Sustainable Recovery of Spent Lithium-ion Battery Cathode via Biomass Reduction Strategy

Abstract

The sustainable recycling of spent lithium-ion battery (LIB) cathodes using biomass reduction strategies has emerged as a transformative approach that aligns circular economy principles with green chemistry. This paper critically evaluates two complementary routes: biomass reductive leaching and biomass reductive roasting. In reductive leaching, biomass-derived organic acids (e.g., citric, oxalic, acetic, levulinic acids) and waste-derived reductants (e.g., tea waste, fruit peels, food waste hydrolysates) achieve >95% leaching efficiencies for Li, Co, Ni, and Mn from LCO, NCM, LFP, and mixed cathodes under mild conditions (50-95 °C). Process intensification via mechanochemistry, microwave, or ultrasound reduces reaction times to minutes while cutting acid consumption. Deep eutectic solvents (DES) enable selective metal separation with >99% Li/Co selectivity. In reductive roasting, lignocellulosic wastes (e.g., corn stalk, sawdust, bamboo, coffee grounds) serve as renewable reductants, converting cathode materials into water-soluble Li2CO3 and reduced transition metals (CoO, Ni, MnO) at 450-700 °C lower than conventional carbothermal reduction (>1000 °C). The reduction mechanism is governed by biomass pyrolysis gases (e.g., CO, H2, CH4), with CO as the dominant reductant. Spatial separation of biomass and cathode avoids contamination, yielding >99% Li recovery and >99% Li2CO3 purity. Life cycle assessments (LCA) demonstrate that biomassassisted routes reduce energy consumption and greenhouse gas emissions while generating net profits compared to conventional pyrometallurgy and hydrometallurgy. Key challenges include biomass composition variability, incomplete mechanistic understanding, process scale-up, and DES recovery. Future priorities include standardized biomass pretreatment, real-time process control, continuous reactor design, and valorization of solid residues. This review establishes biomass reduction as a low-carbon, economically viable, and scalable platform for LIBs recycling.