A battery module is mainly composed of multiple battery cells. Through proper module design, the temperature of the cells within the entire module can be obtained using a limited number of sampling points. Under normal operation, the temperature of the cells is uniform, but when the battery malfunctions, the temperature of the cells will vary significantly.
With the increasing energy density and decreasing safety margin of lithium batteries, the core issue is knowing the temperature of the individual lithium battery cells. In fact, we now understand that most battery abuse tests are temperature-dependent, and the conditions performed at different temperatures differ. We need to obtain the internal temperature of the battery using temperature sensors.
1. Conditions for obtaining cooling activation
2. Conditions for obtaining power limits (especially for fast charging)
3. Obtain the stop output (zero current output)
4. Detection of precursors to extreme thermal events
A battery module is mainly composed of multiple battery cells. Through proper module design, the temperature of the cells within the entire module can be obtained using a limited number of sampling points. Under normal operation, the temperature of the cells is uniform, but when the battery malfunctions, the temperature of the cells will vary significantly.
●The placement of the temperature sensors here includes:
● Battery surface
● Battery Busbar
● Battery cover surface
The layout within the module needs to consider the temperature acquisition of the battery cells and the busbars. The temperature of the entire module is monitored through several acquisition points, and the temperature data collected by the battery management unit is used to calculate the overall module temperature. This mainly involves comparing the actual battery temperature with the sensor feedback under different operating conditions.
As shown in the figure below, without looking at anything else, just looking at the temperature error caused by different circuits, it is varied. In addition, there are other factors such as surface heat transfer. It is worthwhile for us to collect different data and compare them carefully.
A comprehensive consideration of the temperature sensor's cost, accuracy, temperature range, rapid thermal response, and self-heating error is necessary. When considering high-end vehicles, especially those with high performance and high-rate charging, the heat generated by acceleration response necessitates a temperature sensor with low thermal hysteresis; otherwise, step-like temperature changes cannot be detected. (See the diagram below.)
Another significant issue is the operating temperature range of the temperature sensor, which we discussed earlier. Furthermore, when the temperature exceeds a certain range, typically 85°C, the voltage drop values acquired by the existing circuitry become too large, rendering the temperature readings invalid. Therefore, to obtain temperature data from the existing temperature sensor at the edge of thermal runaway, several conditions need to be met:
● An adjustable voltage divider resistor is required.
● The selected temperature sensor needs to be compatible with a high operating temperature range.
● A different testing mechanism is needed in the software.
●A temperature-linked strategy is required.
Before the actual problem occurs, temperature changes around the battery cell will cause temperature differences in the surrounding area. This is a very direct measure, and the collection and judgment of this data is something we should consider in depth.
In summary, to achieve a high level of confidence, two approaches are needed: collecting more data and considering robust temperature data collection methods to ensure a baseline performance. I believe that temperature detection methods covering higher temperature ranges could be adopted by battery management systems in this regard.
