Preparation And Characterization Of Polythene Based Composite Separators For Lithium-ion Batteries

LIBs are widely used in electronic devices and electric vehicles because they have several important advantages including high energy density and power density,no memory effect,long cycle life,and low self-discharging.As one of the crucial component of LIBs,the separator has great impact on the electrochemical capacity,internal resistance,cycling capability and safety performance of the LIBs.Currently,the commercial lithium-ion battery.separator use polyolefin materials,including polyethylene?PE?separator,polypropylene?PP?separator and trilayer PP/PE/PP separator.Nevertheless,polyolefin separator has the disadvantages of poor wettability and low thermostability at high temperature.Especially for the PE membrane,when the temperature exceeds100?,thermal shrinkage will happen.This is a big challenge for the safety of the battery.In order to improve the thermal stability and wettability of microporous polyolefin membranes,several composite separators were prepared in this paper.The research results are as follows.?1?TiO₂-PMMA/PE composite membrane separators are fabricated by coating one side of microporous polyethylene membrane with poly?methyl methacrylate?modified titanate nanoparticles which are synthesized through emulsifier-free emulsion polymerization of methacrylate-functionalized titanate nanoparticles.The TiO₂-PMMA/PE composite membrane separators exhibit great thermal-shrinking resistance due to the introduction of thermal resistant titanate nanoparticles.After immersed into electrolyte solution,the swelling poly?methyl methacrylate?microspheres leads to the formation of gel electrolyte,thus stabilizing the electrolyte.Moreover,the porous structure of the coated layer can facilitate the swelling of electrolyte and the transport of lithium ions.The electrolyte uptake of separators increased from 97.4%to201.8%,meanwhile the ionic conductivity also increased from 0.43 mS/cm to 0.87 mS/cm.The thus-assembled lithium ion battery shows an improved cycle performance and rate capability.?2?Dispersed PMMA microspheres are prepared by emulsion polymerization method.And the PMMA coating slurry were coated on one side of the PE membrane,formed the asymmetric structure of PMMA/PE composite membrane.Then,the PMMA/PE@PDA composite membrane were prepared by soaking PMMA/PE membrane into dopamine solution.Studies have found that PMMA microspheres is arranged on the surface of PE membrane,formed the interconnected porous structure.The porosity of PMMA/PE membrane and PMMA/PE@PDA membrane respectively is 46.5%,45.8%,not decrease compared to the PE membrane?45%?.The diameter of polydopamine particles is about 100 nm,smaller than the PMMA microspheres?500nm?.The wettability and thermostability of composite membrane is improved due to the function of PMMA and PDA.Meanwhile,the electrolyte uptake and the ionic conductivity is also improved.The thus-assembled lithium ion battery shows an improved cycle performance and rate capability.