KR20200050560A - A anode for lithium secondary battery, the manufacturing method of the same and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, comprising: a lithium metal layer; and indium (In) on at least a portion of the interior and surface of the lithium metal layer. The present invention also relates to a manufacturing method thereof. It is possible to improve the life characteristics of batteries.

Description

Anode for a lithium secondary battery and a manufacturing method thereof and a lithium secondary battery comprising the same {A ANODE FOR LITHIUM SECONDARY BATTERY, THE MANUFACTURING METHOD OF THE SAME AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a negative electrode for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery comprising the same.

Recently, interest in energy storage technology has been increasing. Mobile phones, camcorders and notebook PCs, and furthermore, the field of application to the energy of electric vehicles has been expanded, and efforts for research and development of electrochemical devices are gradually becoming concrete.

The electrochemical device is the area that is receiving the most attention in this aspect, and among them, the development of a rechargeable battery that can be charged and discharged has become a focus of interest, and recently, in order to improve capacity density and energy efficiency in developing such a battery. Research and development on new electrode and battery designs are in progress.

 Among the currently applied secondary batteries, lithium secondary batteries developed in the early 1990s have the advantage of higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolyte solutions. Is in the limelight.

In particular, a lithium-sulfur (Li-S) battery is a secondary battery that uses a sulfur-based material having an SS bond (Sulfur-Sulfur bond) as a positive electrode active material, and uses lithium metal as a negative electrode active material. Sulfur, the main material of the positive electrode active material, is very rich in resources, non-toxic, and has the advantage of having a low weight per atom. In addition, the theoretical discharge capacity of the lithium-sulfur battery is 1675mAh / g-sulfur, and the theoretical energy density is 2,600Wh / kg. The theoretical energy density of other battery systems currently being studied (Ni-MH batteries: 450Wh / kg, Li- FeS battery: 480Wh / kg, Li-MnO ₂ battery: 1,000Wh / kg, Na-S battery: 800Wh / kg), so it is the most promising battery developed to date.

During the discharge reaction of the lithium-sulfur battery, an oxidation reaction of lithium occurs at the anode, and a reduction reaction of sulfur occurs at the cathode. Sulfur before discharge has a cyclic S ₈ structure, and the oxidation of S decreases as the SS bond breaks during the reduction reaction (discharge), and the oxidation of S increases as the SS bond re-forms during the oxidation reaction (charge)- Electric energy is stored and generated using a reduction reaction. Among these reactions, sulfur is converted into a linear structure of lithium polysulfide (Lithium polysulfide, Li ₂ S _x , x = 8, 6, 4, 2) by a reduction reaction in the cyclic S ₈ , and eventually this lithium polysulfide is completely When reduced, lithium sulfide (Li ₂ S) is finally formed. The discharge behavior of the lithium-sulfur battery by the process of reduction with each lithium polysulfide is characterized by displaying the discharge voltage step by step unlike the lithium ion battery.

However, in the case of such a lithium-sulfur battery, since lithium metal is used as a negative electrode, lithium dendrite growth inevitably occurs during charging and discharging. When such lithium dendrites are continuously growing, it is necessary to solve stability problems due to an increase in electrode volume, insufficient electrolyte due to an increase in cathode porosity, and shorts that occur when dendrites grow through a separator.

 Nature Energy volume 2, Article number: 17119 (2017)

After conducting various studies, the present inventors confirmed that if indium is deposited on a lithium metal layer or heat-treated again and then alloyed to be used as a negative electrode, dendrite growth of a needle may be suppressed at the electrode. The invention was completed.

Accordingly, the present invention is to provide a negative electrode for a lithium secondary battery and a method for manufacturing the lithium secondary battery having improved discharge capacity and life characteristics by depositing indium metal on a lithium metal in the negative electrode.

In order to achieve the above object, the present lithium metal layer; And it provides a negative electrode for a lithium secondary battery comprising indium (In) on at least a portion of the interior and surface of the lithium metal layer.

In addition, a) preparing a lithium metal layer; And b) depositing indium on the lithium metal layer; provides a method for manufacturing a negative electrode for a lithium secondary battery comprising a.

In addition, the present invention is the cathode; anode; And electrolyte; provides a lithium secondary battery comprising a.

According to the present invention, according to the use of a negative electrode containing an indium metal in the lithium metal layer, there is an effect that can improve the shape of the lithium negative electrode to improve the life characteristics of the battery.

