KR20180102505A - Zn ion secondary battery having VO2(B) particles as electrode active material - Google Patents

Abstract

A zinc ion secondary battery is provided. The zinc ion secondary battery includes an anode containing VO_2(B) particles as an electrode active material. The VO_2(B) particles are composed of VO_6 octahedrons and the VO_6 octahedrons share corners or edges to form a tunnel. A cathode containing a negative active material into which zinc ions can be inserted is disposed. An electrolyte is disposed between the anode and the cathode. The present invention provides a new electrode active material which is rich in resources compared to lithium, environmentally friendly, inexpensive, and low in risk of pollution by moisture.

Description

[0001] The present invention relates to a zinc ion secondary battery including VO2 (B) particles as an electrode active material,

The present invention relates to a secondary battery, and more particularly, to a zinc ion secondary battery.

The secondary battery refers to a battery that can be charged repeatedly as well as discharged. In a typical lithium secondary battery of the secondary battery, lithium ions contained in the positive electrode active material are transferred to the negative electrode through the electrolyte and then inserted (filled) into the layered structure of the negative electrode active material. Then, lithium ions, which have been inserted into the layered structure of the negative electrode active material, It works through the principle of returning to the anode (discharging). Such a lithium secondary battery is currently commercialized and is being used as a small power source for a cellular phone, a notebook computer, and the like, and it is expected that the lithium secondary battery will also be usable as a large power source such as a hybrid car, and the demand is expected to increase.

However, the composite metal oxide, which is mainly used as a cathode active material in a lithium secondary battery, contains a rare metal element such as lithium and may not meet the increase in demand. Accordingly, studies have been made on a sodium secondary battery using sodium, which is rich in supply and low in cost, as a cathode active material. As an example, Korean Laid-Open Patent Application No. 2012-0133300 discloses A _x MnPO ₄ F (A = Li or Na, 0 <x? 2) as a cathode active material. However, sodium battery systems still have complex stability and environmental problems.

Accordingly, a problem to be solved by the present invention is to provide a new electrode active material which is rich in resources compared to lithium, environmentally friendly, inexpensive, and low in risk of pollution by moisture.

According to an aspect of the present invention, there is provided a zinc ion secondary battery. The zinc ion secondary battery has an anode containing VO ₂ (B) particles as an electrode active material. The VO ₂ (B) particles have a crystal structure composed of VO ₆ octahedra, and the VO ₆ octahedrons form a tunnel sharing a corner or an edge. A negative electrode containing a negative active material into which zinc ions can be inserted is disposed. An electrolyte is disposed between the anode and the cathode.

The VO ₂ (B) particles may have a spherical shape as secondary particles in which rod-shaped primary nanoparticles aggregate. The electrode active material may be a VO ₂ (B) / rGO complex comprising a reduced graphene oxide sheets to secure the VO ₂ (B), along with particles in the VO ₂ (B) particles.

According to another aspect of the present invention, there is provided an electrode active material. The electrode active material has a crystal structure of VO ₆ octahedra, and the VO ₆ octahedrons have VO ₂ (B) particles forming a tunnel while sharing corners or edges. Also provided is a reduced graphene oxide sheet for fixing the VO ₂ (B) particles. The zinc ions may be inserted into the tunnel or the inserted zinc ions may be desorbed. The space group of the crystal structure of the VO ₂ (B) particles may be C 2 / m.

According to another aspect of the present invention, there is provided a method for manufacturing an electrode active material. First, a mixed solution containing reduced graphene oxide and a solvent is prepared (the first step). A vanadium (V) oxide is added to the mixed solution to prepare a mixed solution of the reduced graphene oxide and the vanadium (V) oxide (second step). Thereafter, the mixed solution of the reduced graphene oxide and the vanadium (V) oxide is placed in a closed reactor and heat-treated at a boiling point of the solvent or higher to proceed solvent heat synthesis (third step). The solvent may be anhydrous alcohol. The anhydrous alcohol may be anhydrous ethanol. Before proceeding to the second step, the mixed solution containing the reduced graphene oxide and the solvent may be dispersed by using ultrasonic waves. The solvent thermolysis step may be carried out at 120 to 180 degrees for 10 to 14 hours.

According to the present invention, a zinc ion battery system including VO2 (B) or VO2 (B) / rGO complex as an electrode active material can exhibit excellent charge / discharge characteristics.

