Tailoring Synergistic Ion Environment for Copper Telluride toward High‐Capacity and Ultrastable Acidic Multivalent‐Ion Batteries

Acidic batteries permit a reliable energy supply at low temperatures with low cost and intrinsic safety, yet the development of stable acid-resistant electrodes with high capacity and a reliable lifespan is still challenging. Herein, nonstoichiometric copper telluride (Cu_2-xTe) nanosheets are first explored as high-performance electrodes for acidic batteries to provide a stable capacity release of 409 mAh g^-1 with a record-breaking lifespan of 40 000 cycles and excellent kinetics, enabling operation at a high current density of 20 A g^-1. In contrast to the inherent perception of corrosive destruction of electrode materials by strongly acidic environments, the electrolyte environment enriched with copper ions and hydrogen ions synergistically stabilizes the Cu_2-xTe electrode and drives reversible multielectron transfer asymmetric deep conversion, which is confirmed by in situ synchrotron X-ray diffraction, X-ray absorption spectroscopy, first-principal calculations, and composite electrochemical characterization. Therefore, Cu_2-xTe provides an impressive accumulation capacity of over 4764 Ah g^-1, exceeding that of most acidic batteries, and works well at -20 °C. High-performance Cu_2-xTe electrodes also promote the establishment of Cu_2-xTe//Mn₂O₃ and Cu_2-xTe//Fe acidic full cells enabling stable operation at room temperature and low temperature, offering promising opportunities for electrode progress in advanced acidic batteries.