Abnormal cyclibility in Ni@graphene core-shell and yolk-shell nanostructures for lithium ion battery anodes

Electrochemical pulverization, a commonly undesirable process for durable electrodes, is reinterpreted in popular yolk-shell nanostructures. In comparison with core-shell counterparts, the yolk-shell ones exhibit enhancing ion storage and rate capability for lithium ion battery anodes. The enhancement benefits from lowered activation barriers for lithiation and delithiation, improved surfaces and interfaces for ion availability contributed by endless pulverization of active materials. By controlled etching, stable cycling with significantly improved capacity (∼800 mAh g(-1) at 0.1 A g(-1), 600 mAh g(-1) at 0.5 A g(-1), and 490 mAh g(-1) at 1 A g(-1) vs 140 mAh g(-1) at 0.1 A g(-1)) is achieved at various rates for Ni@Graphene yolk-shell structures. Meanwhile, large rate of 20 A g(-1) with capacity of 145 mAh g(-1) is retained. Given initial pulverization for the activation, the tailored electrodes could stably last for more than 1700 cycles with an impressive capacity of ca. 490 mAh g(-1) at 5 A g(-1). Insights into electrochemical processes by TEM and STEM reveal dispersive pulverized active nanocrystals and the intact protective graphene shells play the leading role.