Patent Application
20220416301
This application claims the benefit of priority of Singapore patent application No. 10201911676S, filed on 4 Dec. 2019, its contents being hereby incorporated by reference in its entirety.
The present disclosure relates to an electrolyte system, in particular, to an electrolyte for use in magnesium ion batteries.
The rapid development of electrical and electronic devices in recent years has renewed interest in the development of energy storage such as rechargeable batteries. Currently, lithium is relied upon heavily as an energy source for such electronic devices. However, there is concern that increasing demands for such lithium-ion batteries may further deplete the limited supply of lithium in the Earth's crust.
Various technologies have been researched and developed as alternatives to lithium ion batteries in recent years. Magnesium ion batteries have shown great potential as an alternative energy source due to its high natural abundance, high volumetric capacity, low reduction potential, and low cost. However, the development of such batteries has been hampered by poor performance of current electrolyte systems. Due to the reactivity of magnesium-based electrodes, organic solvents are typically employed in electrolyte systems for magnesium ion batteries. While several magnesium salts have demonstrated good solubility in such organic solvents, electrolytes comprising these magnesium salts alone often result in poor Coulombic efficiency and poor reversibility of magnesium deposition. As such, the performance of magnesium-ion batteries has been regarded to be poorer than the current lithium-ion batteries.
Magnesium trifluoromethanesulfonate (Mg(OTf)2) is a promising salt for Mg electrolyte. However, Mg(OTf)2-based electrolyte has been rarely reported due to low solubility of Mg(OTf)2 in ether solvents. Enhancing solubility of Mg(OTf)2 in ether solvent is essential to obtain a high performance electrolyte system for Mg-ion batteries.
Accordingly, there is a need to provide an improvement for magnesium-ion batteries which are able to overcome or at least ameliorate the disadvantages discussed above. In particular, it is an object to provide an electrolyte system for magnesium ion batteries which allows efficient plating and stripping of magnesium and demonstrates improved Coulombic efficiency.
In one aspect, there is provided a liquid electrolyte composition comprising:
The presence of the additive may advantageously facilitate the dissociation of magnesium trifluoromethane sulfonate (Mg(OTf)2), thereby improving its solubility in an ether solvent.
The improvement in solubility may advantageously lead to superior Coulombic efficiency (e.g. greater than 99%), and areal capacity (e.g. larger than 5 mAh/cm2).
In another aspect, there is provided a liquid electrolyte composition consisting essentially of:
In another aspect, there is provided a liquid electrolyte composition consisting essentially of:
Alternatively, in the above liquid electrolyte composition, the total concentration of the magnesium ions in the magnesium trifluoromethanesulfonate and magnesium chloride divided by the concentration of the chloride ions of the magnesium chloride is greater than 1.
In another aspect, there is provided an electrochemical cell comprising:
The term “stable”, “stability” and grammatical variants thereof, in the context of this specification, refers to an electrode that can be operated with no sign of short circuiting and/or without experiencing sudden fluctuations in voltage or current or capacity.
The term “homogenous” as used herein refers to substances which comprise components or elements which are the same. The term also refers to mixtures which contain a uniform distribution of components throughout. Homogenous mixtures may have the same composition of components or elements throughout. As described herein, homogenous mixtures may contain only one phase of matter, e.g. only liquid, solid or gas; while homogenous electrodes may contain only a single element.
