Sodium-ion batteries (SIBs) offer a viable alternative to partially or fully replace lithium ion batteries (LIBs) due to their lower cost and increased safety. This paper outlines the compositional optimizations, crystallographic evaluations, and electrochemical behavior of a novel mixed NASICON polyanionic compound, NaFe2PO4(SO4)2 (NFPS). X-ray photoelectron spectrometry (XPS) results showed that cobalt doping produces a higher concentration of oxygen defects compared to undoped samples. Scanning electron microscopy (SEM) analysis results revealed that the modified sample has more uniform pores and pore distribution. Brunauer-Emmett-Teller (BET) measurements showed that doping of Co2+ reduces the specific surface area of NFPS-Co0.08 compared to NFPS. This shortens the sodium ion diffusion pathway and promotes ion dynamics. The addition of Co2+ to the sample significantly improved its performance during galvanostatic charge-discharge tests. The electrochemical activity also is significantly enhanced by Co2+ doping. Na0.84Co0.08Fe2PO4(SO4)2 exhibits superior rate and cycling performance compared to pristine NFPS. After 80 cycles at 25 mA g-1, NFPS-Co0.08 retained discharge specific capacity of 60.8 mA h g-1, which is 1.24 times greater than that of NFPS.

Abstract
1. Introduction
2. Experimental Procedure
    2.1. Chemicals
    2.2. Preparation
    2.3. Structural characterization
    2.4. Electrochemical measurement
3. Results and Discussion
4. Conclusion
References
Author Information

• Yao Liu(School of Chemistry and Life Sciences, Suzhou University of Science and Technology, Suzhou 215009, China)
• Yilei Sun(School of Chemistry and Life Sciences, Suzhou University of Science and Technology, Suzhou 215009, China)
• Zeda Meng(School of Chemistry and Life Sciences, Suzhou University of Science and Technology, Suzhou 215009, China) Corresponding author
• Haixia Wang(Applied Technology College of Soochow University, Suzhou 215009, China)
• Won-Chun Oh(Department of Advanced Materials Science and Engineering, Hanseo University, Seosan 31962, Republic of Korea) Corresponding author