Reversible Magnesium Research Articles

Synchronous regulation on solvation structure and interface engineering to enable reversible magnesium metal batteries

Magnesium (Mg) metal anodes are highly regarded as one of ideal substitutes for lithium (Li) metal anodes owing to their exceptional volumetric capacity, remarkable safety property, and abundant crustal reserves. However, the development of Mg batteries is severely impeded by the limited availability of electrolyte types, particularly non-nucleophilic ones. Mg(TFSI)2-based electrolyte is a recently discovered type of electrolyte which is non-nucleophilic, easily prepared, and highly stable. Nevertheless, due to its challenging de-solvation process and unexpected passivation interlayers, it is not performing as well electrochemically and requires effective modification. Here, organic amine dihydrochlorides (NCxN·2HCl) are selected as additives to Mg(TFSI)2-based electrolytes to regulate solvation structure and electrode interlayer synchronously. It helps rearrange the solvation sheath of Mg2+ and forms a Mg2+-permeable solid electrolyte interphase (SEI) on the surface of anode, facilitating the kinetic. Amine cations could also guide uniform Mg2+ deposition through electrostatic shielding effects. After experiments and simulations, ethylenediamine dihydrochloride (NCCN·2HCl) stands out, contributing to a significantly reduced overpotential (< 0.2 V), realizing about 100 % coulombic efficiency and stable long-term full cell cycling for an impressive 2400 cycles.

Mo3S13 Cluster-Based Cathodes for Rechargeable Magnesium Batteries: Reversible Magnesium Association/Dissociation at the Bridging Disulfur along with Sulfur–Sulfur Bond Break/Formation

Mo₃S₁₃ Cluster-Based Cathodes for Rechargeable Magnesium Batteries: Reversible Magnesium Association/Dissociation at the Bridging Disulfur along with Sulfur–Sulfur Bond Break/Formation

Protective Al2O3 Thin Film Coating by ALD to Enhance the Anodic Stability of Metallic Current Collectors in Ethereal Mg Electrolyte Solutions

Rechargeable magnesium batteries (RMBs) have the potential to contribute towards alternative energy storage due to their low cost, high abundance, dendrites free deposition of Mg and high volumetric energy density. Organometallic complex-based electrolytes in ethereal solutions have been extensively studied in the context of RMBs due to their ability to facilitate highly reversible magnesium deposition in rechargeable magnesium batteries, while demonstrating wide enough electrochemical stability windows. However, these solutions containing unique mixture of organo-halo aluminate complexes have detrimental effect on the anodic stability of metallic current collectors for cathodes, like Ni and Al foils. In this work, we were able to synthesize and isolate Mg2Cl3(THF)6Ph2AlCl2/THF electrolyte as the sole electroactive species using simple precursors: Ph2AlCl and MgCl2 in THF, via atom efficient mono-chloro abstraction Schlenk technique. We characterized the anodic stability of Ni, Ni@C, Al, and Al@C current collectors by monitoring their electrochemical behavior. In addition, we investigated the anodic stability enhancement of various current collectors by Al2O3 thin films coating using Atomic Layer Deposition (ALD). Linear sweep voltametric studies showed that coating current collectors enhanced the oxidative stability of Al and Ni foils by 0.1–0.3 V vs Mg/Mg2+ compared to the uncoated foils. In particular, Al2O3 coated Al@C showed an improved oxidative stability of 2.8 V vs Mg/Mg2+. Our findings show that current collectors protection by ALD coating can help in long-term stability and improving RMBs’ energy density by using high voltage cathode materials, a crucial step in developing practical rechargeable Mg batteries.

Synergy between the coordination and trace ionization of co-solvents enables reversible magnesium electroplating/stripping behavior

The synergy between coordination and trace ionization induces active ionic species formation and simultaneously alleviates electrolyte decomposition.

