Design And Study Of Non-flammable Electrolytes And Organic Electrode Materials For High-Safety Sodium/Potassium-ion Batteries

Since lithium-ion batteries(LIBs)was invented in the last century,it has been widely used in people's daily life.It is an ideal energy storage device with many advantages such as large specific energy,high voltage,long cycle life and green pollution-free.However,due to the low reserves and high cost of lithium resources,its large-scale use will be limited.The sodium and potassium metal resources are high in the earth's crust and have similar physical and chemical properties as lithium metal.Therefore,sodium/potassium-ion batteries(SIBs/PIBs)have gradually attracted scientists' interest.Similar to LIBs,the development of SIBs/PIBs is also limited by safety issues.This safety problem is mainly caused by the highly flammable carbonate-based electrolyte and electrode materials with poor thermal stability.However,there are still many gaps in the research on the safety of SIBs/PIBs.Therefore,developing non-flammable electrolyte and good thermal stable electrode materials is an important technical approach to promote the safety of SIBs/PIBs.Based on this,this paper explores the non-flammable electrolyte for SIBs/PIBs and the electrode system of organic materials for potassium ion batteries.The contents are as follows:(1)In view of the high flammability of carbonate-based electrolytes commonly used in sodium ion batteries,we used 0.9 M NaPF6 FEC/TFEC electrolyte to improve its safety and electrochemical performance.The research result showed that the fluorinated carbonate electrolyte can be completely incombustible in the direct ignition test;Due to the higher viscosity of the fluorinated solvent,the conductivity of the electrolyte is lower,but it is much higher than the all solid electrolyte;Wide electrochemical window with oxidation window up to 5.2 V;Good compatibility with Prussian blue cathode,which has a capacity of 84 mAh g-1 for 50 cycles.In addition,we explored and explained the good compatibility of the electrolyte with the positive electrode by X-ray diffraction,Fourier transform infrared and scanning electron microscope.(2)We first used the completely non-flammability phosphate as the electrolyte of potassium-ion batteries.The result showed that the room temperature conductivity of the high-concentration electrolyte 3.3 M KFSI/TMP is about 3.49 mS cm-1,a wide electrochemical window can reach 4.2 V,and it has a good compatibility with graphite electrodes,after 80 cycles,214 mAh g-1 reversible capacity was delivered at 60 mA g-1.The electrolyte also has a good chemical compatibility with Prussian blue electrode.These results provide a new option for the development of safe potassium-ion batteries.(3)We first used the organic materials with higher thermal stability as electrodes for potassium-ion batteries.Porous polythiophene(PTh)material was successfully prepared by a green and non-polluting solid-phase grinding method.It delivered a average discharge capacity of 56 mAh g-1 at 30 mA g-1 for 80 cycles.This work provides a new way for safe potassium-ion batteries.