Eutectogel Electrolytes For Quasi-Solid-State Zinc-Based Energy Storage Devices

Aqueous zinc-based energy storage devices（zinc ion hybrid capacitors（ZHSCs）,zinc ion batteries（ZIBs））are potential energy storage devices for next-generation wearable electronic devices due to their high safety,low cost,and high energy density.Conventional electrolytes are generally dilute solutions of zinc salts,and ZHSCs and ZIBs have been facing narrow voltage windows and low energy densities due to the low decomposition voltage of water（1.23 V）.As a result of zinc dendrite growth and side reactions,the cycle life of ZHSCs and ZIBs is shortened,which seriously restricts the development of aqueous zinc-based energy storage devices.There is a new type of solvent known as deep eutectic solvent（DES）,which has low volatility,wide voltage window,and safe and environmentally friendly properties.Based on DES,a polymer backbone is introduced to create eutectogel.Using it as an electrolyte for aqueous Znbased energy storage devices can effectively solve the above problems.Based on this,two kinds of eutectogels were prepared and used as electrolytes for ZHSCs and ZIBs,respectively.A series of characterization and testing was performed,and flexible wearable devices were assembled,demonstrating their great potential to be used in flexible portable electronic devices.In Chapter 2,eutectogels based on ternary DES of acrylamide（AM）,zinc perchlorate（Zn（ClO₄）₂）,and water were prepared.The process is simple and convenient and does not require the introduction of external initiators and cross-linkers.The prepared ZnPAM^-1 gel exhibits a high ionic conductivity of 51.7 mS cm^-1.Due to the inhibition of the free water activity in DES,the voltage window of the constructed flexible ZHSC was extended to 0-2.2 V.Moreover,the ZHSC in situ formed exhibits a maximum energy density of 117.5 W h kg^-1 at a power density of 833.8 W kg^-1 and shows admirable cycling stability with 87.6%capacitance retention after 4000 cycles.In addition,the supercapacitor possesses remarkable temperature stability within a range of-20 to 70℃.Furthermore,the assembled flexible device demonstrates excellent bendability from 0° to 180° without scarifying capacitance,displaying great potential for flexible wearable electronic devices.In summary,such a feasible approach provides further insight into the exploration of innovative eutectogel electrolyte systems for assembling quasi-solid-state flexible high-energy storage devices.In Chapter 3,a novel polyzwitterionic eutectogel（PSPE）is constructed with DES（ChCl-EG-Urea）,zwitterionic sulfobetaine,and Zn（ClO₄）₂.Here,we first prepared DES（ChCl-EG-Urea）,which was used as a solvent to dissolve Zn（ClO₄）₂-6H₂O.Afterward,amphoteric monomers（3-（（2（methacryloyloxy）ethyl）dimethylammonio）propane-l-sulfonate（SPE））were added,and a polymerization reaction occurred to produce PSPE.Compared to common hydrogels,the PSPE eutectogel contains no free water,thus widening the electrochemical window and suppressing side reactions and zinc dendrities growth.The zwitterionic structure of sulfobetaine in the eutectogel provided ion migration channels facilitating the electrolyte ion transport,which yielded a high ion conductivity of 7.1 mS cm^-1 at 20℃.The charged groups of the polyzwitterion can also guide the distribution of the ions and promote smooth zinc deposition.Consequently,the Zn//Zn cells with the PSPE eutectogel achieve a long cycle life of over 2200 h at 1 mA cm^-2.Furthermore,the flexible battery assembled with a V₂O₅ cathode and PSPE eutectogel electrolyte can light up the LEDs under different bending angles.Besides,the low volatility of DES and strong electrostatic interactions of zwitterionic groups allow the eutectogel to have excellent water retention.At 60℃ unsealed condition,the PSPE eutectogel retained 87.9%of its initial weight after 55 h.Such a highly conductive and anti-dehydration polyzwitterionic eutectogel shows promising applications in wearable energy storage devices.