Understanding the impedance spectrum of 18650 LiFePO4-cells

Illig, Jörg; Schmidt, Jan Philipp; Weiß, Michael; Weber, André; Ivers-Tiffée, Ellen

doi:10.1016/j.jpowsour.2012.12.020

Cited by 141 publications

(91 citation statements)

References 28 publications

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“…R2 is commonly attributed to the polarization or charge-transfer resistance of the rate limiting electrode. 35 For both cells, the increase in R2 is relatively linear, however the increase is significantly faster for Cell S than Cell T, which reinforces the conclusion that the surface cooled cell degrades at a faster rate.…”

Section: Significance Of Results-as Shown Insupporting

confidence: 70%

Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells

Hunt

Zhao

Patel

et al. 2016

J. Electrochem. Soc.

155

119

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One of the biggest causes of degradation in lithium-ion batteries is elevated temperature. In this study we explored the effects of cell surface cooling and cell tab cooling, reproducing two typical cooling systems that are used in real-world battery packs. For new cells using slow-rate standardized testing, very little difference in capacity was seen. However, at higher rates, discharging the cell in just 10 minutes, surface cooling led to a loss of useable capacity of 9.2% compared to 1.2% for cell tab cooling. After cycling the cells for 1,000 times, surface cooling resulted in a rate of loss of useable capacity under load three times higher than cell tab cooling. We show that this is due to thermal gradients being perpendicular to the layers for surface cooling leading to higher local currents and faster degradation, but in-plane with the layers for tab cooling leading to more homogenous behavior. Understanding how thermal management systems interact with the operation of batteries is therefore critical in extending their performance. For automotive applications where 80% capacity is considered end-of-life, using tab cooling rather than surface cooling would therefore be equivalent to extending the lifetime of a pack by 3 times, or reducing the lifetime cost by 66%. Due to their high energy and power densities, Lithium-ion batteries are a very important component of electric vehicles, and their use has increased dramatically in recent years as the uptake of hybrid and electric vehicles has increased.1-3 One of the major challenges of using lithium-ion batteries in hybrid and electric vehicles is thermal management, 4 which is important in order to manage degradation at an acceptable rate whilst maximizing the performance of the batteries and reducing the risk of thermal runaway. 5-7Many studies have shown that increased temperature leads to an increase in the rate of degradation, 4,[8][9][10][11] therefore the effectiveness of a thermal management system is vital in order to maximize the lifetime performance of the pack. The design of a good thermal management system for a battery pack should consider both the overall temperature of the pack and both intra-cell and internal thermal gradients. Poor design of thermal management systems could be a major contributing factor in increasing degradation rates to unacceptable levels. 12There are many different techniques that can be used to thermally manage batteries in hybrid and electric vehicles. It is possible to use either air or liquid as the cooling medium, and both of these can be used in either a direct (with cooling medium in contact with the cell) or indirect way. In addition to this, different areas of the cell can be cooled, namely the surfaces of the cell or the cell tabs. 13,14 In general, systems employing air as the cooling medium are considered to be simpler and cheaper to implement, although the performance is limited especially in applications where there is a high heat generation rate or if the batteries are being operated in a high ambient tempe...

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Section: Significance Of Results-as Shown Insupporting

confidence: 70%

Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells

Hunt

Zhao

Patel

et al. 2016

J. Electrochem. Soc.

155

119

View full text Add to dashboard Cite

show abstract

“…Without greater effort the speed, strength and nature of reactions can be instantly intuited. This coincides with the mathematical interpretation of the distribution function of relaxation times (DRT, [10][11][12]), where serially connected positive RC elements can be interpreted as a discretization of the continuous DRT of any capacitive system. However, this also implies that the concept of DRT is incomplete, in that it is restricted to positive RC elements and hence to capacitive contributions.…”

Section: Resultssupporting

confidence: 63%

Approximability of impedance spectra by RC elements and implications for impedance analysis

Schönleber

Ivers-Tiffée

2015

Electrochemistry Communications

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116

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“…Artefacts of 3-electrode impedance measurements in Li-ion cells are similar to those observed in solid-oxide fuel cells. These were both observed experimentally and computed theoretically, using a finite-element method to model typical geometric misalignments and frequency mismatches between Libattery electrodes in symmetric, half-and full cells [8,[18][19][20][21][22].…”

Section: Introductionmentioning

confidence: 98%

Impedance Spectra of Energy-Storage Electrodes Obtained with Commercial Three-Electrode Cells: Some Sources of Measurement Artefacts

Levi

Dargel

Shilina

et al. 2014

Electrochimica Acta

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Understanding the impedance spectrum of 18650 LiFePO4-cells

Cited by 141 publications

References 28 publications

Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells

Surface Cooling Causes Accelerated Degradation Compared to Tab Cooling for Lithium-Ion Pouch Cells

Approximability of impedance spectra by RC elements and implications for impedance analysis

Impedance Spectra of Energy-Storage Electrodes Obtained with Commercial Three-Electrode Cells: Some Sources of Measurement Artefacts

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