KR20200100961A - Cathode for lithium secondary battery comprising nanoclay, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a positive electrode for a lithium secondary battery including nanoclay as a positive electrode additive, and a lithium secondary battery including the same. When the nanoclay is applied to the positive electrode of a lithium secondary battery, stable driving of the lithium secondary battery is performed even in a positive electrode having low porosity, and the initial discharge capacity of the battery is increased.

Description

A positive electrode for lithium secondary batteries including nanoclays and lithium secondary batteries having the same {CATHODE FOR LITHIUM SECONDARY BATTERY COMPRISING NANOCLAY, AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a positive electrode for a lithium secondary battery including nanoclay as a positive electrode additive, and a lithium secondary battery having the same and improved initial discharge capacity.

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

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

However, the lithium secondary battery, which has the most excellent characteristics among the secondary batteries available to date, has several problems in being actively used in transportation devices such as electric vehicles and PHEVs, and the biggest problem among them is the limitation of capacity.

Lithium secondary batteries are basically composed of materials such as positive electrodes, electrolytes, and negative electrodes, and among them, positive and negative materials determine the capacity of the battery, so lithium-ion secondary batteries are subject to material limitations of the positive and negative electrodes. Limited by capacity. In particular, since the secondary battery to be used in applications such as electric vehicles and PHEVs should be able to be used as long as possible after being charged once, the discharge capacity of the secondary battery is very important. The biggest limitation to the sales of electric vehicles is that the distance that can be driven after a single charge is much shorter than that of a general gasoline engine car.

The capacity limitation of such a lithium secondary battery is difficult to completely solve due to the structural and material limitations of the lithium secondary battery despite a lot of efforts. Therefore, in order to fundamentally solve the capacity problem of a 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 batteries exceed the capacity limit determined by intercalation reactions of layered metal oxides and graphite of lithium ions, which are the basic principles of existing lithium ion secondary batteries, and replace transition metals and reduce costs, etc. It is a new high-capacity, inexpensive battery system that can bring about.

A lithium-sulfur 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: 3860 mAh/g) can be used to increase the capacity of the battery system. Also, 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 positive and negative active materials. This is a value 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 batteries are attracting attention as new high-capacity, eco-friendly, and inexpensive lithium secondary batteries since it was known that the battery performance can be dramatically improved through the formation of nanocomposites around 2010. It is being done.

One of the major problems of the lithium-sulfur 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 a non-conductor, making the electrochemical reaction at the electrode difficult, and the actual discharge capacity and voltage due to a very large overvoltage. Is that it falls far short of this theory. Early researchers tried to improve the performance by mechanical ball milling of sulfur and carbon or surface coating using carbon, but there was no significant effect.

In order to effectively solve the problem that the electrochemical reaction is limited by the electrical conductivity, as in the example of LiFePO ₄ , one of the other positive electrode active materials (electrical conductivity: 10 ^-9 to 10 ^-10 S/cm), the size of the particle is set to 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 into nano-sized porous carbon nanostructures or metal oxide structures) and physical methods (high energy ball milling) have been reported. Has become.

Another major problem associated with lithium-sulfur batteries is the dissolution of lithium polysulfide, an intermediate product of sulfur produced during discharge, into an electrolyte. As the discharge proceeds, sulfur (S ₈ ) continuously reacts with lithium ions, S ₈ → Li ₂ S ₈ → (Li ₂ S ₆ ) → Li ₂ S ₄ → Li ₂ S ₂ → The phase changes continuously with Li ₂ S, and among them, Li ₂ S ₈ and Li ₂ S ₄ (lithium polysulfide), which are long chains of sulfur, are easily dissolved in general electrolytes used in lithium ion batteries. There is a property to become. When such a reaction occurs, not only the capacity of the reversible anode is greatly reduced, but the dissolved lithium polysulfide diffuses into 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, so that charging and discharging efficiency is rapidly deteriorated. Recently, various methods have been proposed to solve this problem, and can be largely divided 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 suppress the dissolution of polysulfide into the electrolyte by using a new electrolyte such as a functional liquid electrolyte, a polymer electrolyte, or an ionic liquid of a new composition, or the dispersion rate to the negative electrode by controlling the viscosity. This is a method of controlling the shuttle reaction as much as possible.

