Modulating Interfacial Solvent Aggregation Chemistry to Enable Low-Temperature Sodium-Ion Battery

The capability of sodium-ion batteries (SIBs) to operate under extreme temperatures is highly desirable; however, achieving stable performance remains challenging due to limitations in interfacial dynamics. Here, it is revealed that at low temperatures, linear solvents tend to aggregate within the inner Helmholtz plane (IHP), leading to the formation of a solvent-derived solid-electrolyte interphase (SEI) with sluggish Na⁺ diffusion kinetics. To address this issue, it is proposed to leverage the polarization interaction induced by the orbital overlap between the solvent molecules and free radicals as an effective approach to breaking solvent aggregation. This interaction leads to a redistribution of electron density, reducing the electron cloud density and lowering molecular polarity. Significantly, the reduced polarity weakens intermolecular ordering, promoting interfacial restructuring that enhances mass transfer and facilitates the formation of an inorganic-rich SEI. Herein, trimethylsilyl trifluoromethanesulfonate (TMSOTF) is identified as an optimal electric double-layer regulator, which generates radicals in situ and interacts with the solvent to reconstruct the IHP layer. Consequently, commercial hard carbon paired with the TMSOTF-based electrolyte exhibits superior cycling stability, achieving a lifespan over 2400 cycles at -40 °C, whereas the conventional electrolyte fails to sustain cycling. This study provides critical insights into interfacial design strategy for advancing low-temperature battery technologies.