The demand for increased Li-ion batteries with technological advances in wireless electronic devices had led to the demand for high-capacity Li-ion batteries. Si is an attractive candidate as an anode active material for the development of high-capacity Li-ion batteries. Si has a theoretical capacity of 4200 mAh/g(Li22Si5) in reaction with Li+, while the theoretical capacity of graphite anode active material is 372 mAh/g. However, Si has a poor charge-discharge cycle life because of the volume expansion of ∼400% in the lithiation process resulting in strong stress. In order to improve the cycle life of the Si anode, nano-particle powder Si anode, nano-wired Si anode, porosity structure Si anode, and Si anode with shape memory alloy current collector are reported.
Shape memory alloys have unique characteristic that are not found in general metals. This characteristic, called shape memory effect and superelastic property, is due to reversible martensite phase transformation caused by temperature and stress respectively. The shape memory effect restores the deformed alloy to its original shape, and the super-elastic property prevent plastic deformation of the alloy even with numbers of percent strain. Moreover, when the super-elastic properties are expressed, the Applied stress on the shape memory alloy is absorbed into the alloy and relieved.
Thus, in this study, a thin film Si anode with Ti-Nb-Zr shape memory alloys as a current collector was fabricated by DC magnetron sputtering system, a cyclic voltammetry, constant current charge-discharge test, and electrochemical impedance spectroscopy were conducted to study its electrochemical properties. As a result, enhanced cycle-life by super-elastic properties was observed at thin film Si anode deposited on Ti-Nb-Zr shape memory alloy.