WO2020060199A1 - Method for preparing iron sulfide, cathode comprising iron sulfide prepared thereby for lithium secondary battery, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to: a method for preparing iron sulfide (FeS₂), which is selective for and allows high-purity iron sulfide to be prepared in a simple process; a cathode containing iron sulfide (FeS₂) for a lithium secondary battery, in which iron sulfide (FeS₂) adsorbs lithium polysulfide generated during charging and discharging processes of the lithium secondary battery, thereby enabling the battery to increase in charge and discharge efficiency and to improve in lifespan characteristic; and a lithium secondary battery comprising same.

Description

Method for manufacturing iron sulfide, positive electrode for lithium secondary battery comprising iron sulfide prepared therefrom, and lithium secondary battery having same

This application is for Korean Patent Application No. 10-2018-0111788 dated September 18, 2018 and Korean Patent Application No. 10-2019-0114771 for September 18, 2019, and Korean Patent Application No. 10 for September 18, 2018 -2018-0111792 and claiming the benefit of priority based on Korean Patent Application No. 10-2019-0114782 dated September 18, 2019, all contents disclosed in the literature of the Korean patent application are incorporated as part of this specification.

The present invention relates to a method for manufacturing iron sulfide, a positive electrode for a lithium secondary battery including iron sulfide prepared therefrom, and a lithium secondary battery having the same, and more specifically, it is possible to manufacture selective and high purity iron sulfide by a simple process. There is a method of manufacturing iron sulfide (FeS ₂ ) applicable as a positive electrode additive for a lithium secondary battery, and iron sulfide (FeS ₂ ) prepared therefrom adsorbs lithium polysulfide generated during charging and discharging of a lithium secondary battery, thereby The present invention relates to a lithium secondary battery positive electrode including iron sulfide (FeS ₂ ) capable of increasing charging and discharging efficiency and improving lifespan characteristics, and a lithium secondary battery having the same.

Secondary batteries, unlike primary batteries that can only be discharged once, have been established as important parts of portable electronic devices since the 1990s as an electric storage device capable of continuous charging and discharging. In particular, since the lithium 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 smart phones, digital cameras, and notebook computers.

In recent years, lithium secondary batteries have expanded their application areas, and in mid-sized batteries to be used in fields such as cleaners, power tools, electric bicycles, and electric scooters, electric vehicles (EVs) and hybrid electric vehicles (hybrid electric vehicles) ; HEV), Plug-in hybrid electric vehicle (PHEV), various robots, and large-capacity batteries used in fields such as electric storage systems (ESS), demand at high speed Is increasing.

However, lithium secondary batteries, which have the best characteristics among the secondary batteries to date, have several problems to be actively used in transportation equipment such as electric vehicles and PHEVs, and the biggest problem is the limitation of capacity.

The lithium secondary battery is basically composed of materials such as a positive electrode, an electrolyte, and a negative electrode, and among them, since the positive and negative electrode materials determine the capacity of the battery, the lithium secondary battery has a capacity due to the material limitations of the positive and negative electrodes. Is limited by. In particular, the secondary battery to be used in applications such as electric vehicles and PHEVs must be used for as long as possible after one charge, so its discharge capacity is very important.

The capacity limitation of the lithium secondary battery is difficult to completely solve due to the structure and material limitations 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 secondary battery that goes beyond the existing secondary battery concept.

Lithium-sulfur secondary batteries exceed the capacity limits determined by the intercalation reaction of the lithium ion layered metal oxide and graphite into the basic principle of the existing lithium secondary battery, and replace transition metals and reduce costs. It is a new high-capacity, low-cost battery system that can be imported.

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) for ultra-high capacity of the battery system. In addition, since the discharge voltage is about 2.2 V, it theoretically represents an energy density of 2,600 Wh / kg based on the amount of the positive and negative electrode active materials. This is a value that is 6 to 7 times higher than the theoretical energy density of 400 Wh / kg, which is a commercial lithium secondary battery (LiCoO ₂ / graphite) using a layered metal oxide and graphite.

Lithium-sulfur secondary batteries have been attracting attention as new high-capacity, eco-friendly, and low-cost lithium secondary batteries since it is known that the performance of batteries can be dramatically improved through the formation of nanocomposites around 2010. Is being made.

One of the main problems of the lithium-sulfur secondary battery that has been identified to date is that the electrical conductivity of sulfur is close to the non-conductor at about 5.0 × 10 ^-14 S / cm, making electrochemical reactions at the electrode not easy, and the actual discharge capacity and The voltage is far below the theory. Early researchers tried to improve the performance by methods such as mechanical ball milling of sulfur and carbon or surface coating using carbon, but there was no great effect.

In order to effectively solve the problem of the electrochemical reaction being restricted by electrical conductivity, as in the case of LiFePO _{4, which} is one of the other positive electrode active materials (electric conductivity: 10 ^-9 to 10 ^-10 S / cm), the particle size is several tens of nanometers. It is necessary to reduce the size to the following and surface treatment with a conductive material. To this end, various chemicals (melt impregnation with a nano-sized porous carbon nanostructure or metal oxide structure), a physical method (high energy ball milling), etc. are reported. Is becoming.

Another major problem associated with lithium-sulfur batteries is the dissolution of lithium polysulfide, an intermediate product of sulfur generated during discharge, into the electrolyte. As discharge proceeds, sulfur (S ₈ ) reacts continuously with lithium ions to form S ₈ → Li ₂ S ₈ → (Li ₂ S ₆ ) → Li ₂ S ₄ → Li ₂ S ₂ → Li ₂ S. (phase) changes continuously. Among them, Li ₂ S ₈ and Li ₂ S ₄ (lithium polysulfide), which are long-chain chains, have properties that are easily dissolved in a common electrolyte used in lithium ion batteries. When this reaction occurs, not only the reversible anode 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 continue to increase and the charge / discharge efficiency rapidly decreases. Recently, various methods have been proposed to solve these problems, and can be largely divided into a method of improving the electrolyte, a method of improving the surface of the cathode, and a method of improving the properties of the anode.

The method of improving the electrolyte uses a new electrolyte such as a functional liquid electrolyte, a polymer electrolyte, and an ionic liquid of a new composition to suppress the dissolution of polysulfide into the electrolyte or to control the dispersion rate to the cathode through adjustment of viscosity, etc. It is a method to suppress the shuttle reaction as much as possible by controlling.

