Sodium-ion full cell with hard carbon as anode and a layered oxide cathode based on earth abundant elements i.e., Na0.67[Fe0.5Mn0.5]O2 is reported. The irreversible capacity of the negative electrode in the full cell configuration is compensated by the addition of a sacrificial salt such as NaN3 to the P2-Na0.67[Fe0.5Mn0.5]O2 cathode material. 60% increase in the reversible capacity is achieved with the addition of 10% of sodium azide in the composite cathode without compromise on the cycle life. Though, there is a limit in its use because of the capacity fade which can be observed with the further increase in NaN3 content. The quantification of sodium ions at the end of discharge (at 1 V) after 40 cycles by ex-situ X-ray diffraction and solid state nuclear magnetic resonance supports the electrochemical data. Scanning electron microscopy shows the effect of NaN3 on the electrode microstructure in terms of the porosity created by NaN3 decomposition.