Influence of Formation Temperature on Cycling Stability of Sodium-Ion Cells: A Case Study of Na3V2(PO4)2F3|HC Cells

Abstract

Sodium-ion batteries are cheaper and attractive alternatives to lithium-ion batteries, particularly for low-energy and high-power applications. In this regard, a targeted cell design is essential to achieve optimal cycling performances and reduced cell impedance. While optimized electrode and electrolyte formulations are important, the formation protocol -initial cycles that establish the electrode-electrolyte interphase- significantly impacts cell impedance and interphase stability. In this study, we investigate the influence of formation temperature on the nature of interphases formed in Na3V2(PO4)2F3 (NVPF)|hard carbon (HC) cells. Our findings reveal that the interphase’s nature and chemical composition evolve with the formation temperature. Moreover, cell temperature affects interphase dissolution and reformation, suggesting the potential benefits of employing mixed high and low temperatures during formation cycles to achieve desired interphase properties. A formation protocol coupling cycling stages at different temperatures (55 °C–25 °C–0 °C) exhibits an edge over with respect to low impedance, slightly higher reversible capacity and long cycling stability compared to the cells formed solely at 55 °C. The results presented underscore the necessity of exploring formation protocols including not only high temperatures but also colder temperatures, like 0 °C and below. This approach is pivotal for advancing the understanding of interphase dynamics and optimizing sodium-ion battery performance.