Direct recycling of spent lithium-ion batteries for the recovery of cathode active material by solid-state relithiation

1.Introduction – The transition to electric vehicles has become a pressing need to move toward thedecarbonization of the transport sector. Nevertheless, this shift will generate a significant volume of spentlithium-ion batteries (LIBs), necessitating effective recycling strategies. Existing large-scale recyclingmethods, such as pyrometallurgy and hydrometallurgy, allow to reintegrate valuable materials back intothe supply chain, especially critical raw materials [1]. Currently, there is a growing interest in directrecycling, which emerges as a promising technique due to low energy consumption, regenerating thecathode material without destroying its original crystal structure. In this work, an experimental procedurefor direct recycling of spent cathode material has been investigated by solid-state relithiation. 2.Experimental – A spent lithium-nickel-manganese-cobalt oxide LiNi0.5Mn0.3Co0.2O2 (NMC) batterywas first discharged and disassembled. Pretreatment steps included dissolution with triethyl phosphate at120 °C to remove the binder, separation of aluminum and copper foils, and thermal treatment at 720 °Cfor carbon black and graphite removal. Relithiation was carried out by solid-state mixing of the recoveredspent cathode powder with lithium carbonate (Li2CO3) and sintering in air. Different lithium carbonateexcess (10-30 %) and different sintering temperatures (800-900 °C) were investigated. The obtainedpowders were characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) analysis,and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). 3.Results and Discussion – XRD analysis was conducted to investigate the crystalline structure of therecycled cathode materials, and it was compared with the pristine and spent NMC. XRD patternsconfirmed that NMC structure is maintained and homogeneous without impurities (Image 1). Thecalculated intensity ratio I(003)/I(101) of each sample is reported in Table I. Values greater than 1.2confirmed the good layered structure and low Li+/Ni+ cation mixing of all recycled NMC. The Li molarfractions, fLi, calculated as the ratio of Li and transition metal elements (Ni, Co, Mn) by ICP-OESanalysis, are reported in Table I. The results evidenced that 10 % Li excess at 900 °C is not sufficient forthe complete Li stoichiometry recovery in the cathode material; while, using 30 % Li excess with athermal treatment at 800 °C led to a Li fraction of 1.005, thus compensating the Li loss in the spentbattery. The SEM analysis of lithiated samples showed that the applied treatment allows to obtainparticles with the same dimension and morphology as the pristine NMC. 4.Conclusions – This work presented the results of an experimental investigation for the direct recyclingof LIBs spent cathode material. Characterization of recycled NMC demonstrated the successfulregeneration of chemical composition and crystalline structure, obtaining comparable morphology andparticles dimension when using 30 % excess of lithium and sintering at 800 °C. 5.References [1]D. Latini, M. Vaccari, M. Lagnoni, M. Orefice, F. Mathieux, J. Huisman, L. Tognotti, A. Bertei, J.Power Sources, 546, (2022) p. 231979.