Various high energy density rechargeable batteries are being considered for future space applications. Of these, the sodium-sulfur battery is one of the leading candidates. The primary advantage is the high energy density (760 W h kg−1 theoretical). Energy densities in excess of 180 W h kg−1 have been realized in practical batteries. More recently, cathodes other than sulfur are being evaluated. We, at JPL, are evaluating various new cathode materials for use in high energy density sodium batteries for advanced space applications. Our approach is to carry out basic electrochemical studies of these materials in a sodium cell configuration in order to understand their fundamental behaviors. Thus far, our studies have focussed on alternative metal chlorides such as CuCl2 and organic cathode materials such as TCNE.