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| 2. |
- Bessman, Alexander, et al.
(författare)
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Aging effects of AC harmonics on lithium-ion cells
- 2019
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Ingår i: Journal of Energy Storage. - : Elsevier. - 2352-152X .- 2352-1538. ; 21, s. 741-749
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Tidskriftsartikel (refereegranskat)abstract
- With the vehicle industry poised to take the step into the era of electric vehicles, concerns have been raised that AC harmonics arising from switching of power electronics and harmonics in electric machinery may damage the battery. In light of this, we have studied the effect of several different frequencies on the aging of 28 Ah commercial NMC/graphite prismatic lithium-ion battery cells. The tested frequencies are 1 Hz, 100 Hz, and 1 kHz, all with a peak amplitude of 21 A. Both the effect on cycled cells and calendar aged cells is tested. The cycled cells are cycled at a rate of 1C:1C, i.e., 28 A during both charging and discharging, with the exception of a period of constant voltage at the end of every charge. After running for one year, the cycled cells have completed approximately 2000 cycles. The cells are characterized periodically to follow how their capacities and power capabilities evolve. After completion of the test about 80% of the initial capacity remained and no increase in resistance was observed. No negative effect on either capacity fade or power fade is observed in this study, and no difference in aging mechanism is detected when using non-invasive electrochemical methods of post mortem investigation.
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| 3. |
- Bessman, Alexander, 1989-, et al.
(författare)
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Challenging Sinusoidal Ripple-Current Charging of Lithium-Ion Batteries
- 2018
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Ingår i: IEEE Transactions on Industrial Electronics. - : IEEE Press. - 0278-0046 .- 1557-9948. ; 65:6, s. 4750-4757
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Tidskriftsartikel (refereegranskat)abstract
- Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.
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| 4. |
- Bessman, Alexander
(författare)
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Interactions between battery and power electronics in an electric vehicle drivetrain
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The electric machine and power electronics in electric and hybrid electric vehicles inevitably cause AC harmonics on the vehicle's DC-link. These harmonics can be partially filtered out by large capacitors, which today are overdimensioned in order to protect the vehicle's battery pack. This is done as a precaution, since it is not known whether ripple-current has any harmful effect on Li-ion cells.We have measured and analyzed the ripple-current present in a hybrid electric bus, and found that a majority of the power was carried by frequencies in the range 100~Hz to 1~kHz. The single most energetic harmonic in this particular vehicle is believed to have been caused by a misaligned resolver in the motor.We have also designed and built an advanced experimental set-up in order to study the effect of ripple-current on Li-ion cells in the lab. The set-up can cycle up to 16 cells simultaneously, with currents of up to 50~A including a superimposed AC signal with a frequency of up to 2~kHz. The cells' temperatures are controlled by means of a climate chamber. The set-up also includes a sophisticated safety system which automatically acts to prevent dangerous situations before they arise.Using this set-up we tested whether superimposing AC with a specific frequency improves the charging performance of Li-ion cells. Statistical analysis found no improvement over regular DC cycling, and a physics-based model explains the experimental findings.We have also investigated whether ripple-current accelerates the aging of Li-ion cells. Twelve cells were either calendar or cycle aged for one year, with some cells being exposed to superimposed AC with a frequency of 1~Hz, 100~Hz, or 1~kHz. No effect was observed on any of capacity fade, power fade, or aging mechanism.Finally we also tested whether it is possible to heat Li-ion cells from low temperatures using only AC. We propose a method for AC heating of Li-ion cells, and open the discussion for generalizing the technique to larger battery packs.In conclusion, ripple-current has negligible effect on Li-ion cells, except for heating them slightly.
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| 5. |
- Mussa, Abdilbari, et al.
(författare)
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Fast-charging effects on ageing for energy-optimized automotive LiNi1/3Mn1/3Co1/3O2/graphite prismatic lithium-ion cells
- 2019
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Ingår i: Journal of Power Sources. - : ELSEVIER SCIENCE BV. - 0378-7753 .- 1873-2755. ; 422, s. 175-184
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Tidskriftsartikel (refereegranskat)abstract
- The reactions in energy-optimized 25 Ah prismatic NMC/graphite lithium-ion cell, as a function of fast charging (1C-4C), are more complex than earlier described. There are no clear charging rate dependent trends but rather different mechanisms dominating at the different charging rates. Ageing processes are faster at 3 and 4C charging. Cycling with 3C-charging results in accelerated lithium plating but the 4C-charging results in extensive gas evolution that contribute significantly to the large cell impedance rise. Graphite exfoliation and accelerated lithium inventory loss point to the graphite electrode as the source of the gas evolution. The results are based on careful post-mortem analyses of electrodes using: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). SEM results show particle cracking independent of the charging rate used for the cycling. XPS and EIS generally indicate thicker surface film and larger impedance, respectively, towards the edge of the jellyrolls. For the intended application of a battery electric inner-city bus using this type of cell, charging rates of 3C and above are not feasible, considering battery lifetime. However, charging rates of 2C and below are too slow from the point of view of practical charging time.
