The staggering accumulation of end-of-life lithium-ion batteries (LIBs) and the growing scarcity of battery metal sources have triggered an urgent call for an effective recycling strategy. However, it is challenging to reclaim these metals with both high efficiency and low environmental footprint. We use here a pulsed direct current flash Joule heating (FJH) strategy that heats the black mass, the combined anode and cathode, to >2100 K within seconds, leading to ~1000-fold increase in subsequent leaching kinetics. There are high recovery yields of all the battery metals, regardless of their chemistries, using even diluted acids like 0.01 M HCl, thereby lessening the secondary waste stream. The ultrafast high-temperature achieves thermal decomposition of the passivated solid-electrolyte-interphase and valance-state reduction of the hard-to-dissolve metal compounds, while mitigating diffusional loss of volatile metals. Life-cycle-analysis vs current recycling methods shows that FJH significantly reduces the environmental footprint of spent LIB processing, while turning it into an economically attractive process.