High Performance Magnesium Ion Electrolytes

Abstract

Magnesium-ion based battery chemistries have been the subject of intense research because of the inherent high energy density of metallic magnesium anodes. One of the biggest complications that has limited the progress in this area is the development of electrolytes that facilitate the reversible deposition of magnesium metal. Current state of the art electrolytes are based on Grignard-derived magnesium compounds paired with Lewis acids such as aluminum chloride. A few notable exceptions utilize carborane structures as anions, which enable reversible electrochemistry. The presence of chloride ions in many electrolyte solutions has proven to be problematic because they cause pitting and corrode parts commonly used in coin cells. As such, it is imperative that researchers identify pathways that can result in halide-free electrolyte solutions. We have developed a new paradigm for magnesium ion electrolytes, utilizing a robust synthesis pathway that incorporates common reagents. The electrolyte has a large voltage window on stainless steel and aluminum (4-5 V vs. Mg), high conductivity (comparable with lithium ion electrolytes), and near unity Coulombic efficiency. We will discuss characterization of the electrolyte, identity of solution species, and promising methods of modifying the electrolyte for improved figures of merit.