Evaluation of a polymethylpentene fiber mat formed directly on an anode as a battery separator

Battery separator is a porous membrane that separates the positive and negative electrodes to prevent their electrical shorting, yet enables lithium ion transport through the liquid electrolyte in its pores. In this work, a polymethylpentene (PMP) non-woven separator was formed directly on an anode through the electrospinning process. The PMP separator exhibited a much improved thermal dimensional stability compared to a commercial polyolefin separator. It showed negligible shrinkage in the 150 °C oven test, while the shrinkage was close to 55% for a commercial separator in the machine direction. It also enabled good effective ionic conductivity in the range of 1.16-1.44 mS/cm when saturated with the liquid electrolyte of 1 M LiPF6 in ethylene carbonate/diethyl carbonate (1:2 by volume). The cell performance was tested in coin cells with the LiNi1/3Co1/3Mn1/3O2 cathode and the graphite anode. The cells with the PMP separators displayed stable cycling performance and good rate capabilities. However, the PMP separators showed low tensile strengths and the effect of the low tensile strengths on the performance of large format batteries needs further investigation.