Water-Pillared Sodium Vanadium Bronze Nanowires for Enhanced Rechargeable Magnesium Ion Storage

Progress and Challenges of Vanadium Oxide Cathodes for Rechargeable Magnesium Batteries

Among the challenges related to rechargeable magnesium batteries (RMBs) still not resolved are positive electrode materials with sufficient charge storage and rate capability as well as stability and raw material resources. Out of the materials proposed and studied so far, vanadium oxides stand out for these requirements, but significant further improvements are expected and required. They will be based on new materials and an improved understanding of their mode of operation. This report provides a critical review focused on this material, which is embedded in a brief overview on the general subject. It starts with the main strategic ways to design layered vanadium oxides cathodes for RMBs. Taking these examples in more detail, the typical issues and challenges often missed in broader overviews and reviews are discussed. In particular, issues related to the electrochemistry of intercalation processes in layered vanadium oxides; advantageous strategies for the development of vanadium oxide composite cathodes; their mechanism in aqueous, "wet", and dry non-aqueous aprotic systems; and the possibility of co-intercalation processes involving protons and magnesium ions are considered. The perspectives for future development of vanadium oxide-based cathode materials are finally discussed and summarized.

H2O-Mg2+ Waltz-Like Shuttle Enables High-Capacity and Ultralong-Life Magnesium-Ion Batteries

Mg-ion batteries (MIBs) are promising next-generation secondary batteries, but suffer from sluggish Mg2+ migration kinetics and structural collapse of the cathode materials. Here, an H2O-Mg2+ waltz-like shuttle mechanism in the lamellar cathode, which is realized by the coordination, adaptive rotation and flipping, and co-migration of lattice H2O molecules with inserted Mg2+, leading to the fast Mg2+ migration kinetics, is reported; after Mg2+ extraction, the lattice H2O molecules rearrange to stabilize the lamellar structure, eliminating structural collapse of the cathode. Consequently, the demo cathode of Mg0.75V10O24·nH2O (MVOH) exhibits a high capacity of 350 mAh g-1 at a current density of 50 mA g-1 and maintains a capacity of 70 mAh g-1 at 4 A g-1. The full aqueous MIB based on MVOH delivers an ultralong lifespan of 5000 cycles The reported waltz-like shuttle mechanism of lattice H2O provides a novel strategy to develop high-performance cathodes for MIBs as well as other multivalent-ion batteries.

In-situ dynamic catalysis electrode electrolyte interphase enabling Mg2+ insertion in 2D metal-organic polymer for high-capacity and long-lifespan magnesium batteries

Rechargeable magnesium battery is regarded as the promising candidate for the next generation of high-specific-energy storage systems. Nevertheless, issues related to severe Mg-Cl dissociation at the electrolyte-electrode interface impede the insertion of Mg2+ into most materials, leading to severe polarization and low utilization of Mg-storage electrodes. In this study, a metal-organic polymer (MOP) Ni-TABQ (Ni-coordinated tetramino-benzoquinone) with superior surface catalytic activity is proposed to achieve the high-capacity Mg-MOP battery. The layered Ni-TABQ cathode, featuring a unique 2D π-d linear conjugated structure, effectively reduces the dissociation energy of MgxCly clusters at the Janus interface, thereby facilitating Mg2+ insertion. Due to the high utilization of active sites, Ni-TABQ achieves high capacities of 410 mAh/g at 200 mA g-1, attributable to a four-electron redox process involving two redox centers, benzoid carbonyls, and imines. This research highlights the importance of surface electrochemical processes in rechargeable magnesium batteries and paves the way for future development in multivalent metal-ion batteries.

