Stress-relieving defects enable ultra-stable silicon anode for Li-ion storage

Graphite-like coated silicon (Si@G) material has been shown to be only partly useful in addressing the technological problems of high-capacity Si anodes in lithium ion batteries (LIBs). This is because of inevitable and large internal stresses in a Si@G structure induced by instantaneously explosive expansion of Si upon lithiation which destroys the graphitic matrix, and leads to the uncontrolled growth of a solid-electrolyte interphase (SEI) layer, and severe capacity fading. Therefore, it is vital to develop a novel internal-stress-relief strategy for Si@G of the next-generation stable LIBs anodes. Herein, being inspired by a relief valve, we design a nitrogen-doped carbon layer coating on Si nanoparticles (Si@NG) to effectively relief the volume expansion of Si spheres during lithiation. Such homogenous N-doping in each graphitic layer generates uniformly-distributed “hole” defects in the NG network and guarantees a stress relief in the lithiated Si@NG to the maximum extent possible. Therefore, when tested as an anode material for LIBs, Si@NG shows superior cycling stability (1321 mAh·g−1 after 100 cycles at the current density of 2100 mA g−1, about 96.6% capacity retention) and ultra-high initial coulombic efficiency (ICE) of 90.3%. [Display omitted] •N-doped graphitic shell coated Si sphere (Si@NG) shows excellent capacity, cycle life, and initial coulombic efficiency.•The holey defects of NG shell caused by doping induces localized stress concentration during the lithiation process.•The Si@NG structure accommodates the volumetric expansion of Si without deforming the graphitic layer and SEI layers.