Covalent Surface Functionalization of Silicon for Enhanced Cycling Performance

Silicon (Si)-based negative electrodes often have these two prerequisites for improved performance: submicron or nanoscale dimension and additives (generally for electrolytes). In this work, a single approach was implemented to achieve the beneficial effects of both. Functionalized Si particles with an average diameter of less than 300 nm and with good polydispersity indices (0.2 to 0.3) were successfully generated by ball-milling the Si with vinylene carbonate (VC) and polyethylene oxide (PEO). Surface characterization using x-ray photoelectron spectroscopy (XPS) confirms the modification of the Si surface and the presence of the additives even after the electrode fabrication processes. We demonstrate through half-cell cycling that the addition of small amounts of VC result in increased specific capacities compared to the neat Si, i.e., ~370 mAh.g-1 higher for Si-VC electrode after the formation cycles. On the other hand, the presence of PEO introduces a passivating film on the surface of Si that hinders Li+ transport to the electrode as indicated by electrochemical impedance spectroscopy (EIS), resulting in reduced specific capacities, i.e., ~325 mAh.g-1 less relative to the neat Siafter formation. Nevertheless, the Si-PEO system exhibited the most promising cycling stability compared to the neat Si and Si-VC electrodes after extended cycling. Similar observations were drawn from full cell studies using high voltage NMC 811 cathodes, confirming the viability of our approach for the improvement of Si-based next generation lithium-ion batteries.