Fatal Impurity for Electrochemical Mg Deposition/Dissolution

Rechargeable magnesium batteries (RMBs) are promising large-scale stationary energy storage devices. A manufacturing system similar to that used for lithium-ion batteries should be adoptable to the fabrication of RMBs. However, the compatibility of RMB components with atmospheric components other than moisture has not been studied yet. This might be due to the uncertain preconception and misunderstanding of the passivation characteristics of magnesium. In this study, we investigated the effects of atmospheric conditions on the electrochemical dissolution–deposition behavior of magnesium in non-aqueous electrolytes.1 The compatibility of magnesium metal and electrolytes incorporating air-stable weakly-coordinated anions [B(HFIP)4]− or [Al(HFIP)4]− (HFIP: hexafluoro-iso-propoxyl) with dry air was investigated. The results of a simple cyclic voltammetry (CV) clearly demonstrate the far excessive care of magnesium metals against atmospheric O2, because reversible magnesium deposition/dissolution is possible using magnesium metals polished under dry air. However, cells assembled under a dry-air atmosphere show no features of electrochemical magnesium deposition/dissolution. To identify which component of a dry air has a significant detrimental effect on the electrochemical characteristics, systematic CV and open-circuit potential (OCP) measurements were conducted under certain atmospheric conditions with Ar, N2, and O2 and an air-tight voltammetry cell equipped with gas-inlet lines. The platinum and magnesium working electrodes show characteristic responses dependent on the inlet gases, and O2 gas is found to be detrimental for the electrochemical activities of magnesium (Figure 1). The time-profile of OCP and that of O2 content in the electrolyte under steady flow of O2 gas are correlated well, suggesting passivation of magnesium metal upon uptake of O2 in the electrolyte. The electrochemical impedance spectra of symmetric magnesium metal cells using oxygenated and deoxygenated electrolytes and X-ray photoelectron spectra further corroborate inactivation of magnesium by even miniscule amount, ca., 10 ppm, of O2 impurity. Acknowledgement This work was financially supported by the Advanced Low-Carbon Technology-Specially Promoted Research for Innovative Next Generation Batteries Program (ALCA-SPRING, Grant Number JPMJAL1301), NEXT Center of Innovation Program (COI-NEXT, Grant Number JPMJPF2016) of the Japan Science and Technology Agency, and KAKENHI (Grant No. 21K05263) of the Japan Society for the Promotion of Science. Reference T. Mandai and M. Watanabe, under revision. Figure 1

Enabling High-Capacity Electrochemical Magnesium Intercalation in Prussian Blue Cathode Via Synthesis Route Optimization

Magnesium-ion batteries (MIBs) have emerged as a promising candidate for post-lithium-ion batteries. However, their widespread adoption is hindered by the limited number of host materials that can intercalate magnesium ions reversibly in a nonaqueous electrolyte with a high operating voltage, such as Prussian Blue analogues. Unfortunately, the capacity of Prussian Blue is by far limited (<100 mAh g−1), resulting in low energy density, despite their high operating voltage. In this study, we present a systematic synthesis route optimization that allows for high-capacity magnesium ion insertion into Prussian Blue. Our defect-free and water-free Prussian Blue demonstrates reversible magnesium intercalation with a first discharge capacity of 127 mAh g−1 at 25 °C and 156 mAh g−1 at 60 °C, with an average discharge voltage of ~2.1 V (vs. Mg/Mg2+) in a nonaqueous, chloride-free electrolyte. The high-capacity magnesium ion insertion into our optimized Prussian Blue offers insights into the importance of material preparation for high-energy cathode materials in MIBs.

Prussian Blue Analogues as Positive Electrodes for Mg Batteries: Insights into Mg2+ Intercalation.

Potassium manganese hexacianoferrate has been prepared by co-precipitation from manganese (II) chloride and potassium citrate, with chemical analysis yielding the formula K1.72 Mn[Fe(CN)6 ]0.92 □0.08 ⋅ 1.1H2 O (KMnHCF). Its X-ray diffraction pattern is consistent with a monoclinic structure (space group P 21 /n, no. 14) with cell parameters a=10.1202(6)Å, b=7.2890(5)Å, c=7.0193(4)Å, and β=89.90(1)°. Its redox behavior has been studied in magnesium containing electrolytes. Both K+ ions deintercalated from the structure upon oxidation and contamination with Na+ ions coming from the separator were found to interfere in the electrochemical response. In the absence of alkaline ions, pre-oxidized manganese hexacianoferrate showed reversible magnesium intercalation, and the process has been studied by operando synchrotron X-ray diffraction. The location of Mg2+ ions in the crystal structure was not possible with the available experimental data. Still, density functional theory simulations indicated that the most favorable position for Mg2+ intercalation is at 32f sites (considering a pseudo cubic F m-3m phase), which are located between 8c and Mn sites.

