Study On High-voltage Resistant Poly-oxalate Polymer Electrolyte

Solid polymer electrolyte(SPE)is considered as an indispensable material for the construction of high energy density all-solid-state Li-ion batteries due to its advantages of high flexibility,low interfacial resistance and good compatibility with Li-metal anode.However,the shortcomings of SPE such as relatively narrow electrochemical steady window and low ionic conductivity still need to be overcome.In order to solve the above problems,a family of poly-oxalate(POE)structures,with different diol precursors on main chains were prepared and investigated as a SPE,it is found that POEs composed from diols with an odd number of carbons show lower melting point and higher ionic conductivity than those composed from diols with an even number of carbons,and the POE composed from polypentylene oxalate(C5-POE)has the highest Li~+conductivity.In addition,it is found that the HOMO(highest occupied molecular orbital)electrons of C5-POE are mainly localized on the terminal units and therefore more vulnerable to oxidizing decomposition.When the C5-POE were terminated by a strong electron-withdrawing trifluoroacetate unit,not only does the HOMO become more negative,but also the HOMO electrons shift to the middle oxalate units,leading to the improvement of antioxidative capability,the electrochemical window of C5-POE-F is enlarged to 5 V.What is more,introducing active F in C5-POE-F is conductive to generate the Li F-containing solid electrolyte layer(SEI),which significantly improves the interface stability between C5-POE-F and Li-metal anode.Therefore,the polymer structure of C5-POE-F not only achieves the desired compatibility with NMC811 cathode,but also reaches high interfacial stability with Li-metal simultaneously.Compared with traditional EO-based electrolytes,the cycling stability of all-solid-state Li/C5-POE-F-Li/NMC811cells is significantly improved,which provides a potential candidate material for all-solid-state high voltage Li-metal batteries.