The　proliferation　of　waste　lithium　batteries　is　on　the　rise;　however,　the　thermal　treatment　attributes　of　these　batteries　are　largely　overlooked,　and　the　conversion　mechanism　of　lithium　battery　separators　remains　unclear.　This　study　marks　the　first　comprehensive　to　compare　the　thermal　degradation　characteristics,　kinetic　parameters　and　mechanisms,　thermal　degradation　products,　and　degradation　pathways　of　polypropylene　(PP)　and　polyethylene　(PE)　lithium　battery　diaphragms.　The　pyrolysis　temperatures　for　the　PP　and　PE　were　340-500　and　440-530　degrees　C,　respectively.　PP　and　PE　exhibited　average　activation　energies　of　65.19-73.04　and　207.62-209.40　kJ/mol,　respectively.　At　600-800　degrees　C,　the　yields　of　PP　and　PE　pyrolysis　gases　and　gasoline　products　increased　with　increasing　temperature,　while　the　yields　of　diesel　and　paraffin　products　decreased.　The　most　dominant　products　generated　from　the　pyrolysis　of　PP　and　PE　were　olefins,　and　the　amount　of　olefin　products　from　PE　increased　with　increasing　pyrolysis　temperature.　CH3　fracture　was　the　first　reaction　step　that　occurred　during　PP　pyrolysis.　Our　study　provides　useful　information　for　industrial　recycling,　disposal,　and　utilization　of　electric　vehicle　lithium　battery　separators　as　well　as　data　on　the　pyrolysis　behaviours　and　transformation　mechanisms　of　polyolefin　wastes.