Magnesium Batteries Research Articles

On the Origin of Capacity Increase in Rechargeable Magnesium Batteries with Manganese Oxide Cathodes and Copper Metal Current Collectors.

Rechargeable magnesium batteries (RMBs), with Cu as positive electrode current collector (CC), typically display a gradual capacity increase with cycling. Whereas the origin of this was suggested in gradual active material electro-activation, the fact that this is prevalent in many positive electrode material systems remains unexplained. Herein, we elucidate the underlying mechanism through a series of multiscale joint operando X-ray characterizations, including operando synchrotron X-ray diffraction and imaging technology. We select a series of manganese oxides as benchmark positive electrodes and find that no magnesium ions are stored within the lattices of these materials, despite an apparent cell capacity increase with cycling. The origin of capacity increase is rooted in the gradual electrochemical corrosion of metallic Cu, release of Cu(I, II) species in electrolyte, and their subsequent redox activity, resulting in apparent electrode capacity gains. Furthermore, the shuttle and redox speciation of Cu ions trigger the irreversible depletion of both the Cu CC (or any other source) and the magnesium metal, ultimately leading to cell failure. Our work suggests the need to reconsider the appropriateness of using Cu as a positive electrode CC for RMBs.

On the Origin of Capacity Increase in Rechargeable Magnesium Batteries with Manganese Oxide Cathodes and Copper Metal Current Collectors

Rechargeable magnesium batteries (RMBs), with Cu as positive electrode current collector (CC), typically display a gradual capacity increase with cycling. Whereas the origin of this was suggested in gradual active material electro‐activation, the fact that this is prevalent in many positive electrode material systems remains unexplained. Herein, we elucidate the underlying mechanism through a series of multiscale joint operando X‐ray characterizations, including operando synchrotron X‐ray diffraction and imaging technology. We select a series of manganese oxides as benchmark positive electrodes and find that no magnesium ions are stored within the lattices of these materials, despite an apparent cell capacity increase with cycling. The origin of capacity increase is rooted in the gradual electrochemical corrosion of metallic Cu, release of Cu(I, II) species in electrolyte, and their subsequent redox activity, resulting in apparent electrode capacity gains. Furthermore, the shuttle and redox speciation of Cu ions trigger the irreversible depletion of both the Cu CC (or any other source) and the magnesium metal, ultimately leading to cell failure. Our work suggests the need to reconsider the appropriateness of using Cu as a positive electrode CC for RMBs.

Iodine Boosted Fluoro-Organic Borate Electrolytes Enabling Fluent Ion-conductive Solid Electrolyte Interphase for High-Performance Magnesium Metal Batteries.

Rechargeable magnesium batteries are regarded as a promising multi-valent battery system for low-cost and sustainable energy storage applications. Boron-based magnesium salts with terminal substituent fluorinated anions (Mg[B(ORF)4]2, RF = fluorinated alkyl) have exhibited impressive electrochemical stability. Nevertheless, their deployment is hindered by the complicated synthesis routes and the surface passivation of Mganode. Herein, we report the design of an advanced electrolyte formulation comprised of B(HFIP)3and I2in 1,2-dimethoxyethane (DME), which eventually convert into a Mg[B(HFIP)4]2/DME-MgI2 electrolyte system upon interacting with Mg anode. The Mg anode reacts with I2 and the electron-accepting B(HFIP)3, leading to the in-situ formation of a solid-electrolyte interphase layer composed of MgF2 and MgI2 species that can facilitate fast and stable Mg plating/stripping. Compared with the pristine Mg[B(HFIP)4]2/DME electrolyte, the Mg[B(HFIP)4]2/DME-MgI2 electrolyte exhibited superior electrochemical performance including an ultra-low overpotential (~80 mV), high Coulombic efficiency and a long-cycling period over 1500 h. In result, the rechargeable magnesium batteries with Mg[B(HFIP)4]2/DME-MgI2 electrolyte and Mo6S8 cathode show outstanding compatibility, rapid kinetics, and stable cyclability for over 1200 cycles, surpassing all previously reported boron-based electrolytes. This work introduces a promising halogen-enhancement strategy for boron-based Mg-ion electrolytes and is pivotal for the advancement and optimization of multi-valent secondary batteries.

