Cation-Anion Counter-Directed Migration Enabled Synergistic Dual-Interphase Engineering for High-Voltage Li Metal Batteries

Abstract

High-voltage Li metal batteries offer appealing high energy density but suffer from simultaneous interfacial instability at both cathode and anode, where cathode particle degradation, uncontrolled interphase growth, and uneven Li deposition remain major impediments to long-term cycling and calendar life. Here, we introduce a novel concept of counter-directed migratory ionic additives, whose anions and cations move towards the cathode and anode respectively to reconfigure the Helmholtz layer under the intrinsic electric field of the battery. We employ theoretical simulations and in-situ Raman spectra for verification of the field responsiveness and migration behavior of anions/cations. The NO3- anions enriched at the high-voltage cathode, are found to promote inorganic-rich cathode‑electrolyte interphase (CEI) and inhibit electrolyte decomposition. The Pyr13+ cations enriched at the Li anode exert electrostatic shielding effects and electrostatically attract TFSI⁻ anions to facilitate more LiF, while NO3- decomposes into N-containing inorganics, thereby improving the solid electrolyte interphase (SEI) and homogenizing Li deposition. Together, these synergistic dual-interphase improvements translate into enhanced coulombic efficiency, superior rate capability, and significantly improved long-term cycling stability of 4.6 V Li||NCM811 cells. Counter-directed migratory ionic additives provide a versatile and broadly applicable platform to tackle the challenge of synergistic dual-interphase regulation in energy-dense Li metal batteries.