Pulse resistance based online temperature estimation for lithium-ion cells

Knowing the temperature distribution within a battery pack is vital, because of the impact on capacity loss, power degradation and safety. Temperature measurements are usually realized with temperature sensors attached to a limited number of cells throughout the battery pack, leaving the majority of cells in larger battery systems unattended. This work presents a novel sensorless method for determining the temperature of a cell by exploiting the relation of the cell's overpotential and temperature exemplary using a 18650 nickel-rich/silicon-graphite cell, although the method is basically applicable to any cell. Current changes in the battery load are utilized as pulse excitation for the calculation of a direct-current resistance R-DC,R-Delta t determined after a certain time Delta t. Reference pulses at 10/20/30/40 degrees C are recorded to investigate the influence of state-of-charge and pulse rise/fall-time, as well as the pulse-current amplitude and direction on R-DC,R-Delta t. The analysis of the reference pulses shows that a Delta t in the 10 ms to 100 ms regime has the greatest sensitivity to temperature and the least dependence on other parameters. The method is finally validated using a 6s1p-module with an externally constant temperature gradient applied to the serial connection, showing an average estimation error smaller than 1K for each cell.

Automated summary

It is crucial to understand the temperature distribution within a battery pack for its impact on capacity loss, power degradation, and safety. This study introduces a novel sensorless method for determining the temperature of a cell by exploiting the relationship between the cell's overpotential and temperature. Through analysis of reference pulses, it is shown that a Δt in the 10 ms to 100 ms range has the greatest sensitivity to temperature and the least dependence on other parameters.