## 3 Results and Discussion
In the case of phosphorus, these values were higher than those obtained for the smaller amount of H\({}_{2}\)O\({}_{2}\), and slightly lower in the case of fluorine. To sum it all up, in the case of Material I, an increase in the leaching efficiencies of key components, i.e., cobalt, nickel, lithium and copper, was observed, along with an increase in the concentration of sulfuric acid with the addition of 1 dm\({}^{3}\) of hydrogen peroxide. In the case of using 2 dm\({}^{3}\) of hydrogen peroxide for leaching, the leaching efficiencies of the main components, i.e., Co, Ni, Li and Cu, were similarly high and amounted to 94%, 97%, 96%, >98% and 86-90%, respectively. Equally high efficiencies and a similar trend were observed for Mn, Fe, P and F. For Material II, the same behavior of increasing the leaching efficiencies of key components, i.e., cobalt, nickel, lithium and copper, with the increase in the concentration of sulfuric acid, with the addition of 1 dm\({}^{3}\) and 2 dm\({}^{3}\) of hydrogen peroxide, was observed. The highest leaching efficiencies for cobalt, nickel, lithium and copper were obtained using 20% sulfuric acid with 1 dm\({}^{3}\) of hydrogen peroxide for leaching, which were 88.97%, -100%, 96.04% and -100%, respectively. A similar tendency was also observed in this case for Mn, Fe, P and F. Using Material III, the process was characterized by the same tendency of increasing leaching efficiencies of key components, i.e., cobalt, nickel, lithium and copper, with the increase in concentration of sulfuric acid and the addition of 1 dm\({}^{3}\) and 2 dm\({}^{3}\) of hydrogen peroxide. In this case, however, the highest leaching efficiencies of cobalt, nickel, lithium and copper were obtained using 20% sulfuric acid with 2 dm\({}^{3}\) of H\({}_{2}\)O\({}_{2}\), and amounted to 89.93%, -89.73%, -100% and 88.48%, respectively. A similar trend was observed in this case for Mn, Fe, P and F. However, this material was characterized by a low leaching efficiency of F, in comparison to the results obtained for Materials I and II, amounting to about 60%. Based on the obtained results, it was decided that further experiments to determine the optimal solid-to-liquid-phase ratio of the acid leaching process would be carried out using 20% sulfuric acid solution with the addition of 1 dm\({}^{3}\) of hydrogen peroxide. Similar conclusions were reached by the authors of the work written by [PERSON] and [PERSON] [56], indicating that an effective factor supporting the acid leaching of battery masses from Li-ion cells is hydrogen peroxide in amounts similar to those presented in this work. ### Results of the Single-Stage Acid Leaching Method with the Addition of Hydrogen Peroxide  
From the results of single-stage acid leach experiments with the addition of hydrogen peroxide, presented in Table 4, it can be concluded that with a solid-to-liquid-phase ratio of 1:4, higher cobalt concentrations were obtained (for all three materials) in the leaching solution than using a solid-to-liquid-phase ratio of 1:5. The highest cobalt concentration of about 64 g/dm\({}^{3}\) was obtained in the test using Material II. In the case of nickel, the highest concentration of 26 g/dm\({}^{3}\) was obtained in the test using Material I. For all battery masses, higher concentrations were obtained for nickel with a solid-to-liquid-phase ratio of 1:4 compared to 1:5. The free acid concentration ranged from 49.00 to 85.80 g/dm\({}^{3}\), and the pH of the tested solutions ranged from 0.45 to 0.60. For lithium, iron and manganese, the solid-to-liquid-phase ratios of 1:4 and 1:5 resulted in very similar high leaching efficiencies. The manganese leaching efficiency ranged from 82% to 100%, that of lithium ranged from 80% to 99%, and that of copper ranged from 76.50% to 99.72%. For iron, phosphorus and fluorine, the results obtained were very diverse. Therefore, the leaching efficiency for iron ranged from about 58% to 92%, that for phosphorus ranged from 40% to 94%, and that for fluorine ranged from 42% to 76%.