Increasing the Voltage for Sodium Cathode Through Copper and Oxygen Redox

Sodium-ion batteries (SIBs) are appealing for several reasons, including the abundant availability of sodium and independence from precious metals such as cobalt. However, SIBs still lag behind lithium-ion batteries in terms of energy density. A major limitation for SIBs is the relatively low working voltage of their cathodes. To enhance the voltage and thereby improve the energy density of SIBs, it is crucial to explore novel redox couples that operate at higher voltages than the traditional ones based on iron, manganese, and nickel. We have recently developed P3-structured cathode materials for SIBs based on copper and manganese, demonstrating significant capacity at voltages above 3.5 V (vs. Na+/Na). Employing a range of synchrotron-based characterization techniques and density functional theory (DFT) calculations, we have found that both copper and oxygen contribute actively to the electrochemistry of these materials. This presentation will explore our discoveries regarding a new redox role for oxygen and how lithium substitution can enhance oxygen redox activity, thereby increasing capacity.