This study investigates the electrochemical performance of activated biochar derived from brown algae (Sargassum sp.) for lithium-ion battery applications. The biochar, obtained via carbonization of marine biomass, demonstrates excellent stability as a sustainable alternative to conventional anodes like graphite and lithium. Electrochemical tests reveal that the biochar exhibits superior cycling stability, achieving 91% capacity retention after 1000 cycles at 0.5 A g⁻¹ in an ether-based electrolyte (DOL-DME-LiTFSI-LiNO₃) compared to carbonate-based electrolytes (36% capacity retention). These results underscore its potential as a promising material for advanced battery technologies, including lithium-metal-free sulfur batteries, advancing sustainable and efficient energy storage solutions.