Hierarchical Microspheres of Aggregated Silicon Nanoparticles with Nanometre Gaps as the Anode for Lithium‐Ion Batteries with Excellent Cycling Stability

Novel hierarchical microspheres of aggregated silicon nanoparticles (p‐Si microsphere) with nanometre gaps have been synthesized through reverse microemulsion in combination with a modified magnesiothermic reduction approach using silica (∼200 nm) as the precursor. The hierarchical porous structure of p‐Si microspheres is composed of abundant intergranular gaps (100–200 nm) in the interconnected nanosized Si particles, along with ultrafine Si nanosized grains (∼5 nm) and intragranular voids formed in interconnected nanosized Si particles. The hierarchical microspheres of aggregated Si nanoparticles possess a high specific surface area of 136 m 2 g −1 and can achieve a high tap density of 0.3 g cm −3 . Such a novel microstructure with a large surface area and void gaps between interconnected Si nanoparticles can accommodate the volume change of Si during the lithium ion (Li + ) alloying/dealloying process. Meanwhile, the mesoporous structure facilitates Li + penetration into the nano‐Si grain interface, significantly shortening the Li + diffusion pathway as well as enhancing the heterogeneous reaction sites. Such hierarchical microspherical Si anodes demonstrated excellent cycling stability, delivering reversible capacity of 845 mAh g −1 after 200 cycles at 0.2 A g −1 and rate performance with a high reversible capacity of 681 mAh g −1 at 1 A g −1 with 97 % of initial capacity retention.