Organic cathode materials for magnesium ion batteries

Abstract

Organic charge storage materials capable of storing magnesium ions with fast kinetics are disclosed. The organic charge storage materials include bis-benzoquinone derivatives. The bis-benzoquinone derivatives stabilize the materials so that high energy (for example, greater than 600 Wh / kg) and stable cycling (for example, greater than 50% retention after 15 cycles) are simultaneously achieved. Energy storage devices including the bis-benzoquinone derivatives are also disclosed.

Description

ORGANIC CATHODE MATERIALS FOR MAGNESIUM ION BATTERIESSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with Government support under Award No. DE- AR0001548 awarded by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy. The Government has certain rights in this invention.TECHNICAL FIELD

[0002] The present disclosure relates generally to batteries, and more particularly, to organic cathode materials for use in magnesium ion batteries.BACKGROUND

[0003] This section provides background information to facilitate a better understanding of the various aspects of the disclosure and is not an admission of prior ait.

[0004] Magnesium rechargeable batteries are considered among the top candidates for large-scale energy storage due to their high energy density, safety, and abundance of materials. However, the redox reaction in magnesium batteries relies on the exchange of divalent Mg2+as a charge carrier whose solid-state diffusion in insertion materials is sluggish at room temperature. The search for suitable materials capable of storing Mg2+with fast kinetics remains a great challenge to enable magnesium batteries.

[0005] Recently, organic molecular redox compounds have emerged as low-cost charge storage materials with promising electrochemical properties in different battery chemistries. Figure 1A shows an organic magnesium cell structure for electrode materials for magnesium batteries. A typical organic redox molecule is an organic molecule composed of two or more redox centers attached to a cyclic conjugated system, which is illustrated in Figure IB. The redox center is an organic functional group that can undergo a reversible redox reaction during which the functional group changes its oxidation state from neutral to negatively charged. Contrary to their inorganic counterparts, charge storage in such organic molecules is not sensitive to the type and size of metal ions stored.

[0006] Generally, two categories of compounds are considered for charge storage - polymers and small molecules. Polymers arc high molecular weight organic compounds generally composed of three or more repeating units. However, as schematically illustrated in Figure 1C, the molecular tortuosity within these polymers impedes the uptake of Mg2+and causes the electrode to swell during battery operation. Such electrode swelling is accompanied by an uptake of a large amount of electrolyte, which is detrimental to the specific energy of the cell. Small molecules, on the other hand, are low molecular weight organic compounds bearing two or more redox centers. As shown in Figure ID, during battery operation, the redox intermediates (halfreduced state) tend to dissolve in the electrolyte, which allows the uptake of Mg2+to take place in the liquid phase instead of solid-state, thus leading to fast kinetics.

[0007] While small molecule organic redox compounds have been explored for use in nonaqueous magnesium batteries, such compounds suffer from low material-level energy density (e.g., less than 300 Wh / kg) and / or poor cycling stability and previous attempts to apply such molecules to magnesium storage have not been successful. Only pyrene-4,5,9,10-tetraone (PTO) has been reported to overcome these limitations as a potential cathode material for Mg2+storage. However, the production of PTO requires the use of expensive raw materials and purification processes involving column chromatography, which hinder the viability of commercialization. Moreover, the synthesis of PTO is constrained by low yield (30 percent) and the key precursor not being readily available on a large scale.SUMMARY

[0008] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of claimed subject matter.

[0009] In some embodiments, an electrode is provided, the electrode including an active material for magnesium-ion storage, where the active material includes a bis-benzoquinone compound of Formula (I), Formula (II), or combinations thereof; wherein the bis-benzoquinone compound of Formula (I) is:(I), wherein the bis-benzoquinone compound of Formula (II) is;(II), and wherein X is selected from Ci-Ce alkyl; halo; acetamido; amino; Ci-Ce alkoxy; cyano; carboxylate; sulfonyl; or phosphonate. In one embodiment, the electrode includes the bis-benzoquinone compound of Formula (II), wherein X is selected from C1-C3 alkyl; fluoro; chloro; acetamido; amino; C1-C3 alkoxy; cyano; carboxylate; sulfonate; or phosphonate. In another embodiment, the electrode includes the bis-benzoquinone compound of Formula (II), wherein X is selected from methyl; fluoro; chloro; or acetamido. In still another embodiment, the electrode includes the bis- benzoquinone compound of Formula (II), wherein the bis-benzoquinone compound of Formula (II) is any one of compounds (i)-(ix):In further embodiments, the electrode is a cathode. The cathode may be for a battery, such as a magnesium ion battery.

[0010] In further embodiments, an electrochemical energy storage device is provided, the electrochemical energy storage device including an anode, a non-aqueous electrolyte, and a cathode including an active material, the active material including a bis-benzoquinone compound of Formula (I), Formula (II), or combinations thereof; wherein the bis-benzoquinone compound of Formula (I) is:wherein the bis-benzoquinone compound of Formula (II) is:(II), and wherein X is selected from Ci-Ce alkyl; halo; acetamido; amino; Ci-Ce alkoxy; cyano; carboxylate; sulfonyl; or phosphonate. In some embodiments, the active material includes the bisbenzoquinone compound of Formula (II), wherein X is selected from methyl; fluoro; chloro; acetamido; amino; methoxy; cyano; carboxylate; sulfonate; or phosphonate. The electrochemical storage device may be a magnesium ion battery. In one embodiment, the anode may include magnesium metal.