Iodine Boosted Fluoro‐Organic Borate Electrolytes Enabling Fluent Ion‐conductive Solid Electrolyte Interphase for High‐Performance Magnesium Metal Batteries

Rechargeable magnesium batteries are regarded as a promising multi‐valent battery system for low‐cost and sustainable energy storage applications. Boron‐based magnesium salts with terminal substituent fluorinated anions (Mg[B(ORF)4]2, RF = fluorinated alkyl) have exhibited impressive electrochemical stability. Nevertheless, their deployment is hindered by the complicated synthesis routes and the surface passivation of Mg anode. Herein, we report the design of an advanced electrolyte formulation comprised of B(HFIP)3 and I2 in 1,2‐dimethoxyethane (DME), which eventually convert into a Mg[B(HFIP)4]2/DME‐MgI2 electrolyte system upon interacting with Mg anode. The Mg anode reacts with I2 and the electron‐accepting B(HFIP)3, leading to the in‐situ formation of a solid‐electrolyte interphase layer composed of MgF2 and MgI2 species that can facilitate fast and stable Mg plating/stripping. Compared with the pristine Mg[B(HFIP)4]2/DME electrolyte, the Mg[B(HFIP)4]2/DME‐MgI2 electrolyte exhibited superior electrochemical performance including an ultra‐low overpotential (~80 mV), high Coulombic efficiency and a long‐cycling period over 1500 h. In result, the rechargeable magnesium batteries with Mg[B(HFIP)4]2/DME‐MgI2 electrolyte and Mo6S8 cathode show outstanding compatibility, rapid kinetics, and stable cyclability for over 1200 cycles, surpassing all previously reported boron‐based electrolytes. This work introduces a promising halogen‐enhancement strategy for boron‐based Mg‐ion electrolytes and is pivotal for the advancement and optimization of multi‐valent secondary batteries.

Influence of Chloride and Electrolyte Stability on Passivation Layer Evolution at the Negative Electrode of Mg Batteries Revealed byoperandoEQCM-D.

Rechargeable magnesium batteries are promising for future energy storage. However, among other challenges, their practical application is hindered by low coulombic efficiencies of magnesium plating and stripping. Fundamental processes such as the formation, structure, and stability of passivation layers and the influence of different electrolyte components on them are still not fully understood. In this work, we gain unique insights into the initial Mg plating and stripping cycles by comparing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2)- and Mg tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4]2)-based electrolytes, each with and without MgCl2, on gold electrodes by highly sensitive operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) applying hydrodynamic spectroscopy. With the stable Mg[B(hfip)4]2-based electrolytes, highly efficient and interphase-free cycling is possible and passivation layers are attributed to electrolyte contaminants. These are forming and degrading during the so-called initial conditioning process. With the more reactive Mg(TFSI)2-based electrolyte, thick passivation layers with small pores are growing during cycling. We demonstrate that the addition of chloride lowers the amount of passivated Mg deposits in these electrolytes and accelerates the currentless dissolution of the passivation layer. This has a positive effect since we observe the most efficient cycling and uniform deposition when no interphase is present on the electrode.

Influence of Chloride and Electrolyte Stability on Passivation Layer Evolution at the Negative Electrode of Mg Batteries Revealed by operando EQCM‐D

Rechargeable magnesium batteries are promising for future energy storage. However, among other challenges, their practical application is hindered by low coulombic efficiencies of magnesium plating and stripping. Fundamental processes such as the formation, structure, and stability of passivation layers and the influence of different electrolyte components on them are still not fully understood. In this work, we gain unique insights into the initial Mg plating and stripping cycles by comparing Mg bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2)‐ and Mg tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)4]2)‐based electrolytes, each with and without MgCl2, on gold electrodes by highly sensitive operando electrochemical quartz crystal microbalance with dissipation monitoring (EQCM‐D) applying hydrodynamic spectroscopy. With the stable Mg[B(hfip)4]2‐based electrolytes, highly efficient and interphase‐free cycling is possible and passivation layers are attributed to electrolyte contaminants. These are forming and degrading during the so‐called initial conditioning process. With the more reactive Mg(TFSI)2‐based electrolyte, thick passivation layers with small pores are growing during cycling. We demonstrate that the addition of chloride lowers the amount of passivated Mg deposits in these electrolytes and accelerates the currentless dissolution of the passivation layer. This has a positive effect since we observe the most efficient cycling and uniform deposition when no interphase is present on the electrode.

