A Weldable, Low-Cost Graphite-Based Electrode for Mn²⁺/MnO₂ Redox Chemistry with High Volumetric Energy Density

Aqueous rechargeable zinc-manganese batteries show considerable promise for large-scale energy storage owing to their high safety, environmental friendliness, low cost, and competitive energy density. Recently, the Mn²⁺/MnO₂ deposition-dissolution mechanism has gained attention because of its high specific capacity and cycling stability. High-porosity, high-surface area carbon felt has been widely employed as a cathode to facilitate Mn²⁺ transport and MnO₂ deposition, it suffers from non-weldability, high cost, as well as low volumetric energy density. Constructing coat-able slurries offers an alternative. Naturally abundant, low-cost flake graphite is an ideal building block for slurry-processed, weldable cathodes. However, flake graphite cathodes suffer from ion-channel blockage by MnO₂ deposition due to their tightly packed structure. We found that incorporating spherical graphite (SG) expands the electrode framework, thereby creating additional mesopores and macropores. This structural modification enhances Mn²⁺ transport and effectively alleviates pore blockage. The optimized SG-50 electrode sustained over 300 cycles at an areal capacity of 1.5 mAh cm^-2, with a coulombic efficiency of ∼94% and energy densities of 166 Wh L^-1. The estimated cost is 3.4 $/m², demonstrating a remarkable advantage over conventional carbon felt (60 $/m², 11 Wh L^-1). This work provides a practical electrode design strategy for slurry-coated, weldable cathodes in aqueous zinc-manganese systems involving dissolved redox species.