Sol-gel-based synthesis of high-capacity-NaCoO2 cathode for advanced sodium-ion batteries

Abstract

This study presents a successful synthesis of phase-pure P2-NaCoO2 by improving the sol-gel-based calcination temperature, yielding a highly crystalline, well-ordered material having P63/mmc hexagonal symmetry, ideal for reversible sodium-ion batteries (SIBs). Advanced physicochemical techniques confirm its pure hexagonal crystal structure along with the desired stoichiometry. NaCoO2 in Na/1M-NaClO4/NaCoO2 cell demonstrates multiple redox peaks for Co3+/Co4+ redox couple, signifying stable multiphase transitions during charge/discharge cycles and exhibiting exceptional structural and electrochemical stability. The cell demonstrates a high discharge specific-capacity of 155.85 mAh/g at 0.1C with outstanding discharge capacity retention of 136.98, 100.6, 84.78, 78.31, and 72.46 mAh/g at the C-rates of 0.15, 0.2, 0.3, 0.5, and 1.0C, respectively, outperforming previously reported values. It shows a remarkable discharge-energy density of 466.04 Wh/kg at 0.1C. Additionally, the small solution and charge transfer resistance with extremely low double-layer capacitance signifies its excellent electrolyte conductivity and potential for high energy density and slow discharge application. These results imply that NaCoO2 is a high-performance and high-capacity cathode material for lightweight and compact SIBs. © 2024