Fluorinated solvent enhances room-temperature solid-state lithium batteries by weakening Li+ ion and PEO chain interactions

Polyethylene oxide (PEO)-based solid-state batteries have attracted extensive attention due to their scalable processing, flexible and soft interface contact, and excellent compatibility with lithium metal. The low ionic conductivity at room temperature, caused by the strong interaction between PEO chains and lithium ions , however, limits its practical application. Herein, taking the PEO-PAN dual-matrix polymer electrolyte as an example, a weak coordinated solvation structure is enabled by fluoroethylene carbonate (FEC) as a co-solvent during electrolyte preparation. The tiny residual FEC is demonstrated to weaken the interaction between lithium ions and PEO chains while competitively dissociating lithium salts with the residual solvent and anions. In addition, the incorporation of FEC enhances the dispersion of LATP nanoparticle fillers, which reduces the crystallinity of PEO. Furthermore, the anion-derived LiF-rich solid-electrolyte interphase significantly suppresses the formation of lithium dendrites. Consequently, the prepared PEO-PAN-LATP-LiTFSI-5 % FEC (PPLLF) composite solid polymer exhibits an ambient ionic conductivity of ∼ 1 × 10 −4  S cm −1 and enables stable cycling for over 450 h in a Li||Li symmetrical battery at room temperature. The assembled Li|PPLLF|LFP full battery delivers a specific capacity of 137.6 mAh/g after 300 cycles at 0.2C, further demonstrating the effectiveness of the solvation manipulation strategy.