A Multiscale Approach to Magnesium Intercalation Batteries: Safer, Lighter, and Longer-Lasting

Research Goal: The goal of this research has been to design and develop the basic building blocks of inherently safer electrochemical energy storage vectors as replacements for conventional Li-ion batteries. A focus was placed on exploring metastable phase space to identify viable vanadium oxide cathode materials that are capable of reversibly inserting multivalent ions and Li ions from aqueous electrolytes. These materials have been developed with an eye towards the design of all-printed batteries.

Brief Background and Motivation: Lithium-ion batteries are the gold-standard for electrochemical energy storage due to their unrivaled combination of high voltage and exceptional specific and volumetric energy densities; however, the development of ‘beyond-Li-ion’ battery technologies has received considerable attention in an attempt to mitigate growing safety concerns, rising materials criticality constraints, and energy storage limitations enforced by the monovalency of the Li-ion. Safety issues in Li-ion batteries are derived from the intrinsic reactivity of Li and manifest in catastrophic failure arising from dendrite formation and1,2 thermal runaway,2,3 which are further exacerbated by the high flammability of most Li-ion battery electrolytes2. These safety problems are of great concern, particularly in applications, such as manned space flight, where safety and device endurance are paramount. The development of inherently safer battery technologies that do not compromise on energy storage capacity is thus an urgent imperative.

In the case of Mg-ion batteries, it has been argued that the full realization of Mg batteries (i.e., an Mg battery which includes a metallic Mg anode) would enable significant improvements to both safety (e.g., it has been claimed that Mg is not dendrite forming, Mg has a higher melting point than Li thereby reducing the risk of thermal runaway)12 and energy storage density thereby making them safer, lighter and longer-lasting. Indeed, the projected improvements in the volumetric and specific energy densities enabled by this technological pivot would lead to transformational reductions in weight and volume of the packaged cells, relative to existing Li-ion cells, in principle establishing Mg batteries an immediately attractive alternative to Li-ion technology.19 However, the lack of suitable cathode materials capable of reversibly storing the highly polarizing Mg2+ (only a couple of viable oxide materials)17,20–25 has significantly stymied progress towards their full realization. 
In an effort to address this technological knowledge gap, this research has focused on leveraging the discovery of a successful ζ-V2O5 Mg-ion cathode, a major breakthrough during the first year of this NASA NSTR fellowship, towards the development and optimization of additional cathode materials. A closed-loop design approach, has been implemented to elucidate cathode design principles based on experimental evaluation of V2O5 intercalation cathode materials and aided by first-principles calculations and synchrotron characterization techniques.20,26 This approach has led to the discovery of several new V2O5 polymorphs (γ’-V2O5, β-V2O5, λ-V2O5) that have exhibited promising results as cathode materials in Li-ion, multivalent ion, and aqueous Li-ion batteries. Attention has furthermore been given to scaling the synthesis of these materials to enable the design of large-scale prototypes. While this research has focused on the fundamental aspects of the chemistry of these materials it has also sought to achieve functional devices, with a focus on 3D printing of these materials for the design of flexible batteries.

Brief Summary of Specific Results: The research conducted over the course of this fellowship represents a significant step forward in the design of cathode materials for multivalent batteries. We have discovered and characterized the first high-voltage, high-capacity oxide cathode materials for Mg-ion batteries, ζ-V2O5. We have demonstrated that this material can further be used to achieve high capacities in traditional Li-ion battery configurations and is stable while cycling in aqueous Li-ion batteries. We have applied insight from these discoveries to design and synthesize three new polymorphs of V2O5, some of which have demonstrated good cycling in Mg-ion and Ca-ion configurations. While working at NASA facilities, we have adapted these materials, as well as Mg nanoparticles to 2D and 3D printing applications towards fully printable Li- and Mg-ion batteries