Pouch Lithium-ion Battery Research Articles

The indentation analysis triggering internal short circuit of lithium-ion pouch battery based on shape function theory

The indentation analysis triggering internal short circuit of lithium-ion pouch battery based on shape function theory

Electrochemical-thermal modeling and experimental validation of commercial graphite/LiFePO4 pouch lithium-ion batteries

Large-sized lithium-ion battery (LIB) mathematical models are critical in design of cells, packs, and their associated thermal management systems. A high-fidelity fully coupled electrochemical-thermal model for a commercial 20 Ah LIB is developed to simulate the distribution of electrochemical and thermal variables three-dimensionally (3D) through 48 electrode layers in the pouch cell. As a new feature, the details of heat generation and voltage drop due to the tab, current collectors, and associated contact resistances are included in the developed model. A series of galvanostatic charge/discharge tests at operating rates ranging from 1C (20 A) to 5C (100 A) and at room temperature is conducted on the pouch cell and the output voltage and temperature distribution are recorded. The developed model voltage and temperature distribution predictions are successfully compared against the experimental data, demonstrating the accuracy of the model. As a key finding in this work, it is found that self-heating is the main contributor for electrochemical performance improvement in large-sized LIBs over small cells. This is due to the improved kinetic and transport properties of LIB electrodes at elevated temperatures. It is also demonstrated that the temperature variation between the surface and center layers of a pouch cell is not significant at a maximum difference of about 1.7 °C for charge/discharge rates up to 5C (100 A). As a result of this finding, it is suggested that a single temperature measurement close to the tabs at the battery surface would be sufficient for thermal management development and control purposes.

Effects of Polypropylene Orientation on Mechanical and Heat Seal Properties of Polymer-Aluminum-Polymer Composite Films for Pouch Lithium-Ion Batteries.

In this study, polyamide-aluminum foil-polypropylene (PA-Al-PP) composite films with different orientation status of the PP layer were prepared, and their morphology, tensile, peeling and heat seal behavior were studied. The comparative study of tensile and fracture behaviors of single-layer film of PA, Al and PP, as well as the composite films of PA-Al, PP-Al and PA-Al-PP revealed that in PA-Al-PP composite film, the PA layer with the highest tensile strength can share the tensile stress from the Al layer during stretching, while the PP layer with the lowest tensile strength can prevent further development of the small cracks on boundary of the Al layer during stretching. Moreover, the study of heat seal behavior suggested that both the orientation status and the heat seal conditions were important factors in determining the heat seal strength (HSS) and failure behavior of the sample. Four failure types were observed, and a clear correspondence between HSS and failure types was found. The results also elucidated that for the composite film, only in the cases where the tensile stress was efficiently released by each layer during HSS measurement could the composite film exhibit desired high HSS that was even higher than its tensile strength.

Non-uniform effect on the thermal/aging performance of Lithium-ion pouch battery

Non-uniform distribution of current density and temperature is inevitable especially in high C-rate and it can lead to bad performance of battery. Therefore, the non-uniform effect (non-uniform temperature, current density and aging) on the pouch battery performance is studied with experiment and simulation. A new method, which measures the direct current resistance (DCR) based on the discharge curve, is proposed to get more detail of resistance variation. The measurement shows that the resistance of Lithium-ion pouch battery with non-uniform temperature is similar to that of average temperature. Then, effect of non-uniform aging is simulated based on the electro-thermal coupled model. It is found that battery suffering non-uniform aging has smaller discharging capacity relatively. The main cause for the discharge capacity reduction between the uniform and non-uniform aging battery is the big difference of local stoichiometry of cathode electrode θLiFePO4. The capacity reduction in 1C rate occupies about 6% of the permissible capacity loss. Finally, tabs of battery are changed in order to acquire uniform temperature distribution. Battery whose tabs are put on the middle of the top side and the bottom side has a better performance in the opinion of thermal analysis.

State of charge estimation for lithium-ion pouch batteries based on stress measurement

State of charge (SOC) estimation is one of the important tasks of battery management system (BMS). Being different from other researches, a novel method of SOC estimation for pouch lithium-ion battery cells based on stress measurement is proposed. With a comprehensive experimental study, we find that, the stress of the battery during charge/discharge is composed of the static stress and the dynamic stress. The static stress, which is the measured stress in equilibrium state, corresponds to SOC, this phenomenon facilitates the design of our stress-based SOC estimation. The dynamic stress, on the other hand, is influenced by multiple factors including charge accumulation or depletion, current and historical operation, thus a multiple regression model of the dynamic stress is established. Based on the relationship between static stress and SOC, as well as the dynamic stress modeling, the SOC estimation method is founded. Experimental results show that the stress-based method performs well with a good accuracy, and this method offers a novel perspective for SOC estimation.

