Layered porous silicon encapsulated in carbon nanotube cage as ultra-stable anode for lithium-ion batteries

Despite the tremendous efforts in developing Si-based anode materials, the instable structure and electrode/electrolyte interphase caused by the severe volumetric expansion/contraction still remain quite challenging for their application in Li-ion batteries (LIBs). Here we firstly propose and synthesize a micron-sized layered sieve-like porous silicon (LSP-Si) anode material by a facile etching and magnesiothermic reduction strategy. This LSP-Si material possesses special layered porous structure with evenly distributed pores in the layers, forming the interconnected nanonetwork like a sieve. Concomitant with this hierarchal layered porous structure, the LSP-Si microparticle can effectively accommodate the severe volume expansion and mitigate the stress concentration due to the mutual extrusion upon lithiation, and thus stable solid electrolyte interphase (SEI) films can be well maintained. Meanwhile, a large number of mesopores provide well-accessible space for electrolyte penetration, facilitating faster transport and better intercalation kinetics of Li⁺ ions. Further, the LSP-Si microparticle are encapsulated within the CNT cage through the electrostatic adsorption to achieve high mechanical integrity and good electrical contact. Accordingly, the LSP-Si@CNT material delivers a high reversible capacity (1862 mAh g⁻¹ at 100 mA g⁻¹), superior cycling stability (91.9% capacity retention after 500 cycles) and excellent rate capability (1546.8 mAh g⁻¹ at 200 mA g⁻¹ and 719.3 mAh g⁻¹ at 5000 mA g⁻¹). Our work provides a design strategy for high-capacity Si-based micron material viable in the next-generation high-energy LIBs.