Preparation method of alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode

Abstract

Preparation method of alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode. In the present invention, MXene is pretreated with an alkaline reagent to induce the formation of wrinkled MXene nanosheets, and then the alkali-induced wrinkled MXene / BC mixture is filtered into a membrane, freeze-dried, and the BC part is carbonized by means of assisted low-temperature annealing to improve the conductivity of the composite membrane, obtaining a highly conductive three-dimensional porous MXene / BC flexible membrane electrode. The construction of the three-dimensional porous structure not only inhibits the self-stacking phenomenon of MXene sheets but also facilitates the rapid insertion and extraction of ions between the layers. The presence of bacterial cellulose increases the mechanical toughness of the composite membrane. Therefore, the process route of the present invention is simple, without organic additives, the raw materials are widely sourced, and the by-products are easily harmlessly treated, having good economic and environmental effects and being conducive to large-scale industrial applications.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of flexible energy storage materials, and particularly relates to a method for preparing an alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode. Background Art

[0002] As a new type of two-dimensional lamellar material, MXenes have a structure and properties similar to graphene. Due to its rich surface area functional groups, high specific surface area, excellent electrical conductivity and good hydrophilicity, extensive research reports have been obtained in the fields of sensors, biomedicine, electromagnetic absorption and shielding, electrocatalysis, energy storage, etc. The self-supporting flexible membrane electrode prepared based on MXenes is a very promising flexible electrode because it does not require the addition of extra conductive agents and adhesives, and has good flexibility, cycle stability and specific capacity, and has extremely high research value in the application fields of flexible energy storage devices represented by flexible wearable electronic devices, foldable displays, and foldable mobile phones.

[0003] However, there are also some defects in the application of pure MXenes membrane electrodes. First of all, like other two-dimensional nanomaterials, MXenes nanosheets are prone to self-stacking of lamellae due to the strong van der Waals force existing between layers, which greatly reduces the surface active sites available for reaction and the ion transport channels, and ultimately affects the material performance. Secondly, in the preparation process, the MXene membrane prepared by the commonly used vacuum filtration method in the field has a dense membrane structure, which is not conducive to the rapid shuttle of ions between layers. Finally, although the pure MXene self-supporting membrane has excellent flexibility, its toughness still needs to be improved. In recent years, researchers have combined different material characteristics and used the synergistic effect between materials to modify and improve MXenes-based materials. The participation of the second-phase material can effectively alleviate the self-stacking effect of MXenes nanosheets, the three-dimensional structure design expands the reaction area and ion transport channels, and the toughening modification of the second-phase material, etc., have become common technical means to improve the performance of MXenes-based materials.

[0004] Bacterial cellulose (BC), as a kind of cellulose, is a natural polymer one-dimensional nanomaterial synthesized by microbial bacteria. Bacterial cellulose has a large aspect ratio, high purity, stability, good dispersibility and high mechanical strength, and is widely used in the fields of biomedicine, functional textiles, food additives, electronic devices and military industries. Although there are currently some research reports on the combination of bacterial cellulose and 3 C 2 this MXene material, however, as an insulator, the combination of cellulose and MXene will reduce the overall conductivity of the material, thereby reducing the electrochemical performance of the composite electrode. Summary of the Invention

[0005] The object of the present invention is to propose a preparation method of an alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode that can not only improve the structural toughness and electrical conductivity, but also has a higher specific capacity and excellent cycle stability.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] 1) Prepare a white viscous bacterial cellulose solution with a concentration of 0.5 - 5 mg / mL from one-dimensional bacterial nanocellulose, and define it as solution A;

[0008] 2) Subject the etched multi-layer MXene nanosheet solution to low-temperature ultrasonic treatment under argon gas flow, and centrifuge to collect the upper suspension to obtain a single- or few-layer MXene two-dimensional nanosheet sol solution, and define it as solution B.

