Antiphase boundary migration as a diffusion mechanism in a P3 sodium layered oxide

Sodium-ion batteries have emerged as a promising, cost-effective energy storage solution. Critical to the success of these technologies is the efficient transport of ions within the battery electrodes. Here, the authors use first-principles techniques to examine sodium diffusion in a canonical sodium-ion battery cathode material, revealing a new, unconventional mechanism in which the mobile sodium ions are confined to boundaries between otherwise immobile, ordered regions. They provide evidence of a diffusion mechanism that occurs via the collective motion of the boundaries through the material. This behavior is dramatically different from that which is seen in analogous lithium-ion battery materials, and may extend to related candidate electrode materials for beyond-lithium-ion batteries. These mechanistic insights have important implications for the rate of sodium diffusion, which impacts battery charge/discharge speed.