Unexpected Elevated Working Voltage by Na⁺/Vacancy Ordering and Stabilized Sodium-Ion Storage by Transition-Metal...

Na⁺/vacancy ordering in sodium-ion layered oxide cathodes is widely believed to deteriorate the structural stability and retard the Na⁺ diffusion kinetics, but its unexplored potential advantages remain elusive. Herein, we prepared a P2-Na_0.8Cu_0.22Li_0.08Mn_0.67O₂ (NCLMO-12 h) material featuring moderate Na⁺/vacancy and transition-metal (TM) honeycomb orderings. The appropriate Na⁺/vacancy ordering significantly enhances the operating voltage and the TM honeycomb ordering effectively strengthens the layered framework. Compared with the disordered material, the well-balanced dual-ordering NCLMO-12 h cathode affords a boosted working voltage from 2.85 to 3.51 V, a remarkable ~20 % enhancement in energy density, and a superior cycling stability (capacity retention of 86.5 % after 500 cycles). The solid-solution reaction with a nearly "zero-strain" character, the charge compensation mechanisms, and the reversible inter-layer Li migration upon sodiation/desodiation are unraveled by systematic in situ/ex situ characterizations. This study breaks the stereotype surrounding Na⁺/vacancy ordering and provides a new avenue for developing high-energy and long-durability sodium layered oxide cathodes.