Sulfur Heterocyclic Quinone Cathodes for Rechargeable Magnesium Batteries: Discharge Voltage, Cycling Stability, and Reaction Reversibility Improved by Sulfur Substitution

Sulfur Heterocyclic Quinone Cathodes for Rechargeable Magnesium Batteries: Discharge Voltage, Cycling Stability, and Reaction Reversibility Improved by Sulfur Substitution

Cover Feature: Recent Advances in Electrolytes for Magnesium Batteries: Bridging the gap between Chemistry and Electrochemistry (Chem. Eur. J. 61/2024)

Cover Feature: Recent Advances in Electrolytes for Magnesium Batteries: Bridging the gap between Chemistry and Electrochemistry (Chem. Eur. J. 61/2024)

Effect of Chloride Ions on the Electrochemical Performance of Magnesium Metal‐Organic‐Frameworks‐Based Semi‐Solid Electrolytes

AbstractThe majority of research on magnesium (Mg) electrolytes has focused on enhancing reversible Mg deposition, often employing chloride‐containing electrolytes. However, there is a notable gap in the literature regarding the influence of chloride ions in semi‐solid Mg electrolytes. In this study, we systematically explore the impact of chloride ions on Mg deposition/dissolution on a copper (Cu) anode using a semi‐solid electrolyte composed of Mg‐based mixed metal‐organic frameworks, MgCl2 and Mg[TFSI]2. We separate the Mg deposition/dissolution process from changes in the anode's surface morphology In this respect, the morphological and compositional transformations in the electrolyte and electrode following galvanostatic cycling are meticulously investigated. Initial potential cycling reveals the feasibility of Mg deposition/dissolution on Cu electrodes, albeit with reduced reversibility in subsequent cycles. Extending the upper potential limit to 4.0 V vs. Mg/Mg2+ enhances Mg dissolution, attributed to chloride ions facilitating Cu surface dissolution. Our findings provide insights into optimizing semi‐solid electrolytes for advanced Magnesium battery technologies.

Recent Advances in Electrolytes for Magnesium Batteries: Bridging the gap between Chemistry and Electrochemistry.

Rechargeable magnesium batteries (RMBs) have the potential to provide a sustainable and long-term solution for large-scale energy storage due to high theoretical capacity of magnesium (Mg) metal as an anode, its competitive redox potential (Mg/Mg2+:-2.37 V vs. SHE) and high natural abundance. To develop viable magnesium batteries with high energy density, the electrolytes must meet a range of requirements: high ionic conductivity, wide electrochemical potential window, chemical compatibility with electrode materials and other battery components, favourable electrode-electrolyte interfacial properties and cost-effective synthesis. In recent years, significant progress in electrolyte development has been made. Herein, a comprehensive overview of these advancements is presented. Beginning with the early developments, we particularly focus on the chemical aspects of the electrolytes and their correlations with electrochemical properties. We also highlight the design of new anions for practical electrolytes, the use of electrolyte additives to optimize anode-electrolyte interfaces and the progress in polymer electrolytes.

Revolutionizing Battery Longevity by Optimising Magnesium Alloy Anodes Performance

This research explores the enhancement of electrochemical performance in magnesium batteries by optimising magnesium alloy anodes, explicitly focusing on Mg-Al and Mg-Ag alloys. The study’s objective was to determine the impact of alloy composition on anode voltage stability and overall battery efficiency, particularly under extended cycling conditions. The research assessed the anodes’ voltage behaviour and internal resistance across magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) electrolyte formulations using a systematic setup involving cyclic voltammetry on the anode and electrochemical impedance spectroscopy. The Mg-Al alloy demonstrated superior performance, with minimal voltage drop and lower resistance increase than the Mg-Ag alloy. The results showed that the Mg-Al alloy maintained over 85% energy efficiency after 100 cycles, significantly outperforming the Mg-Ag alloy, which exhibited increased degradation and efficiency reduction to approximately 80%. These findings confirm that incorporating aluminium into magnesium anodes stabilises the anode voltage and enhances the overall battery efficiency by mitigating degradation mechanisms. Consequently, the Mg-Al alloy is identified as an up-and-coming candidate for use in advanced battery technologies, offering energy density and cycle life improvements. This study lays the groundwork for future research to refine magnesium alloy compositions further to boost battery performance.

Regulating Electric Double Layer via Self‐Assembled Monolayer for Stable Solid/Electrolyte Interphase on Mg Metal Anode

Modulating the cationic solvation structure with high donor‐number (DN) additive is an effective strategy to construct a stable solid electrolyte interphase (SEI) on the Mg anode, which necessitates meticulous consideration of electrolyte chemistry and substantial quantities of additives. Notably, the electric double layer (EDL) adjacent to anode is pivotal role in SEI formation yet remains understudied. In this study, we propose a novel self‐assembled monolayer (SAM) strategy by utilizing (trifluoromethyl)trimethylsilane (TFTMS, only 2 vol%, 1.4 mol%, 0.135 mol L‐1), a low DN but strong Mg metal absorbability through electron‐withdrawing groups(−CF3), to modulate the complex structure of the Helmholtz absorption plane. Through dipole−dipole interaction between the electronegative fluorine (−CF3 of TFTMS) and electropositive hydrogen (−CH3/−CH2 of solvents), TFTMS weakens solvent−Mg2+ coordination and thus enhances anion−Mg2+ interaction, inducing a stable and dense SEI with superior electronic insulation to realize horizontal Mg plating/stripping. Consequently, the designed electrolytes enable the symmetric cells to cycle stable for up to 1000 hours and reversible Mg plating/stripping under 5 mA cm‐2, they show favorable compatibility with various cathodes. More importantly, the SAM strategy has good generality in other electrolyte systems, demonstrating a simple and effective route to promote the practical application of rechargeable magnesium battery.

