Carbon Modified Li-rich Cathode Materials Li1.26Fe0.22Mn0.52O2 Synthesized via Molten Salt Method with Excellent Rate Ability for Li-ion Batteries

•The nanosized precursor is synthesized via a low temperature molten salt method.•Carbon modified samples are fabricated through coating sucrose on the precursors.•The rate performance of carbon modified materials are highly improved.•The crystallinity and conductivity are optimized by appropriate sucrose treatment.

Li-rich layered oxide cathode Li1.26Fe0.22Mn0.52O2 is synthesized via a low temperature molten salt method, and the carbon modified samples are fabricated through coating sucrose on the precursors with different sucrose ratios. The crystal structure and morphology of the pristine and the carbon modified samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crystal structure appears as a hexagonal α-NaFeO2 layered structure (space group: R3¯m) and is kept after carbon modified. The carbon element distributes uniformly on the surface of the modified samples verified by Energy Dispersive Spectrometer (EDS). The electrochemical performance of the Li1.26Fe0.22Mn0.52O2 Li-rich cathode materials is greatly improved after carbon modification. The cycling stability of the carbon modified samples is also highly improved compared with the pristine. Particularly the rate performance is enhanced by the appropriate coating content of sucrose (1:6), the discharge capacities are 160mAh/g, 133mAh/g and 78mAh/g at 2 C, 3 C and 5 C rate respectively. They also have 83.4%, 82.5% and 83.4% capacity retention after 50cycles at 2 C, 3 C and 5 C respectively. Electrochemical Impedance Spectroscopy (EIS) results demonstrate that the charge transfer resistance of the carbon modified sample decreases obviously. It is suggested that the carbon modification could minimize the cell polarization and increase the electronic conductivity of the Li-rich cathode materials. Additionally, the annealing process of sucrose coating may offer much higher local temperature to improve the crystallization and volatile the excess Li source to suppress Li2CO3 impurity formation verified by the result of XPS.