Field-assisted conductive substrate sparks the redox kinetics of Co9S8 in Li- and Na-ion batteries

As a promising candidate electrode material in both Li- and Na-ion batteries (L/SIBs), the application of Co9S8 is being hindered by its unsatisfactory electrochemical performance caused by the sluggish ion diffusion kinetics and drastic volume expansion. Herein, a hybrid material composed of Co9S8−x, N-doped carbon foam that seeded with Co nanoparticles (Co9S8−x@Co-NC) is constructed. Particularly, theoretical and experimental results imply that a built-in electric field at the interface of Co and NC is observed due to the variation of Fermi levels, forming rich Mott-Schottky-like heterointerfaces, which can significantly enhance the charge transfer capability between the active materials of Co9S8 and conductive NC skeleton. Moreover, the sulfur defects in Co9S8−x can not only effectively lower the energy barrier of the ion diffusion and charge transfer processes, but also endow the target sample with more storage/adsorption/active sites for Li+/Na+ ions, thus improving the rate performance of the Co9S8−x@Co-NC composite. As a result, the Co9S8−x@Co-NC exhibits fast surface-controlled redox kinetics and robust cycling stability. For instance, the Co9S8−x@Co-NC displays impressive Li-storage properties in both half and full cells with a high reversible capacity of 1007.4 mA h g−1 at 0.1 A g−1 after 100 cycles and superior rate capability up to 5 A g−1. Moreover, based on these comprehensive merits, the Co9S8−x@Co-NC composite shows decent electrochemical performance (472.2 and 311.1 mA h g−1 at 0.1 and 10 A g−1, respectively) as an anode for SIBs. This work presents an effective strategy for the construction of Mott-Schottky-like heterointerfaces in Co9S8 based materials and provides specific inspiration for future works designing high-performance electrodes via interfacial engineering.