[0011] In still further embodiments, a vehicle is provided, where the vehicle includes the above-described electrochemical energy storage device.BRIEF DESCRIPTION OF DRAWINGS

[0012] Further features and advantages can be ascertained from the following detailed description that is provided in connection with the drawings described below:

[0013] Figure 1A is a schematic illustration of an organic magnesium cell structure for electrode materials for magnesium batteries.

[0014] Figure IB is a schematic illustration of an organic charge storage molecule.

[0015] Figure 1C is a schematic illustration of a polymeric charge storage material involving electrode swelling upon cycling.

[0016] Figure ID is a schematic illustration of a small organic charge storage material undergoing dissolution-precipitation upon cycling.

[0017] Figure 2 illustrates an expected reaction pathway for a bis-benzoquinone redox unit according to the present disclosure.

[0018] Figure 3 illustrates a general synthesis method for forming the bis-benzoquinone compounds according to the present disclosure.

[0019] Figure 4 A is a cyclic voltammetry curve of Compound 2 measured in 0.1 M TB AP in acetonitrile at 100 mV / s scan rate.

[0020] Figure 4B is a cyclic voltammetry curve of Compound 3 measured in 0.1 M TB AP in acetonitrile at 100 mV / s scan rate.

[0021] Figure 4C is a cyclic voltammetry curve of Compound 4 measured in 0.1 M TB AP in acetonitrile at 100 mV / s scan rate.

[0022] Figure 4D is a cyclic voltammetry curve of Compound 5 measured in 0.1 M TB AP in acetonitrile at 100 mV / s scan rate.

[0023] Figures 5A and 5B are a charge / discharge curve for the first cycle using Compound 2 as an active material and a graph showing the corresponding cycling stability in MMC / G4electrolyte, respectively.

[0024] Figures 5C and 5D are a charge / discharge curve for the first cycle using Compound2 as an active material and a graph showing the corresponding cycling stability in MBF / G4 electrolyte, respectively.

[0025] Figures 6A and 6B are a charge / discharge curve for the first cycle using Compound3 as active material and a graph showing the corresponding cycling stability in MMC / G4 electrolyte, respectively.

[0026] Figures 6C and 6D are a charge / discharge curve for the first cycle using Compound3 as active material and a graph showing the corresponding cycling stability in MBF / G4 electrolyte, respectively.

[0027] Figures 7 A and 7B are a charge / discharge curve for the first cycle using Compound4 as active material and a graph showing the corresponding cycling stability in MMC / G4 electrolyte, respectively.

[0028] Figures 7C and 7D are a charge / discharge curve for the first cycle using Compound4 as active material and a graph showing the corresponding cycling stability in MBF / G4 electrolyte, respectively.

[0029] Figures 8A and 8B are a charge / discharge curve for the first cycle using Compound5 as an active material and a graph showing the corresponding cycling stability in MMC / G4 electrolyte, respectively.

[0030] Figures 8C and 8D are a charge / discharge curve for the first cycle using Compound 5 as an active material and a graph showing the corresponding cycling stability in MBF / G4 electrolyte.DETAILED DESCRIPTION

[0031] It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various illustrative embodiments. Specific examples of components and arrangements are described below to simplify the disclosure. These are, of course, merely examples and are not intended to be limiting. For example, a figure may illustrate an exemplary embodiment with multiple features or combinations of features that are not required in one or more other embodiments and thus a figure may disclose one or more embodiments that have fewer features or a different combination of features than the illustrated embodiment. Embodiments may include some but not all the features illustrated in a figure and some embodiments may combine features illustrated in one figure with features illustrated in another figure. Therefore, combinations of features disclosed in the following detailed description may not be necessary to practice the teachings in the broadest sense and are instead merely to describe particularly representative examples. In addition, the disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not itself dictate a relationship between the various embodiments and / or configurations discussed.

[0032] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art of this disclosure. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well known functions or constructions may not be described in detail for brevity or clarity.

[0033] It is to be understood that any given element of the disclosed embodiments of the invention may be embodied in a single structure, a single step, a single substance, or the like. Similarly, a given element of the disclosed embodiment may be embodied in multiple structures, steps, substances, or the like.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an”and “the” are intended to include the plural (z.e., “at least one”) forms as well, unless the context clearly indicates otherwise.

[0035] The terms “about” and “approximately” shall generally mean an acceptable degree of error or variation for the quantity measured given the nature or precision of the measurements. Numerical quantities given in this description are approximate unless stated otherwise, meaning that the term “about” or “approximately” can be inferred when not expressly stated.

[0036] The term, “alkyl,” means a straight or branched, saturated aliphatic radical having a chain of carbon atoms. The terms, “C1-C3 alkyl” and “Ci-Ce alkyl,” refer to an alkyl group, as defined above, containing at least 1, and at most 3 or 6 carbon atoms, respectively. Examples of such branched or straight-chained alkyl groups include, but are not limited to, methyl, ethyl, n- propyl, isopropyl, isobutyl, n-butyl, t-butyl, n-pentyl, isopentyl, and n- hexyl.

