Effective 3D open-channel nanostructures of a MgMn2O4 positive electrode for rechargeable Mg batteries operated at room temperature

Room-temperature operations of rechargeable Mg coin-cell batteries have been achieved using a Mg alloy negative electrode and a spinel MgMn2O4 (MMO)-positive electrode. The present work focuses on clarifying the effects of the physiochemical properties of the MMO powder including the specific surface area (S-BET) and porosity of the positive electrode on Mg battery performances in practical applications. Finally, optimal specific surface area and porosity parameters were obtained that ensured excellent battery performances as a standard coin-cell at room temperature. A typical MMO powder synthesized using a modified sol-gel method with propylene oxide-driven complex polymerization had a large S-BET > 200 m(2) g(-1), and more than 90% porosity with a triple-tiered 3D open-channel network. Here we evaluated the discharge capacity and the cyclability for room-temperature operation as a function of S-BET in a full cell with a Mg negative electrode as well as half cells with a carbon graphite electrode. Irrespective of whether half cells or a full cell was used, the initial discharge capacity was found to depend linearly on the S-BET of the porous MMO powder in a Mg tetrakis(hexafluoroisopropyl)borate/triglyme electrolyte with a wide potential window, Delta E > 3.6 V. Eventually, the maximum discharge capacity of 220 mA h g(-1) was realized at 25 degrees C in the full cell using the 3D open-channel nanostructure with S-BET = 236 m(2) g(-1). The cyclability in the full cell with the Mg alloy negative electrode, however, degraded with the increasing S-BET, while no cyclability degradation was observed in the half cell with the carbon electrode. A possible mechanism is discussed regarding passivation of the Mg alloy electrode in discharge/charge cycles.

Automated summary

Successful room-temperature operation of rechargeable Mg coin-cell batteries has been achieved using a Mg alloy negative electrode and a spinel MgMn2O4 (MMO)-positive electrode. The study focuses on the effects of physiochemical properties of MMO powder on battery performances, and found that optimal specific surface area and porosity parameters can ensure excellent battery performances at room temperature. The maximum discharge capacity of 220 mA h g(-1) was realized in a full cell using a 3D open-channel nanostructure with S-BET = 236 m(2) g(-1), indicating the importance of S-BET in battery performance.