 8.4 mg of 4-fluoroaniline was added to achieve a molar ratio of amino to carboxyl groups of 2:1, and the dispersion was sonicated again to ensure uniform dispersion. The mixture was subjected to a hydrothermal reaction at 100 °C for 10 hours to induce amidation condensation grafting. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 4-Fluoroaniline functionalized grafted ultrathin cellulose diaphragm.

[0088] (2) Zinc sheets were grafted with 4-fluoroaniline-grafted ultrathin nanocellulose membranes and assembled into zinc-zinc symmetric cells using CR2032 coin cell casings. Electrochemical performance was then tested to investigate the inhibitory effect of the 4-fluoroaniline-grafted ultrathin nanocellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the 4-fluoroaniline-grafted ultrathin nanocellulose membrane before electrochemical performance testing.

[0089] Example 8

[0090] Preparation of L-lysine-functionalized grafted ultrathin cellulose membranes

[0091] (1) 37.7 mg of commercial carboxycellulose nanofibers (model TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 6 mg of L-lysine was added to achieve a molar ratio of amino to carboxyl groups of 2:1. The dispersion was then sonicated again to ensure uniform dispersion. The pH of the mixture was adjusted to 7.5-8.5, and the mixture was subjected to a hydrothermal reaction at 100 °C for 8 hours to induce amidation condensation grafting. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 L-lysine functional grafted ultrathin cellulose membrane.

[0092] (2) Zinc sheets and L-lysine-functionalized grafted ultrathin cellulose membranes were assembled into zinc-zinc symmetrical cells using a CR2032 coin cell casing for electrochemical performance testing to investigate the inhibitory effect of the L-lysine-functionalized grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the L-lysine-functionalized grafted ultrathin cellulose membrane before electrochemical performance testing.

[0093] Example 9

[0094] Preparation of gallic acid-functionalized ultrathin cellulose membranes

[0095] (1) 37.7 mg of commercial carboxycellulose nanofibers (model TOCNF) were dispersed in deionized water to prepare a dispersion with a concentration of 0.5 mg / mL. The dispersion was then sonicated to ensure uniform dispersion. Subsequently, 7.0 mg of gallic acid was added to make the molar ratio of gallic acid molecules to TOCNF carboxyl groups 1:1. The dispersion was then sonicated again to ensure uniform dispersion. The pH of the mixture was adjusted to 4-5, and the mixture was subjected to hydrothermal reaction at 100 °C for 10 hours to induce esterification. After the reaction, the resulting dispersion was vacuum filtered onto a nylon filter membrane (pore size 0.2 μm), dried at room temperature, and the filter membrane substrate was peeled off to obtain a cellulose loading of 3 mg / cm³. 2 Gallic acid functional grafted ultrathin cellulose septum.

[0096] (2) Zinc sheets and gallic acid-functionalized grafted ultrathin cellulose membranes were assembled into zinc-zinc symmetrical cells using CR2032 coin cell casings for electrochemical performance testing to investigate the inhibitory effect of the gallic acid-functionalized grafted ultrathin cellulose membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 hours to allow the electrolyte to fully wet the gallic acid-functionalized grafted ultrathin cellulose membrane before electrochemical performance testing.

[0097] Comparative Example 1

[0098] (1) Zinc sheets with a diameter of 10 mm, punched by a punching machine, and non-woven fabric membranes with a diameter of 16 mm (thickness of 200 μm and pore size of 10-200 μm) were assembled into zinc-zinc symmetric cells using a CR2032 coin cell casing for electrochemical performance testing. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were left to stand at room temperature for 6 hours to allow the electrolyte to fully wet the non-woven fabric membrane before electrochemical performance testing.

[0099] (2) at 1 mA / cm 2 Current density, 0.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 12 As shown, the zinc-zinc symmetric battery using non-woven fabric as the separator exhibited a short circuit after 7 hours of charge-discharge behavior.

[0100] Comparative Example 2

[0101] (1) Zinc sheets with a diameter of 10 mm, punched by a stamping machine, and glass fiber membranes with a diameter of 16 mm (whatmanGF / A, thickness of 260 μm, pore size of approximately 1-100 μm) were assembled into zinc-zinc symmetric cells using a CR2032 coin cell casing for electrochemical performance testing. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were left to stand at room temperature for 6 hours to allow the electrolyte to fully impregnate the commercial glass fiber membrane before electrochemical performance testing.

