| Lithium-ion batteries?LIBs?have been widely used in portable electronic devices,especially electric vehicles,due to their high energy density and good cycle life.As a key component of lithium-ion batteries,the separator prevents direct contact between the positive and negative electrodes while allows free ion transportation.Now,the polyethylene?PE?and polypropylene?PP?microporous membranes have been successfully used in commercial lithium ion batteries due to their good mechanical strength and chemical stability.However,their high heat shrinkage can cause short circuits between electrodes at high temperatures,creating destructive safety issues.In addition,due to their inherent hydrophobicity,they show poor wettability and wettability speed toward liquid electrolyte,resulting in lower ionic conductivity and slower lithium ion migration.In response to the above problems,this paper carried out the modification study of polyolefin microporous membrane by including nano-particles.The main research contents and results are as follows:Preparation and performance study of functional nano-silica coating polyethylene microporous separator:In this paper,the core-shell structured silica-poly?cyclotriphosphazene-co-4,4?-sulfonyldiphenol??PZS?nanoparticles were synthesized and coated on both sides of PE microporous membrane.The PE-SiO2@PZS separator showed higher ionic conductivity(1.04×10-33 s cm-1),compared to pure SiO2 coated separator(8.32×10-4 s cm-1)and PE membrane(8.25×10-4 s cm-1).The rate capacity showed a value of 115 mA h g-1 for PE-SiO2@PZS separator,compared to 105 mA h g-1 for PE membrane and 106 mA h g-1 for PE-SiO2 separator at 8C rate.At the same time,the lower interfacial impedance resistance?63??for the PE-SiO2@PZS separator indicated intimate adhesion between electrode and separator.Effect of functional silica on the structure and properties of polypropylene microporous membranes:the addition of SiO2 and SiO2-PZS fillers showed significant effect on the properties of polypropylene microporous membranes.The PP/SiO2 cast film showed a maximum yield strength of 43.6 MPa and a tensile strength of 82.0 MPa at SiO2 content of 0.5%.Compared to PP membrane,the yield strength and tensile strength were increased by 14.4%and 10.9%.With the SiO2 content increasing,the yield strength,the value of orientation and elastic recovery all showed a downward trend.At the same time,the PP/SiO2 microporous membrane exhibited best gas permeability and the mechanical properties at a content of 0.5%SiO2 fillers.However,the yield strength of PP/SiO2-PZS cast film was lower than that of PP/SiO2 cast film with the same content fillers.With the increase of SiO2-PZS fillers content,the yield strength,the value of orientation and elastic recovery rate showed decrease trend similarly.For the electrochemical properties of PP/SiO2 and PP/SiO2-PZS microporous membranes,the PP/SiO2-PZS microporous membrane showed the largest ionic conductivity at a content of 0.5%filler,which was 1.51×10-3 S cm-1.Compared with the PP separator,it was increased by 0.41×10-3 S cm-1 and was also slightly higher than that of PP/SiO2 microporous membrane with the same content filler.At the same time,the discharge capacity also reached the maximum values of 113 mAhg-1 under the 8C rate,which was 76.35%of the initial discharge capacity?0.5C?compared to the PP separator and PP/SiO2 microporous membrane with the same content filler.Meanwhile,the cells assembled with PP/SiO2-PZS microporous membrane demonstrated better cycle performance than PP and PP/SiO2 microporous membrane under 1C rate with 100time cycles. |
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