Cyclopropenium Cationic-Based Covalent Organic Polymer-Enhanced Poly(ethylene oxide) Composite Polymer Electrolyte for All-Solid-State Li–S Battery

Cyclopropenium cationic-based covalent organic polymer (iCP@TFSI) was successfully prepared through the SN2 reaction and ion replacement process, which can be incorporated into the PEO/LiTFSI matrix as a filler. The obtained solid-state polymer electrolytes were utilized for an all-solid-state lithium–sulfur (Li–S) battery. Padding iCP@TFSI into the PEO matrix not only has a positive influence on both the ionic conductivity and the mechanical capacity of solid-state polymer electrolytes but also increases the stability of the lithium metal anode, which essentially improves the overall cycling ability of all-solid-state Li–S batteries. Among the membranes attained, the PEO-10%iCP@TFSI electrolyte displays the best ionic conductivity up to 1.2 × 10–3 S·cm–1 at 80 °C. The symmetrical lithium battery exhibits higher cycle stability (600 h) due to the higher mechanical properties related to more stable lithium metal interfaces. The Li–S battery based on the PEO-10%iCP@TFSI electrolyte exhibits excellent electrochemical performance with better Coulombic efficiency and outstanding cycling stability. Its capacity is maintained at 490 mAh·g–1 after 500 cycles at 1 C with a 0.032% decay rate each cycle, and the Coulombic efficiency is close to 100% during the whole cycling.