Insights into effects of Co and Mn elements on the cycle stability of ultrahigh‐nickel cathodes charged at same delithiation state

Abstract The introduction of Co and Mn is regarded as an effective strategy to enhance the cycling stability of LiNi x M 1− x O 2 ( x ≥ 0.9) cathodes. However, since the delithiation degrees of respective LiNi x M 1− x O 2 cathodes measured at the fixed cutoff voltage are different, it is necessary to design the appropriate systems to evaluate the specific roles of Co and Mn elements in cyclic stability. Therefore, three LiNi x M 1− x O 2 cathodes, including LiNiO 2 (LNO), LiNi 0.9 Co 0.1 O 2 (NC91), and LiNi 0.9 Mn 0.1 O 2 (NM91) have been chosen for systematically investigating the effect of Co and Mn on cycle durability, which are controlled at the same delithiation state during the electrochemical processes. It is found that the order of cycling stability among the three cathodes is NC91 > LNO > NM91 in the 80 mol% delithiation state. Co substitution suppresses lattice distortion, mitigates transition metal dissolution and structural degradation, further enhancing structural/interface stability, which brings out outstanding cycle stability of NC91. Notably, cycling stability is mainly determined by interfacial stability. Although NM91 exhibits superior structural stability compared to NC91, the worst cycling performance of NM91 is presented, which is attributed to the deteriorated interfacial stability resulting from the Jahn–Teller from Mn 3+ . This study elucidates the effect of Co and Mn on the cycle stability in LiNi x M 1− x O 2 cathodes under the same delithiation state, thereby delivering reasonable guidance for designing advanced ultrahigh‐nickel cathodes.