Metals such as nickel, cobalt, lithium, and manganese are widely used in lithium-ion batteries (LIBs) in electronic devices and electric vehicles. It is forecast that there will be a strong increase in the number of electronic devices and electric vehicles in the coming years. (1) Background: In this paper, the application of ultrasound waves on improving Li, Co, Mn, and Ni leaching efficiency from mixed active cathode materials from different types of LIBs is presented. (2) Methods: Environmentally friendly, low-concentrated (0.75 M) organic acids (oxalic acid, citric acid) and, additionally, sulfuric acid, were used in sonochemical and chemical leaching (stirring process) at a temperature of 60 °C. (3) Results: The results showed significantly higher leaching efficiency of metals with ultrasound-assisted treatment, especially when using organic acids. An average of 50% better leaching results were obtained for Li in oxalic acid (99.6%) and for Co (93.1%) in citric acid during sonochemical leaching. (4) Conclusions: Based on the theory of hydrogen peroxide formation during ultrasound wave transition in solutions, the role of H2O2 as one of the most effective reductants used to enhance cobalt, manganese, and nickel leaching from LIBs is indicated.
