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A cross-linked porous polymer membrane using vinyl-functionalized aluminum oxide (Al2O3) nanoparticles was prepared and used as a separator for lithium-ion batteries (LIBs). Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was first blended with a mixture solution containing poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), vinyl-functionalized Al2O3 nanoparticles (VTMO@Al2O3) as the cross-linker and poly(vinyl pyrrolidone) (PVP) as the pore-forming agent. Subsequently, the membrane was obtained by free radical copolymerization of the above-mentioned mixture and after-treatment. The preparation and properties of the membranes were investigated. It has been found that, under the action of the pore-forming agent of PVP, the obtained membrane (PMAv) had high ionic conductivity (1.37 mS cm−1) at ambient temperature. On account of the existence of the Al2O3 as cross-linking points, the PMAv membrane showed good mechanical strength of 30.4 MPa and excellent thermal stability at 180 °C. Moreover, comparing with the system without PVP or Al2O3 samples, the cell with the PMAv membrane showed the best discharge capacity and most stable capacity retention and cycle performance, indicating that the PMAv membrane is a good polymer separator for LIBs.

In this work, a new porous cross-linked membrane is prepared and used as the separator for rechargeable lithium-ion batteries. The inorganic zinc oxide nanoparticle (nano-ZnO) was added as a pore-forming agent and filler to the preparation process of membranes composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and a cross-linked polymer by the copolymerization from poly(ethylene glycol methyl ether methacrylate) (PEGMEMA), methyl methacrylate (MMA) and octavinyl-T8-silsesquioxane (OVPOSS). The prepared membrane was firstly swollen by propylene carbonate (PC) and nano-ZnO was then eluted by hydrochloric acid to form the microporous structure. The effects of particle size and additive amount of nano-ZnO on the mechanical and electrochemical properties of microporous membranes were studied. SEM analysis showed that 30 nm nano-ZnO was the most suitable diameter for forming microporous structure. It is generally considered that the ionic conductivity is inversely correlated with the mechanical strength of separator. In our research, we have found that 18% addition of nano-ZnO was the most appropriate amount for the preparation of a microporous membrane (CRZ18) with an ionic conductivity of 1.4 mS cm−1 and a tensile strength of 10.7 MPa. Meanwhile, the LiFePO4/Li half-cell assembled with the CRZ18 membrane as a separator exhibited the best C-rate capacity and cycle charge-discharge performance, indicating that the CRZ18 membrane would be a kind of promising separator for the high-performance lithium-ion batteries.

In this study, we constructed a new membrane, which was prepared by free radical polymerization of a mixture containing vinyl-functionalized SiO2 nanoparticles (M-SiO2), modified cellulose acetate (M-CA) and poly(ethylene glycol)dimethacrylate (PEGDMA). The M-SiO2 was the SiO2 nanoparticles coupled with vinyltrimethoxysilane (VTMO), and the M-CA was the cellulose acetate modified with methacryloyl groups. The effects of M-SiO2 content on the porosity, electrolyte uptake and other properties of the membrane were studied. The results showed that the membrane with a suitable M-SiO2 content had good mechanical strength and other properties. For example, the membrane with 15 wt% of M-SiO2 (named as C-CAS15) possessed the excellent comprehensive performance. The mechanical strength of C-CAS15 membrane was up to 14.30 MPa, and it had no obvious dimension change at 200 °C. Meanwhile, the C-CAS15 membrane exhibited a relatively high ionic conductivity of 1.54 mS cm−1. The LiFePO4/GPE/Li half-cell assembled by the C-CAS15 membrane displayed excellent cycle charge-discharge performance and C-rate discharge performance, in which the discharge specific capacity retention could retain 98% after 100 cycles under 0.5 C/0.5 C and the discharge specific capacity could reach above 100 mAh g−1 under the higher C-rate of 4 C. Compared with the commercial PE membrane and the common membranes reported in previous literatures, the prepared C-CAS15 membrane presented better comprehensive performance, which indicated that the C-CAS15 membrane could be a promising separator for high performance lithium-ion batteries.

Separators have drawn substantial attention because of their important role in achieving the safety and good electrochemical performance of lithium-ion batteries. In this study, we report a new type of composite membrane prepared by a combination of fluorinated polypropylene (PP) nonwoven fabric, poly(vinylidene fluoride- co -hexafluoropropylene) (PVdF-HFP) and SiO 2 nanoparticles. 2, 2, 3, 3, 4, 4, 5, 5-Octafluoropentyl methacrylate (OFPMA) is first grafted on the surface of PP nonwoven by plasma treatment to improve the nonwoven’s adhesion with PVdF-HFP. Two kinds of composite separators have been prepared by using the different PP nonwovens together with PVdF-HFP and SiO 2 nanoparticles. They were separately designated as PHS for commercially raw PP nonwoven system and PHS-n for OFPMA-modified PP nonwoven systems (n means plasma treatment time). The morphology, electrolyte uptake, ionic conductivity and electrochemical properties of the composite separators have been analyzed by scanning electron microscope (SEM) analysis, impedance measurement, charge-discharge cycle and C-rate tests, respectively. The results indicate that PHS-10 composite separator using the modified PP nonwoven treated by plasma for 10 min exhibits much better properties than PHS separator, including an improved mechanical property, thermal stability, electrolyte uptake (290 wt%) and ionic conductivity (1.76 mS cm −1 ). More importantly, the LiFePO 4 /Li half-cell assembled with PHS-10 composite separator displays a good C-rate performance, which shows an enhancement in the chemical stability and discharge capacity. The capacity keeps above 150 mA h g −1 after 100 charge–discharge cycles. These performances endow this composite membrane as a promising candidate for high-performance lithium-ion battery separators.