NaClO4 Ethylene Glycol–Water Binary Solution as an Electrolyte for Aqueous Sodium Ion Batteries

Abstract

Aqueous Na-ion batteries are attracting attention as candidates for large-scale rechargeable batteries with a high safety level. We proposed a novel electrolyte composed of NaClO4 dissolved in water, along with ethylene glycol, to serve as an innovative solution for aqueous Na-ion batteries. The potential window of NaClO4 aqueous-based electrolyte expanded as the ethylene glycol concentration increased. Specifically, when incorporating ethylene glycol into a 7 m (= mol kg−1) NaClO4 aqueous electrolyte, we observed a favorable cyclability pattern in the context of the NaTi2(PO4)3 anode, akin to that exhibited by a 17 m NaClO4 aqueous electrolyte. Moreover, the irreversible capacity of NaTi2(PO4)3 decreased as the ethylene glycol concentration increased. This effect was evident even at low rates such as 0.2 mA cm−2. Notably, the NaTi2(PO4)3 anode’s capacity, when utilizing a 7 m NaClO4 solution with a higher fraction of ethylene glycol (XE = 0.5), remained stable at 120 mAh g−1 even after the completion of 15 cycles. On the other hand, the Na2MnP2O7 cathode properties 7 m NaClO4 aqueous electrolyte could not be improved by adding a small amount of ethylene glycol.

Keywords

• aqueous na ion batteries
• water-ethylene glycol binary solution
• nati2(po4)3 anode
• relaxation time of water molecules