The role of structure and interface in the performance of TiSnSb as an electrode for Li-ion batteries
Résumé
The lithium-ion battery electrode material TiSnSb shows excellent electrochemical performance related to its high capacity (550 mA h g−1) and rate capability over 210 cycles. To discriminate between the role of active material and the role of the electrode formulation in the good electrochemical features of the TiSnSb electrodes, a full study comparing the electrochemical mechanisms of TiSnSb and a Ti/ Sn/Sb composite vs Li is undertaken by combining X-ray diffraction (XRD), 121Sb, 119Sn Mössbauer and 7Li NMR spectroscopic in situ measurements. During the first discharge, TiSnSb undergoes a direct conversion reaction while Ti/Sn/Sb composites proceed by a stepwise alloying process, both leading to a mixture of lithium antimonide, lithium stannides, and titanium. More surprisingly the charge occurs differently with a reformation of the "TiSnSb" phase in the first case and the formation of Sn and Sb in the second case. The key role of the interfaces in conversion type reactions is discussed. The nature of the interfaces is linked to the long-range order of elements in the starting material. Furthermore, the length scales of the interfaces between Li3Sb, LixSn and Ti appear to control the reactions that occur on charge.