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

Abstract

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 Mn3+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-Na0.67Li0.05Mn0.95O2, which leads to restrained anisotropic change of Mn-O bond lengths and reinforced bond strength in the [MnO6] octahedra by mitigation of Jahn-Teller distortion and contraction of MnO2layers. This ensures the structural stability during charge and discharge of P′2-Na0.67Li0.05Mn0.95O2and 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−1at 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.