Herein is reported a novel green process involving natural l-tartaric acid leaching, developed for the sustainable recovery of Mn, Li, Co, and Ni from spent lithium-ion batteries (LIBs). Operating conditions affecting the leaching efficiencies of Mn, Li, Co, and Ni, including the concentrations of l-tartaric acid (C4H6O6) and hydrogen peroxide (H2O2), pulp density, temperature, and leaching time, were investigated. The leaching efficiencies were 99.31% for Mn, 99.07% for Li, 98.64% for Co, and 99.31% for Ni under the optimized conditions (4 vol% H2O2, 2 M l-tartaric acid, 17 g/L pulp density, 70 °C, and 30 min). The leaching mechanism was studied preliminarily based on the structure of l-tartaric acid. The kinetics data for the leaching of Mn, Li, Co, and Ni fit best to the shrinking-core model of chemical control. For the first stage, the activation energies (E as) for the leaching of Mn, Li, Co, and Ni were 66.00, 54.03, 58.18, and 73.28 kJ/mol, respectively. For the second stage, the E as for the leaching of Mn, Li, Co, and Ni were 55.68, 53.86, 58.94, and 47.78 kJ/mol, respectively. The proposed hydrometallurgical process was found to be simple, efficient, and environmentally friendly.

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The layered oxides LiNi0.6+x Co0.2–x Mn0.2O2 are promising cathode materials for Li-ion batteries (LIBs) owing to their moderate energy densities and structure stabilities. In this study, we systematically investigate the effects of substitution of Co by Ni on the structures, morphologies, and electrochemical properties of LiNi0.6+x Co0.2–x Mn0.2O2 (0.0 ≤ x ≤ 0.1). The physical characteristics of these materials are studied by particle size analysis, scanning electron microscopy, inductively coupled plasma–atomic emission spectroscopy, Rietveld refinement of X-ray diffraction data, and X-ray photoelectron spectroscopy. The electrochemical properties are investigated by charge–discharge cycling, galvanostatic intermittent titration, and electrochemical impedance spectroscopy. As the Co content decreases and the Ni content increases, the discharge capacity and voltage platform are slightly improved, while the initial efficiency, cycling performance, rate capability, and thermal stability gradually decrease. The decreased kinetic performance is attributed to the increased degree of cation mixing and resistance, which decreases the Li+ diffusivity. Moreover, the activation energy gradually increases with the decrease in the Co content, which decreases the low-temperature performance. Considering its cost, energy density, cycling lifetime, kinetic performance, and safety properties, LiNi0.65Co0.15Mn0.2O2 is a promising cathode candidate for use in LIBs.