Frigid environments notably impair the electrochemical performance of zinc–bromine flow batteries (ZBFBs) due to polybromide solidification, restricting their widespread deployment in cold regions. Here, two independently used complexing agent cations, n-propyl-(2-hydroxyethyl)-dimethylammonium (N[1,1,3,2OH]⁺) and diethyl-(2-hydroxyethyl)-methylammonium (N[1,2,2,2OH]⁺), are proposed to enable ZBFBs to exhibit excellent performance at both low and room temperatures, through the precise regulation of the molecular polarity of polybromide complexes. Benefiting from the optimized design of the carbon number and position on the skeleton, the molecular polarity of the N[1,1,3,2OH]⁺- and N[1,2,2,2OH]⁺-polybromide complexes is appropriately reduced compared with that of choline, which is conductive to the enhancement of bromine capture capability. Interestingly, the intermolecular hydrogen bonding effect of their hydroxyl groups is not significantly enhanced, ensuring that the formed complexes maintain good fluidity at low temperatures. Thus, ZBFBs with a single complexing agent not only demonstrate an impressive average Coulombic efficiency of >95% across 1600 cycles at room temperature, but also can sustain operation with a high current density of 40 mA cm⁻² for 250 cycles at −20 °C. This research significantly advances the comprehensive understanding of the mechanisms involved, thereby substantially contributing to the development of enhanced low-temperature complexing agents.

中文翻译：

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高性能低温锌-溴液流电池中多溴配合物的分子极性调控


由于多溴化物凝固，寒冷环境会显著损害锌溴液流电池 （ZBFB） 的电化学性能，限制了它们在寒冷地区的广泛部署。本文提出了两种独立使用的络合剂阳离子，即正丙基-（2-羟乙基）-二甲基铵 （N[1,1,3,2OH]⁺） 和二乙基-（2-羟乙基）-甲基铵 （N[1,2,2,2OH]⁺），通过精确调节多溴络合物的分子极性，使 ZBFB 在低温和室温下均表现出优异的性能。得益于骨架上碳数和碳位置的优化设计，N[1,1,3,2OH]^- 和 N[1,2,2,2OH]⁺-聚溴配合物的分子极性较胆碱适当降低，有利于增强溴捕获能力。有趣的是，它们的羟基的分子间氢键作用并没有显着增强，从而确保形成的复合物在低温下保持良好的流动性。因此，使用单一络合剂的 ZBFB 不仅在室温下 1600 次循环中表现出令人印象深刻的 >95% 平均库仑效率，而且可以在 -20 °C 下以 40 mA ^cm-2 的高电流密度运行 250 次循环。 这项研究显着促进了对所涉及机制的全面理解，从而为增强型低温络合剂的开发做出了重大贡献。