[0037] The term, “alkoxy,” refers to an alkyl group, as defined above, having an oxygen radical attached thereto. The terms, “C1-C3 alkoxy” and “C1-C6 alkoxy,” refer to an alkoxy group as defined herein where the alkyl moiety contains at least 1, and at most 3 or 6, carbon atoms, respectively. Examples of alkoxy groups include methoxy, ethoxy, propyloxy, tert-butoxy, n- propyloxy, iso-propyloxy, n-butyloxy, iso-butyloxy, and the like.

[0038] The terms, “halogen” or “halo,” refer to an atom selected from fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

[0039] The term, “fluoro,” refers to the fluorine atom (F) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0040] The term, “chloro,” refers to the chlorine atom (Cl) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0041] The term, “iodo,” refers to the iodine atom (I) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0042] The term, “bromo,” refers to the bromine atom (Br) when it is used in the context of a halo functional group or halogen functional group or as a halo substituent or halogen substituent.

[0043] The term, “acetamido,” means -CH3CONH2(NHAc).

[0044] The term, “amino,” means -NH2.

[0045] The term, “carboxylate,” refers to the conjugate base of a carboxylic acid, RCOO’.

[0046] The term, “cyano,” means the radical -CN.

[0047] The term, “sulfonyl,” refers to the group -S(O)2- or - SO2-.

[0048] The term, “sulfonate,” refers to the group SOf .

[0049] The term, “substituted,” refers to independent replacement of one or more (typically 1, 2, 3, 4, or 5) of the hydrogen atoms on the substituted moiety with substituents independently selected from the group of substituents listed below or otherwise specified. In general, a nonhydrogen substituent can be any substituent that can be bound to an atom of the given moiety that is specified to be substituted. Examples of substituents include, but arc not limited to, acyl, acylamino, acyloxy, aldehyde, alicyclic, aliphatic, alkanesulfonamido, alkanesulfonyl, alkaryl, alkenyl, alkoxy, alkoxycarbonyl, alkyl, alkylamino, alkylcarbanoyl, alkylene, alkylidene, alkylthios, alkynyl, amide, amido, amino, aminoalkyl, aralkyl, aralkylsulfonamido, arenesulfonamido, arenesulfonyl, aromatic, aryl, arylamino, arylcarbanoyl, aryloxy, azido, carbamoyl, carbonyl, carbonyls including ketones, carboxy, carboxylates, CF3, cyano (CN), cycloalkyl, cycloalkylene, ester, ether, haloalkyl, halogen, halogen, heteroaryl, heterocyclyl, hydroxy, hydroxyalkyl, imino, iminoketone, ketone, mercapto, nitro, oxaalkyl, oxo, oxoalkyl, phosphoryl (including phosphonate and phosphinate), silyl groups, sulfonamide, sulfonyl (including sulfate, sulfamoyl and sulfonate), thiols, and ureido moieties, each of which may optionally also be substituted or unsubstituted.

[0050] The present disclosure provides bis-benzoquinone compounds for use as organic charge storage materials, such as organic electrode materials. In some embodiments, the bis-benzoquinone compounds of the present disclosure are suitable as cathode materials in magnesium batteries. The disclosed electrode materials based on a bis-benzoquinone redox motif provide a commercially viable solution of affordable and easily synthesized alternative organic electrode materials for magnesium cells that deliver high material-level specific energies at high cycling rates for magnesium-ion storage. The presently disclosed bis-benzoquinone compounds are also easily synthesized and can be produced at large scale.

[0051] In one embodiment, the present disclosure provides a redox active material based on a bis-benzoquinone redox motif. The term “active material” or “redox active material” refers to a material which undergoes a change in oxidation state during operation of an electrochemical system, such as a battery. Figure 2 illustrates the expected redox reaction pathway for a bis- benzoquinone redox unit. As demonstrated in Figure 2, bis-benzoquinone is expected to undergo four consecutive one-electron transfers corresponding to the reduction of the four carbonyl redox units. Without being bound by any particular theory, magnesium cells based on the bis- benzoquinone active materials of the present disclosure provide high specific energy and high cycling rates for magnesium-ion storage.

[0052] In one embodiment, the active material includes an unsubstituted or substituted bis-benzoquinone compound. The active material is capable of storing magnesium ions. In one embodiment, the bis-benzoquinone compound is a compound of formula (I):For example, the bis-benzoquinone compound is 2,2’-bi-p-benzoquinone.

[0053] In another embodiment, the bis-benzoquinone compound is a compound of formula(II):where X is Ci-Ce alkyl; halo; acetamido; amino; Ci-Ce alkoxy; cyano; carboxylate; sulfonyl; or phosphonate.

[0054] In one embodiment, X may be a C1-C3 alkyl. For example, X may be selected from methyl, ethyl, or propyl. In another embodiment, X may be a halo selected from fluoro (F), chloro (Cl), bromo (Br), or iodo (I). In another embodiment, X may be a C1-C3 alkoxy. For instance, X may be selected from methoxy, ethoxy, or propyloxy. In still another embodiment, X may be a sulfate, sulfamoyl, or sulfonate. In another embodiment, X may be phosphonate. In some embodiments, X may be selected from methyl, fluoro, chloro, acetamido, amino, methoxy, cyano, carboxylate, or sulfonate.

