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.
LVDT Dilatometry
Meaning
Measurement techniques utilizing linear variable differential transformers to track thickness changes in battery cells provide real time data on material expansion and contraction. This high precision method allows researchers to observe the volumetric changes that occur as lithium ions move in and out of the electrode structures. An lvdt dilatometry setup consists of a sensitive probe that rests on the surface of the cell and converts physical displacement into an electrical signal.
This data is essential for understanding the mechanical stresses that lead to degradation and for designing housings that can accommodate the expansion. The resolution of these sensors allows for the detection of sub micron changes in the thickness of the battery stack.
Displacement Resolution
Substantial accuracy in measuring the physical growth of a cell is achieved through the use of electromagnetic induction within the transformer. The lvdt dilatometry system provides a continuous stream of data throughout the charge and discharge cycle, mapping the expansion to the specific state of charge. This information helps identify the phase transitions in the active materials, such as the staging of lithium in graphite or the volume change in silicon.
Because the sensor does not make electrical contact with the battery, it can be used in a wide range of environmental conditions without interference.
Test Configuration
Specialized fixtures are used to hold the battery cell and the sensor in a stable alignment while allowing for thermal expansion.
Analysis Utility
Correlation of the mechanical data with the electrochemical performance provides a deeper understanding of the failure modes of the battery. If a cell shows an abnormal rate of expansion during cycling, lvdt dilatometry can reveal the onset of internal pressure build up before it is visible to the naked eye. This early detection is useful for safety testing and for validating new material combinations.
The results are also used to calibrate mechanical models of the battery pack, ensuring that the structural design is sufficient for the intended application. Data from these measurements informs the selection of clamping forces and the design of the thermal management system. The use of this high resolution measurement tool is a requirement for the advanced characterization of modern electrochemical storage devices.