Hydrometallurgy　remains　a　major　challenge　to　simplify　its　complex　separation　and　precipitation　processes　for　spent　lithium-ion　batteries　(LIBs).　Herein,　we　propose　a　Fischer-lactonization-driven　mechanism　for　the　cascade　reaction　of　leaching　and　chelation　of　spent　LIBs.　Citric　acid　undergoes　a　two-step　dissociation　of　the　carboxylic　acid　(-COOH)　and　complexes　with　the　leached　metal　ion,　while　the　residual　-COOH　is　attacked　by　H　protons　to　form　a　protonated　carboxyl　ion　(-COO　-).　Subsequently,　the　lone　pair　of　electrons　in　the　hydroxyl　of　the　same　molecule　attack　the　carbon　atom　in　-COO　-　to　facilitate　ester　bonding,　leading　to　the　formation　of　a　lactonized　gel.　The　leaching　rates　of　Li,　Ni,　Co　and　Mn　are　99.3,　99.1,　99.5　and　99.2　%,　respectively.　The　regenerated　monocrystalline　LiNi0.5Co0.2Mn0.3O2　(NCM523)　has　a　uniform　particle　size　distribution　and　complete　lamellar　structure,　with　a　capacity　retention　rate　of　70.6　%　after　250　cycles　at　0.5　C.　The　mechanism　achieves　a　one-step　chelation　reaction,　and　the　energy　consumption　and　carbon　emissions　are　only　26　%　and　44　%,　respectively,　of　that　of　the　conventional　hydrometallurgical.　The　strategy　achieves　a　double　breakthrough　in　simplifying　the　process　and　improving　environmental　friendliness,　offering　a　sustainable　approach　to　the　re-utilization　of　spent　LIBs.