Micron-sized single-crystal cathodes for sodium-ion batteries.

Confining the particle-electrolyte interactions to the particle surface in electrode materials is vital to develop sustainable and safe batteries. Micron-sized single-crystal particles offer such opportunities. Owing to the reduced surface area and grain boundary-free core, particle-electrolyte interactions in micron-sized single-crystal particles will be confined to the particle surface. Here, we reveal the potential of such materials in sodium-ion batteries. We synthesized and investigated the chemical, electrochemical, and thermal properties of single-crystalline P2-type NaMnMgO as a cathode material for sodium-ion batteries. Single-crystalline NaMnMgO with a mean particle size of 8.1 μm exhibited high cycling and voltage stability. In addition, the exothermic heat released by the charged single-crystal NaMnMgO cathodes was four times lower than that of the corresponding polycrystalline NaMnMgO. This significantly enhances the thermal stability of electrode materials and possibly mitigates thermal runaways in batteries. Surprisingly, single crystals of NaMnMgO were relatively stable in water and ambient atmosphere.