| 1. |
- Finegan, Donal P., et al.
(author)
-
Spatial dynamics of lithiation and lithium plating during high-rate operation of graphite electrodes
- 2020
-
In: Energy and Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 13:8, s. 2570-2584
-
Journal article (peer-reviewed)abstract
- The principal inhibitor of fast charging lithium ion cells is the graphite negative electrode, where favorable conditions for lithium plating occur at high charge rates, causing accelerated degradation and safety concerns. The local response of graphite, both at the electrode and particle level, when exposed to fast charging conditions of around 6C is not well understood. Consequently, the conditions that lead to the onset of lithium plating, as well as the local dynamics of lithium plating and stripping, have also remained elusive. Here, we use high-speed (100 Hz) pencil-beam X-ray diffraction to repeatedly raster along the depth of a 101 µm thick graphite electrode in 3 µm steps during fast (up to 6C) charge and discharge conditions. Consecutive depth profiles from separator to current collector were each captured in 0.5 seconds, giving an unprecedented spatial and temporal description of the state of the electrode and graphite's staging dynamics during high rate conditions. The electrode is preferentially activated near the separator, and the non-uniformity increases with rate and is influenced by free-energy barriers between graphite's lithiation stages. The onset of lithium plating and stripping was quantified, occurring only within the first 15 µm from the separator. The presence of lithium plating changed the behavior of the underlying graphite, such as causing co-existence of LiC6 and graphite in the fully discharged state. Finally, the staging behavior of graphite at different rates was quantified, revealing a high dependency on rate and drastic hysteresis between lithiation and delithiation.
|
|
| 2. |
- Streb, Moritz
(author)
-
Identifying Parameters for Aging-Adaptive Battery Management
- 2024
-
Doctoral thesis (other academic/artistic)abstract
- The modern transportation system is largely based on fossil fuels. To reduce this reliance on oil and gas and thereby drastically reduce emissions, a transition to renewable power sources is necessary. Lithium-ion batteries are the most established candidate for electromobility applications, with suitable energy and power densities. However, their limited lifetime is often further reduced by inadequate battery utilization. Battery usage is overseen by the battery management system relying on different models to determine for instance the charging procedure or estimate the state of charge. Degradation affects internal rate-determining processes and precise battery management is only possible if the used model resolves the battery-internal states and accounts for their changes. In this thesis, I therefore investigate if suitable adjustments to usage can prolong battery lifetime. To achieve such aging-adaptive battery management, the online diagnosis of degradation is paramount. A novel method for the identification of electrochemical parameters relying on optimal experiment design is presented. The operando identification of electrochemical parameters is demonstrated using an established physics-based model and improved accuracy of the model and the estimated parameter set is shown. The method is then utilized to estimate parameter changes in a cycling study on commercial cells, highlighting how beginning-of-life estimates quickly become obsolete. Identified parameter estimates correlate with post-mortem analysis and therefore offer meaningful insight into battery degradation. The information content in real-world driving patterns is investigated for three distinct heavy-duty vehicle types. We show that it is possible to gain meaningful insight into battery degradation from such driving data alone but the information content heavily depends on usage type. Finally, the benefit of the proposed aging-adaptive battery management is demonstrated for fast charging of automotive prototype cells.
|
|
