Enhanced high-voltage cycling stability and rate capability of magnesium and titanium co-doped lithium cobalt oxides for lithium-ion batteries

To improve the high-voltage cycling stability and rate capability, the Mg2+ and Ti4+ co-doping strategy is firstly proposed to modify the LiCoO2 cathode material. The synergistic effect of co-doping with Mg2+ and Ti4+ ions on the structure, morphology and high-voltage electrochemical performance of LiCoO2 is investigated. For the co-doped sample, the introduction of Mg2+ and Ti4+ ions can efficiently optimize the particle size distribution and reduce the aggregation behavior. Compared with the undoped and single-doped samples, the Mg2+ and Ti4+ co-doped LiCoO2 sample presents better high-voltage cycling stability and rate capability due to the fact that the Mg2+ and Ti4+ ions co-doping can make full use of the respective advantages of Mg2+-doping and Ti4+-doping. When cycled at 1.0 C, the co-doped sample exhibits an initial discharge capacity of 179.6 mAh g−1 in the voltage range of 2.75-4.5 V. After 100 cycles, the capacity retention of this sample can reach up to 82.6%. Moreover, the co-doped sample shows better rate performance with high discharge capacity of 151.4 mAh g−1 at 5.0 C. These outstanding results may be attributed to the suppressed phase transition, decreased charge transfer resistance, improved thermal stability, enhanced electrical conductivity and uniform particle size distribution of the Mg2+ and Ti4+ co-doped LiCoO2 sample.