The term “optionally substituted” as used herein means the group to which this term refers may be unsubstituted, or may be substituted with one or more groups independently selected from alkyl, alkenyl, alkynyl, thioalkyl, cycloalkyl, cycloalkylalkyl, cycloalkenyl, cycloalkylalkenyl, heterocycloalkyl, cycloalkylheteroalkyl, cycloalkyloxy, cycloalkenyloxy, cycloamino, halo, carboxyl, oxo, haloalkyl, haloalkenyl, haloalkynyl, alkynyloxy, heteroalkyl, heteroalkyloxy, hydroxyl, hydroxyalkyl, alkoxy, thioalkoxy, alkenyloxy, haloalkoxy, haloalkenyloxy, nitro, amino, nitroalkyl, nitroalkenyl, nitroalkynyl, nitroheterocyclyl, alkylamino, dialkylamino, alkenylamine, aminoalkyl, alkynylamino, acyl, alkyloxy, alkyloxyalkyl, alkyloxyaryl, alkyloxycarbonyl, alkyloxycycloalkyl, alkyloxyheteroaryl, alkyloxyheterocycloalkyl, alkenoyl, alkynoyl, acylamino, diacylamino, acyloxy, alkylsulfonyloxy, heterocyclyl, heterocycloalkenyl, heterocycloalkyl, heterocycloalkylalkyl, heterocycloalkylalkenyl, heterocycloalkylheteroalkyl, heterocycloalkyloxy, heterocycloalkenyloxy, heterocycloxy, heterocycloamino, haloheterocycloalkyl, alkylsulfinyl, alkylsulfonyl, alkylsulfenyl, alkylcarbonyloxy, alkylthio, acylthio, aminosulfonyl, phosphorus-containing groups such as phosphono and phosphinyl, sulfinyl, sulfinylamino, sulfonyl, sulfonylamino, aryl, heteroaryl, heteroarylalkyl, heteroarylalkenyl, heteroarylheteroalkyl, heteroarylamino, heteroaryloxy, arylalkenyl, arylalkyl, alkylaryl, alkylheteroaryl, aryloxy, arylsulfonyl, cyano, cyanate, isocyanate, —C(O)NH(alkyl), and —C(O)N(alkyl)2.
The term “inorganic halide salt” as used herein refers to a halide salt compound that does not contain carbon-hydrogen bonds.
The term “Coulombic efficiency” as used herein refers to the ratio of stripping capacity over plating capacity.
The term “areal capacity” as used herein refers to the capacity of an electrode per unit area.
This term may be expressed in terms of mAh/cm2.
Unless specified otherwise, the terms “comprising” and “comprise”, and grammatical variants thereof, are intended to represent “open” or “inclusive” language such that they include recited elements but also permit inclusion of additional, unrecited elements.
The terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items.
As used herein, the term “about”, in the context of concentrations of components of the formulations, typically means +/−5% of the stated value, more typically +/−4% of the stated value, more typically +/−3% of the stated value, more typically, +/−2% of the stated value, even more typically +/−1% of the stated value, and even more typically +/−0.5% of the stated value.
Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.
Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.
Exemplary, non-limiting embodiments of a liquid electrolyte composition will now be disclosed
The present disclosure relates to a liquid electrolyte composition comprising:
The additive may be an organic halide salt. Without being bound by theory, it was postulated that the interaction between the protonated nitrogen of the above cation of the halide salt and the OTf− anion facilitates the dissociation of Mg(OTf)2 in the ether solvent. Moreover, the halide of the halide salt advantageously assisted in the formation of electroactive species.
The concentration of the magnesium salt may be from about 0.01 M to about 2.5 M, from about 0.05 M to about 2.5 M, from about 0.1 M to about 2.5 M, from about 0.5 M to about 2.5 M, from about 1.0 M to about 2.5 M, from about 1.5 M to about 2.5 M, from about 2.0 M to about 2.5 M, from about 0.01 M to about 2.0 M, from about 0.01 M to about 1.5 M, from about 0.01 M to about 1.0 M, from about 0.01 M to about 0.5 M, from about 0.01 M to about 0.1 M, or from about 0.01 M to about 0.05 M. The concentration of the magnesium salt may be about 2.5M.
Advantageously, the presence of the above-defined halide salt may be capable of promoting solubility of the magnesium salt at room temperature. In embodiments, the magnesium salt may be provided in molar concentrations of from 0.01 M to 2.5 M while the electrolyte composition remains a homogeneous liquid composition.
In embodiments, the magnesium salt may be present in the electrolyte composition in a concentration of not less than 0.5M, not less than 1 M, not less than 1.5 M, not less than 2 M.
The molar ratio of the magnesium salt to the organic halide salt may be from 10:1 to 1:10. Preferably, the molar ratio of the magnesium salt to the organic halide salt may be 1:0.3 to 1:1.2.