Research is actively being conducted to control the shuttle reaction by improving the characteristics of SEI formed on the surface of the cathode. Typically, an oxide film such as Li _x NO _y and Li _x SO _y is added to the surface of the lithium anode by introducing an electrolyte additive such as LiNO ₃ . There is a method of forming and improving the structure, a method of forming a thick functional SEI layer on the surface of lithium metal, and the like.

Finally, methods of improving the characteristics of the positive electrode include forming a coating layer on the surface of the positive electrode 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 a positive electrode structure containing lithium ions, a method of coating the surface of a positive electrode structure with a metal oxide through which lithium ions are conducted, and a porous metal oxide having a large specific surface area and large pores that can absorb a large amount of lithium polysulfide A method of adding to the carbon structure, a method of attaching a functional group capable of adsorbing lithium polysulfide on the surface of a carbon structure, a method of enclosing sulfur particles using graphene or graphene oxide, etc. have been suggested.

Although such efforts are being made, there is a problem that this method is somewhat complicated and the amount of sulfur, which is an active material, can be limited. Therefore, it is necessary to develop a new technology to solve these problems in a complex manner and improve the performance of a lithium secondary battery.

Republic of Korea Patent Publication No. 10-2015-0091280 (2017.1.4), "Lithium sulfur battery and its manufacturing method"

Accordingly, in the present invention, in order to implement a lithium secondary battery with a high energy density, a nanoclay was introduced into the positive electrode of a lithium secondary battery in order to solve problems such as reduction in discharge capacity or impregnation of an electrolyte occurring in a positive electrode having a low porosity. By solving the problem, it was confirmed that the performance of the lithium secondary battery can be improved, thereby completing the present invention.

Accordingly, an object of the present invention is to provide a positive electrode for a lithium secondary battery capable of solving the above problem.

Another object of the present invention is to provide a lithium secondary battery having the positive electrode to improve overvoltage of the battery and increase initial discharge capacity.

In order to achieve the above object, 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 including nanoclay.

In one embodiment of the present invention, the content of the nanoclay is 1 to 15 parts by weight based on 100 parts by weight of the base solid content included in the lithium secondary battery positive electrode.

An embodiment of the present invention is that the nanoclay is lithiated.

In one embodiment of the present invention, the nanoclay is montmorillonite, bentonite, hectorite, saponite, videlite, nontronite, swellable mica, vermiculite, synthetic mica, kanemite, magadite, kenite, kaolinite, Smectite, illite, chlorite, muscobite, pyrophyllite, antigolite, haerokseok, vermiculite, sepiolite, imogolite, sobokite, nacrite, anoxite, sericite, redicite, warm asbestos and antigolite It is one or more selected from the group consisting of.

In one embodiment of the present invention, the active material is a sulfur-carbon composite.

In one embodiment of the present invention, the sulfur-carbon composite contains 60 to 80 parts by weight of sulfur based on 100 parts by weight of the sulfur-carbon composite.

In one embodiment of the present invention, the positive electrode includes a current collector and an electrode active material layer formed on at least one surface of the current collector,

The porosity of the electrode active material layer is 40 to 90%.

In addition, the present invention,

The anode described above; cathode; It provides a lithium secondary battery including a separator and an electrolyte interposed therebetween.

In one embodiment of the present invention, the secondary battery is a lithium-sulfur battery.

The positive electrode for a lithium secondary battery according to the present invention contains nanoclay as an additive, so it can solve the problem of impregnation of the electrolyte that occurs in the positive electrode having a low porosity, and it is possible to transfer lithium ions through the nanoclay. It is possible to stably drive the lithium secondary battery including the battery, and there is an effect of increasing the discharge capacity of the battery.

