Unlocking High‐Voltage and Low‐Temperature Capability in Lithium Metal Batteries via Coupling Bulk Solvation Tailoring with Interfacial Electrostatic “Anchor‐and‐Shield” Strategy

Ether electrolytes in Li‐metal batteries are severely constrained by parasitic anodic oxidation and solvent ring‐opening polymerization (ROP). To overcome this, we propose an “anchor‐and‐shield” strategy using 0.05 M TBABH 4 in 1 M LiFSI DME/DOL. Nucleophilic BH 4 − incorporates into the Li + solvation shell, neutralizing localized Lewis acidity to inhibit ROP propagation. Operando SERS and MD simulations show that TBA + cations enrich in the electrochemical double layer, anchoring FSI − anions via electrostatic interactions to reverse the conventional anion‐lean interphase. This promotes FSI − decomposition, forming a robust inorganic‐rich SEI. Consequently, the DOL dissociation energy decreases to 0.49 eV, boosting the exchange current to 15.84 mA cm −2 and extending Li‐Li lifespan beyond 1800 h. Li‐NCM811 full cells retain 80% capacity after 450 cycles at 25°C and 300 cycles at −20°C. Remarkably, under harsh conditions (50 µm Li, 20 mg cm −2 cathode), the full cell achieves stable operation for over 86 cycles with 80% capacity retention. This strategy enables high‐voltage Li batteries across a wide temperature range down to sub‐zero environments.