Influence of lithium hexafluorophosphate/ethylene carbonate/dimethyl carbonate electrolyte soaking on heat seal strength of polyamide 6/aluminum/cast-polypropylene laminates used as lithium-ion battery packaging

The heat-seal strength of polymer–metal–polymer laminates, widely used in the packaging industry and more recently for pouch lithium-ion batteries, is a critical factor for the integrity of flexible package structures during service. The influences of lithium hexafluorophosphate/ethylene carbonate/dimethyl carbonate (LiPF6/EC/DMC) electrolyte soaking time and storage temperature on heat-seal strength were investigated through T-peel testing using a universal testing machine. Sealed multilayer laminates’ heat-seal strength and their failure modes were measured for specimens sealed at various heat-sealing temperatures and dwell times before and after exposure to room temperature and 60℃ soaking conditions. The soaking condition significantly influences heat-seal strength, especially for the packages heat-sealed at low temperatures and short heat-sealing times. Higher storage temperature during electrolyte-soaking accelerates the heat-seal strength decrease. Failure modes are affected by the soaking conditions and become more complicated than the packages without soaking. The optimized heat-sealing processing window is obtained under a certain soaking condition. The electrolyte hydrogen ion concentration (pH) decreases with longer soaking time and higher storage temperature, indicating that acidification may also contribute to decreased heat-seal strength. The results are important for understanding how stored lithium-ion batteries deteriorate and can help to guide battery design to maximize their shelf life.

Modeling and validation of temperature changes in a pouch lithium-ion battery at various discharge rates

This paper deals with the thermal modeling of temperature rise in a pouch lithium-ion battery with LiFePO4 (also known as LFP) cathode material. The developed model represents the main thermal phenomena in the cell in terms of temperature change. The proposed model is validated with the collected experimental data from a module composed of 11 cells. In the conducted experiments, the different charge and discharge rates of 1/2C, 1C, 2C and 2.5C are applied. It is seen that, the increased discharge rates result in increased temperature on the surface of the battery. When the discharge rate is doubled, from 1C to 2C, cell temperatures have risen by 3.5 times. A simplified model for determining the heat generation is developed and validated with the test results.

Heat seal properties of polymer–aluminum–polymer composite films for application in pouch lithium-ion battery

Failure modes of heat seal properties of polymer–aluminum–polymer composite films.

Dimensional Changes in Automotive Pouch Li-Ion Cells: A Combined Thermo-Mechanical/Electrochemical Study

In this work it is proposed an integrated measurement system able to measure simultaneously mechanical properties, dimensional variations and Young modulus, of a pouch lithium-ion battery under operative conditions. At the same time, the designed integrated system allows also the measurement of both electrochemical main quantities (current and potentials) and temperature distribution. The complex testing capabilities system was implemented in an owner-lab-made apparatus. Experimental data collected both under normal operational conditions, as well as on abused batteries, allow to establish safer operational limits and to determine proper operation conditions to prevent the battery malfunctioning.

Electrothermal and Electrochemical Modeling of Lithium-ion Batteries: 3D Simulation with Experimental Validation

This work presents two lithium-ion battery models which are implemented in the multiphysics software package FIRE®, developed by AVL List GmbH: an efficient electrothermal model based on an empirical voltage/current relationship and a physically based, non-isothermal electrochemical model. The models are applied to a 3D simulation of a high energy lithium-ion pouch battery. Both models are adjusted to measured discharge curves for various currents and temperatures. Then their results are compared and a deep insight into the electrodes is given by the electrochemical model. Here, the importance of 3D effects and temperature influence are pointed out – both effects which are often neglected in electrochemical models presented in literature. Finally, both models are compared to voltage and temperature measurements using a realistic, strongly dynamic driving profile. A highly accurate prediction of the experimental data can be achieved with both models.

Effect of thermal contact resistances on fast charging of large format lithium ion batteries

A two dimensional electrochemical thermal model is developed on the cross-plane of a laminate stack plate pouch lithium ion battery to study the thermal performance of large format batteries. The effect of thermal contact resistance is taken into consideration, and is found to greatly increase the maximum temperature and temperature gradient of the battery. The resulting large temperature gradient would induce in-cell non-uniformity of charging-discharging current and state of health. Simply increasing the cooling intensity is inadequate to reduce the maximum temperature and narrow down the temperature difference due to the poor cross-plane thermal conductivity. Pulse charging protocol does not help to mitigate the temperature difference on the bias of same total charging time, because of larger time-averaged heat generation rate than constant current charging. Suggestions on battery geometry optimizations for both prismatic/pouch battery and cylindrical battery are proposed to reduce the maximum temperature and mitigate the temperature gradient within the lithium ion battery.

