Low-Cost and "Green" Avenue toward Large-Scale Synthesis of In Situ Passivated Si Nanoflakes and Construction of Binder-Free Electrodes.

The high cost and low reproducibility issues of Si as the anode material for lithium-ion batteries still need to be addressed. Herein, we present a facile and scalable bead-grinding technique to down-size the cheap micron-Si into Si nanoflakes with in situ bonded pyromellitic acid (PMA) molecules. The bonded PMA not only deactivates the surfaces of Si nanoflakes but also acts as an artificial solid-electrolyte interface film. Additionally, these bonded PMA together with the free ones enable binder-free electrodes by self-polymerization and effectively improve the Li diffusion kinetics by forming -COOLi, which also has enhanced interactions with the Cu foil. It exhibits a greatly improved initial Coulombic efficiency (ICE) of 71.7% compared to the bare one (62.4%) and an initial charge capacity of 2347.2 mAh g at 80 mA g. After 500 cycles (400 mA g), a charge capacity of 1087.6 mAh g is achieved, representing its superior cyclic stability. By further introducing carboxymethyl cellulose sodium (CMC) into the electrode, the ICE is increased to 80% due to the improved electronic contact. Importantly, the PMA and CMC form elastic networks by esterification reactions, and the resulting Si-PMA-CMC electrode exhibits a remarkable capacity of 1124.6 mAh g after 300 cycles at 50 °C, which is significant for the practical application of the Si anode.