Designing a Magnesium/Sodium Hybrid Battery Using Hierarchical Iron Selenide Architecture as Cathode Material and Modified Dual-Ion Salts in Ether as Electrolyte.

We developed a magnesium/sodium (Mg/Na) hybrid battery using a hierarchical disk-whisker FeSe2 architecture (HD-FeSe2) as the cathode material and a modified dual-ion electrolyte. The polarizable Se2- anion reduced the Mg2+ migration barrier, and the 3D configuration possessed a large surface area, which facilitated both Mg2+/Na+ cation diffusion and electron transport. The dual-ion salts with NaTFSI in ether reduced the Mg plating/stripping overvoltage in a symmetric cell. The hybrid battery exhibited an energy density of 260.9 Wh kg-1 and a power density of 600.8 W kg-1 at 0.2 A g-1. It showed a capacity retention of 154 mAh g-1 and a Coulombic efficiency of over 99.5% under 1.0 A g-1 after 800 long cycles. The battery also displayed outstanding temperature tolerance. The findings of 3D architecture as cathode material and hybrid electrolyte provide a pathway to design a highly reliable Mg/Na hybrid battery.

Catalyzing Desolvation at Cathode-Electrolyte Interface Enabling High-Performance Magnesium-Ion Batteries.

Magnesium ion batteries (MIBs) are expected to be the promising candidates in the post-lithium-ion era with high safety, low cost and almost dendrite-free nature. However, the sluggish diffusion kinetics and strong solvation capability of the strongly polarized Mg2+ are seriously limiting the specific capacity and lifespan of MIBs. In this work, catalytic desolvation is introduced into MIBs for the first time by modifying vanadium pentoxide (V2O5) with molybdenum disulfide quantum dots (MQDs), and it is demonstrated via density function theory (DFT) calculations that MQDs can effectively lower the desolvation energy barrier of Mg2+, and therefore catalyze the dissociation of Mg2+-1,2-Dimethoxyethane (Mg2+-DME) bonds and release free electrolyte cations, finally contributing to a fast diffusion kinetics within the cathode. Meanwhile, the local interlayer expansion can also increase the layer spacing of V2O5 and speed up the magnesiation/demagnesiation kinetics. Benefiting from the structural configuration, MIBs exhibit superb reversible capacity (≈300 mAh g-1 at 50 mA g-1) and unparalleled cycling stability (15 000 cycles at 2 A g-1 with a capacity of ≈70 mAh g-1). This approach based on catalytic reactions to regulate the desolvation behavior of the whole interface provides a new idea and reference for the development of high-performance MIBs.

A Temperature-Tolerant Magnesium-Ion Battery Using Ball Cactus-like MgV2O4 as High-Performance Cathode.

Safe and high-performance secondary batteries using for all-climate conditions with different temperatures are highly required. Here, we develop a three-dimensional ball cactus-like MgV2O4 as cathode material for magnesium-ion (Mg-ion) batteries. After cycling 300 times, the capacity maintains 111.7 mAh g-1, while Coulombic efficiency stabilizes at about 100 %. Under temperatures of 45 °C and -5 °C, the capacities remain stable after 200 cycles. After three rounds of rate-performance tests, the capacity keeps quite stable. It is ascribed to the ball cactus-like morphology buffers the volumetric change during Mg2+ insertion/extraction, and provides sufficient pathways for ion diffusion, which has been verified by constant-current intermittent titration technology. It is believed that the good performance enables the Mg-ion batteries to have a all-climate capability.

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.

Comparison of Construction Strategies of Solid Electrolyte Interface (SEI) in Li Battery and Mg Battery-A Review.

The solid electrolyte interface (SEI) plays a critical role in determining the performance, stability, and longevity of batteries. This review comprehensively compares the construction strategies of the SEI in Li and Mg batteries, focusing on the differences and similarities in their formation, composition, and functionality. The SEI in Li batteries is well-studied, with established strategies that leverage organic and inorganic components to enhance ion diffusion and mitigate side reactions. In contrast, the development of the SEI in Mg batteries is still in its initial stages, facing significant challenges such as severe passivation and slower ion kinetics due to the divalent nature of magnesium ions. This review highlights various approaches to engineering SEIs in both battery systems, including electrolyte optimization, additives, and surface modifications. Furthermore, it discusses the impact of these strategies on electrochemical performance, cycle life, and safety. The comparison provides insights into the underlying mechanisms, challenges, and future directions for SEI research.

