Ascorbate-Promoted Whole-Cell Biocatalysis for Lithium Bio-Recovery from Spent LiFePO4 Cathodes

Abstract

The sustainable recycling of spent lithium iron phosphate (LiFePO4) batteries via bioleaching is critically important yet often constrained by low processing capacity and severe microbial oxidative stress. Herein, we report a highly efficient biocatalytic strategy utilizing Gluconobacter oxydans as a whole-cell biocatalyst for the leaching of spent LFP batteries. We demonstrate that the addition of 25 mM ascorbic acid (AA) dramatically enhances the catalytic performance of this microbial system, achieving a high lithium extraction yield of 92.7% within 7 days at a pulp density of 10.0 g L–1. Transcriptomic and biochemical analyses elucidate a novel synergistic catalytic mechanism: AA not only alleviates intracellular oxidative stress to sustain microbial catalyst but also actively participates in a pyrroloquinoline quinone (PQQ)-mediated extracellular redox cycle. In this cycle, the reduction of PQQ by AA and its subsequent reoxidation by O2 generate H2O2. Under mild acidic conditions (pH ∼4), these H2O2 preferentially drive the catalytic oxidation of LiFePO4 to FePO4, thereby significantly facilitating Li release. The dissolved Li was further recovered from bioleachate as Li3PO4, while the FePO4-rich residues showed effective dye–removal activity, demonstrating residue valorization potential. This work unveils the dual function of AA in fortifying the microbial catalyst and driving mineral oxidation, presenting a practical and economically viable strategy for the integrated recycling of spent LFP batteries.