WO2019194429A1 - Positive electrode for lithium secondary battery comprising goethite, and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium secondary battery comprising goethite as an additive, and a lithium secondary battery comprising same. In a lithium-sulfur battery, in particular, among lithium secondary batteries comprising a positive electrode to which goethite is applied, the goethite can adsorb lithium polysurfide (LiPS) generated in the process of charging and discharging the battery, thereby increasing charging and discharging efficiency of the battery and improving longevity.

Description

A positive electrode for a lithium secondary battery including a gootite and a lithium secondary battery having the same

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0040389 dated April 6, 2018 and Korean Patent Application No. 10-2019-0028552 dated March 13, 2019, All content disclosed in the literature is included as part of this specification.

The present invention relates to a positive electrode for a lithium secondary battery including a gootite as a positive electrode additive and a lithium secondary battery having an improved lifespan.

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 batteries have been attracting attention as new high-capacity, eco-friendly and low-cost lithium secondary batteries since it is known that battery performance can be dramatically improved by forming nanocomposites around 2010. Phosphorus research is 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. To this end, various chemicals (melt impregnation to nano-scale 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. The method of adding to the method, attaching a functional group capable of adsorbing lithium polysulfide on the surface of the carbon structure, and wrapping sulfur particles using graphene or graphene oxide, etc. 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.

Accordingly, in the present invention, in order to solve the problem of lithium polysulfide elution occurring at the positive electrode side of the lithium-sulfur battery and to suppress side reactions with the electrolyte, gothite was introduced into the positive electrode of the lithium-sulfur battery. The present invention was completed by confirming that the battery performance of the lithium-sulfur battery can be improved by solving the problem.

Accordingly, an object of the present invention is to provide a positive electrode additive for a lithium secondary battery that can solve 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 and improved life characteristics of the battery.

In order to achieve the above object, the present invention provides a cathode for a lithium secondary battery containing a gootite.

One embodiment of the present invention is 1 to 15 parts by weight based on 100 parts by weight of the base solids contained in the positive electrode for lithium secondary batteries, the base solids include an active material, a conductive material and a binder.

In one embodiment of the present invention, the gothite is in a rod shape.

One embodiment of the present invention is that the diameter of the Gotite is in the form of a rod of 10 to 50 nm.

One embodiment of the present invention is that the length of the gothite is in the form of a rod of 50 to 500 nm.

One embodiment of the present invention is that the active material is a sulfur-carbon composite.

In another aspect, the present invention, the lithium secondary battery positive electrode containing the gonite; cathode; A separator interposed between the anode and the cathode; It provides a lithium secondary battery comprising a; and an electrolyte.

When the gothite according to the present invention is applied to a positive electrode of a lithium secondary battery, especially a lithium-sulfur battery, it adsorbs lithium polysulfide generated during charging and discharging of the lithium-sulfur battery to increase the reactivity of the lithium-sulfur battery positive electrode. Suppresses side reactions with the electrolyte.

The lithium-sulfur battery equipped with the positive electrode including the gothite does not reduce the capacity of sulfur, and thus can realize a high capacity battery and stably apply sulfur by high loading, and there is no problem such as shorting or heating of the battery. Stability is improved. In addition, the lithium secondary battery including the lithium-sulfur battery has the advantage of high charging and discharging efficiency of the battery and improved life characteristics.

1 and 2 show a scanning electron microscope (SEM) image of the gootite according to the present invention.

Figure 3 shows the results of the X-ray diffraction analysis (XRD) of the gootite in accordance with the present invention.

Figure 4 shows a scanning electron microscope (SEM) image of the lepidocrosite according to a comparative example of the present invention.

5 shows the results of X-ray diffraction analysis (XRD) of the lepidocrosite according to a comparative example of the present invention.

Figure 6 shows the color change results of the lithium polysulfide adsorption experiment of gothite according to the present invention.

7 shows discharge capacity measurement results of a lithium-sulfur battery including a positive electrode according to an exemplary embodiment of the present invention.

8 shows the life characteristics measurement results of a lithium-sulfur battery including a positive electrode according to an embodiment 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.

