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The ultra-fast leaching of strategic metals from spent lithium-ion batteries cathode materials is achieved by the coordination enhanced leaching with inorganic acids and organic reductants. However, the detailed leaching mechanism that led to the fast leaching kinetics is unclear. This research utilizes the controlled variable method to reveal the coordination enhanced leaching mechanism by a comparison of the thermodynamics and kinetics between sulfate acid coupled with L -ascorbic acid (VC) and hydrochloride acid coupled with VC systems. Thermodynamic calculations, online UV–vis spectroscopy, and in-situ Raman spectroscopy are adopted to interpret the leaching mechanisms in the whole leaching process. The leaching of cobalt is controlled by decomposition of crystal structure and diffusion, respectively, in sulfate acid coupled with VC and hydrochloride acid coupled with VC systems, indicating relatively slow kinetics in the former system. The thermodynamic calculations suggest higher fractions and more stable coordination species, i.e., 26.11% CoCl(H 2 O) 5 + and 8.945% CoCl 4 (H 2 O) 2 2- at 363 K, in the latter system, which leads to lower apparent activation energy and might facilitate the rapid leaching kinetics in return. In-situ Raman mapping and depth analysis suggested the formation of coordination species on the crystal structure surfaces, solid-liquid boundaries, and bulk solutions. [Display omitted] • Thermodynamic calculations were utilized to reveal the reaction mechanism. • Reduced apparent activation energy facilitate the rapid leaching kinetics. • Formation of coordination species shift the equilibrium to forwarding directions. • Stable coordination species and high complex factions lead to high leaching ratios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultra-fast leaching of spent LIBs was achieved in low acid concentrations. • Novel synergy-coordination mechanism was use to interpret fast kinetics. • Correlations of both acids with the leaching ratio were studied for the first time. • Quantum chemistry and thermodynamic calculations were adopted to verify hypotheses. Poor economics is the principal factor that hinders the commercialization of hydrometallurgy processing of spent lithium-ion batteries cathode materials. Here, ultra-fast leaching of spent cathode materials (97.72% Li and 97.25% Co leached under S/L ratio: 10 g/L, temperature: 363 K within 10 min) was achieved in 0.5 M hydrochloric acid and 0.5 M L -ascorbic acid system as part of reducing the costs of hydrometallurgy process. The correlations of both acids with the leaching ratios were studied for the first time with the Pearson correlation coefficient. The mixture of 0.5 M hydrochloric acid and 0.5 M L -ascorbic acid demonstrated both faster kinetics and higher leaching volume than those of aqua regia. Adopting quantum chemistry and thermodynamic calculations, four hypothetical mechanisms were proposed to interpret the reaction mechanisms. Synergy-coordination, with the lowest energy, was considered to be the most reasonable mechanism for the leaching of cathode materials. Three scenarios with different leaching systems and conditions were compared to identify the key parameters determining the economics of the leaching process. [ABSTRACT FROM AUTHOR]