Dual Functional Propylene Carbonate Co-Solvent for High Performance Aqueous Zinc-Ion Batteries
Authors: Kakoty Bhaskar , V Rishikesh , Mukherji Srimayee , Ahuja Vinita , Joseph Anjana , Narayana Chandrahas , Balasubramanian Sundaram , Senguttuvan Premkumar 
Published: August 2024

In response to the global rise in energy demand, extensive research has spurred the development of batteries with high energy density, affordable cost, and safety. The present Li-ion batteries are attractive due to their high energy density, but their cost and geopolitical accessibility of raw materials, along with safety-related issues, have led researchers to shift their attention towards aqueous batteries.1,2 In aqueous systems, zinc metal has been regarded as the most promising candidate due to its high specific capacity, low redox potential of Zn-metal, environmental friendliness, and low cost. However, challenges such as the dendritic growth of zinc, hydrogen evolution, corrosion, structural degradation and dissolution of oxide cathodes, and poor coulombic efficiencies (CEs) limit their scope. To address these issues, various studies demonstrate the usage of organic co-solvents and additives such as DMSO3, DMC4, etc. at different concentrations in the electrolytes. However, the overall efficiency of the battery performance is hindered due to the large amount requirements of these additives.
Along this line, we have studied the electrochemical properties of a hybrid water-highly polar propylene carbonate-based electrolyte, which suppresses water-derived parasitic reactions occurring at both the Zn anode and the V2O5 cathode.5 We have observed a significant enhancement in the battery characteristics, such as high coulombic efficiency and stable capacity, merely by tuning the solvation structure of the electrolyte. Upon a small addition of PC (20 wt.%) in 1M Zn(OTf)2 electrolyte, water molecules solvating Zn2+ ions are replaced by carbonate and triflate anions. The solvated Zn-ion species were further electrochemically reduced to form a ZnF2-rich solid electrolyte interphase (SEI), as demonstrated by post-cycling XPS studies. Moreover, the spectroscopy studies suggest the strong interaction of highly basic carbonyl oxygen of PC with water molecules, which in turn suppresses the dissolution of the cathode, enabling exceptional capacities of ∼300 mAh g−1 over 900 cycles at 1 A g−1. We further demonstrate the significance of the dielectric constant and polarity of an additive or cosolvent in the aqueous zinc ion battery electrolyte by contrasting the performance of cyclic propylene carbonate with acyclic dimethyl carbonate.
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