Intercalation Pseudocapacitive Nanoscale Nickel Hexacyanoferrate@Carbon Nanotubes as a High-Rate Cathode Material for Aqueous Sodium-Ion Battery

Prussian blue analogues (PBAs) have been widely investigated as cathode materials in aqueous Na-ion batteries (ASIBs) due to their special open-framework structure. Herein, nanoscale nickel hexacyanoferrate with carbon nanotubes (NiHCF@CNTs, NC for short) has been fabricated via a facile route. According to transmission electron microscopy (TEM) images, NiHCF is a randomly aggregated particle and CNTs are universally tangled with NiHCF. In ASIBs, NC delivers a discharge capacity of 54.1 mAh g(-1) at 0.1 A g(-1). An astonishingly long life with a capacity retention of 80% over 10 000 cycles at 10 A g(-1) is also achieved. Significantly, this material exhibits excellent rate capability with a capacity of 47.9 mAh g(-1) even at an ultrahigh current density of 10 A g(-1). Such superior rate performance is owing to the extrinsic intercalation pseudocapacitive response. This surface-controlled mechanism suggests that developing pseudocapacitive materials is a feasible to promote the rate performance of PBAs as cathodes for ASIBs.