1 shows a scanning electron microscope (SEM) image of montmorillonite (MMT) according to Preparation Example 1 of the present invention.
2 shows a scanning electron microscope (SEM) image of protonated montmorillonite (H-MMT) according to Preparation Example 2 of the present invention.
3 shows a scanning electron microscope (SEM) image of lithiated montmorillonite (Li-MMT) according to Preparation Example 3 of the present invention.
4 shows the results of X-ray diffraction analysis (XRD) of montmorillonite according to Preparation Examples 1 to 3 of the present invention.
5 shows the results of measuring the discharge capacity of lithium secondary batteries according to Examples and Comparative Examples of the present invention.
6 shows the results of measuring the discharge capacity of lithium secondary batteries according to Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement it. However, the present invention may be implemented in various different forms, and is not limited to this specification.

The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

The term “composite” as used herein refers to a material that exhibits more effective functions while forming different phases physically and chemically by combining two or more materials.

The present invention provides a positive electrode for a lithium secondary battery in which the problem of continuous reduction in reactivity of the electrode due to dissolution of lithium polysulfide and shuttle phenomenon, reduction in discharge capacity, and energy density problem are improved by supplementing the disadvantages of the conventional positive electrode for lithium secondary battery. do.

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 further includes nanoclay as a positive electrode additive.

Particularly, the nanoclay is included in the positive electrode of the lithium secondary battery in the present invention to improve the energy density of the battery by reducing the volume of the electrode and to enable the driving of a battery including an electrode having a low porosity, and the lithium secondary battery including the positive electrode It is possible to increase the discharge capacity and improve the life of the battery.

Positive electrode for lithium secondary battery

The present invention provides a positive electrode for a lithium secondary battery including an active material, a conductive material and a binder, and provides a positive electrode for a lithium secondary battery including the nanoclay.

In this case, the positive electrode of the lithium secondary battery may be one in which a base solid component including an active material, a conductive material, and a binder is located on the positive electrode current collector.

As the current collector, it may be preferable to use aluminum or nickel having excellent conductivity.

In one embodiment, 1 to 15 parts by weight of the nanoclay may be included, and preferably 1 to 10 parts by weight may be included based on 100 parts by weight of the base solid content including the active material, the conductive material, and the binder. If it is less than the lower limit of the above numerical range, the effect of the nanoclay may be insignificant and there may be no increase in the discharge capacity. If it exceeds the upper limit, the content of nanoclay, which is a non-conductor, increases, reducing the conductivity of the electrode and increasing the weight of the electrode compared to the increase in discharge capacity Since it can increase the energy density and reduce it, it is appropriately adjusted within the above range.

The nanoclay may be a layered silicate in which at least two plates are stacked, and in one embodiment of the present invention, the nanoclay is'lithiated' in which lithium ions are intercalated between the open interlayer structures. 'It can be.

When the lithiated nanoclay is included in the positive electrode, the porosity of the electrode is lowered to increase the energy density per weight of the electrode, so even in an environment where sufficient impregnation of the electrolyte is difficult, lithium ions are transferred to the electrode through the interlayer structure of the nanoclay to the positive electrode. It can react with sulfur contained in, and as a result, a lithium secondary battery having a high energy density can be implemented.

Since the nanoclay is a form in which one or more layers are stacked, when the stacked length is defined as the thickness and the length of one layer, that is, a single surface is defined as the diameter, the nanoclay according to the present invention has a thickness of 1 nm to It may have a particle size of 10 nm and an average diameter of 100 to 1,000 nm. If the thickness and average diameter of the nanoclay are outside the above ranges, basic physical properties of the nanoclay may not be implemented.

