Acidic–neutral decoupled biphasic electrolytes enhance deposition–dissolution chemistry in Zn–Mn batteries

Abstract

Aqueous Zn–Mn batteries are emerging as promising candidates for next-generation energy storage technologies owing to their advantages including high energy density, low cost, and excellent reliability. However, conventional aqueous electrolytes struggle to meet the dual deposition–dissolution requirements of the Mn²⁺/MnO₂ cathodes and Zn²⁺/Zn anodes simultaneously. The Mn²⁺/MnO₂ two-electron redox reaction in cathodes demands acidic conditions to achieve a theoretical capacity of 616 mA h g⁻¹, twice that of neutral and alkaline systems, yet such conditions inevitably exacerbate Zn anode corrosion and undesirable hydrogen evolution reaction. To address this fundamental conflict, this study designs a self-stratifying aqueous–organic biphasic electrolyte, which successfully decouples the working conditions of the Mn cathodes and Zn anodes. The proof-of-concept Zn–Mn battery employing this biphasic electrolyte enables efficient Mn²⁺/MnO₂ redox chemistry in the acidic aqueous phase and stable Zn plating–stripping in the neutral organic phase, therefore achieving a high discharge voltage of ∼1.8 V, along with a stable cycle life of 90% capacity retention over 250 cycles. This work demonstrates an effective strategy for decoupling acidic and neutral conditions in a biphasic electrolyte and provides insights into the development of high-energy Zn–Mn batteries.