[0102] (2) at 1 mA / cm 2 Current density, 0.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 13 As shown, it can only complete 36 hours of normal charge and discharge behavior before a short circuit occurs.

[0103] (3) At 5 mA / cm 2 Current density, 2.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 14 As shown, it can only complete 40 hours of normal charge and discharge behavior before a short circuit occurs.

[0104] Comparative Example 3

[0105] Preparation of ultrathin cellulose nanofiber membranes

[0106] (1) Commercial cellulose nanofibers (CNF-H2) with mass values ​​of 12.6, 37.7, and 113.1 mg were dispersed in deionized water to prepare cellulose nanofiber dispersions with a concentration of 0.5 mg / mL. The dispersions were then uniformly dispersed by ultrasonication. The dispersions were then filtered onto a mixed cellulose aqueous filter membrane (0.8 μm pore size) substrate using vacuum filtration. After drying at room temperature, the filter membrane substrate was peeled off, yielding cellulose nanofiber loadings of 1, 3, and 9 mg / mL, respectively. 2 An ultrathin cellulose nanofiber membrane. The loading amount is 3 mg / cm³. 2 The ultrathin cellulose nanofiber membrane has a thickness of approximately 20 μm, and the thickness cross-sectional diagram is shown below. Figure 15 As shown. Figure 16 The loading capacity is 3 mg / cm³ 2 The image shows the surface morphology of an ultrathin cellulose nanofiber membrane. As can be seen from the image, the ultrathin cellulose nanofiber membrane is made of cellulose nanofibers wound together, and has a relatively dense morphology with a few nanopores.

[0107] (2) Zinc sheets and ultrathin cellulose nanofiber membranes were assembled into zinc-zinc symmetric cells using a CR2032 coin cell casing for electrochemical performance testing to investigate the inhibitory effect of the ultrathin cellulose nanofiber membrane on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled cells were allowed to stand at room temperature for 6 h to allow the electrolyte to fully wet the ultrathin cellulose nanofiber membrane before electrochemical performance testing.

[0108] (3) At 5 mA / cm 2 Current density, 2.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 17 As shown. Loading amounts of 1, 3, and 9 mg / cm³ were used. 2 The zinc-zinc symmetric batteries with ultrathin cellulose nanofiber separators can undergo normal charge-discharge behavior for 94, 55, and 330 hours, respectively. In contrast, the zinc-zinc symmetric batteries assembled from ordinary non-woven fabric separators and ordinary commercial glass fiber separators in Comparative Examples 1 and 2 can only complete normal charge-discharge behavior for 7 hours and 40 hours, respectively, after which short circuits occur.

[0109] Comparative Example 4

[0110] Preparation of ultrathin TEMPO oxidized cellulose nanofiber membranes

[0111] (1) 37.7 mg of commercial TEMPO oxidized cellulose nanoparticles (model TOCNF) were dispersed in deionized water to prepare a TEMPO oxidized cellulose nanoparticle dispersion with a concentration of 0.5 mg / mL. The dispersion was then uniformly dispersed by ultrasonication. The dispersion was then filtered onto a mixed cellulose aqueous filter membrane (pore size 0.8 μm) substrate by vacuum filtration. After drying at room temperature, the filter membrane substrate was peeled off to obtain a TEMPO oxidized cellulose nanoparticle loading of 3 mg / mL. 2 Ultrathin TEMPO oxidized nanocellulose membrane.

[0112] (2) Zinc sheets and ultrathin TEMPO oxidized cellulose nanoparticles were assembled into a zinc-zinc symmetric battery using a CR2032 coin cell casing for electrochemical performance testing to investigate the inhibitory effect of the ultrathin TEMPO oxidized cellulose nanoparticles on zinc dendrites. The electrolyte was a 2 mol / L zinc sulfate aqueous solution. The assembled battery was allowed to stand at room temperature for 6 h to allow the electrolyte to fully wet the ultrathin TEMPO oxidized cellulose nanoparticles before electrochemical performance testing.

