Hierarchical Carbon Nano Fibres for Flexible Zn-Air Batteries

Nanostructured functional materials, specifically carbon nanofibres/nanotubes, are attractive due to their chemical stability and electrochemical properties. Carbon based structures across different length scales have already been used in a range of energy applications including carbon papers for proton exchange membrane fuel cells, carbon nanofibers for supercapacitors and carbon nanotubes as conductive additives in lithium-ion batteries. The development of hierarchical, designed nanomaterials bridging length scales is required for next generation devices because each length scale of interest offers certain advantages, macro-scale fibres offering ease of fabrication and nano-scale tubes offering superior electrochemical performance. Functional carbon nanofibers with hierarchical architectures are essential components in advanced energy applications. Here, we present a simple approach to preparing highly engineered, hierarchical nanofibers and a simple heat treatment. This simple synthesis route has been successfully developed to prepare a 3D structure consisting of large backbone fibres decorated with hierarchical, small carbon nanotubes produced via in-situ growth during carbonisation. The carbon nanofiber with hierarchical structure can significantly enhance the nanoporous 3D carbon network by increasing the specific surface area and number of electron and ion pathways, resulting in a doubled power density when compared to the carbon nanofiber without hierarchical structure. When utilized as an air cathode in the solid-state zinc-air battery, the carbon nanofiber with hierarchical structure showed markedly better electrochemical performance, delivering a long cycle life while remaining highly flexible.