Ruigang Zhang

Boron Clusters as Highly Stable Magnesium-Battery Electrolytes†

Boron clusters are proposed as a new concept for the design of magnesium-battery electrolytes that are magnesium-battery-compatible, highly stable, and noncorrosive. A novel carborane-based electrolyte incorporating an unprecedented magnesium-centered complex anion is reported and shown to perform well as a magnesium-battery electrolyte. This finding opens a new approach towards the design of electrolytes whose likelihood of meeting the challenging design targets for magnesium-battery electrolytes is very high.

Understanding the electrochemical mechanism of K-αMnO2 for magnesium battery cathodes.

Batteries based on magnesium are an interesting alternative to current state-of-the-art lithium-ion systems; however, high-energy-density cathodes are needed for further development. Here we utilize TEM, EDS, and EELS in addition to soft-XAS to determine electrochemical magnesiation mechanism of a high-energy density cathode, K-αMnO2. Rather than following the typical insertion mechanism similar to Li(+), we propose the gradual reduction of K-αMnO2 to form Mn2O3 then MnO at the interface of the cathode and electrolyte, finally resulting in the formation of K-αMnO2@(Mg,Mn)O core-shell product after discharge of the battery. Understanding the mechanism is a vital guide for future magnesium battery cathodes.

Quantitatively Predict the Potential of MnO2 Polymorphs as Magnesium Battery Cathodes.

Despite tremendous efforts denoted to magnesium battery research, the realization of magnesium battery is still challenged by the lack of cathode candidate with high energy density, rate capability and good recyclability. This situation can be largely attributed to the failure to achieve sustainable magnesium intercalation chemistry. In current work we explored the magnesiation of distinct MnO2 polymorphs using first-principles calculations, focusing on providing quantitative analysis about the feasibility of magnesium intercalation. Consistent with experimental observations, we predicted that ramsdellite-MnO2 and α-MnO2 are conversion-type cathodes while nanosized spinel-MnO2 and MnO2 isostructual to CaFe2O4 are better candidates for Mg intercalation. Key properties that restrict Mg intercalation include not only sluggish Mg migration but also stronger distortion that damages structure integrity and undesirable conversion reaction. We demonstrate that by evaluating the reaction free energy, structural deformation associated with the insertion of magnesium, and the diffusion barriers, a quantitative evaluation about the feasibility of magnesium intercalation can be well established. Although our current work focuses on the study of MnO2 polymorphs, the same evaluation can be applied to other cathode candidates, thus paving the road to identify better cathode candidates in future.