A double-crosslinked cellulose gel electrolyte, its preparation method and application

Abstract

This invention provides a double-crosslinked cellulose gel electrolyte, its preparation method, and its application. The preparation method includes the following steps: preparing a Tempo-oxidized cellulose nanoparticle dispersion and a cellulose solution separately; then mixing the two, stirring evenly, and adding a chemical crosslinking agent to carry out a crosslinking reaction to obtain a cellulose gel; soaking the cellulose gel in water to obtain the double-crosslinked cellulose gel electrolyte. This invention uses cellulose as a backbone and Tempo-oxidized cellulose nanoparticles as fillers and reinforcing agents to carry out a crosslinking reaction to obtain a cellulose gel electrolyte. It contains abundant hydroxyl and carboxyl functional groups, forming a three-dimensional network structure with good mechanical strength and a dynamic hydrogen-bonded crosslinking network, thereby effectively inhibiting zinc dendrite growth and side reactions.

Description

Technical Field

[0001] This invention belongs to the field of materials science, specifically relating to a double cross-linked cellulose gel electrolyte, its preparation method, and its application. Background Technology

[0002] Rechargeable batteries, as a major representative of electrochemical energy storage technology, play an indispensable role in the storage of renewable energy sources such as solar, wind, tidal, and geothermal energy, thereby meeting the urgent requirements of environmental friendliness and sustainable development. In recent years, rechargeable zinc-ion batteries have gained popularity due to their high theoretical specific capacity (820 mAh g / g). -1 Zinc-ion batteries have attracted much attention due to their advantages such as low redox potential (-0.763V for the standard hydrogen electrode), abundant zinc reserves, non-flammability, and environmental friendliness. However, the electrochemical performance of aqueous zinc-ion batteries is constrained by key issues such as dendrite growth, corrosion, hydrogen evolution reaction (HER), byproduct generation, and cathode dissolution. Hydrogel electrolytes, with their advantages of wide operating voltage range, good adsorption affinity, high ionic conductivity, and relatively stable system, are widely used in aqueous zinc-ion batteries.

[0003] Cellulose is the most abundant natural polymer on Earth, possessing advantages such as good thermal stability, excellent mechanical properties, and low cost. As a key component of hydrogel electrolytes in zinc-ion batteries, cellulose has been extensively studied. Besides providing mechanical strength to prevent dendrite growth, the cellulose structure also helps to immobilize water molecules, thereby limiting free water content and reducing interfacial side reactions. Currently, cellulose-based hydrogel electrolytes are often mixed with other synthetic polymers (such as polyacrylamide) to improve mechanical strength, but this approach limits the biodegradability of the material and increases processing costs. Therefore, developing a cellulose-based gel electrolyte with high stability, cyclicability, and the ability to withstand high current densities for aqueous zinc-ion batteries remains a challenge. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing a double-crosslinked cellulose gel electrolyte.

[0005] Another object of the present invention is to provide a double-crosslinked cellulose gel electrolyte prepared by the above method. This double-crosslinked cellulose gel electrolyte uses cellulose as a base, giving it good mechanical properties, environmental friendliness, and electrochemical stability, making it suitable for use in aqueous zinc-ion batteries and other flexible electronic devices.

[0006] Another object of the present invention is to provide the application of the above-mentioned double cross-linked cellulose gel electrolyte.

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

[0008] A method for preparing a double-crosslinked cellulose gel electrolyte includes the following steps: preparing a Tempo oxidized nanocellulose dispersion and a cellulose solution respectively, then mixing the two, stirring evenly, adding a chemical crosslinking agent to carry out a crosslinking reaction to obtain a cellulose gel, taking out the cellulose gel and soaking it in water to remove excess borax and CNF, thereby obtaining the double-crosslinked cellulose gel electrolyte.

[0009] Preferably, the solid content (mass fraction) of the Tempo-oxidized nanocellulose dispersion is 1-5 wt%; the solid content (mass fraction) of the cellulose solution is 1-5 wt%.