Studies have been actively conducted to control the shuttle reaction by improving the properties of the SEI formed on the surface of the cathode. Typically, electrolyte additives such as LiNO ₃ are added to the surface of the lithium anode to form oxide films such as Li _x NO _y and Li _x SO _y . And a method for forming a thick functional solid-electrolyte interphase (SEI) layer on the surface of the lithium metal.

Lastly, a method of improving the properties of the anode includes a method of forming a coating layer on the surface of the anode particle or adding a porous material capable of catching the dissolved polysulfide to prevent the dissolution of polysulfide. A method of coating the surface of a positive electrode structure containing, a method of coating the surface of a positive electrode structure with a metal oxide that conducts lithium ions, and a positive electrode having a large specific surface area and large pores capable of absorbing large amounts of lithium polysulfide. , A method of attaching a functional group capable of adsorbing lithium polysulfide on the surface of the carbon structure, a method of wrapping sulfur particles using graphene or graphene oxide, and the like.

Although such efforts are underway, this method is rather complicated and there is a problem that the amount of sulfur that can be added as an active material is limited. Therefore, there is a need to develop new technologies to solve these problems in combination and improve the performance of lithium-sulfur batteries.

In order to solve the above-mentioned problems, as a result of conducting various studies related to the positive electrode additive of the lithium secondary battery, the iron precursor and the sulfur precursor are mixed and heat-treated, but the high-purity iron sulfide is selectively controlled by controlling the heat treatment temperature and process time. It was confirmed that it can be produced.

Accordingly, an object of the present invention is to provide a method for manufacturing iron sulfide, which is a positive electrode additive for a lithium secondary battery of high purity through a simple process.

In addition, in order to solve the problem of elution of lithium polysulfide occurring on the positive electrode side of the lithium secondary battery and suppress side reactions with the electrolyte, iron sulfide (FeS ₂ ) produced by the above manufacturing method was introduced into the positive electrode of the lithium secondary battery. As a result, it was confirmed that the battery performance of the lithium secondary battery can be improved by solving the above problems, thereby completing the present invention.

Accordingly, another object of the present invention is to provide a positive electrode additive for a lithium secondary battery capable of solving the problem caused by lithium polysulfide.

In addition, another object of the present invention is to provide a lithium secondary battery having the positive electrode having improved life characteristics of the battery.

In order to achieve the above object, the present invention, (1) mixing the iron precursor and the sulfur precursor to form a mixture; And (2) heat-treating the mixture in an inert gas atmosphere; provides a method for producing iron sulfide (FeS ₂ ).

In addition, the present invention, as a positive electrode for a lithium secondary battery comprising an active material, a conductive material and a binder, the positive electrode provides a positive electrode for a lithium secondary battery containing iron sulfide (FeS ₂ ).

In addition, the present invention, the lithium secondary battery positive electrode; cathode; A separator interposed between the anode and the cathode; And electrolyte; provides a lithium secondary battery comprising a.

According to the present invention, there is an advantage in that it is possible to prepare iron sulfide of high purity with a selective process by a simple process including the step of mixing the iron precursor and the sulfur precursor and heat-treating it.

In addition, when the prepared iron sulfide (FeS ₂ ) is applied to the positive electrode of a lithium secondary battery, lithium polysulfide generated during charging and discharging of the lithium secondary battery is adsorbed to increase the reactivity of the positive electrode of the lithium secondary battery and cause side reactions with the electrolyte. Suppress.

In addition, the lithium secondary battery provided with the positive electrode containing the iron sulfide (FeS ₂ ) does not cause a reduction in the capacity of sulfur, so it is possible to implement a high-capacity battery and stably apply sulfur with high loading, thereby improving the overvoltage of the battery. And there is no problem of short circuit, heat generation, etc. of the battery, thereby improving the battery stability. In addition, the lithium secondary battery has an advantage of high charging and discharging efficiency of the battery and improving life characteristics.

1 shows a scanning electron microscope (SEM) image of iron sulfide (FeS ₂ ) according to Preparation Example 1 of the present invention.

2 shows a scanning electron microscope (SEM) image of iron sulfide (FeS ₂ ) according to Preparation Example 2 of the present invention.

Figure 3 shows the X-ray diffraction analysis (XRD) results of iron sulfide (FeS ₂ ) according to Preparation Example 1 of the present invention.

Figure 4 shows the X-ray diffraction analysis (XRD) results of iron sulfide (FeS ₂ ) according to Preparation Example 2 of the present invention.

Figure 5 shows the X-ray diffraction analysis (XRD) comparison results of iron sulfide (FeS ₂ ) according to Preparation Example 1 and Comparative Preparation Example 1 of the present invention.

6 shows the X-ray diffraction analysis (XRD) results of the product (NH ₄ Fe (SO ₄ ) ₂ ) according to Comparative Preparation Example 2 of the present invention.

7 shows X-ray diffraction analysis (XRD) comparison results of the product according to Comparative Preparation Example 3 of the present invention.

8 and 9 show the results of measuring the discharge capacity of a lithium secondary battery manufactured according to an embodiment and a comparative example of the present invention.

Hereinafter, with reference to the accompanying drawings to be easily carried out by those of ordinary skill in the art to which the present invention pertains will be described in detail. However, the present invention can be implemented in many different forms, and is not limited to this specification.

The terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor can appropriately define the concept of terms in order to best describe his or her invention. Based on the principle that it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention.

As used herein, the term “composite” refers to a substance that combines two or more materials to form physically and chemically different phases and express more effective functions.

The lithium secondary battery is manufactured by using a material capable of intercalation / deintercalation of lithium ions as a negative electrode and a positive electrode, and charging an organic electrolyte or a polymer electrolyte between the negative electrode and the positive electrode, and lithium ions are inserted at the positive and negative electrodes. And an electrochemical device that generates electrical energy by oxidation / reduction reaction when desorption, and according to one embodiment of the present invention, the lithium secondary battery is lithium-sulfur containing 'sulfur' as an electrode active material of a positive electrode. It can be a battery.

The present invention relates to a method for manufacturing iron sulfide (FeS ₂ ), and specifically, it can be produced as iron sulfide having a shape and physical properties that can improve the discharge capacity and life characteristics of a battery by applying it as a positive electrode additive for a lithium secondary battery. It's about how.

In addition, the present invention complements the disadvantages of the positive electrode for a lithium secondary battery, and provides a positive electrode for a lithium secondary battery with improved problems of continuous reactivity of an electrode due to dissolution and shuttle phenomenon of lithium polysulfide and a problem of reduction in discharge capacity. . Specifically, the positive electrode for a lithium sulfur-cell provided in the present invention is characterized by including an active material, a conductive material, and a binder, and even iron sulfide (FeS ₂ ) as a positive electrode additive.

