Mg-ion Insertion Research Articles

Next-generation magnesium-ion batteries: The quasi-solid-state approach to multivalent metal ion storage.

Mg-ion batteries offer a safe, low-cost, and high-energy density alternative to current Li-ion batteries. However, nonaqueous Mg-ion batteries struggle with poor ionic conductivity, while aqueous batteries face a narrow electrochemical window. Our group previously developed a water-in-salt battery with an operating voltage above 2 V yet still lower than its nonaqueous counterpart because of the dominance of proton over Mg-ion insertion in the cathode. We designed a quasi-solid-state magnesium-ion battery (QSMB) that confines the hydrogen bond network for true multivalent metal ion storage. The QSMB demonstrates an energy density of 264 W·hour kg-1, nearly five times higher than aqueous Mg-ion batteries and a voltage plateau (2.6 to 2.0 V), outperforming other Mg-ion batteries. In addition, it retains 90% of its capacity after 900 cycles at subzero temperatures (-22°C). The QSMB leverages the advantages of aqueous and nonaqueous systems, offering an innovative approach to designing high-performing Mg-ion batteries and other multivalent metal ion batteries.

Communication—Lithium Titanate as Mg-Ion Insertion Anode for Mg-Ion Sulfur Batteries Based on Sulfurated Poly(acrylonitrile) Composite

Spinel lithium-titanate Li4Ti5O12 (LTO) is a promising anode material for magnesium batteries due to its non-toxicity, low-cost, zero-strain characteristics and long-term stability. Nevertheless, the application of LTO in a magnesium full cell has been rarely investigated. Herein, we give a proof of concept for the feasibility of LTO as anode in full magnesium ion batteries, which might prevent the passivation of metallic Mg anodes. Mg2+ was electrochemically inserted into LTO prior to cycling against a sulfur-based cathode material, i.e. sulfurated poly(acrylonitrile), SPAN, resulting in stable cycle performance with 800 mAh gS −1 at 0.3C and high-rate capability.

Highly stable magnesium-ion-based dual-ion batteries based on insoluble small-molecule organic anode material

Magnesium-ion batteries (MIBs) are promising candidates for large-scale energy storage applications owing to their high volumetric capacity, low cost, and no dendritic hazards. However, the development of the MIBs is restricted owing to the obstacles of incompatibility between Mg metal and conventional electrolytes as well as the lack of suitable cathode materials with fast ion reaction kinetics, which lead to low working voltage, poor rate performance and unsatisfied cycling stability. In this work, a magnesium-ion based dual-ion battery (Mg-DIB) is constructed, using 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as organic anode, expanded graphite (EG) with high potential and fast anion diffusion kinetics as cathode, and ionic liquid as electrolyte. The PTCDI was demonstrated to go through threefold coordination mechanism and hydrogen bond formation during Mg-ion insertion, which shows good insolubility in organic electrolytes and good structural stability. As a result, the Mg-DIB was demonstrated to exhibit a reversible discharge capacity of 57.7 ​mAh g−1 at 2C in the voltage range of 1–4 ​V, and good cycling stability with capacity retention of 95.7% after 500 cycles at 5C, which present a new way to design high-performance MIBs and other energy storage devices.

Copper sulfide nanoparticles as high-performance cathode materials for Mg-ion batteries

Rechargeable magnesium batteries are appealing as safe, low-cost systems with high-energy-density storage that employ predominantly dendrite-free magnesium metal as the anode. While significant progress has been achieved with magnesium electrolytes in recent years, the further development of Mg-ion batteries, however, is inherently limited by the lack of suitable cathode materials, mainly due to the slow diffusion of high-charge-density Mg-ions in the intercalation-type host structures and kinetic limitations of conversion-type cathodes that often causes poor cyclic stability. Nanostructuring the cathode materials offers an effective means of mitigating these challenges, due to the reduced diffusion length and higher surface areas. In this context, we present the highly reversible insertion of Mg-ions into nanostructured conversion-type CuS cathode, delivering high capacities of 300 mAh g−1 at room temperature and high cyclic stability over 200 cycles at a current density of 0.1 A g−1 with a high coulombic efficiency of 99.9%. These materials clearly outperform bulk CuS, which is electrochemically active only at an elevated temperature of 50 °C. Our results not only point to the important role of nanomaterials in the enhancement of the kinetics of conversion reactions but also suggest that nanostructuring should be used as an integral tool in the exploration of new cathodes for multivalent, i.e., (Mg, Ca, Al)-ion batteries.