[0010] Preferably, the mass ratio of cellulose in the cellulose solution, Tempo oxidized nanocellulose in the Tempo oxidized nanocellulose dispersion, and chemical crosslinking agent is 1:(0.04-0.5):(0.25-0.5).

[0011] Preferably, the chemical crosslinking agent is sodium tetraborate decahydrate (borax).

[0012] Specifically, the preparation method of the double-crosslinked cellulose gel electrolyte includes the following steps:

[0013] (1) Disperse the oven-dried cellulose in water, add Tempo, sodium bromide and sodium hypochlorite in sequence, stir at room temperature, add sodium hydroxide solution dropwise to keep the pH of the suspension at 10.5-11 until it no longer changes, add ethanol to terminate the reaction; then homogenize the washed oxidized cellulose under high pressure to obtain a uniformly dispersed Tempo oxidized nanocellulose dispersion.

[0014] (2) Add cellulose powder to a mixed solvent of alkali / urea / water and stir until there is no obvious solid to obtain a cellulose solution;

[0015] (3) Mix the Tempo oxidized nanocellulose dispersion obtained in step (1) with the cellulose solution obtained in step (2), stir until completely mixed and homogeneous, then add a chemical crosslinking agent, stir vigorously to make it fully crosslinked, let it stand at room temperature, and soak it in water to remove excess CNF and sodium tetraborate decahydrate to obtain the double crosslinked cellulose gel electrolyte.

[0016] The mass ratio of oven-dried cellulose, Tempo, and sodium bromide in step (1) is 10:(0.12-0.16):(0.8-1.2).

[0017] In step (1), the homogenization and dispersion process of nanocellulose is carried out under a homogenization pressure of 20-70 MPa and a homogenization cycle of 5-30 times.

[0018] The stirring conditions described in step (2) are: stirring at a temperature of -20℃ to -15℃ for 3h to 6h, and stirring speed of 500r / min to 1500r / min; the mass fraction ratio of alkali, urea and water in the alkali / urea / water mixed solvent is 7:12:81.

[0019] The amount of cellulose added in the Tempo oxidized nanocellulose dispersion in step (2) is 10wt% to 32wt%.

[0020] The stirring conditions described in step (3) are: stirring for 10 to 15 minutes at a temperature of 25℃ to 30℃, and stirring speed of 500 r / min to 1500 r / min.

[0021] The standing conditions described in step (3) are 24h to 36h at room temperature.

[0022] The double-crosslinked cellulose gel electrolyte described in this invention can be used in aqueous zinc-ion batteries and other flexible electronic devices.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] This invention utilizes cellulose as a backbone and Tempo-oxidized nanocellulose (CNF) as a filler and reinforcing agent to undergo a cross-linking reaction, yielding a cellulose gel electrolyte. It contains abundant hydroxyl and carboxyl functional groups, forming a three-dimensional network structure with good mechanical strength and a dynamic hydrogen-bonded cross-linking network, thereby effectively suppressing zinc dendrite growth and side reactions.

[0025] The preparation method of this invention is simple and efficient, with low raw material cost and wide availability. The resulting cellulose gel electrolyte has good mechanical properties, environmental friendliness and electrochemical stability, and can be used in aqueous zinc-ion batteries and other flexible electronic devices. Attached Figure Description

[0026] Figure 1 These are scanning electron microscope images of the double cross-linked cellulose gel electrolytes prepared in Examples 1-4 of this invention.

[0027] Figure 2 These are comparison diagrams of the tensile stress-strain curves of the double cross-linked cellulose gel electrolytes prepared in Examples 1-4 of this invention.

[0028] Figure 3 It is the ionic conductivity of the double cross-linked cellulose gel electrolytes prepared in Examples 1 to 4 of this invention.

