Kinked silicon nanowires-based electrode configuration for lithium-ion batteries

Abstract

Silicon has been in the spotlight of the next generation anode materials due to its distinctive Li-related features such as the ability to form Li rich compounds, corresponding to an exceptional capacity of 3579 mAh/g at low working voltages. In exchange, many engineering concerns are associated to the structural deformation during lithium alloying that can lead to material pulverization as well as limited cycling life. We detail on an anode configuration based on interconnected kinked Si nanowires (k-SiNWs) fabricated by metal assisted chemical etching. A chemical peeling step is introduced to facilitate the separation of the etched k-SiNWs from their originating Si substrate. The three-dimensional (3D) interconnected k-SiNWs-based anode materials are assembled, using a conventional vacuum filtration technique, with multi-walled carbon nanotubes. The k-SiNWs are expected to be more robust to lithiation-induced stresses as they typically behave like microsprings. In addition, the kinks provide interlocking joints resulting in a fairly resilient anode material. Furthermore, the evaluation of the mechanical properties of the anode assemblies revealed a foam-like architecture that benefits from high porosity. These 3D Si-based assemblies were galvanostatically cycled in conventional electrolytes and ionic liquids. The electrochemical evaluation of the 3D Si-based anode assemblies showed valuable cycling life in ionic liquids compared to conventional electrolytes, retaining 70% of the initial capacity and displaying an average Coulombic efficiency of 97.5% after 50 cycles. Further performance improvements were obtained by coating the k-SiNWs with a 33 nm Ni coating. The exemplary mechanical behavior and electrochemical robustness were assigned to the kinked morphology of the SiNWs