Advantageously, it was surprisingly found that providing the above molar ratios of Mg salt to organic halide salt may lead to improved stability. For instance, electrolyte compositions having the above defined molar ratios may be used for reversible plating of magnesium (Mg) in excess of 500 cycles without substantial change in Coulombic efficiency. In embodiments, the change in Coulombic efficiency across 500 cycles of plating/stripping was found to deviate less than 5% from a mean value.
The N-heterocyclic cation may be selected from the group consisting of: an optionally substituted three-membered heterocyclic structure, an optionally substituted four-membered heterocyclic structure, an optionally substituted five-membered heterocyclic structure, an optionally substituted six-membered heterocyclic structure, an optionally substituted seven-membered heterocyclic structure, an optionally substituted eight-membered heterocyclic structure, and an optionally substituted nine-membered heterocyclic structure. The N-heterocyclic cation may preferably be 1-Ethyl-3-methylimidazolium (EMIM).
The heterocyclic structure may comprise 1, 2, 3, 4, 5, 6, 7, 8, or 9 heteroatoms.
The heteroatoms may be independently selected from the group consisting of nitrogen, oxygen, and sulfur.
The heteroatoms may be the same or different. The heterocyclic structure may comprise a saturated or an unsaturated ring.
The heterocyclic structure may be selected from the group consisting of aziridinium, azetidinium, pyrrolidinium, pyrrolinium, pyrrolium, imidazolium, pyrazolium, triazolium, tetrazolium, thiazolium, oxazolium, piperidinium, pyridinium, piperazinium, pyridazinium, pyrimidonium, pyrazinium, triazinium, morpholinium, oxazinium, thiomorpholinium, azepinium, azocanium and azonanium.
The organic halide salt may be selected from the group consisting of fluoride, chloride, bromide and iodide.
The electrolyte composition may comprise a mixture of at least two or more of said organic halide salts, said organic halide salts being distinct from each other.
The organic halide salt may be 1-ethyl-3-methylimidazolium chloride.
In embodiments, the provision of 1-ethyl-3-methylimidazolium chloride as the organic halide salt may provide an electrolyte composition comprising the magnesium salt in a molar concentration of 0.5M or greater. The 1-ethyl-3-methylimidazolium chloride may be provided in concentrations of from about 0.01 M to 10 M, from about 0.01 M to 5 M, or from about 0.01 M to 2 M. The combination of 1-ethyl-3-methylimidazolium chloride (EMImCl) and magnesium trifluoromethane sulfonate (Mg(OTf)2) in ether advantageously resulted in Coulombic efficiency of Mg plating/stripping of 99% and areal capacity of the Mg anode of 1 mAh/cm2.
In one embodiment, the combination of magnesium trifluoromethane sulfonate and 1-ethyl-3-methylimidazolium chloride in the electrolyte composition at a molar ratio of 1:1.2 advantageously resulted in Coulombic efficiency of above 98% and reversible Mg plating/stripping for 400 cycles without substantial loss in efficiency.
The organic halide salt may comprise a quaternary ammonium cation, said cation comprising a structure of N+ R1R2R3R4, wherein each of R1, R2, R3, and R4 may be the same or different and wherein each of R1, R2, R3, and R4 may be an optionally substituted alkyl group.
Each of R1, R2, R3, and R4 may be independently selected from an optionally substituted C1-C10 alkyl, or an optionally substituted C2-C5 alkyl, or an optionally substituted C2-C6 alkyl, or an optionally substituted C4-C6 alkyl. Each of R1, R2, R3, and R4 may be a halogenated alkyl group.
The halogenated alkyl group may be an alkyl fluoride, alkyl chloride, alkyl bromide or alkyl iodide compound.
Each of R1, R2, R3, and R4 may be independently selected from the group consisting of: methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. The R1, R2, R3, and R4 of the halide salt may be butyl.
The organic halide salt may be tetrabutylammonium chloride.
