Prismatic Cell Solid State Volume Change during Lithiation
Solid-state prismatic expansion demands dynamic stack compression and strict header weld strain limits to prevent interfacial delamination and capacity fade.
Structural Tie Rod
Meaning
High strength tension members used to secure battery modules within a chassis provide the necessary clamping force to withstand vibration and external impact forces during use. These mechanical components are essential for maintaining the alignment and compression of the individual cells that make up the energy storage system. A structural tie rod is typically made of high tensile steel or aluminum and runs the length of the module to join the end plates together.
By providing a rigid frame, these rods ensure that the cells remain in a stable position even when the vehicle is subjected to high acceleration or mechanical shock. The design and placement of these rods are critical for both the mechanical durability and the safety of the battery pack.
Tensile Strength
Resistance to stretching and breaking under load is the primary requirement for the materials used in the construction of these support members. The structural tie rod must be able to maintain its length and the applied tension even as the internal pressure from the expanding cells increases. If the rods were to stretch or fail, the clamping force on the cells would be lost, leading to increased internal resistance and potential electrical failures.
Engineers select the diameter and material of the rods based on the maximum expected loads during the most extreme operating conditions.
Vibration Resistance
Repeated mechanical stress from the road surface or the operation of the vehicle can lead to the loosening or fatigue of the fasteners.
Material Selection
Compatibility with the surrounding environment and the other components in the battery pack is a factor in the choice of the rod material. The structural tie rod must resist corrosion from moisture and potential electrolyte leaks to ensure it does not weaken over time. Protective coatings or the use of stainless steel can improve the longevity of these components in harsh operating environments.
Additionally, the thermal expansion coefficient of the rod must be similar to that of the module housing to prevent large changes in the clamping force as the temperature fluctuates. The assembly process involves precise torque control to ensure that each rod is tightened to the correct specification. This careful attention to detail is a requirement for the production of robust and reliable battery systems for the automotive industry.