Coupling Manipulation of Interfacial Chemistry and Coordination Structure in Vanadium Oxides Enables Rapid Magnesium Ion Diffusion Kinetics

AbstractRechargeable magnesium batteries (RMBs) are a highly promising energy storage system due to their high volumetric capacity and intrinsic safety. However, the practical development of RMBs is hindered by the sluggish Mg2+ diffusion kinetics, including at the cathode‐electrolyte interface (CEI) and within the cathode bulk. Herein, we propose an efficient strategy to manipulate the interfacial chemistry and coordination structure in oligolayered V2O5 (L−V2O5) for achieving rapid Mg2+ diffusion kinetics. In terms of the interfacial chemistry, the specific exposed crystal planes in L−V2O5 possess strong electron donating ability, which helps to promote the degradation dynamics of C−F/C−S bonds in the electrolyte, thereby establishing the inorganic‐organic interlocking CEI layer for rapid Mg2+ diffusion. In terms of the coordination structure, the straightened V−O structure in L−V2O5 provides efficient ions diffusion path for accelerating Mg2+ diffusion in the cathode. As a result, the L−V2O5 delivers a high reversible capacity (355.3 mA h g−1 at 0.1 A g−1) and an excellent rate capability (161 mAh g−1 at 1 A g−1). Impressively, the interdigital micro‐RMBs is firstly assembled, exhibiting excellent flexibility and practicability. This work gives deeper insights into the interface and interior ions diffusion for developing high‐kinetics RMBs.

Evaluation of various properties of ribbons of Mg-9%Al-3%Ca-based anode material for magnesium batteries produced by single-roll rapid solidification

Evaluation of various properties of ribbons of Mg-9%Al-3%Ca-based anode material for magnesium batteries produced by single-roll rapid solidification

3D Tunnel Copper Tetrathiovanadate Nanocube Cathode Achieving Ultrafast Magnesium Storage Reactions through a Charge Delocalization and Displacement Mechanism.

Rechargeable magnesium batteries are attractive candidates for large-scale energy storage applications because of the low cost and high safety, but the scarcity and inferior performance of the cathode materials are hindering the development. In the present study, a kind of copper tetrathiovanadate (Cu3VS4) cathode is designed and developed with a comprehensive consideration of the chemical and electronic structures. The vanadium and sulfur atoms form chemical bonds with high covalent proportion, facilitating electron delocalization via the vanadium-sulfur bonds. This reduces the interaction with the bivalent magnesium cation and induces the coredox of vanadium and sulfur. The crystal structure of Cu3VS4 has interlaced 3D tunnels for solid-state magnesium cation transport. The Cu3VS4 cathode shows a high capacity of 350 mA h g-1 at 100 mA g-1, an outstanding rate performance of 67 mA h g-1 at 10 A g-1, and stable cycling for 1000 cycles at 5 A g-1 without obvious capacity fading. Prominently, a high areal mass load of 3.5 mg cm-2 could be achieved without obvious rate capability decay, which is quite favorable to pair with the high-capacity magnesium metal anode in practical application. The mechanism investigation and theoretical computation demonstrate that Cu3VS4 undergoes first a magnesium intercalation and then a displacement reaction, during which the crystal structure is maintained, assisting the reaction reversibility and cycling stability. All the copper, vanadium, and sulfur elements experience redox and contribute to the high capacity. Moreover, the weakened interaction with magnesium cations, well-kept 3D cation transport tunnels, and high electronic conductivity result in the superior rate performance and high areal active material loading. The present study develops a high-performance cathode for rechargeable magnesium batteries and reveal the design principle based on both of chemical and electronic structures.

