Investigation of current sharing and heat dissipation in parallel-connected lithium-ion battery packs

Zhang, Yichao; Zhao, Ruxiu; Dubie, Jacob; Jahns, T.M.; Juang, Larry W.

doi:10.1109/ecce.2016.7855217

Cited by 9 publications

(5 citation statements)

References 12 publications

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“…Since the behaviour of the cells in parallel connection is comparable to an electrical current divider, the current through the hotter cells increases significantly, which leads to faster ageing of these cells. This behaviour has already been demonstrated in the literature for parallel connected cells [130,131]. The ageing of module 0.5C/4P is thus mainly determined by the inner cells of different CLs.…”

Section: Impact Of Module Architecturesupporting

confidence: 67%

From the production of the single cell to the end of life of the battery module: the development of parameter variation of lithium-ion cells

Oeser¹

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(English) In lithium-ion batteries, depending on the requirements, many individual cells are connected in series and parallel. Despite very similar individual cell parameters after production, they can develop differently during the subsequent ageing process due to intrinsic and extrinsic influences. A pronounced parameter variation of the assembled cells ultimately leads to a reduced utilisation of the lithium-ion battery and thus also to a reduced lifetime. The aim of this work is therefore to gain a better understanding of the origin and development of parameter variation during the ageing process. The work is divided into three major parts. At the beginning, parameters such as capacity and internal resistance of 480 brand-new cells of one production batch are recorded. The obtained values allow the calculation of the production-related parameter variation of the cells. In order to investigate the development of the parameter variation during cell ageing, numerous ageing tests are carried out in this work. These are divided into single cell tests and module tests. With the help of single cell ageing tests, the development of the parameter variation of unconnected cells is investigated. Here, several cells are combined into groups and aged under identical conditions. In order to show the influence of different operating conditions on the parameter variation during single cell ageing, the cell groups are aged at different temperatures and different load currents. Finally, by ageing various self-built modules, the development of the parameter variation of cells connected in series and in parallel is investigated. By varying the load current and the number of cells connected in parallel, further dependencies are investigated. The measured data show that both the load on the cells and the ambient temperature have a decisive influence on the development of parameter variation. Operating conditions near the lithium plating boundary are particularly problematic. Since the onset of lithium plating varies slightly between the ageing cells, there are extreme differences in the ageing rate over a certain period of time. This ultimately leads to large parameter variations in the tests carried out. The cells used in this work are cylindrical cells in 18650 format with a nominal capacity of 2.6 Ah (Samsung ICR18650-26J). The high-energy cells consist of a NMC cathode and a graphite anode. (Català) Les bateries de ions de liti estan formades per l’associació sèrie i paral·lel de diferents cel·les en funció dels requeriments. Malgrat que els processos productius asseguren molt poques variacions en la fabricació, aquestes poden evolucionar en el temps de manera diferent degut a les influències internes o externes. Si aquesta variació dels paràmetres de cada cel·la és molt gran es reduirà la capacitat i la vida útil de la bateria. L’objectiu d’aquest treball és aprofundir en el coneixement de l’origen dels fenòmens que provoquen la variació dels paràmetres característics de la bateria durant el seu ús i el pas del temps. El treball està dividit en tres grans parts. Inicialment, s’han mesurat paràmetres com la capacitat o la resistència interna de 480 cel·les noves del mateix lot. Els valors obtinguts han permès calcular la variació de paràmetres deguda al procés productiu. Per tal d’investigar la variació dels paràmetres també durant l’ús i envelliment de les cel·les s’han realitzat tests tant de cel·les individuals com de mòduls de bateries. Amb l’ajut de l’envelliment de cel·les individuals s’investiga l’envelliment de cel·les no connectades entre elles. A partir d’aquest punt, diferents cel·les s’han convinat en grup i s’han envellit en les mateixes condicions. Per tal de poder observar la influència de les diferents condicions d’operació en la variació dels paràmetres durant l’envelliment, altres grups s’han envellit en diferents condicions de temperatura i càrrega. Finalment, mitjançant l’envelliment de diferents grups de cel·les connectades en sèrie i en paral·lel formant una bateria s’han envellit i monitoritzat els seus paràmetres. Les dades obtingudes mostren que tant el nivell de càrrega de les cel·les com la temperatura ambient tenen una influència decisiva en la variació dels paràmetres. Condicions d’operació properes a la metal·lització del liti (lithium plating) són particularment problemàtiques. Atès que l'inici de la metal·lització del liti varia lleugerament entre les cèl·lules envellides, existeixen diferencies extremes entre cel·les. Això provoca grans variacions dels paràmetres de les cel·les envellides. Les cel·les usades en aquest treball són cilíndriques del tipus 18650 amb una capacitat nominal de 2.6 Ah. Les cel·les, d’alta energia, consisteixen un càtode NMC i un ànode de grafit

