INfluence oF ageIng mechaNIsm on the mechanical and safeTY behavior of LIB cells
The charging and discharging of lithium-ion batteries (LIBs) is accompanied by undesirable electrochemical reactions between the electrolyte and the active materials within the cell. Depending on the boundary conditions under which the batteries are operated, different degradation effects occur that influence the mechanical behaviour and especially the safety of LIBs. The impact of these changes on battery safety is the focus of this project.
Objective:
To define a method for assessing the state of safety of LIBs in the event of a road accident, taking into account the product history, in order to provide the best possible protection for all persons involved in an accident but also for the environment.
Research questions:
How do the specific electrical and electrochemical ageing influences of LIB cells and LIB modules affect their mechanical and safety behaviour in a crash load case? Are aged LIB cells and LIB modules still safe for use in vehicles after a crash? The content of this research question is linked to the preceding project "SafeBattery".
The following studies will be carried out in order to answer these research questions in detail:
Influence of electrical ageing strategies
- Investigation of the mechanical behaviour of fresh, artificially aged LIBs and LIBs used in an electric vehicle
Influence of electrical and electrochemical ageing of current LIB cells and LIB modules on their mechanical and safety behaviour in a crash load case
- In-depth investigations of the mechanical behaviour of aged cells under different load cases compared to fresh batteries
- Identification of all degradation mechanisms that have occurred
- Identification of the influence of electrical ageing on mechanical behaviour and LIB failure
- Investigation of the influence of boundary conditions (e.g., pressure distribution, temperature) on ageing and swelling mechanisms in a battery cell stack in comparison to single cell tests
- Identification of parameters that can be measured in a non-destructive way and show a correlation with the degradation of mechanical properties (derivation of corresponding metrics)
- Identification of the mechanical properties (e.g., load thresholds for tension, compression or shear, stiffness, rate effects, energy dissipation) that are most sensitive to ageing effects
Influence of electrical and electrochemical ageing on "all-solid-state" LIB cells
- Investigations of interfacial ageing effects and failure mechanisms as a function of temperature and pressure are studied by electrochemical means and a variety of spectroscopic techniques. For this purpose, three models of solid-state cells are used, which differ with respect to the solid electrolyte (LiBH4-based, thiophosphates, garnet-type Li7La3Zr2O12).
- Improved understanding of the interfacial properties of the Li|electrolyte region and the Li|cathode interface
- Understanding of ceramic-polymer composites; in particular, Li+ ion transfer processes and ion dynamics will be investigated by broadband impedance spectroscopy and Li NMR.
Mapping of the mechanical behaviour of aged cells in explicit finite element models
- Developing an explicit FEM DLM (Finite Element Method – Double Lattice Method) of an aged LIB cell to investigate the detailed mechanisms within an electrically aged cell under crash loading
- Understanding the key ageing mechanisms affecting the mechanical properties of a LIB and creating appropriate modelling approaches
Safe prolonged use of LIB cells and LIB modules that have been subjected to impact loading
- Investigating whether aged LIB cells can still be operated safely after a vehicle crash. This includes studies on electrical ageing as well as possible further crash loads.
- Basic research on how singular events (e.g., small deformation of the battery in the course of a crash) influence its behaviour in further use. Are there effects that can lead to accelerated degradation?
