Lithium-ion battery performance and degradation in stationary energy storage
Time: Fri 2024-11-22 10.00
Location: K1, Teknikringen 56, Stockholm
Video link: https://kth-se.zoom.us/webinar/register/WN_-cR6rkTsSxSNmP2GKyugCg
Language: English
Subject area: Chemical Engineering
Doctoral student: Mathilda Ohrelius , Tillämpad elektrokemi
Opponent: Associate Professor Daniel Stroe, Aalborg Universitet, Danmark
Supervisor: Professor Göran Lindbergh, Tillämpad elektrokemi; Professor Rakel Wreland Lindström, Tillämpad elektrokemi
QC 20241023
Abstract
Electrification is our most promising strategy to create a sustainable energy system and decrease our dependence on fossil fuels. A balanced power grid system is the backbone of the electrified society, distributing electricity from renewable energy sources and powering our vehicles, industries, and electronics. Lithium-ion batteries are a key technology for both stationary and mobile energy storage and their optimal utilization should be carefully considered. Various degradation mechanisms contribute to performance fade in lithium-ion batteries. A key area of battery research is therefore to detect and characterize these mechanisms and predict their effects on battery performance. In this thesis, the performance of batteries is investigated in battery energy storage system (BESS) applications. The research questions cover different types of grid balancing services, methods to evaluate battery state of health (SOH) as well as the mechanisms causing the capacity and power fade. A combination of physics-based modelling and electrochemical techniques are applied, and the results combined to better understand the degradation and its consequences.
Frequency regulation, peak shaving, as well as a multi-service application are studied to evaluate battery performance and degradation stress factors and recommendations on operating conditions are developed. Cells with less than 65% of their nominal capacity are successfully utilized in a second application but evaluating SOH by the traditional methods is found to be insufficient. By updating electrochemical parameters in a physics-based model against data from the aged cells, sources of the performance loss are identified. This approach is further advanced as electrochemical impedance spectroscopy isused for parameter estimation. Cell degradation coupled to electrolyte consumption is highlighted. An improved SOH evaluation metric is suggested to explain the phenomenon of degradation resulting in uneven current distribution. This improved understanding of the internal cell degradation and in situ methods for quantitative evaluation will contribute to smarter utilization and longer battery lifetime.