A blended membrane based on poly(oxyphenylene benzimidazole) (PBI) and ethyl cellulose (EC) exhibits heat resistance and good electrochemical performance. The prepared blended polymer gel membranes show no visible dimensional change after being held at 350 °C for 30 min, whereas the polyethylene (PE) separator almost completely melts. In addition to excellent thermal stability, the self-supporting blended membranes also exhibit a uniform thermal distribution during the heating process from 60 to 200 °C. Additionally, the ionic conductivities of the PBI/EC blended membranes with different ratios are 1.24 mS cm–1 (1:1), 2.58 mS cm–1 (1:2), and 1.68 mS cm–1 (1:3), which are much higher than those of the PE separator (0.39 mS cm–1). Compared to that of the PE separator (113 mAh g–1), the cell with a separator of PBI/EC = 1:2 retained a discharge capacity of 131 mAh g–1 after 150 cycles at 0.5C. Meanwhile, the rate performance of the cell was also better than that of the PE separator, especially at high currents (5C). All of the results indicate that this blended polymer gel membrane with good thermal stability is expected to be applied to high-performance lithium-ion batteries.
Developing a nonflammable electrolyte is an efficient strategy to eliminate fire hazards and improve battery safety. Electrolytes containing nonflammable phosphate solvents enhance battery safety to a certain extent, but their compatibility with electrodes remains an obstacle. Here, a nonflammable electrolyte based on carbonate solvent is designed to resolve this dilemma while guaranteeing battery performance. We demonstrate that a nonflammable electrolyte employing the popular film-forming solvent ethylene carbonate (EC) and 1,2-dimethoxyethane (DME) with 2.3 mol kg−1 lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) has excellent thermal stability owing to the unique solution molecule structure. What’s more, the nonflammable electrolyte possesses excellent compatibility with both LiNi0.6Co0.2Mn0.2O2 and graphite electrode. The initial specific capacity and capacity retention rate of graphite/LiNi0.6Co0.2Mn0.2O2 punch cells employing this electrolyte are 169.3 mAh g−1 and 98.7% (after 50 cycles), respectively, which are comparable to those of cells employing traditional carbonate electrolytes. Besides, short-circuit test of the pouch cell suggests that the release of gases accompanied by decomposition of electrolyte under abuse conditions is effectively suppressed. All of these results show a promising prospect of this nonflammable electrolyte for application in high-safety Li-ion batteries.
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