Towards High-Capacity Silicon Anodes for Lithium-Ion Batteries: On the Influence of Loading and Surface Coating on the Cyclability

The development of efficient energy storage systems is of great importance in view of the increasing demand in electrical energy both for stationary and mobile applications. Silicon (Si) is an abundant and nontoxic material and provides one of the highest theoretical specific capacities (approx. 4000 mAh/g) of all known anode active materials. However, severe mechanical stresses, low coulombic efficiencies and irreversible capacity losses during cycling of silicon anodes are critical issues that need to be addressed.

For “real world” applications, it is indispensable to increase the gravimetric and volumetric energy densities of Li-ion batteries (e.g., by tailoring the areal loading of electrodes). Low active material loadings lead to high rate capability and good cyclability but result in low practical energy densities (and areal capacities). In this work, we show that systematic investigations of Si-based anodes with different silicon loadings help finding the optimum between cycling stability and areal capacity. Furthermore, we describe a straightforward pyrolysis process that allows for carbon encapsulation of silicon nanoparticles, which thus enhances the electrode stability, including rate capability and capacity retention. Batteries using the silicon/carbon nanocomposite demonstrate specific capacities of >2000 mAh/g and areal capacities of approx. 2 mAh/cm² over 200 cycles. The different materials employed were analyzed in detail via TEM, REM, Raman- and IR-spectroscopy, and galvanostatic charge/discharge measurements. In addition, we present results on the volume changes (cell “breathing”) and SEI formation upon cycling from in operando AFM measurements.