Cyclic Ether-based Electrolyte And Interfacial Properties Of Between Electrode And Electrolyte In Potassium-ion Batteries

Potassium-ion batteries(KIBs)are considered as a vital complementary technology for lithium-ion batteries(LIB s)in large-scale applications due to its advantages of relatively low cost,suitable working potential and fast K+migration.However,at present,KIBs are mainly faced with the key problem of poor stability of electrode/electrolyte interface and consequent serious performance degradation.Therefore,it is very important to solve the key problem of poor stability of electrode/electrolyte interface for the development of KIBs.Based on this,the electrode/electrolyte interface stability is improved by optimizing the composition and structure of the electrolyte,and the performance of the battery is improved.First of all,a strategy by regulating the solvation structure of ester electrolyte with cyclic ether was firstly proposed to construct a stable solid electrolyte interface layer(SEI)on the surface of graphite electrode,which significantly improved the potassium storage performance of graphite.The mechanisms of SEI formation and its influence on the electrochemical performance were revealed by in-situ spectroscopy and electrochemical characterization techniques.The related research results provide a new idea for the design of high-performance electrolyte.On this basis,based on the ring-opening polymerization of cyclic ether,gel polymer electrolytes with high oxidation potentials and good interface stability were designed enabling highperformance potassium ion solid state batteries,which provides important theoretical guidance and experimental reference for the design of highperformance solid potassium ion battery.The main research results are as follows:(1)By introducing cyclic ether solvent(tetrahydrofuran,THF)into traditional ester electrolyte,the solvation structure of electrolyte was regulated,and the two-electron reduction decomposition reaction of EC was promoted.Combined with ring opening polymerization reaction of cyclic ether itself,the electrochemically stable,highly ionic conductive,K2CO3-and PEO-rich SEI layer was constructed.Electrochemical studies show that:When the charge and discharge current density is 84 mA g-1,the first charge capacity of graphite anode in EC/DEC/THF electrolyte is 268.6 mAh g-1,and the capacity remains 196.1 mAh g-1(retention rate is 73.0%)after 100 cycles,which is 3 times that of graphite electrodes using EC/DEC and EC/DEC/G2 electrolytes.(2)On the basis of the above research,gel polymer electrolytes are formed through ring-opening polymerization of cyclic ether electrolyte,which effectively inhibited the reactivity of ether oxygen bond and improved the oxidation resistance potential of electrolyte.By adding succinonitrile,the polymerization state of the polymer chain was regulated,and the ionic conductivity of the gel polymer electrolyte was enhanced to 10-5 S cm-1 at room temperature.It is found that the gel polymer electrolyte can form the electrode/electrolyte interface with good stability and low interfacial impedance on the surface of potassium metal electrode and Prussian blue positive electrode by electrochemical characterization,which makes K/K symmetric battery and K/PB solid state battery exhibit excellent electrochemical stability.The polarization voltage is only 0.2 V at a K depositing/dissolving current rate of 0.1mA cm-2 for K/K symmetrical battery,and the polarization voltage remains unchanged after 100 h cycle.When K/PB solid state battery is charged and discharged at operating potential of 2.5-4.2 V and current density of 100 mA g-1,the discharge capacity is 70 mAh g-1,and the capacity retention rate is 88.5%after 100 cycles.