[0055] Specific examples of bis-benzoquinone compounds of the present disclosure include the following:5,5’-dichloro- 5,5’ -difluoro-2,2’ -2,2’ -bi-p-benzoquinone; 5,5’-dimethyl-2,2’-bi- 2,2’- p-benzoquinone; bi-p-benzoquinone; bi-p-benzoquinone;5,5’-acetamido-2,2’-bi- 5,5’-dimethoxy-2,2’- 5,5’-diamino-2,2’- 5,5’-dicyano-2,2’- p-benzoquinone; bi-p-benzoquinone; bi-p-benzoquinone; bi-p-benzoquinone;2,2’-bi-p- 2,2’-bi-p- benzoquinone-5 , 5 ’ - benzoquinone-5,5 ’ - dicarboxylic acid; disulfonic acid.

[0056] Figure 3 illustrates a general synthesis method for forming the bis-benzoquinone compounds of the present disclosure. The bis-benzoquinone compounds of the present disclosurecan be produced by a straightforward synthesis using water and organic solvent. Tn one embodiment, as shown in Figure 3, the precursor compound is treated with an aqueous solution of ceric ammonium nitrate (CAN) in deionized water. Treatment generally occurs at room temperature for overnight. The obtained precipitate can then be filtered, washed with deionized water, and vacuum dried. Advantageously, only simple filtration is required to isolate pure resulting bis-benzoquinone compounds with high yield (for example, up to about 80%). While the foregoing synthesis method has been exemplified herein, those skilled in the ail will appreciate that the compounds of the present disclosure may be synthesized using any synthetic method known in the art.

[0057] The active materials of the present disclosure, including the bis-benzoquinone compounds disclosed herein, are contemplated for use as organic magnesium battery materials. In one embodiment, the disclosed active materials are used for an electrode in an electrochemical energy storage device. For example, the electrochemical energy storage device may be a magnesium ion battery including an anode, a non-aqueous electrolyte, and a cathode, where the cathode is comprised of the active material including the bis-benzoquinone compounds disclosed herein. In this embodiment, the anode for the magnesium is magnesium metal. The non-aqueous electrolyte may include any magnesium salt that allows for the flow of electrical charge between the cathode and anode of a magnesium-ion battery. Examples of magnesium electrolytes are solutions of magnesium salts dissolved in organic solvents. The magnesium salts include, but are not limited to, magnesium carboranes, magnesium (fluoro)alkoxyborates, magnesium (fluoro)alkoxyaluminate, magnesium bis(trifluoromethanesulfonimide), magnesium borohydrides, magnesium (fluoro)phenolates, magnesium (fluoro)alkoxides, or magnesium bis(hexamethyldisilazide). The organic solvents include, but are not limited to, solvents or mixtures of solvents selected from dimethoxyethane, diglyme, triglyme, tetraglyme, tetrahydrofuran, methyl phosphates, ethyl phosphates, and acetonitrile.

[0058] Magnesium ion battery cells based on the bis-benzoquinone active materials of the present disclosure provide high specific energies and high cycling rates for magnesium-ion storage. Without being bound by any particular theory, it is believed that the bis-benzoquinone compounds of the present disclosure stabilize the active materials so that high energy and stable cycling are simultaneously achieved. This is surprising considering many organic molecular redoxcompounds prove to be inefficient for magnesium ion storage despite their excellent electrochemical performances in lithium-ion batteries.

[0059] In one embodiment, when used in magnesium cells, the bis-benzoquinone active materials of the present disclosure demonstrate specific energies of about 350 Wh / kg or greater. In another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate specific energies of about 400 Wh / kg or greater. In still another embodiment, the bis- benzoquinone active materials of the present disclosure demonstrate specific energies of about 450 Wh / kg or greater. In yet another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate specific energies of about 500 Wh / kg or greater. In another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate specific energies of about 550 Wh / kg or greater. In still another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate specific energies of about 600 Wh / kg or greater.

[0060] In further embodiments, when used in magnesium cells, the bis-benzoquinone active materials of the present disclosure demonstrate a capacity retention after 15 cycles of about 50 percent or greater. In another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate a capacity retention after 15 cycles of about 60 percent or greater. In still another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate a capacity retention after 15 cycles of about 65 percent or greater. In yet another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate a capacity retention after 15 cycles of about 70 percent or greater. In another embodiment, the bis-benzoquinone active materials of the present disclosure demonstrate a capacity retention after 15 cycles of about 75 percent or greater. In still further embodiments, the bis-benzoquinone active materials of the present disclosure demonstrate a capacity retention after 15 cycles of about 80 percent.

[0061] The high energy and stable cycling demonstrated by the bis-benzoquinone active materials of the present disclosure confirm the fast kinetics of magnesium ion uptake in the bis- benzoquinone system. Due to the fast kinetics of magnesium ion uptake, the bis-benzoquinone active materials of the present disclosure are suitable for use in magnesium-ion batteries in a variety of applications. For example, the bis-benzoquinone active materials of the present disclosure can be used in magnesium-ion batteries for vehicles, such as electric vehicles. The bis-benzoquinone active materials of the present disclosure can also be used in magnesium-ion batteries for a variety of consumer electronics. In still further embodiments, the bis-benzoquinone active materials may be used as redox mediators in solar cells, electrocatalysis, electrochemical tests, and / or chemical reactions.