Particularly, the iron sulfide (FeS ₂ ) is included in the positive electrode of the lithium secondary battery in the present invention, and lithium polysulfide is transferred to the negative electrode by adsorbing lithium polysulfide, thereby reducing the problem of reducing the life of the lithium secondary battery and lithium By suppressing the reduced reactivity due to polysulfide, it is possible to increase the discharge capacity of the lithium secondary battery including the positive electrode and improve the life of the battery.

Method for manufacturing iron sulfide

The method for manufacturing iron sulfide (FeS ₂ ) according to the present invention includes (1) mixing an iron precursor and a sulfur precursor to form a mixture, and (2) heat treating the mixture in an inert gas atmosphere.

The iron precursor according to the present invention means a material capable of forming iron sulfide (FeS ₂ ) by reacting with a sulfur precursor, and an example of a preferred iron precursor is iron nitrate represented by Fe (NO ₃ ) _{3 ·} 9H ₂ O, γ It may be iron hydroxide represented by -FeOOH or a combination thereof. However, considering the fact that the performance of the battery is different due to the structural difference of iron sulfide produced (see the discharge capacity comparison experiment in the examples below), iron nitrate (Fe (NO ₃ ) _{3 ·} 9H ₂ O as the iron precursor) It is more preferable to apply iron hydroxide (γ-FeOOH, or Lepidocrocite) rather than).

The sulfur precursors include thiourea (CH ₄ N ₂ S), ammonium thiosulfate ((Ammonium Thiosulfate, (NH ₄ ) ₂ S ₂ O ₃ ), sulfur (S), etc., but in the case of ammonium thiosulfate, the present invention According to the manufacturing method according to the method, a side reaction may occur in which NH ₄ Fe (SO ₄ ) ₂ and the like are generated instead of complete sulfurization, and when sulfur (S) itself is used as a sulfur precursor, iron to be described later Even when the reaction proceeds with a molar ratio of (Fe) and sulfur (S) of 1: 8 or more, iron sulfide (FeS ₂ ) of uniform components may not be generated, such as Fe ₇ S ₈ and FeS ₂ being mixed. Therefore, in order to prepare iron sulfide (FeS ₂ ) according to the present invention, it is preferable to use thiourea (Thiourea, CH ₄ N ₂ S) having a relatively high boiling point (in the case of Fe ₇ S _{8 as} a side reaction product, lithium) Problem that can deteriorate the performance of the battery by reacting with the binder in the anode of the secondary battery It has).

The iron precursor and the sulfur precursor may be mixed by a method known to those skilled in the art. The mixing ratio of the iron precursor and the sulfur precursor may be a molar ratio of iron (Fe) and sulfur (S) contained in the iron precursor and the sulfur precursor is 1: 8 or more, preferably 1:10 or more. If the molar ratio of sulfur is less than the above range, a side reaction of Fe ₇ S ₈ or the like may occur through a heat treatment process to be described later due to insufficient sulfur content, which may cause a side reaction with the above-described binder, and thus the above range It is desirable to maintain the mixing ratio of sulfur.

Next, the present invention includes the step of heat-treating the mixture of step (1) in an inert gas atmosphere. Through the heat treatment process, an iron precursor and a sulfur precursor react to produce iron sulfide (FeS ₂ ). The heat treatment may be performed at 400 to 600 ° C, preferably 400 to 500 ° C. According to an embodiment of the present invention, the heating rate of the heat treatment may be controlled between 5 and 20 ° C per minute. If the temperature increase rate exceeds 20 ° C / min, the decomposition rate of the sulfur precursor, which is a reactant, is excessively high, so that the amount of sulfur reacting with the iron precursor may decrease, and as a result, Fe ₇ S ₈ is not the desired iron sulfide (FeS ₂ ). There is a problem that can be produced in the form. In addition, if the heating rate is less than 5 ° C / min, there may be a problem that the production time of the desired product may be too long, so it is appropriately adjusted within the above range.

In addition, the heat treatment may be performed for 1 to 3 hours in the above temperature range, preferably 1 to 2 hours. If the heat treatment temperature is less than 400 ° C or shorter than the heat treatment time, the iron precursor and the sulfur precursor may not react sufficiently to produce desired iron sulfide (FeS ₂ ). In addition, when the heat treatment temperature exceeds 600 ° C or longer than the heat treatment time, the size of the generated iron sulfide (FeS ₂ ) particles may increase or, unlike the desired iron sulfide (FeS ₂ ), unnecessary oxides may be generated. Therefore, since it may be difficult to synthesize iron sulfide (FeS ₂ ) of desired physical properties according to the present invention, it is appropriately adjusted within the temperature and time in the above range.

The heat treatment in step (3) may be performed in an inert gas atmosphere. The inert gas atmosphere may be performed under (i) an inert gas atmosphere in which the gas inside the reactor is replaced with an inert gas, or (ii) in a state where the inert gas is continuously introduced to continuously replace the gas in the reactor. . In the case of (ii), for example, the flow rate of the inert gas may be 1 to 500 mL / min, specifically 10 to 200 mL / min, and more specifically 50 to 100 mL / min.

Here, the inert gas may be selected from the group consisting of nitrogen, argon, helium, and mixtures thereof, and preferably nitrogen.

Iron sulfide (FeS ₂ ) according to an embodiment of the present invention is crystalline, and results of X-ray diffraction analysis using CuKα rays (111), (200), (210), (211), (220), (311) XRD peaks of), (222) and (321) planes are 2θ = 28.4 ± 0.2 °, 32.9 ± 0.2 °, 36.9 ± 0.2 °, 40.6 ± 0.2 °, 47.3 ± 0.2 °, 56.0 ± 0.2 °, 58.9 ± 0.2, respectively. °, 61.5 ± 0.2 ° and 64.0 ± 0.2 ° peak appeared, through which it can be seen that iron sulfide (FeS ₂ ) according to the present invention was synthesized.

The iron sulfide (FeS ₂ ) prepared by the above-described manufacturing method may have a crystallinity of an average particle size of several hundreds nm to several μm, for example, 0.1 to 10 μm. If the average particle diameter exceeds 10 μm, it may not fit well with other electrode materials of the lithium secondary battery, and when the same amount is added, the performance improvement effect of the battery compared to iron sulfide (FeS ₂ ) having a relatively small average particle diameter Can be insignificant. On the other hand, when iron hydroxide (γ-FeOOH) is applied as the iron precursor, iron sulfide (FeS ₂ ) containing plate-shaped particles having an average particle diameter of several hundred nm to several μm may be prepared, and in this case, as described above. , It has the advantage that the performance of the battery is better by the structural difference of iron sulfide (see the discharge capacity comparison experiment in the following examples).

