(300e) Developing Non-Aqueous and Low-Temperature Iron Batteries with V2O5 Nanowire Cathodes

Batteries remain as one of the promising technologies to store and deploy energy upon demand. The most successful Li-ion technology is limited for large-scale application due to the safety challenges probed using the organic solvents. However, multivalent metal-based batteries such as Mg, Al, Zn, Ca etc. remain as promising and potential alternatives to the Li-ion technology due to their huge abundance in the earth’s crust, multiple electrons transfer upon redox reactions, ambient in the environment, non-toxic and remarkably high theoretical capacity. Another type of multivalent metal, Iron, is often overlooked as an electrode for energy storage applications due to the positive standard redox potential value (-0.44V). However, its huge presence in the earth’s crust (5.63 wt% vs. 0.002wt% for Li), ability to exist in eight oxidations states (i.e. -2 to +6), and significantly lower cost (0.06 USD.kg^-1 vs. 19.2 USD.kg^-1 for Li) remain significant for the possibility to explore Iron as an potential electrode.

Deep eutectic electrolytes (DEEs) are analogues of ionic-liquids and offers appreciably high ionic conductivity, wide thermal and potential window, low volatility, facile preparation, low-cost, non-toxicity etc. Here, we report a non-aqueous and DEE based on triethylamine hydrochloride (TEAHCl) with Iron(III) chloride (FeCl₃) for the application of rechargeable Iron batteries. The depression of freezing point for the 1.7:1 molar ratio containing TEAHCl:FeCl₃ is identified as <0 °C through the differential scanning calorimetry. The structural property correlation to the ionic complexations formed in DEEs were thoroughly investigated using the Fourier Transform Infrared and Raman spectroscopies which concludes the presence of FeCl₄^- and Fe₂Cl₇^-. The DEEs show appreciably high ionic conductivity of ~1.2 mS.cm^-1 and ~100% efficiency of plating and stripping in a symmetric Fe||Fe cell, sustaining for >400 hours. V₂O₅ nanowires, synthesized via hydrothermal routes, used as cathode against Fe anode. Fe||1.7:1 Et₃NHCl:FeCl₃||V₂O₅ cell showed open circuit potential of ~1.0V. The galvanostatic cycling in the potential window of 0.0-2.5V vs. Fe/Fe⁺³ retrieves a high capacity of ~80 mAh/g. The charge storage mechanism of the cell is thoroughly delineated by imparting XRD and XPS analysis on the cycled electrodes. Our research effort to design a non-aqueous electrolyte for Iron batteries certainly assist to gain the characteristic properties of Iron as an electrode and helps to formulate a strong working hypothesis in the future.