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

由于对使用化石燃料的环境担忧，可充电电池在储能应用方面得到了关注。作为电池的关键部件，电解液充当电荷(通常以离子的形式)在一对电极之间转移的媒介。一种类型的电解质是由溶解于水(水)或有机分子(非水)的溶剂中的盐组成的电解质溶液。在电池运行期间，这些电解液通常处于液体状态。尽管水溶液具有安全、无毒、成本低等优点，但其电化学稳定窗口通常很窄(约1.23V)，超过这个窗口会发生不希望发生的水电解，从而引发电池电解液和电极的一系列问题。对于含有有机溶剂的非水电解液，主要问题之一是它们的易燃性，这可能会在电池使用和故障期间造成安全问题。本项目致力于下一代锌离子电池用新型非水电解液的研究。这项基础性研究将对进一步推进技术进步、实现更具成本效益、更安全和更耐用的电池的努力产生深远影响。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，这有助于向碳净零的未来过渡。该项目还支持本科生和研究生研究人员进行多学科研究，接触STEM教育中代表性不足的群体。所研究的非水电解液是以锌盐为基础，溶解在深共晶溶剂(DES)中，形成三元体系。该新体系具有成本低、不可燃性、期望的电化学性能和环境友好性等优点。这代表了一种新的方法，可以克服与上述水和非水电解质相关的固有问题。本研究的目的是：1)利用差示扫描量热法(DSC)、X射线衍射仪(XRD)等技术绘制二元和三元相图，测定各二元系和三元系中各组分的熔点，特别是各向同性液相区的三元共熔点和其他组分；2)获得熔点较低的组份的其他物理和电化学性能，包括密度、粘度、离子电导率和电化学稳定窗口；3)通过光谱表征(如核磁共振、拉曼和傅立叶变换红外光谱)以及原子和分子模拟，了解锌离子和可能的络合物对这些组成中的分子相互作用和溶剂化结构的影响；以及4)利用OPANDO光学显微镜、扫描电子显微镜和其他先进技术了解阳极/电解液界面行为(例如电镀/剥离库仑效率、树枝晶形成)和阴极/电解液界面(例如界面稳定性、电化学反应机理)。该项目的目标是为DES系统的结构、性能和性能之间的关系提供基本的见解，并促进为电网规模的能量存储设计先进的电池电解液。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.