The Charge Storage Mechanism and Durable Operation in Olivine–Lithium–Iron–Phosphate for Mn-based Hybrid Batteries

Aqueous batteries have garnered considerable attention because of their cost-effectiveness, sufficient capacity, and non-flammable water-based electrolytes. Among these, manganese batteries are particularly attractive owing to their stability, abundance, affordability, and higher energy density. With a lower redox potential (Mn: −1.19 V vs SHE) than zinc (Zn: −0.76 V vs SHE), manganese batteries theoretically offer superior energy density over traditional zinc-based systems. In this study, LiFePO₄ is introduced as a cathode material in aqueous manganese-based hybrid batteries for the first time. Through electrochemical characterization and advanced structural and spectroscopic analyses, the charge storage mechanisms of protons in to the FePO₄ are elucidated. Cation diffusion pathways are also investigated via diffusion barrier calculations. This study presents manganese hybrid batteries with a good stability and capacity of ≈109.2 mAh g⁻¹ at 40 mA g⁻¹, alongside a cycle retention of 42.1% after 3000 cycles at 320 mA g⁻¹. Furthermore, an Mn²⁺/Li⁺ hybrid battery, achieving ≈1.6 V and superior durability (81.5% @ 1000th), is proposed.