In embodiments, the provision of tetrabutylammonium chloride as the organic halide salt may provide an electrolyte composition comprising the magnesium salt in a molar concentration of 0.5 M or greater. The tetrabutylammonium chloride may be provided in concentrations of from about 0.01 M to 10 M, from about 0.01 M to 5 M, or from about 0.01 M to 2 M. The combination of tetrabutylammonium chloride (TBAC) with magnesium trifluoromethanesulfonate advantageously resulted in an average Coulombic efficiency of Mg plating/stripping of 97.5% over 500 cycles of Mg plating/stripping and areal capacity of up to 5 mAh/cm2.
The concentration of the organic halide salt may be from about 0.01 M to about 10 M, from about 0.05 M to about 10 M, from about 0.1 M to about 10 M, from about 0.5 M to about 10 M, from about 1 M to about 10 M, from about 3 M to about 10 M, from about 5 M to about 10 M, from about 7 M to about 10 M, from about 0.01 M to about 7 M, from about 0.01 M to about 5 M, from about 0.01 M to about 3 M, from about 0.01 M to 2 M, from about 0.01 M to about 1 M, from about 0.01 M to about 0.5 M, from about 0.01 M to about 0.1 M, or from about 0.01 M to about 0.05 M.
The additive may an inorganic halide salt.
The total concentration of the cations of the inorganic halide salts and the magnesium ions of the magnesium salt divided by the concentration of the anions of the inorganic halide salt may be from greater than about 1 to about 5 in the electrolyte composition. The total concentration of the cations of the inorganic halide salts and the magnesium ions of the magnesium salt divided by the anions of the inorganic halide salt may be from about 1.25 to about 2.5 in the electrolyte composition.
The cations of the inorganic halide salts may be lithium ion, sodium ions, cesium ions, magnesium ions, barium ions, or aluminum ions. The cations of the inorganic halide salts may be magnesium ions. The inorganic halide salts may be magnesium fluoride, magnesium chloride, magnesium bromide, or magnesium iodide.
The inorganic halide salts may be a fluoride salt, a chloride salt, a bromide salt or an iodide salt. The chloride salt may be selected from the group consisting of lithium chloride (LiCl), sodium chloride (NaCl), cesium chloride (CsCl), magnesium chloride (MgCl2), barium chloride (BaCl2) and aluminum chloride (AlCl3). The halide salt may be magnesium chloride (MgCl2). Other combinations of halide salts based on the cations and halide anions mentioned herein are also part of this disclosure.
By having a [Mg2+]:[Cl−] ratio of greater than 1, or a total concentration of the Mg2+ divided by the concentration of the Cl− of greater than 1, the solubility of the magnesium trifluoromethane sulfonate in ether was unexpectedly improved, which resulted in superior Coulombic efficiency and areal capacity. For instance, when 0.4 M of MgCl2 is combined with 0.6 M of magnesium trifluoromethanesulfonate in ether, a clear, homogenous solution is surprisingly obtained. The improvement in solubility advantageously leads to superior Coulombic efficiency and cycle life.
The concentration of the magnesium trifluoromethanesulfonate may be from about 0.01 M to about 1.5 M, from about 0.05 M to about 1.5 M, from about 0.1 M to about 1.5 M, from about 0.5 M to about 1.5 M, from about 1.0 M to about 1.5 M, from about 1.3 M to about 1.5 M, from about 0.01 M to about 1.3 M, from about 0.01 M to about 1.0 M, from about 0.01 M to about 0.5 M, from about 0.01 M to about 0.1 M, from about 0.01 M to about 0.05 M. The concentration of the magnesium trifluoromethanesulfonate may be about 1.5 M.
Advantageously, the presence of the above-defined halide salt may be capable of promoting solubility of the magnesium salt. In embodiments, the magnesium trifluoromethanesulfonate may be provided in molar concentrations of 0.01 M to 1.5 M while the electrolyte composition remains a homogeneous liquid composition.
