STUDY OF HIGH PERFORMANCE SILICON BASED ANODES FOR ELECTRIC VEHICLES (EVs) BATTERIES

In order to increase the energy density of the lithium battery, better anodes and cathodes are still required. Silicon has attracted much attention because its theoretical capacity is 4200mAhg⁻¹, an order of magnitude greater than that of graphite. Nevertheless, the main disadvantage of high-capacity anode materials is their very large volume expansion and contraction (~320% ) during Li insertion/de-insertion, followed by cracking and pulverization of the anode material. Si nanostructures have the advantage of a shorter diffusion distance for lithium species, which can improve the power performance of the battery. Studying of large surface capacity anodes (high Si loading) is almost nonexistent. In this work, in addition to the synthesis and characterization of novel three-dimensional high-capacity SiNWs and SiNPs-based anodes, we focused on studying their degradation mechanisms. We have been able to produce remarkably high loadings of 3-15 mAh/cm², very low irreversible capacity (of the order of only 10% for the 3-4 mAh/cm² samples), current efficiency greater than 99.5% and a fast charge–discharge rate (up to 2.7C (20mA/cm²) which is not common for silicon anodes). These properties meet the requirements of lithium batteries for portable and electric-vehicle applications. These SiNWs-based binder free anodes and the SiNPs anodes have been cycled for 200 – 300 cycles, exhibiting a stable cycle life after which, at least 70-80% are still connected to the substrate. The thickness and the resistance of the Solid Electrolyte Interphase (SEI, Peled 1979) grow with time and with cycling. The structure and composition changes of the SiNWs, the SiNPs and of the SEI will be reported.