Walnut-inspired microsized porous silicon/graphene core–shell composites for high-performance lithium-ion battery anodes

Silicon is considered an exceptionally promising alternative to the most commonly used material, graphite, as an anode for next-generation lithium-ion batteries, as it has high energy density owing to its high theoretical capacity and abundant storage. Here, microsized walnut-like porous silicon/reduced graphene oxide (P-Si/rGO) core–shell composites are successfully prepared via in situ reduction followed by a dealloying process. The composites show specific capacities of more than 2, 100 mAh·g^-1 at a current density of 1, 000 mA·g^-1, 1, 600 mAh·g^-1 at 2, 000 mA·g^-1, 1, 500 mAh·g^-1 at 3, 000 mA·g^-1, 1, 200 mAh·g^-1 at 4, 000 mA·g^-1, and 950 mAh·g^-1 at 5, 000 mA·g^-1, and maintain a value of 1, 258 mAh·g^-1 after 300 cycles at a current density of 1, 000 mA·g^-1. Their excellent rate performance and cycling stability can be attributed to the unique structural design: 1) The graphene shell dramatically improves the conductivity and stabilizes the solid– electrolyte interface layers; 2) the inner porous structure supplies sufficient space for silicon expansion; 3) the nanostructure of silicon can prevent the pulverization resulting from volume expansion stress. Notably, this in situ reduction method can be applied as a universal formula to coat graphene on almost all types of metals and alloys of various sizes, shapes, and compositions without adding any reagents to afford energy storage materials, graphene-based catalytic materials, graphene-enhanced composites, etc.