An efficient sequential mechanochemical activation and complexation leaching for enhanced recovery of valuable metals from spent lithium-ion batteries was explored. The cathode material of lithium cobalt oxide (LiCoO₂) was firstly ground in a planetary ball mill, and then diluted into an ethylene diamine tetraacetic acid (EDTA) and hydrogen peroxide (H₂O₂) leaching solution. One hundred percent of cobalt (Co) and 98.2% of lithium (Li) could be leached from the activated LiCoO₂ materials compared with the non-activated (the leaching efficiencies of 7.9% for Co and 4.1% for Li), indicating that the mechanochemical activation process could significantly improve the EDTA/H₂O₂ mixed liquor complexation leaching of valuable metals from spent LIBs. The involved kinetics and mechanism were explored by carrying out characterization and theoretical calculations. Results demonstrated that an exponential kinetic model could well describe the mechanochemical process, and the Avrami equation leaching model provided a satisfactory fitting relevant for the subsequent improved leaching process. The breakage of the layer structure, the Co–O-Co unit, and the LiCoO₂ surface, along with a decrease in activation energy, resulted in the enhancement of the leaching efficiency following mechanochemical activation. Enhanced leaching of Co was owing to the reduction of Co(III) to Co(II) instantaneously forming Co(II)-EDTA chelates. The acidity of EDTA and H₂O₂ promoted upgrade dissolution of lithium after mechanochemical activation for LiCoO₂. This efficient and benign recovery process is of great significance for recycling spent LIBs.