Carbon nanotube-stabilized CoS dual-shell hollow spheres for high-performance K-ion storage.

In this work, carbon nanotube-coated dual-shell Co9S8 hollow spheres are studied as anode materials for K-ion batteries. The unique hollow structure and carbon nanotubes synergistically enhance the conductivity and resolve the critical drawbacks of Co9S8 electrodes, including large volume variation, structural instability and interfacial changes. Thus, the electrode delivers a stable reversible capacity of 320.5 mA h g-1 at 0.1 A g-1 after 200 cycles with a capacity retention of 91%. At 1.0 A g-1, the capacity is 163.9 mA h g-1 after 1000 cycles with a capacity retention of 73.6%. An investigation of the electrode reaction mechanism indicates that the surface capacity also contributes to the outstanding electrochemical performance.