Lithium-Metal-Free Sulfur Batteries with Biochar and Steam-Activated Biochar-Based Anodes from Spent Common Ivy

Lithium-sulfur batteries are emerging as sustainable replacements for current lithium-ion batteries. The commercial viability of this novel type of battery is still under debate due to the extensive use of highly reactive lithium-metal anodes and the complex electrochemistry of the sulfur cathode. In this research, a novel sulfur-based battery has been proposed that eliminates the need for metallic lithium anodes and other critical raw materials like cobalt and graphite, replacing them with biomass-derived materials. This approach presents numerous benefits, encompassing ample availability, cost-effectiveness, safety, and environmental friendliness. In particular, two types of biochar-based anode electrodes (non-activated and activated biochar) derived from spent common ivy have been investigated as alternatives to metallic lithium. We compared their structural and electrochemical properties, both of which exhibited good compatibility with the typical electrolytes used in sulfur batteries. Surprisingly, while steam activation results in an increased specific surface area, the non-activated ivy biochar demonstrates better performance than the activated biochar, achieving a stable capacity of 400 mA h g⁻¹ at 0.1 A g⁻¹ and a long lifespan (>400 cycles at 0.5 A g⁻¹). Our results demonstrate that the presence of heteroatoms, such as oxygen and nitrogen positively affects the capacity and cycling performance of the electrodes. This led to increased d-spacing in the graphitic layer, a strong interaction with the solid electrolyte interphase layer, and improved ion transportation. Finally, the non-activated biochar was successfully coupled with a sulfur cathode to fabricate lithium-metal-free sulfur batteries, delivering a specific energy density of ~600 Wh kg⁻¹.