[0062] EXAMPLES

[0063] The following non-limiting examples demonstrate bis-benzoquinone compounds that may be made in accordance with the present disclosure. The examples are merely illustrative of the preferred embodiments of the present disclosure and are not to be construed as limiting the disclosure, the scope of which is defined by the appended claims.

[0064] Materials and methods

[0065] Synthesis of Compounds 2-5

[0066] Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra were recorded on a Thermo Scientific Nicolet iS5 spectrometer. 'H NMR spectra were recorded on JEOL ECA-500 MHz spectrometers. Chemical shifts are reported in ppm (8) with the residual signals of deuterated solvents used for calibration. UV-vis spectra were recorded on Agilent Cary 60 spectrometer. The following precursors and solvents were purchased from commercial suppliers and used as received: 1,4-Dimethoxy toluene, 1- chloro-2,5-dimethoxybenzene, 2-fluoro- 1 ,4-dimethoxybenzene, and 2',5'-dimethoxyacetanilide from TCI chemicals; ceric ammonium nitrate (CAN), tetraglyme (G4), dimethoxyethane (DME) and tetra-n-butylammonium perchlorate (TBAP) from Sigma Aldrich; and acetonitrile and ferrocene from Alfa Aesar.

[0067] Synthesis of 5,5’-dimethyl-2,2’-bi-p-benzoquinone (hereinafter referred to as “Compound 2”): 10 g (66 mmol) of commercial 1,4- dimethoxy toluene was dissolved in 250 mL of acetonitrile and was treated with an aqueous solution of 133 g (242 mmol) of CAN in 250 mL of deionized water at room temperature for overnight according to the procedure disclosed in Love el al. (“Electronic effects in the oxidation of 1 ,4-Dimethoxybenzene derivatives with ceric ammonium nitrate,” Synthetic Communications, 2022, 52, 1581-1589). The obtained precipitate was filtered off, washed with deionized water, and then vacuum dried at 70°C overnight. The resulting yellow powder was 5,5’-dimethyl-2,2’-bi-p-benzoquinone (Compound 2). Yield: 85%.NMR (CDC13): 5 6.82 (s, 2H), 6.71 (d, 2H), 2.11 (d, 6H). v = 3269, 3062, 2954, 1646, 1626, 1527, 1432, 1373, 1232, 1203, 1122, 1033, 1009, 927, 883, 715, 640 cm"1.

[0068] Synthesis of 5,5’-dichloro-2,2’-bi-p-benzoquinone (hereinafter referred to as “Compound 3”): 5 g (29 mmol) of commercial 1-chloro- 2,5-dimethoxybenzene was dissolved in 125 mL of acetonitrile and was treated with an aqueous solution of 29 g (107 mmol) of CAN in 125 mL of deionized water at room temperature for overnight according to the procedure disclosed in Love et al. (2022). The obtained precipitate was filtered off, washed with deionized water, and then vacuum dried at 70°C overnight. The resulting yellow powder was 5,5’-dichloro-2,2’-bi-p- bcnzoquinonc (compound 3). Yield: 41%. ' H NMR (CDCI3): 8 7. 12 (s, 2H). 7.00 (d, 2H). v = 3050, 1666, 1651, 1606, 1568, 1318, 1192, 1005, 906, 847, 789, 726, 635, 587 cm’1.

[0069] Synthesis of 5,5’-difhioro-2,2’-bi-p-benzoquinone (hereinafter referred to as “Compound 4”): 10 g (64 mmol) of commercial 2-fluoro- 1,4-dimethoxybenzene was dissolved in 250 mL of acetonitrile and was treated with an aqueous solution of 130 g (237 mmol) of CAN in 250 mL of deionized water at room temperature for overnight according to the procedure disclosed Love et al. (2022). The obtained precipitate was filtered off, washed with deionized water, and then vacuum dried at 70°C overnight. The resulting yellow powder was 5,5’-difluoro-2,2’-bi-p- benzoquinone (Compound 4). Yield: 40%.NMR (CDC13): 8 6.87 (s, 2H), 6.58 (d, 2H). v = 3073, 1683, 1650, 1601, 1357, 1238, 1198, 1148, 828, 884, 811, 774, 767, 723, 698, 676, 651 cm-1.

[0070] Synthesis of 5,5’-acetamido-2,2’-bi-p-benzoquinone (hereinafter referred to as “Compound 5”): 5 g (25 mmol) of commercial 2', 5'- dimethoxyacetanilide was dissolved in 125 mL of acetonitrile and was treated with an aqueous solution of 51 g (93 mmol) of CAN in 125 mL of deionized water at room temperature for overnight according to the procedure disclosed Love et al. (2022). The obtained precipitate was filtered off, washed with deionized water, and then vacuum dried at 70°C overnight. The resulting yellow powder is 5,5’-acetamido-2,2’-bi-p- benzoquinone (Compound 5). Yield: 70%. 'H NMR (DMSO-d6): 6 9.87 (s, 2H), 7.47 (s, 2H), 6.96 (s, 2H), 2.21 (s, 6H). u = 3309, 1671, 1657, 1633, 1600, 1518, 1369, 1322, 1223, 1187, 1162, 899, 739, 710, 595 cm’1.