The concentration of the one or more inorganic halide salt may be from about 0.01 M to about 10 M, from about 0.05 M to about 10 M, from about 0.1 M to about 10 M, from about 0.5 M to about 10 M, from about 1 M to about 10 M, from about 3 M to about 10 M, from about 5 M to about 10 M, from about 7 M to about 10 M, from about 0.01 M to about 7 M, from about 0.01 M to about 5 M, from about 0.01 M to about 3 M, from about 0.01 M to about 1 M, from about 0.01 M to about 0.5 M, from about 0.01 M to about 0.1 M, from about 0.01 M to about 0.05 M.
The concentration of the one or more inorganic halide salt may be about 0.2 M. The combination of magnesium trifluoromethanesulfonate and 0.2 M MgCl2 may advantageously result in an average Coulombic efficiency of 99.4% over 1000 Mg plating/stripping cycles. Further advantageously, the combination may result in an areal capacity of 5 mAh/cm2.
In embodiments, the magnesium trifluoromethanesulfonate may be present in molar concentrations of up to 1.5 M, when the magnesium chloride salt is present at a concentration of about 1 M, while the electrolyte composition remains a homogeneous liquid composition.
The magnesium ions and the halide ions may be present in the electrolyte composition in a [Mg2+]:[Cl−] ratio of from about >1:1 to 5:1. The magnesium ions and the halide ions may be present in the electrolyte composition in a [Mg2+]:[Cl−] ratio of 2.5:1 to 1.25:1. Alternatively, the magnesium ions and the halide ions may be present in the electrolyte composition such that the concentration of the Mg2+ ions divided by the concentration of the halide ions (such as Cl−) may be in the range of greater than about 1 to about 5. The magnesium ions and the halide ions may be present in the electrolyte composition such that the concentration of the Mg2+ ions divided by the concentration of the halide ions (such as Cl−) may be in the range of about 1.25 to about 2.5.
The present disclosure relates to a liquid electrolyte composition consisting essentially of:
In such electrolyte composition, where the additive is the inorganic halide salt, the inorganic halide salt is a magnesium halide salt. The magnesium halide salt may be magnesium fluoride, magnesium chloride, magnesium bromide, or magnesium iodide. The magnesium salt comprising the trifluoromethane sulfonate anion and the magnesium halide salts are the only metallic salts present. Therefore, this electrolyte composition does not contain non-magnesium metallic salts.
The total concentration of the cations of the inorganic halide salts and the magnesium ions of the magnesium salt divided by the anions of the inorganic halide salt may be from greater than about 1 to about 5 in the electrolyte composition. The total concentration of the cations of the inorganic halide salts and the magnesium ions of the magnesium salt divided by the anions of the inorganic halide salt may be from about 1.25 to about 2.5 in the electrolyte composition. In such an electrolyte composition, the inorganic halide salt is the magnesium halide salt.
Therefore, the total concentration refers to the total of the concentration of the magnesium ions in the magnesium halide salt and the concentration of the magnesium ions in the magnesium salt.
When the inorganic halide salt is magnesium chloride, by having a [Mg2+]:[Cl−] ratio of greater than 1, or a total concentration of the Mg2+ divided by the concentration of the Cl− of greater than 1, the solubility of the magnesium trifluoromethane sulfonate in ether was unexpectedly improved, which resulted in superior Coulombic efficiency and areal capacity. For instance, when 0.4 M of MgCl2 is combined with 0.6 M of magnesium trifluoromethanesulfonate in ether, a clear, homogenous solution is surprisingly obtained. The improvement in solubility advantageously leads to superior Coulombic efficiency and cycle life.
The concentration of the magnesium trifluoromethanesulfonate may be from about 0.01 M to about 1.5 M, from about 0.05 M to about 1.5 M, from about 0.1 M to about 1.5 M, from about 0.5 M to about 1.5 M, from about 1.0 M to about 1.5 M, from about 1.3 M to about 1.5 M, from about 0.01 M to about 1.3 M, from about 0.01 M to about 1.0 M, from about 0.01 M to about 0.5 M, from about 0.01 M to about 0.1 M, from about 0.01 M to about 0.05 M. The concentration of the magnesium trifluoromethanesulfonate may be about 1.5M.
