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储存的领先技术。尤其是锂硫电池技术，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。该项目将探索一种新的电催化概念，以提高硫化锂电池的性能。具体地说，目标是提高充放电率和抑制电池失活，这两者都限制了当前锂-S电池的性能。除技术方面外，该项目还包括教育和外联活动，重点是从初中和高中到研究生的代表性不足的学生。锂离子电池技术的发展受到几个关键障碍的阻碍，包括元素S和放电产物Li2S在阴极的低电导率，高过电位，以及由于可溶的多硫化锂(LiPS)中间体从阴极扩散到锂负极反应而导致的S阴极的快速容量衰减，即众所周知的“穿梭效应”。开发对LiP中间体具有很强吸附能力的过渡金属硫化物电催化剂，以加速S和Li2S这两种不溶最终产物的转化。该项目致力于基于新的电催化概念，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，这两种材料都强烈附着在高导电性的还原氧化石墨烯(RGO)纳米片上。具体目标包括：(1)催化剂的合成和表征(包括对LiP的吸附和电催化转化能力)；(2)电催化LiP的捕集和转化(分别通过在层间和S/C阴极中掺杂杂化材料)；(3)将MoS_2/RGO和VS_4/RGO电催化转化为S。MoS_2/RGO和VS_4/RGO催化剂将被引入到锂负载的Li_2S/C正极中，以降低Li2S初始脱氢的活化能，实现稳定和可逆的Li_2S/C正极。电化学表征将与非原位和操纵面显微拉曼光谱研究相关联，以更好地了解动态充放电过程，并提供对电催化的机理见解。这些研究将为实现锂S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、催化和储能技术方面的跨学科培训。项目小组将参加夏季STEM夏令营，与高中生/中学生(特别是堪萨斯州的女孩)接触，并使用该项目开发的材料提供动手讲习班。将通过与历史上的黑人学院和大学(HBCU)路易斯安那州泽维尔大学(XULA)的大力合作，接待来自XULA的来访本科生，在堪萨斯州立大学进行夏季电能储存研究。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。

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.