Cellulose hydrogel film, preparation method thereof and application of cellulose hydrogel film in supercapacitor

Abstract

The invention discloses a cellulose hydrogel film, a preparation method thereof and application of the cellulose hydrogel film in a supercapacitor, and belongs to the technical field of capacitors. The method comprises the following steps: removing impurities from bacterial cellulose, and crushing to obtain bacterial cellulose dispersion liquid; the preparation method comprises the following steps: dissolving sodium alginate in a urea-sodium hydroxide mixed solution, freezing, sequentially adding microcrystalline cellulose and bacterial cellulose dispersion liquid, quickly stirring to form white viscous liquid, defoaming and carrying out acid precipitation on the white viscous liquid to obtain the cellulose hydrogel film, and the cellulose hydrogel film has high structural stability and excellent electrochemical performance, has the conductivity of 5.874 S / m, and has good electrochemical performance. According to the present invention, the graphene-based composite material is adopted as the gel electrolyte and is assembled with the carbon cloth electrode to form the supercapacitor, the high capacitance retention rate is maintained under the high current density, and the gel shows the low self-discharge rate and the excellent energy density, and has important application potential in the flexible energy storage field.

Description

Technical Field

[0001] The invention relates to a hydrogel film, in particular to a microcrystalline cellulose-bacterial cellulose-sodium alginate composite hydrogel film, and also to a preparation method thereof and application thereof as a supercapacitor gel electrolyte. Background Art

[0002] With the advancement of science and technology, portable flexible electronic products such as flexible displays, implantable biosensors, electronic skin, health detection, etc. have developed rapidly. As an energy storage device for flexible electronics, it needs to meet specific advantages, such as high capacitance performance, long-lasting mechanical flexibility and long-term cycle stability. Gel electrolytes play an important role in the production of flexible and wearable solid-state supercapacitors. The development of gel polymer electrolytes with high ionic conductivity, excellent mechanical properties, good contact with electrodes and high stability is of great theoretical and practical significance.

[0003] Cellulose is an inexhaustible and renewable organic polymer in nature. In particular, cellulose hydrogel can absorb and retain a large amount of water molecules, but is insoluble in aqueous media. It has many excellent properties such as mechanical properties, biocompatibility, safety, non-toxicity and degradability. It has been developed for use as a gel diaphragm and solid electrolyte for flexible supercapacitors. Cellulose-based gel electrolytes have attracted widespread attention in flexible supercapacitors due to their renewability, biocompatibility, adjustable mechanical properties and good ionic conductivity. However, limited by the weak lateral aggregation and recrystallization of cellulose chains in cellulose hydrogels, cellulose hydrogels exhibit high elasticity, but weak mechanical strength and fragility, which seriously hinders their practical application. At present, researchers mainly improve the mechanical and electrochemical properties of cellulose gels through physical or chemical crosslinking methods (such as freeze-thaw, chemical crosslinker modification, etc.). For example, (“High-performance flexible and self-healable quasi-solid-state zinc-ion hybrid supercapacitor based on borax-crosslinked polyvinyl alcohol / nanocellulose hydrogel electrolyte”, Chen M F., et al. Journal of Materials Chemistry A, 2019, 7 (46): 26524-26532.) disclosed that a quasi-solid-state zinc-ion hybrid supercapacitor electrolyte with self-healing properties was prepared by crosslinking polyvinyl alcohol / nanocellulose hydrogel with borax, showing excellent cycle stability. In addition, (“Research on the preparation and application of nanocellulose and its composite materials”, Li Yuting et al., Synthesis Technology and Application, 2023, 38(03): 19~24) reviewed the preparation methods of nanocellulose composite materials and pointed out their application potential in flexible energy storage devices. Although cellulose gels show good application prospects in supercapacitors, there are still the following challenges: (1) Insufficient structural stability: Traditional cellulose gels are prone to structural collapse at high current density, resulting in rapid capacitance decay. (2) Low ionic conductivity: The insulating property of cellulose itself limits the efficiency of charge transfer, and the conductivity needs to be improved by doping with conductive materials (such as carbon nanotubes and conductive polymers). (3) Self-discharge problem: Due to the uneven ion migration inside the gel, cellulose-based supercapacitors often have a high self-discharge rate. To address the above problems, researchers have adopted a variety of optimization strategies: (1) Introducing cross-linking agents: such as sodium alginate (SA), polyvinyl alcohol (PVA), etc., to enhance the gel network through hydrogen bonding or chemical cross-linking. (2) Composite conductive materials: such as graphene, MXene, etc., to improve the electronic / ionic conductivity of the gel.(3) Structural design optimization: such as constructing a porous structure to facilitate ion transport.

