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_0.6Co_0.2Mn_0.2O₂ 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.