(Invited) Current Status and Bottlenecks of the Intercalation of Mg into Spinel Oxides

摘要

Electrochemical energy storage was an important enabler of the wireless revolution and it is touted as a key component of a society that shifts away from its dependence on fossil fuels. Li-ion batteries are the primary technology when high energy devices are required. However, despite their improved functionality over older systems (e.g. lead-acid car batteries), they do not quite yet meet the emerging energy demands in transportation and grid markets. This roadblock sparked interest in the development of batteries that utilize Mg~(2+) as ionic carrier. Theoretical predictions indicate that couples exist between a Mg metal negative electrode and oxide positive electrodes that could surpass the current practical limits of current devices. However, severe practical challenges have limited the study of the electrochemical properties of oxides to the simple elucidation of the viability and reversibility of the fundamental reactions of intercalation of Mg~(2+). Among the candidate oxides, the general family of spinel-type M_2O_4 (M=transition metal) are considered as leading contenders. In this talk, we will present the most up-to-date insight into the ability of spinel oxides to diffuse Mg~(2+). These observations will be paired with the outcomes of electrochemical reactions in nonaqueous electrolytes, since the use of Mg metal requires rigorously anhydrous environments. We will discuss the evidence supporting intercalation of Mg~(2+), and describe changes that correlate with both the identity of M and the existence of defects in the spinel structure. Critical to the endeavor is the ability to synthesize particles at small dimensions, as is the characterization of chemical and physical phenomena using a combination of tools providing information at different scales. The discussion will naturally lead us to reveal foundational bottlenecks that must be overcome to make Mg electrochemistry viable for energy storage.