KR101864812B1 - Magnesium salts - Google Patents

Abstract

The present invention relates to a salt of the general formula: Mg ^{2 +} (L _x ) ₆ (PF ₆ ) ₂ , wherein L is dichloromethane, cyclic ether; Or a nitrile of the general formula RC≡N. The method of preparing a salt comprises the steps of providing a Mg metal, activating the Mg metal in a first drying solution comprising a first ligand solution (L ₁ ), adding a dried solution of the activated Mg metal and L ₁ 2 ligand solution comprising: a step, the treated Mg metal solution treated as NOPF ₆ in a dry solution of claim 2 comprising the (L ₂₎ removing the remaining solvent by heating under vacuum and the salt was recrystallized the residual solid Wherein L _x comprises a mixture of L ₁ and L ₂ . The salt may be used as a salt in an electrolyte or as an additive to an electrolyte in a battery or battery.

Description

Magnesium salt {MAGNESIUM SALTS}

The present invention relates to a salt of magnesium hexafluorophosphate. Additionally, the present invention relates to a process for the preparation of magnesium hexafluorophosphate salts and the use of magnesium hexafluorophosphate salts as electrolytes in batteries or batteries.

Lithium-ion batteries are currently used in a variety of electronic devices. The use of a lithium-ion battery is overwhelming than other battery technologies due to the ability of the lithium-ion battery to be recharged without a significant reduction in charge capacity in the short term. In addition, due to the energy density of lithium-ion batteries, lithium-ion batteries can be used in portable products such as laptop computers and mobile phones. However, lithium batteries have been known to have a reduced charge capacity over time. Moreover, problems of thermal runaway and overheating have been extensively reported.

Many lithium-ion electrolyte systems have been developed and studied using a wide variety of lithium salts, including LiBF ₄ , LiClO ₄ , LiNTF ₂ , LiPF ₆ , LiAsF ₆ and LiSbF ₆ as well as others. LiPF ₆ is the preferred electrolyte in lithium-ion cells due to the balance of some properties that have been found not to have any other lithium salts. However, there are concerns over the long-term use of lithium batteries, as lithium is relatively less abundant in the crust and the current price of lithium is higher than other alkali and alkaline earth metals.

In a first aspect, the invention provides a salt of general formula (i)

Mg ^{2 +} (L) _x (PF ₆ ) ₂ (i)

In the above general formula (i), x represents a number of 1 to 6; L are each the following compounds: halomethane, cyclic crown ether; Or a nitrile of the general formula R-C? N.

It has been theoretically recognized that alkaline earth metals such as magnesium can be used as an electrolyte solution in electrochemical cells and batteries. Magnesium is very abundant in the crust, and therefore cheaper per tonne than other alkali and alkaline earth metals. Magnesium also has a higher charge capacity than lithium. Moreover, in a magnesium-ion battery, the magnesium metal can be used as a metal anode without the danger of thermal runaway because no dendrite is formed on the magnesium metal. However, despite this information, magnesium has not been widely applied as an electrolyte or as an anode material because it is stable in a wide voltage range and difficult to form an electrolyte compatible with a plurality of electrodes.

As described above, lithium hexafluorophosphate salts are preferred electrolytes in lithium ion batteries. However, the barrier to the use of magnesium hexafluorophosphate based electrolytes in magnesium-ion batteries is that the synthesis of alkaline earth metal hexafluorophosphate salts is costly and often problematic (often with low purity < RTI ID = 0.0 > Of the material) can be more. Furthermore, PF ₆ in MgPF ₆ ^- anion is reacted with magnesium metal anode, passivated (passivating) MgF ₂ Layer. ≪ / RTI > However, it has been confirmed that the magnesium hexafluorophosphate salt of the present invention can be easily synthesized in a solution under relatively mild conditions and that the resulting salt can be used as an electrolyte in a coin battery battery without occurrence of passivation at the anode .

