High‐Performance PE‐BN/PVDF‐HFP Bilayer Separator for Lithium‐Ion Batteries

Abstract

Highly efficient and thermally stable polyethylene‐hexagonal boron nitride/poly(vinylidene fluoride‐hexafluoropropylene) (PE‐BN/PVDF‐HFP) bilayer separator with microporous structure is prepared, for the first time with a wet chemistry method. The incorporation of hexagonal boron nitride particles in PE matrix promotes the interfacial interaction between PE and PVDF‐HFP layers to prevent separation of layers and supresses dendrite growth owing to the strong adsorption energy with polymers, large interactive surface area, and superior mechanical capability. The PVDF‐HFP layer provides additional thermally stable backbone while its inherent hydrophilic property and highly porous structure improve the overall performance of the separator. The bilayer separator owns a high electrolyte uptake of 348% and a thermal shrinkage of 6.6% upon annealing at 140 °C for 1 h. The lithium iron phosphate/lithium cell with the as‐prepared separator owns a high ionic conductivity up to 4.4 × 10−4 S cm−1, and a room‐temperature capacity of 120 mAh g−1 at 2 C with a 95% capacity retention after 500 cycles and a capability of 108 mAh g−1 at 4 C. The PE‐BN/PVDF‐HFP separator is a promising alternative of traditional multilayer separators for high‐performance lithium‐ion batteries.

Recent Development in Separators for High‐Temperature Lithium‐Ion Batteries

“…c) SEM image of separators prepared through the phase inversion method. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

“…The most commercially used separators for LIBs at large scale are polyolefin separators (PE or PP). These separators exhibit good electrochemical stability and mechanical strength, but they suffer from low thermal stability, less compatibility with liquid electrolytes, and not efficiently capable to retain electrolyte during the charge–discharge process . The low thermal and dimensional stability of these separators is owing to the low melting temperatures (130 °C for PE and 165 °C for PP) of material and formation of the porous structure through stretching method.…”

“…The rate performances of LIBs with modified PP separator are also improved. Waqas et al reported another novel strategy to increase the adhesion between PE and PVDF‐HFP coated layers by incorporating 2D material ( h ‐BN) in the substrate during preparation through the wet‐chemistry method. The incorporated h ‐BN in PE substrate increases the interfacial interaction between PE and PVDF‐HFP layers, as shown in Figure a, which improves the bonding between layers.…”

“…Separator is one of the important components of LIBs that is not directly involved in the electrochemical reaction, however, its properties, structure, and composition greatly influence the performance of batteries with respect to internal resistance, long cycle performances, high capacity, and safety . The basic functions of the separator are to prevent the contact between anode and cathode to avoid internal short circuits, store liquid electrolyte, and permit the migration of ions during the charge–discharge process . The ideal separator should possess high mechanical strength, robust thermal stability, low internal resistance, high electrolyte wettability, and high porosity.…”

“…However, at high‐temperatures, the LIBs depict abnormal performances due to the decomposition of lithium salts present in the electrolyte, low thermal stability of separators, and instability of electrodes. The high temperatures introduce thermal fluctuations inside batteries during the charge–discharge process, which results in internal short circuits and leading to thermal runaway and fire explosion . Many incidents have been reported recently regarding the fire explosion of LIBs mainly caused by the internal short circuits and thermal runaway.…”