Binder-free and flexible delta-MnO2@multiwalled carbon nanotubes as high-performance cathode material for aqueous magnesium ion battery.

In order to develop a high-performance electrode material for aqueous magnesium ion battery (AMIB), we report a binder-free and flexibleδ-MnO2@multiwalled carbon nanotubes on carbon cloth (δ-MnO2@MWCNTs/CC) composite by a simple hydrothermal method. The MnO2nanoflakes are deposited on the surface of CC coated with high conductivity MWCNTs to form three-dimensional hierarchy architecture, which improves the electrochemical performances. Theδ-MnO2@MWCNTs/CC electrode displays a discharge capacity of 246.7 mAh g-1at a current density of 50 mA g-1and its capacitance retention at a current density of 1000 mA g-1can reach 80% after 2000 cycles. Furthermore, the AMIB system is assembled byδ-MnO2@MWCNTs/CC as cathode and activated carbon as anode, which dispays a discharge capacity of 72.4 mAh g-1at 100 mA g-1. Theδ-MnO2with interlayer structure can provide sufficient space for the insertion/deinsertion of Mg2+ions into/from the lattice of host materials without the change of phase. This work prepares a high-performance and flexible electrode material for low-cost AMIB system.

Disulfide-Bridged (Mo3S11) Cluster Polymer: Molecular Dynamics and Application as Electrode Material for a Rechargeable Magnesium Battery.

Exploring novel electrode materials is critical for the development of a next-generation rechargeable magnesium battery with high volumetric capacity. Here, we showed that a distinct amorphous molybdenum sulfide, being a coordination polymer of disulfide-bridged (Mo3S11) clusters, has great potential as a rechargeable magnesium battery cathode. This material provided good reversible capacity, attributed to its unique structure with high flexibility and capability of deformation upon Mg insertion. Free-terminal disulfide moiety may act as the active site for reversible insertion and extraction of magnesium.

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.

Improvements in the Electrochemical Performance of Sodium Manganese Oxides by Ti Doping for Aqueous Mg-Ion Batteries.

In recent times, the research on cathode materials for aqueous rechargeable magnesium ion battery has gained significant attention. The focus is on enhancing high-rate performance and cycle stability, which has become the primary research goal. Manganese oxide and its derived Na-Mn-O system have been considered as one of the most promising electrode materials due to its low cost, non-toxicity and stable spatial structure. This work uses hydrothermal method to prepare titanium gradient doped nano sodium manganese oxides, and uses freeze-drying technology to prepare magnesium ion battery cathode materials with high tap density. At the initial current density of 50 mA g-1 , the NMTO-5 material exhibits a high reversible capacity of 231.0 mAh g-1 , even at a current density of 1000 mA g-1 , there is still 122.1 mAh g-1 . It is worth noting that after 180 cycles of charging and discharging at a gradually increasing current density such as 50-1000 mA g-1 , it can still return to the original level after returning to 50 mA g-1 . Excellent electrochemical performance and capacity stability show that NMTO-5 material is a promising electrode material.

Boosting Magnesium Ion Storage Behavior via Heteroelement Doping in a Porous Tunnel Framework Cathode for Aqueous Mg-Ion Batteries.

To relieve the overwhelming pressure on fossil energy, aqueous magnesium ion batteries attracted tremendous attention owing to their low cost and high safety. However, the cathode materials are apt to occur lattice distortion because of the electrostatic interaction between magnesium ions and crystal. The 2×2 manganese octahedral molecular sieve with potassium ions and water located in the tunnels (K-OMS-2), utilized as a cathode material for chargeable magnesium ions batteries, is exposed to irreversible Mg2+ intercalation/deintercalation due to lattice distortion, which heavily damages the electrochemical properties and declines the capacity. Herein, we carry out an ion doping strategy to overcome the above issues, leading to an enhanced Mg Mg2+ storage behavior. The Nb or V cation is successfully doped into K-OMS-2 by a facile reflux method under room temperature. The specific surface area is enlarged by the addition of cations, which promise a large electrode-electrolyte contact area. The Nb and V doped K-OMS-2 present a capacity of 252.6 and 265.9 mAh/g at 20 mA/g, respectively. This work demonstrates an ion doping approach toward exploiting the stable and high-capacity Mg-ion battery cathode and provides potential cathode materials for a large-scale aqueous Mg-ion-based energy storage system.

