Rotating-disk electrode analysis of the oxidation behavior of dissolved LiO in Li-O batteries.

The development of the rechargeable Li-O battery (LOB) has encountered several bottlenecks till date. One of the biggest challenges is to lower the oxidation potential of LiO, 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 LiO, so that the dissolved LiO 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 LiO soluble electrolytes. The relationship between the solubility of LiO 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 LiO than electrolytes with high DN, and thus exhibit higher LiO oxidation rates. Nevertheless, higher LiO 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.