Synthesis And Applied Research Of Composite-modified Separators For Lithium-ion Batteries

In recent years,the energy and environmental crisis caused by environmental pollution and the gradual depletion of fossil energy has become the focus of international attention.Therefore,the development of the new energy industry for energy conservation and environmental protection has become an important stratege for manycountries.Among them,Lithium-ion batterieshavebeen widely used in power,energy storage and other new energy fields because of its high energy density,stable performance and green environmental protection.However,due to thelowthermal stability of organic electrolyte,Li-ion batteries with high energy are easy to occur burning and explosive accidents in short circuit or impact,which limits its development.As one of the key materials,separators play a key role in avoiding battery short circuit,especially in high temperature conditions.which directly determines the safety of lithium-ion batteries.Therefore,the new separators with high temperature resistance and high safety are an important issue to improve the safety and cycling performance of lithium-ion battery.This article gives an overview of the problems of the polyethylene（PE）and polypropylene（PP）separators.New single-layer or multi-layer coating modified separators with excellent thermal stability are prepared by coating ceramic（Al₂O₃）and aramid fiberon the surface of PE separators By comparing the physical propertiesand electrochemical performance of separator before and after modification,the effect of modified membrane on the battery performance and safety is studied.The main results are as follows:（1）The physical parameters of PEand PP membrane and the performance of the as-prepared 18650 cylindrical batteriesareinvestigated.The results show that the mechanical strength,air permeability physical parameters of PE separator are better than that of PP separator.The electrochemical performance and safety of the PE batteries separator are better than that of PP batteries.（2）Ceramic/PE composite separators（Al₂O₃-PE separator）and boehmite/PE composite separator（γ-Al OOH-PE separator）are preaperd,and the effects of coating materials on the separator performance are also studied.Results show that the thermal shrinkage rate of Al₂O₃-PE separator andγ-Al OOH-PE separator in the transverse direction（TD）decreased by 21.1%and 32.3%compared with PE separator,respectively.The low temperature discharge performanceofthe batteries prepared by Al₂O₃-PE separator andγ-Al OOH-PE separator increased by 2.8%and 2.6%,respectively.More importantly,the cycle performances of Al₂O₃PE andγ-Al OOHPE separators improved by18.2%and 13.4%,respectively.In addition,the heavy impact and heating performance of the battery are both improved.（3）PE separator,Al₂O₃-PE separator and（polyvinylidene fluoride）PVDF-PE separator are coated by aramid fibers via micro-concave coating method to prepare aramid fibers/PEcompositeseparator,aramid fibers/Al₂O₃-PE composite separator,and aramid fibers/PVDF-PE composite separator,respectively.The results show thatthe thermal shrinkage rates of aramid fibers/PE,aramid fibers/Al₂O₃-PE and aramid fibers/PVDF-PE composite separators in the TD direction decreased by 28.0%,50.0%,and 1.0%compared with PE separator,respectively.Moreover,the low temperature discharge performance of the all batteries at-20℃increased by 3.5%,4.9%,and 2.6%,respectively.The cycle life of the three kinds of batteriesincreased by12.1%,32.2%and 20.2%,respectively.In addition,the battery that prepared byaramid fibers/Al₂O₃-PEcompsite separator has highr thermal stability,resulting ingood performance in overcharge test and improved performence of nail-penetration test,which plays a positive role in improving the safety of Li-ion batteries...