Recovery of valuable metal elements from spent lithium-ion battery via a low temperature ammonium persulfate roasting approach

Abstract

A low-cost and eco-friendly recycling method is crucial for recovering valuable elements from end-of-life lithium-ion batteries (LIBs), which plays a vital role in addressing resource scarcity and reducing the environmental impact. This study aims to develop a low-temperature pyro-metallurgical combined process to recycle spent LiNi0.5Co0.2Mn0.3O2 (NCM523). Unlike traditional pyrometallurgy methods that generate liquid alloys and slags at temperatures exceeding 1000 °C, the (NH4)2S2O8 roasting approach operates at 350 °C and converts NCM523 to water-soluble sulfates, exhibiting remarkable leaching efficiencies of Li, Ni, Co, and Mn, with values of 99.43 %, 99.87 %, 98.88 %, and 99.19 %, respectively. Systematic studies were conducted to investigate the influence of roasting temperature, (NH4)2S2O8-to-NCM mass ratio, and roasting time on the sulfation process. Furthermore, the mechanism of sulfation reaction was identified by combining experiments with thermodynamic calculation. At temperatures above 160 °C, (NH4)2S2O8 decomposes into (NH4)2S2O7, which reacts with NCM. Lithium in a layered structure forms Li2SO4, while transition elements form MnSO4, Li2Co (SO4)2, and NiSO4. At around 350 °C, (NH4)2S2O8 further decomposes into NH4HSO4, releasing SO2 and NH3. SO2 reacts with remaining NCM or unsulfated transition metal oxides, converting them into MnSO4, Li2Co (SO4)2, and NiSO4. Above 800 °C, the metal sulfates decompose into stable oxides. This study presents a low-temperature sulfation method that effectively disintegrates the crystal structure of lithium metal oxides without the need for acids or reducing agents.