Cobalt sulfides have been popularly used in energy storage because of their high theoretical capacity and abundant redox reactions. However, poor reaction kinetics, rapid capacity decay, and severe polarization owing to volume changes during electrochemical reaction are still huge challenges for cobalt sulfides in practical applications. Herein, cobalt sulfide yolk-shell spheres were synthesized by phosphorus doping (P-CoS) to stabilize the structure of cobalt sulfides and improve their electronic/ion conductivity. Kinetic tests and density functional theory calculations confirm that the introduction of phosphorus into cobalt sulfides greatly reduces the diffusion barrier of Li+ in the intrinsic structure, thereby improving the reaction kinetics of electrode materials during the Li+ insertion/extraction process. In consequence, the P-CoS electrode delivers a high lithium storage capacity (781 mAh g-1 after 100 cycles at 0.2 A g-1 ), excellent rate capability (489 mAh g-1 at 10 A g-1 ), and outstanding cycling stability (no significant capacity decay over 4000 cycles at 5 A g-1 ). Especially for sodium-ion battery application, the P-CoS electrode expresses a striking capacity of approximately 260 mAh g-1 at 2 A g-1 after 900 cycles.
Keywords: anion doping; anode; cobalt sulfides; lithium/sodium-ion batteries; yolk-shell spheres.
© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.