Synergistic Regulation of Interfacial Potential and Anionic Covalency for High-Voltage Cobalt-Free All-Solid-State...

High-voltage cobalt-free all-solid-state lithium batteries (ASSLBs) represent a promising pathway toward high-energy-density and sustainable energy storage. However, their practical viability is fundamentally hindered by a coupled interfacial failure mechanism involving kinetic bottlenecks at the space-charge layer (SCL) and the electrochemical instability of interfacial lattice oxygen. Here, we propose a synergistic regulation to decouple these constraints in 5 V-class LiNi_0.5Mn_1.5O₄ (LNMO) ASSLBs. We reveal that the large lithium (Li) chemical potential mismatch at the LNMO/electrolyte interface drives a Li-deficient SCL, while the high voltage triggers interfacial oxygen release, causing severe interfacial structural degradation. To address this, a stable interface was constructed where interfacial potential and anion covalency are regulated synergistically. Specifically, a high-dielectric BaTiO₃ (BTO) coating layer was introduced to regulate interfacial potential and suppress SCL formation, while sulfate-derived S─O covalent bonds stabilized the interfacial lattice oxygen. Consequently, the BTO-S-LNMO ASSLB achieves a notable increase in reversible capacity from 52 to 116 mAh g^-1 at 0.1 C and enables high-rate capacity up to 3 C and exhibits long-term durability at 1 C. This work establishes a paradigm of coupling dielectric regulation and anion-chemistry stabilization to unlock the potential of high-voltage LNMO ASSLBs.