[0009] 3) Add solution A to solution B according to the mass ratio of solution A: solution B: alkaline solution C = (0.05 - 1):1:10. After ultrasonic treatment or magnetic stirring for 20 - 45 min, then add alkaline solution C and perform ultrasonic treatment or magnetic stirring again for 100 - 200 min to obtain a mixed solution D;

[0010] 4) Filter the mixed solution D through a vacuum filtration device, and obtain a self-supporting flexible membrane E without additives after freeze-drying and peeling;

[0011] 5) Place the dried flexible membrane E in a tube furnace filled with inert gas, and obtain a three-dimensional porous flexible membrane after low-temperature annealing.

[0012] In step 1), the one-dimensional bacterial nanocellulose with a diameter of 50 - 100 nm and a length of - 20 μm is dispersed by ultrasonic treatment or magnetic stirring to form solution A.

[0013] The multi-layer MXene nanosheet solution in step 2) is prepared by uniformly mixing Ti powder, TiC powder, and Al powder in a molar ratio of Ti:TiC:Al = 1:2:1.2, calcining at 1350 °C for 2 h in an inert atmosphere, grinding, passing through a 400-mesh sieve, and then subjecting the Ti 3 AlC 2 ceramic powder to liquid-phase etching.

[0014] The etching agent is hydrofluoric acid or a mixed acid of hydrochloric acid and lithium fluoride.

[0015] In step 2), the etched multi-layer MXene nanosheet solution is ultrasonically treated at 5 - 15 °C under argon gas protection with an ultrasonic power of 200 W for 60 - 180 min, and centrifuged at 3000 - 3500 rpm for 30 - 60 min to obtain a 0.5 - 5 mg / mL single- or few-layer MXene two-dimensional nanosheet sol solution.

[0016] The alkaline solution C in step 3) is a lithium hydroxide, sodium hydroxide, potassium hydroxide solution with a concentration of 120-180 mg / mL, an ammonia water solution with a concentration of 25%-28%, or an ethylenediamine solution.

[0017] In step 4), the filter membrane of the vacuum filtration device is a hydrophilic cellulose ester membrane with a pore size of 0.22 μm and a diameter of 50 mm.

[0018] In step 5), the flexible film E is placed in a tubular furnace filled with argon and annealed at 250-400 °C for 1-2 h.

[0019] In the present invention, MXene is pretreated with an alkaline reagent to induce the formation of wrinkled MXene nanosheets. Then, the alkali-induced wrinkled MXene / BC mixture is filtered into a film, freeze-dried, and annealed at a low temperature to partially carbonize BC to improve the conductivity of the composite film, obtaining a highly conductive three-dimensional porous MXene / BC flexible film electrode. The construction of the three-dimensional porous structure not only inhibits the self-stacking of MXene sheets but also facilitates the rapid insertion and extraction of ions between the layers. The presence of bacterial cellulose also increases the mechanical toughness of the composite film. Therefore, the process route of the present invention is simple, without organic additives, the raw materials are widely available, and the by-products are easily harmlessly treated, having good economic and environmental effects and being conducive to large-scale industrial applications.

[0020] Beneficial effects:

[0021] First, the present invention uses an alkaline reagent to induce the MXene nanosheets, forming wrinkled MXene nanosheets. The flocculated MXene can be quickly filtered into a film within a few seconds, shortening the film-forming time by hundreds of times, greatly shortening the process cycle, and reducing energy consumption.

[0022] Second, the modified material bacterial cellulose used has a wide source and low price, having outstanding cost advantages.

[0023] Third, the low-temperature carbonization of bacterial cellulose is achieved by annealing. On the one hand, it improves the conductivity of the composite film. On the other hand, bacterial cellulose, as an interlayer pillar material, inhibits the self-stacking of MXene nanosheets, and the remaining pores after carbonization provide more and larger pores for the insertion and extraction of ions, which is beneficial to the electrochemical performance of the membrane electrode.

[0024] Fourth, different ratios of materials can be combined to adjust composite films with different physical and chemical properties. The prepared composite film can be self-supporting without additional additives, has excellent mechanical flexibility, and is suitable for large-scale industrial production. Description of the drawings

[0025] Appendix Figure 1Optical photograph of the alkali-induced porous MXene / bacterial cellulose flexible membrane electrode prepared under the conditions of Example 1 of the present invention.

