Detoxification and Targeted Conversion of Waste Lithium Battery Electrolyte to Light Hydrocarbons via In Situ Catalytic Pyrolysis: Roles of Li, Ni, Co, and Mn Elements

Spent lithium-ion battery electrolytes contain fluorine-, sulfur-, and phosphorus-bearing toxins, necessitating deep detoxification and directional conversion into C1–C6 light hydrocarbons. To elucidate the specific catalytic roles and sequential activation of cathode metals (Li, Ni, Co, Mn), this work systematically deconvolutes their mono- and multi-metallic migration mechanisms over a CaO-ZSM-5* catalyst during vacuum catalytic pyrolysis (530 °C, 100 Pa). Results reveal that Li+ and Ni2+ dominate C–O bond cleavage in carbonates and CaO-ZSM-5*-assisted decarboxylation and oxygen fixation, significantly increasing the relative hydrocarbon content. Conversely, Co2/3+ and Mn4+ release reactive oxygen species, causing deep oxidation of hydrocarbons into CO2 and antagonizing the targeted conversion. In multi-metallic systems, forming composite metal oxides (MxNyOz) increases the energy barrier for releasing active catalytic ions, hindering carbonate cleavage and leaving unreacted carbonate feedstocks. For detoxification, F and P are effectively immobilized as CaF2 and Ca2P2O7. The relative content of detected gas-phase nitriles is minimized to <2% due to the strong antagonistic effect of Ni2+ on Li+-promoted hexanedinitrile cleavage, while sulfur species derived from 1,3-propane sultone are converted to SO2 and ultimately mineralized as calcium and metal-sulfur salts. Mechanistically, product distributions and crystallographic properties suggest a hypothesized sequential activation model—Li+ → Ni2+ → Mn4+—governing reactivity, whereas Co2/3+ does not participate in the synergistic detoxification and selective upgrading process. This migration–reaction coupling framework provides critical insights for cathode-assisted in situ catalytic pyrolysis and closed-loop electrolyte recycling.