Meltblown Polyvinylidene Difluoride as a Li-Ion Battery Separator

Among the types of Li-ion battery separators, the benefits of nonwoven mats are high porosity with low mass and low average production cost. Nonwoven polyvinylidene difluoride (PVDF) shows promise as a separator because of its chemical and mechanical stability and good absorption of organic electrolytes used in Li-ion cells. We investigated the use of a melt-blowable PVDF (Kynar resin RC 10,287, Arkema, Inc.) to produce meltblown PVDF mats, with the objective of elucidating its properties as a separator in Li-ion batteries. Meltblown PVDF mats were fabricated with high quality on a 1.2 m wide Reicofil R4 meltblown pilot line and subsequently consolidated through thermal compaction in a hydraulic press. The resulting mats showed high homogeneity (low roping and fiber entanglements), an average pore size as small as 0.9 μm, and average fiber diameter as small as 1.4 μm, yielding a high surface area and electrolyte uptake. After thermally compacting the nonwoven mat, the thickness and pore size decrease along with electrolyte absorbance and ionic conductivity. The highest conductivity of the electrolyte-infused mat was ∼9.6 mS/cm (room temperature with 1 M LiPF6 in ethylene carbonate/dimethyl carbonate 1:1 w/w), and the first-cycle capacity of a Li/LiCoO2 cell containing the meltblown PVDF separators was 140 mA h/g. Here, we assessed meltblown PVDF as a Li-ion battery separator by studying its physical, chemical, and electrochemical properties.