KR101413004B1 - Electrolyte Having Novel Structure and Magnesium Secondary Battery Comprising the Same - Google Patents

Abstract

The present invention relates to an electrolyte for a magnesium secondary battery comprising magnesium ion and a magnesium imidazolium salt containing N-heterocyclic carbine coordinately bonded to the magnesium ion as an ionic salt.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an electrolyte having a novel structure and a magnesium secondary battery including the electrolyte,

The present invention relates to an electrolyte having a novel structure and a magnesium secondary battery comprising the same, and more particularly, to an electrolyte for a magnesium secondary battery comprising N-heterocyclic carbine coordinatively bonded to magnesium ions and magnesium ions, And more particularly to a magnesium secondary battery comprising an electrolyte.

As technology development and demand for mobile devices have increased, the demand for secondary batteries as energy sources has been rapidly increasing. Many researches have been conducted on lithium secondary batteries with high energy density and discharge voltage among such secondary batteries. .

Such lithium secondary batteries mainly use lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and lithium mixed transition metal oxide as cathode active materials. Despite their excellent performance, they are expensive to manufacture per cell, and there is a risk of ignition or explosion , There is a fear of depletion of lithium resources in the future. In recent years, researches on saltwater and magnesium secondary batteries have been actively conducted as an alternative.

A magnesium secondary battery is a secondary battery in which a magnesium metal is used as a negative electrode and magnesium ions are inserted into and discharged from a positive electrode active material to enable charging and discharging. The secondary battery is advantageous in that a large amount of raw materials can be obtained from salt water and minerals and light in weight. In addition, the lithium secondary battery has been theoretically attracted attention as a next generation secondary battery because the energy density is twice or more theoretically, is low in cost, and stable in the atmosphere.

However, development of a magnesium secondary battery including a cathode active material having a high energy density and an electrolyte having a wide potential region beyond the lithium secondary battery has been difficult.

One of these difficulties is related to the ion conductive electrolyte. In the process of forming the electric circuit by the ion conductive electrolyte passing the ions between the cathode and the anode, most of the electrolyte forms a film on the cathode, It is an issue to stop. Particularly, when a cyclic carbonate or a chain carbonate widely used as an electrolyte of a conventional lithium secondary battery is used for a magnesium secondary battery, a coating is formed on the surface of magnesium used as a negative electrode, thereby deteriorating the performance of the secondary battery and stopping the electrochemical reaction .

In order to solve these problems, there has been proposed a method of using a Grignard reagent which does not form a film on the surface of the cathode and has a merit of continuously charging and discharging. However, .

Specifically, the electrochemical reaction at the cathode is Mg ↔ Mg ^{2 + +} 2e ^- and has the forward the time of electric discharge, the reverse reaction proceeds at the time of charging, the anode _{^{Mg y MX + zMg 2 + ↔}} Mg y + z MX + 2e - (M = metal ion). Here, it is important to develop a stable cathode active material by reversibly reacting with the magnesium ion contained in Mg _y MX. It has been confirmed that the above-described electrolyte such as Grignard reversibly deposits magnesium, but since the Grignard electrolyte is a strong electron donor, And destabilizes the negative electrode active material, thereby making it difficult to use the positive electrode active material.

Accordingly, it is urgent to develop an electrolyte capable of inhibiting the film formation of magnesium and widening the oxidation potential region while stabilizing the anode.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-described problems of the prior art and the technical problems required from the past.

The inventors of the present application have conducted intensive studies and various experiments and have found that a magnesium imidazolium salt substituted with an N-heterocyclic carbine form of an alkyl group having electronegativity in a Grignard reagent as described later It was confirmed that a magnesium film was not formed on the negative electrode and that the oxidation potential area was wide and high efficiency characteristics were obtained, and thus the present invention was completed.

Accordingly, the electrolyte for a magnesium secondary battery according to the present invention is characterized in that it contains an ionic salt of magnesium imidazolium salt including N-heterocyclic carbine in which magnesium ion and magnesium ion are coordinately bound.

