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A sustainable cow hair‐based biocarbon/sulfur composite was prepared via a melt‐diffusion process and used as cathode for lithium–sulfur (Li−S) batteries, exhibiting high capacity, good rate capability, and excellent cyclability. The effect of the activation process during the formation of the biocarbon was deeply analyzed by thermogravimetry, N2 adsorption, X‐ray photoelectron spectroscopy, scanning and transmission electron microcopy, among others. A correlation between the composition and the surface area with the electrochemical performance was found. The best results were obtained using an activated sample and composite electrode containing 73 wt % sulfur, which present an initial discharge capacity of around 1200 mAh/g and 799 mAh/g after 100 cycles at a current density of 0.1 A/g. Moreover, a specific capacity of ~701 mAh/g was measured at 1 C. The great electrochemical performance of this electrode in Li−S batteries is attributed to the porous carbon structure. Taking into account that hair is one of the major waste produced in the leather sector, this work presents a promising approach to reuse this material by giving it added value through the preparation of carbon/sulfur composites for high‐performance Li−S batteries. [ABSTRACT FROM AUTHOR]

The demand for more efficient energy storage devices has become increasingly important in order to face the ongoing energy transition. In this regard, it is equally important to attain the production of these devices with the lowest possible environmental impact. In light of this, the use of waste materials and low‐polluting methods has become a strategic priority. In this study, brewers' spent grains were utilized as raw material to produce anodic electrodes for lithium‐ion batteries (LIBs). The synthesis process involves only two pyrolysis steps at low temperatures without any chemical treatment, reducing energy investment and waste generation. The result is a porous biocarbon structure—with mixed graphitic and amorphous characteristics—decorated with silica nanoparticles. The presence of silica greatly enhances storage capacity. The obtained biocarbon based electrodes exhibites a capacity of 455 mAh g−1 after 100 cycles, surpassing the standard anode material commonly used in commercial LIBs. [ABSTRACT FROM AUTHOR]