1 is a photograph confirming the surface of the negative electrode according to Experimental Example 1.
Figure 2 is a photograph confirming the surface of the negative electrode of Example 1 and Comparative Example 1 according to Experimental Example 2.
3 is a graph showing an initial discharge profile of Example 1 and Comparative Example 1 according to Experimental Example 3.
4 is a graph showing a second discharge profile of Example 1 and Comparative Example 1 according to Experimental Example 3.
5 is a graph showing the life characteristics of Example 1 and Comparative Example 1 according to Experimental Example 3.
6 is a photograph confirming the surfaces of the cathodes of Example 2 and Comparative Example 1 according to Experimental Example 4.
7 is a graph showing an initial discharge profile of Example 2 and Comparative Example 1 according to Experimental Example 4.
8 is a graph showing the life characteristics of Example 2 and Comparative Example 1 according to Experimental Example 4.
9 is a photograph confirming the surface of the negative electrode of Example 3 and Comparative Example 1 according to Experimental Example 5.
10 is a graph showing an initial discharge profile of Example 3 and Comparative Example 1 according to Experimental Example 5.
11 is a graph showing the life characteristics of Example 3 and Comparative Example 1 according to Experimental Example 5.

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

In the drawings, parts not related to the description are omitted in order to clearly describe the present invention, and similar reference numerals are used for similar parts throughout the specification. In addition, the size and relative size of the components indicated in the drawings are independent of the actual scale, and may be reduced or exaggerated for clarity of explanation.

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

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

The lithium-sulfur battery uses sulfur as a positive electrode active material and lithium metal as a negative electrode active material. When discharging a lithium-sulfur battery, an oxidation reaction of lithium occurs at the negative electrode, and a reduction reaction of sulfur occurs at the positive electrode. At this time, the reduced sulfur is combined with lithium ions that have been moved from the negative electrode and is converted into lithium polysulfide, and finally involves a reaction to form lithium sulfide.

Lithium-sulfur batteries have a much higher theoretical energy density than conventional lithium secondary batteries, and sulfur used as a positive electrode active material is abundant in resources and has low cost, so it is in the spotlight as a next-generation battery due to the advantage of lowering the manufacturing cost of the battery. have.

Despite these advantages, due to the low electrical conductivity and lithium ion conduction properties of the positive electrode active material sulfur, it is difficult to realize all theoretical energy densities in actual driving.

In particular, since lithium metal is used as a negative electrode, lithium dendrite inevitably occurs during charging and discharging, and when lithium dendrite continues to grow, the volume of the electrode increases and the porosity of the negative electrode increases. Not only does the shortage of electrolytes occur, but also the problem of stability caused by the occurrence of shorts that occur when dendrite grows through the separation membrane and remains a problem to be solved.

Cathode for lithium secondary battery

The negative electrode for a lithium secondary battery of the present invention

Lithium metal layer; And indium (In) on at least a portion of the interior and surface of the lithium metal layer.

In the present invention, the negative electrode for a lithium secondary battery has a structure including indium (In) on at least a portion of the inside and the surface of the lithium metal layer.

In the present invention, the lithium metal layer may be a lithium metal or a lithium alloy. At this time, the lithium alloy contains an element capable of alloying with lithium, specifically, lithium and Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, It may be an alloy with one or more selected from the group consisting of Sr, Sb, Pb, In, Zn, Ba, Ra, Ge and Al.

The lithium metal layer may be in the form of a sheet or foil, and in some cases, a lithium metal or lithium alloy is deposited or coated on a current collector by a dry process, or a metal or alloy on a particle is deposited or coated by a wet process or the like. Can be in the form of

At this time, the method of forming the lithium metal layer is not particularly limited, and a known method of forming a metal thin film, a lamination method, a sputtering method, or the like can be used. In addition, the case where the metal lithium thin film is formed on the metal plate by initial charging after assembling the battery without the lithium thin film in the current collector is also included in the lithium metal layer of the present invention.

The lithium metal layer may be adjusted in width according to the shape of the electrode to facilitate electrode manufacturing. The thickness of the lithium metal layer may be 1 to 500 μm, preferably 10 to 350 μm, and more preferably 30 to 150 μm.