[0026] Appendix Figure 2 X-ray diffraction pattern of the alkali-induced porous MXene / bacterial cellulose flexible membrane electrode under the conditions of Example 1 of the present invention.

[0027] Appendix Figure 3 Galvanostatic charge-discharge performance diagram of the alkali-induced porous MXene / bacterial cellulose flexible membrane electrode prepared under the conditions of Example 1 of the present invention. Detailed implementation mode

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] Example 1:

[0030] 1) One-dimensional bacterial nanocellulose with a diameter of 50-100 nm and a length of ~20 μm was ultrasonically dispersed to prepare a white sticky bacterial cellulose solution with a concentration of 0.5 mg / mL, defined as solution A;

[0031] 2) Ti powder, TiC powder, and Al powder were uniformly mixed in a molar ratio of Ti:TiC:Al = 1:2:1.2. Under an inert atmosphere, it was calcined at 1350 °C for 2 h, then ground and passed through a 400-mesh sieve to obtain Ti 3 AlC 2 ceramic powder. The Ti 3 AlC 2 ceramic powder was etched with a mixed acid solution of HCl and LiF to obtain a multi-layer MXene nanosheet solution. The etched multi-layer MXene nanosheet solution was ultrasonically treated at 5 °C and a ultrasonic power of 200 W for 60 min under argon protection, centrifuged at 3500 rpm for 60 min, and the upper suspension was collected to obtain a 0.5 mg / mL single- and few-layer MXene two-dimensional nanosheet sol solution, defined as solution B;

[0032] 3) Solution A was added to solution B according to a mass ratio of solution A: solution B: alkaline solution C = 0.05:1:10. After ultrasonic or magnetic stirring for 20 min, alkaline solution C was added and ultrasonic or magnetic stirring was carried out again for 100 min to obtain a mixed solution D;

[0033] Among them, the alkaline solution used was a sodium hydroxide solution with a concentration of 150 mg / mL;

[0034] 4) The mixed solution D was filtered by a vacuum filtration device. The filter membrane of the vacuum filtration device used a water-based cellulose ester membrane with a pore size of 0.22 μm and a diameter of 50 mm, and was freeze-dried and peeled to obtain a self-supporting flexible membrane E without additives;

[0035] 5) Place the dried flexible film E in a tubular furnace filled with argon and anneal it at 250 °C for 2 h to obtain a three-dimensional porous flexible film.

[0036] Figure 1 This is an optical photograph of the alkali-induced porous MXene / bacterial cellulose flexible film electrode prepared under the conditions of Example 1 of the present invention. The prepared additive-free self-supporting composite flexible film is easy to peel off from the polyester cellulose film, and still maintains good flexibility after alkali induction and low-temperature annealing treatment, showing a wrinkled and porous surface morphology.

[0037] Figure 2 This is the X-ray diffraction pattern of the alkali-induced porous MXene / bacterial cellulose flexible film electrode prepared under the conditions of Example 1 of the present invention, and the pure MXene flexible film without alkali induction and bacterial cellulose modification is used as a comparative sample. It can be seen from the figure that the alkali-induced porous MXene / bacterial cellulose flexible film (A-M / BC) has a strong diffraction peak at the position representing the (002) crystal plane and no other impurity peaks, proving that the MXene phase has not changed after alkali induction and low-temperature annealing treatment, and the product has good crystallinity. And compared with the pure MXene film, because the diffraction peak angle shifts to the left, it is proved that the layer spacing of the treated and modified composite film expands, which is more conducive to the shuttle of ions between the films, reflecting the potential of better electrochemical performance.

[0038] Figure 3 This is the galvanostatic charge-discharge performance diagram of the alkali-induced porous MXene / bacterial cellulose flexible film electrode prepared under the conditions of Example 1 of the present invention, where at a current density of 1 A g -1 the mass specific capacity of the composite film electrode prepared in Example 1 reached 251 F g -1 .

