Hierarchical pomegranate-structure design enables stress management for volume release of Si anode

Abstract

Si is a promising anode material for lithium-ion batteries owing to its high theoretical capacity. However, large stress during (de)lithiation induces severe structural pulverization, electrical contact failure, and unstable solid-electrolyte interface, which hampers the practical application of Si anode. Herein, a Si-based anode with a hierarchical pomegranate-structure (HPS-Si) was designed to modulate the stress variation, and a sub-micronized Si-based sphere was assembled by the nano-sized Si nanospheres with sub-nanometer-sized multi-phase modification of the covalently linked SiO2–x, SiC, and carbon. The sub-micronized HPS-Si stacked with Si nanospheres can avoid agglomerates during cycling due to the high surface energy of nanomaterials. Meanwhile, the reasonable pore structure from SiO2 reduction owing to density difference is enough to accommodate the limited volume expansion. The Si spheres with a size of about 50 nm can prevent self-cracking. SiO2–x, and SiC as flexible and rigid layers, have been synergistically used to reduce the surface stress of conductive carbon layers to avoid cracking. The covalent bonding immensely strengthens the link of the modification with Si nanospheres, thus resisting stress effects. Consequently, a full cell comprising an HPS-Si anode and a LiCoO2 cathode achieved an energy density of 415 Wh kg−1 with a capacity retention ratio of 87.9% after 300 cycles based on the active materials. It is anticipated that the hierarchical pomegranate-structure design can provide inspiring insights for further studies of the practical application of silicon anode.