| As we all know,the application of commercial polyfin membranes was limited due to itself characristic.For example,the porosity and uptake were relatively low,and membrane and electrolyte were independently existing which led to a problem of leakage of electrolyte.This increased the risk of danger during the using of Li-ion batteries.PVDF electrospinning membrane was one of candidates to replace commercial membranes.Electrospinning method can fabricate littery nano-fibrous membrane,it possessed higher porosity and uptake to promote electrochemical and cycle perofoemance.In addition,PVDF nano fibers can uptake electrolyte to form gel polymer electrolyte(GPE).There was no extra liquid electrolyte existing in batteries,so batteries were not easy to happen the phenomenon of leakage and batteries were safer to be used.Heince,this article chose organic-inorganic Octaphenyl-Polyhedral oligomeric silsesquioxane(OPS)as added material to modify PVDF electrospinning membrane.We fabricated the BPPS and FPPS maembranes through suspension liquid and dissolution-blending methods,respectively.Furthermore,the SEM,TG-DSC,uptake performance,electrochemical and cycle properties were used to evalute the overall performance of separators:In terms of BPPS membrane,(1)The OPS articles disturb the crystallization behavior of PVDF polymer.The average fiber-dimater showed a clear decline,in which the AFD of B4 membrane was 285 nm.And the morphology of fiber surface showed a different change of bark-like surface.According to the mapping picture of EDS,the ops distributed uniformly in PVDF separators,without any agglomeration.Meanwhile,separators possessed good thermal stability,the thermal shrinkage of BPPS membranes stayed below 0.5%;(2)The thinner fibers and rough morphology led to the improvence of mechanical properties of BPPS membranes.The porosity and uptake of B4 reached to 70.2%and 974%,respectively.Rough fiber surface and thinner fibers made BPPS membranes presented better electrolyte uptake property;(3)On the other hand,rougher fibrous srface increased the friction between fibers when they were being stretched.The breaking strength of B2 membranes came to 12.7 Mpa,which was 693.7%higher than B0membranes.The excellent mechanical property of BPPS separators gived it chance to be used in Li-ion batteries;(4)The electrochemical properties of BPPS membranes were enhanced.The ionic conductivity of B2 membranes was 4.2 × 10-3 S/cm,the interfical resistance was 285? and the electrochemical window 5.6 V.(5)The first cycle discharge capacity of B2 separator was 145.8 mAh/g.The discharge capacity retention was 80.1%after 200 cycles at room temperature;The rate measurement demonstrated that the discharge capacity retention was 81.5%up from 0.1C to 2C.When it changed to 0.1C again,the discharge capacity reverted to 93.4%of first cycle discharge capacity;In terms of FPPS membrane,(1)There was not an obvious change in the surface of FPPS membrane like BPPS membrane,the fibrous diameter distribution trended to be more and more uniform.In particular,the porosity and liquid uptake of F4 membrane were 75.6%and 650.5%.The uniform addition of ops in FPPS membranes enhanced the thermal stability of separators,the thermal shrinkage of F4 membrane was 1.3%,with a decrease of 77.2%compared to pure PVDF membrane;(2)The mechanical property of FPPS membrane was improved,in which the breaking strength of F4 was 9.4 Mpa,with a increase of 422.2%compared to pure PVDF membrane;(3)FPPS membranes possessed well interfacial stability,its interfacial resistance was only 116 ?;Its ionic conductivity was up to 2.65 ×10-3 S/cm at room temperature and the electrochemical window was 5,1 V;(4)The first cycle discharge capacity of 146.4?148.1?144.6 ? 143 mAh/g,respectively.F4 had a discharge capacity retention of 90.8%after 50 cycles at 0.1C,with a increase of 41.4%compared to F1 membrane.The measurement data demonstrated that BPPS and FPPS membranes were promising candidates to be used in Li-ion batteries. |
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