Olivine LiMn1-xFexPO4 (x = 0.5, 0.4, 0.3, 0.2) coated with carbon are prepared as the cathode materials for the aqueous rechargeable lithium-ion batteries (ARLBs). Li+ insertion-extraction behaviors of the as-prepared materials in LiNO3 aqueous electrolyte with/without dissolved oxygen are studied by cyclic voltammograms (CVs) and electrochemical impedance spectra (EIS). The Li+ diffusion coefficient of LiMn1-xFexPO4 in LiNO3 aqueous electrolyte is first reported. The results indicate that eliminating the dissolved oxygen in the aqueous electrolyte could decrease the charge transfer-resistance and increase the Li+ diffusion coefficient of (LiMn1-xFexPO4/C)//LiV3O8 ARLBs, which also improves the electrochemical properties of the ARLBs. The initial discharge specific capacity of LiMn0.6Fe0.4PO4/C is 112 mA h g(-1) at 0.1 C-rate, which provides a new candidate cathode material for ARLBs.