[0113] (3) At 5 mA / cm 2 Current density, 2.5 mAh / cm 2 The cutoff capacity was used as the test condition for constant current charge-discharge testing, and the charge-discharge curve is shown below. Figure 18 As shown. A loading of 3 mg / cm³ was used. 2 The zinc-zinc symmetric battery with the ultrathin TEMPO oxidized nanocellulose separator can undergo 204 hours of normal charge-discharge behavior. In contrast, the zinc-zinc symmetric battery in Comparative Example 2, assembled with a common commercial glass fiber separator, can only complete 40 hours of normal charge-discharge behavior before short-circuiting occurs.

[0114] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a functional grafted ultrathin nanocellulose membrane, characterized in that, Includes the following steps: (1) Disperse cellulose nanofibers or oxidized cellulose nanofibers uniformly in water to obtain an aqueous cellulose suspension; (2) Disperse or dissolve the functional molecules uniformly in an aqueous cellulose suspension to obtain a mixture; (3) The mixture obtained in step (2) is subjected to a chemical grafting reaction under heating, hydrothermal or room temperature conditions to obtain a dispersion of surface-functionalized cellulose nanofibers. The dispersion was used to form a wet film on the corresponding film-forming substrate through a film-forming process. After drying at room temperature, the substrate was peeled off to obtain the functional grafted ultrathin nanocellulose membrane. The functional molecules described in step (2) include at least one of the following: thionicotinamide, 4-fluoroaniline, L-arginine, 5-aminoisophthalic acid, p-aminobenzoic acid, polyethyleneimine, ε-polylysine hydrochloride, diethylenetriamine, triethylenetetramine, 2-aminoterephthalic acid, tetraethylenepentamine, gallic acid, citric acid-β-cyclodextrin, L-lysine, tannic acid, N-hydroxymethylacrylamide, pyridoxine, L-histidine, and polyethylene glycolamine.

2. The preparation method according to claim 1, characterized in that, The diameter of the cellulose nanofibers and oxidized cellulose nanofibers mentioned in step (1) is 1-50 nm and the length is 0.5-30 µm; the concentration of the aqueous cellulose suspension is 0.1-10 mg / mL, preferably 0.5-1 mg / mL.

3. The preparation method according to claim 1, characterized in that, In step (2), the feeding ratio of functional molecules to cellulose nanofibers rich in hydroxyl groups or oxidized nanocellulose rich in carboxyl groups is as follows: the molar ratio of the active groups contained in the functional molecules to the carboxyl groups on the surface of oxidized nanocellulose or the hydroxyl groups on the surface of cellulose nanofibers is 1:1 to 10:

1.

4. The preparation method according to claim 1, characterized in that, In step (3), the chemical grafting reaction includes hydrothermal method, water bath heating method or room temperature reaction method.

5. The preparation method according to claim 4, characterized in that, The chemical grafting reaction is carried out at room temperature or hydrothermally at 60-150 °C for 2-48 hours.

6. The preparation method according to claim 1, characterized in that, The chemical grafting reaction in step (3) is as follows: when the functional molecule contains a primary amino molecule, the pH value of the mixture obtained in step (2) is adjusted to 7.5-8.5, and then the chemical grafting reaction is carried out; when the functional molecule contains a phenolic hydroxyl molecule, the pH value of the mixture obtained in step (2) is adjusted to 4-5, and then the chemical grafting reaction is carried out.

7. The preparation method according to claim 1, characterized in that: The film-forming process in step (3) includes at least one of filtration, casting, or coating; the film-forming substrate includes a mixed cellulose aqueous filter membrane or a nylon filter membrane.

8. The preparation method according to claim 1, characterized in that: The amounts of the cellulose aqueous suspension in step (1) and the dispersion obtained after the chemical grafting reaction in step (3) satisfy the following: the loading of the cellulose nanofibers is 0.5-10 mg / cm³. 2 Preferably 1-6 mg / cm 2 The loading of the functional molecules is 0.1-9 mg / cm³. 2 Preferably 0.3-5 mg / cm 2 ...

9. A functional grafted ultrathin nanocellulose membrane prepared by the preparation method according to any one of claims 1-8.

10. A water-based zinc-based energy storage system, characterized in that, It includes the functional grafted ultrathin nanocellulose membrane as described in claim 9.

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