A few years ago, magnesium hydride has been demonstrated to be a candidate for conversion-type anode for Li-ion batteries [1]. In fact, this material features high theoretical capacity 2037 mAh.g^-1, compared to graphite-anode, and low charge-discharge polarization [1]. However, the reversible capacity is still a challenge owing to the poor conductivity of the involved entities (MgH₂/LiH), along with compatibility issues with carbonate-based liquid electrolytes. By considering safety factor and environment, LiBH₄ solid electrolyte has been demonstrated to be suitable for the development of all-solid Li-ion batteries based on MgH₂ anode [2], in which the enhanced mobility of the Li⁺ ions and H^– exchange effects play a key role during the electrochemical cycling. On the other hand, CoO has been reported to undergo a conversion reaction as negative electrode, but the high working potential and large cycling hysteresis hinders its quick application in Li-ion batteries [3]. Accordingly, the present work aims the study of the effect of an electrochemically “active” oxide such as CoO on the cycling performance of MgH₂ anode (molar ratio 1:3), a mixture having a theoretical capacity around 1376 mAh.g^-1. The final goal is to reach higher cycling performances by facing the electrical conductivity issue of metal hydrides and inhibit the formation of Li–Mg alloys in the presence of an oxide with large voltage window. Discharge-charge galvanostatic profiles were demonstrated for the 75MgH₂·25CoO paired anode in which two reversible plateaus can be distinguished using LiBH₄as solid electrolyte at 120°C, the later being above its phase transition with higher ionic conductivities. The prepared and optimized active materials were characterized using X-ray diffraction and photoelectron spectroscopy (XPS) before and after the electrochemical tests in a half-cell. The mechanistic properties of the hydride–oxide paired anode are presented as function of the milling time, composition and cyclability performance.

Acknowledgements

This work is financially supported by Research Council of Norway under the program EnergiX, Project no. 244054, LiMBAT - "Metal hydrides for Li-ion battery anodes".

References

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