A new high voltage alluaudite sodium battery insertion material

Large-scale stationary storage forms a key sector that can be economically served by sodium-ion bat-teries. In realizing practical sodium-ion batteries, discovery and development of novel cathodes is essential. In this spirit, alluaudite-type Na2Fe2(SO4)(3) was reported in 2014 to have the highest Fe3+/Fe2+ redox potential (similar to 3.8 V vs. Na). This finding led to reports on various PO(4)(3-)and SO(4)(2-)based alluaudite compounds exhibiting high energy densities. In 2017, MoO(4)(2-)based alluaudite, Na2.67Mn1.67(MoO4)(3), was found as a 3.45 V cathode material. Exploring molybdenum chemistry further, this work reports alluaudite type Na3.36Co1.32(MoO4)(3) (NCMo) as a novel versatile electroactive cathode for Li-ion and Na -ion batteries. It was synthesized by a wet solution-combustion route with a restricted annealing duration of 1 min at 600 degrees C. Calorimetric study revealed the formation enthalpy from component oxides (Delta H degrees(f,ox) =-575.49 +/- 7.75 kJ/mol) to be highly exothermic. Unlike the sulfate class of alluaudites, this material is highly stable in air and moisture (Delta H-ds = 537.42 +/- 0.78 kJ/mol). Having an ionic conductivity of 6.065 x 10(-8) S/cm (at 50 degrees C), it offers a pseudo two-dimensional Na+ migration pathway. Without any material optimization, NCMo was found to work as a high-voltage insertion cathode (ca. 4.0 V vs. Na/Na+ and 4.1 V vs. Li/Li+) in sync with theoretically predicted potential of 3.98 V (vs. Na/Na+). Ex-situ X-ray diffraction and photoelectron spectroscopy studies revealed the occurrence of solid-solution redox mechanism solely involving Co3+/Co2+ redox centre. It benchmarks Na3.36Co1.32(MoO4)(3) as a novel electrochemically active Mo-based alluaudite-type polyanionic cathode insertion material. (c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

This study reports a novel versatile electroactive cathode material Na3.36Co1.32(MoO4)(3) for Li-ion and Na-ion batteries, which exhibits high stability and ionic conductivity. It can function as a high-voltage insertion cathode and has a solid-solution redox mechanism involving Co3+/Co2+ redox centres.