Secondary aqueous lithium-ion batteries with spinel Li2Mn4O9 or Li4Mn5O12, as the anode and LiMn2O4 as the cathode are investigated. The aqueous electrolyte contains 6 M LiNO3 and 0.0015 M OH-. The Li2Mn4O9/LiNO3/LiMn2O4 and Li4Mn5O12,/LiNO3/LiMn2O4 aqueous cells deliver approximately 100 m Ah g(-1) capacity at an average voltage of 1-1.1 V. This aqueous lithium-ion system eliminates safety concerns and offers considerably cost-effective technology for manufacturing.