Design of cellulose/polyethylene oxide/EMITFSI-based composite electrolyte with synergistic transport mechanism for high-performance solid-state lithium batteries

Despite its theoretically high energy density, polymer solid-state lithium batteries (PSSLBs) exhibit lower actual energy density. This discrepancy arises from the low ionic conductivity of the polymer solid-state electrolyte (PSSE) due to the coupling of lithium ion (Li⁺) transport to the relaxation of polymer chain segments. The objective of this study is to optimize the Li⁺ transport in PSSE. This is achieved by incorporating 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) to plasticize both cellulose and polyethylene oxide (PEO). By leveraging the synergistic effects of cellulose and PEO, an ion-conducting network is established. This network allows Li⁺ to form multiple Li-O coordination simultaneously with the hydroxyl group (OH) of cellulose and the ether group (EO) of PEO, thereby enabling Li⁺ to transport between the two polymers in a decoupled manner. The PSSE demonstrated an ionic conductivity of 4 × 10^-4 mS/cm (at room temperature) and a Li⁺ transference number of 0.43, significantly exceeding traditional PEO-based values of 10^-5 mS/cm and 0.1–0.2. Additionally, the high voltage stability of EMITFSI extends the electrochemical stability window of PSSE, achieving a stability window of 5 V. The assembled LiFePO₄/Li cell achieved a specific capacity of 138 mA h/g at 50℃ (0.5C) with a capacity retention rate of 80 % after 280 cycles. This represents an innovative method for preparing high-energy–density solid-state lithium batteries.