Preparation And Electrochemical Properties Of Solid-state Flexible Supercapacitors Based On Double Network Gel

At present,with the gradually increase of using smart electronic products by people,the need for performance of device also get growing correspondingly.In recent years,electronic devices have attracted a lot of attention in the market with the advantages of being portable,wearable and foldable,and are gradually becoming commercialized.Among these electronic devices,flexible supercapacitors stand out because of their high power density,moderate energy density,fast charge and discharge speed,long cycle life and good mechanical flexibility.And the electronic equipment occupies an increasing proportion.The key to the design of flexible supercapacitors lies in the flexible electrode materials with high performance and easy processing and designing and preparing theelectrolyte materials.In recent years,the electrodes of solid-state supercapacitors are mainly made of transition metal oxides,conducting polymers and carbonaceous materials,and the electrolyte usually use polymer hydrogel containing H₂SO₄.Among these materials,hydrogels are considered as ideal candidates due to their flexible three-dimensional networks,high deformability,high hydrophilicity andserving as electrodes and electrolytes at the same tine.Hydrogels with high ionic content can provide high ionic conductivity while maintaining their original shape and size,thereby reducing the risk of liquid leakage during various mechanical deformations.In addition,the novel hybrid hydrogel composed of active material and polymer matrix possesses inherent porous structure,excellent electrical conductivity and flexibility.However,there are still several bottlenecks to develop solid-state supercapacitors based on hydrogels.Firstly,the high interfacial impedance between the current collector and the hydrogel electrode results in a large electron transport and diffusion resistance from the electrode to the current collector.Secondly,the incompatibility between active materials and hydrogel matrix further limits the processability of such hydrogels.As a result,many high-performance active materials cannot be incorporated into hydrogel electrodes,and the content of suitable active materials is also limited to a low level.Therefore,it is still an ambitious challenge to develop a new strategy for fabricating solid-state supercapacitors with high performance.Based on these,the main research works and results are as follows:（1）A novel dual network gel system was developed,and a novel lyotropic liquid crystal was introduced into the polyvinyl alcohol（PVA）hydrogel system,which effectively enhanced the compatibility between the active material and the hydrogel matrix.,and increased the content of active material（up to 25.0 wt%）.The electrodes of solid-state supercapacitors were coated on carbon cloth withcross-linking and curing,which effectively reducing the migration resistance of electrodes transfering from electrode material to current collector.The experimental results show that the specific capacitance value of the supercapacitor based on the double-network hydrogel electrode can reach 871.4 m F/cm~2at the current density of 0.5m A/cm~2,the corresponding area energy density is 140μWh/cm~2,and the areal power density is 270μW/cm~2.After 5000 charge-discharge cycles,the specific capacitance remained about 85.5%,indicating its excellent mechanical and electrochemical stability.In addition,we also used dual network gel precursors for 3D printing inks to print electrodes on carbon cloth for assembling all-solid-state supercapacitors.The experimental results show that the CV,GCD and EIS curves of the supercapacitors by 3D printed are similar to those of the blade-coated supercapacitors.When the current density is 0.5 m A/cm~2,the specific capacitance of the supercapacitor is about 483.9 m F/cm~2,the corresponding areal energy density is 68.2μWh/cm~2,and the areal power density is 2511.9μW/cm~2.（2）On the basis of the double network hydrogel,the mixed solvent of H₂SO₄,dimethyl sulfoxide（DMSO）and H₂O was used as the double network gel solvent,so that the double network organohydrogel can be produced at a high temperature of 90°C and an ultra-low temperature of-80°C.Its gel precursor was coated between two sheets of PANI-carbon cloth electrodes,and after cross-linking and curing,it was used as an electrolyte for wide-temperature solid-state supercapacitors.By optimizing the content of DMSO,the best double-network organohydrogel electrolyte was prepared.At the ultra-low temperature of-80°C,the capacitance retention rate of the supercapacitor based on the double-network organohydrogel electrolyte reached 84.3%.（3）On the basis of the double-network hydrogel electrolyte membrane,the PANI-double-network hydrogel membrane was prepared to make the polyaniline conductive electrode material on the surface of the gel membrane by in-situ polymerization to form an electrolyte and an electrode.The integrated film was then assembled into a flexible supercapacitor using the PANI-dual network hydrogel film and carbon cloth.By optimizing the aniline concentration,it was found that when the aniline concentration was 0.2 M,the supercapacitors assembled by PANI-double network hydrogel film and carbon cloth had the best performance.The areal specific capacitance is 160.2 m F/cm~2at a current density of 0.2m A/cm~2.When the power density is 101.5μW/cm~2,the energy density of the device is 21μWh/cm~2.78.1%of the capacitance can be maintained after 3000 galvanostatic charge-discharge cycles at 2.0 mA/cm~2.