Electrochemical performances of layered LiM1−yMy′O2 (M=Ni, Co; M′=Mg, Al, B) oxides in lithium batteries
Abstract Electrochemical performances of substituted layered oxides LiM 1− y M y ′O 2 (M=Ni, Co and M′=Mg, Al, B) as cathode materials in lithium batteries have been investigated. These materials have been made through a solid state reaction of precursors in an oxygen rich atmosphere. X-ray diffraction and infrared measurements have been carried out. Structural data have shown that a single phase, impurity free, can be made through careful selection of precursors, except for the B substituted compounds, for which residual impurity phases were observed due to a more glassy nature of the products. The voltage profiles of the layered oxides and substituted oxides were monitored against a lithium electrode. The overall capacity of the oxides have been reduced due to the sp metal substitution, however, a more stable charge–discharge cycling performance has been observed when electrodes are charged to 4.3 V as compared to the performances of the native oxides. At the cut-off voltage of 4.4 V, the charge capacity of the Li//LiNi 0.95 Al 0.05 O 2 cell is ca. 165 mAh/g. Boron doped LiCoO 2 also provides very low polarization during charge–discharge cycling, with a capacity over 130 mAh/g when charged up to 4.3 V versus a lithium anode. A sample of LiNiO 2 with 5% Mg substitution delivers a capacity of 168 mAh/g.