Defluorination and directional conversion to light fuel by lithium synergistic vacuum catalytic co-pyrolysis for electrolyte and polyvinylidene fluoride in spent lithium-ion batteries

Abstract

To overcome the drawbacks of current recycling technologies and achieve clean utilization of toxic substances in spent lithium-ion batteries, a lithium synergistic vacuum catalytic co-pyrolysis method was proposed to defluorinate electrolyte and polyvinylidene fluoride with directional conversion to light fuel. The gas chromatography–mass spectrometry results indicated, compared to the control group, that adding CaO-ZSM-5 catalyst increased the light fuel (alcohols and hydrocarbons) content of the pyrolysis gas from 61.8 % to 91.47 % under the optimal conditions (530 °C and initial pressure of 100 Pa), whereas the total proportion of esters and toxic organic compounds decreased from 32.58 % to 3.99 %. Moreover, the ethylene carbonate and hexanedinitrile content of the electrolyte was enriched to 85 % in the pyrolysis oil. Notably, fluoride was not detected in the pyrolysis oil and gas, achieving a 98.16 % defluorination rate, implying that hazardous waste was transformed to ordinary waste, thereby greatly avoiding toxic emissions to the environment. The X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy data indicated that fluorine was fixed in the form of CaF2. X-ray photoelectron spectroscopy and XRD analysis of the catalytic pyrolysis residue confirmed that nonferrous metals in the cathode material were converted into simple substances and oxides. Finally, possible co-pyrolysis mechanisms of the organic compounds are proposed, including Li+ generation, chain initiation, catalytic pyrolysis, and directional conversion.