Effect of Controlled-Atmosphere Storage and Ethanol Rinsing on NaNi0.5Mn0.5O2 for Sodium-Ion Batteries

NaNi0.5Mn0.5O2 is a promising sodium-ion battery cathode material that has been extensively studied. However, the air sensitivity of this material limits practical application and is not well understood. Here, we present a detailed study of NaNi0.5Mn0.5O2 powders stored in different atmospheres (oxygen, argon, and carbon dioxide), either dry or wet. X-ray diffraction and Fourier transform infrared measurements were used to characterize the materials and their surface species before and after controlled-atmosphere storage. It was determined that the exposure of untreated NaNi0.5Mn0.5O2 powders to moisture results in desodiation and material degradation, leading to poor cycling. This effect was found to be caused by reactive surface species. From these results, a simple ethanol washing method was found to significantly reduce the air-reactivity and improve the electrochemical performance of NaNi0.5Mn0.5O2 by removing surface impurities formed by air exposure.