Oxygen-Storage Materials to Stabilize the Oxygen Redox Activity of Three-Layered Sodium Transition Metal Oxides

To double the energy density of lithium- and sodium-ion batteries there is a need to activate simultaneously cationic and anionic redox reactions at the intercalation-type electrodes. In contrast to the cationic redox activity, the oxygen redox activity enforces an enhancement in the surface reactivity of the oxides leading to their poor reversibility and cycling stability. Herein, we propose a new concept to stabilize oxygen redox activity by using oxygen-storage materials as an efficient buffer supplying and receiving oxygen during alkali ion intercalation. As a proof-of-concept, the study is focused on CeO₂ as a modifier of sodium nickel-manganese oxide with a three-layer sequence, P3-Na_2/3Ni_1/2Mn_1/2O₂. The CeO₂-modified P3-Na_2/3Ni_1/2Mn_1/2O₂ displays a drastic increase in the reversible capacity following the order Na⁺ intercalation < Li⁺ intercalation < Li⁺,Na⁺ cointercalation.