Research development on electrolytes for magnesium-ion batteries.

Magnesium-ion batteries (MIBs) are considered strong candidates for next-generation energy-storage systems owing to their high theoretical capacity, divalent nature and the natural abundancy of magnesium (Mg) resources on Earth. However, the development of MIBs has been mainly limited by the incompatibility of Mg anodes with several Mg salts and conventional organic-liquid electrolytes. Therefore, one major challenge faced by MIBs technology lies on developing safe electrolytes, which demonstrate appropriate electrochemical voltage window and compatibility with Mg anode. This review discusses the development of MIBs from the point-of-view of the electrolyte syntheses. A systematic assessment of promising electrolyte design strategies is proposed including liquid and solid-state electrolytes. Liquid-based electrolytes have been largely explored and can be categorized by solvent-type: organic solvent, aqueous solvent, and ionic-liquids. Organic-liquid electrolytes usually present high electrochemical and chemical stability but are rather dangerous, while aqueous electrolytes present high ionic conductivity and eco-friendliness but narrow electrochemical stability window. Some ionic-liquid electrolytes have proved outstanding performance but are fairly expensive. As alternative to liquid electrolytes, solid-state electrolytes are increasingly attractive to increase energy density and safety. However, improving the ionic conductivity of Mg ions in these types of electrolytes is extremely challenging. We believe that this comprehensive review will enable researchers to rapidly grasp the problems faced by electrolytes for MIBs and the electrolyte design strategies proposed to this date.

Electronic structure engineering on NiSe2 micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries.

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg2+ and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe2 micro-octahedra was modulated by nitrogen doping (N-NiSe2) through hydrothermal method followed by a pyrolysis process and this N-NiSe2 micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe2 micro-octahedra shows more redox active sites and faster Mg2+ diffusion kinetics compared with NiSe2 micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg2+ ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg2+ adsorption sites. As a result, the N-NiSe2 micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g-1 at the current density of 50 mA g-1, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g-1. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.

Ether-Water Hybrid Electrolyte Contributing to Excellent Mg Ion Storage in Layered Sodium Vanadate.

Magnesium ion batteries have potential for large-scale energy storage. However, the high charge density of Mg2+ ions establishes a strong intercalation energy barrier in host materials, causing sluggish diffusion kinetics and structural degradation. Here, we report that the kinetic and dissolution issues connected to cathode materials can be resolved simultaneously using a tetraethylene glycol dimethyl ether (TEGDME)-water hybrid electrolyte. The lubricating and shielding effect of water solvent could boost the swift transport of Mg2+, contributing to a high diffusion coefficient within the sodium vanadate (NaV8O20·nH2O) cathode. Meanwhile, the organic TEGDME component can coordinate with water to diminish its activity, thus providing the hybrid electrolyte with a broad electrochemical window of 3.9 V. More importantly, the TEGDME preferentially amassed at the interface, leading to a robust cathode electrolyte interface layer that suppresses the dissolution of vanadium species. Consequently, the NaV8O20·nH2O cathode achieved a specific capacity of 351 mAh g-1 at 0.3 A g-1 and a long cycle life of 1000 cycles in this hybrid electrolyte. A mechanism study revealed the reversible interaction of Mg2+ during cycles. This organic water hybrid electrolyte is effective for overcoming the difficulty of multivalent ion storage.

Advancing towards a Practical Magnesium Ion Battery.

