Electron microscopical characterization of Sn/SnSb composite electrodes for lithium-ion batteries

Lithium storage alloys such as Sn/SnSb are promising new anode materials for Li-ion batteries. Due to a proper design of the active Sn/SnSb material as well as the composite electrode, capacities exceeding 500 mAh g−1 have been achieved with this system for more than 30 cycles. The observation of micro- and nano-structural changes in the composite electrode during charge/discharge cycling is of immense importance for a further improvement of the cycling performance. Electron microscopy (SEM and TEM) in combination with analytical techniques (EFTEM, EDXS and EELS) has been used for the characterization of Sn/SnSb raw powder as well as the Sn/SnSb composite electrodes. The pristine morphology and the changes of morphology during cycling of the electrode material have been studied. Furthermore, the chemical composition and particularly compositional fluctuations within the composite material have been investigated using EFTEM and EDXS. The electron microscopy results indicate that parts of the active material get finer during the initial cycles. Moreover, amorphous regions are detected in the cycled material. The experimental results are discussed with regard to the reaction mechanism of SnSb with Li.