1 is a schematic view showing an active material for a zinc secondary battery according to an embodiment of the present invention.
2 is a schematic diagram showing the crystal structure of the VO ₂ (B) particles described with reference to FIG.
FIG. 3 is a graph showing X-ray diffraction (XRD) analysis results of the powders obtained in Production Examples 1 and 2. FIG.
4 is SEM (scanning electron microscopy) photographs of the powder obtained in Production Example 1 and the powder obtained in Production Example 2, respectively.
5 is a graph showing charge / discharge characteristics in the first cycle of the zinc ion reversal batteries obtained in Production Example 3 and Production Example 4. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals designate like elements throughout the specification.

Secondary battery active material

1 is a schematic view showing an active material for a zinc secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, VO ₂ (B) particles 20, which are active materials for a zinc secondary battery, are spherical particles that are aggregated secondary particles while rod-shaped primary particles 20 a having a size of several tens of nanometers are stabilized It can also be called a nano load bundle. These secondary particles can have a diameter of several hundred nanometers. Such VO ₂ (B) particles 20 may have a shape in which the primary particles 20a protrude randomly on the surface, and thus may have a very large surface area.

2 is a schematic diagram showing the crystal structure of the VO ₂ (B) particles described with reference to FIG.

2, the crystal structure of the VO ₂ (B) particles may be composed of distorted VO ₆ 8 tetrahedra, the VO ₆ 8 tetrahedron may form a tunnel with the array, sharing a corner or edge. The tunnel may be perpendicular to the c-axis. The space group of such VO ₂ (B) crystal structure may be C 2 / m.

Zinc divalent ions may be inserted into the tunnel or the inserted zinc divalent ions may be desorbed. Further, as described above, since the VO ₂ (B) particles have a large volume-to-volume surface area, the capacity for ions can be greatly improved.

Referring again to FIG. 1, VO ₂ (B) particles 20 may be provided as a VO ₂ (B) / rGO composite anchored on a reduced graphene oxide sheet 10. The VO ₂ (B) / rGO composite includes a reduced graphene oxide sheet 10 and VO ₂ (B) particles 20 fixed or physically bonded on the reduced graphene oxide sheet 10 .

The reduced graphene oxide sheet 10 is obtained by reducing graphene oxide sheets separated by oxidation and agitation of graphite flakes through heat treatment or chemical treatment, and may be provided with several to several tens of layers of graphene layers. Although this reduced graphene oxide sheet 10 has some oxidized and defective areas compared to pure graphene sheets, it may have better conductivity than other carbon materials. Thus, the reduced graphene oxide sheet 10 to which the VO ₂ (B) particles 20 are fixed can contribute to the improvement of the electrical conductivity of the active material.

The production method of the VO ₂ (B) particles may be as follows.

First, a mixed solution containing vanadium (V) oxide (V ₂ O ₅ ) and a solvent is prepared (step 1-1), and the mixed solution is placed in a closed reactor and heat-treated at a boiling point of the solvent (Step 1-2), the synthesized material is filtered, washed and dried to obtain the VO ₂ (B) particles (Step 1-3).

Meanwhile, the production method of the VO ₂ (B) / rGO composite may be as follows.

First, a mixed solution containing a reduced graphene oxide and a solvent is prepared (Step 2-1), and a vanadium (V) oxide (V ₂ O ₅ ) is added to the mixed solution to form the reduced graphene oxide and the vanadium (Step 2-2). The mixed solution of the reduced graphene oxide and the vanadium (V) oxide is placed in a closed reactor and heat-treated at a boiling point of the solvent or higher to perform solvent thermal synthesis (step 2-3 ), And the synthesized material is filtered, washed and dried to obtain the VO ₂ (B) / rGO complex (Step 2-4). In producing the mixed solution of the step 2-1, the reduced graphene oxide may be dispersed in the solvent by using ultrasonic dispersion.

In the above step 1-1 or step 2-1, the solvent may be an alcohol, and may be, for example, ethanol. Further, the solvent may be an anhydrous alcohol, for example, absolute ethanol. The solvent may act as a reducing agent in the solvent thermolysis step (step 1-2 or step 2-3). In particular, when anhydrous ethanol is used, the vanadium (V) oxide can be reduced to VO ₂ (B) without using any other reducing agent.

The solvent thermolysis step (step 1-2 or step 2-3) may be performed at a temperature higher than the boiling point of the solvent, specifically about 100 to 200 degrees, specifically about 120 to 180 degrees, for example about 140 to 160 degrees , About 8 to 16, specifically about 10 to 14 hours. As a result, while rod-shaped primary particles having a size of several tens of nanometers are stabilized, spherical particles that are aggregated secondary particles can be obtained as reaction products. The secondary particles may also be referred to as nano rod bundles.

The synthesized material may be washed using ethanol as an example of an alcohol, and drying may be performed by heat treatment in an oven in an air atmosphere. The heat treatment may proceed at about 60 to 100 degrees.

