Mitigation of Jahn–Teller distortion and Na(+)/vacancy ordering in a distorted manganese oxide cathode material by Li substitution

Layered manganese-based oxides are promising candidates as cathode materials for sodium-ion batteries (SIBs) due to their low cost and high specific capacity. However, the Jahn–Teller distortion from high-spin Mn(3+) induces detrimental lattice strain and severe structural degradation during sodiation and desodiation. Herein, lithium is introduced to partially substitute manganese ions to form distorted P′2-Na(0.67)Li(0.05)Mn(0.95)O(2), which leads to restrained anisotropic change of Mn–O bond lengths and reinforced bond strength in the [MnO(6)] octahedra by mitigation of Jahn–Teller distortion and contraction of MnO(2) layers. This ensures the structural stability during charge and discharge of P′2-Na(0.67)Li(0.05)Mn(0.95)O(2) and Na(+)/vacancy disordering for facile Na(+) diffusion in the Na layers with a low activation energy barrier of ∼0.53 eV. It exhibits a high specific capacity of 192.2 mA h g(−1), good cycling stability (90.3% capacity retention after 100 cycles) and superior rate capability (118.5 mA h g(−1) at 1.0 A g(−1)), as well as smooth charge/discharge profiles. This strategy is effective to tune the crystal structure of layered oxide cathodes for SIBs with high performance.