Electrochemical energy storage device for securing future renewable energy

An electrochemical cell comprising molten sodium and molten sulphur as the anode and cathode, respectively, with beta alumina electrolyte has never found extensive use. An approach to develop large energy storage device based on aqueous sodium electrolyte at low temperature is described. An electrochemical cell with low cost, safe and utilizing sustainable manganese dioxide (MnO2) cathode coupled with zinc (Zn) anode in aqueous sodium hydroxide (NaOH) electrolyte is reported. The cyclic voltammetric (CV) profiles are found to be quite different in terms of peak position and current response depending on concentration of NaOH electrolyte. Among the concentrations of NaOH studied (2, 5, 7 and 10 M) the best performance was found to be between 5 and 7 M. The CV curves exhibits a pair of reversible redox peaks (within 1e− region) corresponding to sodium ion insertion and extraction but while extending the potential window to second electron reduction resulted in irreversible nature. This is explained to the formation of inhomogeneous reduction reaction due to slow electron diffusion. CV experiments at various scan rates revealed that the MnO2 material may not be suitable enough for higher scan rates indicating a sluggish kinetics occurring in the bulk material. Our study highlights the MnO2 cathode in NaOH electrolyte features a flat discharge voltage of 1.3 V vs. Zn with discharge capacity of 220 mAh/g.

► Aqueous rechargeable battery is suitable for stationary energy storage.
► Battery was fabricated with MnO2 cathode, Zn anode and aqueous sodium electrolyte.
► Role of Na+ cations, scan rate, degree of reduction are optimized.
► Electrochemical cell exhibits high energy density, long cycle life and low cost.