Reshaping Li ⁺ -Polyethylene Glycol Interactions to Boost Li ⁺ Transport in Solid Polymer Electrolytes

Solid polymer electrolytes (SPEs) play a crucial role in solid-state lithium metal batteries (LMBs), offering smooth interfacial contact with the electrodes. Among these, polyethylene glycol (PEG)-based polymers are particularly effective at dissociating lithium salts and generating mobile Li + ions. However, the strong binding between Li + and PEG, coupled with slow polymer segmental motion, significantly limits the Li + transport. Achieving rapid Li + transport by modulating the Li + -PEG interaction is crucial but remains challenging for developing high-performance polymer electrolytes. Here, we introduce trimethylamine oxide (TMAO), a biologically derived osmotic agent, into a solid polymer electrolyte to reshape the Li + -PEG interaction for promoting Li + transport. TMAO can effectively coordinate with Li + through its highly negatively charged oxygen atom and reverse the PEG’s polarization induced by Li +, thereby weakening the Li + -polymer binding. This process significantly enhances the ionic conductivity (1.07 mS cm –1, 25 °C) and improves the cycling stability of lithium metal batteries with LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathodes (96% capacity retention over 300 cycles). This work provides a perspective for promoting Li + transport in SPEs, advancing the performance of solid-state batteries.