Electrochemical properties of Li2MnO3 nanocrystals synthesized using a hydrothermal method

Abstract

In this article, we report the synthesis of Li₂MnO₃ nanocrystals using a hydrothermal process. XRD, SEM, and TEM analyses are performed, and the electrochemical properties of the resultant nanocrystals are investigated. Adding the oxidant KMnO₄ influences the phase purity, size, and shape of the Li₂MnO₃ nanocrystals. An amount of KMnO₄ that exceeds 6% of the total Mn source enhances the formation of the pure monoclinic Li₂MnO₃ phase. The effect of the amount of KMnO₄ on Li₂MnO₃ grain size can be divided into three ranges. Li₂MnO₃ crystals with a size around 28.7 nm and plate morphology are obtained at less than 6% of KMnO₄ content; those with a size of 28.7 nm to 9.8 nm and mixed morphology of plates and rods are obtained at 6% to 11% KMnO₄ content, and those with a size around 9.8 nm and rod morphology are mainly obtained at KMnO₄ content exceeding 11%. Discharge capacities increase with decreasing size of Li₂MnO₃ nanocrystals in a linear relationship. The voltage of the first charge shows a 4.55 V plateau for Li₂MnO₃ nanocrystals with 28.7 nm size, becoming 4.4 V with a decrease in size to 12.2 nm, and splitting into two plateaus at around 3.8 and 4.4 V with a further decrease in size to 9.8 nm. The XRD and XANES results of the Li₂MnO₃ electrodes obtained after charge/discharge experiments show that smaller sizes are more beneficial in maintaining a layered structure than larger nanocrystals.