[0004] Despite many improvements, the application of cellulose gel in supercapacitors still faces the following problems: (1) Balance between mechanical strength and conductivity: high cross-linking degree may reduce ion mobility, while high porosity may sacrifice mechanical properties. (2) Long-term cycle stability: During repeated charge and discharge, the gel may swell or degrade. (3) Difficulty in large-scale preparation: Laboratory preparation methods are difficult to directly apply to industrial production. Summary of the invention

[0005] In view of the defects of the prior art, the first object of the present invention is to provide a cellulose hydrogel membrane, which is cross-linked by bacterial cellulose (BC) and microcrystalline fiber (MC) through a small amount of sodium alginate (SA) to form a highly stable BC / MC / SA gel membrane, which has high structural stability and excellent electrochemical properties, and its conductivity is 5.874 S / m, which is much higher than that of commercially available cellulose paper (about 3.5 times).

[0006] The second object of the present invention is to provide a method for preparing a cellulose hydrogel membrane, which adopts biologically renewable raw materials, has a simple preparation process, is low in cost, and meets the requirements of industrial production.

[0007] The third purpose of the present invention is to provide an application of cellulose hydrogel membrane, which is used as a gel electrolyte and assembled into a supercapacitor with a carbon cloth electrode, and still maintains a capacitance retention rate of 60.7% at a high current density (50 mA / cm²), which is better than the traditional BC / MC gel (48.4%). In addition, the gel exhibits a low self-discharge rate (voltage retention rate of 92.4% after 4000 s) and excellent energy density (77.3 μWh / cm²), and has important application potential in the field of flexible energy storage.

[0008] In order to achieve the above technical objectives, the present invention provides a method for preparing a cellulose hydrogel film, which comprises the following steps:

[0009] 1) removing impurities and crushing the fruit-like bacterial cellulose to obtain a bacterial cellulose dispersion;

[0010] 2) Sodium alginate is dissolved in a urea-sodium hydroxide mixed solution and frozen, and then microcrystalline cellulose and bacterial cellulose powder are added in sequence, and quickly stirred to form a white viscous liquid. The white viscous liquid is defoamed and acid precipitated to obtain a cellulose hydrogel membrane.

[0011] The key to the present invention is to modify the composite gel of bacterial cellulose (BC) and microcrystalline cellulose (MC) by introducing sodium alginate (SA). The introduction of SA significantly enhances the network structure of the gel, improves its compactness through hydrogen bonding, and reduces the porosity, thereby obtaining a BC / MC / SA cellulose gel membrane with high structural stability and excellent electrochemical performance. The results show that the conductivity test shows that the conductivity of the BC / MC / SA gel is 5.874 S / m, which is slightly lower than that of the BC / MC gel (7.125 S / m), but much higher than that of the commercially available cellulose paper (about 3.5 times). As a gel electrolyte of a supercapacitor, BC / MC / SA exhibits excellent electrochemical performance: at a current density of 2 mA / cm², its specific capacitance is 1113 mF / cm², and at a high current density (50 mA / cm²), the capacitance retention rate reaches 60.7%, which is significantly better than BC / MC gel (48.4%). In addition, the BC / MC / SA-based supercapacitor exhibited a low self-discharge rate (voltage retention rate of 0.924 V after 4000 s) and a low leakage current (11.8 μA after 7200 s), further confirming the robustness of its structure. Energy density and power density tests showed that the energy density of BC / MC / SA was 77.3 μWh / cm² at a power density of 500 μW / cm², and it still maintained 46.9 μWh / cm² even at a high power density of 25000 μW / cm², showing good practical application potential.

[0012] As a preferred solution, the impurity removal process is: soaking in water for 5 to 15 minutes, ultrasonic treatment for 3 to 10 minutes, then changing the water, and repeating the water soaking and ultrasonic treatment for more than 5 times. The impurity removal process can remove the hydrophilic small molecules in the fruit-like bacterial cellulose.

