Effects of Nb substitution on structure and electrochemical properties of LiNi0.7Mn0.3O2 cathode materials

Achieving structural stability and enhanced electrochemical performance through Nb-doping into Li- and Mn-rich layered cathode for lithium-ion batteries

Although Li- and Mn-rich layered oxides are attractive cathode materials possessing high energy densities, they have not been commercialized owing to voltage decay, low rate capability, poor capacity retention, and high irreversible capacity in the first cycle. To circumvent these issues, we propose a Li_1.2Ni_0.13Co_0.13Mn_0.53Nb_0.01O₂ (Nb-LNCM) cathode material, wherein Nb doping strengthens the transition metal oxide (TM-O) bond and alleviates the anisotropic lattice distortion while stabilizing the layered structure. During long-term cycling, maintaining a wider LiO₆ interslab thickness in Nb-LNCM creates a favorable Li⁺ diffusion path, which improves the rate capability. Moreover, Nb doping can decrease oxygen loss, suppress the phase transition from layered to spinel and rock-salt structures, and relieve structural degradation. Nb doping results in less capacity contributions of Mn and Co and more reversible Ni and O redox reactions compared to pristine Li_1.2Ni_0.133Co_0.133Mn_0.533O₂ (LNCM), which significantly mitigates the voltage decay (Δ0.289 and Δ0.516 V for Nb-LNCM and LNCM, respectively) and ensures stable capacity retention (82.7 and 70.3% for Nb-LNCM and LNCM, respectively) during the initial 100 cycles. Our study demonstrates that Nb doping is an effective and practical strategy to enhance the structural and electrochemical integrity of Li- and Mn-rich layered oxides. This promotes the development of stable cathode materials for high-energy-density lithium-ion batteries.