Rational Design of Robust Janus Shell on Silicon Anodes for High Performance Lithium Ion Batteries.

The high-capacity silicon material has been regarded as a promising anode for next-generation high-energy lithium ion batteries. However, its practical application is still hindered by the electrode fracture and unstable solid electrolyte interphase during cycling. Herein, we design a structure of encapsulating silicon in the robust "janus shell", in which the internal graphene shell with sufficient void space is used to alleviate the mechanical stress induced by the volume expansion, and the conformal carbon outer shell is introduced to strongly bond the loosely stacked graphene shell and simultaneously seal the nanopores on the surface. With the ultra-stable janus carbon shell, the excellent structural integrity of electrode and stable solid electrolyte interphase layer could be effectively preserved, resulting in the impressive cycling behavior. Indeed, the as-synthesized anodes exhibit excellent cycle stability and high rate performance, delivering a high reversible capacity of 1416 mAh g-1 at a current density of 0.2 A g-1 and 852 mAh g-1 at a high current density of 5 A g-1. Remarkably, the superior capacity retention of 88.5% could be achieved even after 400 cycles at a high current density of 2 A g-1. More importantly, this work opens up a novel avenue to address high-capacity anodes with large volume change.