The term salt used throughout the specification is intended to include the complex magnesium salt with a ligand (L) belonging to the general formula given above. The choice of ligand or mixture of ligands can result in a more stable reaction mixture in the synthesis of the magnesium hexafluorophosphate salt. When x is greater than 1, the ligands may each independently be selected from halomethane, cyclic crown ethers, or nitrile compounds. In the sense of simplifying the reaction mixture during synthesis, when x is greater than 1, L is selected from the following compounds: halomethane, cyclic crown ether; Or a nitrile of the general formula R-C? N. That is, L may include two or more halomethanes, cyclic crown ethers, or nitriles of two or more of the general formula R-C? N.

The halomethane can be chlorinated methane, such as CH ₂ Cl ₂ , CHCl ₃ , CCl ₄ . Chloromethane represents a stable and cost effective drying solvent for synthesis. Dichloromethane (CH ₂ Cl ₂ ) is particularly suitable as a ligand and solvent for the synthesis of magnesium salts due to its low boiling and solubilization characteristics.

The cyclic crown ether can include a typical cyclic crown ether selected from one of the following: [12] -crown-4, [18] -crown-6, [24] -crown-8. Cyclic crown ethers can be used to sequester magnesium cations. The use of a multidentate ligand may be desirable because the magnesium cation is retained in the solution but has a reduced reactivity and can inhibit the magnesium from plating on the electrode surface. These cyclic crown polyethers can be used in combination with halomethane-based solvents such as CH ₂ Cl ₂ , CHCl ₃ , and CCl ₄ without interfering with the desired magnesium salt synthesis.

In terms of the general formula for nitrile and when x is 6 R is independently selected from methyl, ethyl, propyl, butyl, ^t- butyl, pentyl, ethylene, propylene, butylene, pentylene, toluene, May represent an organic group that is selected. Sterically bulky ligands can prevent solvation of the magnesium cation. Thus, in the case of a general formula, R may preferably represent a group that will provide a nitrile that is considered to have low steric hindrance.

L may each be the same nitrile. This makes the synthesis of the salt simpler since the same nitrile solution can be used in both the activation step and the treatment step. For salts, L may be acetonitrile, which is at least sterically hindered nitrile. As an added benefit, the use of acetonitrile provides low solubility as well as good solvation of the magnesium cation, since desolvation under high vacuum can be achieved more easily than with other solvents. This desolvated salt may then be redissolved, for example, using an ether (e. G., THF, diethyl ether) or other donor solvent.

In a second aspect, the invention provides a process for preparing a salt of general formula (ii)

Mg ^{2 +} (L _y ) _x (PF ₆ ) ₂ (ii)

In the above formula (ii), x represents a number of 1 to 6; L _y is selected from the following compounds: halomethane, cyclic crown ether; Or a nitrile of the general formula RC≡N; L _y comprises a mixture of compounds L ₁ and L ₂ ; The method comprises the steps of providing a Mg metal, cleaning and activating the Mg metal in a first drying solution comprising a first compound (L ₁ ), contacting the activated Mg metal with a solution of the first compound L ₁ With NOPF ₆ in a second drying solution comprising a second compound (L ₂ ), removing the residual solvent, and recrystallizing the residual solid to form the salt of formula (ii) .

The residual solvent can be removed by evaporation under vacuum or evaporation such as by heating.

In a third aspect, the present invention provides an electrolyte comprising a salt according to formula (i) or formula (ii). The electrolyte may contain a salt as an additive to a conventional electrolyte, or the salt may be used in a pure solution to form the electrolyte itself with an appropriate solvent.

In a fourth aspect, the present invention provides a battery or battery comprising an electrolyte according to formula (i) or (ii). The salts of the present invention do not have some of the same disadvantages observed in the use of lithium salts in electrochemical cells or batteries. In addition, the salts of the present invention may be used in electrolytes in many cell or battery systems. More specifically, the battery or battery may be, for example, a lithium battery or a lithium-ion battery. However, a battery or battery using the salt of the present invention may more generally be described as a metal-based or metal-ion based battery or battery. Examples of other metal or metal-ion based batteries or batteries may include magnesium, calcium or aluminum metal or ions. When the salts of the present invention are used in electrolytes in metal batteries or batteries, metals such as magnesium, calcium or aluminum can be used as metal anodes without the risk of salt decomposition. Another advantage is that the salt of the present invention may be useful in reducing or limiting the corrosion of aluminum current collectors used in metal or metal-ion based batteries or batteries.

