Impact of Low Temperatures on the Lithiation and Delithiation Properties of Si-Based Electrodes in Ionic Liquid Electrolytes

Lithium-ion batteries are used in various extreme environments, such as cold regions and outer space; thus, improvements in energy density, safety, and cycle life in these environments are urgently required. We investigated changes in the charge and discharge properties of Si-based electrodes in ionic liquid electrolytes with decreasing temperature and the cycle life at low temperature. The reversible capacity at low temperature was determined by the properties of the surface film on the electrodes and/or the ionic conductivity of the electrolytes. The electrode coated with a surface film formed at a low temperature exhibited insufficient capacity. In contrast, a Si-only electrode precoated with the surface film at room temperature exhibited a cycle life at low temperatures in ionic liquid electrolytes longer than that in conventional organic liquid electrolytes. Doping phosphorus into Si led to improved cycling performance, and its impact was more noticeable at lower temperatures.

Automated summary

This study investigates the charge and discharge properties of Si-based electrodes in ionic liquid electrolytes at low temperatures. It is found that the reversible capacity at low temperature is influenced by the properties of the surface film on the electrodes and/or the ionic conductivity of the electrolytes. Precoating Si-only electrodes with a surface film at room temperature improves the cycle life at low temperatures in ionic liquid electrolytes. Doping phosphorus into Si enhances the cycling performance, especially at lower temperatures.