Preparation And Properties Of Polyvalerolactone Electrolyte

High energy density and high safety are the mainstream directions for the future development of lithium-ion batteries.Compared to traditional lithium-ion batteries with graphite as the anode,lithium-ion batteries with metal lithium as the anode can effectively improve energy density.However,side reactions are usually occurred on lithium metal when it comes into contact with commercial electrolytes,and liquid electrolytes themselves have characteristics of volatility,leakage,and flammability,greatly increasing safety risks.With the attention paid to safety and the use of flexible devices,polymer electrolytes have developed rapidly.However,the development of polymer electrolytes is limited by low ionic conductivity and narrow electrochemical windows caused by poor oxidation resistance of the matrix.Therefore,the preparation of a high-performance polymer electrolyte has become a hot research topic.In recent years,Polymer Electrolytes Prepared by ring opening polymerization have been widely studied.Compared with cyclic ethers,polyester matrix prepared by ring opening polymerization of lactones has stronger oxidation resistance.However,when using stannous octanoate（Sn（Oct）₂）as a catalyst,it needs to be carried out at high temperatures and is not conducive to the formation of a passivation layer at the lithium metal interface.This thesis is the first time to catalyze the ring-opening polymerization ofδ-valerolactone（δ-VL）and prepare polyvalerolactone（PVL）electrolytes at lower temperatures,and the effects of catalysts were systematically studied.The specific research contents are as follows:（1）In addition to catalyzingδ-VL ring opening polymerization,lithium hexafluorophosphate（Li PF₆）with Lewis acid can also be used as a lithium salt in electrolyte systems.In order to explore the efficacy of Li PF₆as lithium salt,the performance of polymer electrolytes prepared by adding only Li PF₆、Li PF₆and another commonly lithium salt lithium ditrifluoromethane sulfonate imide（Li TFSI）double salts,was compared.The results indicate that LiPF₆is not suitable as a lithium salt in the polymer electrolyte,but adding a suitable lithium salt Li TFSI is beneficial for improving the interface stability with the lithium anode.（2）The effect of tin trifluoromethanesulfonate（Sn（OTf）₂）as a catalyst on the preparation of polyvalerolactone gel polymer electrolyte（PVL-GPE）was investigated.During the research process,the physical and electrochemical properties of PVL-GPE prepared under different catalyst contents were mainly compared.The results show that adding appropriate catalyst content is conducive to the formation of stable composite solid electrolyte interface layer（SEI）containing Li Sn alloy and lithium fluoride（Li F）,regulating the uniform deposition of lithium and passivating the interface.（3）In addition to the catalyst,the presence of unpolymerized monomers during the ring opening polymerization reaction can also have an impact on battery performance.After removing the monomers,polyvalerolactone solid polymer electrolyte（PVL-SPE）was prepared ex-situ.Its electrochemical window was widened to 4.7 V,and the capacity retention rate of the assembled Li/PVL-SPE/NCM811 cell after 100 cycles was 72%,indicating good cycle performance.