Excellence in Research: Designing Biodegradable Nonaqueous Electrolytes for Grid-Scale Energy Storage

由于对使用化石燃料的环境关注，可再充电电池在能量存储应用中获得了关注。作为电池中的关键组件，电解质充当用于在一对电极之间转移电荷（通常以离子的形式）的介质。一种类型的电解质是由溶解在溶剂中的盐组成的电解质溶液，所述溶剂为水（水性）或有机分子（非水性）。这些电解质在电池操作期间通常处于液态。尽管具有安全、无毒和低成本的优点，但水性电解质通常具有窄的电化学稳定窗口（即，~1.23 V），超过该值会发生不希望的水电解，从而引发电池电解质和电极的一系列问题。对于含有有机溶剂的非水电解质，主要问题之一是它们的高可燃性，这可能会在电池使用和故障期间引起安全问题。本项目致力于新一代锌离子电池用新型非水电解液的研究。这项基础研究将对进一步推进技术的努力产生深远的影响，从而实现更具成本效益，更安全，更耐用的电池。这些技术的广泛应用和市场支持更多地使用可再生能源产生的能源，这有助于向零碳净未来过渡。该项目还支持本科生和研究生研究人员在多学科的研究经验与外联到STEM教育中代表性不足的群体。所研究的非水电解质是基于溶解在深共熔溶剂（DES）中的Zn盐，其形成三元体系。新系统具有几个优点，包括低成本，不燃性，所需的电化学性能，和环境友好。这代表了可以克服与上述水性和非水性电解质相关的固有问题的新方法。本研究的主要目的是：1）利用差示扫描量热法（DSC）、X射线衍射（XRD）等技术构建二元和三元相图，确定二元和三元体系中各组分的熔点，特别是三元共晶点和各向同性液相区的其他组分; 2）获得具有较低熔点的所选组合物的其它物理和电化学性质，包括密度、粘度、离子电导率和电化学稳定性窗口; 3）通过光谱表征（例如，NMR、拉曼和FTIR）以及原子和分子模拟;以及4）理解阳极/电解质界面行为（例如，电镀/剥离库仑效率，枝晶形成）和阴极/电解质界面（例如，界面稳定性、电化学反应机理）进行了研究。该项目的目的是为DES系统的结构、性质和性能之间的关系提供基本的见解，并促进电网规模能量存储的先进电池电解质的设计。该奖项反映了NSF的法定使命，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。

Rechargeable batteries have gained attention for energy storage applications due to environmental concerns over the use of fossil fuels. As a key component in a battery, an electrolyte serves as a medium for the transfer of charges (typically in the form of ions) between a pair of electrodes. One type of electrolytes is electrolyte solutions consisting of salts dissolved in solvents, either water (aqueous) or organic molecules (nonaqueous). These electrolytes are typically in a liquid state during the battery operation. Despite the advantages of safety, non-toxicity, and low cost, aqueous electrolytes generally have a narrow electrochemical stability window (i.e., ~1.23 V), beyond which undesired water electrolysis occurs, triggering a series of problems for the battery electrolytes and electrodes. For nonaqueous electrolytes with organic solvents, one of the major issues is their high flammability, which might cause safety concerns during battery use and failure. This project addresses the research of novel nonaqueous electrolytes for next-generation Zinc (Zn)-ion batteries. This fundamental research will have a profound impact on efforts to further advance the technologies, enabling more cost-effective, safe, and durable batteries. The broad application and market of these technologies supports the increased use of energy generated from renewable sources, which contributes to the transition to a carbon net-zero future. The project also supports undergraduate and graduate researchers in a multi-disciplinary research experience with outreach to underrepresented groups in STEM education. The nonaqueous electrolytes under study are based on Zn salts dissolved in a deep eutectic solvent (DES), which forms a ternary system. The new system has several advantages including low cost, nonflammability, desired electrochemical performance, and environmental friendliness. This represents a new approach that can overcome the inherent issues associated with the above-mentioned aqueous and nonaqueous electrolytes. The objectives of this research are 1) to construct binary and ternary phase diagrams using differential scanning calorimetry (DSC), X-Ray Diffraction (XRD) and other techniques and determine melting points of various compositions in the individual binary systems and the ternary system, particularly the ternary eutectic point and other compositions in the isotropic liquid phase regions; 2) to obtain other physical and electrochemical properties of the selected compositions with lower melting points, including density, viscosity, ionic conductivity, and electrochemical stability window; 3) to understand the influence of Zn ion and the possible complexes on the molecular interactions and solvation structures in these compositions through spectroscopic characterization (e.g., NMR, Raman, and FTIR) and atomistic and molecular simulation; and 4) to understand anode/electrolyte interfacial behaviors (e.g., plating/stripping Coulombic efficiency, dendrite formation) and cathode/electrolyte interface (e.g., interface stability, electrochemical reaction mechanism) using operando optical microscopy, SEM, and other advanced techniques. The goal of this project is to provide fundamental insights into the relationships among structure, property, and performance for the DES system, and facilitate designing advanced battery electrolytes for grid-scale energy storage.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.