For a better understanding of the present invention, an embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:
1 is an X-ray crystal structure of the salt of the present invention;
Figure 2 is a ¹ H NMR spectrum of the salt of the present invention;
Figure 3 is a ¹³ C NMR spectrum of the salt of the present invention;
4 is a ¹⁹ F NMR spectrum of the salt of the present invention;
5 is a ³¹ P NMR spectrum of a salt of the present invention;
FIG. 6 is a graph showing the relative dielectric constants of 0.12 M Mg (CH _{3) in} 1: 1 THF-CH ₃ CN at a rate of 25 mVs ^-1 in three electrode cells comprising a glassy carbon working electrode, a Mg reference electrode, CN) ₆ (PF ₆ ) _{2 is} cyclic voltammogram at the time of cycling of the solution;
7 is a speed of 25 mVs ^-1 on platinum, stainless steel, aluminum, and glassy carbon working _{electrode, 1: 1 THF-CH 3} CN in _{0.12 M Mg (CH 3 CN)} 6 (PF 6) 2 A linear sweep voltamogram at the time of scanning the solution;
8 is a graph showing the relative dielectric constant at 25 ° C at a rate of 50 mV · s ^{-1 in} a symmetrical three electrode Mg | Mg | Mg flooded cell (extension: extension of the region showing Mg plating) 0.12 M Mg (CH ₃ CN) ₆ (PF ₆ ) _{2 in} THF-CH ₃ CN When cycling the solution, is a cyclic voltammogram;
9 is a graph showing the relative dielectric constants of 0.71 M Mg (CH ₃ CN) in 1: 1 THF-CH ₃ CN at 50 mV s ^{-1 in} a symmetric three electrode Mg | Mg | ₆ (PF ₆ ) ₂ When cycling the solution, is a cyclic voltammogram;
10 is a graph showing the relationship between the concentration of 0.71 M Mg (CH ₃ CN) ₆ (PF ₆ ) _{2 in} 1: 1 THF-CH ₃ CN in an Mg anode, a Mo ₃ S ₄ cathode and an Al current collector at a C / Lt; / RTI > illustrates three galvanostatic discharge-charge cycles of a coin cell containing a solution;
FIG. 11 shows the results of a comparison of 0.71 M Mg (CH ₃ CN) ₆ (PF ₆ ) in 1: 1 THF-CH ₃ CN in a Mg anode, a Mo ₃ S ₄ cathode and a carbon film current collector at a C / _{2 &lt}; / _RTI > solution of a coin cell.

Hereinafter, the present invention will be illustrated with reference to the following examples.

Example  One - Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ of  synthesis

Magnesium metal in the form of a magnesium powder (> 99%) from Sigma Aldrich was cleaned and activated with about 10 mg of I ₂ until the color of the solution became colorless. The resulting mixture was solvated dropwise in a dry solution of CH ₃ CN and NOPF ₆ (purchased from ACROS Organics) under an atmosphere of dry N ₂ at room temperature. After addition of the NOPF ₆ solution, the reaction mixture generated colorless gas (NO), which was drained from the reaction flask under dry N ₂ . The solution was heated gently at 45 < 0 > C overnight. The reaction formula is given by the following (1).

After removal of the solvent, the screen twice recrystallized from acetonitrile and heat the yellow-white solid, a white crystalline powder of _{Mg (CH 3 CN) 6 (} PF 6) 2 was obtained in 52% yield.

Example  2 - Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ of  Specification

A single crystal was obtained by dispersing Et ₂ O in a CH ₃ CN solution of Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ . X-ray analysis was performed on the data collected with the Bruker D8 Quest CCD diffractometer and the complex was confirmed to be the desired salt (Fig. 1).

