Hydrated Mg_xV₅O₁₂ Cathode with Improved Mg²⁺ Storage Performance

Abstract

Li + (0.76 Å) holds a great potential to deliver remarkable theoretical energy storage metrics. [10,11] Despite the straightforward concept of taking advantage of a divalent cation, developing rechargeable and stable MIBs has been plagued by various materials limitations, especially the lack of suitable intercalation electrode materials and stable electrolytes featuring wide electrochemical windows. [12-15] Indeed, the greatest of these limitations on simulating the working mechanism of LIBs using intercalation cathodes and anodes is primarily caused by the sluggish solid-state diffusion of divalent Mg ion. This is strongly related to the large polarization of anionic frameworks of electrodes and more intense repulsions among the intercalated divalent Mg ions due to a higher charge-to-radius ratio of Mg 2+ compared to Li +. [16-18] Because of heavy anionic frameworks and moderate polarity of anions, the classical Mo 6 S 8 Chevrel phases and transition metal dichalcogenides show an Mg 2+ screening effect, [19,20] mitigating the solid-state diffusion difficulty of Mg 2+ to some extent. However, the facilitation of Mg 2+ diffusion within these electrode frameworks comes at the cost of average operating potentials (≈1 V vs Mg/Mg 2+) and gravimetric capacities, thus leading to low energy densities. [21,22] Noticeably, the low redox potential feature of these chalcogenide electrodes reveals that they are anodes virtually upon assembling to full MIBs, if cathodes with high operating potentials are applied. Switching to transition metal oxide electrodes can fundamentally elevate operating potentials and increase specific capacities. [20,23-25] Nonetheless, the bivalency nature of Mg 2+ imposes a large energy penalty during the desolvation process at the electrode/electrolyte interface, resulting in insufficient power densities. To improve the rate capability, nanostructure engineering (e.g., increasing interlayer spacing of layered electrodes) and chemical composition control (e.g., structural H 2 O, cation doping) of oxide electrodes can be conducted to modify the kinetics and thermodynamics of Mg 2+ insertion. [26-28] Orthorhombic single-layered V 2 O 5 , consisting of alternating corner-and edge-sharing VO 5 square pyramids (Figure S1, Supporting Information), allows the diffusion of small, monovalent Li ions through the framework. However, the limited interlayer spacing of ≈4.5 Å is not sufficient for the intercalation of larger (e.g., Na +) or multivalent (e.g., Mg 2+) cations. [7,29,30] Employing single-layered V 2 O 5 to design bilayered vanadium bronzes through different chemical approaches enables the applicability Mg-ion batteries (MIBs) possess promising advantages over monovalent Li-ion battery technology. However, one of the myriad obstacles in realizing highly efficient MIBs is a limited selection of cathode materials that can enable reversible, stable Mg 2+ intercalation at a high operating voltage. Here, a scalable method is showcased to synthesize a hydrated Mg x V 5 O 12 cathode, which shows a high capa...

An Aqueous Mg2+‐Based Dual‐Ion Battery with High Power Density

“…[ 6,7 ] Mitigating these issues typically requires heavy chalcogenides with soft anion lattices, such as state‐of‐the‐art Mo 6 S 8 Chevrel phases, to screen the charge of Mg 2+ so as to facilitate Mg 2+ diffusion at high temperature (typically ≥ 50 °C). [ 8–10 ] However, this strategy compromises the specific capacities and operating potentials (≈1 V versus Mg/Mg 2+ ).…”

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)]:…”

“…In the published reports, H 2 O is introduced into interlayers of 2D hosts such as V 2 O 5 or δ-MnO 2 , [30,34] and its charge shielding effect weaken the electrostatic between Mg 2 + and host frameworks, thus facilitating the mobility of Mg 2 + . Herein, EIS analysis is employed to characterize the diffusion coefficient of Mg 2 + in OÀ MoS 2 and HÀ MoS 2 .…”

Layered electrode materials for non-aqueous multivalent metal batteries

“…Metal atom incorporation into V 2 O 5 interlayers (e.g., Mg, Mn, or Na) [135][136][137][138][139] represents another effective strategy to promote the stability of layered V 2 O 5 . For instance, Mg incorporation was achieved through electrochemically discharging V 2 O 5 nanowires to 0.2 V vs. Mg 2+ /Mg.…”