Abstract
In this study, a novel composite separator based on polytetrafluoroethylene (PTFE) coating layers and a commercial polyethylene (PE) separator is developed for high performance Li-ion batteries. This composite separator is prepared by immersing a PE separator directly into a commercial PTFE suspension to obtain a self-binding PTFE/PE/PTFE tri-layered structure. Then, the as-prepared composite separator is further treated with a H2O2/H2SO4 solution to enhance its electrolyte affinity. The results show that the coating layer, consisting of close-packed PTFE particles, possesses a highly ordered nano-porous structure and an excellent electrolyte wettability property, which significantly enhance the ionic conductivity of the composite separator. Due to the presence of the PTFE-based coating layer, the composite separator exhibits better thermal stability compared with the PE separator, reaching the thermal-resistant grade of commercial ceramic-coated separators. By using different separators, CR2032-type unit half-cells composed of a Li anode and a LiFePO4 cathode were assembled, and their C-rate and cycling performances were evaluated. The cell assembled with the composite separator was proven to have better C-rate capability and cycling capacity retention than the cell with the polyethylene separator. It is expected that the composite separator can be a potential candidate as a coating-type separator for high-performance rechargeable Li-ion batteries.
Highlights
Li-ion batteries have been widely used in power-source fields, such as electronic devices, power tools, and electric vehicles [1]
The cell assembled with the composite separator was proven to have better C-rate capability and cycling capacity retention than the cell with the polyethylene separator
To evaluate the effects of and a tensile strength test of the separators were conducted according to the method in [24] to the PTFE coating on cell performances, CR2032-type unit half-cells were assembled by sandwiching investigate the separator’s resistance against the penetration of sharp objects such as Li dendrites
Summary
Li-ion batteries have been widely used in power-source fields, such as electronic devices, power tools, and electric vehicles [1]. In academic research, Al2 O3 [14,15,16] and SiO2 [17,18], as the most common ceramic materials, have been extensively studied to suppress the thermal shrinkage and mechanical breakdown of polyolefin separators. Polytetrafluoroethylene (PTFE) suspension, as a common binder, is widely used for electrode preparation in Li-ion batteries because of its good adhesiveness and chemical stability in organic electrolytes. An electrospun PTFE nano-fiber separator was successfully prepared as the separator for Li-ion batteries, utilizing its natural heat resistance to improve thermal stability [21], which is not straightforward in industry production.
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