Synergetic Modulation of Crystal Facet Orientation and Lattice Stability by Lithium Substitution in P2-Type Layered Oxides for Enhanced Sodium Storage

P2-type layered oxides have emerged as potential cathode material candidates for commercial sodium-ion batteries due to their high specific capacity and working voltage. However, the inherent sluggish diffusion kinetics originating from the large ionic radius of Na⁺ and complex phase transitions during cycling limit the rate capability and cycling performance. Herein, a prismatic Na_0.75Ni_0.33Mn_0.60Li_0.07O₂ (P-NNMLO) cathode with more exposed active facets is synthesized using a lithium substitution modulation strategy, where the {010} surface energy is considerably reduced by lithium, leading to enhanced sodium-ion diffusion kinetics. Lithium substituted in the crystal lattice can also suppress the P2-O2 phase transition at high voltages and mitigate the volume change during cycling. Under the synergetic modulation of external crystal facet orientation and internal crystal structure stabilization, the P-NNMLO cathode delivers a high initial reversible capacity of 123.4 mAh g^-1 at 1 C with a capacity retention of 80.6% after 100 cycles and a rate capability of 59.6 mAh g^-1 at 20 C. The study offers insights into the design of high-rate and long-cycle sodium-ion batteries by using Li substitution to simultaneously optimize the crystal facet orientation and structural robustness of layered oxide cathodes.