To Be or Not to Be – Is MgSc2Se4 a Mg‐Ion Solid Electrolyte?

AbstractMagnesium batteries offer promising potential as next‐generation sustainable energy‐storage solutions due to the high theoretical capacity of the magnesium metal anode. Facilitating dendrite‐free operation of metal anodes necessitates the development of solid electrolytes with high magnesium‐ion conductivity. While the chalcogenide spinel MgSc2Se4 is predicted to exhibit high magnesium ion mobility, unequivocal experimental evidence for magnesium ion conduction beyond short‐range motion is still missing. This study confirms magnesium‐ion transport in MgSc2Se4 through two independent electrochemical methods: electrochemical deposition of magnesium metal and reversible magnesium plating/stripping cycling. To overcome the difficulty of measuring the ionic conductivity of the mixed conducting MgSc2Se4 spinel, a pure ion conducting interlayer is employed in a symmetric transference cell. This approach effectively suppresses the electron transport, allowing accurate characterization of the ionic conductivity. The experimental results confirm a low migration barrier of (386 ± 24) meV for magnesium ion transport in MgSc2Se4 and demonstrate one of the best performances at room temperature among the reported inorganic magnesium solid electrolytes. The findings open a new door for exploring additional mixed magnesium ion conductors and highlight the potential of magnesium chalcogenide spinels as a promising class of magnesium solid electrolytes.

The Effect of Chlorides on the Performance of DME/Mg[B(HFIP)4]2 Solutions for Rechargeable Mg Batteries

One of the major issues in developing electrolyte solutions for rechargeable magnesium batteries is understanding the positive effect of chloride anions on Mg deposition-dissolution processes on the anode side, as well as intercalation-deintercalation of Mg2+ ions on the cathode side. Our previous results suggested that Cl− ions are adsorbed on the surface of Mg anodes and Chevrel phase MgxMo6S8 cathodes. This creates a surface add-layer that reduces the activation energy for the interfacial Mg ions transportation and related charge transfer, as well as promotes the transport of Mg2+ from the solution phase to the Mg anode surface and into the cathodes’ host materials. Here, this work further examines the effect of adding chlorides to the state-of-the-art Mg[B(HFIP)4]2/DME electrolyte solution, specifically focusing on reversible magnesium deposition, as well as the performance of Mg cells with benchmark Chevrel phase cathodes. It was observed that the presence of chlorides in these solutions facilitates both Mg deposition, and Mg2+ ions intercalation, whereby this effect is more pronounced as the purity level of the solution is lowered.

Study on synergy effect of hydrated ionic radius and oxidation state for pre-intercalated cations towards highly reversible magnesium ions batteries

Magnesium ions batteries (MIBs) are promising in that Mg anode shows high theoretical volumetric capacity (3833 mAh cm−3) and is dendrite free deposition upon charging. However, the higher charge/radius ratio of Mg2+ with bivalent nature shows strong electrostatic interaction between Mg2+ and host anion lattice of VS4in situ grown on N doped tubular graphene (VS4/N-TG), causing the sluggish reaction kinetics and poorer structural stability. Therefore, there is great need to develop strategy for modifying VS4/N-TG. Although interlayer pre-intercalation is an effective way to improve the overall cell performance, the systematic study about the various ionic radius and oxidation states of pre-intercalated cations on modulating electronic structure to enhance the electrochemical performance has not been focused. In this study, cations pre-intercalation engineering is achieved in VS4/N-TG for constructing M0.06VS4/N-TG cathode via electrochemical method. After the systematic study about the effect of hydrated ionic radius and oxidation state of various pre-intercalated cations on electrochemical performance of M0.06VS4/N-TG, pre-intercalated Mg2+ with moderate hydrated ionic radius and oxidation state would enlarge the interchain spacing for facilitating magnesium working ions transportation and maintaining structural stability, as well as change the oxidation states of V element as V2+ and V3+ to enhance the electrochemical reactivity. Therefore, Mg0.06VS4/N-TG deliver superior electrochemical properties, including the excellent cycling stability with nearly 100% capacity retention ratio after 1500 cycles, high specific capacity about 170 mAh/g at 50 mA g−1, superior rate capability (107 mAh/g at 1000 mA g−1) and high anti-self-discharge behavior. The highlighted synergic effect of the hydrated ionic radius and oxidation state would guide more energy storage devices design for obtaining the excellent electrochemical performance.

