Enhanced Electrochemical Properties of NaFe2PO4(SO4)2 via Co2+ Doping as Cathode Material for Sodium-ion Batteries

Abstract

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, NaFe 2 PO 4 (SO 4 ) 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 Co 2+ reduces the specific surface area of NFPS-Co0.08compared to NFPS.This shortens the sodium ion diffusion pathway and promotes ion dynamics.The addition of Co 2+ to the sample significantly improved its performance during galvanostatic charge-discharge tests.The electrochemical activity also is significantly enhanced by Co 2+ doping.Na 0.84 Co 0.08 Fe 2 PO 4 (SO 4 ) 2 exhibits superior rate and cycling performance compared to pristine NFPS.After 80 cycles at 25 mA g -1 , NFPS-Co 0.08 retained discharge specific capacity of 60.8 mA h g -1 , which is 1.24 times greater than that of NFPS.