Towards a better understanding of the degradation mechanisms of Li-ion full cells using Si/C composites as anode

Carbon-coated silicon nanoparticles (40 nm diameter) were used to prepare pitch-based Si/C composites with different Si contents and a pitch and graphite-based Si/C/Gr composite. These composites were prepared by pyrolysis at 900 °C of a pitch/Si mixture obtained from the dispersion of Si particles in a solution of pitch in THF. The as-prepared composites delivered high coulombic efficiencies at the first cycle (83–86%) and stable reversible capacities (560–650 mAh g−1) versus lithium. The anodes degradation phenomena while cycling versus NMC622 in a full cell configuration were studied by simple electrochemical tests such as analysing the harvested electrodes in half-cells vs. lithium. The clear improvement on electrochemical performances due to the graphite addition was demonstrated with the suppression of the active particle's disconnection. The pitch and graphite-based composite was proven to accommodate well the silicon volume expansion and to deliver a stable electrochemical capacity of 650 mAh g−1 at the rate of C/5.