WO2020013488A1 - Method for preparing iron oxide - Google Patents

Abstract

The present invention relates to a method for preparing iron oxide and, more specifically, provides a method for selectively preparing high-purity iron oxide by drying and heat-treating Fe(NO₃)₃·9H₂O, wherein the temperature and the time of the drying and heat-treatment are controlled.

Description

Method of manufacturing iron oxide

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0079821 dated July 10, 2018, and all content disclosed in the literature of that Korean patent application is incorporated as part of this specification.

The present invention relates to a method for producing iron oxide applicable to the positive electrode additive of a lithium-sulfur battery.

Secondary batteries, unlike primary batteries that can only be discharged once, have become an important electronic component of portable electronic devices since the 1990s as an electrical storage device capable of continuous charging and discharging. In particular, since the lithium ion secondary battery was commercialized by Sony, Japan in 1992, it has led the information age as a core component of portable electronic devices such as smartphones, digital cameras, and notebook computers.

In recent years, lithium ion secondary batteries have been widely used in applications such as vacuum cleaners, power tools for electric tools, electric bicycles and electric scooters, and electric vehicles (EVs) and hybrid electric vehicles (hybrid electric vehicles). to high-capacity batteries used in applications such as vehicles (HEV), Plug-in hybrid electric vehicles (PHEVs), robots, and Electric Storage Systems (ESS). Demand is increasing.

However, there are some problems to be actively used in transport equipment such as electric vehicles, PHEVs, and lithium secondary batteries, which have the best characteristics among the secondary batteries, and the biggest problem is the capacity limitation.

Lithium secondary battery is basically composed of materials such as positive electrode, electrolyte, negative electrode, etc. Among them, since positive and negative electrode materials determine the capacity of battery, lithium ion secondary battery is due to material limitations of positive and negative electrodes. Limited by capacity In particular, the secondary battery to be used for applications such as electric vehicles, PHEVs, so that the use of as long as possible after a single charge, the discharge capacity of the secondary battery is very important. One of the biggest constraints on the sale of electric vehicles is that the distance that can be driven after a single charge is much shorter than that of a normal gasoline engine.

The capacity limit of such a lithium secondary battery is difficult to solve completely due to structural and material constraints of the lithium secondary battery despite many efforts. Therefore, in order to fundamentally solve the capacity problem of the lithium secondary battery, it is required to develop a new concept of a secondary battery that goes beyond the existing secondary battery concept.

Lithium-sulfur secondary battery goes beyond the capacity limit determined by the insertion / decalation reaction of lithium ion layered metal oxide and graphite, which is the basic principle of conventional lithium ion secondary battery, and transition metal replacement and cost reduction It is a new high-capacity, low-cost battery system that can bring about.

A lithium-sulfur secondary battery is a lithium ion and the sulfur conversion (conversion) reaction at the anode ^- the theoretical capacity resulting from ^{_{(S 8 + 16Li + + 16e}} → 8Li 2 S) reached 1,675 mAh / g anode is lithium metal (theoretical capacity: 3,860 mAh / g) enables ultra high capacity battery systems. In addition, since the discharge voltage is about 2.2 V, it theoretically shows an energy density of 2,600 Wh / kg based on the amount of the positive electrode and the negative electrode active material. This value is 6 to 7 times higher than the energy theoretical energy density of 400 Wh / kg of a commercial lithium secondary battery (LiCoO ₂ / graphite) using a layered metal oxide and graphite.

Lithium-sulfur secondary battery has been attracting attention as a new high-capacity, eco-friendly and low-cost lithium secondary battery since it is known that the battery performance can be dramatically improved by forming nanocomposites around 2010. Is being done.

One of the major problems of the lithium-sulfur secondary battery that has been discovered so far is that the electrical conductivity of sulfur is about 5.0 x 10 ^-14 S / cm, which is close to the non-conductor, so that the electrochemical reaction is not easy at the electrode. The voltage is far below theory. Early researchers tried to improve the performance by methods such as mechanical ball milling of sulfur and carbon or surface coating with carbon, but it was not effective.

In order to effectively solve the problem that the electrochemical reaction is limited by electrical conductivity, as in the example of LiFePO ₄ , one of the other cathode active materials (electric conductivity: 10 ^-9 to 10 ^-10 S / cm), the particle size is tens of nanometers. It is necessary to reduce the size to the following and conduct surface treatment with conductive materials. For this purpose, various chemicals (melt impregnation of nano-sized porous carbon nanostructures or metal oxide structures) and physical methods (high energy ball milling) are reported. It is becoming.