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

The present invention supplements the shortcomings of the conventional lithium-sulfur battery positive electrode, and provides a lithium secondary battery positive electrode which is improved in the problem of continuous degradation of the electrode due to the dissolution and shuttle phenomenon of lithium polysulfide (polysulfide) and reduction of discharge capacity.

Specifically, the positive electrode for a lithium secondary battery provided by the present invention includes an active material, a conductive material, and a binder, and is characterized in that Gothite (α-FeOOH) is applied (included) as a positive electrode additive.

In particular, the gothite is included in the positive electrode of the lithium secondary battery, especially lithium-sulfur battery in the present invention, by adsorbing lithium polysulfide, the lithium polysulfide is transferred to the negative electrode to reduce the life of the lithium-sulfur battery By reducing and suppressing the reduced reactivity due to lithium polysulfide, it is possible to increase the discharge capacity of the lithium-sulfur battery including the positive electrode, and furthermore, to improve the life of the battery.

Method of manufacturing Goatite

The gothite contained in the positive electrode for a lithium secondary battery according to the present invention may preferably be prepared by reacting Fe (NO ₃ ) _{3 ·} 9H ₂ O with N ₂ H _{4 ·} H ₂ O. Since the reaction proceeds using hydrazine, the reaction solution maintains a high pH. First, after Fe (OH) ₃ is generated, goatite is α-FeOOH is produced.

In one embodiment, Goatite may be prepared by reacting 0.1 to 0.3M of N ₂ H ₄ .H ₂ O solution with 0.04 to 0.08M of Fe (NO ₃ ) ₃ .9H ₂ O. The reaction can be prepared by mixing Fe (NO ₃ ) _{3 ·} 9H ₂ O and N ₂ H _{4 ·} H ₂ O aqueous solution within 10 to 120 seconds. When mixing at a higher flow rate than the reaction rate, Fe (OH) ₃ may be rapidly formed at a high pH to generate particles having a large particle size.When mixing at a slower flow rate, phases of the first reacted material and the later reacted material may be produced. As the phases may be different, appropriate control over the reaction rates in this range is required for the production of crystalline pure gothite.

When the reaction proceeds at room temperature, the reaction may proceed for 24 hours at 80 ° C. for 2 hours. The reaction can be reacted by stirring the Fe (NO ₃ ) _{3 ·} 9H ₂ O aqueous solution and N ₂ H _{4 ·} H ₂ O aqueous solution at 300 to 500rpm. Thereafter, the resulting gothite is filtered through a filter paper to allow sufficient air to flow therein, followed by drying at 80 ° C. for 6 to 12 hours to prepare gothite.

The gothite produced by the reaction may be crystalline.

1 and 2 show scanning electron microscope (SEM) images of gothite (α-FeOOH) prepared by the above method. In Figures 1 and 2 it can be seen that the goitite of the 'rod shape' (rod shape) prepared according to the manufacturing method according to the present invention. Goatite prepared by the above production method may have a diameter of 10 to 50 nm, and a length of 50 to 500 nm.

Figure 3 shows the X-ray diffraction analysis (XRD) data results of the gootite prepared by the above production method. As a result of X-ray diffraction analysis of Fig. 3, crystalline Goatite was detected through an effective peak detected at 2θ = 21.223 °, 33.241 °, 34.700 °, 36.055 °, 36.649 °, 39.984 °, 41.186 °, 53.237 °, and 59.023 °. It can be confirmed that is synthesized.

In X-ray diffraction analysis (XRD), the effective (significant or effective) peak refers to a peak that is repeatedly detected in substantially the same pattern in XRD data without being greatly influenced by the analysis conditions or the performer of the analysis. It means a peak having a height, intensity, intensity, etc., which may be 1.5 times or more, preferably 2 times or more, more preferably 2.5 times or more, relative to a background level (backgound level).

Anode for Lithium Secondary Battery

The present invention provides a positive electrode for a lithium secondary battery containing gootite.

In this case, the positive electrode of the lithium secondary battery may be a base solid content including an active material, a conductive material and a binder on the current collector, it may be preferable to use aluminum, nickel and the like excellent in the current collector.

