Anion Pillars Enable High Energy Density Sodium Dual‐Ion Battery With Ultra‐Long Cycle Life

Sodium dual-ion batteries (SDIBs) are emerging as promising energy storage systems due to their low cost, environmental friendliness, and high operating voltage. However, the structural instability of the commonly used graphite cathode limits its long-term performance, posing a significant obstacle to large-scale applications. Here, for the first time, we report the use of the anion pillar strategy in the interlayer of the graphite cathode to expand and maintain permanently the layer spacing, preventing structural collapse and facilitating (de)intercalation, leading to an exceptional electrochemical performance of SDIBs. A high specific capacity of 162 mAh g^-1 at a current density of 200 mA g^-1, corresponding to a high energy density of 560 Wh kg^-1 is achieved. More impressively, the specific capacity can be maintained at 101 mAh g^-1 at a high current density of 2000 mA g^-1, with a high capacity retention of 74.0% after 15 500 cycles is obtained, corresponding to a capacity decay rate as low as 0.0017% per cycle and anion pillars remain stable in the interlayer of graphite. This study presents a novel and effective strategy for improving the performance and stability of graphite cathodes in SDIBs, offering valuable insights for the development of next-generation energy storage systems.