[0013] As a preferred solution, in the urea-sodium hydroxide mixed solution, the urea mass concentration is 10-20%, and the sodium hydroxide mass concentration is 5-10%. In the preferred urea-sodium hydroxide mixed solution, bacterial cellulose powder and microcrystalline cellulose can be fully dissolved, which is conducive to obtaining a uniform hydrogel.

[0014] As a preferred solution, the mass ratio of microcrystalline cellulose to sodium alginate is 20:0.1-1. As the SA ratio increases, the conductivity of the corresponding BC / MC / SA hydrogel membrane gradually increases. When the SA ratio increases to 20:0.5, the conductivity of the corresponding BC / MC / SA hydrogel membrane increases. 1 The conductivity of the gel increased to 5.874 S / m, reaching the maximum, which may be due to the introduction of a large number of oxygen-containing functional groups by SA, which increased the hydrophilicity and promoted the storage and transfer of charges. 2The conductivity of the gel decreased, which may be due to the increase in SA content, the structure became more compact, which hindered the rapid transfer of charge to a certain extent. 1 The conductivity of gel is the best.

[0015] As a preferred solution, the mass ratio of microcrystalline cellulose to bacterial cellulose dispersion is 30:0.5-1.5, wherein the bacterial cellulose dispersion is measured by its dry basis mass. The hydrogel composed of microcrystalline cellulose and bacterial cellulose presents a fiber network structure with nanoparticles, wherein the fibrous structure mainly comes from BC and the nanoparticles come from MC. The combination of the two in a certain ratio makes the gel exhibit better mechanical properties. If the proportion of bacterial cellulose is too high, the mechanical properties will be reduced.

[0016] The invention also provides a cellulose hydrogel membrane, which is obtained by the preparation method.

[0017] The present invention also provides an application of a cellulose hydrogel membrane, which is applied as a flexible supercapacitor gel electrolyte.

[0018] The cellulose hydrogel membrane (BC / MC / SA) of the present invention, as a gel electrolyte for supercapacitors, exhibits excellent electrochemical properties, has high energy density and power density, and has good practical application potential.

[0019] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0020] The present invention modifies bacterial cellulose (BC) and microcrystalline cellulose (MC) composite gel by introducing sodium alginate (SA) to obtain a BC / MC / SA cellulose gel membrane with high structural stability and excellent electrochemical performance. The conductivity of the obtained BC / MC / SA gel is 5.874 S / m, which is slightly lower than that of BC / MC gel (7.125 S / m), but much higher than that of commercially available cellulose paper (about 3.5 times). As a gel electrolyte for supercapacitors, BC / MC / SA exhibits excellent electrochemical performance: at a current density of 2mA / cm², its specific capacitance is 1113 mF / cm², and at a high current density (50 mA / cm²), the capacitance retention rate reaches 60.7%, which is significantly better than BC / MC gel (48.4%). In addition, the BC / MC / SA-based supercapacitor exhibits a low self-discharge rate (voltage retention rate of 0.924 V after 4000 s) and a low leakage current (11.8 μA after 7200 s), further confirming the stability of its structure. Energy density and power density tests show that the energy density of BC / MC / SA is 77.3 μWh / cm² at a power density of 500 μW / cm², and remains at 46.9 μWh / cm² even at a high power density of 25000 μW / cm², showing good potential for practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Infrared spectra of BC / MC / SA and BC / MC.

[0022] Figure 2 (a, b) are SEM images of BC / MC at different magnifications; (c, d) are SEM images of BC / MC / SA at different magnifications.

[0023] Figure 3 The conductivity diagram of BC / MC / SA gel at different MC and SA ratios.

[0024] Figure 4 The conductivity diagrams of BC / MC / SA, BC / MC, and cellulose paper.

[0025] Figure 5 Electrochemical performance of supercapacitors assembled by BC / MC / SA with different MC to SA ratios: (a) GCD curve; (b) CV curve; (c) EIS curve; (d) relationship between specific capacitance and current density; (e) leakage current curve; (f) self-discharge curve.

