Improved high-energy Na-NCM cathode prepared by ion exchange route via application of various ALD treatments

The application of layered oxide compounds as cathode materials for sodium-ion batteries is considered a promising direction for the development of high-energy Na-ion batteries. However, despite many efforts, practical implementation of such electrodes is still challenging, mainly due to structural and surface instabilities associated with the high operating voltage of these cathodes. One of the most effective ways to mitigate these undesirable phenomena is the use of atomic layer deposition (ALD) to form a Nano-sized protective layer on the electrode surface. Application of ALD treatment results in increased electrode stability by preventing irreversible interactions between the electrolyte and cathode material. In search of optimal coating formulations, the effect of various ALD coatings viz. sodium-aluminate, lithium-aluminate, and alumina on the electrochemical performance of Na-NCM cathode synthesized by ion-exchange method. While the initial capacity loss attributed to oxygen release was significantly suppressed in all coated samples, better stability was observed for Na_xAl_yO_z coating. The stabilization mechanism of the Na_xAl_yO_z coating further investigated by XPS, XRD, and TEM revealed improved surface properties that prevent irreversible oxygen loss and migration of manganese from the electrode bulk toward the surface.