Ultrasonic sonochemical synthesis of Na0.44MnO2 insertion material for sodium-ion batteries

The energy-demanding nature of solid-state synthesis can be circumvented by using solvothermal synthesis routes involving milder heat treatment steps. Herein, we exploit one such route, ultrasonic sonochemical method, for the synthesis of Na_0.44MnO₂ insertion material. Using simple oxide and carbonate precursors, the target compound can be successfully prepared by restricting the final annealing (at 900 °C) to within 2 h. Rietveld analysis confirms the purity of final product assuming an orthorhombic framework (s.g. Pbam). Involving a step-wise voltage profile with the average Mn⁴⁺/Mn³⁺ redox potential ∼3 V (vs. Na/Na⁺), it delivers reversible capacity over 110 mAh.g^-1 at a rate of C/10 with decent rate kinetics and cycling stability. Ultrasonic sonochemical synthesis can be employed for synthesis and rapid screening of variety of insertion materials for sodium-ion batteries.