Bilayered nanostructured V2O5 nH2O xerogel constructed 2D nano-papers for efficient aqueous zinc/magnesium ion storage

Aqueous zinc ion batteries (AZIBs) and aqueous magnesium ion batteries (AMIBs) offer powerful alternatives for large-scale energy storage because of their high safety and low cost. Consequently, the design of high-performance cathode materials is essential. In this paper, we present a simple strategy that combines oxygen defect (Od) engineering with a 2D-on-2D homogeneous nanopape-like bilayer V2O5 nH2O xerogel (BL-HVOd NPS). This strategy employs Od to improve Zn2+/Mg2+insertion/extraction kinetics and reduce irreversible processes for high-performance AZIBs/AMIBs. And interlayer water molecules serve as an effective spacer to stabilize the expanded interlayer gap in BL-HVOd NPS, thereby providing extended diffusion channels for Zn2+/Mg2+ during insertion/extraction. The interlayer water molecules help shield the electrostatic interaction between Zn2+/Mg2+ and BL-HVOd NPS lattice, which improves diffusion kinetics during repeated. In addition, electrochemical characterization results indicate that the BL-HVOd NPS can effectively the surface adsorption and internal diffusion of Zn2+/Mg2+. More importantly, the successfully prepared unique 2D-on-2D homogenous nanopaper structure enhances electrolyte/electrode contact and reduces the migration/diffusion path of electrons/Zn2+ and Mg2+, thus greatly improving rate performance. As a result, the BL-HVOd NPS as AZIBs/AMIBs electrodes offer better reversible capacity of 361.8 and 162.8 mA h g-1 (at 0.2 A g-1), while displaying impressively long cycle lifes. This method provides a way to prepare advanced xerogel cathode materials for AZIBs and AMIBs.

Dual-Defect Engineering Strategy Enables High-Durability Rechargeable Magnesium-Metal Batteries

Rechargeable magnesium-metal batteries (RMMBs) are promising next-generation secondary batteries; however, their development is inhibited by the low capacity and short cycle lifespan of cathodes. Although various strategies have been devised to enhance the Mg2+ migration kinetics and structural stability of cathodes, they fail to improve electronic conductivity, rendering the cathodes incompatible with magnesium-metal anodes. Herein, we propose a dual-defect engineering strategy, namely, the incorporation of Mg2+ pre-intercalation defect (P-Mgd) and oxygen defect (Od), to simultaneously improve the Mg2+ migration kinetics, structural stability, and electronic conductivity of the cathodes of RMMBs. Using lamellar V2O5·nH2O as a demo cathode material, we prepare a cathode comprising Mg0.07V2O5·1.4H2O nanobelts composited with reduced graphene oxide (MVOH/rGO) with P-Mgd and Od. The Od enlarges interlayer spacing, accelerates Mg2+ migration kinetics, and prevents structural collapse, while the P-Mgd stabilizes the lamellar structure and increases electronic conductivity. Consequently, the MVOH/rGO cathode exhibits a high capacity of 197 mAh g-1, and the developed Mg foil//MVOH/rGO full cell demonstrates an incredible lifespan of 850 cycles at 0.1 A g-1, capable of powering a light-emitting diode. The proposed dual-defect engineering strategy provides new insights into developing high-durability, high-capacity cathodes, advancing the practical application of RMMBs, and other new secondary batteries.

De-Ammonium Ba0.18V2O4.95/NH4V4O10 Film Electrodes as High-Performance Cathode Materials for Magnesium-Ion Batteries

Magnesium-ion batteries (MIBs) have been pushed into the research boom in the post-lithium-ion batteries era due to their low cost, no dendrite hazard, and high capacity. However, finding suitable cathode materials to improve the slow kinetics of Mg2+ is an ongoing challenge. In this work, Ba0.18V2O4.95/NH4V4O10 film electrodes were grown in one step on indium tin oxide (ITO) conductive glass using a low-temperature liquid-phase deposition method. Temperature was used as the probe condition, and it was concluded that the films annealed at 400 °C had suitable crystallinity and de-ammonium lattice space. At lower current density, with 0.5 M Mg(ClO4)2/PC as the electrolyte, it exhibited an initial discharge capacity of 130.99 mA h m-2 at 210 mA m-2 and 106.52% capacity retention after 100 cycles. In addition, it exhibited excellent electrochemical performance in long-term cycling (92.98% capacity retention after 300 cycles at 600 mA m-2). According to the results of ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), the removal of NH4+ created more lattice space, assisting Ba0.18V2O4.95 to increase the transfer channels of Mg2+, providing more active sites to promote diffusion kinetics (the average DMg2+ was 2.07 × 10-12 cm2 s-1) and specific capacity. Therefore, these film electrodes for scalable Mg2+ storage are promising MIB cathode candidates that exhibit good performance advantages in storage applications.

