Will  cheap,  sustainable  Na-ion  batteries  soon  replace  the  current  Li-ion  battery technology? One of the main challenges to be overcome for the commercialization of Na- ion batteries lies in finding better Na-ion cathode materials. Sodium manganese oxides, Na_xMnO₂,  typically  have  a  high  energy  density  per  unit  volume.  Yet,  these  layered materials undergo a number of phase transitions upon electrochemical cycling which limit their  cycle  life.  In  this  talk  we  will  see  how  solid-state  NMR  and  Density  Functional Theory can be used in combination to understand the structural and electronic processes occurring upon electrochemical cycling of Na_xMnO₂–type compounds. In particular, we have found that NMR spectroscopy can give us invaluable information on the effect introducing of dopant species on the transition metal lattice to enhance the structural stability and the electrochemical performance of Na_xMnO₂ cathodes.