[0071] Electrochemical Characterization

[0072] Pi •ior to investigation of magnesium-storage, the electrochemical properties ofCompounds 2-5 were investigated. Cyclic voltammetry (CV) was performed with a Biologic Science Instrument VMP3. A three-electrode cell setup with a glassy carbon working electrode (3 mm diameter, CH instruments), platinum wire counter electrode (CH instruments), a silver wire pseudo-reference-electrode and a supporting electrolyte including 0.1 M tetra-n-butylammonium perchlorate (TBAP) solution in anhydrous acetonitrile were used for measurements. Typically, 1 mM of active material (Compounds 2-5) was dissolved in the electrolyte solution. The voltammograms were recorded inside a glovebox at a scan rate of 100 mV / s and at room temperature. Ferrocene was added to the solution after testing and used as an internal reference.

[0073] All experiments were performed at room temperature, and all cells were assembled in an mBraun argon-filled glovebox (<0.5 ppm water and oxygen content). Electrochemical measurements were recorded on Bio-Logic VMP3 potentiostat. Active material (Compounds 2- 5), Ketjenblack carbon (KB), and polytetrafluoroethylene (PTFE) binder were mixed in a 3:5:2 mass ratio in an agate mortar for 20 minutes. Isopropanol (Florida Lab, 1.5 mLisopropanoi / gpaste) was used in order to improve the mixing and malleability. The resulting rubber-like composite electrode was calendared, dried in air for 6 hours, and then dried under vacuum at 70 °C for overnight. Afterwards, the self-standing composite electrode was cut into discs of diameter 3 / 16- inch. The typical areal mass loading of these composite electrodes is 2 mg / cm2. A 0.45 M of Mg(CBnHn)2 in G4 (“MMC / G4:) solution (provided by Twelfth Vertex LLC8) and a 0.25 M of Mg[B(OCH(CF3)2)4]2 in G4 (“MBF / G4”) solution were used as the electrolyte. Swagelok cells were assembled using polished magnesium foil with 3 / 16-inch diameter, glass fiber separator (Whatman, Grade GF / A, 7 / 16-inch) impregnated with 70 pL of electrolyte, and above-prepared composite electrodes as cathodes. The Swagelok cells were cycled within the potential window of 0.2-3.3 V vs. Mg2+ / Mg at a cycling rate of 1C and 0.2C for MMC / G4 and MBF / G4 electrolytes, respectively.

[0074] Solubility Measurements

[0075] Solubility measurements of Compounds 2-5 in the MMC / G4 and MBF / G4 electrolytes were taken. First, calibration curves were established by five known concentrations of each compound in dimethoxyethane (DME). To measure the solubility, saturated solutions ofeach compound were prepared by dissolving 5 mg of powder in 200 pL of electrolyte solution and kept under stirring at room temperature overnight. The mixtures were then filtered off to obtain homogeneous orange solutions. Next, 10-50 pL of each solution was diluted in 3 mL of DME to measure the absorbance using UV-vis spectroscopy. The measured absorbance value was used to calculate the concentration of the saturated solution using the calibration curve. The solubilities of Compounds 2-5 in the MMC / G4 and MBF / G4 electrolytes are reported in mmol / L and summarized in Table 2 below.

[0076] Results

[0077] Figures 4A-4D present the cyclic voltammograms (CVs) obtained for Compounds 2-5. As demonstrated in Figures 4A and 4D, Compounds 2 and 5 displayed a sequential four- electron reduction behavior accompanied with high stability on the time scale of CV experiments. In contrast, as shown in Figures 4B and 4C, Compounds 3 and 4 exhibited CVs featuring three reversible reduction peaks with only the first two peaks maintaining stability upon cycling. A possible explanation could be related to the difference in electronegativity of the substituent grafted on bis-benzoquinone unit. The last two cathodic peaks correspond to the formation of radical trianion and tetraanion that are estimated to be energetically unstable for unsubstituted bis- benzoquinone according to density functional theory (DFT) calculations reported in the literature. The presence of electron donating substituents, such as methyl (Compound 2) and acetamido (Compound 5), may stabilize the radical trianion and tetraanion by positive inductive and mesomeric effect, respectively; while these anionic forms could be further destabilized by negative inductive effect in the case of electron withdrawing substituents, such as chloro (Compound 3) and fluoro (Compound 4).

[0078] Half-wave potentials were determined for each couple by averaging the cathodic and anodic peak potentials and are shown in Table 1 below. By comparing the first redox event, the redox potential seems to be tuned according to the conventional electronic effect rationale. In fact, Compounds 3 and 4 exhibited higher redox potentials at -0.604 V and -0.654 V vs. Fc+ / Fc, respectively, whereas Compounds 5 and 2 exhibited lower redox potentials at -0.731 V and -0.844 V vs. Fc+ / Fc, respectively.Table 1 : Half-wave reduction potentials (El / 2) for Compounds 2-5

[0079] The electrochemical performances of the bis-benzoquinone compounds in the solid phase were further evaluated in a two-electrode Mg-organic Swagelok cell using two different weakly-coordinating Mg electrolytes: Mg(CBnHi2)2 in tetraglyme (MMC / G4) and Mg[B(hfip)4h in tetraglyme (MBF / G4).

