Improving the Performance of Potassium Birnessite Cathodes for Sodium-Ion Batteries by Partial Ion Exchange

Abstract

The current study explores the synthesis and electrochemical performance of potassium birnessite as a cathode material for sodium-ion batteries (SIBs), achieved through partial ion exchange resulting from partial potassium deintercalation followed by sodium intercalation during the first electrochemical cycle. Three samples of potassium birnessite (KB400, KB500, and KB600) are synthesized using a sol–gel method and subsequently calcined at different temperatures to evaluate the influence of crystal water and K⁺ ions on structural stability and their electrochemical performance. X-ray diffraction analysis confirms the formation of samples with high crystallinity. Additionally, X-ray fluorescence, X-ray photoelectron spectroscopy, and thermogravimetric analysis are employed to verify their chemical composition and oxidation states. Among the samples, KB500 exhibits the most favorable electrochemical performance, achieving a specific capacity of 175 mAh g^–1 at C/10 when cycled within a voltage range of 1.6–4.2 V. Long-term cycling tests at a narrower potential range of 2–3.6 V demonstrate promising values of 110 mAh g^–1 in capacity for KB500, with a retention of 90% over 80 cycles. The presence of potassium and interlayer water is crucial for enhancing structural stability and ion diffusion. These findings suggest that KB500 could serve as a promising cathode material for SIBs, providing a structurally stable option for energy storage applications.