An organic, cheap and environmental friendly salt, namely disodium rhodizonate Na₂C₆O₆, is tested as Na sacrificial template in a full-cell sodium-ion battery employing a sodium deficient P2 phase, Na_0.67Mn_0.6Fe_0.25Co_0.15O₂ (NaMFC) as cathode, and a carbonaceous material as counter electrode. As a proof of concept, we demonstrated that the decomposition of the sacrificial organic material leads to enhance the specific capacity in the full-cell system, but the electrochemical results are mitigated by the high irreversibility caused by the side products coming from the sacrificial template decomposition. The mechanism of decomposition of the organic additive as well as its impact on the reaction mechanisms are investigated by online electrochemical mass spectroscopy (OEMS), microscopy and Raman/Infrared vibrational spectroscopy. Additionally, operando X-ray diffraction (XRD) demonstrates that during the oxidation of the disodium rhodizonate, the P2-phase undergoes a re-sodiation, which explains the benefit of Na₂C₆O₆ as Na reservoir.