Structurally Engineered Hollow Graphitized Carbon Nanocages as High-Performance Anodes for Potassium Ion Batteries.

Graphite is an attractive anode with high capacity and low cost for potassium ion batteries (PIBs) but suffers from poor cycle performance due to the large interlayer expansion during the potassiation/depotassiation process. Here, we propose structurally engineered hollow graphitized carbon nanocages (HGCNs) as efficient anode materials for PIBs. The HGCNs were synthesized using a one-pot, self-template and self-graphitization approach where direct pyrolysis of nickel citrate converts citrate chains into carbon-shell and simultaneously reduces Ni2+ to form a Ni metal core. This nickel core serves as not only a hard-template to create hollow-cage structure but also a catalyst to facilitate the graphitization of the carbon-shell. The HGCNs synthesized at 1000 °C (HGCN-1000), with its highly graphitized carbon-cage and developed porosity, exhibited an impressive K-storage capacity of 402.2 mAh g-1 at a current density of 30 mA g-1. The synergic combination of hollow morphology with graphitized carbon layers configured a stable structure capable of enduring extreme deformation, endowing HGCN-1000 a robust cyclic stability with a capacity retention of 95.9% over 2000 cycles at 1 A g-1. The proposed strategy provides an efficient route to combat the bottleneck cycling instability issue of graphitic carbon with hollow-graphitized carbon nanocages as promising anode materials for PIBs.