Designing High-Performance Nanostructured P2-type Cathode Based on a Template-free Modified Pechini Method for Sodium-Ion Batteries.

Layered oxides are promising cathode materials for sodium-ion batteries because of their high theoretical capacities. However, many of these layered materials experience severe capacity decay when operated at high voltage (>4.25 V), hindering their practical application. It is essential to design high-voltage layered cathodes with improved stability for high-energy-density operation. Herein, nano P2-Na(MnNiCo)O (NCM) materials are synthesized using a modified Pechini method as a prospective high-voltage sodium storage component without any modification. The changes in the local ionic state around Ni, Mn, and Co ions with respect to the calcination temperature are recorded using X-ray absorption fine structure analysis. Among the electrodes, NCM fired at 850 °C (NCM-850) exhibits excellent electrochemical properties with an initial capacity and energy density of 148 mAh g and 555 Wh kg, respectively, when cycled between 2 and 4.5 V at 160 mA g along with improved cyclic stability after 100 charge/discharge cycles. In addition, the NCM-850 electrode is capable of maintaining a 75 mAh g capacity even at a current density of 3200 mA g. In contrast, the cell fabricated with NCM obtained at 800 °C shows continuous capacity fading because of the formation of an impurity phase during the synthesis process. The obtained capacity, rate performance, and energy density along with prolonged cyclic life for the cell fabricated with the NCM-850 electrodes are some of the best reported values for sodium-ion batteries as compared to those of other p2-type sodium intercalating materials.