Preparation And Performance Study Of POSS Electrospun Polyimide (PI) And Core-shell PES@PVDF-HFP Lithium-ion Battery Separator

At present,there are some problems in commercial separator,such as low porosity,low electrolyte absorption,poor thermal stability,low ionic conductivity and poor stability against high voltage.Therefore,the following two aspects of research work have been done to solve these problems.In the first part of this paper,a polyamic acid/aminopropyllsobutyl polyhedral oligomeric silsesquioxane(PAA/A-POSS)nanocomposites were prepared by in-situ polymerization.Then,a polyimide/aminopropyllsobutyl polyhedral oligomeric silsesquioxane(PI/A-POSS)composite membrane with a novel three-dimensional thermal crosslinking structure was prepared by electrospinning and subsequent imidization.Compared with the commercial PP membrane,the prepared composite membranes show excellent dimensional thermal shrinkage resistance(the membrane has zero size thermal shrinkage within 280 ?).Compared with pure PI membrane,the A3 composite membrane(the content of A-POSS is 3wt%)has smaller average pore size(0.87?m,52.2 % reduction rate),higher porosity(83.8%,20.2% increase rate),smaller electrolyte contact angle(8.2°,80.8% reduction rate),better electrolyte uptake(1149%,95.7% increase rate),better mechanical properties(13.58MPa,124.5%increase rate)and better thermal stability.In addition,compared with pure PI membrane,A3 composite membrane has higher ionic conductivity(2.617mS/cm,342.1% increase rate),lower interfacial resistance(17.65?,84.8% reduction rate)and higher electrochemical stability window(5.21V,16.6% increase rate).It is worth noting that the battery assembled with the A0 separator has a first discharge capacity of 143.9m Ah/g at 0.2C,and its capacity retention rate is almost zero after 200 cycles.However,the battery assembled with the A3 separator has a higher first discharge capacity(169.7mAh/g,17.9% increase rate)and its capacity retention rate is still as high as 95.7%after 200 cycles.Furthermore,compared with A0 separator,the battery assembled with the A3 separator shows excellent rate capacity with a relatively high discharge capacity up to 136.3 mAh/g at 2.0 C and a superior capacity recovery rate of 98.06 %.Therefore,the heat-resistant PI/A-POSS composite separator has a broad application prospect in high-performance and advanced-safety lithium-ion batteries.In the second part,a novel core-shell structured polyethersulfone@poly(vinylidene fluoride-co-hexafluoropropylene)/aminopropyllsobutyl polyhedral oligomeric silsesquioxane(PES@PVDF-HFP/A-POSS(core@shell))composite membrane based on POSS modified was successfully synthesized by electrospinning with PES as core layer and PVDF-HFP/A-POSS as shell.Compared with the pure PVDF-HFP membrane,the PES@PVDF-HFP/A-POSS(core@shell)composite membrane has better mechanical properties(10.45 MPa,225.5 % increase rate),better thermal stability and more excellent dimensional thermal shrinkage resistance(the membrane has almost no dimensional shrinkage within 220?).In addition,compared with the pure PVDF-HFP membrane,the PES@PVDF-HFP/A-POSS(core@shell)composite membrane has smaller average pore size(0.36?m,14.3% reduction rate),higher porosity(89%,14.1% increase rate),smaller electrolyte contact angle(19.6°,12.9% reduction rate)and higher electrolyte uptake(871%,36.7% increase rate).Furthermore,compared with pure PVDF-HFP membrane,the PES@PVDF-HFP/APOSS(core@shell)composite membrane has higher ionic conductivity(2.17mS/cm,59.6% increase rate),lower interfacial resistance(41.36?,54.3% reduction rate)and higher electrochemical stability window(5.26V).Therefore,the PES@PVDF-HFP/APOSS(core@shell)separator has great research value and application potential in highvoltage and high safety lithium-ion batteries.