Ultrafine Co0.85Se nanocrystals dispersed in 3D CNT network as a flexible free-standing anode for high-performance lithium-ion battery

Abstract

Cobalt selenides have drawn much attention in the field of rechargeable batteries owing to their considerable capacity. However, when applied to lithium-ion batteries (LIBs), their electrochemical performances are usually restrained by the limited active sites exploring the electrolyte. In this work, ultrafine Co_0.85Se nanocrystals with an average size of about 17 nm were applied to offer a feasible solution. The smallest grain size of Co_0.85Se ever applied to LIBs showed its advantage in ensuring more Li⁺ active sites. Furthermore, a surface coating strategy was introduced to suppress the aggregations of Co_0.85Se nanocrystals, and carbon nanotubes (CNTs) helped to create a 3D hierarchical porous network, which could greatly facilitate the infiltration of electrolyte and improve the electronic conductivity as well. Due to the intertwined CNTs, the as-prepared composites also exhibited great flexibility. When tested in the half cells of LIBs, they demonstrated excellent rate capabilities of 797, 824, 830, 776, 687 and 548 mA h g⁻¹ at 0.1, 0.2, 0.5, 1, 2, 5 A g⁻¹, respectively, and the outstanding cyclic performance of 1582 mA h g⁻¹ after 80 cycles at 0.2 A g⁻¹. Furthermore, full cells were assembled and they exhibited excellent rate and cyclic performances. With the extraordinary electrochemical performances, the flexible free-standing anode showed potential uses for next-generation wearable devices.