GITT Analysis of Lithium Insertion Cathodes for Determining the Lithium Diffusion Coefficient at Low Temperature: Challenges and Pitfalls

Abstract

Understanding the diffusion of lithium ions in electrode materials for lithium ion batteries is of great importance for their knowledge-based optimization and development of novel materials and cell designs. The galvanostatic intermittent titration technique (GITT) is widely applied in battery research to study the diffusion of lithium in anode and cathode materials depending on the degree of lithiation. While transport properties of electrode materials at high and ambient temperatures are largely available, low temperature diffusion and rate coefficients are hardly reported in the literature and vary by orders of magnitude for identical active materials. Herein, we demonstrate and discuss several challenges and pitfalls in the application and evaluation of GITT measurements for determining the effective chemical lithium ion diffusion coefficient in lithium insertion electrodes, which become especially important at low temperature. This includes theoretical considerations and an experimental analysis of the promising cathode material LiNi0.5Co0.2Mn0.3O2 (NCM523) in the wide temperature range of −40 °C to 40 °C. We show how the choice of experimental conditions for the GITT measurements and of the subsequent mathematical evaluation significantly influence the derived diffusion coefficient. The results suggest that the large scattering of reported values of the diffusion coefficient could be caused by the use of different evaluation procedures. Simple calculation methods appear to be less suited the lower the temperature is. It is shown that the complementary use of GITT and EIS supplemented by detailed knowledge of the microstructure of the electrode significantly improves the accuracy of determining the diffusion coefficient.

Effect of Particle Size and Anion Vacancy on Electrochemical Potassium Ion Insertion into Potassium Manganese Hexacyanoferrates

“…The half of median diameter values obtained by particle size distribution measurement in NMP were utilized for r s . Equation 1 assumes a specific surface area of spherical particles with radius r s and √ t dependence of V for the whole current pulse (see Figure S11c) [30a,c] . The assumption for the surface area was introduced because the nanopore structure of KMnHCF hindered the estimation of electrolyte contact area by gas adsorption measurements [30c,31] .…”

Initial Electrode Kinetics of Anion Intercalation and De‐intercalation in Nonaqueous Al‐Graphite Batteries†

“…The GITT test consists of a series of pulse‐constant current‐relaxation process, and the relaxation process indicates that no current flows through the battery as the electrochemical system is settled. According to the description of the relation achieved from GITT [ 33 ] …”

Determining the Diffusion Coefficient of Lithium Insertion Cathodes from GITT measurements: Theoretical Analysis for low Temperatures**

“…The charge transfer coefficient was supposed as . For an order‐of‐magnitude estimate of the rate constant, we employed the charge transfer resistance derived from EIS measurements on NCM523 [15] . In correspondence to the estimated values in Table 1, we included ‐values ranging from in the following parameter study.…”

“…For the equilibrium potential as a function of the SOL, , we employed the quasi‐equilibrium values shown in Figure 4. They were obtained during GITT measurements at 273 K after a relaxation period of 14400 s between the GITT pulses [15] . Actually, the equilibrium potential slightly depends on temperature.…”

“…However, it becomes significant at low temperature. Because of the increasing charge‐transfer resistance with lowering the temperature, the charging time of the double‐layer capacitance increases, and the potential curve noticeably differs from the idealized pulse in Figure 1 [15] …”