| The safety problem of commercial polyolefin separators become more and more seriously because of the lithium-ion batteries?LIB?'s capacity retention improved.Compared with the polyolefin separators,cellulose membrane possessed excellent properties,such as highly safe,good puncture resistance,perfect resistance to high and low temperature,highly porosity and so on.Therefore,researchers who in the field of LIB separators have shift attention to pure cellulose which is an low-cost and sustainable raw material with fascinating properties.In the present work,cellulose linter,the biomass raw material,was dissolved in NaOH/urea aqueous solution and the cellulose based composite LIB separators were prepared by the phase inversion technique.C haracterization,including SEM FT-IR,XRD,DSC and TG were used to investigate thermal stability and the influence of security on LIB.In addition,the mechanical properties,the elongation at break,the electrolyte uptake and the pure water flux were tested and analyzed.Firstly,the cellulose based composite LIB separators were prepared by the phase inversion method in NaOH/urea aqueous solution,using non-woven fabric as base material of the membranes.It was found that the optimal composition of the casting solution was: 4wt%?cellulose?and 3wt%?PVP?.Under the experimental conditions,the separators can increase the elongation at break and electrolyte uptake by 27.55% and 239% at most,respectively.The tensile strength and pure water flux reached 40.15 MPa and 122.4 L·m-2·h-1,respectively.The composite separators are improved obviously with the electrolyte uptake increased by 40%,the pure water flux increased by 72.6%,compared with the separators without PVP K30.SEM pictures indicated that initial cellulose could be destroyed by the NaOH/urea aqueous solution.It could be found that there were large numbers micropores on the surface of cellulose/PVP K30 membrane but not pure cellulose membrane.XRD results indicated that the regenerated cellulose membrane was converted from cellulose ? to cellulose ?,this system can cause crystallization and the crystallinity decreased.Secondly,the composite LIB separators were prepared by blending modification,with styrene-acrylic emulsion as modifier of cellulose.It was found that the optimal composition of the casting solution was: 4wt%?cellulose?,3wt%?s tyrene-acrylic emulsion?and 3wt%?PVP?.Under the experimental conditions,the tensile strength and elongation at break of modified separator could reach 53.59 MPa and 24.34%,the electrolyte uptake and pure water flux could reach 223% and 120.5 L·m-2·h-1,the thermal shrinkage and maximum force could reach 1.5% and 0.31 N.SEM pictures indicated that the modified membrane displayed typical asymmetric morphology with good dispersive property of styrene-acrylic emulsion particles.SEM and N2 adsorption isotherm indicated that the modified membrane pore diameter become smaller.FT-IR results indicated that the characteristic absorption peaks of cellulose and styrene-acrylic emulsion were reflected in the infrared spectra of cellulose/styrene-acrylic emulsion composite membrane,there was good compatibility between the two components of the composite membrane.FT-IR and DSC results indicated that cellulose have favorable compatibility with s tyrene-acrylic emulsion.TG results showed that styrene-acrylic emulsion helped improve the composite membrane thermal stability.Finally,the cellulose/styrene-acrylic emulsion composite membranes were successfully fabricated by film immersion method in polyvinyl alcohol?PVA?solution without non-woven fabric.Results indicated that,when the PVA concentration was 3wt%,the separator showed the best comprehensive performance.The electrolyte uptake and electrolyte retention could reach 385% and 41.8%,the thermal shrinkage could reach 3.8% at 200 degrees.The porosity of composite membrane was 58.43%.SEM pictures indicated that impregnated composite membrane was more compact without separation.N2 adsorption isotherm indicated that impregnated composite membrane retention had no significant change.ATR-FTIR results showed that the composite membrane was modified successful.TG results indicated that the modified membrane had good thermal stability after impregnation modification. |
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