Effects of Lithium Polysulfides on the Formation of Solid Electrolyte Interfaces in Silicon Anodes.

Lithium-ion batteries are one of the most important energy storage devices of the future and pave the way for a greener society. In this context, the demand for batteries with high energy density is increasing significantly and is reaching the limits of the technology currently in use. Therefore, intensive research is being conducted to utilize a new class of materials for energy storage. The most promising alternatives to today's nickel-based cathode and graphite anode materials are silicon and sulfur. Both silicon and sulfur are abundant and cheap and possess extremely high theoretical specific capacities of 4200 mAh/g and 1675 mAh/g, respectively. One of the biggest challenges with sulfur-based batteries is the polysulfide shuttle effect, which occurs with sulfur cathodes, leading to an insulating passivation layer, especially on the commonly used lithium metal anodes. Therefore, to replace lithium metal anodes with silicon, it is of major importance to understand the reactivity of polysulfides with silicon. To investigate the effect of lithium polysulfides on the performance of the anodes in the critical formation cycles, mesoporous silicon anodes were galvanostatically cycled in electrolytes containing different concentrations of polysulfides. In this process, the anodes were analyzed after one, five and ten cycles by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to determine the composition of the SEI. Higher concentrations of polysulfides in the electrolyte result in more inorganic, oxide-containing species in the SEI. Silicon anodes with lower amounts of surface oxide show little or negative effect on the performance in the presence of polysulfides, while anodes with large amounts of surface oxide show higher impedance during cycling, an effect that is enhanced with increasing polysulfide content.