Mg-Ion Battery Electrode: An Organic Solid’s Herring Bone Structure Squeezed upon Mg-Ion Insertion

We report that crystalline 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), an organic solid, is highly amenable to host divalent metal ions, i.e., Mg2+ and Ca2+, in aqueous electrolytes, where the van der Waals structure is intrinsically superior in hosting charge-dense ions. We observe that the divalency nature of Mg2+ causes never-reported unique squeezing deformation of the electrode structure, where it contracts and expands in different crystallographic directions when hosting inserted Mg-ions. This phenomenon is revealed experimentally by ex situ x-ray diffraction and transmission electron microscopy, and is investigated theoretically by first-principles calculations. Interestingly, hosting one Mg2+ ion requires the coordination from three PTCDA molecules in adjacent columns of stacked molecules, which rotates the columns, thus reducing the (011) spacing but increasing the (021) spacing. We demonstrate that a PTCDA Mg-ion electrode delivers a reversible capacity of 125 mA h g-1, which may include a minor contribution of hydronium storage, a good rate capability of retaining 75 mA h g-1 at 500 mA g-1 (or 3.7 C), and stable cycle life. We also report Ca2+ storage in PTCDA, where a reversible capacity of over 80 mA h g-1 is delivered.

Magnifying Opportunities in Mg Batteries through Metastability

In the March issue of Chem, Andrews, Banerjee, and colleagues devise a clever strategy to synthesize a metastable one-dimensional polymorph of V2O5 and demonstrate reversible chemical and electrochemical Mg intercalation, with 90 mAh/g capacity retained after 50 cycles at an average cell potential of 1.65 V versus Mg metal. Their approach proves fruitful not only in identifying a new functional multivalent cathode material, but also in validating a general concept that metastable compounds can offer sufficiently low migration energies to support reversible cycling with multivalent ions.

Reversible Mg insertion into chevrel phase Mo6S8 cathode: Preparation, electrochemistry and X-ray photoelectron spectroscopy study

Electrical energy storage is absolute for complete usage of all renewable energy sources. Herein, we have studied the electrochemical performance of Chevrel phase Mo6S8 as cathode material towards rechargeable Mg battery. Solution chemistry route is adopted for the synthesis of Mo6S8. The morphology, phase purity is analyzed by Scanning Electron Microscopy, Transmission Electron Microscopy, and X-Ray Diffraction techniques. The cyclic Voltammetry and Galvanostatic charge-discharge studies confirmed the reversibility of Mg-ion insertion. Herein, Mo6S8 cubes show excellent capacity retention of 70 mAh g−1 for 200 cycles at C/5 rate. The role of CNT in improving rate performance was also demonstrated. The reasonable reversible capacity, rate performance, and cycling stability reveal the feasibility of Mo6S8 material for future rechargeable Mg battery. In order to study the kinetics of Chevrel phase compound upon cycling, EIS study was carried out. The redox process upon insertion/extraction is investigated by X-ray Photoelectron spectroscopy which shows no change in oxidation state of a transition metal.

