The impurity Ni 2+ /Ni 3+ phase formation at high-temperatures in the n = 1 R-P phase originates from the In stoichiometric La2NiO4 is, Ni exists mainly in Ni 2+ state, which is stable only at temperatures over 1100 °C82 but in higher order phases Ni tend to be predominantly in Ni 3+ state, which is favourably stable below 900 °C. Therefore, higher-order phases such as La4Ni3O9.78 (L4N3), Pr4Ni3O10± (P4N3) and La2Pr2Ni3O10± (L2P2N3) comprising predominantly of Ni 3+ , expectedly offer long-term stability . This was confirmed by Skinner and co-workers who observed that higher-order phases show increased stability with no impurity phase appearing after 2 weeks of heating of n = 2 and 3 phases at 900°C unlike lower-order phases which show an impurity phase . While this is promising and has been confirmed by several studies but we are leaving discussion on Ruddlesden-Popper phase materials limited here and readers are invited to read the dedicated review on the cathode application of these materials published recently by M. Yatoo and S. Skinner .