In situ synthesis of porous Si dispersed in carbon nanotube intertwined expanded graphite for high-energy lithium-ion batteries

Abstract

Silicon (Si) is perceived as one of the most promising anode materials for next-generation lithium-ion batteries (LIBs). For its practical application, superior electrochemical properties, low cost and scalable production are highly required. Herein, we synthesize a carbon nanotube intertwined expanded graphite/porous Si (CNT/EG/pSi) composite through the in situ magnesiothermic reduction method, where porous Si nanoparticles (NPs) are dispersed in the interspaces constructed by EG sheets, with CNTs intertwined throughout the composite, connecting Si NPs and EG sheets. Mesopores within Si NPs can not only shorten the electron and Li⁺ ion transport distance, but also play an important role in accommodating the huge volume change. EG and CNTs construct a three-dimensional conductive network, improving the electronic conductivity of the composite. Moreover, EG sheets release the excessive local stress over cycles, and CNTs can randomly build new electronic pathways as the structure changes, alleviating the degeneration of the conductive network. Consequently, the CNT/EG/pSi composite exhibits enhanced cycling and rate performances when used as the anode material, delivering reversible specific capacities of 2618 mA h g⁻¹ at 0.2 A g⁻¹ and 1390 mA h g⁻¹ at 4 A g⁻¹, maintaining a capacity of 2152 mA h g⁻¹ after 100 cycles at 0.4 A g⁻¹, with a capacity retention of 84%. This hierarchically structured anode material has a facile and low-cost synthetic route, as well as excellent electrochemical performances, making it attractive for high-performance LIB applications.