The nanoclays are montmorillonite, bentonite, hectorite, saponite, videlite, nontronite, swellable mica, vermiculite, synthetic mica, kanemite, margadite, kenite, kaolinite, smectite, illite, chlorite , Muscobite, Pyrophilite, Antigolite, Haerokseok, Vermiculite, Sepiolite, Imogolite, Sobokite, Nacrite, Anoxite, Sericite, Redicite, Warm Asbestos and Antigolite 1 selected from the group consisting of It may be a species or more, preferably (Na, Ca) _0.33 (Al, Mg) ₂ (Si ₄ O ₁₀ ) (OH) ₂ · nH ₂ O may be a smectite-based mineral montmorillonite having a formula of (montmorillonite).

Meanwhile, the active material among the base solids constituting the positive electrode of the present invention 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 organosulfur compound or a sulfur-carbon 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 does not have electrical conductivity, it may be used in combination with a conductive material. The addition of the nanoclay according to the present 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 a porous structure or a high specific surface area, so long as it is commonly used in the art.

For example, as the porous carbon material, 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 shape is spherical, rod-shaped, needle-shaped, plate-shaped, tube-shaped, or bulk-shaped, and may be used without limitation as long as they are commonly used for lithium secondary batteries.

The active material is preferably 50 to 95 parts by weight of 100 parts by weight of the base solid content, and more preferably 85 parts by weight. If the active material is contained within the above range, it is difficult to sufficiently exhibit the reaction of the electrode, and even if it is contained beyond the above range, it is difficult to exhibit a sufficient electrode reaction due to relatively insufficient amounts of other conductive materials and binders. It is desirable to determine the appropriate content.

In one embodiment, the sulfur-carbon composite may have a sulfur content of 60 to 80 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 is relatively increased, and the specific surface area increases as the content of carbon increases, so that the amount of binder added during slurry preparation should be increased. Increasing the amount of the binder added may eventually increase the sheet resistance of the electrode and act as an insulator to prevent electron pass, which may degrade battery performance. When the content of sulfur exceeds 80 parts by weight, sulfur or sulfur compounds that cannot be combined with the carbon material may be aggregated with each other or re-elute to the surface of the carbon material, making it difficult to receive electrons, and thus it may be difficult to directly participate in the electrode reaction. Adjust accordingly.

Among the base solids constituting the positive electrode of the present invention, the conductive material is a material that serves as a path for electrons to move from the current collector to sulfur by electrically connecting the electrolyte and the positive electrode active material, causing chemical changes in the battery. It is not particularly limited as long as it does not have porosity and conductivity. Graphite-based materials such as 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, aluminum, 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 made to constitute 1 to 10 parts by weight of 100 parts by weight of the base solid content, and may preferably be about 5 parts by weight. If the content of the conductive material contained in the electrode is less than the above range, sulfur that cannot react in the electrode increases, eventually causing a decrease in capacity, and if it exceeds the above range, the high efficiency discharge characteristics and charge/discharge cycle life are adversely affected. It is desirable to determine an appropriate content within the above-described range.

As a base solid, the binder is a material that contains the slurry composition of the base solid that forms the positive electrode to adhere well to the current collector, and is a material that is well soluble in a solvent and is capable of forming a conductive network between the positive electrode active material and the conductive material. use. All binders known in the art may be used unless there is a particular limitation, and 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, a copolymer of polyvinylidene fluoride (trade name: Kynar), poly(ethyl acrylate), poly Tetrafluoroethylene polyvinyl chloride, polytetrafluoroethylene, polyacrylonitrile, polyvinylpyridine, polystyrene, carboxymethyl cellulose, siloxanes such as polydimethylsiloxane, styrene-butadiene rubber, acrylonitrile-butadiene Rubber, a rubber-based binder including styrene-isoprene rubber, an ethylene glycol-based such as polyethylene glycol diacrylate, and derivatives thereof, a blend thereof, a copolymer thereof, and the like may be used, but are not limited thereto.

The binder is to constitute 1 to 10 parts by weight of 100 parts by weight of the base composition included in the electrode, and preferably, it may be 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 are degraded, so that the positive electrode active material and the conductive material may fall off, and if it exceeds the above range, the ratio of the active material and the conductive material in the positive electrode is relatively reduced, resulting in a decrease in battery capacity. Therefore, it is desirable to determine an appropriate content within the above-described range.