In one embodiment, the gothite may be included in the positive electrode for a lithium secondary battery as an amount of 1 to 15 parts by weight based on 100 parts by weight of the base solids including the active material, the conductive material, and the binder, and preferably 1 to 10 parts by weight. It may be included as. If it is less than the lower limit of the numerical range, the adsorption effect of the polysulfide may be insignificant, and if the upper limit is exceeded, the capacity of the electrode may be reduced and may not meet the purpose of increasing the energy density.

The gootite may be used gothite prepared by the production method proposed in the present invention. Thus, the gothite may be crystalline, may have a diameter of 10 to 50 nm, and may have a length of 50 to 500 nm. If the diameter and length are less than the above range, the specific surface area of the particles may increase, making it difficult to manufacture an electrode slurry of the lithium secondary battery, and if the range exceeds the above range, the activity of the gothite may decrease.

Meanwhile, the active material in the base solid constituting the positive electrode of the present invention may include elemental sulfur (S ₈ ), a sulfur-based compound, or a mixture thereof, and specifically, the sulfur-based compound may include 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), and the like.

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 alone is not electrically conductive, it may be used in combination with a conductive material. The addition of goctite according to the invention does not affect the maintenance of this sulfur-carbon composite structure.

The carbon of the sulfur-carbon composite according to the present invention may have any porous structure or 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 nanofibers (GNF), carbon nanofibers (CNF), and activated carbon fibers (ACF); And it may be one or more selected from the group consisting of activated carbon, but is not limited thereto, and the form is spherical, rod-shaped, needle-shaped, plate-shaped, tubular or bulk type, as long as it is commonly used in lithium secondary batteries, especially lithium-sulfur batteries It can be used without limitation.

The active material is preferably 50 to 95 parts by weight of 100 parts by weight of the base solids, and more preferably 70 parts by weight. If the active material is included below the range, it may be difficult to sufficiently exhibit the reaction of the electrode, and even if the active material is included above the range, the amount of the other conductive material and the binder is relatively insufficient and thus it is difficult to exert sufficient electrode reaction. It is desirable to determine the appropriate content within the above range.

Of the base solids constituting the positive electrode of the present invention, the conductive material electrically connects the electrolyte and the positive electrode active material, and acts as a path for electrons to move from the current collector to the sulfur, causing chemical changes in the battery. If it does not have a porosity and conductivity, it will not specifically limit. Graphite-based materials such as, for example, KS6; Carbon blacks such as 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; Or conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole may be used alone or in combination.

The conductive material is preferably 1 to 10 parts by weight of 100 parts by weight of the base solids, preferably 5 parts by weight. If the content of the conductive material included in the electrode is less than the above range, the unreacted portion of sulfur in the electrode increases, eventually causing a decrease in capacity. If the content exceeds the above range, the high efficiency discharge characteristics and the charge and discharge cycle life are adversely affected. It is desirable to determine the appropriate content within the above range because it will have a.

As the base solids, the binder is a material that is included in order to adhere the slurry composition of the base solids, which form the positive electrode, to the current collector. use. All binders 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 Tetrafluoroethylene polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyvinylpyridine, polystyrene, carboxymethyl cellulose, siloxane-based such as polydimethylsiloxane, styrene-butadiene rubber, acrylonitrile-butadiene Rubber, styrene-isoprene rubber containing rubber binder, poly Ethylene glycol-based and derivatives thereof, blends thereof, copolymers thereof and the like may be used, such as butylene glycol diacrylate, but are not limited thereto.

The binder may be composed of 1 to 10 parts by weight of 100 parts by weight of the base composition included in the electrode, preferably about 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 be deteriorated, so that the positive electrode active material and the conductive material may be dropped. If the content of the binder resin is greater than the above range, the ratio of the active material and the conductive material in the positive electrode may be relatively reduced, thereby reducing battery capacity. Therefore, it is preferable to determine the appropriate content within the above-mentioned range.

As described above, the positive electrode including the gothite and the base solids may be manufactured according to a conventional method. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant in a positive electrode active material, and then applying (coating) to a current collector of a metal material, compressing, and drying the positive electrode to prepare a positive electrode. have.

