Mo2C quantum dots inlaid in nitrogen-doped carbon nanofibers as free-standing anodes with long-term stability K-ion storage

Potassium ion batteries (KIBs) have attracted worldwide attention on account of low cost and abundance of resources, and potentially high energy density. However, the development of KIBs is blocked by the sluggish reaction kinetics and the instability electrode materials caused by repetitive intercalation/deintercalation of large ions size of K+. Herein, the novel flexible and free-standing Mo2C/NCNFs anode for KIBs, in which the Mo2C quantum dots are inlaid in N-doped carbon nanofibers, is synthesized via a simple electrospinning route. The rationally designed structure with Mo2C quantum dots uniformly embedded in NCNFs can not only facilitate to accelerate the K+ reaction kinetics but also potentially alleviated the expansion and pulverization of Mo2C during the long-term cycling process. Furthermore, the N doping carbon nanofibers can provide a highway for K+ ions and electrons transport, while the whole electrode also offers a free-standing electrode without the addition of conductive agents and adhesives, facilitating to promote energy density of batteries. As a result, the Mo2C/NCNFs as anode for KIBs demonstrate impressive long-term stability with the capacity fading ratio of only 0.026% per cycle until 1000 cycles at 1.0 A g−1. More importantly, Mo2C/NCNFs as anode for hybrid potassium-ion capacitors (KICs) deliver a high energy/power density of 88.2 W h kg−1/629.9 W kg−1, as well as excellent capacity retention of about 80.4% after 1000 cycles. The versatile strategy, excellent cycling stability and ultra-robust flexibility make the Mo2C/NCNFs a great prospect for application in the field of alkali metal ion batteries, electrocatalyst and flexible wearable devices.