Research On The Construction And Performance Of A New Gel Electrolyte For Zinc Ion Hybrid Capacitors

Zn-ion hybrid capacitors（ZIHS）possess many advantages,such as high energy density,high power density,high safety and environmental protection.These advantages make it become a promising ideal energy storage device.There are two types of ZIHS:capacitor-type cathode||battery-type anode ZIHS and battery-type cathode||capacitor-type anode ZIHS.Although the basic research of ZIHS has made uncommon achievements,it still confronts many challenges,such as further improving the energy density of ZIHS,increasing the cycle life of ZIHS,broadening the operating temperature range of ZIHS,and inhibiting the dendrite growth of zinc electrode.Therefore,in view of the above aspects,this paper designs and constructs a new type of high-performance gel polymer electrolyte（GPE）to improve the performance of ZIHS.The main contents are as follows:（1）Cellulose reinforced polyvinyl alcohol-based hydrogel was prepared by freeze/thaw cycle with microcrystalline cellulose（MCC）,hydroxyethyl cellulose（HEC）and polyvinyl alcohol（PVA）as raw materials and a suprammolecular gel electrolyte（SGPE）was obtained after absorbing zinc sulphate solution.This polyvinyl alcohol-based SGPE has better mechanical properties.Battery-type cathode||capacitor-type anode ZIHS were assembled by polyvinyl alcohol-based SGPE,activated carbon（AC）anode electrode and Mn O₂ cathode electrode.It could operate stably in a wide voltage range of 0～1.9 V.At 0.1 A g^-1,it exhibited specific capacitance of 31.5 F g^-1,energy density of 15.0 Wh kg^-1 and power density of 65.6 W kg^-1.In addition,the specific capacitance retention of ZIHS is about 78%after 16000 charge-discharge cycles at current density of 2 A g^-1.（2）Polyvinyl alcohol/sodium alginate composite hydrogel was prepared by freeze/thaw cycle with polyvinyl alcohol,sodium alginate（SA）,glycerol and boric acid as raw materials,and another SGPE was obtained after absorbing zinc sulphate solution.Owing to intertwined hydrogen bond and ionic bond networks,the optimized SGPE exhibited high tensile strength of 0.19 MPa and high Zn²⁺conductivity of 89.7 m S cm^-1.Capacitor-type cathode||battery-type anode ZIHS were assembled by polyvinyl glycol/sodium alginate-based SGPE,AC anode electrode and Zn cathode electrode.It can operate stably in a wide voltage range of 0.2～2.0 V.It showed excellent electrochemical properties,such as:good rate capability,low self-discharge rate,high energy density(66.65 Wh kg^-1)and power density(3567.3W kg^-1).More importantly,it displayed unprecedented cycling durability with capacitance retention of～84%and columbic efficiency of 100%after 110,000 cycles at 5 A g^-1 due to the suppressed growth of zinc dendrites by tier upon tier pore-walls in SGPE.（3）A kind of（eutectic point<-90℃）deep eutectic solvent（DES）was prepared with Zinc perchlorate hexahydrate,ethylene glycol（EG）.Then a strategy was adopted to reinforce the properties of Polyacrylamide（PAM）-based GPE by incorporating sulfonated poly（ether ether ketone）（SPEEK）chains.The GPE exhibited excellent flexibility,mechanical property and ionic conductivity of 7.3 m S cm^-1at-40℃.The capacitor-type cathode||battery-type anode ZIHS based on such a GPE could deliver an energy density of 66.83 Wh kg^-1 at a power density of 187.96 W kg^-1 and display outstanding cycling stability with～95.5%capacitance retention after 20000 cycles.Moreover,flexible ZIHS devices had a wide working temperature ranging from-40℃～60℃and could work under various severe conditions,such as pressing,bending,puncturing,and cutting.