Meltem Yanilmaz

A review of recent developments in membrane separators for rechargeable lithium-ion batteries

In this paper, the recent developments and the characteristics of membrane separators for lithium-ion batteries are reviewed. In recent years, there have been intensive efforts to develop advanced battery separators for rechargeable lithium-ion batteries for different applications such as portable electronics, electric vehicles, and energy storage for power grids. The separator is a critical component of lithium-ion batteries since it provides a physical barrier between the positive and negative electrodes in order to prevent electrical short circuits. The separator also serves as the electrolyte reservoir for the transport of ions during the charging and discharging cycles of a battery. The performance of lithium-ion batteries is greatly affected by the materials and structure of the separators. This paper introduces the requirements of battery separators and the structure and properties of five important types of membrane separators which are microporous membranes, modified microporous membranes, non-woven mats, composite membranes and electrolyte membranes. Each separator type has inherent advantages and disadvantages which influence the performance of lithium-ion batteries. The structures, characteristics, manufacturing, modification, and performance of separators are described in this review paper. The outlook and future directions in this research field are also given.

Free-standing polyaniline–porous carbon nanofiber electrodes for symmetric and asymmetric supercapacitors

Polyaniline (PANI)–porous carbon nanofiber (PCNF) composites were generated by in situ polymerization of aniline on PCNFs for use as flexible, binder-less electrodes for high-performance supercapacitors. The effect of polymerization time on the electrode performance was studied by using symmetric cell configuration. Because of the high faradic current and good charge transfer between PCNFs and PANI, a maximum specific capacitance of 296 F g−1 and excellent rate performance were achieved for PANI–PCNF electrodes. PANI–PCNF electrodes also showed good capacitance retention (98%) after 1000 charge–discharge cycles. Furthermore, an asymmetric cell was successfully fabricated by using PANI–PCNF as the positive electrode and PCNFs as the negative electrode. Energy density and power density were improved significantly by using the asymmetric cell configuration. The resultant PANI–PCNF//PCNF asymmetric supercapacitor exhibited an energy density of 353 W h kg−1 with the power density of 609 W kg−1 at a current density of 1 A g−1.

High-strength, thermally stable nylon 6,6 composite nanofiber separators for lithium-ion batteries

Abstract Electrospun nylon 6,6 composite nanofiber membranes containing TiO2 or SiO2 nanoparticles were fabricated, and their physical and electrochemical properties were assessed for use as high-strength, thermally stable separators for lithium-ion batteries. Experimental results demonstrated that TiO2/nylon 6,6 and SiO2/nylon 6,6 nanofiber membranes not only displayed good mechanical strength and excellent thermal stability, but also showed improved electrochemical properties compared to commercial polypropylene membrane separator. Larger liquid electrolyte uptake, higher ionic conductivity, higher electrochemical oxidation limit, and lower interfacial resistance with lithium were obtained for TiO2/nylon 6,6 and SiO2/nylon 6,6 nanofiber membranes. Among all membranes studied, SiO2/nylon 6,6 nanofiber membranes showed the highest ionic conductivity and lowest interfacial resistance with lithium owing to their highest porosity and well-dispersed nanoparticles. In addition, Li/LiCoO2 and Li/LiFePO4 cells containing these composite nanofiber membranes demonstrated high cell capacities, good cycling performance, and superior C-rate performance at room temperature.