CAREER: Elucidation and Development of Electrolyte and Interface Mechanisms Governing Calcium Redox in Nonaqueous Environments

电化学储能在存储来自间歇性可再生能源（如太阳能和风能）的能量，并使这些能源适合电气化运输方面发挥着关键作用。当今的锂（Li）离子和新兴的基于Li金属的电池具有高能量密度，但是它们沿着对Li资源稀缺的日益关注而遭受安全和性能问题。钙（Ca）是下一代电池的基础：它是地壳中第五丰富的元素，预计使用Ca金属阳极的电池具有与Li对应物相当的储能能力，并具有提高安全性的潜力。然而，Ca电池的开发受到许多挑战的阻碍，包括在Ca金属阳极上形成阻碍可逆性的阻塞界面，以及需要设计针对二价Ca离子电化学特别优化的电解质。这项研究将建立对钙基电化学反应和由此产生的钙金属界面的基本理解。为了实现这些目标，本研究将创建工具来进行新的实验，定量分析钙电解质和界面热化学，这将指导改进的钙电池的设计。作为这项工作的另一个成果，中学生将参与使用这项研究成果的积极虚拟教学模块，同时满足马萨诸塞州的教育标准，使科学家和工程师接触，并激励追求STEM职业。这项研究工作将对化学物质进行有针对性的实验研究，控制Ca离子氧化还原行为并阐明Ca固体电解质界面（SEI）化学和性质的热力学和界面参数。指导这项工作的中心假设是，Ca 2+离子溶剂化的自由度提高，为干预电化学途径提供了新的机会，如果更好地理解，可以解锁可逆性和反应选择性。要开发的工具来测试这一假设包括一个新的热力学框架，用于测量溶剂化的钙状态，使用反应量热法;金属沉积方法，以准备高品质的钙金属界面的基础研究;一个operando的方法来探测化学动力学的钙SEI形成;和阴极转化反应，涉及钙和CO2测试和加强理解的钙2+溶剂化如何影响反应性。结果将被整合，以确定决定电化学参数的基本来源：氧化还原电位，库仑效率，循环寿命和倍率性能，并在其中确定改善它们的策略。总的来说，这项工作将在钙电池的阳极、阴极和电解质方面取得进展。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Electrochemical energy storage plays a critical role in storing energy from intermittent renewable sources, such as solar and wind energy, and making these sources suitable for electrified transportation. Today’s lithium (Li)-ion and emerging Li metal-based batteries have high energy densities, but they suffer from safety and performance issues along with increasing concerns about scarcity of Li resources. Calcium (Ca) presents a compelling alternative as the basis for next-generation batteries: it is the 5th most abundant element in the earth’s crust, and batteries utilizing Ca metal anodes are projected to have energy storage capabilities comparable to Li counterparts with potential for improved safety. However, development of Ca batteries has been hindered by numerous challenges, including formation of blocking interfaces on Ca metal anodes that impede reversibility, and the need to design electrolytes specifically optimized for divalent Ca ion electrochemistry. This research will build the fundamental understanding of Ca-based electrochemical reactions and the resulting interfaces on Ca metal. To achieve these aims, this research will create tools to conduct novel experimental, quantitative analysis of Ca electrolyte and interface thermochemistry that will guide design of improved Ca batteries. As an additional outcome of the work, middle-school students will engage in active virtual teaching modules that use outcomes of this research while fulfilling a Massachusetts state education standard, bringing exposure to scientists and engineers and motivating pursuit of STEM careers.This research effort will conduct a targeted experimental study of the chemical, thermodynamic and interface parameters that govern Ca ion redox behavior and elucidate Ca solid electrolyte interphase (SEI) chemistry and properties. The central hypothesis guiding this work is that the heightened degrees of freedom in Ca2+ ion solvation present new opportunities to intervene in electrochemical pathways, which can allow reversibility and reaction selectivity to be unlocked if better understood. The tools to be developed to test this hypothesis include a new thermodynamic framework for measuring the solvated Ca state using reaction calorimetry; metal deposition methodologies to prepare high-quality Ca metal interfaces for fundamental study; an operando approach to probe the chemical dynamics of Ca SEI formation; and a cathode conversion reaction involving Ca and CO2 to test and strengthen understanding of how Ca2+ solvation affects reactivity. The results will be integrated to identify the fundamental origins that determine electrochemical parameters: redox potential, Coulombic efficiency, cycle life, and rate capability, and therein identify strategies to improve them. Collectively, this work will yield progress in anode, cathode, and electrolyte aspects of Ca batteries.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.