A good artcle on batteries in Power Electronics, triggered by  the Samsung Galaxy Note 7 Debacle, and the not to distant past mess with the ‘hover board’ craze. The article links to a pretty detailed recent study of coming high power density battery technologies.   

The eMagazine http://www.powerelectronicsnews.com/ is a good source on power electronics across the power and technology range. A good way to keep up on a rapidly changing field.

The article talks about a variety of battery chemistries including sodium as shown in the following graphic.

An enormous variety of sodium-ion battery variations are being considered by researchers worldwide as surveyed here regarding their operation voltages versus specific capacities for cathode materials (a) and anode materials (b) in order to find a combination that make them competitive with Li-ion. SOURCE: Macmillan Publishers Ltd

However the main reason I show this graphic is the incredible density of information that the graphic data presenter/artist at Macmillan Publishers was able to insert into a relatively small and simple chart. For me as a technologist this gives me the ability to data dive and compare and contrast very quickly when considering alternatives. My experience in buying reports or data repositiories of one sort or another is that the quality of this sort of chart is key to the value of the document