Another major problem associated with lithium-sulfur secondary batteries is the dissolution of lithium polysulfide, an intermediate of sulfur produced during discharge, into the electrolyte. As the discharge proceeds, sulfur (S ₈ ) continuously reacts with lithium ions such that S ₈ → Li ₂ S ₈ → (Li ₂ S ₆ ) → Li ₂ S ₄ → Li ₂ S ₂ → Li ₂ S, etc. (Phase) is continuously changed. Among them, long chains of sulfur such as Li ₂ S ₈ and Li ₂ S ₄ (lithium polysulfide) are easily dissolved in general electrolytes used in lithium ion batteries. When this reaction occurs, not only the reversible cathode capacity is greatly reduced, but also the dissolved lithium polysulfide diffuses to the cathode, causing various side reactions.

Lithium polysulfide, in particular, causes a shuttle reaction during the charging process, which causes the charging capacity to continuously increase, thereby rapidly decreasing the charge and discharge efficiency. Recently, various methods have been proposed to solve this problem, and can be classified into a method of improving the electrolyte, a method of improving the surface of the negative electrode, and a method of improving the characteristics of the positive electrode.

The method of improving the electrolyte is to prevent the dissolution of polysulfide into the electrolyte using new electrolytes such as a functional liquid electrolyte, a polymer electrolyte, and an ionic liquid of a new composition, or to control the viscosity and the like to disperse the negative electrode. This is to control the shuttle reaction as much as possible.

Research is actively conducted to control the shuttle reaction by improving the characteristics of the SEI formed on the surface of the anode. Typically, electrolyte additives such as Li _x NO _y and Li _x SO _y are added to the surface of the lithium anode by adding an electrolyte additive such as LiNO ₃ . And a method of forming a thick functional SEI layer on the surface of the lithium metal.

Finally, methods to improve the characteristics of the anode include forming a coating layer on the surface of the anode particles to prevent the dissolution of polysulfide or adding a porous material that can catch the dissolved polysulfide. A method of coating the surface of the positive electrode structure containing the electrode, a method of coating the surface of the positive electrode structure with a metal oxide conducting lithium ions, and a porous metal oxide having a large specific surface area and large pores capable of absorbing a large amount of lithium polysulfide. A method of adding to the method, attaching a functional group capable of adsorbing lithium polysulfide to the surface of the carbon structure, and encapsulating sulfur particles using graphene or graphene oxide and the like have been proposed.

While such efforts are underway, there is a problem that the method is not only complicated but also limited in the amount of sulfur as an active material. Therefore, it is necessary to develop new technologies to solve these problems in combination and to improve the performance of lithium-sulfur batteries.

The present inventors have conducted various studies to solve the above problems, but as a raw material of iron oxide, Fe (NO ₃ ) ₃ · 9H ₂ O is heat-treated, by controlling the heat treatment temperature and process time to selectively iron oxide of high purity It was confirmed that it could be manufactured.

Accordingly, it is an object of the present invention to provide a method for producing high purity iron oxide through a simple process.

In order to achieve the above object, the present invention,

(1) dissolving Fe (NO ₃ ) ₃ .9H ₂ O in an aqueous solvent to prepare Fe (NO ₃ ) ₃ .9H ₂ O aqueous solution;

(2) drying the Fe (NO ₃ ) ₃ .9H ₂ O aqueous solution; And

(3) heat-treating the dried Fe (NO ₃ ) ₃ .9H ₂ O to obtain iron oxide represented by Chemical Formula 1;

It provides a method for producing iron oxide comprising a.

[Formula 1]

Fe _x O ₃ (where 1.7 ≤ x <2)

One embodiment of the present invention is that the concentration of Fe (NO ₃ ) ₃ · 9H ₂ O aqueous solution of step (1) is 0.5 to 5.0 M.

One embodiment of the invention is that the drying of step (2) is carried out at a temperature of 70 to 90 ℃.

One embodiment of the invention is that the drying of step (2) is carried out for 4 to 12 hours.

One embodiment of the present invention is that the heat treatment of step (3) is carried out at 120 to 170 ℃.

One embodiment of the invention is that the heat treatment of step (3) is carried out for 16 to 36 hours.

One embodiment of the present invention is to form the secondary particles by the primary particles of the iron oxide aggregated.

In one embodiment of the present invention, the primary particles have a particle diameter of 10 to 80 nm.

In one embodiment of the present invention, the secondary particles have a particle diameter of 1 to 5 μm.

