Rotating-disk electrode analysis of the oxidation behavior of dissolved Li(2)O(2) in Li–O(2) batteries

The development of the rechargeable Li–O(2) battery (LOB) has encountered several bottlenecks till date. One of the biggest challenges is to lower the oxidation potential of Li(2)O(2), which is the insulating and insoluble discharge product. A possible solution to this problem is to use high acceptor number (AN) or donor number (DN) solvents to increase the solubility of Li(2)O(2), so that the dissolved Li(2)O(2) can diffuse to the cathode surface and get oxidized at a relatively low potential. Herein, we explored the efficiency and side-reactions in the LOB charge process with different Li(2)O(2) soluble electrolytes. The relationship between the solubility of Li(2)O(2) and charging rate was analyzed quantitatively with ultraviolet-visible (UV-Vis) spectroscopy and rotating disk electrode experiments. As a result, electrolytes with high AN usually have higher solubility for Li(2)O(2) than electrolytes with high DN, and thus exhibit higher Li(2)O(2) oxidation rates. Nevertheless, higher Li(2)O(2) solubility in high AN electrolytes also induces more severe side reactions and easily passivates the electrode surface. The trade-off between charging reaction rate and electrolyte stability is a key issue to be considered when designing high performance LOB electrolytes.