Theoretical Progress of 2D Six-Membered-Ring Inorganic Materials as Anodes for Non-Lithium-Ion Batteries

The use and storage of renewable and clean energy has become an important trend due to resource depletion, environmental pollution, and the rising price of refined fossil fuels. Confined by the limited resource and uneven distribution of lithium, non-lithium-ion batteries have become a new focus for energy storage. The six-membered-ring (SMR) is a common structural unit for numerous material systems. 2D SMR inorganic materials have unique advantages in the field of non-lithium energy storage, such as fast electrochemical reactions, abundant active sites and adjustable band gap. First-principles calculations based on density functional theory (DFT) can provide a basic understanding of materials at the atomic-level and establish the relationship between SMR structural units and electrochemical energy storage. In this review, the theoretical progress of 2D SMR inorganic materials in the field of non-lithium-ion batteries in recent years is discussed to summarize the common relationship among 2D SMR non-lithium energy storage anodes. Finally, the existing challenges are analyzed and potential solutions are proposed.

Size-Controllable Nickel Sulfide Nanoparticles Embedded in Carbon Nanofibers as High-Rate Conversion Cathodes for Hybrid Mg-Based Battery

The integration of highly-safe Mg anode and fast Li+ kinetics endows hybrid Mg2+ /Li+ batteries (MLIBs) a promising future, but the practical application is circumvented by the lack of appropriate cathodes that enable the realization of an enough participation of Mg2+ in the reactions, resulting in a high dependence on Li+ . Herein, the authors develop a series of size-controllable nickel sulfide nanoparticles embedded in carbon nanofibers (NiS@C) with synergistic effect of particle diameter and carbon content as the cathode material for MLIBs. The optimized particle size is designed to maximize the utilization of the active material and remit internal stress, and appropriate carbon encapsulation efficiently inhibiting the pulverization of particles and accelerates the ability of conducting ions and electrons. In consequence, the representative NiS@C delivers superior electrochemical performance with a highest discharge capacity of 435 mAh g-1 at 50 mA g-1 . Such conversion cathode also exhibits excellent rate performance and remarkable cycle life. Significantly, the conversion mechanism of NiS in MLIBs is unambiguously demonstrated for the first time, affirming the corporate involvement of both Mg2+ and Li+ at the cathodic side. This work underlines a guide for developing conversion-type materials with high rate capability and cyclic performance for energy storage applications.

Bimetallic sulfide NiCo2S4 yolk-shell nanospheres as high-performance cathode materials for rechargeable magnesium batteries

Constructing bimetallic sulfides with ideal structures could effectively alleviate the poor cycling stability of rechargeable Mg batteries due to a bimetallic synergistic effect. An exquisite yolk-shell structured bimetallic sulfide NiCo₂S₄ synthesized via a two-step solvothermal hydrothermal method is investigated as a cathode material for rechargeable Mg batteries. With the bimetallic strategy and well-designed architecture, the as-synthesized yolk-shell NiCo₂S₄ exhibits outstanding Mg-storage performance, demonstrating a superior reversible capacity (270 mA h g^-1 at 50 mA h g^-1), a high rate capability, and a specific capacity retention of 91% over 400 cycles (2.2% capacity decay per cycle). The in-depth mechanism investigation reveals the two-step conversion reaction process and the bimetallic synergistic effect in the Mg-storage process. Based on DFT calculations and kinetic investigations, the bimetallic synergistic effect effectively alleviates the Jahn-Teller effect and distortion in the crystal lattices and increases active reaction sites, thus largely enhancing the electrochemical Mg-storage performance. The superior electrochemical performance of NiCo₂S₄ not only demonstrates the viability of the bimetallic strategy but also sheds light on the use of nanostructure design for high-performance cathode research.