According to the present invention, Fe (NO ₃ ) ₃ · 9H ₂ O can be produced by a simple process comprising the step of drying and heat treatment, and can be produced iron oxide of high purity, and control the temperature and time of the drying and heat treatment There is an advantage in that it is possible to control the shape and purity of the iron oxide to be produced.

In addition, the manufactured iron oxide may increase the life characteristics and the discharge capacity of the lithium-sulfur battery when applied as a positive electrode additive of the lithium-sulfur battery.

1 shows a scanning electron microscope (SEM) image of iron oxide (Fe _1.766 O ₃ ) according to Preparation Example 1 of the present invention.

2 shows a scanning electron microscope (SEM) image of iron oxide (Fe _1.766 O ₃ ) according to Preparation Example 2 of the present invention.

3 shows X-ray diffraction analysis (XRD) results of iron oxide (Fe _1.766 O ₃ ) according to Preparation Example 1 of the present invention.

4 shows the results of X-ray diffraction analysis (XRD) of iron oxide (Fe _1.766 O ₃ ) according to Preparation Example 2 of the present invention.

Figure 5 shows the change in chromaticity of the lithium polysulfide adsorption reaction according to the preparation and comparative examples of the present invention as a UV absorbance measurement results.

6 shows discharge capacity measurement results of a lithium-sulfur battery including a positive electrode according to Examples and Comparative Examples of the present invention.

Hereinafter, with reference to the accompanying drawings to be easily carried out by those skilled in the art will be described in detail. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the scope of the present invention.

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The present invention relates to a method for manufacturing iron oxide, and relates to a method for producing iron oxide having a form and properties that can be applied as a positive electrode additive of a lithium-sulfur battery to improve the discharge capacity and life characteristics of the battery.

Method of producing iron oxide according to the present invention is _{(1) Fe (NO 3)} 3 · by dissolving 9H ₂ O in distilled water, Fe (NO _{3) 3} · preparing a 9H ₂ O solution, (2) the Fe (NO ₃ ) drying the ₃ · 9H ₂ O aqueous solution and (3) heat treating the dried Fe (NO ₃ ) ₃ · 9H ₂ O to obtain iron oxide represented by the following Chemical Formula 1.

[Formula 1]

Fe _x O ₃ (where 1.7 ≤ x <2)

The Fe (NO ₃ ) ₃ · 9H ₂ O can be prepared in the form of an aqueous solution by dissolving in an aqueous solvent, preferably Fe (NO ₃ ) ₃ · 9H ₂ O can be dissolved in DIW (deionized water) and the like. . The concentration of the aqueous solution may be 0.5 to 5.0 M, preferably 1.0 to 2.0 M. If it is less than 0.5 M, the evaporation rate of the aqueous solution may be slowed to increase the crystal of iron oxide to be produced or the yield of iron oxide may be lowered. If it is more than 5.0 M, the iron oxide may be agglomerated. It may not be suitable for application as a positive electrode additive.

The Fe (NO ₃ ) ₃ .9H ₂ O aqueous solution may be further subjected to a pretreatment step of drying prior to heat treatment for iron oxide production. The drying may be carried out at 70 to 90 ℃, preferably at 75 to 85 ℃. In addition, the drying may be performed for 4 to 12 hours in the above temperature range, and preferably for 5 to 8 hours. If less than the temperature or the drying time is short, excess water of the reactant Fe (NO ₃ ) ₃ · 9H ₂ O may remain, after which the water may evaporate unevenly during the heat treatment process according to the present invention. Iron oxide represented by Formula 1 may not be synthesized. In addition, when the temperature exceeds or the drying time is long, the oxidation reaction by heat treatment may proceed in part after all of the reactants Fe (NO ₃ ) ₃ · 9H ₂ O evaporated. In this case, a non-uniform oxidation reaction may occur through the heat treatment process, and the material represented by Chemical Formula 1 may not be synthesized, so it is properly adjusted within the above range. The drying pretreatment step may be performed using a convection oven in an environment where sufficient air is introduced.

The Fe (NO ₃ ) ₃ · 9H ₂ O may be heat-treated after the drying pretreatment to produce iron oxide represented by Chemical Formula 1. The heat treatment may be performed at 120 to 170 ° C, preferably at 150 to 160 ° C.

