Design of a Novel Apparatus for the in-situ Formulation and Characterization of Safer Electrolytes

LIB和SC都是替代储能装置，它们分别通过轨道电子交换（化学）和静电（物理）分离正负电荷来存储能量。这些商业电化学装置中使用的大多数液体电解质都是通过将盐（如锂盐）或四氟硼酸四乙基铵分别溶解在烷基碳酸盐混合物或乙腈（ACN）等特定溶剂中获得的。然而，与所选电解质的稳定性有关的许多问题限制了它们的使用寿命。例如，文献报道，当高电位作用于电极时，锂离子电池电解质在高电位下的氧化反应导致甲烷、乙烷、二氧化碳和一氧化碳等气体的形成，这增加了密封电池内的压力，从而改变了电解质的物理性质。而在SC案例中，与使用四氟硼酸四乙基铵和ACN基电解质有关的主要问题是其安全性，因为在某些特殊条件下，ACN在燃烧时会产生氰化氢（HCN）。实际上，HCN的产生量取决于ACN的体积、火的温度和环境。然而，如果不同时了解它们在存在和不存在外部刺激（气体、温度等）的情况下的热力学性质、流体相平衡和电化学性质，就无法对这些问题进行评估。该项目将通过首先开发一种基于等时饱和度技术的新型原始设备来解决这一问题，该设备使用气相色谱法分析气相组成，结合不同的电化学设备(伏安计，电位器或gavalnostat)，允许通过pVTxy测量在实际条件下同时测定流体相平衡，以及用于LIB和SC应用的各种电解质的电化学特性，以了解限制电解质使用寿命和安全性的因素。此外，在这个项目中，一种方法包括研究离子液体，ILs，作为添加剂组分，而不是作为介质，也将在有用的技术溶剂中进行研究，如烷基碳酸盐（用于LIB），乙腈和其他二腈结构（用于SC）。这样做的目的是为了保持每种溶剂的优点，并通过添加少量的IL来改善它们的缺点（腐蚀性，挥发性）。为了澄清IL和熔盐之间的区别，我们还将研究使用四氟硼酸四乙基铵在sc中的类似经验。为此，我们计划将重点放在电解质配方对其独特性质的影响上，如溶剂化，体积，热，利用本项目提出的原始装置和QUB已经开发的不同实验和理论技术进行电化学、热力学和输运性质的研究。此外，每种电解质的电化学稳定性将通过应用不同的充放电循环来确定，并通过分析气相组成随时间和温度的变化来确定。此外，还将就地研究乙烷和二氧化碳等降解产物对电解质性能的影响。通过对所选电解质中乙烷和二氧化碳溶解度的测定，得出使用熔盐代替传统熔盐的主要优点和缺点，并提出提高锂离子电池和锂离子电池应用中电解质稳定性的关键参数。

LIB and SC are both alternative energy storage devices, which store energy via orbital electron exchange (chemically) and by electrostatically (physically) separating positive and negative charges, respectively. Most liquid electrolytes used in these commercial electrochemical devices are obtained by dissolving a salt like lithium salt, or tetraethylammonium tetrafluoroborate in a specific solvent like alkylcarbonate mixture or the acetonitrile (ACN), respectively. Nevertheless, many issues often linked to the stability of selected electrolytes limit their lifetime. For example, it is reported in the literature that the oxidation reaction of the LIB electrolyte at high potentials leads to the formation of gases like methane, ethane, carbon dioxide and carbon monoxide when high potentials are applied to the electrode, which increases the pressure inside the sealed cell and modify then the physical properties of the electrolytes. While in the case of SC, the main issue links to the use of the tetraethylammonium tetrafluoroborate and ACN-based electrolyte is its safety since under certain special conditions ACN can produce hydrogen cyanide (HCN) when is burned. In fact, amount of HCN produced depends on volume of ACN, temperature of fire and environment. Nevertheless, these issues cannot be evaluated without the simultaneous knowledge of their thermodynamic properties, fluid phase equilibria and electrochemical properties in presence and in absence of external stimulus (presence of gas, temperature, etc.). This project will address this perspective by developing first a new and original apparatus based on an isochoric saturation technique, supplied by an analysis of the gas phase composition using a Gas Chromatography, combined with different electrochemical devices (voltamperometer, potentiostat or gavalnostat) that allows the simultaneous determination in real conditions of the fluid phase equilibria through pVTxy measurements and the electrochemical properties of a wide range of electrolytes for LIB and SC applications in order to understand factors, which limit electrolytes lifetime and safety. Additionally, during this project, an approach which consists to cover these properties with the objectives to study ionic liquids, ILs, as an additive component, and not as a media, will be also investigated in useful technological solvents like alkylcarbonates (for their uses in LIB), acetonitrile and other dinitrile structures (for their uses in SC). This choice was made with the objective to keep the advantages of each solvent and improve their disadvantages (corrosive, volatile) by adding small quantity of IL. To clarify the differences between ILs and molten salts, similar experiences will be also investigated using the tetraethylammonium tetrafluoroborate for its use in SC.For that, we plan to focus then our effort on the effect of the electrolyte formulation on their unique properties like the solvation, volumetric, thermal, electrochemical, thermodynamic and transport properties by using the original apparatus proposed in this project and different experimental and theoretical techniques already available and developed at QUB. Additionally, the electrochemical stability of each electrolyte will be determined by applying different charge-discharge cycles and by analysing then the gas phase composition changes over the time and temperature. Furthermore, the effect of presence of degradation products, like ethane and carbon dioxide, on the properties of the electrolytes will be also investigated in situ. The determination of the ethane and carbon dioxide solubility in the selected electrolytes will be then determined to dress some conclusions on the main advantages and disadvantages to use ILs rather than classical molten salts, as well as, to propose key parameters to improve the stability of electrolytes for LIB and SC applications.