A post-lithium battery era is envisaged, and it is urgent to find new and sustainable systems for energy storage. Multivalent metals, such as magnesium, are very promising to replace lithium, but the low mobility of magnesium ion and the lack of suitable electrolytes are serious concerns. This review mainly discusses the advantages and shortcomings of the new rechargeable magnesium batteries, the future directions and the possibility of using solid electrolytes. Special emphasis is put on the diversity of structures, and on the theoretical calculations about voltage and structures. A critical issue is to select the combination of the positive and negative electrode materials to achieve an optimum battery voltage. The theoretical calculations of the structure, intercalation voltage and diffusion path can be very useful for evaluating the materials and for comparison with the experimental results of the magnesium batteries which are not hassle-free.

Reshaping two-dimensional MoS2 for superior magnesium-ion battery anodes.

Few-atom-thick two-dimensional (2D) molybdenum disulfide (MoS2) monolayers possess numerous crucial applications in energy storage. Usually, the strategy of activating interfacial electron transfer was employed to promote their performance. Herein, we reshape the structure of materials to excite their subinterfacial and interfacial electron transfer for superior metal-ion batteries. As an example, we rationally design and reconfigure the structure of 2D MoS2 and propose a new stable structure, B-MoS2, which has an S-Mo-S sandwich structure with a buckled square lattice. The B-MoS2 monolayer is a promising anode material for magnesium-ion batteries (MgIBs) with a high capacity (921.3 mA h g-1) and a low averaged open circuit voltage (0.154 V). Multiscale underlying mechanisms for the storage of Mg and Li ions in MoS2 are provided. Based on the electronic level, the high capacity is ascribed to the occurrence of interfacial and subinterfacial electron transfer between metal ions and B-MoS2. Based on the atomic level, the insertion-adsorption mechanism or adsorption-insertion mechanism is determined for different ion storage at B-MoS2. The intrinsic metallic property of B-MoS2 and the enhanced electronic conductivity of Mg/B-MoS2 systems as well as low migration barriers (∼0.604 eV) of Mg ions at MoS2 suggest that the B-MoS2 anode has fast charge/discharge rates. This work offers novel concepts (i.e. subinterfacial electron transfer and its activation) for superior energy storage materials, and proposes new multiscale underlying mechanisms for ion storage in the MoS2 family.

Magnesium Ion Storage Properties in a Layered (NH4)2V6O16·1.5H2O Nanobelt Cathode Material Activated by Lattice Water.

Magnesium ion batteries have attracted increasing attention as a promising energy storage device due to the high safety, high volumetric capacity, and low cost of Mg. However, the strong Coulombic interactions between Mg2+ ions and cathode materials seriously hinder the electrochemical performance of the batteries. To seek a promising cathode material for magnesium ion batteries, in this work, (NH4)2V6O16·1.5H2O and water-free (NH4)2V6O16 materials are synthesized by a one-step hydrothermal method. The effects of NH4+ and lattice water on the Mg2+ storage properties in these kinds of layered cathode materials are investigated by experiments and first-principles calculations. Lattice water is demonstrated to be of vital importance for Mg2+ storage, which not only stabilizes the layered structure of (NH4)2V6O16·1.5H2O but also promotes the transport kinetics of Mg2+. Electrochemical experiments of (NH4)2V6O16·1.5H2O show a specific capacity of 100 mA·h·g-1 with an average discharge voltage of 2.16 V vs Mg2+/Mg, highlighting the potential of (NH4)2V6O16·1.5H2O as a high-voltage cathode material for magnesium ion batteries.

Hierarchical Copper Sulfide Porous Nanocages for Rechargeable Multivalent-Ion Batteries.

Copper sulfide (CuS) has been identified as a promising positive electrode material for some multivalent-ion batteries (such as the magnesium-ion battery) because of its high theoretical capacity, environmental friendliness, and wide availability. However, the clumsy multivalent-ion with high polarity inclines toward sluggish ion insertion/de-insertion, leading to inadequate electrochemical performance. In this work, the hierarchical CuS porous nanocages are successfully fabricated via a facile one-step room-temperature liquid-phase process and evaluated as positive electrode materials for rechargeable magnesium batteries. Owing to the structural advantages, a high reversible magnesium storage capacity of 228 mA h g-1 is attained, which is superior to the previously reported results under similar conditions. Besides, the application of CuS as positive electrode materials for calcium-ion, zinc-ion, iron-ion, and aluminum-ion batteries is investigated. The hierarchical CuS porous nanocages display promising electrochemical performance in those multivalent-ion battery systems. Our work proves the superiority of the nanostructure design in improving the electrochemical performance of positive electrode materials for multivalent-ion batteries.

