Controlling at elevated temperature the sodium intercalation capacity and rate capability of P3-Na_2/3Ni_1/2Mn_1/2O₂ via selective substitution of Ni by Mg

Authors: Mariya Kalapsazova, Pavel Markov, Krassimir Kostov, Ekaterina Zhecheva, Diana Nihtianova and Radostina Stoyanova

Batteries & Supercaps 10.1002/batt.202000137

Abstract: The integration of sodium ion batteries into large-scale energy storage systems will become feasible in the case when their performance becomes less sensitive towards the ambient temperature. Herein, we demonstrate firstly the elaboration of the oxide-based electrode material with optimized layered structure and composition that is designed to work at elevated temperatures.
Through selective substitution of Mg²⁺ ions for Ni²⁺ in the three layered oxide, P3-Na_2/3Ni_1/2Mn_1/2O₂, the oxidation state of Ni ions, the cationic distribution in the layers, the sodium intercalation capacity and the rate capability is manipulated. The electrochemical behavior of P3-Na_2/3Ni_1/3Mg_1/6Mn_1/2O₂ is discussed on the basis of ex-situ diffraction, microscopic and spectroscopic methods in terms of redox activity of the lattice oxygen, the reversible transfer of Mg²⁺ and Ni²⁺ ions between layers during Na⁺ intercalation, thermal stability of cycled electrodes and surface reactivity of the layered oxide towards the ionic liquid (IL) electrolyte. At 40 ^oC, the rate capability of the oxide is improved upon using an IL electrolyte rather than the carbonate-based electrolyte.