¹ H, ¹³ C, ¹⁹ F and ³¹ P NMR spectra of a white crystalline powder of Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ are shown in FIGS. 2 to 5, respectively. In particular, the ¹⁹ F and ³¹ P NMR spectra showed doublet and heptet, respectively, characteristic of PF ₆ ^- anions. Unless otherwise indicated, NMR spectra were recorded on a Bruker 500 MHz AVIII HD Smart Probe spectrometer ( ¹ H, ³¹ P 202 MHz, ¹³ C 125 MHz, ¹⁹ F 471 MHz at 500 MHz) or a Bruker 400 MHz AVIII HD Smart Probe spectrometer ¹ H at ³¹ MHz, ³¹ P 162 MHz, ¹³ C 101 MHz, ¹⁹ F 376 MHz). The chemical shifts (δ, ppm) are given for the residual solvent signals for ¹ H and ¹³ C, for 85 P ₃ H ₄ PO _{4 for} ³¹ P and for CCl ₃ F for ¹⁹ F.

The bulk purity of Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ was confirmed by elemental analysis (C, H and N). Elemental microanalytical data were obtained from microanalysis services at the University of Cambridge, Chemistry. Additionally, the IR spectrum of ^{1 represents} the expected C? N stretching band at 2299 cm ^-1 . FT-IR spectroscopic measurements were performed using the PerkinElmer Universal ATR sampling accessories.

Example  3 - as an electrolyte salt Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ of  Usage

All reported cyclic voltammetry and linear sweep voltammetry experiments reported below were carried out in a glove box (MBraun) under a dry argon atmosphere using a dry solvent. Cyclic voltametry and linear sweep voltametry were performed using IVIUM CompactStat.

6 shows the cyclic voltammetry of a 0.12 M Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ solution present in a ratio of 1: 1 with THF-CH ₃ CN. The electrolyte was applied for 20 or more cycles at a rate of 25 mVs ^-1 using a glass carbon working electrode (purchased from Alvatek Limited), a Mg reference electrode and a counter electrode (magnesium ribbon (99.9%) from Sigma Aldrich) -0.5 V and 1.5 V vs Mg. The electrolyte could be cycled for more than 20 cycles with only a moderate loss in plating / stripping current, and a small delamination overvoltage (about 0.25 V vs. Mg) and a plating start at 0 V vs Mg / Mg ^{2 +} Respectively. Extensive features were observed at about 0 V vs Mg / Mg ^{2 +} , which again appears to be the result of a capacitive effect resulting from a surface-area glassy carbon electrode with a high positive potential.

The electrochemical stability of the optimized Mg (PF ₆ ) ₂ electrolyte was investigated using platinum Pt (99.95% platinum wire purchased from Alfa Aesar), glassy carbon (GC), stainless steel (ss) (Results are shown in FIG. 7) by performing linear swept voltametry (LSV) using an aluminum (Al) working electrode (purchased from Dexmet Corp.). On the Pt and GC electrodes, the onset of electrolyte oxidation occurs at about 3 V vs. Mg / Mg ^{2 +} , while on the ss electrode, oxidation occurs at a voltage of about 1.5 V vs Mg / Mg ^{2 +} . In fact, no current is observed when scanning with 4 V vs. Mg / Mg ^{2 +} using an Al working electrode, suggesting that the Al surface is passivated. 1: 1 THF-CH ₃ CN electrolyte solvent mixture, excellent electrochemical stability, and plated on GC than 0.12 M electrolyte solution in pure CH ₃ CN under the same condition was confirmed to exhibit a reversible separation.

Example  In the 4 - Mg - ion battery, Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ of  Usage

Mg (CH ₃ CN) ₆ (PF ₆ ) ₂ salt as an electrolyte in a symmetric cell (Mg | Mg | Mg) was studied using Mg as a working electrode. Battery cycling was performed on the Arbin BT2043 battery test system. THF-CH ₃ CN and 1: 0.12 to 1 ratio exists, _{M Mg (CH 3 CN) 6} (PF 6) 2 Solution and _{0.71 M Mg (CH 3 CN)} 6 (PF 6) 2 Both solutions were cycled between -0.5 V and 1.5 V vs Mg at a rate of 50 mV · s ^-1 for 10 cycles. Figures 8 and 9 show the voltammograms of a 0.12 M electrolyte solution and a 0.71 M electrolyte solution. These solutions exhibited reversible plating and exfoliation of Mg for 10 cycles with little or no loss of plating current density. The reversibility of these processes does not in fact indicate a weakening of the current density, suggesting that the Mg electrode does not comprise insulating or passivating film.

