Effect of Cross-Linking and Surface Treatment on the Functional Properties of Electrospun Polybenzimidazole Separators for Lithium Metal Batteries

Abstract

In this work, electrospun PBI separators with a highly porous structure and nanofiber diameter of about 90−150 nm are prepared using a multi-nozzle under controlled conditions for lithium metal batteries. Cross-linking with α, α-dibromo-p-xylene and surface treatment using 4-(chloromethyl) benzoic acid successfully improve the electrochemical as well as mechanical properties of the separators. The resulting separator is endowed with high thermal stability and excellent wettability (1080 to 1150%) with commercial liquid electrolyte than PE and PP (Celgard 2400) separators. Besides, attractive cycling stability and rate capability in LiFePO 4 /Li cells are attained with the modified separators. Prominently, CROSSLINK PBI exhibits a stable Coulombic efficiency of more than 99% over 100 charge−discharge cycles at 0.5 C, which is superior to the value of cells using commercial PE and PP (Celgard 2400) separators. The half cells assembled using the CROSSLINK PBI separator can deliver a discharge capacity of 150.3 mAh g −1 at 0.2 C after 50 cycles corresponding to 88.4% of the theoretical value of LiFePO 4 (170 mAh g −1 ). This work offers a worthwhile method to produce thermally stable separators with noteworthy electrochemical performances which opens new possibilities to improve the safe operation of batteries.

Electrospinning of High-Performance Nanofibres: State of the Art and Insights into the Path Forward

“…PBI was dissolved in DMAc at concentrations between 14 and 18 wt% and electrospun to determine the optimal polymer concentration. At PBI concentrations of 14 and 15 wt%, highly beaded nanofibres were observed [28]. Between 16 and 18 wt%, smooth and even fibres were formed via electrospinning.…”

“…Due to its high thermal resistance, PBI lends itself to many applications for nanofibrous membranes. PBI nanofibrous membranes have been studied for applications including lithium-ion battery separators, fuel cells, water electrolyzers, respiratory masks, and carbon nanofibre precursors [26,28,[30][31][32]. PBI is readily dissolved in DMAc alone and in the presence of aprotic salts such as LiCl and LiBr [26,63,64].…”

“…Instead, studies that examined PBI nanofibres for a specific application also performed optimization processes for the electrospinning process. Jung et al [28] observed the impact of the PBI concentration in the polymer solution on the nanofibre diameter. PBI was dissolved in DMAc at concentrations between 14 and 18 wt% and electrospun to determine the optimal polymer concentration.…”

“…It was found that the combination of 15 wt% PBI, 15 kV, and 100 µL/h was the most effective for a reproducible electrospinning process with smaller fibre diameters. A variety of post-treatments have been examined to enhance the mechanical pr ties of the PBI nanofibrous membrane [26,28,32]. Chemical treatments are a common to encourage the crosslinking of polymers after electrospinning.…”

“…For high-performance polymers, electrospinning has been used to produce nanofibres from polymers including m-aramid [7][8][9][10][11][12], p-aramid [3,[13][14][15], PAI [5,[16][17][18][19][20][21], PBO [16,[22][23][24][25], and PBI [26][27][28][29][30][31][32][33]. Although some reviews have considered high-performance nanofibre fabrication for specific applications [34,35], or a specific type of high-performance fibre [14,36], no reviews so far have summarized the general progress in the electrospinning of highperformance nanofibres.…”