[0080] Figures 5A-5D show the charge / discharge curves for the first cycle and the corresponding capacity retention versus cycle number of a magnesium battery using Compound 2 as the active material. As shown in Figure 5A, in the MMC / G4 electrolyte, the cell exhibited a specific capacity of 419 mAh / g, corresponding to a material utilization of 95%, and an average discharge voltage of 1.72 V vs. Mg2+ / Mg, resulting in a material-level specific energy of 600 Wh / kg. Compound 2 maintained 50% of its capacity after 15 cycles (Figure 5B). As shown in Figure 5C, in the MBF / G4 electrolyte, Compound 2 attained a lower specific capacity of 386 mAh / g, corresponding to a material utilization of 87%, at an average discharge voltage of 1.67 V vs. Mg2+ / Mg. The resulting specific energy was 539 Wh / kg and the capacity retention was 56% after 15 cycles (Figure 5D).

[0081] Figures 6A-6D show the charge / discharge curves for the first cycle and the corresponding capacity retention versus cycle number of a magnesium battery using Compound 3 as the active material. As shown in Figure 6A, in the MMC / G4 electrolyte, the cell attained a specific capacity of 288 mAh / g, corresponding to a material utilization of 76%, and an average voltage of 1.69 V vs. Mg2+ / Mg, resulting in a material-level specific energy of 416 Wh / kg. Compound 3 maintained 71% of its capacity after 15 cycles (Figure 6B). As shown in Figure 6C, in the MBF / G4 electrolyte, Compound 3 achieved a higher specific capacity of 371 mAh / g, corresponding to a material utilization of 87%, at the same average discharge voltage (1.69 V vs. Mg2+ / Mg). The resulting specific energy was 629 Wh / kg and the capacity retention dropped to 46% after 15 cycles (Figure 6D).

[0082] Figures 7A-7D show the charge / discharge curves for the first cycle and the corresponding capacity retention versus cycle number of a magnesium battery using Compound 4 as active material. As shown in Figure 7A, in the MMC / G4 electrolyte, the battery exhibited a specific capacity of 287 mAh / g, corresponding to a material utilization of 67%, and an average voltage of 1.62 V vs. Mg2+ / Mg, resulting in a material-level specific energy of 384 Wh / kg. Compound 4 maintained 65% of its capacity after 15 cycles (Figure 7B). As shown in Figure 7C, in the MBF / G4 electrolyte, Compound 4 attained a higher specific capacity of 359 mAh / g, corresponding to a material utilization of 83%, at an average discharge voltage of 1.65 V vs. Mg2+ / Mg. The resulting specific energy was 493 Wh / kg and the capacity retention dropped to 50% after 15 cycles (Figure 7D).

[0083] Figures 8A-8D show the charge / discharge curves for the first cycle and the corresponding capacity retention versus cycle number of a magnesium battery using Compound 5 as the active material. As shown in Figure 8A, in the MMC / G4 electrolyte, the cell exhibited a specific capacity of 320 mAh / g, corresponding to a material utilization of 98%, and an average voltage of 1.71 V vs. Mg2+ / Mg, resulting in a material-level specific energy of 475 Wh / kg. Compound 5 maintained 80% of its capacity after 15 cycles (Figure 8B). As shown in Figure 8C, in the MBF / G4 electrolyte, Compound 5 exhibited similar specific capacity (328 mAh / g) and an average discharge of 1.68 V vs. Mg2+ / Mg. The resulting specific energy was 480 Wh / kg and the capacity retention dropped to 60% after 15 cycles (Figure 8D).

[0084] In the MMC / G4 electrolyte, all compounds (Compounds 2-5) exhibited similar voltage profiles characterized with a single discharge pseudo-plateau followed with a slope region, except for Compound 2 that showed two pseudo-plateaus. The observed specific capacities ranged from 287 to 419 mAh / g and the average discharge voltages were 1.6- 1.7 V vs. Mg2+ / Mg. The resulting material-level specific energies spanned from 384 to 600 Wh / kg, with Compound 2 possessing the highest specific energy followed by Compounds 5, 3, and 4. These energy metrics were achieved at a high C-rate of 1C and at room temperature, confirming the fast kinetics of Mg2+uptake in the bis-benzoquinone system. Compounds 2 and 5 were able to reach a material utilization greater than 95%, indicating the reduction of almost four carbonyl redox units, whereas Compounds 3 and 4 attained a material utilization of maximum 75% indicating the reduction of only three carbonyl redox units. This aligns with the molecular electrochemistry observed in cyclicvoltammetry, suggesting that Compounds 3 and 4 intrinsically possess the ability to accept only three electrons. The capacity retention after 15 cycles were 50%, 65%, 71% and 80% for Compounds 2, 4, 3 and 5, respectively. This trend indicates that cycling stability followed the order Compounds 5>3>4>2, which can be attributed to the difference in solubility for each compound in the electrolyte, either in its neutral and / or half reduced state.