Advantageously, the presence of the above-defined halide salt may be capable of promoting solubility of the magnesium salt. In embodiments, the magnesium trifluoromethanesulfonate may be provided in molar concentrations of 0.01 M to 1.5 M while the electrolyte composition remains a homogeneous liquid composition.
The concentration of the one or more inorganic halide salt may be from about 0.01 M to about 10 M, from about 0.05 M to about 10 M, from about 0.1 M to about 10 M, from about 0.5 M to about 10 M, from about 1 M to about 10 M, from about 3 M to about 10 M, from about 5 M to about 10 M, from about 7 M to about 10 M, from about 0.01 M to about 7 M, from about 0.01 M to about 5 M, from about 0.01 M to about 3 M, from about 0.01 M to about 1 M, from about 0.01 M to about 0.5 M, from about 0.01 M to about 0.1 M, from about 0.01 M to about 0.05 M.
The concentration of the one or more inorganic halide salt may be about 0.2 M. The combination of magnesium trifluoromethanesulfonate and 0.2 M MgCl2 may advantageously result in an average Coulombic efficiency of 99.4% over 1000 Mg plating/stripping cycles.
Further advantageously, the combination may result in an areal capacity of 5 mAh/cm2.
In embodiments, the magnesium trifluoromethanesulfonate may be present in molar concentrations of up to 1.5 M, when the magnesium chloride salt is present at a concentration of about 1 M, while the electrolyte composition remains a homogeneous liquid composition.
The magnesium ions and the halide ions may be present in the electrolyte composition in a [Mg2+]:[Cl−] ratio of from about >1:1 to 5:1. The magnesium ions and the halide ions may be present in the electrolyte composition in a [Mg2+]:[Cl−] ratio of 2.5:1 to 1.25:1.
The present disclosure relates to a liquid electrolyte composition consisting essentially of:
The concentration of the magnesium trifluoromethanesulfonate salt may be about 2.5 M.
Advantageously, the presence of 1-ethyl-3-methylimidazolium chloride, tetrabutylammonium chloride, or a mixture thereof may be capable of promoting solubility of magnesium trifluoromethanesulfonate. Magnesium trifluoromethanesulfonate may be present at molar concentrations of up to 2.5 M, while the electrolyte composition remains a homogeneous liquid composition.
The present disclosure relates to a liquid electrolyte composition consisting essentially of:
Alternatively, in the above liquid electrolyte composition, the total concentration of the magnesium ions in the magnesium trifluoromethanesulfonate and magnesium chloride divided by the concentration of the chloride ions of the magnesium chloride is greater than 1.
The concentration of the magnesium trifluoromethanesulfonate salt may be about 1.5 M.
Advantageously, the presence of magnesium chloride may be capable of promoting solubility of magnesium trifluoromethanesulfonate. Magnesium trifluoromethanesulfonate may be present at molar concentrations of up to 1.5 M, while the electrolyte composition remains a homogeneous liquid composition.
The solvent may not comprise water.
The present disclosure relates to an electrochemical cell comprising:
Non-limiting examples of the invention will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.
Mg(OTf)2 and EMImCl in Ether Solvent
Experimental results confirmed the prediction on the positive effect of 1-Ethyl-3-methylimidazolium chloride (EMImCl) additive to the performance of magnesium trifluoromethanesulfonate (Mg(OTf)2)-based electrolyte. In this invention, several electrolyte compositions with formula presented by x M Mg(OTf)2+y M EMImCl in monoglyme (x=0.25, 0.5, 0.75, 1; y=0.15, 0.3, 0.6, 1.0) are presented. As shown in
It should be noted here that the electrolyte solutions consisting of Mg(OTf)2 and EMImCl in other ethers and their mixtures are also obtainable by controlling Mg(OTf)2:EMImCl molar ratio. In addition, the combination of EMImCl with other magnesium salts, including Mg(TFSI)2 and magnesium perchlorate (Mg(ClO4)2), was examined. These electrolytes, however, demonstrate poor electrochemical performance. It is probably due to instability of TFSI− and ClO4− anions against reduction at Mg metal surface.
