Lithium metal batteries offer a huge opportunity to develop energy storage systems with high energy density and high discharge platforms. However, the battery is prone to thermal runaway and the problem of lithium dendrites accompanied by high energy density and excessive charge and discharge. This study presents an assisted assembly technique (AAT) based on flexible barium titanate (BTO) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers for preparation of a battery separator. AAT was used to combine the BTO diaphragms with high thermal stability and the PVDF-HFP diaphragms with good Elasticity and piezoelectricity, and the thermal stability was improved by 200 and 125% increase in battery cycle life compared to PVDF-HFP diaphragms alone. And demonstrated excellent thermal closure performance between 160 and 200 °C. Furthermore, the piezoelectric effect of the composite film prevents the growth of lithium dendrites in the vertical direction, avoiding the trouble of lithium dendrites penetrating the battery separator. Therefore, the two safety guarantee properties of the composite separator greatly enhance the safety and service life of the battery, which allows the application of lithium batteries to be further improved in the application scenario and application scale.
The thermal safety of lithium-ion batteries (LIBs) is a major obstacle to expanding LIBs applications. High-safety separators with a thermal shutdown feature are considered the most promising and appealing thermal protection strategy for LIBs to avoid thermal runaway. Herein, a high-safety poly (ethylene-co-vinyl acetate)/poly (ether ether ketone)/poly (ethylene-co-vinyl acetate) (EVA/PEEK/EVA) composite separator is fabricated by dip-coating and thermally induced phase separation. Once the operating temperature exceeds 80 °C inadvertently (the thermal runaway onset temperature), the EVA layers of the EVA/PEEK/EVA separator are converted into barrier membranes to cut off ion transport and prevent battery reactions. Meanwhile, the PEEK substrate remains dimensionally stable even at temperatures up to 240 °C to avoid the dangers associated with thermal inertia after shutdown. Moreover, compared to the polyolefin separator (commercially available), the EVA/PEEK/EVA separator shows an increase of 42% and 77.1% in ionic conductivity and discharge capacity at the rate of 4C, respectively. Therefore, the EVA/PEEK/EVA separator can secure the LIBs without sacrificing electrochemical performance, and further expand the application of LIBs.
Hui Chang,Guohong Kang,Zengqi Zhang,Wei Liu,Yongcheng Jin
Safety hazards associated with separators in lithium-ion batteries are more pronounced in light of the significant improvement of energy density of batteries, hindering their wide application. In this research, asymmetric poly (vinylidene fluoride) (PVDF)-coated polyimide separators with three-dimensionally homogeneous microporous (3DHM API/PVDF) structure are prepared, in which a PVDF layer with a thickness of 6 μm on one side of polyimide. Polyimide, as the base film, has a high heat-resistant temperature which ensures that as-prepared separators will not be shrunk and burned. The coated PVDF layer imparts 3DHM API/PVDF with thermal shutdown function at 175 °C due to the melting of PVDF. The temperature difference between the shutdown and meltdown temperature is over 100 °C, ensuring that the LIB assembled with 3DHM API/PVDF is safe for use. Moreover, the interconnected microporous structure of the separator facilitates the formation of 3D Li+ transport pathways and uniformity of lithium deposition, suppressing lithium dendrite growth. The coin cells assembled by 3DHM API/PVDF exhibit similar electrochemical performance to that of a commercial polypropylene separator at room temperature. Therefore, the novel 3DHM API/PVDF separator may be a promising candidate for a significantly safer LIB.
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