Efficiencies of Various in situ Polymerizations of Liquid Electrolytes and the Practical Implications for Quasi Solid‐state Batteries

In situ polymerization of liquid electrolytes is currently the most feasible way for constructing solid-state batteries, which, however, is affected by various interfering factors of reactions and so the electrochemical performance of cells. To disclose the effects from polymerization conditions, two types of generally used in situ polymerizing reactions of ring-opening polymerization (ROP) and double bond radical polymerization (DBRP) were investigated on the aspects of monomer conversion and electrochemical properties (Li⁺ -conductivity and interfacial stability). The ROP generated poly-ester and poly-carbonate show a high monomer conversion of ≈90 %, but suffer a poor Li⁺ -conductivity of lower than 2×10^-5 S cm^-1 at room temperature (RT). Additionally, the terminal alkoxy anion derived from the ROP is not resistant to high-voltage cathodes. While, the DBRP produced poly-VEC(vinyl ethylene carbonate) and poly-VC(vinylene carbonate) show lower monomer conversions of 50-80 %, delivering relatively higher Li⁺ -conductivities of 2×10^-4 S cm^-1 at RT. Compared two polymerizing reactions and four monomers, the VEC-based F-containing copolymer possesses advantages in Li⁺ -conductivity and antioxidant capacity, which also shows simultaneous stability towards Li-metal with the help of LiF-based passivating layer, allowing a long-term stable cycling of high-voltage quasi solid-state cells.