[0026] Figure 6Electrochemical performance of supercapacitors assembled with different BC / MC / SA, BC / MC and cellulose paper: (a) GCD curve; (b) CV curve; (c) EIS curve; (d) rate performance curve; (e) leakage current curve; (f) self-discharge curve; (g) relationship between power density and energy density. DETAILED DESCRIPTION

[0027] The following specific examples are intended to further illustrate the present invention rather than to limit the scope of protection of the claims.

[0028] The reagents used in the following specific examples are all conventional commercially available reagents.

[0029] Chemical structure characterization of cellulose gel membrane: The chemical structure of cellulose gel membrane is tested by infrared spectrometer using attenuated total reflection Fourier transform infrared (ATR). Sample preparation method: The cellulose gel membrane is freeze-dried.

[0030] Microscopic morphology characterization: The microscopic morphology of the cellulose gel membrane was characterized by scanning electron microscopy (SEM). Sample preparation method: The freeze-dried BC / MC / SA cellulose gel membrane was directly glued to the sample stage with conductive glue and gold-sprayed for 150 s.

[0031] Ionic conductivity test: A 1 cm × 1 cm cellulose gel membrane and a stainless steel mesh electrode sheet were assembled into a "sandwich" device, and an electrochemical impedance spectroscopy test was performed using a CHI760E electrochemical workstation to obtain the solution resistance R. The conductivity was then calculated using the formula.

[0032] Conductivity σ (mS·cm -1 )The calculation formula is shown below:

[0033]

[0034] Where L (cm) represents the average gel thickness; R (Ω) represents the resistance of the tested solution; S (cm 2 ) represents the area of ​​the stainless steel mesh and the gel facing each other

[0035] Electrochemical performance: Test items and conditions: (1) Cyclic voltammetry (CV): Test voltage window 0.0 V - 1.0 V, scan rate 5 mV·s -1 , draw the current density-voltage curve, the current density calculation formula is: I*1000 / S, I (A) is the charge and discharge current, S (cm 2 ) is the effective area of ​​the electrode sheet. (2) Constant current charge and discharge test (GCD): The current density tested is 1, 2, 5, 10, 20, 30, and 50 mA cm-2 , the voltage window is 0.0-1.0 V. (3) Electrochemical impedance spectroscopy (EIS): the applied amplitude is 5 mV, the frequency range is 100 kHz to 0.01 Hz. (4) The self-discharge performance is tested by open circuit voltage-time, the duration is 4000 s, and the voltage-time curve is recorded. (5) The leakage current is the current collected by keeping the supercapacitor at a constant voltage of 1.0 V, and the measurement time is 7200 s.

[0036] Electrochemical related data calculation: specific capacitance (C, mF / cm 2 ): , where I, Δt, S and ΔV are the current size, discharge time, area of ​​single electrode and voltage difference in GCD test respectively.

[0037] Energy density (E, μWh / cm 2 ): , where C and V are the specific capacitance and window voltage in the GCD test respectively.

[0038] Power density (P, μW / cm 2 ): , where E and Δt are the energy density and discharge time in the GCD test, respectively.

[0039] Example 1

[0040] 1. Pretreatment of bacterial cellulose:

[0041] First, soak 200 g of fruit-like bacterial cellulose (BC) in deionized water for 10 min, and then ultrasonicate for 5 min. After changing the deionized water, repeat the above operation for more than 5 times to remove impurities. Then, grind the fruit-like cellulose into rice paste using a wall-breaking machine.

[0042] 2. Preparation of cellulose gel membrane:

[0043] (1) First, take 2.4 g of urea and 1.4 g of sodium hydroxide and add them to a small beaker containing 15.6 mL of deionized water, and stir until they are completely dissolved. Then, add a certain amount of sodium alginate (SA) to the above solution, stir and ultrasonically treat to form a uniform and transparent solution, seal it and place it in a refrigerator for pre-freezing for 2 h.

[0044] (2) Take 1.15 g of microcrystalline cellulose (MC) and 0.036 g of BC and add them to the frozen solution in (1) in sequence. Stir rapidly for 5 min to form a white viscous solution.

[0045] (3) Pour the viscous liquid in (2) into a centrifuge tube and centrifuge at 2000 r for 2 min to remove bubbles.