The iron sulfide (FeS ₂ ) produced by the above-described manufacturing method can effectively adsorb lithium polysulfide eluted during charging and discharging of a lithium secondary battery, and is suitable as a cathode material of a lithium secondary battery. It does not cause the performance of the battery can be improved.

Anode for lithium secondary battery

The present invention provides an anode for a lithium secondary battery including an active material, a conductive material, and a binder, the anode comprising a lithium sulfide (FeS ₂ ) produced through the above-described manufacturing method.

At this time, the positive electrode of the lithium secondary battery may include a current collector and an electrode active material layer formed on at least one surface of the current collector, and the electrode active material layer may include a base solid content including an active material, a conductive material, and a binder. . As the current collector, it may be preferable to use aluminum, nickel or the like having excellent conductivity.

As an embodiment, the iron sulfide (FeS ₂ ) may be included in an amount of 0.1 to 15 parts by weight based on 100 parts by weight of the base solid content including the active material, the conductive material, and the binder, and specifically 1 to 15 parts by weight, preferably 5 to 10 parts by weight. If it is less than the lower limit of the numerical range, the adsorption effect of polysulfide may be insignificant, and if it exceeds the upper limit, the capacity of the electrode is reduced, which is not preferable. The iron sulfide (FeS ₂₎ can be used for the iron sulfide (FeS ₂₎ prepared by the method presented in this invention.

On the other hand, among the base solids constituting the positive electrode of the present invention, the active material may include elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof, and the sulfur-based compound is specifically Li ₂ S _n (n≥1), an organic sulfur compound, or a carbon-sulfur complex ((C ₂ S _x ) _n : x = 2.5 to 50, n≥2).

The positive electrode for a lithium secondary battery according to the present invention may preferably include an active material of a sulfur-carbon composite, and since the sulfur material is not electrically conductive alone, it can be used in combination with a conductive material. The addition of iron sulfide (FeS ₂ ) according to the present invention does not affect the maintenance of this sulfur-carbon composite structure.

In one embodiment, the sulfur-carbon composite may have a sulfur content of 60 to 90 parts by weight based on 100 parts by weight of the sulfur-carbon composite, and preferably 70 to 75 parts by weight. If the content of sulfur is less than 60 parts by weight, the content of the carbon material of the sulfur-carbon composite increases relatively, and as the content of carbon increases, the specific surface area increases, so that the amount of binder added during slurry production must be increased. Increasing the amount of the binder added eventually increases the sheet resistance of the electrode and acts as an insulator preventing electron pass, which can degrade battery performance. If the sulfur content exceeds 90 parts by weight, the sulfur or sulfur compounds that are not combined with the carbon material may be difficult to directly participate in the electrode reaction due to aggregation or re-eluting to the surface of the carbon material, making it difficult to directly participate in the electrode reaction. Adjust accordingly.

The carbon of the sulfur-carbon composite according to the present invention may be either a porous structure or a high specific surface area as long as it is commonly used in the art. For example, the porous carbon material includes graphite; Graphene; Carbon blacks such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); Carbon fibers such as graphite nanofiber (GNF), carbon nanofiber (CNF), and activated carbon fiber (ACF); And it may be at least one selected from the group consisting of activated carbon, but is not limited thereto, and its shape is spherical, rod-shaped, needle-shaped, plate-shaped, tubular or bulk-type, and can be used without limitation as long as it is commonly used in lithium secondary batteries.

The active material is preferably 50 to 95 parts by weight of 100 parts by weight of the base solid content, more preferably 70 parts by weight or less. If the active material is included below the above range, it is difficult to sufficiently exhibit the reaction of the electrode, and even if it is included above the above range, the amount of other conductive materials and binders is relatively insufficient, so that it is difficult to exert sufficient electrode reaction within the above range. It is desirable to determine the appropriate content.

Among the base solids constituting the positive electrode of the present invention, the conductive material is a material that electrically connects the electrolyte and the positive electrode active material to serve as a path for electrons to move from the current collector to sulfur, and to change the battery chemically. It is not particularly limited as long as it has porosity and conductivity without causing it. Graphite-based materials such as KS6; Carbon blacks such as super P (Super-P), carbon black, denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon derivatives such as fullerene; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder, and nickel powder; Alternatively, conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination.

The conductive material is preferably configured to constitute 1 to 10 parts by weight of 100 parts by weight of the base solid content, preferably 5 parts by weight or less. If the content of the conductive material included in the electrode is less than the above range, a portion of the electrode that does not react increases in the sulfur, and eventually, a capacity decrease occurs, and if it exceeds the above range, high efficiency discharge characteristics and charge and discharge cycle life are adversely affected. It is desirable to determine the appropriate content within the above-described range.

As a base solid, the binder is a material containing a slurry composition of a base solid that forms a positive electrode to adhere well to a current collector, and is a material that is well soluble in a solvent and can well constitute a conductive network between a positive electrode active material and a conductive material. use. Any binder known in the art can be used, unless otherwise specified, preferably poly (vinyl) acetate, polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, alkylated polyethylene oxide, crosslinked polyethylene oxide , Polyvinyl ether, poly (methyl methacrylate), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, copolymer of polyvinylidene fluoride (trade name: Kynar), poly (ethyl acrylate), poly Siloxane groups such as tetrafluoroethylene polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyvinylpyridine, polystyrene, carboxymethyl cellulose, polydimethylsiloxane, styrene-butadiene rubber, acrylonitrile-butadiene Rubber, rubber-based binder containing styrene-isoprene rubber, polyester Ethylene glycol-based such as styrene glycol diacrylate and derivatives thereof, blends thereof, and copolymers thereof may be used, but are not limited thereto.

The binder is made to constitute 1 to 10 parts by weight of 100 parts by weight of the base composition included in the electrode, preferably 5 parts by weight. If the content of the binder resin is less than the above range, the physical properties of the positive electrode may deteriorate and the positive electrode active material and the conductive material may drop off. If the content exceeds the above range, the ratio of the active material and the conductive material in the positive electrode may be relatively reduced to decrease the battery capacity. Therefore, it is preferable to determine an appropriate content within the above-described range.

