High rate capability caused by surface cubic spinels in Li-rich layer-structured cathodes for Li-ion batteries

Modified Li-rich layered cathode Li(Li0.2Mn0.54Ni0.13Co0.13)O-2 has been synthesized by a simple strategy of using surface treatment with various amounts (0-30 wt.%) of Super P (carbon black). Based on detailed characterizations from X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS), it is suggested that the phase transformation from Li2MnO3-type of structure to spinel-like phase take place at the surface regions of particles during post annealing process at 350 degrees C, leading to increase in both first coulombic efficiency and rate capability, from 78% and 100 mAh(.)g(-1) (charge capacity at 2500 mA(.)g(-1)) of the pristine material to 93.4% and 200 mAh(.)g(-1). The evidences of spinel formation and the reasons for electrochemical enhancement are systematically investigated.