Development of 2D Thermal Battery Model for Lithium-ion Pouch Cells

This paper represents a simulation model for a 2D-thermal model applied on a Lithium-ion pouch battery. This model is able to describe the transient response of the thermal distribution accurately. The heat generation parameters used in this model have been obtained experimentally from dedicated estimation technique. The experimental and simulation are performed at different charge and discharge current rates. The experimental results are in good agreement with the developed model. The battery thermal distributions using natural and forced convection cooling are studied.

On the stress characteristics of graphite anode in commercial pouch lithium-ion battery

The stress of graphite anode in commercial pouch lithium-ion battery is characterized ex-situ by using micro-Raman mapping technique at 2 μm lateral resolution. The results show that the stress in graphite anode is always compressive and its distribution is inhomogeneous both in the manufacturing process and in cycling process. The stress mainly generates and accumulates in the early stage of cycling process, which causes not only big anode thickness swelling but also graphite particles cracking or even degrading. The deterioration of electrical contact of graphite particles from current collector caused by anode volume expansion and formation of solid electrolyte interface (SEI) in fresh surface of cracked graphite particle is responsible for the faster capacity fading of pouch battery in this early stage.

Composite Multifunctional Lithium-Ion Batteries

The goal of this work was to design a battery that serves as the structural material as well as the power source for a vessel. The combination of both mechanical and electrochemical aspects within one material defines the component as a multifunctional material, or in this case, a multifunctional battery. The initial work focused on the fabrication of a novel multifunctional lithium ion battery structure, where reinforcement composite fibers were substituted and utilized as active components within the electrodes and separator, enduring cyclic voltage-capacity testing. The second part of this work investigated an approach to modify a conventional lithium ion pouch battery architecture by creating perforations through the cell architecture in order to reduce delamination or wrinkling of the battery during bending loads. The future aim is to fabricate the battery as part of the composite structure instead of a separate piece of the structure.

Calibration and finite element simulation of pouch lithium-ion batteries for mechanical integrity

Mechanical tests were performed on pouched and bare lithium-ion cells under five loading conditions. These included through-thickness compression, in-plane unconfined compression, in-plane confined compression, hemispherical punch indentation and three-point bending. From the measured load–displacement data, the individual compression stress–strain curves were calculated for the separator, the active anode and cathode materials. The FE model was developed, composed of shell elements, representing the Al and Cu foil, and solid elements for the active material with a binder lumped together with the separator. Very good correlation was obtained between LS Dyna numerical simulation and test results for the through-thickness compression, punch indentation and confined compression. Closed form solutions were also derived to reveal the underlying physics and identify important groups of parameters. It was also demonstrated that a thin pouch enclosure provided considerable reinforcement and in some cases changed the deformation and failure mechanism. The present computational model of an individual cell provides a fundamental building block for modeling battery modules and battery packs across different length scales. The present test program differs substantially from the nail indentation or punch crush loading performed by the industry, and provides data for the development of an advanced constitutive model needed for strength/weight optimization and safety assessments of Li-ion batteries.

Development and on-orbit operation of lithium-ion pouch battery for small scientific satellite “REIMEI”

A lithium-ion battery was developed using off-the-shelf pouch cells and launched with a small scientific satellite “REIMEI.” The cells were potted with polyurethane or epoxy resin to protect the battery from vacuum in space. Preliminary experimental test results of pouch cells potted in a soft aluminum cap suggested that the cells tended to swell in vacuum, although they had been reinforced with the resins. Bread board models (BBMs), in which pouch cells were potted with resins in a hard aluminum case, were fabricated for cycle life performance tests in the laboratory. The test results indicated that the performance of epoxy-potted BBM was superior to that of the polyurethane-potted BBM. The measured cell resistance implied that the electrolyte solution leaked through the polyurethane resin, resulting in premature deterioration. The epoxy resin was used for the flight battery. The end-of-discharge-voltage (EoDV) trend of the flight battery on orbit was compared with the laboratory test results corrected based on a post-launch cycle test using a fresh cell. The corrected EoDV trend in the laboratory was in good agreement with the on-orbit trend for the early cycle period, indicating that the on-orbit battery was not inadvertently affected by conditions in space.