Flexible Co9S8–Carbon Nanofibers Architecture for Lithium-Ion Batteries: A Comprehensive Study of the Nature of Lithium Storage

A conversion-type anode with superior theoretical specific capacity and medium operating voltage is regarded as a potential solution for the next generation of high-performance lithium-ion batteries (LIBs) anode. However, the practical application of a conversion-type anode is hindered by the sluggish conversion reaction kinetics and ambiguous conversion reaction mechanism. Herein, a flexible Co9S8-carbon nanofibers composite foam (Co9S8@CF-700) with unique ganglion-like architecture is ingeniously designed and synthesized through an electrospinning strategy. Tested as an LIBs anode, a carbon nanofibers network with prominent conductivity, highly reversible additional capacity, and excellent buffering capability ensure the enhanced conversion reaction kinetics of flexible Co9S8@CF-700 relative to Co9S8 nanoparticles. Furthermore, a comprehensive high temporal-spatial resolution in situ measurement system combining in situ X-ray diffraction (XRD) and in situ magnetometry techniques is proposed and applied to reveal the adsorption-conversion-space charge/intercalation lithium storage mechanism of Co9S8@CF-700. Specifically, in situ XRD detects the conversion reaction in the medium voltage region, and the in situ magnetometry monitors the capacitive behavior in the high-voltage region and the space charge/intercalation lithium storage behavior in the low-voltage region. This work opens a new avenue for enhancing the lithium storage kinetics and exploring the energy storage mechanism of LIBs conversion-type anode.