The reaction of a new negative electrode material NiSb2 vs lithium was investigated by 121Sb Mössbauer 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 Li3Sb. On charge, the Mössbauer analysis showed that the pristine NiSb2 is not reconstructed as expected for a conversion reaction, but that the high pressure-NiSb2 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 → Li2Sb transformation takes place followed by the Li2Sb → Li3Sb transformation. In a second step the high-pressure NiSb2 phase further reacts with Li to form Li3Sb + Ni0. Thanks to this mechanism, 100% of the initial reversible 520 mAh g − 1 capacity is sustained after 15 cycles.