[0085] In the MBF / G4 electrolyte, all compounds (Compounds 2-5) revealed voltage profiles similar' to that observed in MMC / G4, with average discharge voltages of 1.6-1.7 V vs. Mg2+ / Mg. The observed specific capacities spanned from 332 to 386 mAh / g, highlighting a notable increase for Compounds 3 and 4 and a slight decrease for Compound 2. The resulting material-level specific energies were 480, 496, 537 and 539 Wh / kg for Compounds 5, 4, 3 and 2, respectively. These energy metrics were obtained at a relatively low C-rate of 0.2C, owing to the lower ionic conductivity of the MBF / G4 electrolyte compared to the MMC / G4 electrolyte. In terms of cycling stability, all compounds exhibited relatively lower cyclability, with Compound 5 demonstrating the highest cyclability, retaining 60% of its capacity after 15 cycles. Following closely were compounds 2, 4, and 3, with capacity retentions of 56%, 50%, and 46% after 15 cycles, respectively.

[0086] To better understand the difference in the cycling stability among Compounds 2-5, the solubility of each compound was measured in the pristine state in MMC / G4 and MBF / G4 using UV-vis absorbance spectroscopy. The obtained results are summarized in Table 2.Table 2: Measured solubility of Compounds 2-5 in two electrolyte solutionsIn the MMC / G4 electrolyte, Compounds 3, 2, and 4 exhibited the highest solubility, with concentrations of 207±l mmol / L, 185±1 mmol / L, and 171±1 mmol / L, respectively. In contrast, Compound 5 was found to be significant less soluble (1.6+0.1 mmol / L), owing to the presence of hydrogen bonding. This indicated that the solubility followed the order compounds 5>4>2>3, which is consistent with the observed differences in cyclability during the cell operation. On the other hand, the solubility in the MBF / G4 electrolyte exhibited almost a tenfold increase for allcompounds compared to that in the MMC / G4 electrolyte, with concentrations of 1289+1 mmol / L, 902±l mmol / L, and 11±0.1 mmol / L, for compounds 2, 3, and 5, respectively. Compound 4 stood out with a fourfold increase of solubility. Such a substantial rise in solubility aligns with the observed low cycling stability in the MBF / G4 electrolyte. Given the same cation and solvent are used between the two electrolyte solutions, where the anion is the only distinguishing factor, the notable contrast in solubility could be ascribed to potential intermolecular interactions between the anion and the bis-benzoquinone motif.

[0087] The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the disclosure. Those skilled in the art should appreciate that they may readily use the disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and / or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the disclosure. The scope of the invention should be determined only by the language of the claims that follow. The term “comprising” within the claims is intended to mean “including at least” such that the recited listing of elements in a claim are an open group. The terms “a,” “an” and other singular terms are intended to include the plural forms thereof unless specifically excluded.

Claims

CLAIMSWhat is claimed is:

1. An electrode, comprising: an active material for magnesium-ion storage, the active material comprising a bisbenzoquinone compound of Formula (I), Formula (II), or combinations thereof; wherein the bis-benzoquinone compound of Formula (I) is:wherein the bis-benzoquinone compound of Formula (II) is:wherein X is selected from Ci-Ce alkyl; halo; acetamido; amino; Ci-Ce alkoxy; cyano; carboxylate; sulfonyl; or phosphonate.

2. The electrode of claim 1, comprising the bis-benzoquinone compound of Formula (II), wherein X is selected from C1-C3 alkyl; fluoro; chloro; acetamido; amino; C1-C3 alkoxy; cyano; carboxylate; sulfonate; or phosphonate.

3. The electrode of claim 1, comprising the bis-benzoquinone compound of Formula (II), wherein X is selected from methyl; fluoro; chloro; or acetamido.

4. The electrode of claim 1 , comprising the bis-benzoquinone compound of Formula (II), wherein the bis-benzoquinone compound of Formula (II) is any one of compounds (i)-(ix):

5. The electrode of claim 1, comprising the bis-benzoquinone compound of Formula (II), wherein the bis-benzoquinone compound of Formula (II) is:

6. The electrode of claim 1, comprising the bis-benzoquinone compound of Formula (II), wherein the bis-benzoquinone compound of Formula (II) is:

7. The electrode of claim 1, comprising the bis-benzoquinone compound of Formula (II), wherein the bis-benzoquinone compound of Formula (II) is:(iii).

8. The electrode of claim 1, comprising the bis-benzoquinone compound of Formula (II), wherein the bis-benzoquinone compound of Formula (II) is:(iv).

9. The electrode of claim 1, wherein the electrode is a cathode.

10. The electrode of claim 9, wherein the cathode is for a battery.

11. The electrode of claim 10, wherein the battery is a magnesium ion battery.

12. An electrochemical energy storage device, comprising: an anode, a non-aqueous electrolyte, and the electrode of claim 1.

13. The electrochemical energy storage device of claim 12, wherein the active material comprises the bis-benzoquinone compound of Formula (II), wherein X is selected from methyl; fluoro; chloro; acetamido; amino; methoxy; cyano; carboxylate; sulfonate; or phosphonate.

14. The electrochemical energy storage device of claim 12, wherein the storage device is a magnesium ion battery.

15. The electrochemical energy storage device of claim 14, wherein the anode comprises magnesium metal.

16. The electrochemical energy storage device of claim 14, wherein the electrode is a cathode.

17. A vehicle comprising: the electrochemical energy storage device of claim 12.

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