In addition, the heat treatment may be performed for 16 to 36 hours in the above temperature range, and preferably for 18 to 24 hours. If the heat treatment temperature is less than 120 ° C or shorter than the heat treatment time, the reaction may not be terminated and a reaction residue such as Fe (OH) ₂ NO ₃ , which is not the structure of Chemical Formula 1, may remain. In addition, a stable material, such as and the size of the particles that the heat treatment temperature exceeds 170 ℃ or is generated if longer than the annealing time may be increased bundle is expressed in the form, and Fe ₂ O _3, unlike the iron oxide of the formula (1) Can be generated. Therefore, it may be difficult to synthesize the iron oxide of the desired physical properties according to the present invention, so it is appropriately adjusted within the temperature and time of the above range. The heat treatment step may be performed using a convection oven in an environment in which sufficient air is introduced.

The Fe (NO ₃ ) ₃ · 9H ₂ O is HNO ₃ (g) is degassed during the heat treatment step, to produce a material represented by the formula (1). Oxidized water of iron in Formula 1 may have a variety of oxidation water according to the heat treatment time and temperature, preferably x is 1.7 ≤ x <1.9, more preferably 1.7 ≤ x <1.8, preferred one of the present invention In some embodiments, in Chemical Formula 1, x may be 1.766.

The prepared iron oxide may be one of the primary particles to form a secondary particle. In this case, the primary particles may have a particle diameter of 10 to 80 nm, preferably 20 to 50 nm. The secondary particles formed by agglomeration of the primary particles may have a particle diameter of 1 to 5 μm, and preferably 2 to 3 μm. As the particle diameter of the secondary particles decreases within the above range, it is suitable as a cathode material of a lithium-sulfur secondary battery, and when the particle diameter of the secondary particles is larger than the above range, the particle size is large and may not be suitable as a cathode additive of a lithium-sulfur battery. have.

When the iron oxide prepared by the method of manufacturing iron oxide as described above is applied to a lithium-sulfur battery, lithium polysulfide eluted during charging and discharging of the lithium-sulfur battery can be adsorbed, thereby improving the performance of the lithium-sulfur secondary battery. You can.

Hereinafter, the present invention will be described in more detail with reference to examples and the like, but the scope and contents of the present invention may not be interpreted as being reduced or limited by the following examples. In addition, if it is based on the disclosure of the present invention including the following examples, it will be apparent that those skilled in the art can easily carry out the present invention, the results of which are not specifically presented experimental results, these modifications and modifications are attached to the patent It goes without saying that it belongs to the claims.

Preparation Example 1 Preparation of Iron Oxide (1)

Fe (NO ₃ ) ₃ .9H ₂ O (Sigma-Aldrich) was dissolved in DIW (deionized water) to prepare a 2.0 M aqueous solution. The prepared aqueous solution was dried at 80 ° C. for 6 hours in a convection oven. Thereafter, heat treatment was performed at 155 ° C. for 18 hours in a convection oven to produce iron oxide represented by Fe _1.766 O ₃ .

Preparation Example 2 Preparation of Iron Oxide (2)

Iron oxide was prepared in the same manner as in Preparation Example 1, except that the heat treatment time was performed for 24 hours.

Experimental Example 1: SEM (scanning electron microscope) analysis

SEM analysis (S-4800 FE-SEM by Hitachi, Ltd.) was performed on Fe _1.766 O ₃ , which is iron oxide prepared in Preparation Examples 1 and 2, respectively. 1 is a SEM analysis results of Fe _1.766 O ₃ prepared in Preparation Example 1, Figure 2 is a graph showing the SEM analysis results for the iron oxide prepared in Preparation Example 2.

Referring to FIGS. 1 and 2, SEM analysis was performed at a magnification of 100 k. As a result, it was confirmed that particles of several tens of nm in diameter were aggregated to form secondary particles having a size of 1 to 5 μm.

Experimental Example 2: XRD (X-ray Diffraction) Analysis

XRD analysis (D4 Endeavor from Bruker) was performed on Fe _1.766 O ₃ , which is iron oxide prepared in Preparation Examples 1 and 2, respectively.

₃ is an XRD analysis of Fe _1.766 O ₃ prepared in Preparation Example 1, Figure 4 is a graph showing the XRD analysis of the iron oxide prepared in Preparation Example 2.

3 and 4, it was confirmed that Fe _1.766 O ₃ containing a large amount of oxygen compared to Fe ₂ O ₃ of the stable phase was prepared, 2θ = 24.2 ± 0.1 °, 33.8 ± 0.1 °, 36.0 ± 0.1 The XRD peaks of °, 40.8 ± 0.1 °, 49.4 ± 0.1 ° and 53.8 ± 0.1 ° _showed that the pure phase iron oxide (Fe _1.766 O ₃ ) was selectively prepared.

