Design Of Multidentate Electrolyte System For Potassium Secondary Batteries And The Study Of The Ionic Solvation Structure

The application of commercial lithium-ion batteries in large-scale energy storage is limited by the shortage of lithium resources and high cost.Potassium has received extensive attention as a natural resource several orders of magnitude higher than lithium.Therefore,potassium-ion batteries are in the hot spot,and the potassium-metal anode is the best anode material for potassium-ion batteries due to its high theoretical specific capacity(687m A h g^-1).However,the unstable plating and stripping process and dendrite growth of potassium anode seriously hinder its development.Therefore,a mixed electrolyte based on tetraethylene glycol dimethyl ether（G4）and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether（TTE）solvents and potassium bis（fluorosulfonyl）imide（KFSI）salt was proposed in this paper.This electrolyte can provide a synergistic effect of multiple coordination sites to regulate the solvation structures of potassium ions and participate in the formation of stable solid electrolyte interphase（SEI）layer with high ionic conductivity,thus promoting the stability of potassium metal plating and stripping process and inhibiting the growth of the dendrites on the surface.The characterizations of symmetric cells show that the batteries assembled with mixture-based electrolyte can be stably cycled over 2000 h with little change in polarization voltage.Meanwhile,the electrochemical impedance spectroscopy measurements show that the R_ctvalues after each cycled could be stable in a small range from 2500 to 2800Ω,indicating the SEI layer is much stable.In order to verify the applicability of the mixture-based electrolyte in the new battery system,we assembled potassium-sulfur batteries for electrochemical characterization.It is found that this electrolyte can not only stabilize the potassium metal anode,but also suppress the shuttle effect caused by the sulfur cathode.We proposed a kind of mixture-based electrolyte system aim to the characterizations of the potassium ions and the problems of the new battery systems.This selection strategy can provide an new idea and direction for the future research of this kind of batteries.