As described above, the anode including iron sulfide (FeS ₂ ) and the base solid content may be prepared according to a conventional method. For example, a mixture of a solvent, a binder, a conductive material, and a dispersant may be mixed with a positive electrode active material, if necessary, to prepare a slurry, and then coated (coated) on a current collector of a metal material, compressed, and dried to produce a positive electrode. have.

For example, when preparing the positive electrode slurry, iron sulfide (FeS ₂ ) is first dispersed in a solvent, and then the obtained solution is mixed with an active material, a conductive material, and a binder to obtain a slurry composition for positive electrode formation. Then, the slurry composition is coated on a current collector and then dried to complete an anode. At this time, in order to improve the electrode density, if necessary, compression molding may be performed on the current collector. There is no limitation in the method for coating the slurry, for example, doctor blade coating, dip coating, gravure coating, slit die coating, spin coating coating, comma coating, bar coating, reverse roll coating, screen coating, and cap coating.

At this time, as the solvent, one capable of uniformly dispersing the positive electrode active material, the binder, and the conductive material, as well as those capable of easily dissolving iron sulfide (FeS ₂ ) are used. As the solvent, water is most preferable as the water-based solvent, and the water may be DW (Distilled Water) distilled second, or DIW (Deionzied Water) distilled third. However, the present invention is not limited thereto, and if necessary, a lower alcohol that can be easily mixed with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol. Preferably, they can be used by mixing with water.

In one embodiment, the positive electrode includes a current collector and an electrode active material layer formed on at least one surface of the current collector, and the electrode active material layer includes an active material, a conductive material, a binder, and iron sulfide (FeS ₂ ) according to the present invention, The porosity of the electrode active material layer may be 60 to 75%, specifically 60 to 70%, preferably 60 to 65%.

In the present invention, the term "porosity (porosity)" refers to the ratio of the volume occupied by the pores to the total volume in a certain structure, uses% as its unit, is used interchangeably with terms such as porosity, porosity, etc. You can.

In the present invention, the measurement of the porosity is not particularly limited, and according to an embodiment of the present invention, for example, the size (micro) by BET (Brunauer-Emmett-Teller) measurement method or mercury penetration method (Hg porosimeter) And meso pore volume.

If the porosity of the electrode active material layer is less than 60%, the filling degree of the base solids containing the active material, the conductive material, and the binder is too high, and sufficient electrolyte solution capable of exhibiting ionic conductivity and / or electrical conduction between the active materials is obtained. Since it cannot be maintained, the output characteristics or cycle characteristics of the battery may be deteriorated, and the overvoltage and discharge capacity of the battery are severely reduced, so that the effect of including iron sulfide (FeS ₂ ) according to the present invention may not be properly expressed. There is. When the porosity exceeds 75% and has an excessively high porosity, there is a problem in that the physical and electrical connection with the current collector is lowered, the adhesive strength is lowered and the reaction becomes difficult, and the increased porosity is filled with an electrolyte solution, thereby lowering the energy density of the battery. Since there is a possible problem, it is appropriately adjusted within the above range. According to one embodiment of the present invention, the porosity may be performed by a method selected from the group consisting of a hot press method, a roll press method, a plate press method and a roll laminate method.

In one embodiment of the present invention, the positive electrode may have a loading amount of sulfur per unit area of 3 to 7 mAh / cm ² , preferably 4 to 6 mAh / cm ² . In general, when the loading amount is 6 mAh / cm ^{2 or} more, overvoltage of the battery occurs and the discharge capacity decreases, but the present invention includes a high loading amount of 4 to 6 mAh / cm ² including iron sulfide (FeS ₂ ) at the positive electrode. Edo also has the effect of improving the overvoltage and improving the discharge capacity of the battery.

Lithium secondary battery

Meanwhile, the present invention provides a lithium secondary battery including a positive electrode for a lithium secondary battery, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte.

At this time, the negative electrode, the separator and the electrolyte may be composed of common materials that can be used in lithium secondary batteries.

Specifically, the negative electrode is a material capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ) as an active material, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, lithium metal Alternatively, a lithium alloy can be used.

The material capable of reversibly occluding or releasing the lithium ion (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. In addition, a material capable of reversibly forming a lithium-containing compound by reacting with the lithium ion (Li ⁺ ) may be, for example, tin oxide, titanium nitrate or silicon. Further, the lithium alloy may be, for example, an alloy of lithium and a metal selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Al and Sn.

In addition, the negative electrode may further include a binder selectively together with the negative electrode active material. The binder plays the role of pasting the negative electrode active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and buffering effects for expansion and contraction of the active material. Specifically, the binder is the same as described above.

In addition, the negative electrode may further include a current collector for supporting the negative electrode active layer including a negative electrode active material and a binder. The current collector may be specifically selected from the group consisting of copper, aluminum, stainless steel, titanium, silver, palladium, nickel, alloys thereof, and combinations thereof. The stainless steel may be surface treated with carbon, nickel, titanium or silver, and an aluminum-cadmium alloy may be used as the alloy. In addition, calcined carbon, a non-conductive polymer surface-treated with a conductive agent, or a conductive polymer may be used.

In addition, the negative electrode may be a thin film of lithium metal.

The separator uses a material that allows lithium ions to be transported between the positive electrode and the negative electrode while insulating or insulating them from each other, but can be used without particular limitation as long as it is used as a separator in a lithium secondary battery. It is preferable to have a low resistance and excellent electrolyte-moisturizing ability.

More preferably, as the separator material, a porous, non-conductive or insulating material may be used, such as an independent member such as a film, or a coating layer added to the positive electrode and / or the negative electrode.

Specifically, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer is used alone. It may be used as or by laminating them, or a conventional porous non-woven fabric, for example, a high-melting point glass fiber, a polyethylene terephthalate fiber, or the like may be used, but is not limited thereto.

The electrolyte is a non-aqueous electrolyte containing a lithium salt, and is composed of a lithium salt and an electrolyte. As the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, and an inorganic solid electrolyte are used.

The lithium salt is a material that can be easily dissolved in a non-aqueous organic solvent, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiB (Ph) _4, LiPF ₆ , LiCF ₃ SO ₃ , _{LiCF 3 CO 2, LiAsF 6,} LiSbF 6, LiAlCl 4, LiSO 3 CH 3, LiSO 3 CF 3, LiSCN, LiC (CF 3 SO 2) 3, LiN (CF 3 SO 2) 2, chloroborane lithium, lower aliphatic It may be one or more selected from the group consisting of lithium carboxylate, lithium 4-phenyl borate and imide.