Experimental Example 3: Polysulfide Adsorption Capacity Experiment

The lithium polysulfide adsorption capacity of Fe _1.766 O ₃ and carbon nanotubes (CNT) according to Preparation Examples 1 and 2 was confirmed by absorbance analysis of ultraviolet rays (UV, Agilent 8453 UV-visible spectrophotometer), and is shown in FIG. 5. It was.

As shown in Figure 5, the iron oxide Fe _1.766 O ₃ and CNT according to the present invention in the range of 300 to 700nm wavelength adsorbed lithium polysulfide was confirmed that the intensity of the ultraviolet absorbance (intensity) is reduced, the CNT It was found that the iron oxides of Preparation Examples 1 and 2 were more excellent in adsorption capacity of lithium polysulfide.

Experimental Example 4 Comparative Experiment of Discharge Capacity of Lithium-Sulfur Battery

In order to test the discharge capacity of the lithium-sulfur battery according to the type of cathode material, the discharge capacity was measured after configuring the positive electrode and the negative electrode of the lithium-sulfur battery as shown in Table 1 below.

The positive electrode of Comparative Example (1) is a sulfur-carbon composite, the positive electrode of Example (1) comprises a sulfur-carbon composite and Fe _1.766 O ₃ of Preparation Example 1, the positive electrode of Example (2) is a sulfur-carbon composite And Fe _1.766 O _{3 In} Preparation Example 2 It was included. At this time, the measurement current was 0.1C, the voltage range was 1.8 to 2.6V, and the result is shown through FIG. 6.

	Lithium-sulfur battery
	cathode	anode
Comparative Example (1)	Metal lithium	Sulfur-carbon composite + conductive material + binder (90: 5: 5, weight ratio)
Example (1)	Metal lithium	Sulfur-carbon composite + conductive material + binder + Fe 1.766 O 3 (10 parts by weight) of Preparation Example 1 (90: 5: 5: 10, weight ratio)
Example (2)	Metal lithium	Sulfur-carbon composite + conductive material + binder + Fe 1.766 O 3 (10 parts by weight) of Preparation Example 2 (90: 5: 5: 10, weight ratio)

As shown in FIG. 6, compared to Comparative Example (1), it was confirmed that the Example to which Fe _1.766 O ₃ was added has a higher initial discharge capacity, and the Fe _1.766 O ₃ which is iron oxide according to Preparation Example (2) was included. In the case of Example (2), it was confirmed that the initial discharge capacity further increased compared to Example (1). Therefore, it can be seen that the iron oxide according to the present invention is effective in increasing the initial discharge capacity of the lithium-sulfur battery.

Claims (9)

1. (1) dissolving Fe (NO ₃ ) ₃ .9H ₂ O in an aqueous solvent to prepare Fe (NO ₃ ) ₃ .9H ₂ O aqueous solution;

   (2) drying the Fe (NO ₃ ) ₃ .9H ₂ O aqueous solution; And

   (3) heat-treating the dried Fe (NO ₃ ) ₃ .9H ₂ O to obtain iron oxide represented by Chemical Formula 1;

   Iron oxide manufacturing method comprising a.

   [Formula 1]

   Fe _x O ₃ (where 1.7 ≤ x <2)
2. The method of claim 1,

   The concentration of Fe (NO ₃ ) ₃ · 9H ₂ O aqueous solution of the step (1) is 0.5 to 5.0 M method for producing iron oxide.
3. The method of claim 1,

   The drying of step (2) is a method for producing iron oxide, characterized in that carried out at a temperature of 70 to 90 ℃.
4. The method of claim 3,

   Drying of step (2) is a method for producing iron oxide, characterized in that carried out for 4 to 12 hours.
5. The method of claim 1,

   The heat treatment of step (3) is a method of producing iron oxide, characterized in that proceeds at 120 to 170 ℃.
6. The method of claim 1,

   The heat treatment of step (3) is a method for producing iron oxide, characterized in that carried out for 16 to 36 hours.
7. The method of claim 1,

   The iron oxide is a method for producing iron oxide, characterized in that the primary particles are agglomerated to form secondary particles.
8. The method of claim 7, wherein

   The primary particle is a manufacturing method of iron oxide, characterized in that the particle size of 10 to 80 nm.
9. The method of claim 7, wherein

   The secondary particles are a method for producing iron oxide, characterized in that the particle size of 1 to 5 ㎛.

Images