The current battery thermal management (BTM) system integrating indirect heating and PCM cooling structures still suffers from relatively low heating efficiency and high energy consumption. In this work, we develop a BTM structure, which possesses both heating and cooling functionalities, by directly wrapping thin heating films around the cells inserted in a phase change material cooling module. Compared to the indirect heating structure, this novel direct contact structure allows direct heat transfer from the heating film to the batteries and thereby presents a more effective heating performance and lower energy consumption. For example, under the ambient temperature of 0 °C, the direct heating strategy with a heating power of 80 W delivers the shortest heating time of 78 s along with a temperature difference (ΔT) of 3.07 °C, thereby demonstrating the highest comprehensive evaluation factor of 0.645 and lowest energy consumption of 3.9%. Under the more severe ambient temperature of −20 °C, a heating time of 384 s with a ΔT of 3.77 °C can be achieved at a direct heating power of 60 W, suggesting the highest comprehensive evaluation factor of 0.503 and a lower energy consumption of 14.5%.

H-bond cross-linked polyimide (HPI) nanofibermodified polyethylene (PE) composite separators with high thermal stability, excellent electrolyte wettability, and improved electrochemical performance are prepared by electrospinning and alkaline hydrolysis processes. Due to the high thermal stability of the layer of HPI nanofiber, the dimension stability of the HPI@PE separator is greatly enhanced compared to the PE separator, without obvious thermal shrinkage at 200 °C. In comparison to the PE separators, lithium-ion batteries (LIBs) assembled with the HPI@PE composite separators show better cycling performance and rate capability, which are ascribed to the high polarity and developed porosity of the HPI nanofiber layer, which gives the separator excellent electrolyte wettability (electrolyte uptake and retention are 204 and 65%, respectively), low bulk resistance (3.1 Ω), and high ionic conductivity (0.46 mS cm −1 ). Therefore, the assembled Li/HPI@PE/LiCoO 2 cell achieves a specific capacity of 105.5 mA h g −1 as well as a capacity retention of 80.7% after 200 cycles at the discharge rate of 1 C. These results indicate that the prepared HPI@PE separator is applicable toward safe, long-life, and high-rate LIBs.

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