[0039] Example 2:

[0040] 1) Ultrasonically disperse one-dimensional bacterial nanocellulose with a diameter of 50-100 nm and a length of ~20 μm to prepare a white viscous bacterial cellulose solution with a concentration of 1 mg / mL, defined as solution A;

[0041] 2) Uniformly mix Ti powder, TiC powder, and Al powder in a molar ratio of Ti:TiC:Al = 1:2:1.2, calcine at 1350 °C for 2 h in an inert atmosphere, and then grind and pass through a 400-mesh sieve to obtain Ti 3 AlC 2 ceramic powder, and use HF acid for liquid-phase etching of Ti 3 AlC 2A multilayer MXene nanosheet solution is obtained from ceramic powder. The etched multilayer MXene nanosheet solution is sonicated for 90 min at 5 °C and a sonication power of 200 W under argon protection, centrifuged at 3500 rpm for 50 min, and the upper suspension is collected to obtain a 1 mg / mL single- and few-layer MXene two-dimensional nanosheet sol, defined as solution B.

[0042] 3) Add solution A to solution B according to the mass ratio of solution A: solution B: alkaline solution C = 0.1:1:10. After sonication or magnetic stirring for 25 min, then add alkaline solution C and sonicate or magnetic stir again for 120 min to obtain a mixed solution D.

[0043] Among them, the alkaline solution uses a sodium hydroxide solution with a concentration of 120 mg / mL.

[0044] 4) Filter the mixed solution D through a vacuum filtration device. The filter membrane of the vacuum filtration device uses a hydrophilic cellulose ester membrane with a pore size of 0.22 μm and a diameter of 50 mm. After freeze-drying, it is peeled off to obtain a self-supporting flexible membrane E without additives.

[0045] 5) Place the dried flexible membrane E in a tubular furnace filled with argon and anneal it at 300 °C for 2 h to obtain a three-dimensional porous flexible membrane.

[0046] Example 3:

[0047] 1) Dispersed one-dimensional bacterial nanocellulose with a diameter of 50 - 100 nm and a length of ~20 μm by magnetic stirring to prepare a 2 mg / mL white viscous bacterial cellulose solution, defined as solution A.

[0048] 2) Mix Ti powder, TiC powder, and Al powder evenly according to the molar ratio of Ti:TiC:Al = 1:2:1.2. Under an inert atmosphere, calcine at 1350 °C for 2 h, then grind and pass through a 400-mesh sieve to obtain Ti 3 AlC 2 ceramic powder. Use hydrofluoric acid for liquid-phase etching of Ti 3 AlC 2 ceramic powder to obtain a multilayer MXene nanosheet solution. The etched multilayer MXene nanosheet solution is sonicated for 120 min at 10 °C and a sonication power of 200 W under argon protection, centrifuged at 3500 rpm for 45 min, and the upper suspension is collected to obtain a 2 mg / mL single- and few-layer MXene two-dimensional nanosheet sol, defined as solution B.

[0049] 3) Add solution A to solution B according to the mass ratio of solution A: solution B: alkaline solution C = 0.25:1:10. After sonication or magnetic stirring for 30 min, then add alkaline solution C and sonicate or magnetic stir again for 150 min to obtain a mixed solution D.

[0050] Among them, the alkaline solution is a potassium hydroxide solution with a concentration of 180 mg / mL;

[0051] 4) Filter the mixed solution D through a vacuum filtration device. The filter membrane of the vacuum filtration device is a hydrophilic cellulose ester membrane with a pore size of 0.22 μm and a diameter of 50 mm. After freeze-drying, peel it off to obtain a self-supporting flexible membrane E without additives;

[0052] 5) Place the dried flexible membrane E in a tubular furnace filled with argon and anneal it at 350 °C for 2 h to obtain a three-dimensional porous flexible membrane.

