Abstract
The solid-state diffusion coefficient of the electrode active material is one of the key parameters in lithium-ion battery modelling. Conventionally, this diffusion coefficient is estimated through the galvanostatic intermittent titration technique (GITT). In this work, the validity of GITT and a faster alternative technique, intermittent current interruption (ICI), are investigated regarding their effectiveness through a black-box testing approach. A Doyle-Fuller-Newman model with parameters for a LiNi0.8Mn0.1Co0.1O2 electrode is used as a fairly faithful representation as a real battery system, and the GITT and ICI experiments are simulated to extract the diffusion coefficient. With the parameters used in this work, the results show that both the GITT and ICI methods can identify the solid-state diffusion coefficient very well compared to the value used as input into the simulation model. The ICI method allows more frequent measurement but the experiment time is 85% less than what takes to perform a GITT test. Different fitting approaches and fitting length affected the estimation accuracy, however not significantly. Moreover, a thinner electrode, a higher C-rate and a greater electrolyte diffusion coefficient will lead to an estimation of a higher solid-state diffusion coefficient, generally closer to the target value.
Highlights
A lithium (Li) ion battery is a complicated electrochemical system and its performance is dependent on a multitude of material properties, among which the solid-state diffusion coefficient Ds of Li+ is one of the key parameters, since the mass transport in these particles is the rate-limiting processes for thin electrodes, and the corresponding resistances constitute a major part of the total battery overpotential
Coefficient can be theoretically estimated from density functional theory (DFT) [1], [2] or Molecular Dynamics (MD) simulations [3], [4], it is more frequently experimentally determined by electrochemical approaches, including the galvanostatic intermittent titration technique (GITT), potentiostatic intermittent titration technique (PITT), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) [5]
The simulated voltage profiles during the GITT and intermittent current interruption (ICI) tests are shown in Fig. 3, which resemble the experimental results reported in literature [11], [9]
Summary
A lithium (Li) ion battery is a complicated electrochemical system and its performance is dependent on a multitude of material properties, among which the solid-state diffusion coefficient Ds of Li+ is one of the key parameters, since the mass transport in these particles is the rate-limiting processes for thin electrodes, and the corresponding resistances constitute a major part of the total battery overpotential. In the GITT test, a current pulse is applied when the cell is in an equilibrium state and the voltage response follows a linear relationship with the square root of time. Using ICI, the voltage response during a current interruption is monitored, which follows a linear relationship with the square root of time. Since the ICI method does not require the cell to be in an equilibrium state, the most time consuming part in the GITT method, i.e. the relaxation period, can be omitted
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