Sulfur-doped CoP@ Nitrogen-doped porous carbon hollow tube as an advanced anode with excellent cycling stability for sodium-ion batteries

Transition metal phosphides have attracted increasing attention as anode materials for sodium-ion batteries (SIBs). Cobalt phosphide (CoP) has been deemed as prospective anode materials owing to its high theoretical capacity. Nevertheless, the defects of cobalt phosphides are evident. Low conductivity, the non-negligible volume expansion and aggregation of particles during sodiation/desodiation process result in poor cycling performance and rapid capacity decay, which greatly limit their applications. Herein, we designed a hollow-nanotube structure of sulfur-doped cobalt phosphide (S-CoP) nanoparticles coated by nitrogen-doped porous carbon (S-CoP@NPC), which can be successfully synthesized via an ordinary hydrothermal process followed by the low-temperature phosphorization/sulfuration treatment. The doping of sulfur element provides more active sites, meanwhile, the carbon coating largely helps to avoid the agglomeration of nanoparticles, alleviate volume expansion and improve the conductivity of materials. The S-CoP@NPC composite presents stable cycling performance, showing a discharge specific capacity of 230 mAh g(-1) over 370 cycles at 0.2 A g(-1). In addition, it also exhibits good rate capability with a discharge specific capacity of 143 mAh g(-1) at 5 A g(-1), even when the current density returns to 0.2 A g(-1), the discharge specific capacity can recover 213 mAh g(-1). Furthermore, the kinetic analysis of SCoP@NPC composite explains that the excellent cycling and rate performance benefit from the extrinsic pseudocapacitive behavior. (C) 2020 Elsevier Inc. All rights reserved.