Polyoxometalate Heterogeneous Nanostructures As Cathodes for Mg2+ Ion Storage

As global energy demands continue to rise each year, current state-of-the-art Li-ion battery (LIB) systems are predicted to reach the limit in the amount of energy that they can supply. In addition to this, LIBs are also limited by the low resource availability of Li metal. One proposed solution is to move away from LIBs to multivalent ion systems; of these alternatives, magnesium (Mg) is considered a promising material for the next generation of rechargeable batteries. Unlike Li, Mg metal does not form dendritic structures during cycling which would allow it to be employed as an anode which has a specific capacity of 2205 mAh/g compared to 777 mAh/g of the graphite anode that is currently used in LIBs. Mg also has a very high elemental abundance in the earth’s crust (2.44x104 ppm) which would drive down the production cost while simultaneously ensuring the longevity of these batteries in terms resource availability. Most importantly, the divalent nature of the Mg-ion means that it can carry twice the amount of charge per ion compared to Li. This is largely related to the high volumetric capacity (3833 mAh/ml) of Mg which is superior to even that of Li metal. While there is potential for Mg to replace LIBs, commercialization of these batteries has been hindered by sluggish insertion kinetics into cathode host materials as a direct result of the strong coulombic interactions experienced by the divalent Mg-ion. Due to this drawback, conventional metal oxide or sulfide insertion cathodes for Mg batteries tend to exhibit low capacities and operating voltages. In response to this, a large portion of Mg battery research is currently focused on the development of novel materials capable of functioning as cathodes for fast and efficient Mg-ion insertion. The idea proposed in this work is to depart from the conventional intercalation mechanism of LIBs and move towards a molecular cluster battery (MCB) based on polyoxometalate (POM) metal oxygen cluster molecules of early transition metals (Mo, W, V, or Nb). The unique redox activity of POMs are due to their intrinsic ability to form highly stable reduced and oxidized species allowing them to partake in fast reversible electron transfer reactions. Although POMs are also able to function as electron reservoirs, POMs themselves have negligible electronic conductivity as well as high solubility in both aqueous and organic media. Therefore, in order for these materials to be used as electrodes for electrochemical energy storage, they must first undergo hybridization with highly conductive insoluble substrates such as conductive organic polymers (COPs) or multi-walled carbon nanotubes (MWCNTs). The fabrication of heterogenous cathodes provide a “wiring” effect by electrically connecting the POM molecules allowing them all to take part in the redox chemistry while simultaneously anchoring them to a substrate, thus preventing any loss of active material to electrolyte dissolution during cycling. By taking advantage of the synergistic effect of pairing the ionically conductive POM molecule with the electrically conductive substrate; the resulting cathode material will thus be capable of fast electron transfer reactions with high ionic mobility. In this work, hybrid nanostructured electrodes of poly-3,4-ethylenedioxythiophene (PEDOT) and a phosphomolybdic acid (H3PMo12O40) POM have been fabricated electrochemically and applied as cathodes for Mg-ion storage. Preliminary cyclic voltammetry and galvanostatic cycling data have demonstrated an enhancement in the capacity of the PEDOT cathode after integration of the POM molecules throughout the polymer matrix. The initial cycling studies have also shown that the PEDOT-POM redox peaks are still present after 7 days of soaking in the organic electrolyte which suggests that the POM molecules do not readily dissolve out of the PEDOT matrix. This work highlights the potential of redox active POM inorganic clusters to function as cathodes with the capability of advancing the current state of Mg batteries.

Investigation of structural, dielectric and sensing properties of MgCl<sub>2</sub>/PVDF composite films prepared via solution casting technique

This article investigates the effect of Mg insertion into the Polyvinylidene fluoride (PVDF). The composite films were prepared using solution casting technique. XRD, and FTIR characterizations were done to study the structural changes in the MgCl 2 /PVDF composite films. The dielectric study reveals the improvement in the dielectric constant and conductivity with the insertion of Mg ions in the PVDF composite. The MgCl 2 /PVDF composite has immense potential in sensing and actuator applications.

Communication—Investigation of Anatase-TiO2 as an Efficient Electrode Material for Magnesium-Ion Batteries

Magnesium-ion batteries (MIBs) have twofold volumetric energy density than that of lithium without the dendritic deposition morphology associated with Li, which makes MIBs attractive options. We investigate the feasibility of using anatase-phase TiO2 as an electrode material for MIBs. Electrochemical, microscopic, and spectroscopic analyses are performed in order to probe Mg-ion insertion as well as determine the limitation of TiO2 as a viable electrode material.

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.

A highly reversible, low-strain Mg-ion insertion anode material for rechargeable Mg-ion batteries

Rechargeable magnesium (Mg) batteries have been attracting increasing attention recently because of the abundance of the raw material, their relatively low price and their good safety characteristics. However, rechargeable Mg batteries are still in their infancy. Therefore, alternate Mg-ion insertion anode materials are highly desirable to ultimately mass-produce rechargeable Mg batteries. In this study, we introduce the spinel Li4Ti5O12 as an Mg-ion insertion-type anode material with a high reversible capacity of 175 mA h g−1. This material possesses a low-strain characteristic, resulting in an excellent long-term cycle life. The proposed Mg-storage mechanism, including phase separation and transition reaction, is evaluated using advanced atomic scale scanning transmission electron microscopy techniques. This unusual Mg storage mechanism has rarely been reported for ion insertion-type electrode materials for rechargeable batteries. Our findings offer more options for the development of Mg-ion insertion materials for long-life rechargeable Mg batteries.

