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Durability Aspects of Fast Charging, Mechanical Constraint, and Inhomogeneity in Lithium-Ion Batteries
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering. KTH The Royal Institute of Technology. (Applied Electrochemistry)ORCID iD: 0000-0003-3436-6134
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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. 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. , p. 56
Series
TRITA-CBH-FOU ; 2018:13
Keywords [en]
Lithium-ion batteries; NMC(111); Graphite; Cycle ageing, Fast-charging; Inhomogeneity; Current distribution; Pressure; Curvature; Temperature.
National Category
Chemical Engineering
Research subject
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-226512ISBN: 978-91-7729-753-6 (print)OAI: oai:DiVA.org:kth-226512DiVA, id: diva2:1198746
Public defence
2018-05-09, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180419

Available from: 2018-04-19 Created: 2018-04-18 Last updated: 2018-04-19Bibliographically approved
List of papers
1. Fast charging effects on ageing for energy-optimized automotive NMC/graphite prismatic lithium-ion cells.
Open this publication in new window or tab >>Fast charging effects on ageing for energy-optimized automotive NMC/graphite prismatic lithium-ion cells.
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-226538 (URN)
Note

QC 20180420

Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2018-04-24Bibliographically approved
2. Fast-charging to a partial state of charge in lithium-ion batteries: A comparative ageing study
Open this publication in new window or tab >>Fast-charging to a partial state of charge in lithium-ion batteries: A comparative ageing study
Show others...
2017 (English)In: Journal of Energy Storage, ISSN 2352-152X, Vol. 13, p. 325-333Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Fast-charging, Charging to partial SOC, Non-destructive analysis, Lithium-ion battery ageing, Battery management, Charging protocol
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-220495 (URN)10.1016/j.est.2017.07.004 (DOI)000417183300033 ()2-s2.0-85028014032 (Scopus ID)
Funder
Swedish Energy AgencyStandUp
Note

QC 20171222

Available from: 2017-12-22 Created: 2017-12-22 Last updated: 2018-04-24Bibliographically approved
3. Effects of external pressure on the performance and ageing of single-layer lithium-ion pouch cells
Open this publication in new window or tab >>Effects of external pressure on the performance and ageing of single-layer lithium-ion pouch cells
2018 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 385, p. 18-26Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Current distribution, Lithium-ion battery, Mechanics, Non-uniform ageing, Pressure
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-224547 (URN)10.1016/j.jpowsour.2018.03.020 (DOI)000430779400003 ()2-s2.0-85043458948 (Scopus ID)
Funder
Swedish Energy Agency, 30770-3StandUp
Note

QC 20180321

Available from: 2018-03-21 Created: 2018-03-21 Last updated: 2018-07-23Bibliographically approved
4. Inhomogeneous active layer contact loss in a cycled prismatic lithium-ion cell caused by the jelly-roll curvature.
Open this publication in new window or tab >>Inhomogeneous active layer contact loss in a cycled prismatic lithium-ion cell caused by the jelly-roll curvature.
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-226541 (URN)
Note

QC 20180420

Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2018-04-24Bibliographically approved
5. Lithium-ion battery performance and ageing under uneven temperature distribution.
Open this publication in new window or tab >>Lithium-ion battery performance and ageing under uneven temperature distribution.
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-226540 (URN)
Note

QC 20180420

Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2018-04-24Bibliographically approved

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