Reversible Magnesium Metal Cycling in Additive-Free Simple Salt Electrolytes Enabled by Spontaneous Chemical Activation.

Rechargeable magnesium (Mg) batteries can offer higher volumetric energy densities and be safer than their conventional counterparts, lithium-ion batteries. However, their practical implementation is impeded due to the passivation of the Mg metal anode or the severe corrosion of the cell parts in conventional electrolyte systems. Here, we present a chemical activation strategy to facilitate the Mg deposition/stripping process in additive-free simple salt electrolytes. By exploiting the simple immersion-triggered spontaneous chemical reaction between reactive organic halides and Mg metal, the activated Mg anode exhibited an overpotential below 0.2 V and a Coulombic efficiency as high as 99.5% in a Mg(TFSI)2 electrolyte. Comprehensive analyses reveal simultaneous evolution of morphology and interphasial chemistry during the activation process, through which stable Mg cycling over 990 cycles was attained. Our activation strategy enabled the efficient cycling of Mg full-cell candidates using commercially available electrolytes, thereby offering possibilities of building practical Mg batteries.

A Passivation-Free Solid Electrolyte Interface Regulated by Magnesium Bromide Additive for Highly Reversible Magnesium Batteries.

Highly reversible Mg battery chemistry demands a suitable electrolyte formulation highly compatible with currently available electrodes. In general, conventional electrolytes form a passivation layer on the Mg anode, requiring the use of MgCl2 additives that lead to severe corrosion of cell components and low anodic stability. Herein, for the first time, we conducted a comparative study of a series of Mg halides as potential electrolyte additives in conventional magnesium bis(hexamethyldisilazide)-based electrolytes. A novel electrolyte formulation that includes MgBr2 showed unprecedented performance in magnesium plating/stripping, with an average Coulombic efficiency of 99.26% over 1000 cycles at 0.5 mA/cm2 and 0.5 mAh/cm2. Further analysis revealed the in situ formation of a robust Mg anode-electrolyte interface, which leads to dendrite-free Mg deposition and stable cycling performance in a Mg-Mo6S8 battery over 100 cycles. This study demonstrates the rational formulation of a novel MgBr2-based electrolyte with high anodic stability of 3.1 V for promising future applications.

Cover Feature: Mixed Metal‐Organic Frameworks as Efficient Semi‐Solid Electrolytes for Magnesium‐Ion Batteries (Batteries &amp; Supercaps 10/2022)

The Cover Feature reveals the challenges magnesium-ion batteries face in reaching lithium-ion battery technology, including finding the appropriate electrolyte, improving divalent-ion diffusion, and finding the appropriate electrode materials. Mixed metal-organic frameworks were synthesized in one-pot and investigated as a possible semi-solid electrolyte enabling the reversible magnesium deposition/stripping process. More information can be found in the Research Article by H. K. Hassan, T. Jacob and co-workers.

Off-Planar, Two-Dimensional Polymer Cathode for High-Rate, Durable Rechargeable Magnesium Batteries.

Rechargeable magnesium batteries are of considerable interest due to their high theoretical capacity, and they are projected as good alternates for stationary energy storage and electric vehicles. Sluggish Mg2+ kinetics and scarce availability of suitable cathode materials are major issues hindering the progress of rechargeable magnesium batteries. Herein, a conjugated, off-planar, two-dimensional (2D) polymer is explored for reversible magnesium storage. The polymer cathode reveals high capacity and high cycling stability with high rate capability. Replacing the Mg metal anode with the Mg alloy, AZ31 further enhances the ion storage performance. At a high current density of 2 A g-1, stable capacity is shown for almost 5000 cycles with 99% Coulombic efficiency. A composite of carbon nanotube with the polymer delivers capacity values higher (>1.5 times) than that of a pristine polymer at a current density of 2 A g-1 and shows cycling up to 5 A g-1. Electrokinetic studies reveal a contribution of pseudocapacitive nature, and the mechanism is investigated by ex situ X-ray photoelectron spectroscopy and infrared spectroscopy. The use of 2D polymer electrodes opens up opportunities for developing high-rate, high-capacity, and stable rechargeable magnesium ion batteries.

