High-Rate Nonaqueous Mg-CO₂ Batteries Enabled by Mo₂C-Nanodot-Embedded Carbon Nanofibers

The widespread acceptance of nonaqueous rechargeable metal-gas batteries, known for their remarkably high theoretical energy density, faces obstacles such as poor reversibility and low energy efficiency under high charge-discharge current densities. To tackle these challenges, a novel catalytic cathode architecture for Mg-CO2 batteries, fabricated using a one-pot electrospinning method followed by heat treatment, is presented. The resulting structure features well-dispersed molybdenum carbide nanodots embedded within interconnected carbon nanofibers, forming a 3D macroporous conducting network. This cathode design enhances the volumetric efficiency, enabling effective discharge product deposition, while also improving electrical properties and boosting catalytic activity. This enhancement results in high discharge capacities and excellent rate capabilities, while simultaneously minimizing voltage hysteresis and maximizing energy efficiency. The battery exhibits a stable cycle life of over 250 h at a current density of 200 mA g(-1) with a low initial charge-discharge voltage gap of 0.72 V. Even at incredibly high current densities, reaching 1600 mA g(-1), the battery maintains exceptional performance. These findings highlight the crucial role of cathode architecture design in enhancing the performance of Mg-CO2 batteries and hold promise for improving other metal-gas batteries that involve deposition-decomposition reactions.