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, Co^2/3+ 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 (M_xN_yO_z) 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 Co^2/3+ 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.