The concentration of the lithium salt is preferably 0.2 to 2M, depending on several factors, such as the exact composition of the electrolyte mixture, the solubility of the salt, the conductivity of the dissolved salt, the conditions for charging and discharging the cell, the working temperature and other factors known in the field of lithium batteries. It may be 0.6 to 2M, and more preferably 0.7 to 1.7M. If the concentration of the lithium salt is less than the above range, the conductivity of the electrolyte may be lowered to degrade the electrolyte performance, and if it exceeds the above range, the viscosity of the electrolyte may increase and mobility of lithium ions (Li ⁺ ) may be reduced, so within the above range. It is desirable to select an appropriate concentration.

The non-aqueous organic solvent is a material capable of dissolving the lithium salt well, and preferably 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, and dioxolane (Dioxolane, DOL) ), 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methylpropyl carbonate (MPC), ethyl propyl carbonate , Dipropyl carbonate, butyl ethyl carbonate, ethyl propanoate (EP), toluene, xylene, dimethyl ether (DME), diethyl ether, triethylene glycol monomethyl ether (TEGME), Diglyme, tetraglyme, hexamethyl phosphoric triamide, gamma-butyrolactone (GBL), acetonitrile, propionitrile, ethylene carbonate (EC), propylene carbonate (PC), N-methylpi Lollidon, 3-methyl-2 -Oxazolidone, acetic acid esters, butyric acid esters and propionic acid esters, dimethylformamide, sulfolane (SL), methylsulfolan, dimethylacetamide, dimethylsulfoxide, dimethylsulfate, ethylene glycol diacetate, dimethylsulfite, or ethylene An aprotic organic solvent such as glycol sulfite may be used, and one or more mixed solvents may be used.

Preferably, the organic solid electrolyte is a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphoric acid ester polymer, a poly edgeation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ionic Polymers containing dissociation groups and the like can be used.

As the inorganic solid electrolyte of the present invention, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO4-Li ₂ S-SiS _{2 and} other nitrides of Li, halide, sulfate, and the like can be used.

The shape of the lithium secondary battery as described above is not particularly limited, and may be, for example, a jelly-roll type, a stack type, a stack-folding type (including a stack-Z-folding type), or a lamination-stack type, preferably It may be a stack-folding type.

After preparing the electrode assembly in which the positive electrode, the separator, and the negative electrode are sequentially stacked, they are placed in a battery case, and then an electrolyte is injected into the upper portion of the case and sealed with a cap plate and gasket to assemble to produce a lithium secondary battery. .

The lithium secondary battery may be classified into a cylindrical shape, a square shape, a coin shape, a pouch shape, and the like, and may be divided into a bulk type and a thin film type according to the size. The structure and manufacturing method of these batteries are well known in the art, so detailed descriptions thereof are omitted.

The lithium secondary battery according to the present invention, configured as described above, contains iron sulfide (FeS ₂ ) to adsorb lithium polysulfide generated during charging and discharging of the lithium secondary battery, thereby increasing the reactivity of the anode of the lithium secondary battery and applying it The lithium secondary battery has an effect of increasing discharge capacity and life. In addition, when the iron sulfide (FeS ₂ ) according to the present invention is included, there is an advantage that the overload is improved and the discharge capacity is improved even in the electrode having high loading and low porosity.

Hereinafter, the present invention will be described in more detail through examples and the like, but the scope and content of the present invention may be reduced or limited by the examples below. In addition, if it is based on the disclosure of the present invention including the following examples, it is obvious that a person skilled in the art can easily carry out the present invention in which experimental results are not specifically presented, and patents to which such modifications and corrections are attached Naturally, it is within the scope of the claims.

[Production Example 1] Preparation of iron sulfide

Iron nitrate hydrate (Fe (NO ₃ ) _{3 ·} 9H ₂ O) (Sigma-Aldrich) 1.9 g as an iron precursor and Thiourea (CH ₄ N ₂ S) (Sigma-Aldrich) 3.6 g as a sulfur precursor Mixed (Fe: S = 1:10 molar ratio).

The mixture was treated with argon gas at a flow rate of 100 mL / min and heat-treated at 400 ° C for 1.5 hours. At this time, the rate of temperature increase for heat treatment was 10 ° C per minute. Iron sulfide (FeS ₂ ) was prepared through the heat treatment.

[Production Example 2] Preparation of iron sulfide

Iron sulfide with plate-like particles was performed in the same manner as in Preparation Example 1, except that 0.42 g of iron hydroxide (γ-FeOOH) was used instead of iron nitrate hydrate (Fe (NO ₃ ) _{3 ·} 9H ₂ O) as an iron precursor ( FeS ₂ ) was prepared.

[Comparative Production Example 1] Preparation of iron sulfide

It was carried out in the same manner as in Example 1, except that the molar ratio of sulfur (S) to iron (Fe) was 1: 4.

[Comparative Production Example 2] Preparation of iron sulfide

It was carried out in the same manner as in Example 1, except that 1.4 g of ammonium thiosulfate ((Ammonium Thiosulfate, (NH ₄ ) ₂ S ₂ O ₃ ) was used instead of Thiourea (CH ₄ N ₂ S) as a sulfur precursor. .

[Comparative Production Example 3] Preparation of iron sulfide

It was carried out in the same manner as in Example 1, except that 1.5 g of sulfur (S) was used instead of Thiourea (CH ₄ N ₂ S) as the sulfur precursor.

[Experimental Example 1] SEM (scanning electron microscope) analysis

SEM results (S-4800 FE-SEM of Hitachi Co., Ltd.) were performed on the iron sulfide (FeS ₂ ) prepared in Preparation Examples 1 and 2, and the results are shown in FIGS. 1 and 2. Preparation Example 1 is shown in FIG. 1 and Preparation Example 2 in FIG. 2, respectively.

1 and 2, as a result of performing the SEM analysis of Preparation Example 1 with a magnification of 20k, it was confirmed that amorphous iron sulfide (FeS ₂ ) particles having a particle size of µm were formed, and SEM analysis of Production Example 2 was performed. , It was confirmed that plate-shaped iron sulfide (FeS ₂ ) particles having a particle diameter of several hundred nm to several μm were formed.

[Experimental Example 2] XRD (X-ray Diffraction) analysis

XRD analysis (D4 Endeavor of Bruker Corporation) was performed on the iron sulfide (FeS ₂ ) prepared in Preparation Examples 1 and 2. 3 is a graph showing the results of XRD analysis for iron sulfide (FeS ₂ ) prepared in Preparation Example 1, and FIG. 4 is a graph showing the results of XRD analysis for iron sulfide (FeS ₂ ) prepared in Preparation Example 2.