As described above, the positive electrode including the nanoclay and the base solid may be prepared according to a conventional method. For example, after preparing a slurry by mixing and stirring a solvent, a binder, a conductive material, and a dispersant as necessary in a positive electrode active material, it is applied (coated) to a current collector of a metal material, compressed, and dried to prepare a positive electrode. have.

For example, when preparing the positive electrode slurry, nanoclay is first 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 dried to complete the positive electrode. At this time, if necessary, it may be manufactured by compression molding on the current collector in order to improve the electrode density. The method of coating the slurry is not limited, for example, Doctor blade coating, Dip coating, Gravure coating, Slit die coating, Spin coating coating), comma coating, bar coating, reverse roll coating, screen coating, cap coating, and the like.

At this time, as the solvent, a positive electrode active material, a binder, and a conductive material may be uniformly dispersed, as well as those capable of easily dissolving nanoclays. As such a solvent, water is most preferable as an aqueous solvent, and in this case, the water may be distilled water (DW) obtained by secondary distillation or deionzied water (DIW) obtained by tertiary distillation. However, the present invention is not limited thereto, and if necessary, lower alcohol that can be easily mixed with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol, and preferably, these may 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 the nanoclay according to the present invention, and the electrode active material The porosity of the layer may be 40 to 90%, specifically 45 to 80%, and preferably 50 to 75%.

In the present invention, the term "porosity" means the ratio of the volume occupied by pores with respect to the total volume in a structure, and uses% as a unit, and is used interchangeably with terms such as porosity and porosity. I 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 a Brunauer-Emmett-Teller (BET) measurement method or a mercury permeation method (Hg porosimeter) And meso pore volume can be measured.

If the porosity of the electrode active material layer is less than 40%, the filling level of the base solid content including the active material, the conductive material, and the binder becomes too high, so that sufficient electrolyte solution capable of showing ionic conduction and/or electrical conduction between the active materials 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 may be severely reduced, so that the effect of including the nanoclay according to the present invention may not be properly expressed. If the porosity exceeds 90% and the porosity is too high, the physical and electrical connection with the current collector is lowered, resulting in a decrease in adhesive strength and difficulty in reaction.The increased porosity is filled with an electrolyte, resulting in a lower energy density of the battery. There is a possible problem, so 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 lamination method.

Lithium secondary battery

On the other hand, the present invention

It provides a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed therebetween, and an electrolyte, wherein the positive electrode is the positive electrode as described above.

At this time, the negative electrode, the separator, and the electrolyte may be made of conventional materials that can be used in a 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 reversibly forming a lithium-containing compound by reacting with lithium ions, and lithium metal Alternatively, a lithium alloy can be used.

The material capable of reversibly occluding or releasing lithium ions (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. 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 active material. The binder serves as a paste of the negative active material, mutual adhesion between the active materials, adhesion between the active material and the current collector, and a buffering effect against 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 active layer including a negative 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 separates or insulates the positive electrode and the negative electrode from each other and enables transport of lithium ions between them, but can be used without special restrictions as long as it is used as a separator in a general lithium secondary battery. It is preferable that it has a low resistance against and has excellent electrolyte moisture absorption ability.

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

Specifically, a porous polymer film, for example, an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, etc. Or, it may be used by laminating them, or a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, etc. 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, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like 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 from the group consisting of lithium carboxylate, lithium 4-phenyl borate, and lithium imide.

The concentration of the lithium salt is 0.2 to 2M, preferably, 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 battery, the working temperature and other factors known in the lithium battery field. 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 electrolyte performance may be deteriorated. If the concentration of the lithium salt is greater than the above range, the viscosity of the electrolyte may increase and the mobility of lithium ions (Li ⁺ ) may decrease. It is desirable to select an appropriate concentration.

