High voltage Zn/LiCoO2 hybrid aqueous rechargeable battery

Abstract

The rapid development of portable and wearable devices requires new generation energy storage systems possessing high energy density, high safety warranty, and low-cost. Despite the outstanding performance of lithium-ion batteries, their further application is severely limited by their safety risks. Those safety issues are derived from the heavy reliance on toxic, flammable, and volatile organic electrolytes. In contrast, aqueous zinc-based batteries have the advantages of non-flammability, low-cost, and eco-friendliness, which are ideally suitable for portable applications. However, the energy density and reversibility of most reported aqueous Zn-based batteries are far from satisfactory. First of all, there are not many choices for cathode materials with high discharge plateaus. Next, side reactions and corrosion occur simultaneously on zinc anode during the cycling process. As a commercial cathode material, lithium cobalt oxide (LCO) attracts increasing attention due to its high discharge plateaus, high volumetric capacity, and excellent reversibility. However, the cycling stability of LCO in aqueous solutions is still a challenging problem due to the severe side-reactions. In this thesis, a high-voltage zinc-based hybrid battery with LCO cathode and the mild-alkaline electrolyte is developed. In the first chapter, the stability of the LCO cathode was improved by investigating the effects of pH and salt concentrations on battery cycling performance. In the following chapter, the effects of different electrolyte anion on the corrosion and stripping/plating behaviours were studied. It was demonstrated that the reversibility of LCO could be improved significantly with increasing electrolyte pH. Additionally, the mild-alkaline acetate electrolyte exhibits a wide electrochemical window to 2.15V, and improved reversibility of zinc anode compare with other electrolytes (based on Cl-, SO42-, and NO3- ions). The hybrid Zn/LCO battery with this mild-alkaline acetate-based electrolyte provides a flat and high discharge voltage at 1.94 V, resulting in a high energy density of 162 Wh/kg. The battery remained 72 % capacity after 120 cycles with 96 % coulombic efficiency even at 0.2 C.