[0029] Figure 4This is a comparison of the cycle stability of zinc-ion batteries assembled with the double cross-linked cellulose gel electrolyte prepared in Example 1 of the present invention, and with those assembled with single cellulose borax cross-linked gel and single cellulose gel electrolyte. Detailed Implementation

[0030] 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. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0031] Example 1

[0032] A method for preparing a double-crosslinked cellulose gel electrolyte, comprising the following steps:

[0033] (1) Disperse 1g of oven-dried cellulose in 100mL of water, add 0.016g Tempo and 0.1g of sodium bromide in sequence, slowly add 6.67mL of liquid sodium hypochlorite, stir at room temperature, add 0.5mol / L sodium hydroxide solution dropwise to keep the pH of the suspension at around 10 until it no longer changes, and add 10mL of ethanol to terminate the reaction. Then wash with a dialysis bag, and use a homogenizer to homogenize the washed oxidized cellulose under high pressure to obtain a uniformly dispersed Tempo oxidized nanocellulose dispersion. The mass fraction (solid content) of nanocellulose in the dispersion is 1.6%; the homogenization pressure is 50MPa, and the homogenization is performed 5 times.

[0034] (2) Dissolve 2.0g of cellulose powder in 48g of sodium hydroxide / urea / deionized water mixed solvent (sodium hydroxide / urea / deionized water mass ratio of 7:12:81) after pre-cooling (temperature of -15℃), stir for 3h until the cellulose powder is completely dissolved to obtain a cellulose solution, the mass fraction of cellulose in the system is 4%;

[0035] (3) At room temperature, 12.24g of the Tempo oxidized nanocellulose dispersion obtained in step (1) was added to 50g of the cellulose solution obtained in step (2), and the mixture was stirred rapidly until it was uniform. Then, 1g of sodium tetraborate decahydrate was added and stirred vigorously for 15 minutes (at a speed of 800r / min) to ensure that the cellulose was fully cross-linked.

[0036] Finally, the cellulose mixture was poured into a polytetrafluoroethylene mold and left to stand at room temperature for 36 hours to form a double cross-linked cellulose gel. The gel was then soaked in deionized water to remove excess Tempo oxidized nanocellulose and sodium tetraborate decahydrate, thus obtaining the double cross-linked cellulose gel electrolyte.

[0037] Example 2

[0038] A method for preparing a double-crosslinked cellulose gel electrolyte, comprising the following steps:

[0039] (1) Disperse 1g of oven-dried cellulose in 100mL of water, add 0.016g Tempo and 0.1g of sodium bromide in sequence, slowly add 6.67mL of liquid sodium hypochlorite, stir at room temperature, add 0.5mol / L sodium hydroxide solution dropwise to keep the pH of the suspension at around 10 until it no longer changes, and add 10mL of ethanol to terminate the reaction. Then wash with a dialysis bag, and use a homogenizer to homogenize the washed oxidized cellulose under high pressure to obtain a uniformly dispersed Tempo oxidized nanocellulose dispersion. The mass fraction (solid content) of nanocellulose in the dispersion is 1.6%; the homogenization pressure is 50MPa, and the homogenization is performed 5 times.

[0040] (2) Dissolve 2.0g of cellulose powder in 48g of sodium hydroxide / urea / deionized water mixed solvent (sodium hydroxide / urea / deionized water mass ratio of 7:12:81) after pre-cooling (temperature of -15℃), stir for 3h until the cellulose powder is completely dissolved to obtain a cellulose solution, the mass fraction of cellulose in the system is 4%;

[0041] (3) At room temperature, 24.48g of the Tempo oxidized nanocellulose dispersion obtained in step (1) was added to 50g of the cellulose solution obtained in step (2), and the mixture was stirred rapidly until it was uniform. Then, 1g of sodium tetraborate decahydrate was added and stirred vigorously for 15 minutes (at a speed of 800r / min) to ensure that the cellulose was fully cross-linked.

[0042] Finally, the cellulose mixture was poured into a polytetrafluoroethylene mold and left to stand at room temperature for 36 hours to form a double cross-linked cellulose gel. The gel was then soaked in deionized water to remove excess Tempo oxidized nanocellulose and sodium tetraborate decahydrate, thus obtaining the double cross-linked cellulose gel electrolyte.