Mg(OTf)2 and TBAC in Ether Solvent
The solubility of Mg(OTf)2 was also increased by adding 0.3M (tetrabutylammonium chloride) TBAC into 0.5M Mg(OTf)2 in monoglyme (dimethoxyethane, DME), as shown in
Mg(OTf)2 and MgCl2 in Ether Solvent
It was also found that the inorganic chloride (MgCl2) also helps to improve the solubility of Mg(OTf)2 in ether solvent, by carefully controlling the molar ratio between Mg2+ and Cl− in ether solvent.
In particular, electrolytes with [Mg2+]:[Cl−] ratio greater than 1 were found to be clear and stable.
The electrochemical performance of the electrolyte described herein was evaluated by fabricating a 2032 coin cell comprising the electrolyte, as illustrated in
In asymmetric (Al—C//Mg) cell test, the coin-cell consists of a polished Mg disk (1.27 cm2) as a counter electrode, 2 layers of Celgard separator, Al—C disk (carbon coated Aluminum foil) (1 cm2) as a working electrode, and 25 μl of Mg(OTf)2 electrolyte. In symmetric (Mg//Mg) cell tests, the Al—C disk was replaced by an Mg disk (1.27 cm2).
The asymmetric cell was galvanostatically cycled with a current density of 0.5 mA/cm2. First, an areal capacity of 0.1 tnAh/cm2 of Mg was plated onto Al—C working electrode, Mg was then stripped until the voltage reaches 1.2 V. The Coulombic efficiency (CE) was defined as the ratio of stripping capacity to plating capacity.
Mg(OTf)2 and EMImCl in Ether Solvent
The reversible Mg plating/stripping was successfully demonstrated in 0.5 M Mg(OTf)2+0.3 MEMImCl in monoglyme (
In the first cycle, Coulombic efficiency of the cell was relatively low (49%), which is due to the irreversible reduction of electrolyte components and/or contaminants (e.g. moisture). With increased cycle number, Coulombic efficiency of the cell increased significantly and reached 99% in subsequent cycles.
Among these electrolyte compositions, the cell using 0.5 M Mg(OTf)2+0.3 M EMImCl in monoglyme electrolyte showed best performance. This cell delivered the highest initial Coulombic efficiency (ICE) (49%) and highest Coulombic efficiency was recorded at 99% in subsequent cycles. The longest cycle life of 260 cycles was also achieved at this composition. At higher concentration of Mg(OTf)2 (above 0.5 M), the cells showed lower Coulombic efficiency, which was probably due to high viscosity of electrolyte solution and increased concentration of contaminants. Therefore, the optimum concentration of Mg(OTf)2 is 0.5 M.
Herein, 0.5 M Mg(OTf)2+0.6 M EMImCl in monoglyme was considered as the optimum composition for Mg plating/stripping. At this composition, the Mg plating/stripping cycles were highly reversible up to 400 cycles with a slightly increasing overpotential, from ±0.35 V in early cycles to ±0.6 V at the 400th cycle. In addition, a high ionic conductivity of 5.1 mS/cm was recorded at this electrolyte composition.
The choice of ether solvents for this electrolyte system is not limited to monoglyme. As a representative example, reversible plating/stripping of Mg in an electrolyte consisting of 0.5 M Mg(OTf)2+0.6 M EMImCl in triglyme (
High Areal Capacity of Mg Anode
Towards practical application of Mg metal anode, the Al—C//Mg cells were cycled at high areal capacity of 0.5 mAh/cm2 and 1 mAh/cm2 (
Mg(OTf)2 and TBAC in Ether Solvent
Several electrolyte compositions with formula represented by x M Mg(OTf)2+y M TBAC in monoglyme (x=0.5; y=0.15, 0.3, 0.6, 1) were examined. The experiments were conducted to evaluate the key technical performance of high-performance electrolyte systems, including Mg plating/stripping Coulombic efficiency and cycle life under different cycling conditions. The electrolyte combination consisting of 0.5 M Mg(OTf)2 and 0.3 M TBAC in monoglyme shows excellent electrochemical performance in a half-cell test. Table 4 summarizes the key technical features of the designed electrolyte formula.
