Design of boronated polysaccharide-based solid polymer electrolytes with synergistically enhanced ionic transport and mechanical properties.

Solid polymer electrolytes (SPEs) with diverse and controllable structures have garnered considerable interest. However, in conventional SPEs, lithium-ion (Li+) transport is typically coupled with polymer segmental motion, leading to low ionic conductivity and an inherent trade-off between conductivity and mechanical strength. In this study, we develop boron modified polysaccharide electrolytes (BPS) through dehydration-induced covalent bonding between BOH4- and hydroxyl groups of the polysaccharide. The resulting closely packed and highly ordered coordination sites composed of oxygen/boron collectively create direct and efficient pathways for Li+ conduction. This is reflected in the zero phase response across an exceptionally broad frequency range (103-105 Hz), indicating rapid and unimpeded Li+ migration. These unique Li+ conducting pathways decouple ion conduction from polymer segmental dynamics, enabling both high ionic conductivity (7.90 × 10-4 S cm-1) and superior mechanical robustness (11.70 MPa). The BPS membrane also exhibits a high Li+ transference number (0.78) and a wide electrochemical stability window (up to 4.7 V). Importantly, the assembled solid-state LFP|BPS|graphite full-cell delivers over 200 stable cycles at 0.1C. This work provides a solid scientific basis for understanding rapid Li+ transport in SPEs and accelerates their practical implementation in solid-state battery systems.