Atomically Thin Materials for Next-Generation Rechargeable Batteries

Atomically thin materials (ATMs) with thicknesses in the atomic scale (typically <5 nm) offer inherent advantages of large specific surface areas, proper crystal lattice distortion, abundant surface dangling bonds, and strong in-plane chemical bonds, making them ideal 2D platforms to construct high-performance electrode materials for rechargeable metal-ion batteries, metal-sulfur batteries, and metal-air batteries. This work reviews the synthesis and electronic property tuning of state-of-the-art ATMs, including graphene and graphene derivatives (GE/GO/rGO), graphitic carbon nitride (g-C₃N₄), phosphorene, covalent organic frameworks (COFs), layered transition metal dichalcogenides (TMDs), transition metal carbides, carbonitrides, and nitrides (MXenes), transition metal oxides (TMOs), and metal-organic frameworks (MOFs) for constructing next-generation high-energy-density and high-power-density rechargeable batteries to meet the needs of the rapid developments in portable electronics, electric vehicles, and smart electricity grids. We also present our viewpoints on future challenges and opportunities of constructing efficient ATMs for next-generation rechargeable batteries.

Rechargeable Mg-Ion Full Battery System with High Capacity and High Rate

Thanks to the low cost, free dendritic hazards, and high volumetric capacity, magnesium (Mg)-ion batteries have attracted increasing attention as alternative energy storage devices to lithium-ion batteries. Despite the successful development of electrode materials, the real-life application potential of Mg-ion full battery systems (MIFBSs) is largely hindered by the lack of suitable electrode couples and hence low diffusion kinetics, which induce low specific capacity, poor rate performance, and low working voltage. Herein, we report an aqueous rechargeable MIFBS by employing copper hexacyanoferrate (CuHCF) as the cathode and 3,4,9,10-perylene-tetracarboxylic acid diimide (PTCDI) as the anode in 1 moL L^-1 MgCl₂ electrolyte. The combination of PTCDI//CuHCF allows efficient redox and convenient intercalation/deintercalation of Mg²⁺ at the electrodes while facilitating a fast transfer of Mg²⁺ between the two electrodes. As a result, the system delivers a high capacity of ∼120.3 mAh g^-1 at a current density of 0.5 A g^-1 after 200 operation cycles with a broadened voltage range (0-1.95 V) and maintains a capacity of ∼97.8 mAh g^-1 at 2.0 A g^-1 after 1000 cycles. Even at a high current density of 5.0 A g^-1, the battery provides a steady capacity of ∼81.4 mAh g^-1 over 5000 cycles. Moreover, after being applied at 11.0 A g^-1, the system can deliver a capacity of ∼126.5 mAh g^-1 at 0.5 A g^-1. This work emphasizes the great promise of developing suitable electrode couples for aqueous MIFBSs to achieve high capacity and high rate.

Vanadium oxide bronzes as cathode active materials for non-lithium-based batteries

Lithium as critical resource prompted interest for non-lithium-based batteries. This highlight review discusses vanadium oxide bronzes as one of the material families being considered as cathode for non-lithium-based batteries.

General Liquid-Driven Coaxial Flow Focusing Preparation of Novel Microcapsules for Rechargeable Magnesium Batteries

Magnesium batteries have been considered promising candidates for next-generation energy storage systems owing to their high energy density, good safety without dendrite formation, and low cost of magnesium resources. However, high-performance cathodes with stable capacity, good conductivity, and fast ions transport are needed, since many conventional cathodes possess a low performance and poor preparation controllability. Herein, a liquid-driven coaxial flow focusing (LDCFF) approach for preparing a novel microcapsule system with controllable size, high loading, and stable magnesium-storage performance is presented. Taking the MoS2-infilled microcapsule as a case study, the magnesium battery cathode based on the microcapsules displays a capacity of 100 mAh g-1 after 100 cycles. High capacity retention is achieved at both low and high temperatures of -10, ‒5, and 45 °C, and a stable rate-performance is also obtained. The influences of the liquid flow rates on the size and shell thickness of the microcapsules are investigated; and electron and ion diffusion properties are also studied by first-principle calculations. The presented LDCFF method is quite general, and the high performance of the microcapsules enables them to find broad applications for making emerging energy-storage materials and secondary battery systems.