研究人员正设法提高低温环境下的电池性能

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通过可充电电池技术储存能量,我们的数字生活方式从此充满了动力,一方面,可再生的能源又可以被纳入电网。然而,在寒冷条件下的电池功能仍然是一个挑战,促使人们研究改善电池的低温性能。水性电池(在液体溶液中)在低温下的放电速率(衡量每单位时间内放出的能量)方面比非水性电池好。

香港大学的工程师们的新研究最近发表在《纳米研究能源》杂志上,提出了用于低温水溶液电池的水溶液电解质的最佳设计元素。该研究根据几个指标审查了水电解质的物理化学特性(决定其在电池中的性能):相图、离子扩散率和氧化还原反应的动力学。

低温水溶液电池的主要挑战是,电解质冻结,离子扩散缓慢,氧化还原动力学(电子转移过程)因此而迟缓。这些参数与电池中使用的低温水基电解质的物理化学特性密切相关。

因此,为了提高电池在寒冷条件下的性能,需要了解电解质对寒冷(-50 oC至-95 oC / -58 oF至-139 oF)的反应。研究作者和副教授Yi-Chun Lu说:"为了获得高性能的低温水溶液电池(LT-ABs),研究水溶液电解质随温度变化的物理化学特性以指导低温水溶液电解质(LT-AEs)的设计非常重要。"

Design-Strategies-for-Low-Temperature-Aqueous-Electrolytes.jpg

图中显示了水电解质的设计策略,包括防冻热力学、离子扩散动力学和界面氧化还原动力学。

研究人员比较了用于储能技术的各种LT-AE,包括Li+/Na+/K+/H+/Zn2+-电池、超级电容器和流动电池技术。该研究整理了许多其他报告中有关各种LT-AEs性能的信息,例如用于Zn/MnO2水电池的防冻水凝胶电解质;以及用于Zn金属电池的乙二醇(EG)-H2O混合电解质。

他们系统地研究了这些报道的LT-AEs的平衡和非平衡相图,以了解它们的防冻机制。相图显示了电解质相在不同温度下的变化。该研究还考察了LT-AEs的导电性与温度、电解质浓度和电荷载体的关系。

研究作者Lu预测,"理想的防冻水电解质不仅应该表现出低冰点温度Tm,还应该拥有强大的过冷能力",即液体电解质介质甚至在低于冰点温度时仍保持液体状态,从而实现超低温下的离子传输。

研究作者发现,使电池能够在超低温下运行的LT-AEs大多表现出低冰点和强过冷能力。此外,"强大的过冷能力可以通过提高最小结晶时间t和增加电解质的玻璃化温度和冻结温度(Tg/Tm)的比率值来实现"。

通过降低发生离子转移所需的能量,调整电解质的浓度,以及选择某些能促进快速氧化还原反应速率的电荷载体,可以改善所报道的用于电池的LT-AE的电荷传导性。Lu说:"降低扩散激活能,优化电解质浓度,选择具有低水合半径的电荷载体,以及设计协同扩散机制,将是改善LT-AEs离子传导性的有效策略。"

在未来,作者希望进一步研究有助于改善低温下水电池性能的电解质的物理化学特性。Lu说:"我们希望通过设计具有低冰点温度、强过冷能力、高离子导电性和快速界面氧化还原动力学的水基电解质来开发高性能的低温水电池(LT-ABs)。"

A new study by engineers at the University of Hong Kong, recently published in the journal Nano Research Energy, suggests the best design elements for aqueous solution electrolytes for cryogenic aqueous solution batteries. In this study, the physical and chemical properties of water electrolytes (which determine their performance in the battery) are reviewed according to several indicators: phase diagram, ion diffusivity and redox kinetics.

The main challenges of low temperature aqueous solution batteries are electrolyte freezing, slow ion diffusion and slow redox kinetics (electron transfer process). These parameters are closely related to the physical and chemical properties of the low temperature water-based electrolyte used in the battery.

Therefore, in order to improve the performance of the battery under cold conditions, it is necessary to understand the response of electrolytes to cold (- 50 oC to-95 oC /-58 oF to-139 oF). Research author and associate professor Yi-Chun Lu said: & quot; in order to obtain high performance cryogenic aqueous solution battery (LT-ABs), it is very important to study the physical and chemical characteristics of aqueous electrolyte varying with temperature in order to guide the design of cryogenic aqueous electrolyte (LT-AEs). & quot

The figure shows the design strategy of water electrolyte, including antifreezing thermodynamics, ion diffusion kinetics and interfacial redox kinetics.

The researchers compared a variety of LT-AE for energy storage technologies, including Li+/Na+/K+/H+/Zn2+- batteries, supercapacitors and mobile battery technologies. This study collates information from many other reports on the performance of various LT-AEs, such as antifreeze hydrogel electrolytes for Zn/MnO2 water batteries and ethylene glycol (EG)-H2O mixed electrolytes for Zn metal batteries.

They systematically studied the equilibrium and non-equilibrium phase diagrams of these reported LT-AEs to understand their antifreezing mechanisms. The phase diagram shows the change of electrolyte phase at different temperatures. The relationship between the conductivity of LT-AEs and temperature, electrolyte concentration and charge carrier was also investigated.

The author Lu predicted that the ideal antifreeze water electrolyte of quot; should not only show low freezing point temperature Tm, but also have strong supercooling ability & quot;, that is, the liquid electrolyte medium remains liquid even below the freezing point temperature, so as to realize ion transport at ultra-low temperature.

The authors found that most of the LT-AEs which enables the battery to operate at ultra-low temperature show low freezing point and strong supercooling ability. In addition, the strong undercooling ability of & quot; can be realized by increasing the minimum crystallization time t and increasing the ratio of glass transition temperature to freezing temperature (Tg/Tm) of the electrolyte & quot;.

The charge conductivity of the reported LT-AE used in batteries can be improved by reducing the energy required for ion transfer, adjusting the concentration of electrolytes, and selecting some charge carriers that can promote the rapid redox reaction rate. Lu said: & quot; reducing diffusion activation energy, optimizing electrolyte concentration, selecting charge carriers with low hydration radius and designing cooperative diffusion mechanism will be effective strategies to improve the ion conductivity of LT-AEs. & quot

In the future, the author hopes to further study the physical and chemical properties of electrolytes which are helpful to improve the performance of water battery at low temperature. Lu said: & quot; We hope to develop high performance cryogenic water batteries (LT-ABs) by designing water-based electrolytes with low freezing point temperature, strong undercooling capacity, high ionic conductivity and fast interfacial redox kinetics. & quot

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