Toward Ultrahigh‐Capacity Aqueous Zinc‐Metal Batteries: Synergistic Engineering of a Cu‐Doped Bi ₂ Te ₃ Cathode and an NH ₄ Cl‐Modified Electrolyte

ABSTRACT Electrolyte engineering mainly focuses on improving the Zn‐metal anode, which reduces dendrites and the hydrogen evolution reaction. However, optimizing electrolytes for high‐performance cathodes remains underexplored. This imbalance directly limits full‐cell performance from meeting commercial standards. This study employs a copper‐doped Bi ₂ Te ₃ (Cu _x Bi _{2‐ x} Te ₃ ) cathode combined with an NH ₄ Cl‐modified electrolyte to achieve high‐performance aqueous Zn‐metal batteries. In this co‐engineering approach, the Cu dopant manipulates the electronic structure of the Te atom and increases Cl ⁻ adsorption energy. Meanwhile, the NH ₄ Cl additive efficiently regulates the electrochemical behaviors of Cu _x Bi _{2‐ x} Te ₃ cathode. Systematic electrochemical analysis shows that NH ₄ Cl additive possesses two key roles: (1) introducing NH ₄ ⁺ storage along with Zn ² ⁺/H⁺ insertion, and (2) activation of reversible Te ²⁻ /Te ⁴⁺ redox chemistry through Cl–mediated coordination. Consequently, the Cu _x Bi _{2‐ x} Te ₃ cathode achieves an ultra‐high specific capacity of 811.9 mA h g ⁻¹ at 0.5 A g ⁻¹ –surpassing most reported metal chalcogenide‐based cathodes. By bridging cathode design and electrolyte modulation, this work demonstrates a universal potential strategy for developing high‐energy, durable aqueous batteries, with implications extending to other multivalent ion storage systems.