Understanding sodium-ion diffusion in layered P2 and P3 oxides via experiments and first-principles calculations: a bridge between crystal structure and electrochemical performance

摘要

Atomic-level insights into the structure and electrochemistry of sodium-ion crystals may help develop lower-cost rechargeable batteries. Layered materials known as transition-metal sodium oxides have an ion-accessible framework that makes them promising candidates for alternative batteries based on sodium ions, instead of lithium ions. But significant volume changes during battery operation can alter the crystal phase of the layered structure and its associated electrochemical properties. To decipher these structure-property relationships, Haoshen Zhou from Japan's AIST institute and co-workers simultaneously synthesized two phases of the layered sodium oxides and analyzed them by using electron microscopy, quantum calculations and galvanic cells. They discovered that, even though the two structures had nearly identical compositions, the high-temperature phase containing two separated Na-sites significantly lowered ion diffusion barriers – improving rate capability and cycling in these batteries.