Hard carbon spheres interconnected by carbon nanotubes as high-performance anodes for sodium-ion batteries

Hard carbon is one of the most promising candidates of anode materials for sodium-ion batteries (SIBs). However, its insufficient electrical conductivity resulted from the non-graphitizable structure is a main obstacle to increasing its capacity and rate performance in devices. To resolve this issue, here carbon nanotubes (CNTs) connected hard carbon spheres (HCSs) composite was prepared by carbonizing CNTs supported 3-aminophenol-formaldehyde resin spheres. The seamless bonding of CNTs onto HCSs provide a long-range conductive path for electron transport and the porous skeleton allowing convenient ion diffusion. The as-prepared HCSs-CNTs composite shows a reversible capacity of 151.7 mAh g−1 after 160 cycles when used as anode materials for SIBs. It also exhibits outstanding long-life cycling performance and rate capability, achieving a capacity of 95.1 mAh g−1 at 1000 mA g−1 after 500 cycles and 71.7 mAh g−1 at 3000 mA g−1. In particular, it is worth noticing that the capacitive behavior of HCSs-CNTs electrode makes a major contribution to the enhanced rate capability.