Carbon Mediated In Situ Cathode Interface Stabilization for High Rate and Highly Stable Operation of All‐Solid‐State Lithium Batteries

Abstract Interfacial stability issues at the cathode remain a bottleneck to developing durable and high‐power all‐solid‐state lithium batteries (ASSLBs). In fact, the presence of conductive carbon in the cathode, necessary for high capacity and power capability, is believed to aggravate the stability woes. Thus, it is typically excluded from the cathode mix. Herein, employing a model functionalized carbon, it is shown that a small carbon surface oxygen functionality can in situ engineer a robust carbon–solid electrolyte interphase, which arrests conductive carbon‐mediated degradation of Li 6 PS 5 Cl into reactive polysulfides that degrades the active LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC) cathode. Such interfacial stabilization, as confirmed by ex situ spectroscopic and in situ impedance analysis, combined with fast charge transport facilitated by functionalized yet conductive carbon and lowly resistive cathode interphases, elevates the performance. This is evidenced by stable cycling at room temperature (22 °C) and elevated temperatures (60 °C), high rate capability, a Coulombic efficiency of 99.8%, and ≈100% capacity retention after 1000 cycles and >90% retention over 2000 cycles at 60 °C. Functionalized carbon‐mediated in situ cathode interfacial engineering offers a simple and scalable approach to designing durable ASSLB cathodes, with the potential for broader application across various NMC cathodes and compatible solid electrolytes.