[0043] Example 3

[0044] A method for preparing a double-crosslinked cellulose gel electrolyte, comprising the following steps:

[0045] (1) Disperse 1g of oven-dried cellulose in 100mL of water, add 0.016g Tempo and 0.1g of sodium bromide in sequence, slowly add 6.67mL of liquid sodium hypochlorite, stir at room temperature, add 0.5mol / L sodium hydroxide solution dropwise to keep the pH of the suspension at around 10 until it no longer changes, and add 10mL of ethanol to terminate the reaction. Then wash with a dialysis bag, and use a homogenizer to homogenize the washed oxidized cellulose under high pressure to obtain a uniformly dispersed Tempo oxidized nanocellulose dispersion. The mass fraction (solid content) of nanocellulose in the dispersion is 1.6%; the homogenization pressure is 50MPa, and the homogenization is performed 5 times.

[0046] (2) Dissolve 2.0g of cellulose powder in 48g of sodium hydroxide / urea / deionized water mixed solvent (sodium hydroxide / urea / deionized water mass ratio of 7:12:81) after pre-cooling (temperature of -15℃), stir for 3h until the cellulose powder is completely dissolved to obtain a cellulose solution, the mass fraction of cellulose in the system is 4%;

[0047] (3) At room temperature, 6.12g of Tempo oxidized nanocellulose dispersion obtained in step (1) was added to 50g of cellulose solution obtained in step (2), and stirred rapidly until the mixture was uniform. Then, 1g of sodium tetraborate decahydrate was added and stirred vigorously for 15 minutes (rotation speed of 800r / min) to ensure that the cellulose was fully cross-linked.

[0048] Finally, the cellulose mixture was poured into a polytetrafluoroethylene mold and left to stand at room temperature for 36 hours to form a double cross-linked cellulose gel. The gel was then soaked in deionized water to remove excess Tempo oxidized nanocellulose and sodium tetraborate decahydrate, thus obtaining the double cross-linked cellulose gel electrolyte.

[0049] Example 4

[0050] A method for preparing a double-crosslinked cellulose gel electrolyte, comprising the following steps:

[0051] (1) Disperse 1g of oven-dried cellulose in 100mL of water, add 0.016g Tempo and 0.1g of sodium bromide in sequence, slowly add 6.67mL of liquid sodium hypochlorite, stir at room temperature, add 0.5mol / L sodium hydroxide solution dropwise to keep the pH of the suspension at around 10 until it no longer changes, and add 10mL of ethanol to terminate the reaction. Then wash with a dialysis bag, and use a homogenizer to homogenize the washed oxidized cellulose under high pressure to obtain a uniformly dispersed Tempo oxidized nanocellulose dispersion. The mass fraction (solid content) of nanocellulose in the dispersion is 1.6%; the homogenization pressure is 50MPa, and the homogenization is performed 5 times.

[0052] (2) Dissolve 2.0g of cellulose powder in 48g of sodium hydroxide / urea / deionized water mixed solvent (sodium hydroxide / urea / deionized water mass ratio of 7:12:81) after pre-cooling (temperature of -15℃), stir for 3h until the cellulose powder is completely dissolved to obtain a cellulose solution, the mass fraction of cellulose in the system is 4%;

[0053] (3) At room temperature, 12.24g of the Tempo oxidized nanocellulose dispersion obtained in step (1) was added to 50g of the cellulose solution obtained in step (2), and the mixture was stirred rapidly until it was uniform. Then, 0.5g of sodium tetraborate decahydrate was added and stirred vigorously for 15 minutes (at a speed of 800r / min) to ensure that the cellulose was fully cross-linked.

[0054] Finally, the cellulose mixture was poured into a polytetrafluoroethylene mold and left to stand at room temperature for 36 hours to form a double cross-linked cellulose gel. The gel was then soaked in deionized water to remove excess Tempo oxidized nanocellulose and sodium tetraborate decahydrate, thus obtaining the double cross-linked cellulose gel electrolyte.

