Design And Electrochemical Performance Of Aqueous Flexible Energy Storage Devices With High Energy Density

The rapid development of portable and flexible electronics has triggered intensive research activities on aqueous flexible energy storage devices that have high safety,low cost,excellent rate performance and good mechanical robustness.However,the narrow stable electrochemical window of water(?1.23 V)and dissolution of high-capacity electrode materials in aqueous systems seriously hinder the improvement of the energy density and cycling stability.To solve the above issues,we design here sodium and zinc ion devices with excellent electrochemical performance via optimizing the electrolyte and electrode materials.The research contents of this dissertation are as follows:(1)An activated carbon(AC)//MnO₂ sodium-ion asymmetric supercapacitor was designed and assembled by applying binder-free?-MnO₂ nanoflower as cathode,AC as anode and low-cost 17 m Na ClO₄ as electrolyte.Experimental results clearly demonstrate that the strong hydrogen bonds of free water molecules were significantly broken in 17 m Na ClO₄,which broadens the electrochemical stability window of the electrolyte.We further designed a novel sodium polyacrylate(PAM)-17 m Na ClO₄ gel electrolyte with high ionic conductivity and excellent mechanical flexibility and constructed a quasi-solid-state asymmetric supercapacitor.The resulting maximum energy density is 49.8 Wh kg^-1,exceeding many recently reported supercapacitors.Additionally,the device exhibits excellent flexibility under different bending states.(2)A battery-supercapacitor hybrid device was assembled by using battery-type Na Ti₂(PO₄)₃ nanowire array as anode,pseudocapacitive?-MnO₂ nanoflower array as cathode and 17 m Na ClO₄ as electrolyte.Benefiting from the synergistic effect of electrode materials and electrolyte,the device exhibits high capacity(208.6 C g^-1)and wide voltage window(2.8V).Furthermore,a flexible quasi-solid-state rechargeable battery-supercapacitor hybrid device was designed.It delivers high energy densities(76.37 Wh kg^-1),surpassing aqueous Na Ti₂(PO₄)₃//AC battery-supercapacitor hybrid device and AC//?-MnO₂ asymmetric supercapacitor.Interestingly,the practical application of as-prepared hybrid device was successfully demonstrated by powering a digital timer under different bending angles.(3)Aqueous zinc ion batteries(AZIBs)are particularly advantageous due to high theoretical capacity(?820 m Ah g^-1)of Zn/Zn²⁺conversion.Herein,a flexible Zn//K_0.486V₂O₅battery was designed.It delivers a maximum specific capacity of 419.4 m Ah g^-1,which is evidently superior to recently reported Zn//V-based batteries.The performance enhancement should be ascribed to the large interlayer spacing and 1D single-crystalline structure of K_0.486V₂O₅.In addition,15 m Zn Cl₂ electrolyte with limited water molecules significantly prevents the dissolution of K_0.486V₂O₅.Consequently,the Zn//K_0.486V₂O₅ battery exhibits the best cycling stability with?95.02%capacity retention after 1400 cycles.Furthermore,a novel sodium carboxymethyl cellulose-moderate concentration Zn Cl₂ gel electrolyte was designed for the first time and a quasi-solid-state Zn//K_0.486V₂O₅ battery was assembled,capable of delivering a maximum energy density of 83.81 Wh kg^-1,low self-discharge rate,and good environmental(temperature,pressure)suitability.(4)A dual(alkaline and near neutral)electrolyte separated with a K⁺conductive membrane was introduced to assemble a new Fe//MnO₂ battery with high voltage and high energy density.This electrolyte system adequately exploits the high specific capacity and low redox potential of Fe nanorod array as an anode in alkaline solution,and the large capacity and high redox potential of?-MnO₂ nanoflower array as a cathode in near-neutral solution.The as-fabricated Fe//MnO₂ battery demonstrates exceptional electrochemical performance with high capacity and excellent cyclability(8500 cycles).Impressively,it shows a remarkable energy density of 127.34 Wh kg^-1 at 227 W kg^-1 based on the total mass of the active materials.Additionally,the quasi-solid-state gel electrolyte was used to replace the traditional liquid electrolyte,and a new flexible device was first assembled,which can power the red LED screen at bending state.These results clearly demonstrate the promising application potentials of as-prepared Fe//MnO₂ battery in a variety of wearable and portable electronics.