Effect Of Surface Modification On Atomic Layer Deposited Alumina Polyethylene Composite

Atomic layer deposition?ALD?technology is a surface self-limiting thin film growth technology that can control the coating thickness precisely.We studied ALD coated polyolefin membrane to form nano-alumina polyolefin composites.However,the non-reactive groups on the polyolefin membrane can not initiate ALD growth directly,resulting in a low growth efficiency in the early stage reaction and final formation of alumina clusters on polyolefin surface.To improve the properties of polyethylene?PE?membrane coated by ALD alumina,the PE membrane surface was surface-modified and then followed up with ALD Al₂O₃.The main topics in this research are as following:?1?The PE membrane surface was modified with different concentrations of polyvinyl alcohol?PVA?and then followed up with ALD Al₂O₃.The modified composite membranes were characterized by thermal resistance,thickness,and SEM of cross section to determine suitable concentration of PVA solution.The effects of PVA modification on ALD alumina coating PE membrane were characterized by means of scanning electron microscopy?SEM?,Fourier Transform infrared spectroscope?FTIR?and Inductive coupling plasma emission spectrometry?ICP?.The results indicated that the PVA surface modification could increase the hydroxyl group?-OH?on the PE membrane as the ALD reaction sites effectively.When the PE membrane surface was modified with PVA,the subsequent ALD growth efficiency was improved significantly,and alumina thin film formation on PE membrane fibers instead of island-shaped Al₂O₃ cluster was achieved.It was also found that the thermal shrinkage of the modified composite membrane was enhanced,thickness increase of the composite membrane and the damage of the mechanical structure were reduced as well.?2?There are non-reactive groups in polyvinylidene fluoride?PVDF?which can react with trimethylaluminum?TMA?,such as hydroxyl group in PVA.Therefore,an exploratory study was conducted to verify the effect of PVDF modification on ALD alumina coating PE membrane.The results indicated that PVDF thin film could be formed on the PE membrane fibers by by simple dipping method to prevent the ALD from reacting on subsurface of the fibers.The precursor was adsorbed easily and uniformly on PVDF with strong van der Waals force,and then the subsequent ALD growth efficiency was improved significantly.The alumina thin film was formed on the PE membrane fibers.?3?Dipping with polyvinylidene fluoride-hexafluoropropylene?PVDF-HFP?solution and PVDF-HFP powder coating were applied on PE membrane fibers,and effects on subsequent ALD Al₂O₃ modification were compared.The results indicated that it was difficult to form complete thin film coverage on PE membrane fibers by dipping into PVDF-HFP solution.Since PVDF-HFP were powders,the contact area on PE membrane fibers was small.PVDF-HFP after dipping and drying tended to agglomerate into large particles and remained in the gaps between the fibers,which will cause reduced porosity of the composite film after ALD coating,thickness increase of the composite membrane was enhanced as well.ALD alumina coating on PVDF-HFP powder coated PE membrane was easier.This method could improve the thermal shrinkage of the composite membrane with less amount of alumina coating.Under optimized condition,the thickness increase and the porosity decrease were reduced,and the batteries could be charged and discharged normally.The properties of PE membrane modified by PVA,PVDF and PVDF-HFP and then followed up with ALD Al₂O₃ were excellent.The preparation of these materials provided basis for the application of ALD on polyolefin membrane.