The electrolyte consisting of Mg(OTf)2 salt and TBAC additive in ether solvents demonstrated excellent performance in Mg//Al—C asymmetric cell tests. The Mg//Al—C cell demonstrated high average Coulombic efficiency of 97.5% over 500 cycles, when operated at a current density of 0.5 mA/cm2 and areal capacity of 0.1 mAh/cm2 (
The Mg//Al—C cells were also cycled at various current densities and areal capacities to evaluate their robustness. High current densities translated to high power density, while high areal capacities translated to high energy density. The cells demonstrated excellent rate capability with current density up to 4 mA/cm2 and maintained Coulombic efficiency above 98% (
The cycle life of Mg//Al—C cells is significantly dependent on the areal capacity of the plating/stripping process (
Mg(OTf)2 and MgCl2 in Ether Solvent
The four electrolyte compositions which form clear solutions (Table 1) were examined. The experiments were conducted to evaluate the key technical performance of high-performance electrolyte systems, including Mg plating/stripping Coulombic efficiency and cycle life under different cycling conditions. Here, we present the electrochemical performance of the electrolyte combination of Mg(OTf)2 and MgCl2 in monoglyme solvent. Electrolyte combinations based on other solvents are obtainable by controlling [Mg2+]:[Cl−] ratio in an ether solvent or mixtures of ether solvent. Table 5 summarizes the key technical features of the designed electrolyte formula.
The electrolyte combination of Mg(OTf)2 salt and MgCl2 in monoglyme demonstrated excellent performance in Mg//Al—C asymmetric cell tests. The combination of 0.3 M Mg(OTf)2 and 0.2 M MgCl2 in monoglyme was found to be the optimal formula for Mg plating/stripping process. The Mg//Al—C cell demonstrated high average Coulombic efficiency of 99.4% over 1000 cycles at a current density of 0.5 mA/cm2 and areal capacity of 0.1 mAh/cm2 (
The Mg//Al—C cells were also cycled at various high current densities and high areal capacities to evaluate their robustness for practical application. High current densities translated to high power density, while high areal capacities translated to high energy density. The cells demonstrated excellent rate capability with current density up to 2.5 mA/cm2 and maintained Coulombic efficiency above 98% (
Mg(OTf)2 and EMImCl in Ether Solvent
Examination of Mg deposition film on Al—C electrode revealed uniform and non-dendritic morphologies even at high areal capacity (1 mAh/cm2) before and after Mg deposition (
Mg(OTf)2 and TBAC in Ether Solvent
Non-dendritic Mg deposition is an important criterion for safe battery operation. The morphology of a deposited Mg film was examined using scanning electron microscopy (SEM) (
Mg(OTf)2 and MgCl2 in Ether Solvent
Non-dendritic Mg deposition is also an important criterion for safe battery operation. The morphology of a deposited Mg film was examined using scanning electron microscopy (SEM) (
Mg(OTf)2 and EMImCl in Ether Solvent
Symmetric Mg//Mg cells were employed to further investigate the stability of the Mg metal anode in the 0.5 M Mg(OTf)2+0.6 M EMImCl in monoglyme electrolyte at high areal capacity (
Mg(OTf)2 and TBAC in Ether Solvent
The Mg//Mg symmetric cell also demonstrated excellent cycling performance up to 400 cycles or 800 h (
Mg(OTf)2 and MgCl2 in Ether Solvent
The Mg//Mg symmetric cell also demonstrated excellent cycling performance up to 250 cycles or 500 h (
The disclosed electrolyte may be used in electrochemical cells, particularly magnesium ion batteries. As such electrolytes allow efficient plating and stripping of magnesium from a working electrode, such electrolytes may be used for the fabrication and assembly of magnesium-ion batteries which may be used as energy sources in various electrical and electronic devices.
Due to its ease of manufacture, the electrolytes described herein may also be produced on an industrial scale for easy assembly of magnesium ion electrochemical cells, which may be used as an alternative energy storage system to presently available technologies.
It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10201911676S | Dec 2019 | SG | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SG2020/050721 | 12/4/2020 | WO |
