Reversible Zn and Mn deposition in NiFeMn-LDH cathodes for aqueous Zn–Mn batteries

Abstract

Introducing NiFeMn-Layered Double Hydroxide (LDH) as an innovative cathode material for Zn–Mn batteries, this study focuses on bolstering the electrochemical efficiency and stability of the system. We explored the effect of varying Zn/Mn molar ratio in the electrolyte on the battery's electrochemical performance and investigated the underlying reaction mechanism. Our results show that an electrolyte Zn/Mn molar ratio of 4 : 1 achieves a balance between capacity and stability, with an areal capacity of 0.20 mA h cm⁻² at a current of 0.2 mA and a capacity retention rate of 53.35% after 50 cycles. The mechanism study reveals that during the initial charge–discharge cycle, NiFeMn–CO₃ LDH transforms into NiFeMn–SO₄ LDH, which then absorbs Zn²⁺, Mn²⁺, and SO₄²⁻ ions to form a stable composite substrate. This substrate enables the reversible deposition–dissolution of Mn ions, while Zn ions participate in the reaction continuously, with most Mn- and Zn-containing compounds depositing in an amorphous phase. Although further optimization is needed, our findings provide valuable insights for developing Zn–Mn aqueous batteries, highlighting the potential of LDHs as cathode substrates and the pivotal role of amorphous compounds in the reversible deposition–dissolution process.