Methodically controlled Na3Zr2Si2PO12 solid electrolyte nano-coating layer on O3-type cathodes via multifunctional polyacrylic acid for high-performance and moisture stable sodium-ion batteries

Sodium has the advantage of being more abundant than lithium. Therefore, sodium-ion batteries (SIB) have attracted attention as next-generation secondary batteries to replace lithium-ion batteries (LIB). NaNixFeyMnzO2 (x + y + z = 1), an O3-type sodium-based layered cathode material, is considered a promising cathode material because sodium can occupy a significant portion of the O3-type structure. However, the rate capability, cycle life, and capacity reduction are obstacles to actual application because of the low Na-ion conductivity caused by the O3-type sodium structure characteristics and inherent moisture vulnerability. In this study, a simple ethanol-based precursor pre-coating process using a fast Na-ion conductive material was designed to effectively improve the electrochemical performance of the cathode material. Na3Zr2Si2PO12 with a NASICON structure, a high-ion-conductivity phosphate-based solid electrolyte, was used as the coating material. In addition, a uniform coating layer was formed on the surface of the cathode using polyacrylic acid, a polymer material with a driving force for the coating precursor.