Optimization Of Continuous Nanoparticulate Coating Technology For Porous Flexible Media

In this paper,atmospheric pressure plasma-enhanced chemical vapor deposition（AP-PECVD）technology is used to modify porous polyethylene（PE）membrane through the mixture of Ar,O₂ and HMDSO gases.The influence of different plasma discharge parameters on the structure and properties of the porous flexible PE medium were studied,including two different electrode forms,coplanar dielectric barrier discharge（CDBD）and bulk dielectric barrier discharge（VDBD）and the other plasma conditions.The experimental results of FE-SEM,FTIR,XPS,UV-vis,contact angle,Gurley value,thermal shrinkage,mechanical strength etc..have shown that the modified membrane has a Si O_xC_yH_z hybrid particulate coating on the surface,and its hydrophilicity,gas permeability and thermal stability etc..have been improved.And the assembled button battery also shows improved performances in many aspects.In the form of CDBD discharge,its discharge mode is mainly based on the"H"type discharge wires between the electrode gap,and the number of"H"type discharge wires increases with the applied power.When the discharge power is high enough,the number and the sliding speed of the discharge wires between the electrode gaps are also increased.The experiment results displayed that this CDBD form of discharge realized the single-sided modification of the separator.The upper surface of the separator far away from the electrode was found to be deposited a nanoparticulate film of Si O_xC_yH_z flocculent morphology,containing functional groups such as C=O,-OH,Si-CH₃,Si-O and Si-O-Si etc.When the treatment time reached at 60 s,the wettability of the upper surface is highly hydrophilic（WCA<5°）,while the wettability the lower surface in contact with the electrode is still hydrophobic and its morphology is not significantly different from its original one.At the same time,the upside of the treated sample also showed a significant improvement difference in the moisture permeability from its down surfaces.The research results show that after CDBD plasma treatment,the treated samples show a single-sided wettability.This has good application prospects in the preparation of porous flexible membranes with anisotropic properties.Besides,in CDBD,as the increase of gas flow ratio of oxygen to HMDSO,more particles were found to be deposited on the upper surface of the sample and its porosity is reduced.At lower discharge power,the particles size was in sub-micron and the water contact angle is 82°,which is not much improved compared with the untreated film.Controlling the gas flow ratio and the power can indirectly affect the particle size distribution and its wettability.In VDBD dynamic continuous processing,COMOSL was used to simulate the gas flow rate in the coating cavity.The results indicate that the gas flow in the discharge area was stable and uniform in the x,y and z directions.The OES spectra showed that Si emission spectrum was detected in the discharge area.This proves that the monomer HMDSO has been effectively dissociated.When the treatment time of the separator reaches 60 s,Si O_xC_yH_z nanoparticles with a relatively uniform distribution of about 20 nm are deposited on the surface of the PE surface,and the particles adhere and grow along the fiber structure.As the treatment time increases,the Si-O-Si structure in the chemical composition of the particle film becomes more stable;the water contact angle of the sample is the minimum of 21°when the treatment time is 40 s.When the ratio of O₂ to HMDSO is 1:1,the hydrophilicity of the sample is the best,and the liquid absorption rate is also greatly improved,which provides more room for improvement in the electrolyte storage of the separator.The decrease in discharge energy density affects the morphology of the deposited coating particle film.When the gas flow rate of O₂and HMDSO reaches a high level of 20 sccm,the fiber structure of the sample becomes smooth,and the organic component of the particle film accounts for a high proportion.The structural characteristics of the separator treated with the optimal discharge parameters of VDBD were further analyzed and the performance of the button batteries assembled with such separator are measured.The analysis results show that the water contact angle of the coated separator is reduced from 121°to 21°,and the aging experiment results show that the hydrophilicity can be maintained for at least 30 days.After thermal treatment at 120°C,the air permeability of the coated sample is basically unchanged,which overcomes the shortcoming of the air permeability decrease of the original samples in the thermal treatment and meets the requirements of the assembly for the separator of the lithium-ion battery.The battery performance test results show that the impedance value of the battery assembled with the coated separator has been reduced,and the charge conduction has been improved.At a rate of 1 C discharge of the battery,its coulombic efficiency is improved.Within 3C rate discharge of the battery,the membrane modified by plasma showed satisfied performance.In this paper,CDBD discharge is used to achieve the anisotropic wettability improvement of the PE separator.The upper surface wettability and moisture permeability of PE with a thickness of 12μm flexible porous PE film have been coated with a very thin nanoparticle film and is significantly improved,which provides a single-sided plasma treatment method for the flexible porous medium.Through the study of VDBD dynamic continuous treatment,the plasma parameters are optimized and a rapid and efficient treatment of the separator is realized.The hydrophilicity of the treated separator was improved a lot and can be maintained for long storage time.The thermal shrinkage and the performance of all aspects of the assembled button battery have also been improved.This will improve the practical applications of AP-PECVD on coating of battery separator or other porous flexible medium.