Simulation and Measurement of the Current Density Distribution in Lithium-Ion Batteries by a Multi-Tab Cell Approach

Abstract

A single-layered NMC/graphite pouch cell is investigated by means of differential local potential measurements during various operation scenarios. 44 tabs in total allow for a highly resolved potential measurement along the electrodes whilst the single layer configuration guarantees the absence of superimposed thermal gradients. By applying a multi-dimensional model framework to this cell, the current density and SOC distribution are analyzed quantitatively. The study is performed for four C-rates (0.1C, 0.5C, 1C, 2C) at three temperatures (5 • C, 25 • C, 40 • C). The maximum potential drop as well the corresponding SOC deviation are characterized.The results indicate that cell inhomogeneity is positively coupled to temperature, i.e. the lower the temperature, the more uniform the electrodes will be utilized. Within the past decades, demand for lithium-ion batteries in mobile applications has significantly increased. Due to their well proven performance as well as their stability in long-term usage, lithium-ion batteries became the technology of choice for electrochemical energy storage devices.1,2 Still, the specific energy density as well as cycle life are constantly being optimized by either commercializing new active materials, electrolytes and additives or by reducing the fraction of non-active parts within a battery. Often, this corresponds to thicker electrodes or larger form factors leading to capacities of up to 100 Ah per cell. In these large format cells, severe gradients in current density and temperature distribution can occur along the electrode stack, 3-9 which might provoke a performance loss during operation due to inhomogeneous utilization. Also non-properly adapted thermal conditioning can have a crucial impact on the performance of larger cells. [10][11][12] Modeling of internal distributions of potential and temperature along the electrodes is quite challenging, since even to calculate only a few cycles, a lot of computational resources are required for fully resolved models. In literature, there are many examples for spatially resolved multi-dimensional modeling approaches, 8,9,[13][14][15][16] which aim at representing the cell's internal behavior in terms of potential, current density, state of charge (SOC) and temperature distribution. Unfortunately, all of these examples lack a detailed, i.e. spatially resolved experimental validation, which is capable of tracking internal variables instead of measuring the surface temperature at a few spots and considering the overall battery's terminal voltage. Also, only a few examples of direct measurements of the internal current density distribution were published so far. Zhang et al.6,7 built a specific LFP/graphite prototype cell for this purpose. A segmented cathode was used for analyzing the current distribution during discharge at varying C-rates and temperatures. This setup allows for a precise monitoring of the current of each electrode element individually. Large deviations in SOC of up to several percent were identified during the process...

Modeling and simulation of inhomogeneities in a 18650 nickel-rich, silicon-graphite lithium-ion cell during fast charging

“…Using less complex test procedure such as electrochemical impedance spectroscopy (EIS), current density and local potential distribution along the electrode was investigated towards the inuence of alternating excitation currents, temperature, tab pattern and frequency for a modied 26650 LFP/C cell with four tabs [34]. Subsequently, a single layered NMC/C pouch cell with several measurement tabs along the electrode revealed the dependency of local current peaks towards the electrode OCPs and was used to validate the MuDiMod [24], which is used in this work.…”

“…The MuDiMod consists of several p2D models calculating electrochemical potentials and lithium-ion concentrations perpendicular to the current collectors, the 2D model accounting for the electrical potential along the current collectors and the 3D model calculating the local temperature within the jelly roll of the cylindrical cell. As the basic MuDiMod is already published in previous works [24,25] with an extension of using eective spatial discretization techniques [26], only novel implemented techniques or submodels are outlined here.…”

“…In this work, a commercial 3.35 Ah NMC-811/SiC (INR18650-MJ1, LG Chem [21]) lithium-ion battery is characterized via calorimetry, infrared thermography and open-circuit potential (OCP) experiments. Based on the experimental part, a newman-type [22] pseudo-two dimensional (p2D) model and a Multi-Dimensional Model (MuDiMod) [23,24,25,26] are parameterized and validated for a simulation study on the latest, widley discussed eld of fast charging [27,28,29,30]. In this matter, charge-rate capability and tendency of lithium plating is analyzed for the high-capacity and a standard NMC-111/C material in highly and moderatly densied electrodes…”

The Impact of Environmental Factors on the Thermal Characteristic of a Lithium–ion Battery

“…Heat incorporation is a passive phenomenon quantified by material heat capacity [29][30][31]. Interior design improvements in heat removal are reported for electrode and stack modification with the focus on the minimizing of internal resistance contributions, enhancing thermal conductivity on a material level [32], or within the stack arrangement [33], as well as the customizing of the battery tap [34][35][36] and the terminal layout [37]. Exterior design cooling types in general embrace air [38][39][40], liquid [41,42], heat pipe [3,43], phase change material (PCM) [44,45] or hybrids [18,46] with a focus on multiple cell arrangements and interconnects under the influence of system application and management.…”

Current Distribution Measurements in Parallel-Connected Lithium-Ion Cylindrical Cells under Non-Uniform Temperature Conditions

“…Non-uniform impedance is also be caused by potential gradients along the current collectors, and this effect has been studied recently. 28,30,[46][47][48][49] U eq, j = U eq, j − U eq,avg [1] A simplified case where U eq is zero can occur, and in this case the impedance block is the only contributor to non-uniform current. This models the behavior observed in our pulse results, and also the behavior observed in portions of our charge depleting discharge where the slope of U eq versus SOC is effectively zero, and thus non-uniform SOC cannot cause non-uniform U eq .…”