For example, in the production of the positive electrode slurry, first, the gothite is dispersed in a solvent, and the obtained solution is mixed with an active material, a conductive material, and a binder to obtain a slurry composition for forming a positive electrode. Thereafter, the slurry composition is coated on a current collector and then dried to complete a positive electrode. At this time, if necessary, it can be manufactured by compression molding the current collector in order to improve the electrode density. There is no limitation to the method of coating the slurry, for example, doctor blade coating, dip coating, gravure coating, slit die coating, spin coating It can be prepared by coating, comma coating, bar coating, reverse roll coating, screen coating, cap coating, and the like.

In this case, as the solvent, a positive electrode active material, a binder, and a conductive material may be uniformly dispersed, as well as those which can be easily dispersed to gothite. As such a solvent, water is most preferable as an aqueous solvent, and in this case, the water may be secondary distilled water (DW) or tertiary distilled water (DIW). However, the present invention is not limited thereto, and if necessary, lower alcohols that can be easily mixed with water may be used. The lower alcohols include methanol, ethanol, propanol, isopropanol, butanol, and the like. Preferably, they may be used in combination with water.

Lithium secondary battery

On the other hand, the present invention provides a lithium secondary battery comprising a separator and an electrolyte interposed between the positive electrode, the negative electrode, the positive electrode and the negative electrode for a lithium secondary battery including the goctite.

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

Specifically, the negative electrode is a material capable of reversibly intercalating or deintercalating lithium ions (Li ⁺ ) as an active material, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal Or lithium alloys.

The material capable of reversibly occluding or releasing the lithium ions (Li ⁺ ) may be, for example, crystalline carbon, amorphous carbon or a mixture thereof. In addition, the material capable of reacting with the lithium ions (Li ⁺ ) to form a lithium-containing compound reversibly may be, for example, tin oxide, titanium nitrate or silicon. In addition, 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 optionally further include a binder together with the negative electrode active material. The binder serves to paste the negative electrode active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and buffer effect on the 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 a 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 nonconductive 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 is a material that allows the transport of lithium ions between the positive electrode and the negative electrode while separating or insulated from each other, if used as a separator in a conventional lithium secondary battery can be used without particular limitation, in particular, the ion of the electrolyte It is desirable to have a low resistance to migration and excellent electrolyte-moisture capability.

More preferably, the separator material may be a porous, non-conductive or insulating material, for example, an independent member such as a film, or a coating layer added to the anode and / or the cathode.

Specifically, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc. It may be used as a lamination or or a conventional porous non-woven fabric, for example, a non-woven fabric made of glass fibers, polyethylene terephthalate fibers of high melting point, etc. may be used, but is not necessarily limited thereto.

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

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 at least one from the group consisting of lithium carbonate, lithium phenyl borate, imide.

The concentration of the lithium salt is preferably 0.2-2 M, 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 charging and discharging conditions of the cell, the operating temperature and other factors known in the lithium battery art. It may be 0.6 to 2M, 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 and the performance of the electrolyte may be lowered. If the concentration of the lithium salt is less than the above range, the viscosity of the electrolyte may be increased, thereby reducing the mobility of lithium ions (Li ⁺ ), and thus within the above range. It is desirable to select the appropriate concentration.

The non-aqueous organic solvent is a material capable of dissolving lithium salts, preferably 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, dioxolane (Dioxolane, DOL ), 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl 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 Ralidone, 3-methyl-2- Oxazolidone, acetic acid ester, butyric acid ester and propionic acid ester, dimethylformamide, sulfolane (SL), methyl sulfolane, dimethylacetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol diacetate, dimethyl sulfite, or ethylene glycol An aprotic organic solvent such as sulfite may be used, and may be used in the form of one or more of these mixed solvents.

As the organic solid electrolyte, preferably, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, poly etchation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, ionic Polymers containing dissociation groups and the like can be used.

The inorganic solid electrolyte of the present invention is preferably 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 Nitrides, halides, sulfates, and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium secondary battery may be those commonly used in the art, such as a lithium-sulfur battery and a lithium metal battery, and may exemplarily represent a lithium-sulfur battery that best meets the spirit of the present invention.

The shape of the lithium secondary battery is not particularly limited, and may be, for example, jelly-roll type, stack type, stack-fold type (ex: stack-Z-fold type), or lamination-stack type, among them, stack-fold type. This may be desirable.

