Fast Cationic and Anionic Redox Reactions in Li2RuO3-Li2SO4 Positive Electrode Materials

For the application of lithium-ion batteries (LiBs) to a large-scale power source for electric vehicles, positive electrode materials with high energy and power densities should be developed. Although Li-excess materials are regarded as high-capacity positive electrodes, there are several issues in the anionic redox reactions, such as oxygen gas evolution and large resistance, which lead to capacity fading and limitation of high-current operation. Here, we report the high-current operation of an electrochemical cell using the Li2RuO3–Li2SO4 positive electrode in LiBs. The cell using Li2Ru0.8S0.2O3.2 showed a high capacity of 350 mAh g–1 with an average discharge voltage of 2.9 V vs Li at 25 °C. By introducing an amorphous matrix based on Li2SO4, a high diffusion coefficient was maintained during the whole charge–discharge process, and low charge-transfer resistance was maintained even at a high oxidation state up to 4.2 V vs Li. As a result, extremely high current operation, such as 40 C rate, was achieved