The non-aqueous organic solvent is a material capable of dissolving a lithium salt well, preferably 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, 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 (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 Rolidone, 3-methyl-2-oxazolidone, acetic acid ester, butyric acid ester and propionic acid ester, dimethylformamide, sulfolane (SL), methylsulfolane, dimethylacetamide, dimethyl sulfoxide, dimethyl sulfate, ethylene glycol di An aprotic organic solvent such as acetate, dimethyl sulfite, or ethylene glycol sulfite may be used, and one or two or more of them may be used in the form of a mixed solvent.

The organic solid electrolyte is preferably a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a poly etch lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, an ionic A polymer or the like containing a dissociating group may be used.

As the inorganic solid electrolyte of the present invention, 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 , Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ nitrides, halides, and sulfates of Li such as S-SiS ₂ may 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, and is preferably It may be a stack-folding type.

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

The lithium secondary battery may be classified into a cylindrical type, a square type, a coin type, a pouch type, etc. according to the shape, 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 this field, and thus detailed descriptions are omitted.

The lithium secondary battery including the above-described configuration can increase the energy density of the electrode because the battery can be driven at a low porosity by including the nanoclay in the positive electrode, and the lithium secondary battery to which it is applied has a discharge capacity and lifespan characteristics. It has an increasing effect.

Hereinafter, the present invention will be described in more detail through examples, etc., but the scope and contents of the present invention are reduced or limited by the following examples, and thus cannot be interpreted. In addition, if based on the disclosure content of the present invention including the following examples, it is clear that the present invention for which no specific experimental results are presented can be easily carried out by a person skilled in the art, and such modifications and modifications are attached to the patent. It is natural to fall within the scope of the claims.

Manufacturing example One. Nano Clay Produce

K10 powder (Aldrich) was put into an oven with nanoclay and dried at 155° C. for 1 hour to prepare montmorillonite (hereinafter, MMT), a positive electrode additive for lithium secondary batteries.

Manufacturing example 2. Protonation Made Nano Clay Produce

50 g of the nanoclay of Preparation Example 1 was added to 1 L of 1.0MH ₂ SO ₄ solution and reacted at room temperature for 24 hours. Thereafter, the solvent was removed through centrifugation, and sufficiently dried in an oven at 80° C. for 12 hours to prepare a protonated montmorillonite (hereinafter, H-MMT).

Manufacturing example 3. Lithiation Made Nano Clay Produce

50 g of the protonated montmorillonite of Preparation Example 2 was added to 1 L of 1.0 M LiOH solution and reacted at room temperature for 24 hours. Thereafter, the solvent was removed through centrifugation, and then sufficiently dried in an oven at 80° C. for 12 hours to prepare lithiated montmorillonite (hereinafter, Li-MMT).

Example One. Nano Clay Manufacture of lithium secondary battery including added positive electrode

First, 10 parts by weight of montmorillonite relative to the total weight (100 parts by weight) was added and dissolved in the base solid content (active material, conductive material, and binder) to which the montmorillonite prepared in Preparation Example 1 was added to water as a solvent. Thereafter, with respect to the obtained solution, a total of 100 parts by weight of the base solid content, that is, 88 parts by weight of the sulfur-carbon composite (S/C 75:25) as an active material, 5 parts by weight of Denka Black as a conductive material, and styrene butadiene rubber as a binder/ 7 parts by weight of carboxymethyl cellulose (SBR/CMC 7:3) 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 3.5mAh/cm ² , and the porosity of the electrode was 68%.

Then, a coin cell of a lithium secondary battery including the positive electrode, the negative electrode, the separator, and the electrolyte prepared as described above was manufactured as follows. Specifically, the positive electrode was punched and used as a 14phi circular electrode, and a polyethylene (PE) separator was punched with 19phi, and a 150um lithium metal was punched for use as a negative electrode.

Example 2. Nano Clay Manufacture of lithium secondary battery including added positive electrode

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 10 parts by weight of the protonated montmorillonite (H-MMT) prepared in Preparation Example 2 was added with a nanoclay based on 100 parts by weight of the total base solid content. .

