CoS nanoparticle encapsulated S-doped carbon nanofiber/nanotube hybrid grown on exfoliated graphite for long-lifespan and high-rate potassium ion batteries

Exfoliated graphite (EG) as important matrix material for potassium-ion batteries (PIBs) suffers from its inherent low surface activity, which results in poor interactions with active matter (e.g. metal sulfides) and undesired initial capacity decay of the EG-based electrodes. To address these issues, in this study, an attempt for EG’ surface engineering has been carried out through a stepwise gas-phase strategy. A S-doped carbon nanofiber/nanotube (CNF/CNT) hybrid was in-situ introduced on the surface of EG to form a novel micro-/nano- multiscale matrix structure. CoS nanoparticles are encapsulated in the inner of CNFs and CNTs. The special core–shell configuration not only prevents the aggregation of CoS during the sulfidation process, but also confines the active nanoparticles to avoid pulverization and maintains stable integrated electrode structure. Moreover, the couple effect between the active site-rich nature of CNFs and the high conductivity of CNTs as well as the formation of 3D porous network contribute to substantially elevated reversible capacity (411 mAh g −1 ), excellent initial cycling stability and rate capability (184 mAh g −1 at 2.0 A g −1 ). The effective surface modification strategy dominated by rational hybridization of CNFs and CNTs provides a new avenue for the development of high-performance electrode materials in PIB applications.