On September 1, Tsinghua News Network announced that all-solid-state batteries, which utilize non-flammable solid-state electrolytes in place of organic ones, are heralded as the next generation of battery technology. This is attributed to their ability to combine high energy density with superior safety. Nevertheless, in conventional designs, solid-state electrolytes solely conduct ions without storing charge, constituting over 50% of the composite electrode. This characteristic restricts the enhancement of energy density. The research team, spearheaded by Zhang Qiang from Tsinghua University’s Department of Chemical Engineering, has introduced a voltage window matching criterion. This was achieved through an in-depth study of the composition, structure, and redox chemistry of halides, allowing the electrolyte to contribute to capacity while still conducting lithium ions. Experimental results demonstrate that LiNbOCl4, which boasts high ionic conductivity, when paired with a high-nickel cathode NCM90, attains a composite cathode energy density of 768.6 Wh/kg. Moreover, the halogen reversibility is evident as (exhibiting) I > Br > Cl.