High-capacity, fast-charging and long-life magnesium/black phosphorous composite negative electrode for non-aqueous magnesium battery

Secondary non-aqueous magnesium-based batteries are a promising candidate for post-lithium-ion battery technologies. However, the uneven Mg plating behavior at the negative electrode leads to high overpotential and short cycle life. Here, to circumvent these issues, we report the preparation of a magnesium/black phosphorus (Mg@BP) composite and its use as a negative electrode for non-aqueous magnesium-based batteries. Via in situ and ex situ physicochemical measurements, we demonstrate that Mg ions are initially intercalated in black phosphorus two-dimensional structures, forming chemically stable MgxP intermediates. After the formation of the intermediates, Mg electrodeposition reaction became the predominant. When tested in the asymmetric coin cell configuration, the Mg@BP composite electrode allowed stable stripping/plating performances for 1600 h (800 cycles), a cumulative capacity of 3200 mAh cm−2, and a Coulombic efficiency of 99.98%. Assembly and testing of the Mg@BP | |nano-CuS coin cell enabled a discharge capacity of 398 mAh g−1 and an average cell discharge potential of about 1.15 V at a specific current of 560 mA g−1 with a low decay rate of 0.016% per cycle for 225 cycles at 25 °C.

Experimental and computational insights into oxygen vacancy-rich MoO2-x/N-doped carbon nanowires as high-performance cathode for magnesium batteries and magnesium-lithium hybrid batteries

This work aims to develop efficient cathode materials for magnesium based batteries, which are considered promising next-generation energy storage and conversion devices. One major challenge in magnesium based batteries is the strong Coulomb interaction between magnesium ions and cathode materials, which hinders ion storage and diffusion. To overcome this, we designed and synthesized oxygen vacancy-rich MoO2-x/N-doped carbon nanowires (MoO2-x-NC-NWS). The materials were prepared through a controlled synthesis process, ensuring the incorporation of N-doped carbon and oxygen vacancies, which play crucial roles in improving magnesium ion diffusion and storage. The prepared MoO2-x-NC-NWS demonstrated superior energy storage performance, achieving a capacity of 64 mAh/g in magnesium batteries and 263 mAh/g in magnesium-lithium hybrid batteries at a current density of 50 mA/g. Theoretical calculations further confirmed that oxygen vacancies enhance the diffusion capabilities of magnesium and lithium ions, thereby improving the overall energy storage performance. Therefore, the controllable synthesis of defects such as oxygen vacancies and the development of composite cathode materials are clearly effective strategies for enhancing the performance of magnesium-based battery cathodes. Meanwhile, this rational design of MoO2-based nanostructures provides valuable insights into the development of high-performance cathode materials for magnesium-based energy storage systems.

Constructing dilute Mg-1.0In binary alloy: A pathway to enhanced anode performance in Mg-air battery

Magnesium anode is a critical material in Mg-air battery; however, the contradiction between mitigating self-corrosion and promoting activation poses a significant obstacle to the rapid advancement of primary magnesium batteries. Herein, this issue is addressed by constructing a dilute Mg-1.0In binary alloy with 1 wt% indium as the anode material. The equiaxed dendrites and moderate indium concentration gradient in the as-cast anode facilitate the formation of a protective surface film, leading to a low corrosion rate of 0.20 mm y−1 and enhancing the stability prior to discharge. Moreover, during the battery discharge process, this unique microstructure enables the redeposition of metallic indium and indium hydroxide, thereby dramatically accelerating the shedding of oxidation products and suppressing side hydrogen evolution reaction. The Mg-1.0In anode in a Mg-air battery delivers a discharge capacity of 1587 mA h g−1 and an average voltage of 1.46 V at 10 mA cm−2, outperforming most of previously reported magnesium anodes and the control samples with various indium contents. This work would inspire the achievement of superior Mg-air battery performance through the use of binary magnesium anode system in as-cast state, as opposed to a more complex and time-consuming multi-component anode design involving heat treatment and plastic deformation.

Se-Doping on Co4S3 Cathode Based on Soft Anion Chemistry to Enhance Magnesium Storage Performance.

Rechargeable magnesium batteries (RMBs) have gradually got attention due to the high theoretical capacity, low cost and high security. However, the lack of suitable cathode materials has been a major obstacle to the development of RMBs. Transition metal sulfides (TMSs) have been studied extensively because of their high theoretical specific capacity and other advantages. However, the diffusion rate of Mg2+ in TMSs is slow and side reactions are easy to occur. In this work, soft anion doping strategy was adopted at Co4S3 cathode material. After doping the appropriate content of Se, it showed the specific capacity of 248 mAh g-1 at a current density of 100 mA g-1. The mechanism of magnesium storage was investigated by ex-situ technique. This work laid a foundation for researching cobalt-based sulfide in cathode materials of RMBs.

Polyanthraquinone with Facile Synthesis as a Cathode Material for Rechargeable Magnesium Batteries

Polyanthraquinone with Facile Synthesis as a Cathode Material for Rechargeable Magnesium Batteries