As a result of X-ray diffraction analysis using CuKα rays, referring to FIGS. 3 and 4, iron nitrate hydrates (Fe (NO ₃ ) _{3 ·} 9H ₂ O) and iron hydroxides (γ-FeOOH) as iron precursors of Preparation Examples 1 and 2 The XRD peaks of the (111), (200), (210), (211), (220), (311), (222), and (321) planes respectively reacted with the thioureas were 2θ = 28.4 ± 0.2 ° , 32.9 ± 0.2 °, 36.9 ± 0.2 °, 40.6 ± 0.2 °, 47.3 ± 0.2 °, 56.0 ± 0.2 °, 58.9 ± 0.2 °, 61.5 ± 0.2 ° and 64.0 ± 0.2 ° showing XRD peaks, Preparation Example 1 and The iron precursor of 2, iron nitrate hydrate (Fe (NO ₃ ) _{3 ·} 9H ₂ O), and iron hydroxide (γ-FeOOH) reacted with excess sulfur to confirm the formation of crystalline iron sulfide (FeS ₂ ) in the pure phase. , XRD peak of sulfur was not observed, and it was found that all of the excess sulfur was removed during the heating process of heat treatment.

Meanwhile, XRD analysis results for the products according to Comparative Preparation Examples 1 to 3 are shown in FIGS. 5 to 7, respectively.

Referring to FIG. 5, in Comparative Production Example 1 in which the molar ratio of sulfur (S) to iron (Fe) was 1: 4, the peak of Fe ₇ S ₈ was confirmed instead of iron sulfide (FeS ₂ ) as desired in the present invention. , When the molar ratio of sulfur (S) to iron (Fe) is 1:10 or more, it is confirmed that the single phase iron sulfide (FeS ₂ ) according to the present invention is synthesized, and The molar ratio was found to affect the composition of the final product to be prepared.

Referring to FIG. 6, when ammonium thiosulfate ((NH ₄ ) ₂ S ₂ O ₃ ) is used as a sulfur precursor, a side reaction occurs and a peak of NH ₄ Fe (SO ₄ ) ₂ appears instead of iron sulfide (FeS ₂ ). I could confirm.

Referring to FIG. 7, when sulfur (S) itself is used as a sulfur precursor, Fe ₇ S ₈ is mixed instead of FeS ₂ in a single phase even when the molar ratio of sulfur (S) to iron (Fe) is 1:10. When the molar ratio of sulfur (S) to iron (Fe) is 1: 2 or less, FeS ₂ desired in the present invention was not generated, and as a result of insufficient sulfur ratio, Fe ₇ S ₈ and iron oxide ( Fe ₃ O ₄ ) It was confirmed that the mixture is produced.

[Example 1] Manufacture of lithium secondary battery including positive electrode with iron sulfide added

First, 5 parts by weight of iron sulfide (FeS ₂ ) prepared in Preparation Example 1 compared to the total weight (100 parts by weight) of base solids (active material, conductive material, and binder) to which iron sulfide (FeS ₂ ) is added as water as a solvent is introduced. And dissolved. Then, with respect to the obtained solution, 100 parts by weight of the total solid content of the base, that is, 90 parts by weight of a sulfur-carbon composite (S / CNT 75:25 weight ratio) as an active material, 5 parts by weight of Denka Black as a conductive material, and styrene butadiene rubber as a binder / Carboxymethyl cellulose (SBR / CMC 7: 3) 5 parts by weight was added and mixed to prepare a positive electrode slurry composition.

Subsequently, the prepared slurry composition was coated on a current collector (Al Foil), dried at 50 ° C. for 12 hours, and pressed with a roll press machine to prepare a positive electrode. At this time, the loading amount was 5.3 mAh / cm ² , and the porosity of the electrode was set to 68%.

Thereafter, a coin cell of a lithium secondary battery including an anode, a cathode, a separator, and an electrolyte prepared according to the above was prepared as follows. Specifically, the positive electrode was punched and used as a 14 phi circular electrode, and a polyethylene (PE) separator was punched to 19 phi, and a 150 um lithium metal was punched to 16 phi as the negative electrode.

[Example 2] Manufacture of lithium secondary battery including positive electrode with iron sulfide added

The lithium secondary battery was performed in the same manner as in Example 1, except that iron sulfide (FeS ₂ ) having plate-like particles prepared in Preparation Example 2 was used instead of iron sulfide (FeS ₂ ) prepared in Preparation Example 1. It was prepared (ie, electrode porosity is 68%).

[Example 3] Manufacture of lithium secondary battery including positive electrode with iron sulfide added

By rolling the electrode containing iron sulfide (FeS ₂ ) with the plate-shaped particles prepared in Preparation Example 2, except that the porosity of the electrode was changed from 68% to 62%, the Example 2 and A lithium secondary battery was manufactured in the same manner.

[Comparative Example 1] Manufacture of lithium secondary battery including positive electrode without iron sulfide added

A total of 100 parts by weight of the base solid content in water as a solvent without containing iron sulfide (FeS ₂ ), that is, 90 parts by weight of a sulfur-carbon composite (S / CNT 75:25 weight ratio) as an active material, and 5 parts by weight of denka black as a conductive material , 5 parts by weight of styrene butadiene rubber / carboxymethyl cellulose (SBR / CMC 7: 3) as a binder was added and mixed to prepare a positive electrode slurry composition.

Subsequently, the prepared slurry composition was coated on a current collector (Al Foil) and dried at 50 ° C. for 12 hours to prepare a positive electrode. At this time, the loading amount was 5.3 mAh / cm ² , and the porosity of the electrode was 68%.

Thereafter, a coin cell of a lithium secondary battery including an anode, a cathode, a separator, and an electrolyte prepared according to the above was prepared as follows. Specifically, the positive electrode was punched and used as a 14 phi circular electrode, and a polyethylene (PE) separator was punched to 19 phi, and a 150 um lithium metal was punched to 16 phi as the negative electrode.

[Comparative Example 2] Manufacture of lithium secondary battery including positive electrode without iron sulfide added

A lithium secondary battery was manufactured in the same manner as in Comparative Example 2, except that the porosity of the electrode was changed from 68% to 62% by rolling the electrode.

[Experimental Example 3] Comparative experiment of discharge capacity of lithium secondary battery

In order to test the discharge capacity of the lithium secondary battery according to the type of positive electrode material, as described in Table 1 below, the discharge capacity of the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was measured. At this time, the measurement current was 0.1C, the voltage range was 1.8 to 2.6 V, and the results are shown in FIGS. 8 and 9.

