Erosion mechanism of refractories in a pyro-processing furnace for recycling lithium-ion secondary batteries

Abstract

The refractory lining in a furnace is always damaged and peels off when spent lithium-ion secondary batteries (LIB) are pyro-processed in a rotary kiln. To develop highly durable refractories and to elucidate the erosion behavior, various analyses such as scanning electron microscopy/energy dispersive X-ray spectroscopy, laser-induced breakdown spectroscopy, inductively coupled plasma atomic emission spectroscopy, ion chromatography, and X-ray diffraction were performed on the linings sampled from different sections of a refractory. Our results suggested the following mechanisms in Al2O3–SiO2–CaO refractory damage during pyro-processing of spent LIB packs. First, Li2O, P2O5, LiF, and HF were formed by thermal decomposition of electrolyte constituents of the lithium-ion secondary batteries. When HF reacts with SiO2, Al2O3, and CaO on the surface of the refractory, each fluoride that forms vaporizes and melts. When Li2O and P2O5 (as well as LiF) react with the Al2O3–SiO2 refractory, an Li2O–Al2O3–SiO2–P2O5(-LiF) phase with a low melting point forms and penetrates into the refractory through pores, grain boundaries, and cracks, resulting in peeling off.