PEO-based electrolyte with coordination-entropy-increase strategy for all-solid-state lithium metal batteries.

Polyethylene oxide (PEO)-based solid-state polymer electrolytes (SPEs) are promising key materials for all-solid-state lithium metal batteries because of their good processability and compatibility with Li metal. However, their practical deployment is limited by the low Li+ conductivity, which mainly originates from the high migration energy barrier induced by strong Li-polymer coordination. Here, this work proposes a coordination-entropy-increase driven all-solid-state electrolyte, PEO-LiTFSI-MgCl2-AlCl3-ZrCl4 (SPE-MAZ). The introduction of multi-cations induces diverse coordination structures on PEO chains, creating Li+ sites with varied binding strengths and distinct energy barriers. These features narrow the energy differences between adjacent sites, facilitate Li+ mobility, and achieve enhanced ionic conduction. SPE-MAZ delivers an ionic conductivity of 0.103 mS cm-1 at room temperature (RT, 30 °C). The assembled Li/SPE-MAZ/Li symmetric cells maintain stable operation for over 1700 h at 60 °C. The LiFePO4/SPE-MAZ/Li full cells achieve a specific capacity of 115.1 mAh g-1 at 60 °C and 5 C, with 80% capacity retention preserved after 100 cycles at RT and 0.1 C. This coordination-entropy-increase strategy leads to the realization of SPEs featuring both high conductivity and good stability, offering a novel perspective for SPEs design.