A green strategy for spent lithium-ion battery recycling via SO2-driven cobalt reduction

Abstract

Recovering valuable metals from spent lithium-ion batteries (SLIBs) is crucial for environmental protection and resource sustainability. Traditional methods for recycling SLIBs are plagued by high costs, energy demands, and the generation of toxic waste. Here we present a ‘waste-for-waste’ strategy that overcomes these barriers by using waste ferrous sulfate (WFS)—an abundant industrial byproduct—as a potent sulfating agent to recycle LiCoO₂ (LCO) cathodes. Our results demonstrate that WFS-assisted roasting, followed by selective precipitation, recovers lithium (>99%) and cobalt (>98%) with minimal waste. Kinetic studies and Density Functional Theory (DFT) modeling reveal a novel SO₂-driven electron donation mechanism, where SO₂ gas released from WFS decomposition preferentially adsorbs at cobalt sites, reducing Co³⁺ to Co²⁺ and enabling efficient gas–solid phase sulfation. Ecological and economic analyses show that the chemical reagents and energy consumption for this process are only 27% and 30% of those of traditional metallurgical methods, respectively. The green strategy was also successfully extended to other mainstream SLIBs, including LiMn₂O₄, LiFePO₄, and LiCo_xMn_yNi_zO₂, achieving high leaching efficiencies of valuable elements. This conceptually new pathway circumvents the internal diffusion limitations seen in conventional methods. This work not only provides a scalable and economically compelling solution for the circular battery economy but also establishes a new paradigm for upcycling industrial waste into high-value chemical reagents.