Role of Structure and Interfaces in the Performance of TiSnSb as an Electrode for Li-Ion Batteries

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 omposite vs Li is undertaken by combining X-ray diffraction (XRD), Sb-121, Sn-119 Mossbauer and Li-7 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.