Sodium-Ion Capacitors Based On Multi-Layered Ionogel Electrolytes

The development of next-generation large-scale energy storage techniques is being stimulated by an increasing demand in sustainable and renewable energy resources due to climate change and the lack of enough fossil fuels.Sodium-ion capacitors(SICs)have attracted extensive attentions due to the availability of abundant cheap,environmental friendly sodium resources.Meanwhile,security risks and volume restrictions of energy storage devices have stimulated the study of solid-state sodium-ion capacitors.This thesis will be focusing on the construction of high performance high-voltage solid-state sodium-ion capacitors.In particularly,the studies on structure design,energy storage mechanism and solid electrolyte interface matching of solid electrolyte and electrodes have been performed systemically.Detailed outcomes are presented as follows:(1)An asymmetric ionogel electrolyte was constructed to provide stable electrode/electrolyte interfaces on account of the different energy storage mechanisms of opposite electrodes.In addition,anatase/bronze mixed phase titanium dioxide nanohybrid electrode,TiO2(A)/TiO2(B)@C/CNT,had been prepared by a microwave-assisted solvothermal method.Abundant crystallization sites for titanium dioxide were provided by multiwalled carbon nanotubes(MWCNTs).A high specific-surface-area nanosheet arrays coated with an amorphous carbon layer were obtained.The modification could improve effectively the conductivity of the electrode and shorten the transport distance of sodium ions.Owing to the double kinetic-matchings design,a sodium-ion capacitor could exhibit a high energy density of 94.8 Wh·kg-1 and an ultra-long-term ability of 10000 cycles with a capacity retention rate of 82.4%.This work provides a new strategy to design hybrid capacitors incorporating the electrodes with diverse ion storage mechanisms.(2)A high thermally stable ionogel electrolyte was constructed by employing thermally stable polyacrylonitrile(PAN)and polyimide(PI)as the matrix and ionic liquid as plasticizer.Such an electrolyte would provide a possibility of tolerating high temperature.Note that PAN layer with a high oxidation resistance could provide a stable high-voltage interface with the activated carbon cathode,and effectively expand the working voltage of SICs up to 4.5 V.In addition,the T-Nb2O5/rGO nanohybrid electrode was prepared by an exfoliation-rolling process,its conductivity was improved effectively due to the presence of reduced graphene oxide nanosheets.The combination of nanotubes and high specific-surface-area reduced graphene enhanced the kinetic characteristics of T-Nb2O5/rGO.At 90℃,optimized SIC could provide an ultra-high energy density of 109.9 Wh·kg-1,and a capacity retention rate maintained 91.4%after 6000 cycles.(3)A finite element method,based on the COMSOL Multiphysics software,was used to simulate the ion distribution and voltage distribution in a sodium-ion capacitor.The PDADMATFSI layer was proved to be able to alleviate effectively the concentration gradient and polarization at the anode/electrolyte interface by simulating the distribution of sodium ions.The thickness of the PAN layer was optimized through the simulation of voltage distribution.