Ionic liquid assisted hydrothermal synthesis of 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 for lithium ion batteries

Abstract The uniform lithium-rich manganese-based 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 cathode materials are synthesized by a hydrothermal strategy with assistant of 1-butyl-3-methylimidazolium chloride ([BMIm]Cl) ionic liquid. The microstructures and electrochemical performances of the prepared cathode materials are characterized by XRD, SEM, TEM and electrochemical measurements. Compared with the original sample, the unique micro-morphology and better layered structure and less cation mixing of the obtained compounds with [BMIm]Cl ionic liquid give the material a sufficient contact between the solid/liquid interface (electrode and electrolyte) and facilitated the process of Li+ intercalation/deintercalation, which availing to improved electrochemical kinetics properties with excellent rate capability and remarkable cycling stability. The analysis of the kinetics of electrode reaction (EIS) proved that the charge transfer resistance value can be decreased by adding appropriate amount of [BMIm]Cl ionic liquid, and thus reduce the diffusion pathways of Li+ ions and electrons, which is well consistent with the rate capability test results. Specifically, when the amount of the [BMIm]Cl ionic liquid reaches 0.5 g, the 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 exhibited a higher initial capacity of 269.7 mAh g-1, and the capacity retention after 65 cycles was 93.0%.