The magnesium imidazolium salt is a structure in which an alkyl group having electronegativity in the Grignard reagent is substituted with a stable N-heterocyclic carbine form. More specifically, the chemical structure of the Grignard reagent is RMgX (R = alkyl group, X = Cl, Br, etc.) and substituting the alkyl group into the N-heterocyclic carbine form as described above, And magnesium is coordinated to the electron pair. Therefore, the bond between carbon and magnesium weakens and the magnesium can stably fall into ionic form.

The electrolyte may comprise a polar aprotic solvent, and the polar aprotic solvent may be one selected from the group consisting of THF, DMSO, DMF, Acetone, Acetonitrile, and HMPA, Particularly preferred is THF.

The concentration of the magnesium imidazolium salt may be preferably from 0.1 M to 0.5 M, and more preferably from 0.2 M to 0.4 M. [ When the concentration of the magnesium imidazolium salt is less than 0.1 M, the magnesium ion concentration is low and the electric capacity can not be exhibited at all. When the magnesium imidazolium salt concentration is more than 0.5 M, the ion mobility is significantly reduced Which is undesirable.

In one preferred example, the magnesium imidazolium salt may be a salt represented by the following formula (1).

(1)

(One)

In this formula,

R ₁ and R ₂ are each independently an alkyl or aryl group;

THF is tetrahydrofuran;

The alkyl group is a straight or cyclic alkyl group having 1 to 10 carbon atoms, and the aryl group is a substituted or unsubstituted aryl group having 4 to 8 carbon atoms.

The substituted aryl group may be, for example, an alkyl group substituted with an alkyl group having 1 to 5 carbon atoms, an alkenyl group, etc., and an aryl group substituted with an amine, a halogen, etc., but is not limited thereto.

The electrolyte according to the present invention may further comprise a Lewis acid together with a magnesium imidazolium salt. The Lewis acid is not particularly limited as long as it can receive the unshared electron pair of N-heterocyclic carbin as an electron pair acceptor. For example, it is selected from the group consisting of AlCl ₃ , BF ₃ , Cu ²⁺ and NH ₃ And among them, AlCl ₃ is preferable.

At least a portion of the AlCl ₃ is reacted with a magnesium imidazolium salt to be present as a material of Formula 2 below.

(2)

(2)

In the above formula, R ₁ , R ₂ and THF are the same as defined in formula (1).

The mixing ratio of the magnesium imidazolium salt to the aluminum halogen compound is preferably 1: 1 to 3: 1.

The present invention also provides a magnesium secondary battery including the above-described electrolyte, wherein the magnesium secondary battery comprises an anode, a cathode, a separator, and an electrolyte for a magnesium secondary battery.

For example, Mo ₆ S ₈ may be used as the positive electrode active material, and the positive electrode active material may be applied to the current collector, followed by drying and rolling.

The current collector should be stable without causing electrochemical changes in the cell. When the current collector is corroded, the current collecting ability can not be exhibited as the battery cycle is repeated, thereby shortening the life of the battery.

The current collector is preferably made of stainless steel, and more preferably, a material coated with a primer including a conductive material and a polymer material on a metal base.

The metal base material is a metal that is stable at the potential of the magnesium secondary battery and is not particularly limited as long as it can serve to supply and deliver electrons. For example, stainless steel, nickel, titanium, Among them, stainless steel is particularly preferable.

Such a metal substrate has a thickness of about 1 to 150 mu m and may be formed in various forms such as foil, film, sheet, net, porous body, foam, and particularly preferably in the form of a foil.

The primer serves to increase the adhesion of the cathode active material to the metal substrate while suppressing the increase of the internal resistance to the maximum, and may preferably include the conductive material and the polymer material in a weight ratio of 1:10 to 10: 1. If the content of the conductive material is too small, the operating characteristics of the battery are deteriorated due to the increase of the internal resistance. If the content of the polymer material is too small, the desired adhesive force can not be provided.

In addition, a conductive material, a binder, a filler, and the like may be optionally included.

