Direct Re-Functionalization of Spent LFP Cathodes of Lithium-Ion Batteries by Aqueous Electrochemical Process

Lithium-ion batteries (LIBs) find many applications from powering multitudes of portable electronics, to automotive, and stationary energy storage. The current rapid market growth, more specifically in mobility and stationary energy storage, has resulted in an exponential increase in the usage of LIBs since early 2000. It is predicted that this market may reach 6.3 TWh by 2030. Inevitably, the quantity of spent LIBs will follow the same trend, causing important challenges to the waste management system. Consequently, we expect an important increase of spent lithium batteries available for recovery during the next decade raising the pressure on the emerging LIBs recycling industry. In addition to this rapid increase in volume of spent batteries, the recent migration from cobalt and nickel rich cathodic materials to lithium iron phosphate (LiFePO4, LFP) will impact significantly the current hydrometallurgical processes both on their efficiency and on their profitability. Indeed, the industry has focused until now on recovering the most valuable elements like lithium, cobalt, and nickel while iron and phosphorus from LFP batteries ending to waste. In this context, new low-cost processes that enable the recovery of LFP as highly valuable products are needed. Direct recycling, that aims to re-functionalize the spent LFP as new active material by keeping its initial orthorhombic structure, responds perfectly to these criteria. Hydro-Québec has developed such a process that includes a hydrometallurgical step extracting selectively Li ions as lithium bicarbonate from LFP black mass followed by the relithiation of the obtained iron (III) phosphate (FePO4, FP). Research in collaboration with McGill University has elucidated the chemistry of the process [1,2] and determined the relithiation step to be crucial to the re-functionalization of LFP since it restores the spent cathode’s Li-ion storage capacity [3]. While most relithiation processes are performed by high-temperature treatments or hydrothermal methods, Hydro-Québec’s process is an ambient temperature aqueous solution electrochemical relithiation method that has been recognized for its potential for industrial applications [4]. The results show that FP can be efficiently relithiated using either Li2SO4 or LiHCO3 electrolyte. The FP reduction reaction follows mostly a Cottrellian behavior, determined from potentiostatic experiments, indicating that diffusion in the solution is a critical mechanism. The application of this electrochemical relithiation process to FP originating from the delithiation of black mass from spent LFP batteries, resulted in a 96% relithiation yield at a current efficiency of 91%. The overall recycling process successfully re-functionalized deeply damaged spent LFP recovering up to 99% of the LFP’s original discharge capacity, achieving up to 153 mAh g-1 at C/12. Meanwhile, the initial discharge capacity of the re-functionalized LFP at 1C attained 119 mAh g-1, which interestingly increased upon cycling, reaching 131 mAh g-1 after 225 cycles. This increase could be associated with electrochemical activation promoted by cycling-induced LFP crystal annealing and/or by electrochemical milling. Hence, the final recycled LFP is a re-functionalized cathodic active material suitable for reuse in new LFP battery manufacturing. [1] F. Larouche, et al.; J. Electrochem. Soc. 169 (2022) 73509. [2] F. Larouche, et al.; Ind. Eng. Chem. Res. 62 (2023) 903–915. [3] F. Larouche, et al.; J. Power Sources 624 (2024) 235533. [4] E. Beletskii, et al.; Energy Environ. Mater. (2024) 1–17.

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