Example 3. Nano Clay Manufacture of lithium secondary battery including added positive electrode

A lithium secondary battery was manufactured in the same manner as in Example 1, except that 10 parts by weight of the lithiated montmorillonite (Li-MMT) prepared in Preparation Example 3 was added with a nanoclay based on 100 parts by weight of the total base solid content. .

Example 4. Nano Clay Manufacture of lithium secondary battery including added positive electrode

A lithium secondary battery was manufactured in the same manner as in Example 3, except that a sulfur-carbon composite (S/C 70:30) was used as an active material and the porosity of the electrode was 73%.

Example 5. Nano Clay Manufacture of lithium secondary battery including added positive electrode

A lithium secondary battery was manufactured in the same manner as in Example 3, except that a sulfur-carbon composite (S/C 70:30) was used as an active material and the porosity of the electrode was 53%.

Comparative example One. Nano Clay Manufacture of lithium secondary battery including unadded positive electrode

It proceeded in the same manner as in Example 1, except that nanoclay was not added to the positive electrode.

Comparative example 2. Nano Clay Manufacture of lithium secondary battery including unadded positive electrode

A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that a sulfur-carbon composite (S/C 70:30) was used as an active material and the porosity of the electrode was set to 70%.

Comparative example 3. Nano Clay Manufacture of lithium secondary battery including unadded positive electrode

A lithium secondary battery was manufactured in the same manner as in Comparative Example 1, except that a sulfur-carbon composite (S/C 70:30) was used as an active material and the porosity of the electrode was 52%.

Experimental example One. SEM (Scanning Electron Microscope) analysis

The nanoclays prepared in Preparation Examples 1 to 3 were subjected to SEM analysis (S-4800 FE-SEM of Hitachi).

1, 2 and 3 are SEM images of nanoclays prepared in Preparation Examples 1, 2 and 3, respectively.

1 to 3, SEM analysis was performed with magnifications of 5k, 4.5k, and 5k, respectively. In the case of the MMT of Preparation Example 1, it can be seen that the MMT of the plate-shaped structure is lumped into a spherical shape. In the case of H-MMT, it was possible to confirm the plate-shaped particles from which the MMT of the plate-shaped structure was partially peeled off, and in the case of Li-MMT of Preparation Example 3, the degree of peeling was higher, so that most of the particles were plate-shaped.

Experimental example 2. XRD (X-ray Diffraction) analysis

The nanoclays prepared in Preparation Examples 1 to 3 were subjected to XRD analysis (Bruker's D4 Endeavor).

Referring to FIG. 5, in the case of montmorillonite of Preparation Examples 1 and 2, an XRD peak of less than 9° was not observed. The XRD peak was observed to confirm that the nanoclay according to the present invention was an ordered layered structure.

Experimental example 3. Lithium secondary battery discharge capacity comparison experiment (1)

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

At this time, the measurement current was set to 0.1C and a voltage range of 1.8 to 2.5 V, and the results are shown through FIG. 5.

Lithium secondary battery cathode anode Example 1 Metal lithium Sulfur-carbon composite (S/C 75:25) + conductive material + binder + MMT of Preparation Example 1 (88:5:7:10, weight ratio), porosity of electrode (68%) Example 2 Metal lithium Sulfur-carbon composite (S/C 75:25) + conductive material + binder + H-MMT of Preparation Example 2 (88:5:7:10, weight ratio), porosity of the electrode (68%) Example 3 Metal lithium Sulfur-carbon composite (S/C 75:25) + conductive material + binder + Li-MMT of Preparation Example 3 (88:5:7:10, weight ratio), porosity of the electrode (68%) Example 4 Metal lithium Sulfur-carbon composite (S/C 70:30) + conductive material + binder + Li-MMT of Preparation Example 3 (88:5:7:10, weight ratio), porosity of the electrode (73%) Example 5 Metal lithium Sulfur-carbon composite (S/C 70:30) + conductive material + binder + Li-MMT of Preparation Example 3 (88:5:7:10, weight ratio), porosity of the electrode (53%) Comparative Example 1 Metal lithium Sulfur-carbon composite (S/C 75:25) + conductive material + binder (88:5:7, weight ratio), porosity of electrode (68%) Comparative Example 2 Metal lithium Sulfur-carbon composite (S/C 70:30) + conductive material + binder (88:5:7, weight ratio), porosity of electrode (70%) Comparative Example 3 Metal lithium Sulfur-carbon composite (S/C 70:30) + conductive material + binder (88:5:7, weight ratio), porosity of electrode (52%)