	Lithium secondary battery
	cathode	anode
Example 1	Metal lithium	Sulfur-carbon composite (S: CNT = 75: 25) + conductive material + binder + FeS 2 (5 parts by weight) of Preparation Example 1 (90: 5: 5: 5, weight ratio)-Sulfur loading in anode: 5.3 mAh / cm 2 · Porosity of the electrode: 68%
Example 2	Metal lithium	Sulfur-carbon composite (S: CNT = 75: 25) + conductive material + binder + FeS 2 (5 parts by weight) of Preparation Example 2 (90: 5: 5: 5, weight ratio)-Sulfur loading in anode: 5.3 mAh / cm 2 · Porosity of the electrode: 68%
Example 3	Metal lithium	Sulfur-carbon composite (S: CNT = 75: 25) + conductive material + binder + FeS 2 (5 parts by weight) of Preparation Example 2 (90: 5: 5: 5, weight ratio)-Sulfur loading in anode: 5.3 mAh / cm 2 · Porosity of the electrode: 62%
Comparative Example 1	Metal lithium	Sulfur-carbon composite (S: CNT = 75: 25) + conductive material + binder (90: 5: 5, weight ratio) Sulfur loading in the anode: 5.3 mAh / cm 2 · Porosity of the electrode: 68%
Comparative Example 2	Metal lithium	Sulfur-carbon composite (S: CNT = 75: 25) + conductive material + binder (90: 5: 5, weight ratio) Sulfur loading in the anode: 5.3 mAh / cm 2 Porosity of the electrode: 62%

8 and 9 is a graph showing the discharge capacity measurement results of the lithium secondary battery prepared according to an embodiment and a comparative example of the present invention. As shown in FIG. 8, Example 1 in which iron sulfide (FeS ₂ ) prepared in Preparation Example 1 was added to the positive electrode, and Example 2 in which iron sulfide (FeS ₂ ) prepared in Preparation Example 2 was added to the positive electrode. It was confirmed that the overvoltage of the battery was improved and the initial discharge capacity was further increased as compared with the conventional comparative example 1. Therefore, it was found that the iron sulfide according to the present invention has an effect of increasing the initial discharge capacity and improving the overvoltage of the lithium secondary battery.

In particular, Example 2 using iron hydroxide (γ-FeOOH) as an iron precursor of iron sulfide, as shown in FIG. 8, using iron nitrate hydrate (Fe (NO ₃ ) _{3 ·} 9H ₂ O) as an iron precursor of iron sulfide It was confirmed that the initial discharge capacity was superior to that of Example 1, and in the Experimental Example 2 related to XRD analysis, iron sulfide to which iron hydroxide was applied and iron sulfide to which iron nitrate hydrate was applied had the same crystal structure, and thus exhibited different battery performance. From this, it can be seen that the structural difference of iron sulfide plays an additional important role in improving the performance of the battery.

Therefore, through the above, iron sulfide (FeS ₂ ) is added to the anode, but iron sulfide (γ-FeOOH) is prepared as an iron precursor rather than iron nitrate hydrate (Fe (NO ₃ ) _{3 ·} 9H ₂ O) as iron precursor (FeS ₂₎ It was confirmed that it is more preferable to use).

On the other hand, in the case of a general lithium secondary battery, if the porosity of the electrode is lowered, the performance of the battery is lowered due to the decrease in the electrolyte contained in the electrode, but as shown in FIG. 9, even when the porosity of the electrode is lowered, the electrode It was found that the initial discharge capacity of and the overvoltage were improved (comparative control of Example 3 and Comparative Example 2). Accordingly, it was found that iron sulfide (FeS ₂ ) according to the present invention has an effect of improving overvoltage and discharging capacity even in an electrode having a low porosity of high loading.

Claims (15)

1. (1) mixing an iron precursor and a sulfur precursor to form a mixture; And

   (2) heat-treating the mixture in an inert gas atmosphere; a method for producing iron sulfide (FeS ₂ ).
2. The method according to claim 1, the method for producing, iron sulfide (FeS _2), characterized in that the precursor is iron _{Fe (NO 3) 3 · 9H} 2 O, the γ-FeOOH or the combination thereof.
3. The method according to claim 2, characterized in that the iron precursor is γ-FeOOH, a method for producing iron sulfide (FeS ₂ ).
4. The method according to claim 1, The sulfur precursor is characterized in that the thiourea (Thiourea), the method of manufacturing iron sulfide (FeS ₂ ).
5. The method according to claim 1, wherein the mixing of step (1) is characterized in that the molar ratio of sulfur (S) to iron (Fe) is 1: 8 or more, the method of manufacturing iron sulfide (FeS ₂ ).
6. The method according to claim 1, The heat treatment of the step (2) is carried out in an inert gas atmosphere or continuously in the inert gas atmosphere for 1 to 3 hours at 400 to 600 ℃, the temperature rise rate is between 5 to 20 ℃ per minute range Characterized in that, the method of manufacturing iron sulfide (FeS ₂ ).
7. According to claim 6, wherein said inert gas is a method for producing, iron sulfide (FeS _2), characterized in that is selected from the group consisting of nitrogen, argon, helium and mixtures thereof.
8. As a positive electrode for a lithium secondary battery comprising an active material, a conductive material and a binder,

   The positive electrode is a lithium secondary battery positive electrode containing iron sulfide (FeS ₂ ).
9. The positive electrode for a lithium secondary battery according to claim 8, wherein the iron sulfide (FeS ₂ ) comprises plate-shaped particles.
10. The positive electrode for a lithium secondary battery according to claim 8, wherein the content of the iron sulfide (FeS ₂ ) is 0.1 to 15 parts by weight compared to 100 parts by weight of the base solids contained in the positive electrode for a lithium secondary battery.
11. The positive electrode for a lithium secondary battery according to claim 8, wherein the iron sulfide (FeS ₂ ) has an average particle diameter of 0.1 to 10 μm.
12. The positive electrode for a lithium secondary battery according to claim 8, wherein the iron sulfide (FeS ₂ ) is crystalline.
13. The positive electrode for a lithium secondary battery according to claim 8, wherein the active material is a sulfur-carbon composite.
14. The positive electrode for a lithium secondary battery according to claim 13, wherein the sulfur-carbon composite has a sulfur-based content of 60 to 90 parts by weight based on 100 parts by weight of the sulfur-carbon composite.
15. The positive electrode for a lithium secondary battery of claim 8; cathode; A separator interposed between the anode and the cathode; And electrolyte; lithium secondary battery comprising a.

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