From the above results, it can be understood that the Mg (PF ₆ ) ₂ based electrolyte can promote reversible plating and peeling of Mg using a Mg electrode as well as a GC electrode. Additional studies on these new electrolytes have been performed on circular coin battery batteries. A 0.71 M electrolyte solution was used in a coin cell carried out using a Mg anode and a phase cathode (Mo ₃ S ₄ ) on a Chevrel. Since the reactivity of these electrolytes was observed on stainless steel, the possible side reactions were limited using an unreactive carbon film current collector. A coin cell cycled at C / 100 has a reversible charge-discharge profile (shown using Al current collectors and carbon films (carbon-filled polyethylene sold by Goodfellow Cambridge Limited) collectors in Figures 10 and 11, respectively) Respectively. These cells could be cycled for more than three cycles and reached maximum reversible capacities of 51 mAhg ^-1 and 53 mAhg ^-1 , respectively, for Al and carbon film cells, albeit with somewhat reduced capacities. This observed reduction is common in many Mg-ion systems.

Claims (17)

The salt of general formula (i)
Mg ²⁺ (L) _x (PF ₆ ) ₂ (i)
In the above general formula (i)
x represents a number from 1 to 6;
L represents a ligand selected from one of the following compounds:
Halogen methane,
Cyclic crown ether, or
Nitrile compound. The method according to claim 1,
x is greater than 1,
≪ / RTI > wherein L represents a ligand selected from only one of the following compounds:
Halogen methane,
Cyclic crown ether, or
Nitrile compound. The method according to claim 1,
x is 6,
The ligand L is a nitrile compound of the general formula RC≡N,
Wherein R represents an organic group independently selected from methyl, ethyl, propyl, butyl, ^t- butyl, pentyl, ethylene, propylene, butylene, pentylene, toluene, naphthalene or phenyl. The method of claim 3,
And R is the same as in each ligand represented by L. The method according to claim 1,
Wherein each ligand L is acetonitrile. The method according to claim 1,
x is 1,
L is a cyclic crown ether selected from one of [12] -crown-4, [18] -crown-6, [24] -crown-8. The method according to claim 1,
≪ / RTI > wherein said halomethane is dichloromethane. As a method for producing a salt of the general formula (i)
Mg ²⁺ (L _y ) _x (PF ₆ ) ₂ (i)
In the above general formula (i)
x represents a number of 1 to 6,
L _y represents a ligand independently selected from one of the following compounds:
Halogen methane,
Cyclic crown ether, or
Nitrile compounds;
L _y comprises a mixture of a first compound and a second compound;
The method comprises:
Providing a Mg metal,
Cleaning and activating the Mg metal in a first drying solution comprising a first compound,
Treating the solution of the activated Mg metal and the first compound with NOPF ₆ in a second drying solution comprising the second compound,
Removing the residual solvent, and
Recrystallizing the remaining solid to form the salt of formula (i). 9. The method of claim 8,
x is greater than 1,
L _y represents a ligand selected from only one of the following compounds:
Halogen methane,
Cyclic crown ether, or
Nitrile compound. 9. The method of claim 8,
x is 6,
Wherein the first compound and the second compound are each a nitrile compound of the general formula RC? N,
Wherein R represents independently an organic group selected from methyl, ethyl, propyl, butyl, ^t- butyl, pentyl, ethylene, propylene, butylene, pentylene, toluene, naphthalene or phenyl. 11. The method of claim 10,
Wherein the first compound and the second compound are the same nitrile compound. 11. The method of claim 10,
Wherein the first compound and the second compound are both acetonitrile. 9. The method of claim 8,
x is 1,
L _y is a cyclic crown ether selected from one of [12] -crown-4, [18] -crown-6, [24] -crown-8. 9. The method of claim 8,
Lt; RTI ID = 0.0 > dichloromethane. ≪ / RTI > An electrolyte comprising a salt according to any one of claims 1 to 7 or a salt prepared according to a process as defined in any one of claims 8 to 14. A battery or battery comprising the electrolyte according to claim 15. 17. The method of claim 16,
Wherein the battery or the battery is a magnesium battery or a battery, or a magnesium-ion battery or a battery.

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