Liquified Salt-Assisted Upcycling to LMFP Cathode from Waste LFP Batteries

The widespread use of LiFePO₄ (LFP) cathode material in mid-range electric vehicles has led to a significant accumulation of spent LFP. Traditional recycling methods, such as hydrometallurgical and pyrometallurgical processes, are often questioned for their economic viability and environmental impact, particularly concerning LFP cathode recycling. In this aspect, direct recycling has emerged as a promising approach, as it enables replenishing lithium and repairing structure defects in the olivine framework while consuming significantly less water, electricity and raw materials compared to the other two recycling methods. However, upcycling spent LFP to LiMn_1-xFe_xPO₄(LMFP, 0 < x < 1) for improved energy density still remains a challenge due to the inhomogeneous distribution of Mn precursors during pre-mixing process of spent LFP and Mn-/Li-based precursors.

In this work, we developed an advanced direct upcycling method to transform spent LFP into LMFP, driven by liquified Mn-/Li-based salts during a simple planetary centrifugal mixing process. Our approach relies on interfacial wetting between spent LFP particles and the Mn-/Li-salts, where moderate mechanical agitation melts the salts in situ. This creates a colloidal suspension of nanosized LFP dispersed in liquified Mn-/Li-salts, efficiently deagglomerating the LFP particles, reorganizing the crystal structure, and ensuring uniform distribution of Mn and Li within the mixture. This promotes facile ion diffusion during calcination, resulting in a homogeneous composition of LMFP cathode powder. Consequently, the upcycled LMFP demonstrates exceptional cycling stability, retaining approximately 90% of its capacity after 300 cycles at a high rate of 1C.