Preparation and characterization of lithium nickel cobalt oxide powders via a wet chemistry processing

Nickel-rich phases of the solid solutions, LiNi1−yCoyO2 (y=0.1, 0.2, 0.3), were synthesized by a sol–gel method with citric acid as a chelating agent. Various initial conditions were studied in order to find the optimal conditions for the synthesis of LiNi0.8Co0.2O2. The discharge capacity for the compound synthesized under an optimal synthesis condition of 800 °C for 12 h was found to be 187 mAh g−1 in the 1st cycle and it was 176 mAh g−1 after 10 cycles. The other nickel-rich phases, namely, LiNi0.9Co0.1O2 and LiNi0.7Co0.3O2 showed 1st-cycle discharge capacities of 144 and 163 mAh g−1, respectively. The corresponding capacity values were 140 and 159 mAh g−1 in the 10th cycle. Excess lithium stoichiometric phases, LixNi0.8Co0.2O2, where x=1.10, 1.15 and 1.20, resulted in decreased capacity. Structural and electrochemical properties of the synthesized compounds were compared with those of a commercial LiNi0.8Co0.2O2 sample. The effect of calcination temperature and duration, excess lithium stoichiometry and divalent strontium doping in LiNi0.8Co0.2O2 are described. Doping with strontium improved both the capacity and cycling performance of LiNi0.8Co0.2O2.