Accurate Calculation of Solid-State Li+ Diffusion Coefficient and Kinetic Activation Energies for an Artificial Graphite Anode

The slow electrochemical reaction kinetics of artificial graphite is one of the limiting factors for safety of lithium-ion batteries, especially the lack of systematic research on activation energies of various kinetic processes. In this work, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT) were used to investigate key kinetic parameters of artificial graphite such as solid-state Li+ diffusion coefficient (DLi+) and activation energy. The results reveal the evaluation of the chemical diffusion coefficient of same material is independent of the technique and shows a similar value, with DLi+ ranging from 10(-11) to 10(-13) cm(2)<middle dot>s(-1). The activation energies measured by EIS and GITT for solid-state Li+ diffusion in graphite at 50% depth of discharge are 74.5 kJ<middle dot>mol(-1) and 66.8 kJ<middle dot>mol(-1), which are in the same order of magnitude as the activation energies of charge transfer resistance (59.5 kJ<middle dot>mol(-1)), electrode/electrolyte interface membrane impedance (56.1 kJ<middle dot>mol(-1)), and ohmic impedance (6.6 kJ<middle dot>mol(-1)). It demonstrates that the solid-state Li+ diffusion, interface charge transfer process, and Li+ transmission through SEI membrane are significantly affected by temperature. This work provides a reliable parameter basis for establishing more accurate thermal-electrochemical coupling models and designing safer battery thermal management systems for lithium-ion batteries.