Fabrication of hierarchical structured SiO2/polyetherimide-polyurethane nanofibrous separators with high performance for lithium ion batteries

• Electrospinning followed by dip-coating was used to fabricate SiO2/PEI-PU membranes.
• Introducing PEI, PU and SiO2 improved safety, tensile strength and ionic conductivity.
• Coating SiO2 also restrained the micro-shorting and migrated the self-discharge.
• SiO2/PEI-PU membranes based cell exhibited prominent cycling and rate performance.

ABSTRACTThe performance of lithium ion battery based on electrospun nanofibrous membranes has gained a great deal of attention in the past decades, but the intrinsic low mechanical strength and large pore size of electrospun membranes limit their battery performance. To overcome this limitation, a powerful strategy for designing, fabricating and evaluating silica nanoparticles coated polyetherimide-polyurethane (SiO2/PEI-PU) nanofibrous composite membranes is easily developed via electrospinning followed by a dip-coating process. Benefiting from the high porosity, interpenetrating network structure and synergetic effect of PU, PEI and SiO2 nanoparticles, the as-prepared composite membranes exhibit high ionic conductivity (2.33 mS cm−1), robust tensile strength (15.65 MPa) and improved safety (excellent thermal resistance and flame retardant property). Additionally, the as-prepared composite membranes possess relatively narrow pore size distribution with average pore size of 0.58 μm after coating SiO2 nanoparticles, which plays an important role in hindering the micro-shorting and mitigating self-discharge. Significantly, the SiO2/PEI-PU membranes based Li/LiFePO4 cell exhibits more excellent cycling stability with capacity retention of 98.7% after 50 cycles at 0.2 C rate and better rate capability compared with the Celgard membrane based cell. The results clearly demonstrate that this is a promising separator candidate for next-generation lithium ion batteries, which may represent a significant step toward separators with improved performance.

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