NaTi2(PO4)3 as host material for rechargeable magnesium ion batteries

Abstract

Rechargeable magnesium battery has been getting attention due to its various advantages such as non-toxicity, low cost, double-capacity than monovalent ion’s one, and ensuring safety by non-dendritic formation on magnesium metal surface. To realize the good points, researches on magnesium battery have been in active progress. However there are only a few host materials known for rechargeable magnesium battery because of several hurdles for investigating host materials such as slow ion diffusion, high polarization, and difficulty in structural characterization during the cycle. Herein, we have first investigated NASICON-type NaTi2(PO4)3 as a host material for rechargeable magnesium battery. The NaTi2(PO4)3 showed a high structural stability and a low polarization of about 0.1V between charge and discharge processes. The properties have not been reported so far among the host materials for magnesium battery. These results have been obtained through the experiments of cyclic voltammetry, galvanostatic cycle, x-ray diffraction, electron scanning microscopy, energy dispersive x-ray spectroscopy, and elemental mapping. Synthesized NaTi2(PO4)3 powder was identified by X-ray diffraction Rietveld refinement with GSAS program. The insertion/extraction of magnesium into/from NaTi2(PO4)3 was confirmed by structural changes observed in X-ray diffraction patterns. The existence of intercalated magnesium was confirmed by EDS and elemental mapping. Especially the magnesium insertion/extraction instead of sodium was evidenced by comparison of cyclic voltammetry between magnesium and sodium ion cell systems. The intercalation reaction is proved to be reversible from the fact that the structure of NaTi2(PO4)3 was returned to the pristine state after the electrochemical cycles. ⓒ 2015 DGIST