Nitrogen-doped carbon fibers embedding CoOx nanoframes towards wearable energy storage

Abstract

As continuous consumption of the world's lithium reserves is causing concern, alternative energy storage solutions based on earth-abundant elements, such as sodium-ion batteries and zinc–air batteries, have been attracting increasing attention. Herein, nanoframes of CoO_x are encapsulated into carbonized microporous fibers by electrospinning zeolitic imidazolate frameworks to impart both a sodium-hosting capability and catalytic activities for reversible oxygen conversion. The ultrahigh rate performance of sodium-ion batteries up to 20 A g⁻¹ and ultrastable cycling over 6000 cycles are attributed to a dual-buffering effect from the framework structure of CoO_x and the confinement of carbon fibers that effectively accommodates cyclic volume fluctuation. Both in situ Raman and ex situ microscopic analyses unveil the reversible conversion of CoO_x during the sodiation/desodiation process. The excellent ORR activity, superior to that of commercial Pt/C, is mainly ascribed to the abundant Co–N–C species and the full exposure of active sites on the microporous framework structure. Flexible and rechargeable sodium-ion full batteries and zinc–air batteries are further demonstrated with great energy efficiency and cycling stability, as well as mechanical deformability.