[0046] (4) Take 2 mL of the viscous liquid in (3) and spread it evenly on the bottom of the beaker. Then slowly add 0.5 M sulfuric acid solution until the cellulose gel is precipitated into a membrane. Soak it in deionized water to remove impurities, and finally obtain a cellulose gel membrane (BC / MC / SA).

[0047] The mass ratios of MC to SA were 20:0.1, 20:0.5, and 20:1, respectively. The prepared cellulose gel membranes were named BC / MC / SA, BC / MC / SA, respectively. 1 and BC / MC / SA 2 In addition, BC / MC hydrogel films were prepared without adding SA under the same conditions.

[0048] 3. Preparation of activated carbon cloth:

[0049] The carbon cloth was activated by mixed acid oxidation method. The specific steps are as follows: the carbon cloth was immersed in 20 mL of concentrated H 2 SO 4 and 10 mL concentrated HNO 3 To the solution mixture, 3 g KMnO 4 , react at 35℃ for 3 h, then add 100 mL of distilled water. Then add H 2 O 2 The solution was stirred until it became clear, and the carbon cloth was transferred to a 1L beaker. The pure water was replaced every 8 h to remove impurities, and finally activated carbon cloth (CC) was obtained.

[0050] Figure 1 The infrared spectra of BC / MC / SA and BC / MC are shown in Figure 2. Among them, BC / MC has an infrared spectrum of 1023 cm -1 About 1640 cm -1 3339.27 cm -1 The absorption peaks on the left and right are attributed to the CO stretching vibration, C=O stretching vibration and OH vibration peaks in the BC / MC structure. After adding SA, the corresponding BC / MC / SA infrared spectrum is at 3340 cm -1 About 1640 cm -1 and 1023 cm -1 The characteristic peaks of OH, C=O and CO also appeared at 1644.24 cm -1 3356.7 cm -1 The characteristic peaks of C=O bond and OH shifted. This may be because the introduction of SA introduced more C=O and OH functional groups on the one hand, and formed hydrogen bonds with BC and MC on the other hand, so that the vibration peaks of C=O and OH shifted.

[0051] The morphology of BC / MC and BC / MC / SA materials is as follows Figure 2 As shown. Among them, the SEM image of BC / MC ( Figure 2 Figures a and b) show a fiber network structure with nanoparticles. The fibrous structure mainly comes from BC, and the nanoparticles come from MC. This fiber-particle cross-linked structure gives the gel good mechanical properties. In contrast, after adding SA, the structure of BC / MC / SA becomes dense, the porosity decreases, and the nanoparticles disappear ( Figure 2 c and d). This may be due to the reaction between the oxygen-containing functional groups in SA and the oxygen-containing functional groups in BC and MC to form hydrogen bonds, thereby increasing the solubility of BC and MC. Stronger hydrogen bonding can further enhance the strength of cellulose gel.

[0052] Conductivity analysis: Effect of different MC to SA ratios on BC / MC / SA gel conductivity:

[0053] Figure 3 The conductivity of BC / MC / SA gel prepared with different MC to SA ratios. When the MC to SA ratio is 20:0.1, the conductivity of the corresponding BC / MC / SA hydrogel film is 4.717 S / m. When the MC to SA ratio is increased to 20:0.5, the conductivity of the corresponding BC / MC / SA hydrogel film is 4.717 S / m. 1 The conductivity of the gel increased to 5.874 S / m. This may be due to the introduction of a large number of oxygen-containing functional groups by SA, which increased the hydrophilicity and promoted the storage and transfer of charges. When the ratio of MC to SA continued to increase to 20:1, BC / MC / SA 2 The conductivity of the gel decreased to 3.577 S / m. This may be because as the SA content increased, the structure became more compact, which to some extent hindered the rapid transfer of charges. It can be seen that when the ratio of MC to SA was 20:0.5, the corresponding BC / MC / SA 1 The conductivity of gel is the best.

[0054] Comparative analysis of electrical conductivity of BC / MC, BC / MC / SA gel and cellulose paper: Figure 4 The conductivity comparison chart of BC / MC, BC / MC / SA gel and cellulose paper. It can be seen from the comparison that the conductivity of BC / MC / SA (MC / SA mass ratio is 20:0.5) gel (5.874 S / m) is slightly lower than that of BC / MC gel (7.125 S / m). This may be because the doping of SA makes the gel structure more compact, which hinders the rapid transfer of charges to a certain extent. Despite this, the conductivity of BC / MC / SA gel is still much higher than that of commercially available cellulose paper, about 3.5 times that of cellulose paper.

