High Capacity Mg Batteries Based on Inert and Non-Nucleophilic Carborane Electrolytes

University Of California-Riverside, Riverside CA

Investigators

Abstract

Non-Technical Abstract Over the last decade there has been an explosion of technological advances in rechargeable portable devices and electric vehicles. However, innovations that reduce the cost, improve the sustainability, and increase the storage capacity offered by state-of-the-art Li-ion technology have not kept pace with this revolution. In addition, Li-ion batteries can undergo catastrophic failure, which results in unpredictable fires. Mg-based batteries are an attractive alternative to Li-ion systems because Mg is less expensive, much more abundant, inherently safer, and can store twice the amount of charge. With the support from the Solid State and Materials Chemistry program in the Division of Materials Research, this project will develop Mg-batteries that are more powerful and cost effective than traditional Li-ion systems. A key enabling factor of this project is the implementation of special electrolytes composed of collections of carbon and boron atoms called carboranes. Undergraduate and graduate students in the Chemistry Department at the University of California Riverside (UCR) are mentored in this program and participate in research. Additionally, the Principal Investigator (PI) and Co-PI have integrated a mentorship program into the project for disadvantaged high school students. In the summer months, these high school students participate in the proposed research at UCR. The anticipated outcome of these activities is the increased recruitment and retention of students from underrepresented groups in STEM fields. Technical Abstract Mg-based batteries are an attractive alternative to Li-ion systems, but suitable electrolytes are lacking. Electrolytes for Mg batteries must be completely resistant to decomposition and ideally non-nucleophilic. The goal of this project is to produce Mg-based batteries that are less expensive, inherently safer, more sustainable and powerful than state-of-the-art-Li-ion technology. A key feature of this work is implementing inert and non-nucleophilic carborane based electrolytes, which will enable the realization of high capacity Mg-batteries. This project will be accomplished via three specific aims. Aim 1 utilizes novel chemical reduction methodology to prepare halide free electrolytes of simple dicationic Mg carborane salts. Because the carborane anions are both highly oxidatively stable and non-nucleophilic, they are suitable for applications as Mg battery electrolytes for systems that utilize either high voltage intercalation or S cathodes. Aim 2 encompasses the design of monocationic carborane electrolytes featuring supporting ligands. Implementation of novel transmetalation methodology allows access to monocationic Mg complexes that contain carborane counter anions, which are suitable electrolytes for high voltage intercalation cathodes. In addition, the preparation of sulfur compatible "passivated" electrolytes derived from the reaction of N-Heterocyclic Carbenes (NHCs) with S8 is under investigation. In Aim 3, the electrolytes prepared in Aims 1 and 2 are coupled with suitable cathode materials to produce prototype rechargeable Mg-batteries. Both layered molybdenum and vanadium sulfides as well as thiospinel vanadium and chromium sulfides are utilized as intercalation type cathodes. In addition, sulfur cathodes based on sulfur-carbon composites with two types of carbon hosts having distinctly different pore sizes are under investigation.