After manufacturing an electrode assembly in which the positive electrode, the separator, and the negative electrode are sequentially stacked, the electrode assembly may be placed in a battery case, and then the electrolyte may be injected into the upper part of the case and sealed assembled with a cap plate and a gasket to manufacture a lithium secondary battery.

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

The lithium secondary battery according to the present invention, which is configured as described above, lithium-sulfur battery, including the gothite to adsorb lithium polysulfide generated during charge and discharge of the lithium-sulfur battery to increase the reactivity of the battery positive electrode Ultimately, it has the effect of increasing the discharge capacity and life of the battery.

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.

[Production Example 1] Preparation of Gothite

Mix 0.5M Fe (NO ₃ ) _{3 ·} 9H ₂ O (Aldrich, 98% purity) with 0.3M N ₂ H _{4 ·} H ₂ O (Aldrich, purity more than 98%) for 50 seconds It was. At this time, the mixture was stirred at 80 rpm at 400 rpm for 2 hours. After filtration through the filter paper, sufficient air was introduced to dry at 80 ℃ for 8 hours to prepare a gootite (α-FeOOH).

[Production Example 2] Preparation of Repidocrosite

0.5 M Fe (NO ₃ ) ₃ 9H ₂ O (Aldrich, 98% purity) was mixed with 0.3 M NaBH ₄ (purity> 95%) for 50 seconds. At this time, the mixture was stirred for 40 minutes at 400 rpm at room temperature, and it was confirmed that hydrogen gas was generated during the reaction. After filtering through a filter paper, enough air was introduced to dry at 80 ℃ for 8 hours to prepare a lepidocrocite (γ-FeOOH).

Example 1 Preparation of Lithium Secondary Battery (Lithium-Sulfur Battery) Including Gothic-Added Positive Electrode

First, the gothite prepared from Preparation Example 1 was added to 10 parts by weight of the total weight (100 parts by weight) and dispersed in a base solid (active material, conductive material, and binder) into which gothite was added to water as a solvent. . Subsequently, with respect to the obtained solution, a total of 100 parts by weight of the base solids, that is, 90 parts by weight of sulfur-carbon composite (S / C 7: 3) as the active material, 5 parts by weight of denca black as the conductive material, and styrene butadiene rubber / 5 parts by weight of carboxymethyl cellulose (SBR / CMC 7: 3) was added and mixed to prepare a positive electrode slurry composition.

Subsequently, the prepared positive electrode 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 3.5mAh / cm ² , and the porosity of the electrode was 60%.

Then, in addition to the positive electrode prepared as described above, a lithium-sulfur battery in the form of a coin cell including a negative electrode, a separator and an electrolyte was prepared as follows. Specifically, the anode was punched out using a 14 phi circular electrode, and the polyethylene (PE) separator was punched out with 16 phi as a 19 phi and 150 um lithium metal as a cathode.

Comparative Example 1 Preparation of Lithium Secondary Battery (Lithium-Sulfur Battery) Containing a Positive Electrode without Gotite

A coin-cell lithium-sulfur battery was prepared in the same manner as in Example 1, except that no gothite was added to the positive electrode.

Comparative Example 2 Preparation of Lithium Secondary Battery (Lithium-Sulfur Battery)

A coin-coated lithium-sulfur battery was prepared in the same manner as in Example 1, except that 10 parts by weight of the lepidocrocite prepared from Preparation Example 2 was added to 100 parts by weight of the base solid instead of the gootite. It was.

Experimental Example 1 SEM (Scanning Electron Microscope) Analysis

SEM analysis (S-4800 FE-SEM of Hitachi, Ltd.) was respectively performed on the goitite prepared from Preparation Example 1 and the lepidocrosite prepared from Preparation Example 2. 1 and 2 are SEM images of the gothite prepared in Preparation Example 1, and FIG. 4 is an SEM image of the repidocrosite prepared in Preparation Example 2.

SEM analysis of the Goatite prepared from Preparation Example 1 at 50k magnification (corresponding to FIG. 1) and 250k magnification (corresponding to FIG. 2). As shown in FIGS. shape) 'Gothite,

As a result of SEM analysis of the lepidocrocite prepared from Preparation Example 2 at a magnification of 50k, it was possible to confirm the 'plate-like' lepidocrocite as shown in FIG. 4.

