Sodium layered oxide cathode materials

This chapter introduces the most common structural polymorphs of layered oxides (O3, P3, and P2) acting as positive electrodes for Na-ion batteries. It describes prototype examples and recent developments on high-voltage and low-cost layered oxides based on Ni, Mn, Fe, and Cu redox centers, which have been classified based on unary, binary, and ternary systems. The chapter describes examples of layered oxides with oxygen redox activity and highlights the main strategies reported to invoke this type of reaction. Sodium layered oxides tend to undergo structural transformations during sodium extraction/insertion. There has been a large research effort focused on the development of sodium layered oxides based on cheap, sustainable, and nontoxic elements, particularly iron and manganese. The chapter focuses on layered oxides based on manganese, iron, and copper redox centers, since these hold the most promise for the fulfillment of the aim of cheap, safe, and sustainable energy storage.