Metal-air batteries are attracting more and more attention from researchers around the world. And non-aqueous lithium-oxygen (Li-O2) battery is the main topic in this field, because of its exceptional theoretical specific energy (3,505 Wh/kg). However, there are still a lot of challenges for developing highly efficient and durable Li-O2 batteries. Although the first step in the discharge process in the one-electron reduction of oxygen to superoxide (O2-), LiO2 formed is unstable and will disproportionate into lithium peroxide (Li2O2) and oxygen (O2) simultaneously. And the charge process is about the oxidation of Li2O2 into O2. Due to their asymmetric reaction mechanisms, the overpotential of the charge process (~1-1.5 V) is much higher than that of the discharge process (~0.3 V). The high charging potential would not only leave the battery with a low energy efficiency, but also induce a series of side reactions of electrolyte and the carbon air electrode. To overcome this problem, the effect of cations on the oxygen redox process was studied. And it is shown that its reversibility with larger cations is much better than that with Li+. Then the possibility of using the simple O2/O2- redox couple for the battery processes was explored by stabilizing O2- with potassium ions (K+). It is confirmed by XRD and Raman that mainly crystalline potassium superoxide (KO2) is formed during battery discharge and oxidized during the charge process. More importantly, without the use of any catalysts, the battery discharge/charge potential gap can reduced to less than 50 mV.

Low-overpotential potassium-oxygen battery based on potassium superoxide

246th National Meeting (2013)

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