Electrochemical investigations of Na0.7CoO2 cathode with PEO-NaTFSI-BMIMTFSI electrolyte as promising material for Na-rechargeable battery

Abstract

We report herein the development of a sodium polymer battery consisting of solid polymer electrolyte (SPE) system (polymer + ionic liquid and salt) as an electrolyte and sodium cobalt oxide as cathode material. Solid polymeric membranes (SPMs) were synthesized using polymer polyethyleneoxide (PEO), ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI) (10–40 wt.%), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) salt. Na0.7CoO2 cathode material was prepared using solid-state reaction route. These solid polymeric membranes were optimized using various experimental techniques such as thermogravimetric analysis, differential scanning calorimetry, and electrochemical impedance spectroscopy (EIS). It was found that the membrane containing 40 wt.% of IL has high room temperature (~ 30 °C), ionic conductivity (~ 4.1 × 10−4 S cm−1), Na+ transference number (~ 0.39), and good thermal stability. The optimized polymeric membrane shows high electrochemical potential window (~ 3.6 V) vs. Na/Na+, a specific discharge capacity of ~ 138 mAhg−1 (at 0.1 C rate) and maximum coulombic efficiency (~ 99%) for the prepared cell Na | SPE | Na0.7CoO2. Thus, the membrane containing 40 wt.% IL polymer electrolyte and Na0.7CoO2 as cathode is promising material for the formation of sodium rechargeable battery.