Ultrathin PEO based electrolyte for high voltage lithium metal batteries enabled by polymer host-plasticizer interactions

Poly(ethylene oxide) (PEO) stands out in solid-state Li metal batteries (SSLMBs) for its high viability, low expanse and superior compatibility with Li anode, but its insufficient ionic conductivity at ambient temperature and limited electrochemical stability windows make it difficult to work at ambient temperature and pair with high voltage cathode materials. Herein, an ultrathin dual-solvent PEO based polymer electrolyte (DSPE) with 22 μm is proposed to tackle these issues. The introduction of tetraethylene glycol dimethyl ether (TEGDME) and succinonitrile (SN) as plasticizers friendly to Li anode and NCM622, respectively, not only greatly improves the conductivity of PEO at room temperature, but also significantly enhances the compatibility of electrolyte-electrode interface. More importantly, the PEO polymer host-solvent interactions successfully anchor the free solvent small molecules of TEGDME and SN around PEO host to avoid their damage to the electrolyte-electrode interface. Improved NCM622|DSPE|Li battery provides prominent cycle life with a capacity retention of 80.0 % after 300 cycles at 0.1C at 30 °C. The application of PEO based polymer electrolyte in SSLMBs is successfully realized by taking advantage of polymer host-plasticizer interactions.