Ni-doped spinel LiNi x Mn2−x O4 (x =0, 0.05, 0.10) samples were prepared by a sol–gel method. Structure and morphology of the samples were characterized by X-ray diffraction, scanning electron microscopy, Brunnauer–Emmet–Teller method and inductively coupled plasma atomic absorption spectrometry. The electrochemical behavior as a cathode material (positive mass) for aqueous rechargeable lithium batteries (ARLBs) was investigated by cyclic voltammetry, electrochemical impedance spectroscopy, capacity measurements and cycling tests. The results show that the LiNi0.1Mn1.9O4 electrode presents the best rate and cycling performance but low reversible capacity. In contrast, the LiNi0.05Mn1.95O4 electrode shows a higher reversible capacity and relatively good cycling behavior. At a current density of 150mAg−1, LiNi0.05Mn1.95O4 delivers a reversible capacity of 102mAhg−1. At the relative high current densities of 1500 and 3000mAg−1, the LiNi0.05Mn1.95O4 electrode still delivers reversible capacities of 95.0 and 88.7mAhg−1, respectively. The Ni-doped samples show excellent cycling life in 0.5molL−1 Li2SO4 aqueous solution. The capacity retention ratios for LiNi0.05Mn1.95O4 and LiNi0.10Mn1.90O4 after 800 cycles at a current density of 1500mAg−1 are 79.4% and 91.1%, respectively, much higher than that for the undoped LiMn2O4 at only 37.8%.