Explore Electrocatalysis to Improve the Cathode Performance in Li-S Batteries

锂离子电池是电动汽车和大规模可再生能源存储的领先技术。特别是锂硫电池技术，由于其材料的可用性和高能量密度，是下一代锂离子电池的先驱。该项目将研究一种新的电催化概念，以提高硫化锂电池的性能。具体来说，目标是提高充电/放电速率，抑制电池失活，这两者都限制了当前锂电池的性能。除了技术方面，该项目还包括教育和推广活动，重点关注从初中、高中到研究生阶段的代表性不足的学生。锂电池技术的进步受到几个关键障碍的阻碍，包括元素S和阴极放电产物Li2S的低电导率，高过电位，以及由于可溶性多硫化锂（LiPS）中间体从阴极扩散到与锂阳极反应而导致的S阴极容量快速衰减，众所周知的“穿梭效应”。探索具有强吸附LiPS中间体的过渡金属硫化物电催化剂，以加速S和Li2S这两种不溶性终产物之间的转化。该项目着重于基于新的电催化概念提高阴极性能，使用两种类型的杂化材料作为电催化剂，即二维（2D）原子层状MoS2和准一维链状VS4，两者都强附着在高导电还原氧化石墨烯（rGO）纳米片上。具体目标包括：(1)催化剂的合成和表征（包括它们对LiPS的吸附和电催化转化的能力）；(2)电催化LiPS捕获和转化（分别通过在中间层和S/C阴极中加入杂化材料）；(3)电催化Li2S转化为S。在锂负载的Li2S/C阴极中加入MoS2/rGO和VS4/rGO催化剂，以降低Li2S初始分解的活化能，使Li2S/C阴极稳定可逆。电化学表征将与非原位和operando微拉曼光谱研究相关联，以提供对动态充电/放电过程的良好理解，并提供电催化的机理见解。这些研究将为实现锂电池这一重要的可持续能源技术的全部潜力提供解决方案。除了技术目标外，该项目还为两名研究生和一名本科生提供纳米材料合成/表征、电化学、催化和储能技术的跨学科培训。项目团队将参加暑期STEM夏令营，与高中生/中学生（特别是堪萨斯州的女孩）交流，并提供使用本项目开发的材料的实践研讨会。将通过与路易斯安那州泽维尔大学（XULA），一所历史悠久的黑人学院和大学（HBCU）的强有力合作，开展外展工作，接待来自XULA的访问本科生，在堪萨斯州立大学进行电能存储的夏季研究。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。

Lithium-ion batteries are leading technologies for electric vehicles and large-scale renewable energy storage. Lithium-sulfur battery technology, in particular, is a forerunner of next-generation lithium-ion batteries due to their material availability and their high energy density. The project will investigate a new electrocatalytic concept for improving the performance of lithium sulfide batteries. Specifically, the goal is to enhance charge/discharge rates and suppress battery deactivation, both of which are limiting the performance of current Li-S batteries. Beyond the technical aspects, the project includes educational and outreach activities, focusing on underrepresented students from middle- and high-school to graduate level. Advances in LiS battery technology are hindered by several critical barriers, including the low electrical conductivity of elemental S and discharged product Li2S at the cathode, high overpotentials, and the rapid capacity fading of the S cathode due to diffusion of soluble lithium polysulfide (LiPS) intermediates from the cathode to react with the Li anode, notoriously known as the “shuttle effect”. Transition metal sulfide electrocatalysts with strong adsorption of LiPS intermediates will be explored to accelerate the conversion between S and Li2S, the two insoluble end products. The project focuses on improving the cathode performance based on the new electrocatalytic concept using two types of hybrid materials as the electrocatalysts, i.e. the two-dimensional (2D) atomic layered MoS2 and the quasi-1D chain-like VS4, both strongly attached on highly conductive reduced graphene oxide (rGO) nanosheets. The specific objectives include (1) catalyst synthesis and characterization (including their ability for LiPS adsorption and electrocatalytic conversion); (2) electrocatalytic LiPS trapping and conversion (via hybrid materials incorporation in the interlayer and the S/C cathode, respectively), and (3) electrocatalytic conversion of Li2S to S. The MoS2/rGO and VS4/rGO catalysts will be incorporated in the lithium-loaded Li2S/C cathode to reduce the activation energy of the initial delithiation of Li2S and enable a stable and reversible Li2S/C cathode. Electrochemical characterizations will be correlated with both ex-situ and operando micro-Raman spectroscopy studies to provide a good understanding of the dynamic charge/discharge processes and render mechanistic insights of the electrocatalysis. These studies will provide solutions to realize the full potentials of the Li-S batteries, an important sustainable energy technology. In addition to the technical objectives, this project provides cross-disciplinary training in nanomaterials synthesis/characterization, electrochemistry, catalysis and energy storage technologies to two graduate students and one undergraduate student. The project team will participate in summer STEM camps to engage with high/middle school students (particularly girls in Kansas) and provide hands-on workshops using the materials developed in this project. An outreach effort will be made through a strong collaboration with Xavier University of Louisiana (XULA), a Historically Black Colleges and Universities (HBCU), to host visiting undergraduate students from XULA for summer research on electrical energy storage in Kansas State University.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.