First-Principles Insight into the Impact of Oxygen Substitution in Na3V2(PO4)2F3 Cathodes on the Structural Evolution, Redox Mechanism, and Na-Ion Migration

• Published in: Journal of physical chemistry. C Vol. 128; no. 1; pp. 31 - 37
• Main Authors: Chen, Yiheng, You, Yiwei, Cao, Xinrui, Lü, Tie-Yu, Zhu, Zi-Zhong, Wu, Shunqing
• Format: Journal Article
• Language: English
• Published: American Chemical Society 11-01-2024
• Subjects: C: Energy Conversion and Storage
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.3c06377

Sodium vanadium phosphate fluoride (Na3V2(PO4)2F3, NVPF) has emerged as a promising NASICON-type cathode material for sodium-ion batteries due to its 3D Na-ion diffusion channels, high voltage, and high theoretical capacity. However, issues with Na-ion diffusion kinetics and electrical conductivity have limited its electrochemical performance. In this work, first-principles calculations were employed to systematically investigate the structural evolution, average voltage, magnetism, and electronic structure of Pnnm NVPF and partially the O-substituted product Na3V2(PO4)2F2O. Compared to disordered P42/mnm, ordered Pnnm NVPF exhibited lower desodiation voltages and Na+ migration barriers, resulting in improved electrochemical properties. Additionally, Na3V2(PO4)2F2O enabled extract more Na+ near the electrolyte stability limit, enhancing capacity and energy density. However, lattice contraction from O substitution also increased Na+ diffusion barriers in Na3V2(PO4)2F2O. Distinct redox mechanisms were revealed for the two materials, offering vital information for optimizing NASICON cathodes.