CAREER: Electronic Transport in Sulfide-Based Lithium Solid Electrolytes

锂离子电池已经成功地为便携式电子设备供电，但在电气化运输和电网存储应用中，它们面临着安全性和能量密度的挑战。利用不可燃固体电解质（SEs）的固态电池被认为是一种有前途的安全和高能存储系统。作为一种电化学储能系统，锂离子电池的工作原理是，只有离子通过电池内部的电解质在阴极和阳极之间穿梭，而电子在充电和放电时流经外部电路。电解质应具有高离子导电性和低电子导电性，以确保电子不能直接在电池内部移动而引起自放电。在提高电池SEs离子电导率方面，人们做了大量的工作。然而，对固态电池的寿命、能量密度和循环稳定性有着重要影响的电子导电性却很少得到研究。本项目旨在研究硫化物基锂固体电解质中的电子输运机制。最终目标是为设计用于高性能固态电池的电子绝缘se获得关键的科学见解。多学科研究为培养研究生和本科生科研人员提供了多种机会。该项目涉及课程开发和固体教学费用运输的教学创新，并包括针对K-12学生的多项外展活动，特别是那些历史上和传统上代表性不足的群体。预计拟议的研究将对维持和推进美国电池技术的领先地位以及实现国家到2050年完全脱碳的战略目标产生影响。教育工作也有望有助于STEM教育和储能领域的劳动力发展。技术总结：这个假设驱动的提案旨在了解硫化物基锂固体电解质（SEs）的电子输运机制，包括二元Li2S-P2S5， Li10GeP2S12和Li6PS5Cl。本项目的研究目标是确定锂硒的本征电子导电性，揭示其电压依赖性，确定锂硒电子导电性的主要原因和载流子。这些目标是通过实验和理论方法的结合来实现的，包括合成具有可控成分，结晶度和微观结构的陶瓷SEs，基于Hebb-Wagner方法的先进和原位电化学测量，以及混合离子和电子导体中少数载流子的缺陷平衡和输运理论。该研究有望为理解硫化物基Li se中电子载流子的缺陷化学和输运提供重要见解，并为高能量密度、长寿命固态电池建立电子绝缘se的设计原则。该提案还旨在实施一种创新的方法，向电化学储能领域的学生介绍“固态离子学（SSI）”，即固体中离子和电子缺陷的传输和反应。SSI在锂离子电池的发现和主导中发挥了关键作用，但SSI相关主题的指导主要集中在燃料电池中用于能量转换应用的氧化物基材料。本方案的另一个教育目标是利用虚拟现实技术开发一个学习模块，用于教授固体中的三维、弯曲和各向异性电荷输运。该奖项反映了美国国家科学基金会的法定使命，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。

NON-TECHNICAL SUMMARYLithium-ion batteries have succeeded in powering portable electronics, but they face the challenges of safety and energy density for applications in electrification transportation and grid storage. Solid-state batteries that utilize nonflammable solid electrolytes (SEs) are being considered as a promising approach for safe and high-energy storage systems. As an electrochemical energy storage system, a lithium-ion battery works in a way that only ions shuttle between cathode and anode through an electrolyte inside the battery while electrons flow through the external circuit during charge and discharge. The electrolyte should have a high ionic conductivity but low electronic conductivity to ensure that the electrons cannot travel directly inside the battery to cause self-discharge. Significant efforts have been devoted to improving the ionic conductivity of battery SEs. However, the electronic conductivity, which has important implications in the life-time, energy density, and cycling stability of solid-state batteries has rarely been studied. This CAREER proposal aims to study the mechanisms of electronic transport in sulfide-based Li solid electrolytes. The ultimate goal is to gain critical scientific insights for designing electronically insulating SEs for high-performance solid-state batteries. The multi-disciplinary research provides multiple opportunities for training graduate and undergraduate researchers. The project involves curriculum development and pedagogical innovations for teaching charge transport in solids, and includes multiple outreach activities to K-12 students, particularly those from historically and traditionally underrepresented groups. The proposed research is expected to be impactful with respect to the maintenance and advancement of the US battery technology leadership and achievement of the Nation’s strategic goal of full decarbonization by 2050. The education efforts are also expected to be helpful for STEM education and workforce development in the field of energy storage. TECHNICAL SUMMARYThis hypothesis-driven proposal aims to understand the mechanisms of electronic transport in sulfide-based lithium solid electrolyte (SEs), including binary Li2S-P2S5, Li10GeP2S12, and Li6PS5Cl. The research goals of the project are to determine the intrinsic electronic conductivity of Li SEs, reveal their voltage dependence, and identify the dominant causes and charge carriers for the electronic conduction in Li SEs. These goals are achieved through a combination of experimental and theoretical approaches, including synthesis of ceramic SEs with controlled composition, crystallinity, and microstructure, advanced and in-situ electrochemical measurements based on the Hebb-Wagner approach, and theory of defect equilibria and transport for minority carriers in mixed ionic and electronic conductors. The proposed research is expected to provide critical insights to understand defect chemistry and transport of electronic carriers in sulfide-based Li SEs and establish design principles of electronically insulating SEs for high-energy-density, long-calendar-life solid-state batteries. This proposal aims also to implement an innovative approach for the introduction of “solid state ionics (SSI)” – i.e., transport and reactions of ionic and electronic defects in solids – to students in the field of electrochemical energy storage. SSI play a critical role in the discovery and domination of lithium-ion batteries, but the instruction of SSI-related topics has been primarily focused on oxide-based materials in the context of fuel cells for energy conversion applications. Another educational goal for the proposal is to develop a learning module with the aid of virtual reality technology for teaching three-dimensional, tortuous, and anisotropic charge transport in solids.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.