Sodium-ion batteries are among the most promising alternatives to lithium-based technologies for grid and other energy storage applications due to their cost benefits and sustainable resource supply. For the cathode—the component that largely determines the energy density of a sodium-ion battery cell—one major category of materials is P2-type layered oxides. Unfortunately, at high state-of-charge, such materials tend to undergo a phase transition with a very large volume change and consequent structural degradation during long-term cycling. Here we address this issue by introducing vacancies into the transition metal layer of P2-Na_0.7Fe_0.1Mn_0.75□_0.15O₂ (‘□’ represents a vacancy). The transition metal vacancy serves to suppress migration of neighbouring Na ions and therefore maintain structural and thermal stability in Na-depleted states. Moreover, the specific Na−O−□ configuration triggers a reversible anionic redox reaction and boosts the energy density. As a result, the cathode design here enables pouch cells with energy densities of 170 Wh kg⁻¹ and 120 Wh kg⁻¹ that can operate for over 600 and 1,000 cycles, respectively. Our work not only suggests a feasible strategy for cathode design but also confirms the possibility of developing a battery chemistry that features a reduced need for critical raw materials.

由于其成本效益和可持续的资源供应，钠离子电池是电网和其他储能应用中锂基技术最有前途的替代品之一。对于阴极（在很大程度上决定钠离子电池能量密度的组件）来说，主要材料类别是 P2 型层状氧化物。不幸的是，在高荷电状态下，此类材料往往会经历相变，并在长期循环过程中发生非常大的体积变化，并随之发生结构退化。在这里，我们通过在P2-Na _0.7 Fe _0.1 Mn _0.75 □ _0.15 O ₂的过渡金属层中引入空位来解决这个问题（“□”代表空位）。过渡金属空位用于抑制邻近钠离子的迁移，从而在贫钠状态下保持结构和热稳定性。此外，特定的Na−O−□构型会引发可逆的阴离子氧化还原反应并提高能量密度。因此，这里的阴极设计使得软包电池的能量密度为170 Wh kg ^-1和120 Wh kg ^-1，可以分别运行超过600和1,000个循环。我们的工作不仅提出了一种可行的阴极设计策略，而且还证实了开发一种减少对关键原材料需求的电池化学物质的可能性。