Structural Reinforcement through High-Valence Nb Doping to Boost the Cycling Stability of Co-Free and Ni-Rich LiNi_0.9Mn_0.1O₂ Cathode Materials

As an important Co-free and Ni-rich layered oxide, LiNi_0.9Mn_0.1O₂ (NM91) has garnered significant interest as a promising cathode material for lithium-ion batteries. Despite its attractively high specific capacity, the intrinsic structural instability poses a great challenge to its electrochemical performances, especially cycling performance. In this work, we circumvent the structural instability issue of NM91 through high-valence Nb doping. Our findings reveal that high-valence Nb⁵⁺ dopants were successfully incorporated into the lattice of LiNi_0.9Mn_0.1O₂, functioning as interlayer pillars that reinforce the structure and mitigate the detrimental H2 → H3 phase transition. This results in greatly improved cycling stability and rate capability of the cathode. The discharge capacities of 1%Nb-NM91 reached 211.8 mA h g^–1 at 0.1 C and 159.3 mA h g^–1 at 5 C, with a retention rate of 95.6% after 100 cycles at 0.5 C, even superior to the previously reported lower Ni content counterparts, including LiNi_0.8Co_0.15Al_0.05O₂, LiNi_0.8Co_0.1Mn_0.1O₂, and so forth. This study demonstrates that high-valence Nb doping is a promising strategy to overcome the structural instability issue in LiNi_0.9Mn_0.1O₂ and underscores the potential of Co-free Ni-rich layered oxides as cathode materials for lithium-ion batteries.