[0055] Effects of different MC to SA ratios on the electrochemical properties of BC / MC / SA gel membranes:

[0056] Symmetric supercapacitors were assembled with the gel and mixed acid treated carbon cloth (CC) electrodes, and the electrochemical performance was tested. The ratios of MC to SA were 20:0.1, 20:0.5, and 20:1, respectively, and the prepared cellulose gel membranes were named BC / MC / SA, BC / MC / SA, and 1 and BC / MC / SA 2 The electrochemical performance test results are as follows: Figure 5 shown.

[0057] Figure 5 a is the supercapacitor assembled by BC / MC / SA with different MC and SA ratios at 2 mA / cm 2 GCD curves under . All GCD curves show approximately symmetrical triangles, indicating that they have good charge and discharge reversibility. This is mainly because the CC electrode is mainly based on the double layer mechanism.

[0058] Figure 5 Figure b is the CV curve of the device at a scan rate of 5 mV / s. The CV curves of the supercapacitors at different MC to SA ratios are rectangular in shape, and a clear redox peak appears between 0 and 0.2 V, which is attributed to the redox reaction of the oxygen-containing functional groups introduced after the activation of the carbon cloth. The areas enclosed by the CV curves of the devices prepared at different ratios are similar, indicating that their capacitances are comparable.

[0059] Figure 5 Figure c is the EIS curve of the device. In the high-frequency region, the intersection of EIS and the real axis represents the solution resistance (Rs). The diameter of the semicircle in the mid-frequency region represents the charge transfer resistance. The smaller the semicircle, the smaller the charge transfer resistance. Supercapacitors with different MC to SA ratios show a straight line in the low-frequency range, and almost no semicircle is observed in the high-frequency range, indicating that they have low charge transfer resistance and faster ion diffusion. This is because the three-dimensional network of cellulose gel and the close contact between the gel and the electrode are conducive to ion transport.

[0060] from Figure 5 As shown in Figure d, when the ratio of MC to SA is 20:0.5, the corresponding BC / MC / SA gel film has a 2 The capacitance is 1113 mF / cm 2 When the current density increases to 50 mA / cm 2, its capacitance still retains 60.68%, showing excellent rate performance. The excellent electrochemical performance comes from the three-dimensional porous network of the BC / MC / SA gel membrane and its excellent water retention, which greatly promotes the storage and rapid transmission of charge. As the ratio of MC to SA increases, the specific capacitance of the supercapacitor decreases slightly. This may be because as the SA content increases, the gel structure becomes denser, which hinders the rapid transmission of charge to a certain extent.

[0061] Figure 5 In the figure, e and f are the leakage current and self-discharge curves. For the same energy storage device, self-discharge and leakage current are positively correlated. BC / MC / SA, BC / MC / SA 1 and BC / MC / SA 2 After 4000 s under open circuit voltage test, the voltages were 0.924 V, 0.926 V and 0.894 V, respectively, and the leakage currents were 11.8 μA, 11.1 μA and 19.4 μA, respectively, after being kept at 1 V potential for 7200 s. It can be seen that the supercapacitors with different MC to SA ratios all exhibit smaller leakage currents and lower self-discharge drop rates.

[0062] Comparative analysis of electrochemical performance of BC / MC / SA, BC / MC and cellulose paper:

[0063] BC / MC / SA, BC / MC hydrogels and commercially available cellulose paper were used as gel separators and assembled with CC electrodes to form supercapacitors, and their electrochemical properties were compared.

[0064] Depend on Figure 6 As shown in a, BC / MC / SA, BC / MC gel and cellulose paper-based supercapacitors have a 2 The GCD curves at the time of the experiment all showed an approximately symmetrical triangle, showing excellent Coulomb efficiency. The corresponding CV curves also clearly showed the pseudocapacitive peak of the oxygen-containing functional groups in CC ( Figure 6 b). Among them, the CV curve areas of BC / MC / SA gel and BC / MC gel-based supercapacitors are comparable and significantly larger than that of cellulose paper. This is mainly because the three-dimensional structured hydrogel has a better specific surface area and hydrophilicity than cellulose paper, which is more conducive to the storage and rapid transmission of charges, thus showing better electrochemical performance.

