Realizing High Capacity and Zero Strain in Layered Oxide Cathodes via Lithium Dual-Site Substitution for Sodium-Ion...

Sodium-ion batteries have garnered unprecedented attention as an electrochemical energy storage technology, but it remains challenging to design high-energy-density cathode materials with low structural strain during the dynamic (de)sodiation processes. Herein, we report a P2-layered lithium dual-site-substituted Na_0.7Li_0.03[Mg_0.15Li_0.07Mn_0.75]O₂ (NMLMO) cathode material, in which Li ions occupy both transition-metal (TM) and alkali-metal (AM) sites. The combination of theoretical calculations and experimental characterizations reveals that Li_TM creates Na-O-Li electronic configurations to boost the capacity derived from the oxygen anionic redox, while Li_AM serves as LiO₆ prismatic pillars to stabilize the layered structure through suppressing the detrimental phase transitions. As a result, NMLMO delivers a high specific capacity of 266 mAh g^-1 and simultaneously exhibits the nearly zero-strain characteristic within a wide voltage range of 1.5-4.6 V. Our findings highlight the effective way of dual-site substitution to break the capacity-stability trade-off in cathode materials for advanced rechargeable batteries.