121Sb Mossbauer study of the electrochemical reaction of NiSb2 vs lithium

The reaction of a new negative electrode material NiSb(2) vs lithium was investigated by 121Sb Mossbauer spectroscopy to highlight the mechanism occurring upon the cycling of the battery. Structural and electronic modifications induced by the reaction with lithium have been characterised for different depths of discharge/charge. The first discharge was clearly identified as a conversion process which leads to the formation of Li(3)Sb. On charge, the Mossbauer analysis showed that the pristine NiSb(2) is not reconstructed as expected for a conversion reaction, but that the high pressure-NiSb(2) polymorph and antimony are formed. Once the first cycle achieved, a different mechanism takes place upon the second discharge. In a first step, the Sb -> a Li(2)Sb transformation takes place followed by the Li(2)Sb -> Li(3)Sb transformation. In a second step the high-pressure NiSb(2) phase further reacts with Li to form Li(3)Sb + Ni0. Thanks to this mechanism, 100% of the initial reversible 520 mAh g1 capacity is sustained after 15 cycles.