Electrochemistry

Biography

Biography: Ulrike Langklotz

Abstract

Carbon coated silicon nanowires (SiNW) are the nanostructure of choice for binder-free high capacity anodes. These anodes with adjusted active mass loading and advanced morphology were grown by chemical vapor deposition (CVD). The high mass loadings (up to 6 mg_Si/cm²) in combination with the lightweight carbon foil used as substrate and current collector predestines these anodes for applications where high energy densities are required, e.g. for automotive applications. The requirements in high power devices are especially challenging with respect to the (de)lithiation reactions. Thus, (complex) carbon coated SiNW anodes with varying morphology and mass loading are examined regarding their performance as well as the kinetics of the charge-discharge reactions. The specific capacity and cycle stability as well as the achievable C-rates strictly depend on these parameters. The anodes offer capacities up to 2 mAhcm^-2, initial coulomb efficiencies higher than 80% and capacity fading of less than 10% over 100 cycles. The established process with high uniformity allows detailed examinations of the charge-discharge curves of samples with tuned properties and clearly shows an effect of the SiNW morphology on the phase transitions in the initial cycles, which in turn can be crucial regarding the degradation behavior of the anodes. Finally, galvanostatic intermittent titration technique (GITT) is applied to analyze the charge transfer and diffusion overpotentials of the (de)lithiation reaction. The overpotentials are basic kinetic parameters of these reactions, and they enable the estimation of the rate determining processes.