| Compared with traditional lithium ion batteries,solid state batteries（SSBs）have many advantages,such as high energy density,good thermal stability,and safe operation,and have broad application prospects.Among all kinds of solid-state electrolytes（SSE）,polyester based gel polymer electrolyte（GPE）has received more and more attention and research in the fields of flexible electronics,flexible energy storage devices,wearable devices,etc.due to its high ionic conductivity,excellent electrochemical stability and flexibility.However,polyester based gel polymer electrolytes working at high temperature and high mechanical strength are still challenging.Therefore,the purpose of this paper is to improve the thermal stability and mechanical strength of gel polymer electrolytes through physical and chemical methods such as polymer skeleton modification,polymer blending,and addition of inorganic or organic fillers.The specific research content is as follows:（1）A new carbonate ionic liquid（CIL-TFSI）was successfully synthesized,and a PEO based gel polymer electrolyte（CIL-TFSI/GPES-1.5）doped with carbonate ionic liquid was prepared by solution casting method.It was found that the doping of carbonate ionic liquid can reduce the crystallinity of PEO polymer and the carbonyl group on carbonate has a strong interaction with lithium ion,which promotes the dissolution of lithium salt,resulting in a very high ionic conductivity of 1.34×10-3 S cm-1 for GPE-1.5.and the high oxidation resistance of carbonate ionic liquid makes GPE-1.5 have a wide voltage window（4.5 V）,which can meet the requirements of high-voltage lithium metal batteries.In addition,the lithium-ion transfer number(t Li+)is 0.60,which is higher than most of the data reported in the literature.Further,cells assembled with CIL-TFSI/GPEs-1.5 materials can be discharged at lower multiplicity of 0.1 C up to 151 m Ah g-1 and still have 85%capacity retention after 230 cycles.This work can provide a new idea for the development of gel polymer electrolytes with carbonate functionalization,which is of great significance for the development and utilization of high-pressure solid LMB in the future.（2）The mixture of polymerizable carbonate monomer（TGAB）,crosslinking agent trimethylolpropane tri（3-mercaptopropionate）（TPTMP）and liquid electrolyte was immersed into porous PAN spinning fiber membrane by a simple in-situ mercaptan click polymerization process to obtain PAN based polycarbonate gel polymer electrolyte（PTCEO/PAN-GPE）with high electrochemical stability window,high mechanical strength and high temperature resistance.The introduction of TGAB not only reduces the highest occupied molecular orbital（HOMO）energy level of the copolymer,but also widens the electrochemical stability window;Moreover,a double cross-linked network is formed by in-situ polymerization in the pores of the PAN spinning film,which improves the mechanical properties of the electrolyte.The prepared PTCEO/PAN-GPE exhibits excellent electrochemical performance and thermal stability,including a wide electrochemical window（up to 5.2 V）,high conductivity(at 25°C,1.6×10-4 S cm-1)and high temperature resistance（150°C）.PTCEO/PAN-GPE were used as electrolytes for symmetric Li/Li,Li/LFP and Li/LCO batteries,respectively,and showed excellent electrochemical performance.Symmetrical lithium batteries can provide a cycle capacity of over 800 hours at room temperature.Li/PTCEO/PAN-GPE/LFP batteries exhibit excellent cycle stability at a C/2 rate of 120°C for 100 cycles,maintaining a specific capacity of 91.25%.Li/LCO batteries also exhibit excellent capacity retention capabilities over a long-term cycle at a voltage range of 3.0 to 4.5 V.Our work can provide a new path for developing LMB high-temperature and high-pressure GPEs with good safety and high performance,which is very helpful for designing advanced electrolyte systems for high energy density lithium metal batteries. |
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