Cell Temperature Sensing

Cell temperature sensing is a critical function of any Battery Management System (BMS) this is because the cell temperature needs to be kept within a band to maintain safe operation. This band is narrower still to maintain the lifetime of the cell and hence reduce ageing.

Cell Temperature

For each cell the manufacturer will define temperature limits for normal and safe operation.

Some of these temperatures are hard limits for the continued safe operation of the cell.

For most cells they will operate best between 15°C and 35°C.

Jinasena et al [1] break the sensing down into Hard and Soft Sensors. Using this as an initial list we can extend this further into a more complete list of sensors:

• Hard Sensors
  • Contact
    • Thermocouples
    • Thermistors
    • Resistance Temperature Detectors
    • Optical Fibre Sensors
  • Contactless
    • Electrochemical Impedance Spectroscopy
    • Johnson Noise Thermometry
    • Infrared Laser Thermometer
• Soft Sensors
  • Mathematical Model Based Estimators
    • Bulk Internal Temperature Estimators
    • Distributed Internal Temperature Estimators
  • Hybrid Model Based Estimators

Written based on the support and sponsorship of: AVANT Future Mobility, Quarto Technical Services, TAE Power Solutions, h.e.l group and The Limiting Factor. 

Hard Sensors

This is an actual physical sensor that is in contact with the cell or contactless. In the case of hard sensors there is also the number and location to be considered.

The location and number of temperature sensors is important to consider. Often it is not practical to fit a temperature sensor on every cell, also, extra sensors might not give you more detailed information.

Smart Battery Development

Research is ongoing to put sensors inside the battery cell, thus giving the ability to measure key internal variables such as electrode potentials, current, temperature, mechanical stress and internal pressure.

You do need to consider redundancy as a single thermistor is very cheap as a part, but could be very expensive to replace. Hence often two sensors are used for a group of cells with the BMS able to use those two signals to check operation and one failure can be managed.

Soft Sensors

Process or plant models designed to estimate many parameters, including the temperature of the cell.

Downside is that this is specific to the cell and is likely to be dependent on a number of parameters, including the SOC and SOH of the cell. Hence it is likely that a large test data set will be required.

The upside is that these soft sensors don’t have the failure modes associated with physical sensors that can become disconnected or just break.

Calibration

With any type of sensor we need to calibrate the system against the pack design. This will require the pack to be instrumented with lots of temperature sensors and for the pack and cooling system to be operated over the full envelope.

References

1. Asanthi Jinasena, Lena Spitthoff, Markus Solberg Wahl, Jacob Joseph Lamb, Paul R. Shearing, Anders Hammer Strømman and Odne Stokke Burheim, Online Internal Temperature Sensors in Lithium-Ion Batteries: State-of-the-Art and Future Trends, Front. Chem. Eng., 16 February 2022, Sec. Electrochemical Engineering, Volume 4 – 2022
2. Comparing Contact and Non-Contact Temperature Sensors, AZO Sensors
3. B. Gulsoy, T.A. Vincent, J.E.H. Sansom, J. Marco, In-situ temperature monitoring of a lithium-ion battery using an embedded thermocouple for smart battery applications, Journal of Energy Storage, Volume 54, 2022