The kinetics of Li-ion deintercalation in the Li-rich layered Li1.12[Ni0.5Co0.2Mn0.3]0.89O2 studied by electrochemical impedance spectroscopy and galvanostatic intermittent titration technique

The kinetics of Li-ion deintercalation in Li1.12[Ni0.5Co0.2Mn0.3]0.89O2 samples is studied by electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) during the first charge process. The impedance response of Li1.12[Ni0.5Co0.2Mn0.3]0.89O2 largely depends on the open-circuit voltage (OCV) of the cell, showing that the mechanism of electrode kinetics under different potentials is dominated by different electro-chemical reactions. Meanwhile, the equivalent circuit is proposed to simulate the EIS data, deducing the circuit elements (Ri and Ci) which are normally modeled as a multistep process of electro-chemical reactions. The change trend of Rsf (the resistance of SEI film) and Rct (the charge-transfer resistance) in the first charge process are exactly similar. The Cdl (double-layer capacitance) as a function of voltage gradually increases, particularly after 4.5 V. The maximum of Csf (the film capacitor) observed in the first charge process shows that the most intensive ionic fluxes will appear when the Li1.12[Ni0.5Co0.2Mn0.3]0.89O2 electrode reach to the transient equilibrium at different levels of deintercalation. To study the faster capacity fading of Li1.12[Ni0.5Co0.2Mn0.3]0.89O2 during the first charge process, the Li-ion diffusion coefficient (DLi) is also calculated based on the results of EIS and GITT.