Interfacial modification of NaCoO2 positive electrodes with inorganic oxides by simple mixing and the effects on all-solid-state Na batteries

Abstract

All-solid-state Na polymer batteries are desired as the next generation of high-capacity batteries owing to their high safety and abundant resources. However, the degradation of the positive electrode/electrolyte interface with cycling leads to a decrease in capacity and a significant increase in interfacial resistance. In this study, to suppress the interfacial degradation, we prepared positive electrode sheets through a combination of simple mixing and pasting with the addition of binders and conductive additives, using NaCoO₂ coated with two types of inorganic oxides as the active material. The influence of the coatings on the electrochemical properties of the fabricated all-solid-state Na polymer battery was investigated by performing constant-current charge–discharge tests, and the coating morphology was characterized by electron microscopy and spectroscopic measurements. Compared with the non-coated positive electrode, the coated electrodes not only enhanced the battery capacity and improved the cycling characteristics but also effectively suppressed the formation of byproducts during charge–discharge cycling, owing to the electrochemical stability and Na⁺ conductivity of the inorganic oxide coatings. Moreover, despite the chemically unstable properties of powdered NaCoO₂, the application of this mixing method effectively suppressed its degradation.