Zinc secondary battery

A zinc secondary battery according to an embodiment of the present invention includes a cathode containing the above-described active material as a cathode active material, a cathode containing a cathode active material into which zinc divalent ions can be inserted, and an electrolyte disposed therebetween .

<Anode>

The cathode active material, the conductive material, and the binder may be mixed to obtain a cathode material. At this time, the conductive material may be a carbon material such as natural graphite, artificial graphite, coke, carbon black, carbon nanotube, and graphene. The binder may be a thermoplastic resin such as polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene, vinylidene fluoride copolymer, fluorine resin such as propylene hexafluoride, and / or polyolefin resin such as polyethylene or polypropylene .

The positive electrode material can be coated on the positive electrode collector to form the positive electrode. The positive electrode current collector may be a conductive material such as Al, Ni, or stainless steel. The positive electrode material may be applied on the positive electrode collector by a method such as a pressing method using a paste or an organic solvent, applying the paste on a current collector, and pressing and fixing the paste. Examples of the organic solvent include amine-based solvents such as N, N-dimethylaminopropylamine and diethyltriamine; Ethers such as ethylene oxide and tetrahydrofuran; Ketone type such as methyl ethyl ketone; Esters such as methyl acetate; Aprotic polar solvent such as dimethylacetamide, N-methyl-2-pyrrolidone and the like. The paste may be applied on the positive electrode current collector using, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<Cathode>

The negative electrode active material may be a metal, a metal alloy, a metal oxide, a metal fluoride, a metal sulfide, and a natural graphite, an artificial graphite, a coke, a carbon black, a carbon nanotube, And a carbon material such as a pin.

A negative electrode material can be obtained by mixing a negative electrode active material, a conductive material, and a binder. At this time, the conductive material may be a carbon material such as natural graphite, artificial graphite, coke, carbon black, carbon nanotube, and graphene. The binder may be a thermoplastic resin such as polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene, vinylidene fluoride copolymer, fluorine resin such as propylene hexafluoride, and / or polyolefin resin such as polyethylene or polypropylene .

The anode material can be applied on the anode current collector to form the anode. The positive electrode current collector may be a conductive material such as Al, Ni, or stainless steel. The negative electrode material may be applied to the positive electrode current collector by press molding, or by making a paste using an organic solvent or the like, applying the paste to a current collector, and pressing and fixing the paste. Examples of the organic solvent include amine-based solvents such as N, N-dimethylaminopropylamine and diethyltriamine; Ethers such as ethylene oxide and tetrahydrofuran; Ketone type such as methyl ethyl ketone; Esters such as methyl acetate; Aprotic polar solvent such as dimethylacetamide, N-methyl-2-pyrrolidone and the like. The paste may be applied on the negative electrode current collector by, for example, a gravure coating method, a slit die coating method, a knife coating method, or a spray coating method.

<Electrolyte>

The electrolyte may be a liquid electrolyte containing a metal salt and a solvent dissolving the metal salt. Specifically, the zinc salt may be ZnSO ₄ , Zn (NO ₃ ) ₂ or the like, or a mixture of two or more thereof may be used. In addition, the solvent may be an aqueous solvent or an organic solvent.

However, the electrolyte is not limited thereto, and may be a polymer type solid electrolyte or a ceramic type solid electrolyte in which the liquid electrolyte is impregnated in a polymer. In the polymer type solid electrolyte, the polymer may be a polymer compound including at least one of a polyethylene oxide-based polymer compound, a polyorganosiloxane chain, or a polyoxyalkylene chain. As the ceramic solid electrolyte, inorganic ceramics such as sulfides, oxides, and phosphates of the metal may be used. The solid electrolyte may serve as a separator to be described later, and in such a case, a separator may not be required.

<Separator>

A separator may be disposed between the anode and the cathode. Such a separator may be a material having a form such as a porous film made of a material such as a polyolefin resin such as polyethylene or polypropylene, a fluororesin or a nitrogen-containing aromatic polymer, a nonwoven fabric or a woven fabric. The thickness of the separator is preferably as thin as long as the mechanical strength is maintained in that the volume energy density of the battery is high and the internal resistance is small.

<Manufacturing Method of Metal Secondary Battery>

A negative electrode, a separator, and a negative electrode are laminated in this order to form an electrode group, if necessary, the electrode group is rolled up and stored in a battery can, and the sodium secondary battery can be manufactured by impregnating the electrode group with an electrolyte. Alternatively, the electrode assembly may be formed by laminating the positive electrode, the solid electrolyte, and the negative electrode, and if necessary, the electrode assembly may be rolled up and stored in the battery can to manufacture the metal secondary battery.

