Enhancement of the fragile interface of high voltage LiCoO2 by surface gradient permeation of trace amounts of Mg/F
Low-concentration gradient-modified samples ofLiCoO2 were prepared by sintering at 1 050 ℃ using high-temperature solid-phase method,and were coated with LiF doping(LCOLF,LCO@LF)and MgF2 doping(LCOMF,LCO@MF).The material morphologies and electrochemical properties were compared and analyzed utiliz-ing characterization tests such as X-ray photoelectron spectroscopy,transmission electron microscopy,and electro-chemical techniques.The results show that in bulk-doping composite electrodes,the thermogravimetric test demon-strated that LCOLF had optimal thermal stability.In LCOMF crystals,crystal plane spacing of(003)and(104)con-tracted;after 70 cycles at 1C rate under 45 ℃,the specific capacities of LCOLF and LCOMF were 141.45 and 166.98 mAh·g-1 respectively,and their cycling performance was superior to that of the LiCoO2.In the surface-coated composite electrodes,LCO@LF and LCO@MF grains had clean surfaces and the bond valence of lattice oxygen was enhanced toward higher binding energy;LCO@MF built a solid and compact coating layer,and the specific capacity and capacity retention after 70 cycles were 183 mAh·g-1 and 91.26％(that of LCO@LF were respectively 154.38 mAh·g-1 and 77.54％).The cycling performance of surface-coated composite electrodes was significantly better than that of bulk-doping composite electrodes.
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