Experimental Example 2 X-ray diffraction analysis

XRD analysis (Bruker's D4 Endeavor) was performed on the gothite prepared in Preparation Example 1 and the lepidocrocite prepared in Preparation Example 2, respectively. 3 is an XRD analysis result for the gothite prepared in Preparation Example 1, and FIG. 5 is a graph showing an XRD analysis result for the lepidocrocite prepared in Preparation Example 2.

As a result of XRD analysis on the gothite and repidocrosite prepared from Preparation Examples 1 and 2, respectively, XRD peaks as shown in FIGS. 3 and 5 were derived, and thus, crystalline ingots of the pure phase were obtained. Tight and repidocrosite were confirmed to be produced.

 Experimental Example 3 Evaluation of Goatite's Lithium Polysulfide Adsorption Capacity

As a result of visual observation of the lithium polysulfide adsorption capacity of the gothite prepared in Preparation Example 1 through a change in chromaticity, as shown in FIG. 6, the red color of the lithium polysulfide reacted with the gothite was lightened. It was confirmed that Goatite had excellent lithium polysulfide adsorption capacity.

Experimental Example 4 Evaluation of discharge capacity of lithium secondary battery (lithium-sulfur battery)

Using the lithium-sulfur batteries prepared in Example 1, Comparative Examples 1 and 2, the discharge capacity according to the type and type of the positive electrode additive was measured and shown in FIG. 7. At this time, the measurement current was 0.1C and the voltage range was 1.8-2.5V.

As a result, the lithium-sulfur battery of Example 1 in which the gothite was contained in the positive electrode had an initial discharge capacity as compared with the lithium-sulfur battery of Comparative Example 1 in which the gothite was not contained in the positive electrode, as shown in FIG. 7. It can be seen that about 100 mAh / g is higher. In addition, it was confirmed that the initial discharge capacity of the battery was also higher than that of Comparative Example 1 in the case of Comparative Example 2 in which repidocrosite was applied instead of gootite. Accordingly, it was found that both gothite and lepidocrocite are effective for increasing the initial discharge capacity of lithium-sulfur batteries.

Experimental Example 5 Life Cycle Assessment of Lithium Secondary Battery

Using the lithium-sulfur batteries prepared in Example 1, Comparative Examples 1 and 2 was measured in the life cycle characteristics of the battery shown in Figure 8 shown. In the voltage range of 1.8 to 2.5V, 0.1C discharge / 0.1C charge 3 Cycle, 0.2C discharge / 0.2C charge 3 Cycle, 0.5C discharge / 0.3C charge was repeated repeatedly.

In the case of the battery according to Comparative Example 1, the battery according to Comparative Example 2 degenerated at about 120 cycles, while the battery according to Example 1 did not degenerate even at 160 cycles or more. As a result, it can be seen that the lithium-sulfur battery including gotite in the positive electrode has excellent life characteristics according to cycles.

Claims (8)

1. A positive electrode for a lithium secondary battery containing a gootite.
2. The method according to claim 1, wherein the content of the gothite is 1 to 15 parts by weight based on 100 parts by weight of the base solids contained in the positive electrode,

   The base solid content, an active material, a conductive material and a binder, characterized in that the lithium secondary battery positive electrode.
3. The positive electrode for a lithium secondary battery of claim 1, wherein the gothite has a rod shape.
4. The positive electrode for a lithium secondary battery of claim 3, wherein the gothite has a rod shape having a diameter of 10 to 50 nm.
5. The positive electrode for a lithium secondary battery according to claim 3, wherein the gothite has a rod shape having a length of 50 to 500 nm.
6. The positive electrode for a lithium secondary battery according to claim 2, wherein the active material is a sulfur-carbon composite.
7. A lithium secondary battery positive electrode according to any one of claims 1 to 6; cathode; A separator interposed between the anode and the cathode; And an electrolyte; comprising a lithium secondary battery.
8. The lithium secondary battery according to claim 7, wherein the lithium secondary battery is a lithium-sulfur battery.

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