| The influence of Si nanoparticle coating on the electrolyte decomposition in Li-ion batteries Silicon is probably the most promising anode material for Li-ion batteries because of its 10 times higher specific capacity compared to the current graphite. Drawbacks are lithiation-induced volume changes and the continuous formation of a Solid Electrolyte Interphase (SEI), due to reaction with the unstable electrolyte, upon cycling of the electrode. Therefore, silicon-based anodes have not yet been able to convince on an industrial scale. A recent strategy is to focus on the influence of coatings and composite materials in order to control the volume changes and protect against the electrolyte, and consequently SEI-formation. To this end, the evolution of the SEI, as well as several applied coatings, on nanosilicon electrodes during the first electrochemical cycles is monitored. A unique combination of two specific techniques is used: 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. Furthermore, the combination of TEM and EIS is optimized to allow a fast screening of new electrode materials. For the first time, a TEM-EELS fingerprint signal of carbonate structures from the SEI is discovered, which can be used to differentiate between SEI and a graphitic carbon matrix. Furthermore, the shielding effect of the carbon coating is described. An alumina coating on the other hand inhibits the SEI formation. Finally, the mechanical properties of the applied coatings are investigated by in situ TEM experiments. |
