Li and Mn-rich layered oxide cathodes although exhibit high specific capacities ≥240 mAh g−1, suffer from capacity fading and discharge voltage decay during prolonged cycling to potential higher than 4.5 V. This study aimed at exploring an interesting Co-free Li and Mn rich cathode material and to understand how the upper potential applied affects its capacity and average discharge voltage upon prolonged cycling. Li1.17Ni0.25Mn0.58O2 cathodes were explored in Li cells by galvanostatic charge-discharge cycling in several potential ranges. The specific capacity, capacity retention and average discharge voltage were compared with and without activation to 4.6–4.8 V when cycled to different upper potential limits. This cathode material exhibited a high discharge capacity of 242 mAh g−1 when cycled in the potential range of 2.3–4.6 V after activation to 4.8 V with gradual capacity fading and average discharge voltage decreasing from 3.62 V to 3.55 V during 100 cycles. When cycled in the potential range of 2.3–4.3 V after activation to 4.6 V, it exhibited a relatively stable capacity >160 mAh g−1 and stable average discharge voltage of 3.61 V, during 100 cycles. Thus, with optimized operating condition, the Li and Mn-rich cathode material Li1.17Ni0.25Mn0.58O2 is promising for lithium-ion batteries.