No abstract

With the increasing popularity of electric vehicles, the fast charging of lithium (Li) batteries is attracting increasing attention. However, the rapid decline in battery capacity caused by fast charging and accidents caused by Li dendrites piercing the separator greatly restrict fast‐charging applications. Herein, an electrospun polyacrylonitrile/polyvinylidene fluoride/boehmite (PAN/PVDF/12 wt.% AlO(OH)) and gel polymer polyethylene oxide/polyvinylidene fluoride‐hexafluoropropylene/lithium bis(trifluoromethanesulfonyl)imide/boehmite (PEO/PVDF‐HFP/12.6 wt.% LiTFSI /10 wt.% AlO(OH)) pressed together to form a two‐layer functional separator is designed. The electrospun separator improves the high‐temperature resistance of the entire separator due to its special structure. After the 1 h heat treatment at 220 °C, the thermal shrinkage rate of the double‐layer separator reaches 10.1%, showing good thermal stability. At 0.2 C, the discharge capacity retention rate is 99.4% after 100 cycles. After 1000 cycles at a rate of 10 C, the discharge capacity remains at 88% of the initial value. The two‐layer separator exhibits better capacity retention and superior rate performance than PP, providing an effective approach for commercializing fast‐charging functional separators.

Ethylene-octene copolymer (POE) samples exposed to-radiation under a series of absorbed doses have been investigated using thermal analysis, sol-gel analysis and solid state 13 C nuclear magnetic Resonance (NMR). The chemical shift of POE was assigned and peak evolution as a function of radiation dose was discussed. An obviously evolution is that the peak area of 33.6 ppm decreases as a function of the increase of radiation dose, and at the same time, the peak shape broadens gradually. This indicates that the chain scission occurred between-C and branch chain C (methine) or between C1 (the sidegroup hexyl) and branch chain C (methane) after radiation. The chain scission is severer with the increase of absorbed dose.The 13 C NMR spectra of the corresponding gels confirmed the result. The variation in linewidth of the resonance at 33.6 ppm in samples of POE irradiated to different doses was attributed to information of chain, scission, new cross linking, and crystalline components.