CAREER: Electronic Transport in Sulfide-Based Lithium Solid Electrolytes

非技术锂离子电池已经成功地为便携式电子设备提供了动力，但它们在电气化、交通运输和电网存储方面的应用面临着安全和能量密度方面的挑战。利用不可燃固体电解液(SE)的固态电池被认为是安全和高能量存储系统的一种有前途的方法。作为一种电化学储能系统，锂离子电池的工作原理是，在充放电过程中，只有离子通过电池内部的电解液在正负极之间穿梭，而电子则通过外部电路流动。电解液应具有高离子导电性但低电子导电性，以确保电子不会直接进入电池内部导致自放电。在改善电池的离子导电性方面已经投入了大量的努力。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传导性却鲜有人研究。这项职业计划旨在研究硫化物基锂固体电解质中的电子输运机制。最终目标是获得关键的科学见解，为高性能固态电池设计电子绝缘SE。多学科研究为研究生和本科生的培养提供了多种机会。该项目涉及教学固体中电荷传输的课程开发和教学创新，并包括面向K-12学生的多项外联活动，特别是那些来自历史和传统代表性不足群体的学生。预计这项拟议的研究将对保持和提升美国电池技术的领先地位，以及实现美国到2050年全面脱碳的战略目标产生影响。预计教育工作还将有助于能源储存领域的STEM教育和劳动力发展。技术总结这一假设驱动的提议旨在了解硫化物基锂固体电解质(SES)中的电子输运机制，包括Li2S-P2S5、Li10GeP2S12和Li6PS5Cl。该项目的研究目标是确定锂硒的本征电子电导率，揭示其与电压的关系，并找出锂硒电子传导的主要原因和电荷载流子。这些目标是通过实验和理论相结合的方法来实现的，包括合成成分、结晶度和微结构可控的陶瓷Se，基于Hebb-Wagner方法的先进的现场电化学测量，以及离子和电子混合导体中少数载流子的缺陷平衡和输运理论。这项研究有望为理解硫化物锂离子电池中的缺陷化学和电子载流子的输运提供重要的见解，并为高能量密度、长日历寿命的固态电池建立电子绝缘电池的设计原则。这项建议还旨在实施一种创新的方法，向电化学能量储存领域的学生介绍“固态离子(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统治中发挥着关键作用，但SSI相关主题的指导主要集中在用于能量转换的燃料电池背景下的氧化物材料。该提案的另一个教育目标是在虚拟现实技术的帮助下开发一个学习模块，用于教授三维、曲折和各向异性的固体电荷传输。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。

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.