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 LiNi0.6Co0.2Mn0.2O2 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.