Session: Advances in Materials Synthesis & Characterization of Li-ion, Na-ion & Multi-Valent Batteries:

Sodium-ion batteries and hybrid dual metal ion batteries are considered as promising alternatives to lithium-ion batteries in terms of energy density, safety and environmental issues, and low cost of materials. However, the sensibility of their performance towards the ambient temperature is an obstacle to their integration into large-scale energy storage systems.
Herein, we demonstrate the temperature-induced reactivity of three-layered oxide: P3-Na_2/3Ni_1/3Mg_1/6Mn_1/2O₂ (NM16), designed with optimized composition and structure aims to work at elevated temperatures. The electrochemical behavior of P3-Na_2/3Ni_1/3Mg_1/6Mn_1/2O₂ as a positive electrode is studied in both type of cells – sodium and hybrid lithium-sodium ones, and in presence of conventional carbonate-based and advanced ionic liquids-based (IL) electrolytes. The structural changes and surface reactivity of the layered oxide after cycling are monitored by ex-situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses.
In sodium cells the layered structure of P3-NM16 during Na⁺ intercalation is preserved and any significant phase changes are not observed. It is found that at 40 ^oC, the rate capability of the oxide is improved upon cycling using an IL electrolyte rather than the carbonate-based electrolyte. The IL electrolyte exhibits a low surface reactivity towards layered oxide, irrespective of the operating temperature. The dominant electrolyte-electrode interaction appears to be the adsorption of the electrolyte ions. In contrast, the carbonate-based electrolyte has been shown to be highly reactive, resulting in the formation of interface rich on inorganic and organic decomposition products.
In hybrid Li/Na ion cell, the interaction between P3-NM16 and lithium electrolyte begins before the electrochemical reaction, resulting in a transformation of P3 into O3 type of structure. Along with the structural transformation, a film enriched with LiF, NaF, electrolyte-decomposed products grows on the oxide surface. The film composition depends on the operating temperature and with its increasing the decomposed products become denser. The best cycling stability and rate capability is observed when P3-NM16 operates in hybrid Li/Na ion cell using IL-based electrolyte at 40 ^oC.
In addition the performance of the oxide in hybrid Li/Na ion cell is better than that in single sodium-ion cell which emphasizes the advantage of dual Li⁺,Na⁺ ion intercalation.

Krassimir Kostov

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