Study of carbon surface-modified Li[Li_(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2 for high-capacity lithium ion battery cathode

摘要

Carbon surface-modified Li-excess layered oxide solid solution Li[Li _(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2 cathode is fabricated through a liquid phase route using polyvinylpyrrolidone as carbon source. X-ray diffraction and X-ray photoelectron spectroscopy indicate that the crystal structure and the chemical states of elements for Li[Li _(0.2)Mn_(0.54)Ni_(0.13)Co_(0.13)]O_2 are kept after carbon surface treatment. The high-resolution transmission electron microscopy demonstrated the existence of very little carbon on the surface and the clear boundary after carbon treatment. The carbon surface-modified sample delivers a discharge capacity of 293.2 mAh g~(-1) at C/10 rate (suppose 1 C rate = 250 mA g~(-1)) and 191.6 mAh g~(-1) at 1 C rate between 2.0 and 4.8 V; the capacity retention rate is ～86 % after 70 cycles at 1 C rate. Superior electrochemical properties can be contributed to the carbon surface modification in these aspects including minimizing nanoparticle aggregation and cell polarization, increasing the electronic conductivity, suppressing the elimination of oxide ion vacancies, as well as suppressing the formation of the thick solid electrolyte interfacial layer. Moreover, the annealing process of carbon surface modification might be able to consume Li_2CO_3 impurity partly and cause the recrystallization of the surface disordered layer.