Study on Synergy Effect of Hydrated Ionic Radius and Oxidation State for Pre-Intercalated Cations Towards Highly Reversible Magnesium Ions Batteries

Study on Synergy Effect of Hydrated Ionic Radius and Oxidation State for Pre-Intercalated Cations Towards Highly Reversible Magnesium Ions Batteries

Chelated electrolytes for divalent metal ions.

Chelating electrolytes reorganize ion solvation and enable reversible magnesium batteries.

Non-passivating Anion Adsorption Enables Reversible Magnesium Redox in Simple Non-nucleophilic Electrolytes

Non-passivating Anion Adsorption Enables Reversible Magnesium Redox in Simple Non-nucleophilic Electrolytes

Reversible Magnesium Metal Anode Enabled by Cooperative Solvation/Surface Engineering in Carbonate Electrolytes

HighlightsA cooperative solvation/surface engineering approach is reported to achieve the reversible Mg plating/stripping in conventional carbonate electrolytes.Benefitting from the strategy, Mg2+ can easily overcome the reduced desolvation barrier and penetrate the Mg2+-conducting polymer coating, deposited on the Mg metal anode successfully, promoting the application of magnesium anode in carbonate electrolytes toward high-energy rechargeable batteries.

A low-cost and high-performance rechargeable magnesium battery based on povidone iodine cathode

Rechargeable magnesium battery is a potential candidate for large-scale energy storage applications owing to the high natural abundance and dendrite-free features of the magnesium metal anode, but exploration of high-capacity cathode is hindering the development. In the present study, a high-performance rechargeable magnesium battery is constructed based on a low-cost cathode of povidone iodine, which is widely used as medical disinfector. The electrochemically active iodine is anchored with the polyvinylpyrrolidone host with chemical interaction, which is stronger than the physical adsorption with carbon materials. The povidone iodine cathode exhibits a high reversible magnesium storage capacity (200 mAh g−1 based on I element and 80 mAh g−1 based on PVPI), an outstanding rate capability (70 mAh g−1 at 1600 mA g−1) and a remarkable cycling durability (0.18% capacity decay per cycle). A mechanism investigation demonstrates reversible magnesium storage reaction of PVP-I3–/PVP-I–. The chemical interaction of iodine with PVP effectively eliminates the shuttle effect, enhances the coulombic efficiency and alleviates the self discharge. The present work provides a low cost cathode for rechargeable magnesium batteries, and the strategy herein delivers insights for the performance enhancement of battery systems embarrassed by shuttle effect.

Co0.85Se hollow polyhedrons entangled by carbon nanotubes as a high-performance cathode for magnesium secondary batteries

Magnesium secondary batteries are suitable for large-scale applications owing to the low cost and dendrite-free features of the magnesium metal anode. Currently, exploration of high-performance cathodes is the main challenge of magnesium batteries, and rational structure design strategies are the cores of cathode material development. In the present study, a new approach is introduced combining hollow structure and conductive framework. ZIF-67 derived Co0.85Se hollow polyhedrons entangled by carbon nanotubes (Co0.85Se/CNTs) are fabricated and investigated as rechargeable magnesium battery cathodes. The hollow structure facilitates Mg2+ transportation and the CNT framework favors electron conduction, constructing active nanodomains for highly reversible magnesium storage reactions. Co0.85Se/CNTs shows a high capacity of 194 mAh g−1 and a superior rate capability providing 95 mAh g−1 at 1000 mA g−1. Prominently, the rigid CNTs enhance the stability of the Co0.85Se/CNTs composite and improve the cyclability. A 76% capacity retention is maintained after 500 cycles at 200 mA g−1, corresponding to a decay of 0.048% per cycle. This work highlights a micro-nanostructure favoring magnesium storage reaction reversibility and cyclability, which would enlighten rational electrode design for the storage of magnesium cations.