Synergistic combination of ether-linkage and polymer-in-salt for electrolytes with facile Li⁺ conducting and high stability in solid-state lithium batteries

In developing solid polymer electrolytes (SPEs), networked SPE (NSPE) and polymer-in-salt (PiS) configurations are effective strategies to achieve high ionic conductivity. The ether linkage of poly(ethylene oxide) (PEO) effectively dissociates salts, among which salt Li[N(SO₂F)₂] (LiFSI) exhibits excellent Li⁺-conductive characteristics. The present study synthesizes a PiS-NSPE comprising 55 wt% LiFSI and 45 wt% PEO-based NSPE. The PiS configuration creates aggregated Li⁺_n-FSI⁻_m domains for Li⁺ transport through the decoupling ion-conductive mechanism and the NSPE, with high-voltage tolerance, dissociates LiFSI and segregates the Li⁺_n-FSI⁻_m domains into interconnected clusters for Li⁺ percolation. With such a synergistic combination, the PiS-NSPE exhibits an ionic conductivity of 2.3 × 10⁻³ S cm⁻¹ and a Li⁺-transference number of 0.69 at 30 ℃. Protected by LiFSI, the PiS-NSPE is electrochemically stable until 4.6 V (vs. Li/Li⁺). The elastic feature enables the PiS-NSPE to withstand the Li-anode volume change and the lithiophilic FSI⁻-derived interlayer facilitates smooth Li deposition. The high compatibility between the PiS-NSPE and electrode materials results in the excellent performance of commercial-scale cathodes (∼10 mg cm⁻² in active mass) in batteries. The synergy between PEO-based NSPEs and high-content LiFSI is promising in realizing the practical application of SPEs in all-solid-state batteries.