Effect of Lithium/Transition‐Metal Ratio on the Electrochemical Properties of Lithium‐Rich Cathode Materials with Different Nickel/Manganese Ratios for Lithium‐Ion Batteries

A lithium‐rich nickel‐manganese‐based material (Li 1.2 Ni 0.2 Mn 0.6 O 2 ) exhibited a high discharge capacity at a low C‐rate. However, this material has problems in that it has a poor rate performance, large potential hysteresis, and poor cycle performance. Although increasing the Ni/Mn ratio for Li 1.2 Ni 0.2 Mn 0.6 O 2 ameliorated these problems, it decreased the discharge capacity. In this study, the lithium/transition‐metal (Li/TM) ratios for lithium‐rich layer‐structured cathodes with different Ni/Mn ratios were controlled to attain a high discharge capacity, high rate performance, small potential hysteresis, and high cycle performance. For a low‐Ni/Mn‐ratio (Li 1.2 Ni 0.2 Mn 0.6 O 2 ) cathode, a decrease in the Li/TM ratio deteriorated the discharge capacity. Conversely, for cathodes with a high Ni/Mn ratio (Li 1.2 Ni 0.25 Mn 0.55 O 2 and Li 1.2 Ni 0.3 Mn 0.5 O 2 ), the decreases in the Li/TM ratios improved the discharge capacity. In addition, for the high‐Ni/Mn‐ratio cathodes, the decrease in the Li/TM ratio from 1.2/0.8 to 1.18/0.82 increased the discharge capacity at a high C‐rate (3 C) from 157 to 183 Ah kg ‐1 (Li 1.2 Ni 0.25 Mn 0.55 O 2 ) and from 139 to 156 Ah kg ‐1 (Li 1.2 Ni 0.3 Mn 0.5 O 2 ). Furthermore, the decrease in the Li/TM ratio suppressed potential hysteresis and capacity degradation during cycling for the high‐Ni/Mn‐ratio cathodes.