Synthesis Of Novel Polycarbonate Electrolytes Towards High Performance Solid State Lithium Batteries

The classic lithium ion batteries based liquid electrolyte suffers from inflammable and explosive.People have begun to focus on solid polymer electrolyte as it can effectively solve the defects.Polymer electrolytes have been widely used in the lithium ion battery for many portable electronic devices on account of their advantages,such as light quality,good viscoelastic and easily processed into film,etc.With development of electrode materials,polymer electrolyte played a key role in the solid polymer lithium ion battery.（1）Two novel polycarbonates PDEC and PTEC were synthesized via transesterification reaction.They were all slight yellow amorphous solid at ambient temperature,and the glass transition temperature were below-20 oC,which can be used as polymer electrolyte in lithium ion batteries.The polycarbonate with molecular weight around of 8000 g·mol-1 was synthesized by diethyl carbonate and corresponding diols with the mole ratio of 1.2:1.（2）The sustainable cellulose-supported PDEC-LiTFSI and PTEC-LiTFSI polymer electrolytes have been developed by solution casting technique,respectively.Experimental results showed that the ionic conductivity of the PTEC-LiTFSI polymer electrolyte was than that of PDEC-LiTFSI.Because the PTEC has lower glass transition temperature,which can improve the motion activity of molecular chain segment.It was proven that the optimized ionic conductivity of PTEC based electrolyte reached up to 1.12×10-5 S·cm-1 at 25 °C with a decent lithium ion transference number of 0.39 and a wide electrochemical window about 4.5 V vs.Li+/Li.In addition,the PTEC based Li/LiFePO₄ cell could be reversibly charged and discharged at 0.05 C-rates at ambient temperature.Moreover,the higher voltage Li/LiFe_0.2Mn_0.8PO₄ cell（cutoff voltage 4.35 V）possessed considerable rate capability and excellent cycling performance even at ambient temperature.（3）Design and synthesis of a new type of fluoro polycarbonate（PTFBC）.PTFEC is white solid powder at ambient temperature with molecular weight of 207500 g·mol-1,dispersion of 2.3 and a melting temperature of 105.2 oC.We prepared the homogenous PTFBC polymer electrolyte by solution-casting method.The film has good flame retardant effect.It was proven that the ionic conductivity of PTFBC based electrolyte reached up to 1.31×10-4 S·cm-1 at ambient temperature with a wide electrochemical window about 5 V and a decent lithium ion transference number of 0.52.PTFBC polymer electrolyte with excellent electrochemical performance in the high voltage battery system has a bright prospect in application.