Nanostructured V2O5/Sn Mg-Ion Full Batteries

Nanostructured V2O5/Sn Mg-Ion Full Batteries

Effect of chalcogen substitution in mixed Mo 6S 8− nSe n ( n = 0, 1, 2) Chevrel phases on the thermodynamics and kinetics of reversible Mg ions insertion

The effect of the partial substitution of S by Se atoms in the Mo 6Se 8− n S n Chevrel phases (CPs), ( n = 0, 1, 2), on the reversible intercalation of Mg ions into these hosts was studied by a combination of cyclic voltammetry (CV), galvanostatic cycling, potentiostatic intermittent titration (PITT) and electrochemical impedance spectroscopy (EIS) techniques. Based on the previously published structural characterizations of the CP compounds under study, we describe herein the thermodynamic effect of the substitution in terms of the transformation of a single peak of the differential capacitance for the pure Mo 6X 8 phases (X = S or Se), into a set of a lower amplitude and broader peaks for the mixed (S, Se) CPs, located at less positive potentials compared to that for the pure CP. This is due to the preferential ordering of the Se anions (as compared to that of S anions) in their sites in the CP's crystal structure. In addition to the thermodynamic effect of the substitution, the geometry of the transition state for the mobile Mg ions is modified, thus facilitating the insertion of Mg ions into the partially substituted CP compounds (the kinetic effect). Thereby, the partial charge trapping that characterizes Mg ion insertion into sulfide-based CPs at low temperatures vanishes in the Mg x Mo 6S 6Se 2 compounds. This was nicely confirmed by impedance (EIS) measurements in combination with chronopotentiometry.

The effect of milling on the performance of a Mo6S8 Chevrel phase as a cathode material for rechargeable Mg batteries

In the present study, we explored how milling Mo6S8 Chevrel phase in inert or air atmosphere affects their electrochemical behavior as a Mg-ion insertion material for rechargeable Mg batteries. Electrochemical tools such as slow scan rate cyclic voltammograms and potentiostatic intermittent titration technique have been used in conjunction with X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy. In contrast to the deterioration observed for milling Mo6S8 in air, it’s milling under Ar results in specific capacity increase due to improved Mg-ion diffusion kinetics. It was shown that in spite of the conservation of the bulk crystallographic structure, both for air and the Ar-milled materials, they differ significantly in the average particle sizes and the degree of surface oxidation state.

Distinction between Energetic Inhomogeneity and Geometric Non-Uniformity of Ion Insertion Electrodes Based on Complex Impedance and Complex Capacitance Analysis

Electrochemical insertion of Mg ions into Mo6S8 Chevrel phase is a unique, model system for studying the nature of the energetic inhomogeneity of the host sites suitable for ions accommodation. We show that the two energy state model can be successfully used for describing the very specific Mg ions insertion kinetics into the host, in particular, as relates to a drastic increase of Mg ions mobility in the vicinity of the critical potential of 1.25 V (vs Mg). This is accompanied by very pronounced changes of the impedance spectra. On the other hand, similar behavior of impedance spectra could be obtained for geometrically nonhomogeneous intercalation electrodes, comprising a distribution of thicknesses. One can frequently meet both these cases in practice for a vast variety of intercalation electrodes (e.g., for lithiated graphite, composite Li(x)MO2, M = Mn, Ni, Co, etc.). In this paper, we developed a methodology aimed at a reliable distinction between the two alternatives, based on complex impedance and complex capacitance analysis.

Kinetic and Thermodynamic Studies of Mg2 + and Li + Ion Insertion into the Mo6 S 8 Chevrel Phase

Slow-scan rate cyclic voltammetry (SSCV) and chronopotentiometry were used for a quantitative comparison of the thermodynamic and kinetic characteristics of and -ion insertion into the chevrel phase compound. The Li-insertion process consists mainly of three stages with the relative stoichiometries 1:2:1, corresponding to the formation of and respectively. The kinetics of the intercalation is relatively fast. Mg-ion insertion was found to have the stoichiometry 2:2, i.e., and are formed. The initial magnesiation and the final demagnesiation of the chevrel phase reveal intrinsically slow kinetics, accompanied by a substantial decrease in the intercalation level. This probably results from a low ionic conductivity of the electrode bulk caused by both small concentration and low mobility of the Mg ion in this potential region, related to the sites that the Mg intercalants occupy in the phase. A moderate increase in temperature results in a drastic increase of ion mobility. In solution, the difference of the two sequential insertions of Mg ion into the chevrel phase was found to be 0.26 V, i.e., by 0.08 V lower than that for the insertion of Li ion. © 2004 The Electrochemical Society. All rights reserved.