[0053] Example 4:

[0054] 1) Ultrasonically disperse one-dimensional bacterial nanocellulose with a diameter of 50 - 100 nm and a length of ~20 μm to prepare a white viscous bacterial cellulose solution with a concentration of 4 mg / mL, defined as solution A;

[0055] 2) Uniformly mix Ti powder, TiC powder, and Al powder in a molar ratio of Ti:TiC:Al = 1:2:1.2. Under an inert atmosphere, calcine at 1350 °C for 2 h, then grind and pass through a 400-mesh sieve to obtain Ti 3 AlC 2 ceramic powder. Use a mixed acid liquid phase etching of Ti 3 AlC 2 ceramic powder to obtain a multi-layer MXene nanosheet solution. For the etched multi-layer MXene nanosheet solution, under argon protection, ultrasonically treat it at 10 °C with a ultrasonic power of 200 W for 150 min, and centrifuge at 3000 rpm for 40 min. Collect the upper suspension to obtain a 4 mg / mL single- and few-layer MXene two-dimensional nanosheet sol solution, defined as solution B;

[0056] 3) Add solution A to solution B according to a mass ratio of solution A:solution B:alkaline solution C = 0.5:1:10. After ultrasonic or magnetic stirring for 40 min, then add alkaline solution C and stir ultrasonically or magnetically for another 180 min to obtain a mixed solution D;

[0057] Among them, the alkaline solution is an ammonia water solution with a concentration of 28%;

[0058] 4) Filter the mixed solution D through a vacuum filtration device. The filter membrane of the vacuum filtration device is a hydrophilic cellulose ester membrane with a pore size of 0.22 μm and a diameter of 50 mm. After freeze-drying, peel it off to obtain a self-supporting flexible membrane E without additives;

[0059] 5) Place the dried flexible membrane E in a tubular furnace filled with argon and anneal it at 400 °C for 2 h to obtain a three-dimensional porous flexible membrane.

[0060] Example 5:

[0061] 1) One-dimensional bacterial nanocellulose with a diameter of 50-100 nm and a length of ~20 μm was dispersed by magnetic stirring to prepare a white viscous bacterial cellulose solution with a concentration of 5 mg / mL, defined as solution A;

[0062] 2) Ti powder, TiC powder, and Al powder were uniformly mixed in a molar ratio of Ti:TiC:Al = 1:2:1.2. Under an inert atmosphere, they were calcined at 1350 °C for 2 h, then ground and passed through a 400-mesh sieve to obtain Ti 3 AlC 2 ceramic powder. The Ti 3 AlC 2 ceramic powder was etched with a mixed acid solution of HCl and LiF to obtain a multi-layer MXene nanosheet solution. The etched multi-layer MXene nanosheet solution was ultrasonicated at 15 °C with a power of 200 W for 180 min under argon protection, centrifuged at 3000 rpm for 30 min, and the upper suspension was collected to obtain a 5 mg / mL single- and few-layer MXene two-dimensional nanosheet sol solution, defined as solution B;

[0063] 3) Solution A was added to solution B according to a mass ratio of solution A:solution B:alkaline solution C = 1:1:10. After ultrasonicating or magnetic stirring for 45 min, alkaline solution C was added and ultrasonicated or magnetic stirred again for 200 min to obtain a mixed solution D;

[0064] Among them, the alkaline solution used was an ethylenediamine solution with a concentration of 25%;

[0065] 4) The mixed solution D was filtered by a vacuum filtration device. The filter membrane of the vacuum filtration device used was a water-based cellulose ester membrane with a pore size of 0.22 μm and a diameter of 50 mm. After freeze-drying, it was peeled off to obtain a self-supporting flexible membrane E without additives;

[0066] 5) The dried flexible membrane E was placed in a tubular furnace filled with argon and annealed at 400 °C for 1 h to obtain a three-dimensional porous flexible membrane.