[0065] from Figure 6 It can be observed from the high frequency region of EIS in c that the solution resistance of BC / MC is 3.62 Ω. After the introduction of SA, the solution resistance of BC / MC / SA drops to 2.61 Ω. This may be because SA introduces a large number of oxygen-containing functional groups, which increases the hydrophilicity and thus reduces the solution resistance of BC / MC / SA.

[0066] Figure 6 Medium dBC / MC / SA, BC / MC, cellulose paper-based supercapacitors at 1 mA / cm 2 The specific capacitance at the current density is 1113 mF / cm 2 、1167.6 mF / cm 2 and 1074.4 mF / cm 2 At the same time, with the increase of current density, BC / MC / SA showed better electrochemical stability. 2 The capacitance under the condition is 675.45 mF / cm 2 The capacitance retention rate is 60.7%, which is slightly higher than that of cellulose paper (60.2%) and much higher than that of BC / MC (48.4%). It can be seen that the addition of SA can effectively improve the structural stability of cellulose gel membrane, and the stability of the corresponding BC / MC / SA is comparable to that of commercially available fiber paper.

[0067] Figure 6 Figure (e) is the leakage current curve of BC / MC / SA, BC / MC, and cellulose paper-based supercapacitors. The results show that the leakage currents of BC / MC / SA, BC / MC, and cellulose paper after being constant at 1V for 7200 s are 11.8 μA, 13.1 μA, and 14.3 μA, respectively. It can be seen that BC / MC / SA has the lowest residual current and the best performance.

[0068] Figure 6 Figure f is the self-discharge curve of BC / MC / SA, BC / MC, and cellulose paper-based supercapacitors. The results show that the retained voltage values ​​of BC / MC / SA, BC / MC, and cellulose paper after an open circuit voltage-time test duration of 4000 s are 0.924 V, 0.912 V, and 0.873 V, respectively. Among them, the lower self-discharge drop rate of BC / MC / SA-based supercapacitors further confirms the stability of its structure.

[0069] Figure 6 Figure g is the relationship between the power density and energy density of BC / MC / SA, BC / MC, and cellulose paper-based supercapacitors. The stable structure of BC / MC / SA and its relatively excellent capacitance make it show great practical application value. 2 The energy density is 77.3 μWh / cm 2 When the power density increases to 25000 μW / cm 2 , its energy density is still 46.9 μWh / cm 2 .

Claims

1. A method for preparing a cellulose hydrogel film, characterized in that: The following steps are involved: 1) removing impurities and crushing bacterial cellulose to obtain a bacterial cellulose dispersion; 2) Sodium alginate is dissolved in a urea-sodium hydroxide mixed solution and frozen, and then microcrystalline cellulose and bacterial cellulose dispersion are added in sequence, and quickly stirred to form a white viscous liquid. The white viscous liquid is defoamed and acid precipitated to obtain a cellulose hydrogel membrane.

2. The method for preparing a cellulose hydrogel film according to claim 1, characterized in that: The impurity removal process is: soaking in water for 5 to 15 minutes, ultrasonic treatment for 3 to 10 minutes, then changing the water, and repeating the water soaking and ultrasonic treatment for more than 5 times.

3. The method for preparing a cellulose hydrogel film according to claim 1, characterized in that: In the urea-sodium hydroxide mixed solution, the mass concentration of urea is 10-20%, and the mass concentration of sodium hydroxide is 5-10%.

4. The method for preparing a cellulose hydrogel film according to claim 1, characterized in that: The mass ratio of the microcrystalline cellulose to sodium alginate is 20:0.1-1.

5. The method for preparing a cellulose hydrogel film according to claim 1, characterized in that: The mass ratio of the microcrystalline cellulose to the bacterial cellulose dispersion is 30:0.5-1.5, wherein the bacterial cellulose dispersion is measured by its dry basis mass.

6. A cellulose hydrogel film, characterized in that: Obtained by the preparation method according to any one of claims 1 to 5.

7. The use of a cellulose hydrogel membrane according to claim 6, characterized in that: Application as flexible supercapacitor gel electrolyte.

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