| 1. |
- Mussa, Abdilbari, et al.
(author)
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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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In: Journal of Power Sources. - : ELSEVIER SCIENCE BV. - 0378-7753 .- 1873-2755. ; 422, s. 175-184
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Journal article (peer-reviewed)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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| 2. |
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| 3. |
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| 4. |
- Mussa, Abdilbari, et al.
(author)
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Inhomogeneous active layer contact loss in a cycled prismatic lithium-ion cell caused by the jelly-roll curvature
- 2018
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In: Journal of Energy Storage. - : Elsevier Ltd. - 2352-152X .- 2352-1538. ; 20, s. 213-217
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Journal article (peer-reviewed)abstract
- Internal resistance is a key parameter that affects the power, energy, efficiency, lifetime, and safety of a lithium-ion battery. It grows due to chemical and mechanical battery wear during ageing. In this work, the effect of the jelly-roll winding curvature on impedance rise is investigated. NMC electrode samples, harvested from the curved as well as the flat regions of the jelly-roll from cycle-aged and calendar-aged prismatic cells (25 Ah, hard casing) are investigated by electrochemical impedance spectroscopy. After cycling, larger impedance rise is observed at the outer radius (concave) of the curved region compared to the inner radius (convex) or the flat region of the jelly-roll, and the difference increases with a decrease in the jelly-roll radius of curvature, from the cell skin towards the core. To identify the causes behind the observed difference in the impedance rise, investigations at different external compression (0 and 2.5 MPa) and temperature (5 and 25 °C) are performed. The results show that contact loss between the current collector and the active layer is the main source of the difference in impedance rise. Mechanical mechanisms that may cause the contact loss are discussed and design recommendations to mitigate the rise in impedance are given.
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| 5. |
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| 6. |
- Mussa, Abdilbari Shifa
(author)
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Durability Aspects of Fast Charging, Mechanical Constraint, and Inhomogeneity in Lithium-Ion Batteries
- 2018
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Doctoral thesis (other academic/artistic)abstract
- The development of lithium-ion batteries with higher energy and power density, better safety, and lower cost has significantly contributed to the increased market share of electric vehicles (EVs) in the last decade. However, the expectations of end-users of EVs still require a continuous quest for better performance. One important end-user expectation is the ability of the battery to be charged rapidly, but the durability of lithium-ion batteries could be affected by the fast charging. Hence, detailed investigations are required to understand the extent and mechanism of the degradation for an optimized battery usage and material development. In order to meet the high energy and power required in EVs, multiple large-format cells are connected in series and in parallel. Such a condition leads to an uneven distribution of temperature, pressure, and current in a cell or among cells that may cause locally inhomogeneous ageing and accelerate the global battery ageing. This thesis investigates the effects of charging rate, charging protocol, and external compression on battery durability. The impacts of inhomogeneities induced by cell design constraint, and uneven compression and temperature distributions are also addressed. The studies are based LiNi1/3Mn1/3Co1/3O2/graphite cells. Cell housing for a controlled pressure and temperature application was developed. Electrochemical and material characterization techniques were used in the investigation.The results show that fast charging at a rate equivalent to full charging in 20 minutes (3C rate) or less accelerates battery ageing. The ageing rate is less sensitive to charging rate in a longer charging time, i.e. at 2C and below, where it is determined more by factors such as the extent of full charging. In all cases, the capacity loss is limited by the cyclable lithium loss. External compression of a battery in an optimum range reduces ageing, but compression above or below the optimum range accelerates ageing. Lithium-ion batteries age non-uniformly. Cycling induces an increase in the impedance at the outer radius of curvature of a prismatic cell jellyroll, associated with a loss of contact between the current collector and the electrode coating. An unfavorable current distribution induced by uneven temperature distribution can accelerate battery ageing.
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| 7. |
- Mussa, Abdilbari Shifa, et al.
(author)
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Effects of external pressure on the performance and ageing of single-layer lithium-ion pouch cells
- 2018
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In: Journal of Power Sources. - : Elsevier. - 0378-7753 .- 1873-2755. ; 385, s. 18-26
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Journal article (peer-reviewed)abstract
- The effects of external compression on the performance and ageing of NMC(1/3)/Graphite single-layer Li-ion pouch cells are investigated using a spring-loaded fixture. The influence of pressure (0.66, 0.99, 1.32, and 1.98 MPa) on impedance is characterized in fresh cells that are subsequently cycled at the given pressure levels. The aged cells are analyzed for capacity fade and impedance rise at the cell and electrode level. The effect of pressure distribution that may occur in large-format cells or in a battery pack is simulated using parallel connected cells. The results show that the kinetic and mass transport resistance increases with pressure in a fresh cell. An optimum pressure around 1.3 MPa is shown to be beneficial to reduce cyclable-lithium loss during cycling. The minor active mass losses observed in the electrodes are independent of the ageing pressure, whereas ageing pressure affects the charge transfer resistance of both NMC and graphite electrodes and the ohmic resistance of the cell. Pressure distribution induces current distribution but the enhanced current throughput at lower pressures cell does not accelerate its ageing. Conclusions from this work can explain some of the discrepancies in non-uniform ageing reported in the literature and indicate coupling between electrochemistry and mechanics.
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| 8. |
- Mussa, Abdilbari Shifa, et al.
(author)
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Fast-charging to a partial state of charge in lithium-ion batteries : A comparative ageing study
- 2017
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In: Journal of Energy Storage. - : Elsevier. - 2352-152X. ; 13, s. 325-333
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Journal article (peer-reviewed)abstract
- At electric vehicle fast-charging stations, it is generally recommended to avoid charging beyond similar to 80% State-of-Charge (SOC) since topping-off to full capacity disproportionately increases the charging time. This necessitates studying its long-term impact compared to slower rate charging to full capacity typical of home or residential charging. Here we present the long-term ageing effects on commercial 18650 NMC-LMO/graphite cell cycled between 2.6-4.2 V at three different charging protocols: 1.5 C-rate fast-partial charging ( to 82.5% SOC), 0.5 C-rate slow standard charging without or with a constant-voltage step (to 93% or 100% SOC). Quantitative discharge-curve and postmortem analyses are used to evaluate ageing. The results show that ageing rate increases in the order: fast-partial charging < standard charging < standard charging with constant-voltage period, indicating that higher SOC-range near full capacity is more detrimental to battery life than fast-charging. The capacity fade is totally dominated by cyclable-lithium loss. The similar to 8% NMC-LMO active material loss has negligible impact on the cell capacity fade due to the electrodes excess material in the fresh cell and its moderate loss rate with ageing compared to the cyclable-lithium. Similar ageing modes in terms of capacity fade and impedance rise are found irrespective of the charging protocol.
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