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How do battery temperature sensors help in performance and capacity testing of EV pouch battery cells?

posted by Rugged Monitoring on 2021-06-16

Man setting up and testing the lithium ion battery


EV Pouch Battery CellsWhat are Pouch Battery Cells and what are its benefits?

Many manufacturers and engineers were trying to develop a flexible and lightweight solution to battery design. When pouch cells emerged, it solved many of the issues that engineers and customers had old batteries. The pouch cells are fully sealed and most of these cells are lithium polymer.  Instead of the usual metallic cylinder design and glass-to-metal electric feedthrough, the conductive foil-tabs were wielded to the electrodes of the cell. There are many advantages of a pouch battery cell such as they perform bets in light loading conditions with moderate charging and it can deliver high current loads. Additionally, the metal enclosure decreases the weight and the cell has a 90 % efficiency in packaging. The small cells are mainly used in applications that require high load currents and large cells work bets with light loading and moderate charge times. Furthermore, when pressure builds up in a pouch cell, it merely swells up whereas other battery cells such as cylindrical cells could explode so it is much safer than most battery cells. Also, the pouch cells have an impressive cycle life as the drop in the storage capacity is only 10% after 12 years of usage. 


Why thermal management of lithium ion batteries in electric vehicles is important?

Li-ion batteries are being designed to have a higher capacity and performance while being smaller in size which leads to thermal stress. Also, the development of fast charging cells and its implementation into EVs means that there is additional thermal stress. So, the need for state-of-the-art thermal management system is necessary at every step of EV battery development as the engineers must identify the limitations and hotspots of the battery cell to improve the performance and reliability of their batteries. The batteries are also exposed to harsh environmental and operating conditions such as extreme ambient temperatures which could result in reduction of battery life. Another reason to have thermal profiling equipment is to identify how efficient the high cooling system is because cooling becomes a critical factor of a battery’s longevity, especially at extreme temperatures. Using a battery management system that accurately profiles the data and provides precise Age Estimation analytics for the pouch cell along with delivering accurate results of the cell’s core temperature.  It also helps engineers recognize which material is best to use for anode, cathode, and separator for fast-charging batteries and identify the root cause of heating in fast charging cells. Furthermore, battery engineers need a highly stable and durable measurement system for EV conditions such as high voltage and chemical environments. This system should be resistant to thermal shock, vibration shock, mechanical load, etc. 


Why fiber optics sensors are best choice for battery thermal monitoring in EVs?

Design engineers need systems that provide smart analysis for performance maximization in the pouch battery cell. This smart analysis can be best performed by using fiber optics sensors because they have accurate and noise-free readings that don’t create any kind of strain or pressure in the pouch cell. Also, they have a very very small footprint (0.4mm) so they can fit into the core of the cell and it is adjustable at different locations. These sensors are electrically, magnetically, and chemically stable. This is possible because of the polyimide coating which makes the sensors suitable for chemical environments. Furthermore, FO sensors are much safer to use than traditional temperature monitoring sensors such as thermocouples which are made from metal so they can cause short circuits at high voltages. But this problem doesn’t apply for FO sensors as it uses a GaAs crystal which is a non-metal so it is a lot safer to use than thermocouples and FO sensors also ensure the safety of the battery prototype so there is no risk of fire damage to the cell itself. Additionally, FO sensors produce accurate, reliable, and fast results without any measurement inaccuracies which is not the same for thermocouples as they are susceptible to electromagnetic frequencies. 

  Rugged Monitoring Thermal Profiling Sensors


Rugged Monitoring Thermal Profiling Sensors

Rugged Monitoring’s Fiber Optic battery temperature sensors are being used by battery design/test engineers at each stage for battery performance testing

  • Battery cell core and anode thermal profiling for fast charging
  • Intercell temperature monitoring in Battery Modules
  • Battery pack abuse testing and HV connectors temperature testing

The CANBUS is implemented to communication with Battery Management System or dataloggers. Also, RM sensors and monitors are easy to use as they don’t require calibration or complex inputs along with being rugged and suitable for all test conditions. Also, RM sensors have a higher immunity to electromagnetic interferences which increases the testing accuracy and reliability while being having a very fast response time of 0.1ms to 1ms that helps identify a sudden shift in the temperature within the cells. The state-of-the-art sensors of RM such as  LSENS-B, LSENS-T, LSENS-R are most reliable option that provides accurate, fast results while being easy to setup and use. The EV test rigs come with built in Fiber Optic temperature monitors , R501, O201 etc.