The conductive material is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture including the cathode active material. Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component which assists in bonding of the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 30% by weight based on the total weight of the mixture containing the cathode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene , Polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluorine rubber, and various copolymers.

The filler is optionally used as a component for suppressing the expansion of the electrode, and is not particularly limited as long as it is a fibrous material without causing any chemical change in the battery. Examples of the filler include olefin-based polymerizers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode may generally be a magnesium or magnesium compound in a metal state having a thickness of 3 to 500 μm and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The separation membrane is interposed between the anode and the cathode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. Such separation membranes include, for example, olefinic polymers such as polypropylene, which are chemically resistant and hydrophobic; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte may also serve as a separation membrane.

The magnesium secondary battery may be used as a unit battery in a middle- or large-sized battery module including a plurality of battery cells used as a power source for a middle- or large-sized device requiring high temperature stability, long cycle characteristics, and high rate characteristics.

Preferred examples of the above medium to large devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart, and the like, but the present invention is not limited thereto.

As described above, the magnesium secondary battery using the electrolyte according to the present invention can broaden the oxidation potential area while inhibiting formation of the magnesium film on the negative electrode, and thus can be used as a power source for an electric vehicle or a large-capacity power storage device.

Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto.

≪ Example 1 >

In a flask containing tetrahydrofuran in a glove box in an argon atmosphere, substituted N-heterocyclic carbines in which R ₁ and R ₂ are ethyl and methyl, respectively, and magnesium chloride are added in the formula (1) and stirred for 5 hours, All of the hydrofuran was blown off under vacuum and the remaining solid material was recrystallized from tetrahydrofuran and diethyl ether to prepare a salt for an electrolyte for a magnesium secondary battery.

≪ Example 2 >

The electrolyte for the secondary battery prepared in Example 1 and aluminum trichloride (AlCl ₃ ) were stirred for 24 hours to prepare an electrolyte salt for a magnesium secondary battery.

<Comparative Example>

A 1M hexane solution of dibutylmagnesium and 1M hexane solution of dichloromethyl magnesium was stirred at a ratio of 1: 2 for 48 hours in a flask of argon atmosphere, and then all of the solvent was removed by vacuum, and anhydrous tetrahydrofuran was added to prepare a 0.25M solution .

<Experimental Example>

The electrolytes were prepared by dissolving the salts prepared in Examples 1 and 2 and the salt of Comparative Example 1 in tetrahydrofuran, respectively, and electrochemical performance was tested by using a magnesium foil as an anode and a magnesium foil as a cathode.

Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (9)

1. An electrolyte for a magnesium secondary battery comprising a magnesium imidazolium salt comprising magnesium ion and N-heterocyclic carbin coordinately bonded to the magnesium ion as an ionic salt,
Wherein the electrolyte further comprises an aluminum halogen compound,
Wherein the aluminum halide compound is present as a substance of the following formula (2) by reacting with a magnesium imidazolium salt.

(2)
In this formula,
R ₁ and R ₂ are each independently an alkyl or aryl group;
THF is tetrahydrofuran. The electrolyte of claim 1, wherein the electrolyte comprises a polar aprotic solvent. The electrolyte for a magnesium secondary battery according to claim 1, wherein the concentration of the magnesium imidazolium salt is 0.1 to 0.5 M. 3. The electrolyte for a magnesium secondary battery according to claim 1, wherein the magnesium imidazolium salt is represented by the following formula (1): &lt; EMI ID =

(One)
In this formula,
R ₁ and R ₂ are each independently an alkyl or aryl group;
THF is tetrahydrofuran. The electrolyte for a magnesium secondary battery according to claim 4, wherein the alkyl group is a straight chain or cyclic alkyl group having 1 to 10 carbon atoms, and the aryl group is a substituted or unsubstituted aryl group having 4 to 8 carbon atoms. delete delete The electrolyte for a magnesium secondary battery according to claim 1, wherein the mixing ratio of the magnesium imidazolium salt to the aluminum halogen compound is 1: 1 to 3: 1. A magnesium secondary battery comprising an electrolyte according to any one of claims 1 to 5 and 8.