Development And Research Of High-concentrated Salt Electrolyte Based On Potassium-ion Battery Anode Material

Potassium-ion batteries are potential substitutes for lithium-ion batteries due to their rich potassium resources and high energy density.As one of the main components of batteries,the electrolyte plays an important role in the electrochemical performance of batteries.Therefore,it is of great significance for the future commercialization of potassium-ion batteries to study the effects of electrolyte system and its component,salt concentration and other factors on the performance of potassium-ion anode materials.In this paper,a series of new electrolytes were developed based on KFSI,ester and ether solvents,which were used in potassium-ion batteries based on carbon-based anode materials and metal oxide anode materials.In view of the poor cycling performance and low capacity of the negative electrode of potassium ion battery,the influence of salt concentration and solvent structure on the electrochemical performance of negative electrode materials has been systematically analyzed.The formation mechanism of electrolyte boundary film（SEI）and the process of potassium ion dissolvent（des）are discussed combined with theoretical calculation.（1）The effects of KFSI concentration and molecular chain length of linear ester solvent and ether solvent on the performance of graphite anode were studied.The results show that the increase of KFSI salt concentration can effectively improve the cycling performance of graphite anode in ester electrolyte system.In 4 M KFSI/EC+linear ester electrolyte system,using methyl butyl carbonate（BMC）with longer branched chain as solvent can make graphite electrode have higher reversible specific capacity and long cycle performance.At 1 C(1 C=280 m A g^-1)current density,graphite electrode can stably cycle for 300 cycles and maintain265.4 m Ah g^-1 reversible capacity.By Raman,FTIR,XPS and TEM,it is found that the length of linear ester has little effect on the electrochemical performance of SEI film,mainly by affecting the desolvation process of K⁺.The results show that the increase of KFSI salt concentration can also effectively improve the cycling performance of graphite anode in ether electrolyte.However,the graphite anode can not discharge in 2 M KFSI/tetraethylene glycol dimethyl ether（G4）,but in higher concentration 7 M KFSI ether electrolyte,due to higher viscosity,the capacity has a rising process.Compared with the electrolyte of 4 M KFSI/EC+linear ester,the capacity of graphite anode is slightly lower and its cycling performance is poor at 1 C.Because of the thinner SEI of graphite electrode in ether system,the lower reversible capacity is due to its lower ionic conductivity.（2）A novel Bi₂O₃ nanoflower structure was synthesized,and the effects of electrolyte solvents and salt concentration on Bi₂O₃ anode were investigated.It was found that the electrochemical performance of ester electrolyte（1.5 M KFSI/EC+DEC）was better than that of ether electrolyte（1.5 M KFSI/DME）at the same KFSI salt concentration.At the same time,the long cycle stability of Bi₂O₃ anode was significantly improved by increasing the concentration of KFSI salt in ester electrolyte to 4.0 M.