• Energy Research

The limited fossil fuel supply toward carbon neutrality has driven tremendous efforts to replace fuel vehicles by electric ones. The recycling of retired power batteries, a core energy supply component of electric vehicles (EVs), is necessary for developing a sustainable EV industry. Here, we comprehensively review the current status and technical challenges of recycling lithium iron phosphate (LFP) batteries. The review focuses on: 1) environmental risks of LFP batteries, 2) cascade utilization, 3) separation of cathode material and aluminium foil, 4) lithium (Li) extraction technologies, and 5) regeneration and transformation of cathode materials. Detailed analyses are elaborated with case examples and technical challenges. Our critical analysis demonstrates that compared with retired lithium nickel cobalt manganese oxide (NCM) batteries, LFP batteries do not contain the high-value elements such as Co and Ni, so the economic drive for LFP recycling is compromised although future market prospects are substantial. It is of great practical significance to develop low-carbon and cost-effective Li extraction technologies and regeneration processes for cathode materials to ensure a sustainable and stable development of the LFP battery and EV industry.

Critical metals are key to lithium-ion batteries (LIB), but metal mining has inflicted many socio-environmental harms. Recovering metals from spent LIBs can partially overcome this challenge, but existing recovery and recycling techniques such as pyrometallurgy and hydrometallurgy are either energy intensive or require toxic chemicals. Solvometallurgy, using biodegradable deep eutectic solvents (DESs), has emerged as a greener option, but full life cycle sustainability of DESs remains unclear. Here, using an integrated assessment framework we show that, compared with pyrometallurgy and hydrometallurgy, the weak solubility of metal compounds in hydrogen bond donors (HBDs) and acceptors (HBAs) and their non-recoverability in chemical precipitation routes of the DES approach result in 3.1 times more CO2 eq, ∼5 times more ozone depletion, and 6.5–7.3 times higher costs. Although alternative electrodeposition routes can minimize HBA loss and alleviate chemical impacts, high energy consumption associated with HBDs exacerbates global warming potential. In situ repairing/regeneration of crystalline compounds in cathode materials could offer a more sustainable application for DESs.

This study innovatively combines mechanochemistry and high-temperature thermal reduction to achieve the recovery of valuable metals from spent LIBs. First, under the action of mechanical force, the crystal structure of lithium cobalt oxide (LiCoO2) found in the cathode materials of spent LIBs was destroyed and converted into lithium carbonate (Li2CO3) and Li-free residue (C/Co3O4) using dry ice as a co-grinding reagent. The optimum Li2CO3 recovery conditions were determined to be as follows: a ratio of dry ice: LiCoO2 powder mass of 20:1; a rotation speed of 700 rpm, and a reaction time of 1.5 h. With these conditions the maximum percentage of Li2CO3 recovered was 95.04 wt%. The Co3O4 in Li-free residue was reduced to a high-value Co0 product via a high-temperature (800 °C) heat treatment. Gibbs free energy analysis confirmed that the carbon in the Li-free residue could be used as a self-reducing reagent for the thermal reduction of Co3O4. The reactants and products of each step were characterized by XRD, FT-IR, XPS and SEM techniques. The green route for recycling spent LIBs that this study proposes realizes the green and cost-effective conversion of LiCoO2 to high-value products, which may become an outstanding example of recycling spent LIBs.