The recycling of valuable metals from spent lithium-ion batteries (LIBs) is becoming increasingly important due to the depletion of natural resources and potential pollution from the spent batteries. In this work, different types of acids (2 M citric (C₆H₈O₇), 1 M oxalic (C₂H₂O₄), 2 M sulfuric (H₂SO₄), 4 M hydrochloric (HCl), and 1 M nitric (HNO₃) acid)) and reducing agents (hydrogen peroxide (H₂O₂), glucose (C₆H₁₂O₆) and ascorbic acid (C₆H₈O₆)) were selected for investigating the recovery of valuable metals from waste LIBs. The crushed and sieved material contained on average 23% (w/w) cobalt, 3% (w/w) lithium, and 1–5% (w/w) nickel, copper, manganese, aluminum, and iron. Results indicated that mineral acids (4 M HCl and 2 M H₂SO₄ with 1% (v/v) H₂O₂) produced generally higher yields compared with organic acids, with a nearly complete dissolution of lithium, cobalt, and nickel at 25 °C with a slurry density of 5% (w/v). Further leaching experiments carried out with H₂SO₄ media and different reducing agents with a slurry density of 10% (w/v) show that nearly all of the cobalt and lithium can be leached out in sulfuric acid (2 M) when using C₆H₈O₆ as a reducing agent (10% g/g_scraps) at 80 °C.