[0055] Scanning electron microscopy images of the double-crosslinked cellulose gel electrolytes prepared in Examples 1-4 are shown below. Figure 1 As shown in the figure, it can be clearly seen that the double cross-linked cellulose gel electrolyte prepared by the present invention has a rich spatial network structure constructed by cellulose, which can promote the transport of zinc ions inside the electrolyte.

[0056] The tensile stress-strain curves of the double-crosslinked cellulose gel electrolytes prepared in Examples 1-4 are compared as follows: Figure 2 As shown, the test method involved using a tensile and compressive testing machine (INSTRON 5565, USA) to perform tensile tests on the samples. The tensile specimens were rectangular, with a gauge length of 20 mm, and the tensile / compression rate was 2 mm / min. Each sample was tested 5–7 times, and the average value was taken. Figure 2 It can be seen that the double cross-linked cellulose gel electrolytes in Examples 1 to 4 all have good tensile properties. Among them, Examples 1 and 2 have higher tensile deformation limits due to the addition of more nanocellulose. However, the tensile stress limit of Example 2 is lower due to the excessive nanocellulose content. The tensile properties of Example 3 are slightly inferior to those of Examples 1 and 2 due to the less nanocellulose added and the insufficient chemical cross-linking agent content in Example 4.

[0057] The ionic conductivity of the double-crosslinked cellulose gel electrolytes prepared in Examples 1-4 is as follows: Figure 3 As shown, the test method involved assembling the battery in the order of stainless steel sheet, gel electrolyte, and stainless steel sheet, and then performing electrochemical impedance spectroscopy (EIS) using an electrochemical workstation (CHI 660E) to calculate the ionic conductivity. From... Figure 3 It can be seen that the double cross-linked cellulose gel electrolytes prepared in Examples 1 to 4 all have high ionic conductivity, good electrochemical performance, and can promote the transport of zinc ions.

[0058] Figure 4 This invention compares the cycle stability of zinc-ion batteries assembled with the double-crosslinked cellulose gel electrolyte prepared in Example 1 of this invention, and those assembled with single-cellulose borax crosslinked gel and single-cellulose gel electrolyte. The test method involves using a Blue Battery Detection System (CT2001A) to perform cyclic constant current charge-discharge tests on the Zn||electrolyte||Zn symmetric battery.

[0059] The preparation method of monocellulose borax crosslinked gel is as follows: 2.0g of cellulose powder is dissolved in 48g of a pre-cooled (temperature -15℃) mixed solvent of sodium hydroxide / urea / deionized water (mass ratio of sodium hydroxide / urea / deionized water is 7:12:81), and stirred for 3h until the cellulose powder is completely dissolved to obtain a cellulose solution with a cellulose mass fraction of 4% in the system; at room temperature, 1g of sodium tetraborate decahydrate is added to 50g of cellulose solution and stirred vigorously (speed is 800r / min) to fully crosslink the cellulose; finally, the cellulose mixture is poured into a polytetrafluoroethylene mold and left to stand at room temperature for 36h to form a cellulose gel. The gel is then soaked in deionized water to remove excess sodium tetraborate decahydrate to obtain monocellulose borax crosslinked gel.

[0060] Preparation method of monocellulose gel: 2.0g of cellulose powder was dissolved in 48g of sodium hydroxide / urea / deionized water mixed solvent (mass ratio of sodium hydroxide / urea / deionized water is 7:12:81) after pre-cooling (temperature is -15℃), and stirred for 3h until the cellulose powder was completely dissolved to obtain a cellulose solution with a cellulose mass fraction of 4% in the system; under room temperature conditions, the cellulose solution was poured into a polytetrafluoroethylene mold and allowed to stand at room temperature for 36h to form cellulose gel.