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Section: Impact Of Module Architecturesupporting

confidence: 67%

From the production of the single cell to the end of life of the battery module: the development of parameter variation of lithium-ion cells

Oeser¹

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“…If the cooling media, typically air or liquid, significantly increases in temperature as it flows across the pack or does not cool some parts of the pack as effectively as others, there will be a temperature distribution across the cells. In [37] the liquid cooling system caused a 4⁰C temperature variation between cells in a 4S pack and resulted in a 1% variation in voltage between the cells during operation. Non-uniform temperature was shown to cause a 25% difference in current for two parallel connected cells in [38], and to cause 5% additional aging for a temperature distribution of 5⁰C in [39].…”

Section: B Impact Of Inconsistencies On Pack Performancementioning

confidence: 99%

Lithium-Ion Battery Pack Robust State of Charge Estimation, Cell Inconsistency, and Balancing: Review

2021

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Lithium-Ion battery packs are an essential component for electric vehicles (EVs). These packs are configured from hundreds of series and parallel connected cells to provide the necessary power and energy for the vehicle. An accurate, adaptable battery management system (BMS) is essential to monitor and control such a large number of cells. Series and parallel connected cells also experience different production and operational conditions, which makes it challenging for the BMS to ensure the safe operation of each individual cell. The main functions of the BMS include battery state estimation, cell balancing, thermal management, and fault diagnosis. Robust estimation of the state of charge (SOC) is crucial for providing the driver with an accurate indication of the remaining range. This paper presents the state of art of battery pack SOC estimation methods along with the impact of cell inconsistency on pack performance and SOC estimation. Cell balancing methods, which are necessary due to cell inconsistencies, are discussed as well. Four categories of pack SOC estimation methods are presented, including individual cell, lumped cell, reference cell, and mean cell and difference estimation methods. The SOC estimation methods are compared in terms of algorithm type, computational load, and engineering effort to help practitioners decide which method best fits their application.INDEX TERMS Lithium-ion battery packs, battery management systems, electric vehicles, cell inconsistency, state of charge, cell balancing.

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“…Ye et al [5] compared the performance of two connection types of battery packs, whether they were connected rst in parallel and then in series or rst in series and then in parallel. Zhang et al [6] modeled a battery pack in order to explain the impact of temperature on current unbalance. Gong et al [7] investigated the inuence of cell inconsistency due to heterogeneous aging in cells connected in parallel.…”

Section: Introductionmentioning

confidence: 99%

Reduced Model for Fast Simulation of a Lithium-Ion Battery Pack Taking Into Account Current and State of Charge Dispersion

Vendrame

Forgez

Sayegh

2022

2022 IEEE Energy Conversion Congress and Exposition (ECCE)

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Modeling the electrical behavior of a battery is essential for obtaining information that cannot be directly measured, such as the state of charge (SOC), or that needs a complex instrumentation, such as the individual cell current. Each cell in a battery pack behaves dierently, creating dispersion of current, SOC, voltage and temperature. In this paper, we propose a method to estimate the current and the SOC of each cell in the pack, taking into account dierences in temperature and connection resistances from one cell to another. To reduce computation time, what makes the algorithm more suitable for real-time applications, we simulate only a few cells in detail. For all the other cells, we use a simplied calculation of their resistances based on their temperatures to estimate current and SOC dispersions. Our method reduces the computation time by 60%, while preserving the accuracy of the model.

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Investigation of current sharing and heat dissipation in parallel-connected lithium-ion battery packs

Cited by 9 publications

References 12 publications

From the production of the single cell to the end of life of the battery module: the development of parameter variation of lithium-ion cells

From the production of the single cell to the end of life of the battery module: the development of parameter variation of lithium-ion cells

Lithium-Ion Battery Pack Robust State of Charge Estimation, Cell Inconsistency, and Balancing: Review

Reduced Model for Fast Simulation of a Lithium-Ion Battery Pack Taking Into Account Current and State of Charge Dispersion

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