Abstract
The electrochemical reactions between Li and Na with amorphous/nanocrystalline AlSb thin films prepared by magnetron sputtering are reported for the first time. The films are composed of AlSb and Sb nanoparticles embedded into an amorphous matrix with an overall Sb/Al ratio of 1.13. The reaction with Li proceeds with an average reaction potential of 0.65 V, a reversible capacity of 750 mAh g-1, and very fast reaction kinetics. For instance, a storage capacity close to 500 mAh g-1, corresponding to 70% of the maximum capacity, is achieved at 125 C-rate. In addition, there is only a small increase in overpotentials with increasing current: ~0.15 V at 12 C and ~0.7 V at 125 C. In contrast, the reaction with Na results in average reaction potential of 0.5 V and a storage capacity of 500 mAh g-1 obtained at low currents. The capacity retention and reaction kinetics are presently not satisfactory with pronounced capacity losses upon cycling and large overpotentials with increasing current. The capacity retention can be improved by using fluoroethylene carbonate additive in the Na-ion electrolyte, which highlights that the Solid Electrolyte Interphase plays an important role for the electrode cycling stability. The reaction kinetics is relatively poor and an increase in overpotentials of about 0.9 V at 2 C is observed (retained capacity of about 350 mAh g-1 or 66% of the maximum). The study of the reaction mechanism on thick films (3-5 m) by X-ray diffraction reveals that the electrode material remains amorphous at all potentials. The presence of broad humps, located at the positions expected for Li-Al and Li-Sb line compounds, suggests that during the reaction with Li the atomic short range ordering is similar to the expected phases.
