Macroporous carbon from human hair: A journey towards the fabrication of high energy Li-ion capacitors

Human hair is a cheap and easily available source of carbon to be used as high performance electrode for electrochemical energy storage devices. In the present work, human hair is pre-treated and then activated using NaOH before being employed as electrode. The resulted activated carbon (ACHH) exhibits a high specific surface area of 1116 m² g^-1 which is one of the pre-requisite for it to be used as an electrode for supercapacitor applications. ACHH delivered a specific capacitance of ∼115 F g^-1 at a current density of 100 mA g^-1 in single electrode configuration with Li in the presence of organic medium. This result was followed by the fabrication of symmetric supercapacitor and delivered an energy density of 19.2 Wh kg^-1. The energy density has been further improved by introducing an insertion type electrode, Li₄Ti₅O₁₂ in Li-ion hybrid electrochemical capacitor (Li-HEC) assembly. The combined battery-supercapacitor type reactions in Li-HEC recorded the maximum energy density of 23 Wh kg^-1. An excellent cycleability is noted for both symmetric and Li-HEC in an organic medium.