Designer Redox-Active Catholytes for High-Performance All-Solid-State Lithium Batteries

Advanced cathode designs are essential for all-solid-state lithium batteries (ASSLBs) to bring their pivotal advantages of high energy density into practical energy storage devices. Typical composite cathodes contain a certain fraction (20-50 wt %) of electrochemically "inactive" catholytes, fundamentally compromising the attainable energy density. Here, we put forward the designer redox-active catholyte (DRAC) concept, utilizing the metal oxyhalide Li1+xNbOCl4 as an archetype, to break the energy ceiling imposed by conventional electrode design. Adding to the intrinsically high lithium conductivity, our results demonstrate the tantalizing redox activities of Li1+xNbOCl4 for Li+ storage at ca. 2.6 V vs Li/Li+, accompanied by a unique "lithiation-enhanced electronic conductivity" mechanism. The Li+ intercalation mechanisms of Li1+xNbOCl4 are elucidated, involving a combination of solid-solution and conversion reactions. Compared to a typical cathode using non-redox-active catholytes, the integration of Li1+xNbOCl4 as a DRAC with LiNi0.93Co0.06Mn0.01O2 creates a synergistic effect, empowering the cathode with a 23.07% increase in specific discharge capacity and 17.22% increase in specific energy calculated based on the total weight of LiNi0.93Co0.06Mn0.01O2 and catholyte (cathomass). Our DRAC strategy establishes a new architectural paradigm for the practical applications of ASSLBs, where the high-potential region supports routine operation and the newly unlocked low-potential capacity acts as a dedicated emergency buffer, thereby maximizing the overall utility of practical ASSLBs.