[0067] The preparation method of the present invention can prepare a MXene-based composite flexible film with a three-dimensional porous structure. In terms of the preparation process, the alkali-induced wrinkled MXene can be filtered into a film within a few seconds, and the film-forming period is shortened by several hundred times compared with the untreated MXene sol (usually it takes more than half an hour to filter into a film), saving energy. In terms of the structural design, on the one hand, the MXene nanosheets can be rapidly flocculated after alkali induction, presenting a wrinkled morphology microscopically, and based on this, a three-dimensional porous structure MXene thin film material can be prepared. On the other hand, bacterial cellulose is inserted into the MXene nanosheets as an interlayer pillar to inhibit the stacking of nanosheets, and then partially removed by low-temperature carbonization, constructing more three-dimensional channels for the ion transport between the MXene layers. In terms of the physical and chemical properties, compared with the pure MXene film, the composite film has better structural toughness, higher conductivity, higher specific capacitance and excellent cycle stability, and is an electrode material for wearable electronic energy storage devices with great application potential.

Claims

1. A preparation method of an alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode, characterized in that it includes the following steps: 1) Prepare a white viscous bacterial cellulose solution with a concentration of 0.5-5 mg / mL from one-dimensional bacterial nanocellulose, defined as solution A; 2) For the etched multi-layer MXene nanosheet solution, perform low-temperature ultrasonic treatment under argon gas flow, and centrifuge to collect the upper suspension to obtain a single- or few-layer MXene two-dimensional nanosheet sol solution, defined as solution B; The multi-layer MXene nanosheet solution in step 2) is prepared by uniformly mixing Ti powder, TiC powder, and Al powder in a molar ratio of Ti:TiC:Al = 1:2:1.2, calcining at 1350 °C for 2 h in an inert atmosphere, grinding, passing through a 400-mesh sieve, and then obtaining ceramic powder through liquid-phase etching of Ti 3 AlC 2 ceramic powder 3) Add solution A to solution B according to the mass ratio of solution A: solution B: alkaline solution C = (0.05-1):1:

10. After ultrasonic treatment or magnetic stirring for 20-45 min, then add alkaline solution C and perform ultrasonic treatment or magnetic stirring for 100-200 min to obtain a mixed solution D; 4) Filter the mixed solution D through a vacuum filtration device, and obtain a self-supporting flexible membrane E without additives after freeze-drying and peeling; 5) Place the dried flexible membrane E in a tubular furnace filled with inert gas, and obtain a three-dimensional porous flexible membrane after low-temperature annealing.

2. The preparation method of the alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode according to claim 1, characterized in that: In step 1), the one-dimensional bacterial nanocellulose with a diameter of 50-100 nm and a length of ~20 μm is dispersed by ultrasonic treatment or magnetic stirring to form solution A.

3. The preparation method of the alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode according to claim 1, characterized in that: The etching agent used in the liquid-phase etching is hydrofluoric acid or a mixed acid of hydrochloric acid and lithium fluoride.

4. The preparation method of the alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode according to claim 1, characterized in that: In step 2), for the etched multi-layer MXene nanosheet solution, perform ultrasonic treatment at 5-15 °C and an ultrasonic power of 200 W for 60-180 min under argon protection, and centrifuge at 3000-3500 rpm for 30-60 min to obtain a 0.5-5 mg / mL single- or few-layer MXene two-dimensional nanosheet sol solution.

5. The preparation method of the alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode according to claim 1, characterized in that: The alkaline solution C in step 3) uses a lithium hydroxide, sodium hydroxide, potassium hydroxide solution with a concentration of 120-180 mg / mL, an ammonia water solution or an ethylenediamine solution with a concentration of 25%-28%.

6. The preparation method of the alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode according to claim 1, characterized in that: In step 4), the filter membrane of the vacuum filtration device uses a water-based cellulose ester membrane with a pore size of 0.22 μm and a diameter of 50 mm.

7. The preparation method of the alkali-induced three-dimensional porous MXene-bacterial cellulose flexible membrane electrode according to claim 1, characterized in that: In step 5), the flexible membrane E is placed in a tubular furnace filled with argon and annealed at 250-400 °C for 1-2 h.

Images