As shown in FIG. 5, compared to the battery according to Comparative Example 1, it was confirmed that the overvoltage of the battery was improved and the initial discharge capacity was further increased in all the cells according to Examples 1 to 3 including nanoclay in the positive electrode.

In particular, in the case of the battery of Example 3 including the lithiated nanoclay, it was found that the effect of increasing the discharge capacity of the battery was greater due to the lithium ions intercalated with montmorillonite.

Experimental example 4. Lithium secondary battery discharge capacity comparison experiment (2)

In order to test the initial discharge capacity of the lithium secondary battery according to the type of porosity, the discharge capacity was measured after configuring the positive electrode and the negative electrode of the lithium secondary battery as described in Table 1 above.

At this time, the measurement current was set to 0.1C and a voltage range of 1.8 to 2.5 V, and the results are shown through FIG. 5.

As shown in Figure 6, compared to the battery according to Comparative Example 2, in the case of the battery according to Example 4 including the lithium-ionized nanoclay (Li-MMT) in the positive electrode, the effect of improving overvoltage and increasing initial discharge capacity was confirmed. .

In addition, as a result of measuring the discharge capacity of the battery at low porosity, in the case of the battery according to Example 5 containing the lithiumized nanoclay (Li-MMT) compared to the battery according to Comparative Example 3, the impregnation of the electrolyte solution in the positive electrode was In difficult environments, lithium ions were transferred through lithium-ionized nanoclay (Li-MMT), and the reaction proceeded with sulfur in the positive electrode. As a result, it was confirmed that the battery operated even when the porosity of the positive electrode was low.

Claims (9)

As a positive electrode for a lithium secondary battery comprising an active material, a conductive material and a binder,
The positive electrode is a positive electrode for a lithium secondary battery comprising nanoclay. The method of claim 1,
The content of the nanoclay is 1 to 15 parts by weight based on 100 parts by weight of the solid base contained in the lithium secondary battery positive electrode. The method of claim 1,
The positive electrode for a lithium secondary battery, characterized in that the nanoclay is lithiated. The method of claim 1,
The nanoclays are montmorillonite, bentonite, hectorite, saponite, videlite, nontronite, swellable mica, vermiculite, synthetic mica, kanemite, margadite, kenite, kaolinite, smectite, illite, chlorite , Muscobite, Pyrophilite, Antigolite, Haerokseok, Vermiculite, Sepiolite, Imogolite, Sobokite, Nacrite, Anoxite, Sericite, Redicite, Warm Asbestos and Antigolite 1 selected from the group consisting of A positive electrode for a lithium secondary battery, characterized in that more than a species. The method of claim 1,
The active material is a positive electrode for a lithium secondary battery, characterized in that the sulfur-carbon composite. The method of claim 5,
The sulfur-carbon composite is a positive electrode for a lithium secondary battery, characterized in that the sulfur content is 60 to 80 parts by weight based on 100 parts by weight of the sulfur-carbon composite. The method of claim 1,
The positive electrode includes a current collector and an electrode active material layer formed on at least one surface of the current collector,
The positive electrode for a lithium secondary battery, characterized in that the porosity of the electrode active material layer is 40 to 90%. Including a positive electrode, a negative electrode, a separator and an electrolyte interposed therebetween,
The positive electrode is a lithium secondary battery that is the positive electrode for a lithium secondary battery according to any one of claims 1 to 7. The method of claim 8,
The lithium secondary battery is a lithium secondary battery, characterized in that the lithium-sulfur battery.

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