Constructing nitrogen-doped porous carbon immobilized Co9S8 composite as high-performance anode material for sodium-ion batteries

Transition metal sulfides (TMSs) as anode materials deliver promising potential in achieving high-capacity sodium-ion batteries (SIBs). But the undesirable volume change for structure upon redox process always hinder the realization of satisfactory cycling stability and rate capability. Herein, a novel Co9S8/carbon composite (Co9S8 @NPC) with Co9S8 nanoparticles (NPs) immobilized into nitrogen-doped porous carbon networks was synthesized via the successive procedures of sol-gel, pyrolysis carbonization and in situ sulfidation and employed as anode material for SIBs. By virtue of the yielded porous feature, nitrogen-doping and space confinement of Co9S8 NPs in conductive carbon sheet networks, the Co9S8 @NPC is able to offer integrated merits of sufficient active sites, improved reaction dynamics and rigid structural stability for high-performance Na-storage. As a result, the assembled Co9S8 @NPC electrode possesses large initial discharge/charge capacities (752.5/325.3 mAh g−1 at 50 mA g−1), considerable rate capability (138.5 mAh g−1 at 3000 mA g−1) and high cycling stability (275.3 mAh g−1 at 50 mA g−1 after 100 cycles; 120.4 mAh g−1 at 500 mA g−1 after 3000 cycles). In order to uncover the diffusion and storage mechanism of Na+ ions in the electrode material, pseudocapacitive behavior, reaction dynamics and related theoretical simulation based on first-principles calculations are initially conducted. The facile synthesis strategy and desirable Na-storage performance might enable the Co9S8 @NPC composite great potential in advanced SIBs.