Electrospinning nanofibers as separators for lithium-ion batteries

Nanofibers produced by electrospinning show an interlaced and highly porous structure with a large surface-to-volume ratio. Such property makes the nanofibers useful in several applications such as healthcare, biotechnology, environmental engineering, defense & security, and energy storage. In this study polycaprolactone nanofibers have been tested as a mock-up separator in a lithium metal battery to evaluate the ion transport properties of ultrafine electrospun materials and assess the potential of this fabrication technology for lithium batteries. The membranes were soaked with an electrolyte solution and characterized by electrochemical impedance spectroscopy, finding that the porous structure of the polycaprolactone nanofiber membrane favors a complete and rapid uptake of the electrolyte. Furthermore, the large surface area of the nanofibrous network enhances ion conductivity, improving the power response of the polymer battery as compared with other polymer batteries. The electrochemical performance of a full battery was obtained on a prototype battery assembled by sandwiching the electrolyte-soaked nanofibrous membrane between a lithium anode and a LiFePO4 based cathode. The results showed that the battery can be discharged at high power with a good capacity retention. Despite intrinsic limitation of the polycaprolactone per se, the good performance of these membranes as separator certainly indicates that electrospinning is a relevant candidate method to develop and produce separators for high power batteries.