Enhanced rate performance of nanosized RGO-LiNi0.5Mn1.5O4 composites as cathode material by a solid-state assembly method

In this paper, LiNi0.5Mn1.5O4 (LNMO) coated with various amount of RGO (0, 0.5, 1, and 2wt%) were successfully synthesized by solid-state assembly method. The physical properties of LNMO and RGO-LNMO were investigated by x-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), and transmission electron microscope (TEM). XRD and Raman spectrum exhibit all samples that are well crystallized in P4(3)32 space group; SEM and TEM results show the uniform size of the particles is 1 similar to 2m with octahedral structure, and LNMO is successfully wrapped by RGO. The electrochemical properties of RGO-LNMO visibly improved compared with the bared LNMO, especially at high current rate, which has been proven by galvanostatic charge-discharge test, cycle performance test, and rate capacity test. For example, the bared LNMO delivers a discharge capacity of 39.2mAhg(-1) at 10C rate, while that of 1-wt% RGO-LNMO was 86.2mAhg(-1), which was approximately 2.5 times more than that of the bared LNMO. At 10C rate after 1000cycles, 2-wt% RGO-LNMO delivers a discharge capacity of 50.6mAhg(-1) with a capacity retention of 86.7%, while the bared LNMO delivers a discharge capacity of 27.6mAhg(-1) with a capacity retention of 52.5%, only about 54% of the 2-wt% RGO-LNMO. EIS results show the charge transfer resistance of LNMO decreased after coating with RGO, which was favorable for improving electrochemical performance.