Asymmetric Coordination Enables Decoupled Dynamics of Li⁺ Transport for High-Performance PEO-Based Solid Electrolytes

The strong coupling between Li+ transport and polymer segmental motion is considered to inherently limit the low-temperature performance of all-solid-state polymer electrolytes (ASPEs). Breaking the symmetric coordination environment of Li+ to promote its hopping transport mechanism offers a promising strategy to address this issue. In this work, we incorporate ∼60 wt % succinonitrile (SN) into a polypropylene (PP)-reinforced poly(ethylene oxide) (PEO)–(lithium bis(trifluoromethanesulfonyl)imide) LiTFSI (PPLS) electrolyte to disrupt the Li+ coordination symmetry. Multiple spectroscopies and theoretical calculations reveal that SN competitively coordinates with Li+ against PEO chains, resulting in an asymmetric and weakened Li+ solvation structure. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analyses demonstrate the decoupled dynamics of the Li+ transport from segmental relaxation. The PPLS electrolyte achieves a high ionic conductivity of (5.98 ± 0.585) × 10–5 S/cm at 0 °C and stable Li plating/stripping for >700 h at 0.1 mA/cm2 (25 °C). All-solid-state lithium batteries exhibit exceptional cycling performance at both room temperature and 0 °C. This work reveals the plasticizer-mediated formation of asymmetric Li+ coordination structures and their critical role in decoupling Li+ transport, offering a design paradigm for ASPEs that synergistically enhances ionic conductivity, mechanical robustness, and low-temperature adaptability.