P1 - TRANSFER

TANSFERability of relevant properties between different LIB-cells and LIB-modules

• Development of methods to make numerical models of Li-ion cells more time efficient and accurate:
  • Motivation:
    • Currently, two types of numerical cell models are used in impact and crash simulations of Li-ion batteries: (1) homogenised, time-efficient models, but which do not allow accurate discrimination in terms of failure mode and localisation, and (2) detailed, computationally intensive models, which are unsuitable for whole-battery simulations due to the high number of elements and nodes and the small time steps.
    • In addition, the mechanical properties of the cell single layers are very complex: There are porous, fluid-impregnated or permeable structures (separator, active material) as well as anisotropic and highly strain-rate-dependent layers (separator). Their mechanical behaviour and morphology change with the ageing of the cell ("state-of-health"), the exerted transverse pressure and the charge state ("state-of-charge") and play an important role in cell failure.
  • Objective:
    • To develop computationally efficient, detailed and physically sensible numerical models of Li-ion cells that allow accurate failure mode prediction and localisation – even at an early stage of the vehicle development process.
  • Methods:
    • In order to increase the time efficiency of the models, model order reduction, artificial intelligence (e.g., Artificial Neural Networks) and multi-scale modelling approaches are used.
    • In order to increase the accuracy of the models of the individual components, they are characterised and modelled according to the current state of research: Influences of strain rate, loading direction, triaxiality, ageing and moisture content are collected. Digital image correlation and imaging methods (X-ray microtomography), among others, are used in the characterisation to obtain a maximum of information about the materials.

• Improvement of the boundary conditions for the investigation of the thermal runaway of cells and the subsequent thermal propagation to further cells:
  • Motivation:
    • Thermal runaway and thermal propagation behaviour of cells are usually studied in closed reactors flooded with inert gas. Larger cell units or modules are generally investigated under open air conditions. In a realistic case, however, the air supply may be limited (e.g., if the battery housing only partially leaks). Depending on the air supply, the thermal failure propagation may differ significantly.
  • Objective:
    • To increase the safety for vehicle occupants and environment in case of cell failure by containment.
  • Methods:
    • Larger cell units are investigated in a closed reactor with an inert and reactive gas environment. In addition to different triggering methods (thermal, mechanical, electrical) for thermal runaway, different containment methods (e.g., mica paper) are used.
    • In addition, the influence of a controlled supply of fresh air will be investigated in a test rig that is being developed in the course of SafeLIB P1.