Mechanistic study of novel chemical looping phase separation recovering lithium-ion battery cathode materials with biogas residues

Abstract

The rapid growth of biogas production and lithium-ion battery (LIB) deployment has led to two urgent challenges: the environmental burden of excess biogas residues and the sustainable recycling of spent LIB cathodes. In this work, a novel chemical looping phase separation (CLPS) process is proposed, using pretreated cathode materials as oxygen carriers, which react with the reducing gases produced by the pyrolysis of biogas residues, enabling simultaneous production of high-quality syngas and selective separation of valuable metals. Mechanistically, reduction proceeds through a cascade of cobalt valence changes coupled to oxygen-vacancy formation and outward migration of lattice oxygen, the resulting electronic-ionic reorganization destabilizes the layered Li–O–Co framework, drives Li⁺ efflux to the gas–solid interface, and promotes in situ stabilization of lithium as Li₂CO₃ via reaction with CO₂. Kinetic studies using the Flynn–Wall–Ozawa model demonstrated distinct activation energy regimes, indicating transitions from surface adsorption to lattice oxygen participation. Optimal conditions (900 °C, 1.5 h) achieved recovery efficiencies of 94.3% for lithium and 98.5% for cobalt, and the regenerated lithium carbonate exhibited a high purity of 99.76%. An economic and environmental assessment based on the EverBatt model showed that CLPS reduces energy consumption to 29.5% of the hydrometallurgical route and lowers greenhouse gas emissions compared with both pyro- and hydrometallurgical processes. Moreover, CLPS exhibited the lowest overall cost and generated a projected profit of $20.5 per kilogram of recovered LCO batteries. This study shows that integrating biomass pyrolysis with oxygen-carrier phase separation enables sustainable, low-carbon, and cost-effective LIB recycling while valorizing agricultural residues.