A　novel　synergistic　extractant　consisting　of　a　deep　eutectic　solvent　(DES)　and　tri-n-butyl　phosphate　(TBP)　is　proposed　for　selective　extraction　of　valuable　metals　from　waste　lithium-ion　batteries　(LIBs).　The　extraction　efficiencies　of　Ni2+,　Co2+,　and　Mn2+　were　99.8%,　99.1%,　and　95.9%,　respectively,　and　high-purity　Li+　was　enriched　in　the　raffinate　after　the　single-stage　extraction.　Valuable　metal　salts,　lithium　carbonate　(92.3　wt%)　and　cobalt　oxalate　(94.9　wt%),　were　obtained.　The　DES　+　TBP　extractant　retained　its　high　extraction　performance　even　after　multiple　regeneration　cycles.　The　extraction　process　followed　the　so-called　＂cation　exchange　mechanism＂　with　thermodynamic　properties　of　Delta　H　＜　0,　Delta　G　＜　0,　and　Delta　S　＜　0.　The　molecular-level　extraction　mechanism　demonstrated　that　the　extraction　process　was　dominated　by　both　electrostatic　and　coordination　interactions　between　the　metal　ions　and　DES/TBP,　based　on　quantum　chemical　calculations.　This　study　aims　to　provide　a　new　strategy　for　recycling　valuable　metals　from　waste　LIBs.