LAUSR

Summary Although great efforts have been made in investigating layered metal oxides for high-energy rocking-chair batteries, the capacities of conventional materials have reached the bottlenecks of theoretical values, which are critically dependent on the ability to (de)intercalate the single cation. In this work, we demonstrate a proof of concept, i.e., both cationic and anionic co-(de)intercalation into a typical layered oxide, which is firstly investigated in a P3-Na 0.5 Ni 0.25 Mn 0.75 O 2 . During the electrochemical process, the energy storage is not only provided by the conventional cationic (Na + ) (de)intercalation with the charge compensation of cationic (Ni 2+ ↔Ni 4+ ) reversible redox, but also achieved by the release and uptake of anions (ClO 4 − ) accompanied by an anionic (O 2− ↔O − ) reversible redox. Furthermore, the results show that the anion-participating electrochemical process is a fast-kinetics process, and the feasibility of this mechanism could extend to various anions.