LiMn 2 O 4 (LMO) with a spinel crystal structure is a promising cathode for next-generation Li-ion batteries (LIBs), owing to its low cost and high operating voltage of ~4.4 V. However, due to the Jahn-Teller distortion effect, LMO typically exhibits deteriorated cycling performance, owing to the dissolution of Mn into a liquid electrolyte. In this study, Fe-doped truncated octahedral LMO cathodes with different concentrations were synthesized to improve LMO stability in LIBs. The Fe-doped truncated octahedral LMO was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The Li + ion diffusion coefficients of the cathodes were measured using electrochemical impedance spectroscopy and the galvanostatic intermittent titration technique. Compared to the truncated octahedral undoped LMO, the Fe-doped LMO cathode with an appropriate amount of dopant exhibited the best LIB performance, with the highest Li + ion diffusivity resulting from the increased oxygen vacancy as the path of Li + ion.