Improvement of electrochemical performance of nickel-manganese-based lithium-rich layer-structured cathode material by controlling lithium/transition-metal ratio

Abstract As a cathode material, Li 1.2 Ni 0.2 Mn 0.6 O 2 delivers high discharge capacity at low C-rate but low discharge capacity at high C-rate. Furthermore, a large potential hysteresis occurs during charge and discharge, and the charge-discharge curves change shape during the charge-discharge cycling. Increasing nickel/manganese (Ni/Mn) ratio in Li 1.2 Ni y Mn 0.8− y O 2 improves discharge capacity at high C-rate, but it decreases discharge capacity at low C-rate. To accomplish high discharge capacity at both high and low C-rates, lithium/transition-metal (Li/TM) ratio in high-nickel-content material, namely, Li 1.2 Ni 0.35 Mn 0.45 O 2 , was adjusted. Cathode materials with varied lithium/transition-metal ratio ( x ), namely, Li 1.2− x Ni 0.35+(0.35/0.8) x Mn 0.45+(0.45/0.8) x O 2 ( x  = 0, 0.02, 0.04, 0.06, or 0.08), were prepared, and their electrochemical performances were evaluated. It was found that as x was decreased, discharge capacity first increased then decreased, and Li 1.2− x Ni 0.35+(0.35/0.8) x Mn 0.45+(0.45/0.8) x O 2 ( x  = 0.04), which can be described as Li 1.16 Ni 0.37 Mn 0.47 O 2 , was found to exhibit the highest discharge capacity. Accordingly, the electrochemical properties of Li 1.16 Ni 0.37 Mn 0.47 O 2 were compared with those of a conventional lithium-rich layer-structured cathode material, namely, Li 1.2 Ni 0.2 Mn 0.6 O 2 . The rate performance of Li 1.16 Ni 0.37 Mn 0.47 O 2 was higher than that of Li 1.2 Ni 0.2 Mn 0.6 O 2 . Furthermore, potential hysteresis and shape change of the charge-discharge curves for Li 1.16 Ni 0.37 Mn 0.47 O 2 were smaller than those for Li 1.2 Ni 0.2 Mn 0.6 O 2 . It is thus concluded that changing the composition of the cathode material from Li 1.2 Ni 0.2 Mn 0.6 O 2 to Li 1.16 Ni 0.37 Mn 0.47 O 2 alleviates the drawbacks of lithium-rich layer-structured cathode material, namely, low rate performance, potential hysteresis, and shape change of charge-discharge curves.