Silicon as Negative Electrode Material for Lithium-ion Batteries

The performance of negative electrodes based on Si nanoparticles for Li-ion batteries has been investigated. Electrodes consisted of Si nanoparticles, carbon black and Na-CMC. The investigation covered electrode production parameters such as pre-treatment of the Si-powder, different emulsifiers and cycling with two different electrolytes. Testing of the electrodes’ performance was done electrochemically with two different galvanostatic approaches: constant charge rate and stepped-up charge rate. Electrodes’ morphology, stability and surface chemistry were also evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thickness measurements and X-ray photoelectron spectroscopy (XPS). High electrode capacities were achieved though strong variation depending on electrode thickness has been found. For the best performing electrodes the capacity exceeded 1600 mAh/g with slight fading after 10-15 cycles. The difference in performance could not be assigned to the different production parameters, but had a clear correlation to the thickness of the electrode and the different electrolytes used. Propylene carbonate based electrolyte gives a lower coulombic efficiency and lower capacity retention than an ethylene carbonate-diethyl carbonate based electrolyte. The electrodes could not store any capacity at cycling rates higher than 2C, but were not damaged by cycling rates up to 50C. SEM micrographs revealed that a solid electrolyte interface (SEI) was formed on the electrodes during cycling and their surface analysis by XPS suggested that the SEI was formed by decomposition of electrolyte components