High Voltage Magnesium-ion Battery Enabled by Nanocluster Mg3Bi2 Alloy Anode in Noncorrosive Electrolyte.

Currently, developing high voltage (beyond 2 V) rechargeable Mg-ion batteries still remains a great challenge owing to the limit of corrosive electrolyte and low compatibility of anode material. Here we report a facile one step solid state alloying route to synthesize nanoclustered Mg3Bi2 alloy as a high-performance anode to build up a 2 V Mg-ion battery using noncorrosive electrolyte. The fabricated nanoclustered Mg3Bi2 anode delivers a high reversible specific capacity (360 mAh g-1) with excellent stability (90.7% capacity retention over 200 cycles) and high Coulombic efficiency (average 98%) at 0.1 A g-1. The good performance is attributed to the stable nanostructures, which effectively accommodate the reversible Mg2+ ion insertion/deinsertion without losing electric contact among clusters. Significantly, the nanoclustered Mg3Bi2 anode can be coupled with high voltage cathode Prussian Blue to assemble a full cell using noncorrosive electrolyte, showing a stable cycling (88% capacity retention over 200 cycles at 0.2 A g-1) and good rate capability (103 mAh g-1 at 0.1 A g-1 and 58 mAh g-1 at 2 A g-1). The energy and power density of the as-fabricated full cell can reach up to 81 Wh kg-1 and 2850 W kg-1, respectively, which are both the highest values among the reported Mg-ion batteries using noncorrosive electrolytes. This study demonstrates a cost-effective route to fabricate stable and high voltage rechargeable Mg-ion battery potentially for grid-scale energy storage.

Cycling Stability of a VOx Nanotube Cathode in Mixture of Ethyl Acetate and Tetramethylsilane-Based Electrolytes for Rechargeable Mg-Ion Batteries.

The electrochemical cycling performance of vanadium oxide nanotubes (VOx-NTs) for Mg-ion insertion/extraction was investigated in acetonitrile (AN) and tetramethylsilane (TMS)-ethyl acetate (EA) electrolytes with Mg(ClO4)2 salt. When cycled in TMS-EA solution, the VOx-NT exhibited a higher capacity retention than when cycled in AN solution. The significant degradation of capacity in AN solution resulted from increased charge-transfer resistance caused by the reaction products of the electrolyte during cycling. Mixed TMS-EA solvent systems can increase the cell performance and stability of Mg-electrolytes owing to the higher stability of TMS toward oxidation and the strong Mg-coordination ability of EA. These results indicate that the interfacial stability of the electrolyte during the charging process plays a crucial role in determining the capacity retention of VOx-NT for Mg insertion/extraction.

Nanostructured Layered Cathode for Rechargeable Mg-Ion Batteries.

Nanostructured bilayered V2O5 was electrochemically deposited within a carbon nanofoam conductive support. As-prepared electrochemically synthesized bilayered V2O5 incorporates structural water and hydroxyl groups, which effectively stabilizes the interlayers and provides coordinative preference to the Mg(2+) cation in reversible cycling. This open-framework electrode shows reversible intercalation/deintercalation of Mg(2+) ions in common electrolytes such as acetonitrile. Using a scanning transmission electron microscope we demonstrate that Mg(2+) ions can be effectively intercalated into the interlayer spacing of nanostructured V2O5, enabling electrochemical magnesiation against a Mg anode with a specific capacity of 240 mAh/g. We employ HRTEM and X-ray fluorescence (XRF) imaging to understand the role of environment in the intercalation processes. A rebuilt full cell was tested by employing a high-energy ball-milled Sn alloy anode in acetonitrile with Mg(ClO4)2 salt. XRF microscopy reveals effective insertion of Mg ions throughout the V2O5 structure during discharge and removal of Mg ions during electrode charging, in agreement with the electrode capacity. We show using XANES and XRF microscopy that reversible Mg intercalation is limited by the anode capacity.