A novel ionic liquid (IL) trioctyldodecyl phosphonium bis(2, 4, 4-trimethylpentyl)phosphinate was developed as a recovery agent for cobalt(II) and manganese(II) from spent lithium-ion batteries (LIBs). Absence of organic diluent provides an advantageous factor to IL-based extraction than the conventional one. Co(II) and Mn(II) were extracted quantitatively from the aqueous phase to the IL phase. Extracted Co(II) and Mn(II) were stripped from the IL using water and NH4NO3, respectively. After stripping, the IL can be reused as the extractant, facilitating the realization of a continuous extraction process. The developed hydrophobic IL shows promise as an extractant for Co(II) and Mn(II) from the spent LIBs.