Meaning
Optical sensing elements embedded within or attached to battery cells use reflected wavelengths of light to measure localized changes in temperature and mechanical strain. Researchers and manufacturers utilize a fiber bragg grating sensor to gather real-time, high-fidelity physical data from inside the cell housing during cycle life testing. By monitoring the shifts in the reflected Bragg wavelength, the sensor distinguishes between thermal expansion and electrochemical swelling.
This accurate measurement provides critical insights into the internal state of health of the cell.
Measurement Mechanism
Fibers with periodic variations in the refractive index of the core reflect specific wavelengths while transmitting all others. When a fiber bragg grating sensor experiences physical deformation or temperature changes, the grating period shifts, which alters the reflected wavelength. This optical measurement is immune to electromagnetic interference, making it highly reliable within the high-voltage environment of a battery pack.
Sourcing teams select these sensors for development platforms and prototype testing.
Strain Detection
Mechanical expansion during lithiation and delithiation puts stress on the battery housing and electrode layers. By embedding these sensors directly into the cell, engineers can track the mechanical strain and detect issues such as anode overhang issues or structural deformation. This early strain detection helps developers optimize the mechanical clamping force of the pack.
Furthermore, the high sensitivity of the optical fiber allows it to register minute changes in the electrode volume that traditional pressure sensors would miss, providing an invaluable tool for structural analysis. These sensors can also identify internal gas generation before it causes visible pouch swelling, which acts as an early warning for potential pouch failures.
Thermal Monitoring
Monitoring the internal core temperature of a cell is critical for preventing thermal runaway during fast charging. Traditional thermocouples only measure surface temperatures, which lag behind the internal heat generation. Implementing a fiber bragg grating sensor allows for instantaneous tracking of the internal temperature, which enables the battery management system to adjust charging currents dynamically.
This fast response time protects the cell from thermal damage during extreme operating conditions.
