Metal–organic-frameworks-engaged formation of Co0.85Se@C nanoboxes embedded in carbon nanofibers film for enhanced potassium-ion storage

Abstract Potassium-ion batteries (PIBs) are considered as viable energy storage system due to the abundance and low cost of potassium. However, their development is still hampered by the lack of suitable electrode materials that can withstand the structural deterioration caused during intercalation/deintercalation of large potassium ions. Herein, a flexible and freestanding anode material consisting of Co0.85Se@carbon nanoboxes (Co0.85Se@C) embedded in carbon nanofibers films is fabricated through a metal‒organic-framework-engaged electrospinning strategy coupled to a one-step confined carbonization-selenidation process. The rationally designed electrode with high mass loading of active material offers attractive structural features, particularly Co0.85Se@C nanoboxes with large surface area and requisite void space to accommodate the large volumetric expansion for boosted cycling stability. Moreover, the robust conductive carbon nanofiber network not only improves the electronic conductivity, but also stabilizes the integral structure upon repeated K+ insertion/deinsertion. As a result, this unique nanoarchitecture demonstrates excellent cycling stability as an anode material for PIBs, with a high reversible capacity of 299 mA h g−1 at 1 A g−1 after 400 cycles and achieves remarkable rate performance with a specific capacity of 166 mA h g−1 at 5 A g−1. Most importantly, it is demonstrated that increasing the areal loading of active material in the electrode through a layer-by-layer stacking configuration further improves the energy density of the battery.