Solid-Electrolyte Interphase Evolution of Carbon-Coated Silicon Nanoparticles for Lithium-Ion Batteries Monitored by Transmission Electron Microscopy and Impedance Spectroscopy

The main drawbacks of silicon as the most promising anode material for lithium-ion batteries (theoretical capacity=3572mAhg(-1)) are lithiation-induced volume changes and the continuous formation of a solid-electrolyte interphase (SEI) upon cycling. A recent strategy is to focus on the influence of coatings and composite materials. To this end, the evolution of the SEI, as well as an applied carbon coating, on nanosilicon electrodes during the first electrochemical cycles is monitored. Two specific techniques are combined: Transmission Electron Microscopy (TEM) is used to study the surface evolution of the nanoparticles on a very local scale, whereas electrochemical impedance spectroscopy (EIS) provides information on the electrode level. A TEM-EELS fingerprint signal of carbonate structures from the SEI is discovered, which can be used to differentiate between the SEI and a graphitic carbon matrix. Furthermore, the shielding effect of the carbon coating and the thickness evolution of the SEI are described.