Ion-Regulated Interfacial Solvation Enables Ether Electrolytes for 4.4 V Lithium Metal Batteries

Lithium metal batteries (LMBs) require electrolytes that stabilize both lithium metal anodes (LMAs) and cathodes. Conventional strategies mainly reconstruct bulk solvation structures, often perturbing the intrinsic properties of the electrolyte. Here, we introduce an ion-regulated strategy to selectively tailor interfacial solvation structures (ISS). Surface-enhanced Raman spectroscopy (SERS) reveals cation-dominated solvation at the anode and anion-dominated solvation at the cathode. Accordingly, K+ and BH4– are employed as ionic regulators to modulate DME coordination and suppress interfacial decomposition. Adding only 0.05 M KBH4 enables reversible Li plating/stripping for 160 cycles at 3 mA cm–2 and 1 mAh cm–2 and increases the oxidation onset potential to 5.00 V. Li–LiNi0.8Co0.1Mn0.1O2 (NCM811) full cells retain 85.7% capacity after 100 cycles with a 20 mg cm–2 cathode, 50 μm Li, and a 4.4 V cutoff. These findings demonstrate that manipulating electrode-specific interfacial solvation provides a distinct route toward ether electrolytes for 4.4 V LMBs.