Upcycled spent hand warmers as sustainable multifunctional hosts for high-performance lithium–sulfur cells

Abstract

Lithium–sulfur electrochemical cells, known for their high theoretical charge-storage capacity and low cost, face challenges related to polysulfide dissolution and cycling stability. This study introduces a sustainable approach to enhance lithium–sulfur cell performance by utilizing recycled components from spent hand warmers and refinery desulfurization byproducts. The resulting sulfur-hand warmer composite cathodes exhibit high sulfur loading (6 mg cm⁻²) and outstanding electrochemical stability in a low electrolyte-to-sulfur condition of 10 μL mg_sulfur⁻¹. Compared to conventional sulfur–carbon cathodes, the sulfur-hand warmer composite cathode exhibits superior charge transfer, effective polysulfide confinement, and enhanced cycling stability, delivering a high discharge capacity of 732 mAh g⁻¹ (4.39 mAh cm⁻²), extended cycle life over 100 cycles, and excellent rate capability across C/20 to C/2 rates. We further systematically dissect the individual roles of Fe₃O₄, vermiculite, and activated carbon in spent hand warmers. Composite cathodes derived from these components effectively stabilize polysulfides and enhance electrical conductivity. Fe₃O₄ provides both catalytic activity and strong chemical polysulfide adsorption, while vermiculite offers physical confinement and electrostatic anchoring, and activated carbon ensures effective physical trapping along with high conductivity. As a result, these findings highlight the feasibility of upcycling industrial and consumer waste into high-performance, cost-effective, and environmentally sustainable materials for lithium–sulfur batteries, advancing both battery technology and circular economy objectives.