Preparation And Performance Study Of Hydrogel-based Flexible Solid-state Supercapacitors In Wide Temperature Range

With the continuous progress of the world economic level and the improvement of the national living and cultural level,people’s demand for high-performance flexible electronic devices is getting higher and higher,especially some intelligent electronic devices,such as electronic skin.Under the rapid development of these years,portable,lightweight,wearable intelligent electronic devices have become the focus of people’s attention,and with the continuous maturity of technology gradually tends to commercialize,among which flexible supercapacitors have received extensive attention in the industry because of their advantages of fast charging and discharging speed,high power density,good cycle stability and good flexibility.Hydrogel-based flexible solid-state supercapacitors have become an important development direction of flexible supercapacitors due to their easy packaging,excellent comprehensive performance such as flexibility,safety,and electrochemical energy storage.However,traditional hydrogel-based flexible solid-state supercapacitors also face the following problems and challenges,which greatly limit their practical applications and applications:(1)moisture is easy to freeze at sub-zero temperatures,resulting in low ionic conductivity,which greatly affects the electrochemical performance of flexible supercapacitors;(2)too high temperature will also make the structure of the hydrogel electrolyte unstable,and the water will evaporate too quickly,which will affect the electrochemical performance of the flexible supercapacitor;(3)hydrogels generally have low mechanical strength,and when mechanical damage occurs,it will lead to a significant decrease in the performance of supercapacitors or even failure.Therefore,the development of flexible supercapacitors with high electrochemical performance,excellent environmental adaptability and mechanical stability remains a huge challenge.Based on the above application requirements and technical problems,this paper starts from the structure and formula design of hydrogels,combined with new electrolyte solutions,develops hydrogels with high and low temperature resistance and self-healing,and applies them to flexible solid-state supercapacitors,the main research work and innovation results are as follows:(1)A new low-temperature resistant(or freeze-resistant)organic hydrogel electrolyte was developed,composed of graphene/PVA and dimethyl sulfoxide/water/sulfuric acid electrolyte,the resulting electrolyte not only has high mechanical strength(tensile strength=2.58 MPa)and ionic conductivity(3.9 S/m),but also has excellent low temperature resistance,and still maintains high ionic conductivity(1.0 S/m)at ultra-low temperature of-65°C.In addition,flexible solid-state supercapacitors were prepared and assembled by freeze-thawing crosslinking,and the assembled supercapacitors exhibited high specific capacitance(252.0 F/g),energy density(35.3 Wh/kg)and power density(3192 W/kg)at room temperature.At the same time,even at an extremely low ambient temperature of-65°C,it has an excellent capacitance retention rate of 93%,which solves the contradiction that the specific capacitance and low-temperature retention rate of traditional low-temperature flexible solid-state supercapacitors are difficult to optimize at the same time.(2)A novel high,low temperature and self-healing ternary network organic hydrogel electrolyte consisting of graphene/boric acid/polyvinyl alcohol matrix and dimethyl sulfoxide/water/sulfuric acid electrolyte was developed,and it was assembled with two PANI/carbon cloth electrodes to form a flexible solid-state supercapacitor with a sandwich structure,which showed high capacitance retention(90%)after 5 cutting/self-healing cycles;At the same time,the specific capacitance at 65°C and-65°C is about 237.8 F/g and 152 F/g,respectively,and the corresponding capacitance retention rate of supercapacitors is about 110.5%and 70.7%,respectively.It solves the problem that traditional flexible solid-state supercapacitors are difficult to achieve high temperature resistance and self-healing optimization at the same time.(3)A new flexible solid-state supercapacitor was constructed by combining a carbon fiber/PANI electrode material and freeze-thawing method based on a wide temperature range hydrogel electrolyte based on graphene/polyvinyl alcohol/dimethyl sulfoxide,when the current density is 0.5 m A/cm~2,the specific capacitance of the flexible supercapacitor is 168 m F/cm~2,and even if the current is increased by 5 times,the supercapacitor still has a capacitance retention rate of 83.5%.In addition,the low-temperature electrochemical performance of the flexible solid-state supercapacitor was tested,and the specific capacitance was 110.24 m F/cm~2at-60°C,and its corresponding capacitance retention rate was 74.2%.It solves the problem of low electrochemical performance of traditional hydrogel-based flexible superbase capacitors at low temperatures.