[0061] from Figure 4 It can be seen that the zinc-zinc symmetric battery assembled with monocellulose gel without any reinforcing agent or crosslinking agent could not operate stably after 50 hours of cycling. The monocellulose borax crosslinked cellulose gel, with the addition of a chemical crosslinking agent, enhanced the structural stability, allowing the zinc-zinc symmetric battery assembled with it to cycle stably for 150 hours. The double crosslinked cellulose gel electrolyte prepared in Example 1, which added Tempo oxidized nanocellulose dispersion and a chemical crosslinking agent, enhanced the stability of its fiber skeleton network and increased ion transport channels, allowing the zinc-zinc symmetric battery prepared with it to cycle stably for more than 1000 hours.

[0062] In summary, the double-crosslinked cellulose gel electrolyte prepared in this invention exhibits excellent overall performance. Actual testing revealed that the gel electrolyte possesses abundant hydroxyl and carboxyl functional groups, forming a three-dimensional network structure. It demonstrates good mechanical and electrochemical properties, showing promising prospects for electrochemical applications. Furthermore, the raw material components of this gel electrolyte are safe, and the manufacturing process is low-cost, facilitating industrialization and large-scale application.

[0063] 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 double-crosslinked cellulose gel electrolyte, characterized in that, The process includes the following steps: preparing Tempo oxidized cellulose nanoparticle dispersion and cellulose solution respectively, then mixing the two, stirring evenly, adding a chemical crosslinking agent to carry out a crosslinking reaction to obtain cellulose gel; soaking the cellulose gel in water to obtain the double crosslinked cellulose gel electrolyte.

2. The preparation method according to claim 1, characterized in that, The mass ratio of cellulose in the cellulose solution, Tempo oxidized nanocellulose in the Tempo oxidized nanocellulose dispersion, and chemical crosslinking agent is 1:(0.04-0.5):(0.25-0.5).

3. The preparation method according to claim 1, characterized in that, The chemical crosslinking agent is sodium tetraborate decahydrate.

4. The preparation method according to claim 1, characterized in that, The solid content of the Tempo-oxidized nanocellulose dispersion is 1-5 wt%.

5. The preparation method according to claim 1, characterized in that, The solid content of the cellulose solution is 1-5 wt%.

6. The preparation method according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Disperse the oven-dried cellulose in water, add Tempo, sodium bromide and sodium hypochlorite in sequence, stir at room temperature, add alkaline solution dropwise to keep the pH of the suspension at 10.5-11 until it no longer changes, add ethanol to terminate the reaction; then homogenize the washed oxidized cellulose under high pressure to obtain a uniformly dispersed Tempo oxidized nanocellulose dispersion. (2) Add cellulose powder to a mixed solvent of alkali / urea / water and stir until there is no obvious solid to obtain a cellulose solution; (3) Mix the Tempo oxidized nanocellulose dispersion obtained in step (1) with the cellulose solution obtained in step (2), stir until completely mixed, then add a chemical crosslinking agent, stir to fully crosslink, let stand at room temperature, and finally soak in water to obtain the double crosslinked cellulose gel electrolyte.

7. The preparation method according to claim 6, characterized in that, The mass ratio of oven-dried cellulose, Tempo and sodium bromide in step (1) is 10:(0.12-0.16):(0.8-1.2); the homogenization process of nanocellulose in step (1) is carried out under a homogenization pressure of 20-70 MPa and a homogenization cycle of 5-30 times.

8. The preparation method according to claim 6, characterized in that, The stirring conditions described in step (2) are: stirring at a temperature of -20℃ to -15℃ for 3h to 6h, and stirring speed of 500r / min to 1500r / min; The stirring conditions described in step (3) are: stirring for 10 min to 15 min at a temperature of 25℃ to 30℃ and a stirring speed of 500 r / min to 1500 r / min; The standing conditions described in step (3) are to stand at room temperature for 24 to 36 hours.

9. A double-crosslinked cellulose gel electrolyte prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the double cross-linked cellulose gel electrolyte of claim 9 in aqueous zinc-ion batteries or flexible electronic devices.

Images