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<p>Electric vehicles (EVs) preferably use lithium-ion (Li-ion) cells owing to their high energy density and low self-discharge rates. High power demand by the load causes Li-ion cells to discharge at higher C-rates, resulting in significant heat production and excessive cell temperatures. Therefore, battery thermal management (BTM) is necessary to effectively dissipate the excess heat generated by the cell at higher C-rates and contain the cell temperatures within the safe operating temperature range of 15°–45&#xa0;°C. A passive thermal management method such as the use of PCM can absorb large amount of heat during its phase transition, resulting in heat dissipation from the cell surface. In this work, a Samsung INR18650-25R cylindrical cell with a nominal voltage of 3.6&#xa0;V and a capacity of 2.5&#xa0;Ah was chosen for the investigation. A multi-scale multi-dimension (MSMD) battery model with ECM (equivalent circuit model) e-Chemistry is considered for numerical analysis at the ambient temperature of 35&#xa0;°C. A constant discharge rate of 8C is considered to analyse the thermal behaviour of the cell with a PCM. Further, the standard driving schedules such as US06 and LA92 are imposed to study the effectiveness of the passive thermal management method on the cell under variable current discharge. It is observed that the cell temperature decreases significantly with the thickness of PCM higher than 25% of cell radius and remains almost invariant thereafter at ~ 50&#xa0;°C. The liquid fraction of the PCM is found to be nearly 1 for ‘<i>δ</i>’ up to 25% of cell radius. The liquid fraction decreases considerably at the end of discharge with an increase in ‘<i>δ</i>’, resulting in an increased cell temperature, which is undesirable. Therefore, it is observed that 25% of cell radius is an optimal thickness to maintain the cylindrical cell temperature within a safe operating range. The LIB cell's peak temperature is decreased by 44&#xa0;°C (42%) for the LA92 driving schedule and 26&#xa0;°C (38%) for the US06 driving schedule at the end of the complete battery discharge. Therefore, higher top speed and aggressive driving schedules like LA92 require additional external liquid cooling, as PCM alone cannot contain the battery surface temperatures under safe battery operating limits.</p>

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Thermal impact of PCM thickness on a cylindrical Li-ion cell

  • 期刊论文

  • 发表日期：

    2025年9月13日

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  • Pritam Bhat,
  • Mahesh K. Varpe

摘要

Electric vehicles (EVs) preferably use lithium-ion (Li-ion) cells owing to their high energy density and low self-discharge rates. High power demand by the load causes Li-ion cells to discharge at higher C-rates, resulting in significant heat production and excessive cell temperatures. Therefore, battery thermal management (BTM) is necessary to effectively dissipate the excess heat generated by the cell at higher C-rates and contain the cell temperatures within the safe operating temperature range of 15°–45 °C. A passive thermal management method such as the use of PCM can absorb large amount of heat during its phase transition, resulting in heat dissipation from the cell surface. In this work, a Samsung INR18650-25R cylindrical cell with a nominal voltage of 3.6 V and a capacity of 2.5 Ah was chosen for the investigation. A multi-scale multi-dimension (MSMD) battery model with ECM (equivalent circuit model) e-Chemistry is considered for numerical analysis at the ambient temperature of 35 °C. A constant discharge rate of 8C is considered to analyse the thermal behaviour of the cell with a PCM. Further, the standard driving schedules such as US06 and LA92 are imposed to study the effectiveness of the passive thermal management method on the cell under variable current discharge. It is observed that the cell temperature decreases significantly with the thickness of PCM higher than 25% of cell radius and remains almost invariant thereafter at ~ 50 °C. The liquid fraction of the PCM is found to be nearly 1 for ‘δ’ up to 25% of cell radius. The liquid fraction decreases considerably at the end of discharge with an increase in ‘δ’, resulting in an increased cell temperature, which is undesirable. Therefore, it is observed that 25% of cell radius is an optimal thickness to maintain the cylindrical cell temperature within a safe operating range. The LIB cell's peak temperature is decreased by 44 °C (42%) for the LA92 driving schedule and 26 °C (38%) for the US06 driving schedule at the end of the complete battery discharge. Therefore, higher top speed and aggressive driving schedules like LA92 require additional external liquid cooling, as PCM alone cannot contain the battery surface temperatures under safe battery operating limits.