Fluoride ion batteries (FIB) with quaternary ammonium fluoride electrolytes have recently shown notable room-temperature performance. As the voltage window is known to be limited by the water content, effective synthetic routes for anhydrous quaternary ammonium fluorides are critical for the further development of FIBs. This work describes the high-yield synthesis of an anhydrous quaternary ammonium fluoride salt, N,N-dimethyl-N,N-dineopentylammonium fluoride (Np₂F), via an anion exchange reaction. Karl Fischer titrations determined the water content of the solid anhydrous product to be 71 ppm (1.7 M in MeOH)─an exceptionally low value. The anhydrous Np₂F/bis(2,2,2-trifluoroethyl) ether (BTFE) electrolyte also shows a wide electrochemical window of 3.5 V. Quantifying the relationship between the electrolyte performance and water content, we found that the voltage window decreases from 3.5 to 3.1 V as the water content increases from 25 to 135 ppm.

中文翻译：

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氟离子电池用无水N,N-二甲基-N,N-二戊基氟化铵电解液

使用季铵氟化物电解质的氟化物离子电池（FIB）最近表现出显着的室温性能。由于已知电压窗口受到水含量的限制，无水季铵氟化物的有效合成路线对于FIB的进一步发展至关重要。这项工作描述了通过阴离子交换反应高产率合成无水氟化季铵盐N , N-二甲基-N , N-二戊基氟化铵 (Np ₂ F)。卡尔费休滴定测定固体无水产物的水含量为 71 ppm（1.7 M，在 MeOH 中）——一个极低的值。无水 Np ₂ F/双(2,2,2-三氟乙基)醚 (BTFE) 电解质也显示出 3.5 V 的宽电化学窗口。量化电解质性能与水含量之间的关系，我们发现电压窗口从当水含量从 25 ppm 增加到 135 ppm 时，电压为 3.5 至 3.1 V。