Mechanisms of Water-Stimulated Mg2+ Intercalation in Vanadium Oxide: Toward the Development of Hydrated Vanadium Oxide Cathodes for Mg Batteries

Abstract

As lithium-ion batteries approach their theoretical limits for energy density, magnesium-ion batteries are emerging as a promising next-generation energy storage technology. However, progress in magnesium-ion battery research has been stymied by a lack of available high capacity cathode materials that can reversibly insert magnesium ions. Vanadium Oxide (V2O5) has emerged as one of the more promising candidate cathode materials, owing to its high theoretical capacity, facile synthesis methods, and relatively high operating voltage. This review focuses on the outlook of hydrated V2O5 structures as a high capacity cathode material for magnesium-ion batteries. In general, V2O5 structures exhibit poor experimental capacity for magnesium-ion insertion due to sluggish magnesium-ion insertion kinetics and poor electronic conductivity. However, several decades ago, it was discovered that the addition of water to organic electrolytes significantly improves magnesium-ion insertion into V2O5. This review clarifies the various mechanisms that have been used to explain this observation, from charge shielding to proton insertion, and offers an alternative explanation that examines the possible role of structural hydroxyl groups on the V2O5 surface. While the mechanism still needs to be further studied, this discovery fueled new research into V2O5 electrodes that incorporate water directly as a structural element. The most promising of these hydrated V2O5 materials, many of which incorporate conductive additives, nanostructured architectures, and thin film morphologies, are discussed. Ultimately, however, these hydrated V2O5 structures still face a significant barrier to potential applications in magnesium-ion batteries. During full cell electrochemical cycling, these hydrated structures tend to leach water into the electrolyte and passivate the surface of the magnesium anode, leading to poor cycle life and low capacity retention. Recently, some promising strides have been made to remedy this problem, including the use of artificial solid electrolyte interphase layers as an anode protection scheme, but a call to action for more anode protection strategies that are compatible with trace water and magnesium metal is required.

Progress in high-voltage MgMn2O4 oxyspinel cathode materials for Mg batteries

“…TFSIanions in Mg(TFSI)2), resulting in more "free" Mg 2+ ions available in the electrolyte solution. 44 Another possible explanation for the higher capacity in aqueous electrolytes is proton cycling however, further investigations are required to clarify the observed variabilities in the specific capacity as well as the role of solvent co-intercalation on improving Mg 2+ ion kinetics and its compatibility with the Mg metal anode. Indeed, while water-containing organic and aqueous electrolytes seem to be an ideal choice compared to non-aqueous systems in terms of cathode performance, these preclude from the use of Mg metal due to the formation of a nonconducting and passivating film on its surface consisting mainly of Mg(OH)2 and MgO.…”

Interlayer‐Expanded MoS2 Containing Structural Water with Enhanced Magnesium Diffusion Kinetics and Durability

“…Considering the octahedral coordination preference of Mg 2 + in aqueous electrolyte, the n value is set at 6 ([Mg(H 2 O) 6 ] 2 + , Figure 1b). [16,17,21,30,31] The absorption energy of [Mg(H 2 O) 6 ] 2 + in OÀ MoS 2 is calculated to be À 1.80 eV, significantly more negative [Eq. ( 2)]:…”

“…Among the introduced species, the size of water molecule (H 2 O) is small, avoiding blocking Mg-diffusion kinetics in MoS 2 interlayers. [3,5,16,17] Moreover, the dipolar nature of H 2 O makes it acting a role of charge-shielding layers to reduce the electrostatic intercalation between Mg 2 + and MoS 2 frameworks, accelerating the mobility of Mg 2 + . [18][19][20] In the present work, oxygen-doped MoS 2 (OÀ MoS 2 ) with an enlarged interlayer spacing of 0.94 nm is prepared by a hydrothermal method, and H 2 O is incorporated into its interlayers by an electrochemical assistant method in aqueous electrolyte.…”

“…Under the circumstances, the incorporated ions or molecules play the important role to hold the modified structures. Among the introduced species, the size of water molecule (H 2 O) is small, avoiding blocking Mg‐diffusion kinetics in MoS 2 interlayers [3,5,16,17] . Moreover, the dipolar nature of H 2 O makes it acting a role of charge‐shielding layers to reduce the electrostatic intercalation between Mg 2+ and MoS 2 frameworks, accelerating the mobility of Mg 2+ [18–20] …”

Review on Action Mechanism and Characterization of Natural/Artificial Solid Electrolyte Interphase of Lithium Battery: Latest Progress and Future Directions

“…Not only that, the size of the SEI itself will also affect its own stability. For example, when Bian et al studied tea polyphenols (TP) as a new reactive electrolyte additive applied to lithium-ion batteries, − they found that the additive TP can remove ethylene carbonate and form a stable polymer. It is concluded that the thickness of the SEI film will affect its own stability, and the additive TP can react with unstable free radicals to form a polymer, which greatly improves the stability of the SEI film.…”