Hereinafter, exemplary embodiments of the present invention will be described in order to facilitate understanding of the present invention. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

[Experimental Examples; Examples]

Production Example 1: Preparation of VO ₂ (B) Manufacturing

The mixture of V ₂ O ₅ and ethanol was stirred for 30 minutes. The agitated mixture was placed in an autoclave and heat-treated at 150 ° C for 12 hours to perform thermolysis of solvent. After the synthesis, the resulting material was washed with filtration and ethanol, and then dried overnight in an oven at 80 DEG C under vacuum to obtain a powder.

Production Example 2: Preparation of VO ₂ (B) / rGO composite preparation

rGO (IDT international) was placed in ethanol and dispersed for 1 hour using ultrasonic waves. V ₂ O ₅ was added to the obtained rGO dispersion and stirred for 30 minutes by ultrasonic treatment. At this time, the used V ₂ O ₅ was 1.2 g and the used rGO was 1 wt%, that is, 0.012 g with respect to V ₂ O ₅ . The mixture was placed in an autoclave and subjected to heat treatment at 150 ° C for 12 hours to perform thermolysis of a solvent. After the synthesis, the resulting material was washed with filtration and ethanol, and then dried overnight in an oven at 80 DEG C under vacuum to obtain a powder.

FIG. 3 is a graph showing X-ray diffraction (XRD) analysis results of the powders obtained in Production Examples 1 and 2. FIG.

Referring to FIG. 3, the VO ₂ (B) / rGO composite according to Production Example ₂ shows an XRD pattern consistent with VO ₂ (B) according to Production Example 1. This means that even if VO ₂ (B) forms a complex with rGO, no change in the crystal phase occurs. In addition, the fact that the XRD pattern of VO ₂ (B) / rGO complex coincides with the XRD pattern of VO ₂ (B), despite the presence of rGO, implies that the crystallinity of rGO is very low.

In the XRD patterns of VO ₂ (B) / rGO composite and VO ₂ (B), the main peaks were observed at positions of 2 Θ at 25.238 ° and 49.181 °, which corresponded to (1 10 0) and (0 2 0) It is a peak. The half widths of these peaks are 0.265 and 0.494, respectively. From these results, it can be seen that the powder obtained in the production example has single phase crystals and VO ₂ (B) having a space group of C2 / m.

Table 1 below shows the lattice parameters for the powders obtained in Production Examples 1 and 2.

a / A b / A c / Å β / ^o VO ₂ (B) 11.942 (2) 3.677 (1) 6.294 (1) 104.42 (1) VO ₂ (B) / rGO 11.946 (2) 3.679 (1) 6.298 (1) 104.58 (1)

Referring to Table 1, the lattice constants for the two products show very similar values, which do not show a significant difference in the crystal structure, and that the crystal structure of the VO ₂ (B) / rGO composite is not changed by rGO .

4 is SEM (scanning electron microscopy) photographs of the powder obtained in Production Example 1 and the powder obtained in Production Example 2, respectively.

Referring to Figure _{4, VO 2 (B) /} rGO VO 2 (B) in the composite obtained in Production Example 1 VO ₂ (B) and obtained in Preparation Example 2 were all composed of spherical particles. Also, in both cases, it can be seen that each VO ₂ (B) particle is a secondary particle in which rod-shaped primary particles are aggregated. Therefore, even if rGO is added, it can be seen that the shape of the particles is not changed by the solvent thermo-synthetic method. In the case of the VO ₂ (B) / rGO complex, the VO ₂ (B) spherical particles are fixed on the rGO plate, and the physical bonding between the VO ₂ (B) and the rGO plate is believed to improve the electronic conductivity.

Production Example 3: Preparation of VO ₂ (B), zinc ion secondary battery with positive electrode

A mixture of VO2 (B) powder, a conductive material (Ketjen black: Super P = 1: 1) and a polyvinylidene fluoride prepared in Preparation Example 1 in an organic solvent (NMP (N- Methyl-2-pyrrolidone) to form a slurry. The slurry was coated on a stainless steel foil current collector and dried at 80 ° C. overnight under vacuum to form a positive electrode.

A zinc ion battery was prepared as a coin cell using an aqueous electrolyte solution containing the anode, zinc metal plate as an anode, electrolyte 1M ZnSO ₄ and water as a solvent.

Production Example 4: Preparation of VO ₂ (B) / rGO composite was used.

Except that the VO ₂ (B) / rGO composite powder prepared in Preparation Example 2 was used in place of the VO ₂ (B) powder prepared in Production Example 1, .

