Cellulosic Biomass-Reinforced Polyvinylidene Fluoride Separators with Enhanced Dielectric Properties and Thermal Tolerance

Abstract

Safety issues are critical barriers to large-scale energy storage applications of lithium-ion batteries (LIBs). Using an ameliorated, thermally stable, shutdown separator is an effective method to overcome the safety issues. Herein, we demonstrate a novel, cellulosic biomass-material-blended polyvinylidene fluoride separator that was prepared using a simple nonsolvent-induced phase separation technique. This process formed a microporous composite separator with reduced crystallinity, uniform pore size distribution, superior thermal tolerance, and enhanced electrolyte wettability and dielectric and mechanical properties. In addition, the separator has a superior capacity retention and a better rate capability compared to the commercialized microporous polypropylene membrane. This fascinating membrane was fabricated via a relatively eco-friendly and cost-effective method and is an alternative, promising separator for high-power LIBs.

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“…The incorporation of PLLA distinctly improved the dielectric permittivity of the composite membranes because the impregnation coating of PLLA blocked the electron transport channels. Meanwhile, the relatively low dielectric losses of the matrix can suppress the dielectric heating, thus avoiding thermal breakdown and ameliorating the safety of LIBs . In addition, the dry composite matrix has an AC conductivity of 3.82 × 10 −9 S m −1 at 100 Hz (Figure S3, Supporting Information).…”

“…The variation in the ionic conductivity ( σ ) vs temperature ( T ) is depicted in Figure a (the corresponding AC impedance curves at different temperatures are shown in Figure b–d). As shown, log σ exhibits a significant linear correlation with 1/ T in the temperature range of 25−75 °C (Table S1, Supporting Information), which demonstrates that the Arrhenius model is appropriate for describing the ionic conductivity behavior in these systems . The CEC/CNF/PLLA‐GPEs possess a relatively high activation energy value of 7.26 kJ mol −1 compared to that of the CEC/CNF membrane‐based GPEs (referred to as CEC/CNF‐GPEs) (6.68 kJ mol −1 ), which is mainly because the ionic transport resistance through cortical crystal region is relatively high.…”

“…The scanning electron microscopy (SEM) image indicates that their surfaces are uniform without significant defects, and the internals of the membranes presented a 3D network structure with linked macropores. Similar to most porous membranes prepared via the NIPS method, different sides of as‐prepared membranes have different pore structures because of the discrepancies in solvent diffusivity . Indeed, the addition of CNFs can effectively regulate the pore structure of the membranes, resulting in a uniformity and reduction in the average pore size.…”

“…In the XRD patterns of CEC/CNF membranes, three diffraction peaks can be observed at 10.4°, 18.0°, and 21.0°, which can be attributed to the regularity of the rigid β‐ d ‐glucosamine repeat units . Compared to pristine CEC with a relatively high crystallinity of over 50%, the CEC/CNF/PLLA membranes have a crystallinity of 38% (Table ) . Two main diffraction peaks can be visualized in PLLA pattern at 2 θ = 16.7° and 19.0°, which correspond to (200) and (203) crystal planes of PLLA, respectively.…”

“…The mossy Li layer covers the surface of the active anode and increases the migration resistance of Li ions and leads to a continuous increase in the overpotential during the prolonged cycles. This morphological difference illustrates that the mechanically enhanced PLLA layer on the interface can inhibit the continuous reaction between fresh Li and the electrolyte …”