Update on Na-based battery materials. A growing research path

This work presents an up-to-date information on Na-based battery materials. On the one hand, it explores the feasibility of two novel energy storage systems: Na-aqueous batteries and Na-O-2 technology. On the other hand, it summarises new advances on non-aqueous Na-ion systems. Although all of them can be placed under the umbrella of Na-based systems, aqueous and oxygen-based batteries are arising technologies with increasing significance in energy storage research, while non-aqueous sodium-ion technology has become one of the most important research lines in this field. These systems meet different requirements of energy storage: Na-aqueous batteries will have a determining role as a low cost and safer technology; Na-O-2 systems can be the key technology to overcome the need for high energy density storage devices; and non-aqueous Na-ion batteries have application in the field of stationary energy storage.