Evaluation Example 1: Evaluation of the characteristics of zinc ion

The discharge of the zinc ion secondary battery obtained in Production Example 3 and Production Example 4 was carried out at a constant current discharge of 0.2 mA up to 50 mA / g, and the constant current charging was performed up to 1.1 V at the same rate as the discharging rate.

5 is a graph showing charge / discharge characteristics in the first cycle of the zinc ion reversal batteries obtained in Production Example 3 and Production Example 4. FIG.

When FIG. 5a and FIG 5b, VO ₂ (B) and VO ₂ (B) / rGO composite These results VO ₂ in a zinc cell system has shown the discharge capacity of each of 281 mAhg ^-1 and 298 mAhg ^-1 (B). &Lt; / RTI &gt; In addition, the capacity of VO ₂ (B) could be effectively increased by attaching rGO having excellent conductivity.

6 shows a graph (a) of charge and discharge of the initial cycle of the zinc ion battery obtained through Production Example 3 using the VO ₂ (B) cathode active material and an X-ray XRD graph (b) of the cathode active materials in the initial cycle. To this end, six zinc ion secondary batteries were fabricated and the cells were electrochemically tested to the voltages indicated in the charge and discharge graph (a), and then decomposed to recover the electrodes. The recovered electrodes were washed with distilled water After drying for one day in an oven at 80 ° C, XRD was measured (b).

Referring to FIG. 6, it can be seen that although the 110, 310 / -311, and -511 planes of the XRD peak, VO ₂ (B), are shifted during discharge and charge, no new peak occurs. Specifically, the peak (v) is formed during the discharge reaction and disappears again, which is a side reaction product of Zn ₄ SO ₄ (OH) ₆ .0.5H ₂ O in the ₁ M ZnSO ₄ aqueous solution Respectively. On the other hand, the peak (x) was estimated to be due to a stainless steel foil as a current collector. As described above, are caused, only the charge and discharge process, that is, VO ₂ (B) is zinc ions into the cathode active material do not represent a new XRD peaks of VO ₂ (B) a positive electrode active material in the process of being inserted or desorbed shift, insertion of a zinc ion, or It also means that the crystal structure of the VO ₂ (B) cathode active material is not affected by desorption. At this time, the zinc ions can be inserted into and removed from the tunnel without changing the VO ₂ (B) crystal structure described with reference to FIG.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, This is possible.

Claims (11)

The crystal structure is composed of VO ₆ 8 tetrahedra, the VO ₆ 8 tetrahedra are positive, including VO ₂ (B) particles to form a tunnel, sharing a corner or an edge as an electrode active material;
A negative electrode containing a negative active material into which zinc ions can be inserted; And
And an electrolyte disposed between the positive electrode and the negative electrode. The method according to claim 1,
Wherein the VO ₂ (B) particles have a spherical shape as secondary particles in which rod-shaped primary nanoparticles are aggregated. 3. The method according to claim 1 or 2,
Wherein the electrode active material is a VO ₂ (B) / rGO composite comprising a reduced graphene oxide sheet that fixes the VO ₂ (B) particles together with the VO ₂ (B) particles. The crystal structure is VO ₆ is made up of octahedral, the VO ₆ octahedral VO ₂ that are formed in the tunnel while sharing a corner or edge (B) particles; And
The _{VO 2 (B) VO 2 (} B) / rGO the composite electrode active material comprising a reduced graphene oxide sheets to secure the particles. 5. The method of claim 4,
Wherein the zinc ions are inserted into the tunnel or the inserted zinc ions are desorbed. 5. The method of claim 4,
And the space group of the crystal structure of the VO ₂ (B) particles is C 2 / m. A first step of producing a mixed solution containing reduced graphene oxide and a solvent;
A second step of adding a vanadium (V) oxide into the mixed solution to prepare a mixed solution of the reduced graphene oxide and the vanadium (V) oxide; And
And a third step of subjecting the mixed solution of the reduced graphene oxide and the vanadium (V) oxide to heat treatment at a boiling point or higher of the solvent in a closed reactor to perform thermal solvent synthesis. 8. The method of claim 7,
Wherein the solvent is anhydrous alcohol. 9. The method of claim 8,
Wherein the anhydrous alcohol is anhydrous ethanol. 8. The method of claim 7,
Before proceeding to the second step,
Further comprising dispersing the mixed solution containing the reduced graphene oxide and the solvent using ultrasonic waves. 8. The method of claim 7,
Wherein the solvent thermally-synthesizing step is performed at 120 to 180 degrees for 10 to 14 hours.

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