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| 6. |
- Smith, Alexander J., et al.
(författare)
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Expanded In Situ Aging Indicators for Lithium-Ion Batteries with a Blended NMC-LMO Electrode Cycled at Sub-Ambient Temperature
- 2021
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 168:11, s. 110530-
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Tidskriftsartikel (refereegranskat)abstract
- An important step toward safer and more reliable lithium-ion battery systems is the improvement of methods for detection and characterization of battery degradation. In this work, we develop and track aging indicators over the life of 18650-format lithium-ion batteries with a blended NMC532-LMO positive electrode and graphite negative electrode. Cells are cycled until reaching 80% of their original capacity under combinations of four cycling conditions: ambient and sub-ambient temperatures (29 degrees C and 10 degrees C) and fast and mild rates (2.7 and 1.0C). Loss of lithium inventory dominates aging for all cases, with additional loss of NMC capacity under the combination of sub-ambient temperature and mild rate. A novel, easily acquired polarization factor complements capacity fade analysis; it correlates well with impedance and galvanostatic cycle life and indicates changes in active aging processes. These processes are further revealed by differential voltage analysis (DVA) and incremental capacity analysis (ICA). New indicators and aging scenarios are evaluated for these techniques and supported by post mortem analysis. From in operando cycling data and a single, slow discharge curve, these four methods (capacity fade, polarization factor, DVA, and ICA) comprise a simple, explanatory, and non-invasive toolbox for evaluating aging in lithium-ion battery systems.
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| 7. |
- Smith, Alexander J., et al.
(författare)
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Localized lithium plating under mild cycling conditions in high-energy lithium-ion batteries
- 2023
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Ingår i: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 573
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Tidskriftsartikel (refereegranskat)abstract
- Conditions such as the temperature and pressure experienced by lithium-ion battery components are dependent on cell geometry and can vary widely within a large cell. The resulting uneven degradation is challenging to study at the full cell level but can be revealed upon disassembly and post mortem analysis. In this work, we report localized lithium plating in automotive-grade, prismatic lithium-ion cells, also under cycling conditions generally considered to be mild (e.g., 5–65 %SOC, 23 °C, 0.5C cycle rate). Dead lithium content is quantified using 7Li nuclear magnetic resonance spectroscopy in both electrode and separator samples, corresponding to substantial capacity fade (26–46%) of the full cells. Severe lithium plating is typically initiated in regions near the positive tab, in which both the separators and negative electrodes are ultimately deactivated. High pressure arises during cycling, and we propose a deactivation mechanism based on high local stress due to electrode expansion and external constraint. Further, we develop a model to demonstrate that component deactivation can result in lithium plating even under mild cycling conditions. Notably, components harvested from regions with no detected lithium plating maintained adequate electrochemical performance.
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| 8. |
- Smith, Alexander J.
(författare)
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Tools for characterizing performance degradation in lithium-ion batteries
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium-ion batteries have enabled vast societal changes, ranging in scale from the adoption of personal electronics to electromobility and grid-scale, renewable energy storage. However, all applications face performance fade over time, observed as losses of battery capacity and power. This gradual degradation is most often due to electrochemical aging processes inside the cell, including phenomena causing a loss of cyclable lithium (e.g., lithium plating, growth of the solid‑electrolyte interphase or SEI), a loss of active material (e.g., particle cracking), and/or a loss of ionic or electronic conductivity. In the compiled works, many individual batteries have been aged and analyzed to better understand the conditions contributing to aging in different cell designs. The cells studied include lab-built pouch cells, commercial cylindrical cells (with electrodes LiNixMnyCo1‑x‑yO2‑LiMn2O4/C6 and LiNixCoyAl1‑x‑yO2/C6‑SiOx), and larger automotive-grade prismatic cells (LiNixMnyCo1‑x‑yO2/C6).Complementary in situ and post mortem methods are developed, with relevance for both battery research and battery control systems. Excellent characterization can often be achieved by a combination of differential voltage and incremental capacity analyses. Obtained from a simple, slow cycle, the derivatives of the voltage profile reveal many features that can be tracked over aging. This thesis particularly develops these techniques for blended electrodes, deconvoluting the aging of individual components. Dynamic performance is resolved with a novel polarization factor, impedance spectroscopy, and tools based on current pulses/interruptions. Finally, a protocol based on nuclear magnetic resonance spectroscopy is developed, enabling fast and direct quantification of lithium plating and SEI on harvested battery components. With such tools, we can improve how batteries are used and monitored, paving the way for efficient research and safer, more reliable batteries.
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