Date of Award
Mechanical, Automotive, and Materials Engineering
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By developing and enhancing flexible temperature sensors based on negative temperature coefficient (NTC) thermistor and resistance temperature detector (RTD), this work aimed to increase the precision and dependability of temperature measurements in electric vehicle (EV) battery packs. While the RTD and NTC sensors use platinum, copper, silicon and nickel as sensing materials, in this research, a sensor utilizing carbon nanotube (CNT) materials was demonstrated to create a flexible CNT sensor on a polydimethylsiloxane (PDMS) substrate. It also functions as a negative temperature coefficient (NTC) thermistor, where the resistance decreases as the temperature increases. This design synergizes the high sensitivity of CNTs with the flexibility of PDMS, making it suitable for applications requiring both high sensitivity and conformability, such as wearable devices, flexible electronics, or smart textiles. By adjusting the density and distribution of CNTs, the performance of the sensor can be further optimized to meet the needs of specific applications. The material characteristics of the thermally sensitive materials, such as their electrical and thermal conductivity, relative permittivity, and temperature coefficient of resistance (TCR), were assessed in the initial phase of the investigation. Finite element simulation was used to design and optimize the sensors such that temperature readings could be made with high linearity and precision. A battery cell setup with a temperature range of 24°C to 36°C was used to evaluate the NTC and RTD sensors. The carbon nanotube (CNT)-based sensor exhibited negative temperature coefficient (NTC) behavior, with a linear decrease in resistance change as the temperature increased from 24°C to 36°C. It exhibited a high temperature coefficient of resistance (TCR) of -1.36/°C and a fast response time of 36 seconds, making it a promising material for real-time applications. The flexibility of the sensor was tested by increasing the bending angle from 0° to 180°, and the sensor displayed high sensitivity for 25 and 35 layers of the CNT coating, indicating its suitability for applications requiring dynamic flexibility and consistent performance under mechanical deformation. The uniformity, roughness, and surface morphology of the coated CNTs were measured. The length and diameter of the CNTs were measured to range from 23.0 nm to 41.9 nm. The flexible CNT-based temperature sensor applied in battery monitoring was assessed through controlled heating and cooling cycles, and the results showed typical NTC behavior, with resistance decreasing during heating and increasing during cooling. The research also examined the consistency and long-term stability of the sensors, demonstrating their reliability for practical applications in battery management systems. The flexible CNT sensors presented in this paper can potentially be applied for temperature sensing in conformal and flexible fitting applications, for example, temperature detection in electric vehicle (EV) battery cells and many other similar applications.
Li, Zifan, "Development of Flexible Temperature Sensors for EV (Electric Vehicle) Batteries" (2024). Electronic Theses and Dissertations. 9176.
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