Regulation of the Cathode Inner Helmholtz Plane in Dilute Ether Electrolytes Using Electric-Field-Responsive Solvent for High-Voltage Lithium Metal Batteries

Abstract

Raising the cut-off voltage to 4.6 V can boost the energy density of lithium metal batteries (LMBs) with LiCoO2 cathode. However, the unfavorable cathode electrolyte interphase (CEI) formed on high-voltage cathode when using Li metal-compatible ether electrolytes leads to short lifespan of batteries. Here we harness the battery intrinsic electric field to manipulate the cathode inner Helmholtz plane (IHP) during the battery’s charge through simply introducing an electric-field-responsive solvent into an ether electrolyte. Specifically, 2,2-difluoroethyl trifluoromethanesulfonate (DTS) as a weak solvated co-solvent preferentially adsorbs on the cathode surface under the electric field activation. Owing to the majority of “high-voltage fragile” 1,2-dimethoxyethane ether molecules squeezed out from the IHP by DTS, a LiF-rich and organics-less stable CEI film is formed, which minimizes cathode cracking and structure degradation under high-voltage. The DTS-containing electrolyte shows superior cycling stability of LMBs under harsh conditions of 4.6 V, 4.2 mAh cm-2 cathode loading and 15 μL lean electrolyte. Furthermore, the feasibility of this concept is validated in practical Ah-level pouch full cells. This work highlights the significance of the IHP modulation and interfacial chemistry, providing an alternative pathway towards ether-based electrolytes engineering for high-voltage LMBs.