Preparation of Electrospun Membranes and Their Use as Separators in Lithium Batteries

In this work, electrospun nanofiber membranes are investigated as separators for lithium batteries. Membrane consisting of polyacrylonitrile-polycaprolactone mixtures were produced following a combinatorial approach inspired by design of experiments to identify the relationships between process parameters and microstructural properties. The microstructure of the non-woven fibrous mats was characterized by scanning electron microscopy to measure thickness and fiber distribution. Temperature and relative humidity during membrane deposition were also tracked to include them in the statistical analysis and highlight their influence on the properties of the resulting membranes. The functional evaluation of the membranes was conducted by electrochemical impedance spectroscopy, after soaking the membrane in the electrolyte, to measure ion transport properties. All the separators showed specific conductivities higher than 1.5 × 10−3 S. The electrochemical performance was also evaluated when the membranes were used as actual separators in coin-cells assembled in-house, stacking the electrolyte-soaked membranes between a lithium anode and a LiFePO4-based cathode. Among all, the PAN/PCL 50:50 showed excellent cycling stability, with a high initial capacity of 150 mAhg−1 and a coulombic efficiency of 99.6%.