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.

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Accurate knowledge of transport properties of Li‐insertion materials in application‐relevant temperature ranges is of crucial importance for the targeted optimization of Li‐ion batteries (LIBs). Galvanostatic intermittent titration technique (GITT) is a widely applied method to determine Li‐ion diffusion coefficients of electrode materials. The well‐known calculation formulas based on Weppner's and Huggins’ approach, imply a square‐root time dependence of the potential during a GITT pulse. Charging the electrochemical double layer capacitance at the beginning of a GITT pulse usually takes less than one second. However, at lower temperatures down to −40 °C, the double layer charging time strongly increases due to an increase of the charge transfer resistance. The charging time can become comparable with the pulse duration, impeding the conventional GITT diffusion analysis. We propose a model to describe the potential change during a galvanostatic current pulse, which includes an initial, relatively long‐lasting double layer charging, and analyze the accuracy of the lithium diffusion coefficient, derived by using the Weppner‐Huggins method within a suitably chosen time interval of the pulse. Effects leading to an inaccurate determination of the diffusion coefficient are discussed and suggestions to improve GITT analyses at low temperature are derived.

The development of advanced battery materials requires fundamental research studies, particularly in terms of electrochemical performance. Most investigations on novel materials for Li‐ or Na‐ion batteries are carried out in 2‐electrode half‐cells (2‐EHC) using Li‐ or Na‐metal as the negative electrode. Although such cells are easy to assemble and generally provide sufficient stability, scientists should be aware of any effects that may influence the measurements, and care should be taken when interpreting the corresponding results. The present work addresses specific effects that can affect the electrochemical response of measurements in 2‐EHC. Critical points to be considered for long‐term cycling tests and impedance analyses are discussed and illustrated with relevant examples. The different behavior of electrochemically deposited and pristine alkali metal electrodes is shown, deriving the corresponding impact on the characterization of the actual material of interest. We demonstrate possible impacts of anode‐cathode crosstalk effects on the evaluation of measurements in 2‐EHC and highlight challenges and pitfalls in the interpretation of measurements in 2‐EHC with respect to kinetic and thermodynamic properties and battery performance. These findings contribute to the understanding of the limitations of electrochemical characterization in 2‐EHCs and should be carefully considered by researchers when evaluating novel battery materials.

A major drawback of today's Li-ion batteries is inadequate performance at low temperatures, which slows down user-friendliness and market expansion of electromobility. Due to the systems complexity, many possible low-temperature limitations and various dependencies on the operating conditions exist. The origin of the performance limitations at low temperatures is still controversial and not completely clarified. We herein demonstrate a comprehensive analysis of the performance limitations at low temperatures using a LiNi0.5Co0.2Mn0.3O2-based cathode. To separate the overvoltage phenomena, the complex system is decomposed as much as possible and individual aspects are investigated separately. Complementary electrochemical methods are employed to quantify the C-rate and SOC dependence of the individual overvoltage phenomena. Based on comprehensive analysis of the intercalation kinetics, mass and charge transport, we obtain a coherent picture of the performance limitations as a function of operating conditions. This can serve for targeted optimization or parameterizing models to simulate battery behavior. However, the present work is not only concerned with identifying the low-temperature limits of the system studied but also shows how the rate-determining step of the electrode reaction can be efficiently identified as a function of temperature, SOC, and C-rate, which can serve as guideline for future work.

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