Expandable crosslinked polymer coatings on silicon nanoparticle anode toward high-rate and long-cycle-life lithium-ion battery

Porous and electrically conductive coating on silicon nanoparticles (Si NPs) anode can mitigate the volume expansion during charging or discharging in Li-ion battery (LIB) while conventional protection coating process resulted in non-uniform polymer shell which show low volumetric or areal capacities. Here, we demonstrated that ultra-thin polyacrylonitrile layer can be formed conformally by emulsion-assisted coating process and cross-linked on Si NPs (Si@x-PAN) producing stable and expandable polymer shell which showed a highly stable long-term cycling ability. Areal and specific capacities of Si@x-PAN were an ∼ 2 mAh/cm² and a 2000 mAh/g, respectively. Importantly, we found that capacity decay was only 5 % after 100 cycles and>75 % of capacity was retained even after 1000 cycles (0.5C/0.5C) with the help of a uniform Li-ion current around the Si NPs during continuous charging and discharging. To our knowledge, this long-term stability at reasonable loading levels is one of the highest levels of performance in pure Si anode systems.