Synthesis of Co-Doped High Voltage Lithium Cobalt Oxide with High Rate Electrochemical Performance

Abstract

LiCoO2 can further develops its capacity potential by increasing cut-off voltage, but the irreversible phase transition and structural damage at high voltage will lead to severe capacity fading. Here, we propose a method of multi-doping of four elements Ti, Mg, Al, and Y, which realizes the stable cycling of LiCoO2 at a cut-off voltage of 4.5V through the synergistic effect among the four elements. The cell delivers the increased initial discharge capacity of 173.5mAh/g, with the capacity retention rate as high as 91.1% after 100 charging-discharging cycles at the rate of 1C in the voltage ranging from 3.0 to 4.5 V. Moreover, the capacity retention is still as high as 74.2% after 300 cycles. At the same time, the capacity can still be maintained close to 70% after 100 cycles at the temperature of 50℃. The specific discharge capacity of the cathode is 130.0mAh/g, even if at high rate of 5C. More than 5 times that of unmodified LiCoO2. We studied the stability of the bulk phase and the interface by combining experiment and DFT, and proved that this four-element collaborative doping strategy can improve the structural stability of the material. This work provides a promising idea of multi-element synergistic doping and contributes to solving problem of stable high voltage LiCoO2.

Keywords: High Voltage, High rate, Multielement doping, Cyclic Stability, Synergistic effect, First principles computation