As the demand for electrochemical energy storage surges, the research, development and application of new systems require comprehensive understanding of the electrochemical properties at an ever-increasing pace. A critical parameter for the community, from materials chemists to application engineers, is the diffusion coefficient of the redoxactive species; i.e., Li + , in the case of Li-ion batteries. The GITT has been the most widely applied method for deriving the diffusion coefficient from electrochemical measurements. Derived from Fick's second law, GITT was first demonstrated in 1977 for a bulk Li3Sb electrode. The technique consists of two repeating steps. First, a constant current is applied for a duration where the assumption of semi-infinite diffusion holds. Second, the current is switched off until the voltage becomes invariant, which indicates that equilibrium is reached. Through the analysis of the electrode potential measured during the current pulse and the change in the equilibrium potential, GITT renders the chemical diffusion coefficient of the chargecarrying ions. (The difference between chemical and tracer diffusion coefficients is elaborated in the original GITT manuscript. For simplicity, the former will be referred to as diffusion coefficient in the following text.) Later, the technique was applied to porous composite electrodes of Li-ion-insertion materials, which is the format of the majority of electrodes in state-of-the-art Li-ion batteries. Although practical issues, such as nonuniform current distri-bution, can occur due to the geometry of composite electrodes, the technique serves as a powerful tool for the determination of diffusion coefficients if proper experimental parameters are chosen, 4,5 e.g. appropriate current and duration of the current pulses.