In addition, the lithium metal layer may further include a current collector on one side. Specifically, the lithium metal layer may be a negative electrode, and the current collector may be a negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and these It can be selected from the group consisting of. 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 material, or a conductive polymer, etc. You can also use Generally, a thin copper plate is used as the negative electrode current collector.

In addition, various forms such as fine / uneven film / sheet, foil, net, porous body, foam, nonwoven fabric with fine irregularities formed on the surface can be used.

In addition, the negative electrode current collector is applied in a thickness range of 3 to 500 μm. If the thickness of the negative electrode current collector is less than 3 μm, the current collecting effect is deteriorated. On the other hand, when the thickness exceeds 500 μm, when the cells are assembled by folding, there is a problem in that workability is deteriorated.

The negative electrode for a lithium secondary battery of the present invention contains indium (In) on at least a portion of the interior and surface of a lithium metal layer.

When indium (In) is included in at least a portion of the interior and surface of the lithium metal layer, indium may be included in a form in which indium is deposited on the lithium metal layer, and the deposited indium may be heat treated to form an indium-lithium alloy. It may contain low indium.

At this time, the content of indium contained in at least a part of the interior and surface of the lithium metal layer may be included in 0.1 to 20% by weight compared to the lithium metal. If the content of the indium is lower than 0.1% by weight, there is a problem that it is difficult to serve as a protective film, and if it is higher than 20% by weight, it may be difficult to drive the battery due to overvoltage.

The negative electrode of the present invention may further include a pre-treatment layer made of a lithium ion conductive material and a lithium metal protection layer formed on the pre-treatment layer in addition to the negative electrode active material.

Method for manufacturing negative electrode for lithium secondary battery

The negative electrode for a lithium secondary battery of the present invention comprises: (a) preparing a lithium metal layer; And

(b) depositing indium on the lithium metal layer.

First, the method for manufacturing a negative electrode for a lithium secondary battery of the present invention includes the step (a) of preparing a lithium metal layer.

The lithium metal layer may be formed to a thickness of 10 to 150㎛, the method of forming the lithium metal layer is not particularly limited.

In the present invention, the lithium metal layer may be a lithium metal or a lithium alloy. At this time, the lithium alloy contains an element capable of alloying with lithium, specifically, lithium and Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, It may be an alloy with one or more selected from the group consisting of Sr, Sb, Pb, In, Zn, Ba, Ra, Ge and Al.

The lithium metal layer may be in the form of a sheet or foil, and in some cases, a lithium metal or lithium alloy is deposited or coated on a current collector by a dry process, or a metal or alloy on a particle is deposited or coated by a wet process or the like. Can be in the form of

At this time, the method of forming the lithium metal layer is not particularly limited, and a known method of forming a metal thin film, a lamination method, a sputtering method, or the like can be used. In addition, the case where the metal lithium thin film is formed on the metal plate by initial charging after assembling the battery without the lithium thin film in the current collector is also included in the lithium metal layer of the present invention.

The lithium metal layer may be adjusted in width according to the shape of the electrode to facilitate electrode manufacturing. The thickness of the lithium metal layer may be 1 to 500 μm, preferably 10 to 350 μm, and more specifically 50 to 200 μm.

In addition, the lithium metal layer may further include a current collector on one side. Specifically, the lithium metal layer may be a negative electrode, and the current collector may be a negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and these It can be selected from the group consisting of. 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 material, or a conductive polymer, etc. You can also use Generally, a thin copper plate is used as the negative electrode current collector.

Thereafter, the method for manufacturing a negative electrode for a lithium secondary battery of the present invention includes the step (b) of depositing indium on the lithium metal layer.

In step (b), when depositing indium on the lithium metal layer, any one selected from the group consisting of a physical vapor deposition method, a chemical vapor deposition method, and an atomic layer deposition method It can be deposited by the above method.

When depositing indium on the lithium metal layer, it is preferable to use the vapor deposition method, in this case, the vapor deposition method, conditions of a process pressure of 0.1 to 100 mTorr, sputter power (Sputter power) conditions of 50 to 500 W, sample rotation Speed (Sample rotation speed) can be performed under the conditions of 1 to 50 rpm.

In addition, the method for manufacturing a negative electrode for a lithium secondary battery of the present invention may further include a step (c) of heat treatment of a lithium metal layer on which indium is deposited after performing step (b).

By going through the heat treatment process, the lithium metal and the indium metal of the negative electrode of the present invention can be alloyed, and accordingly, an overvoltage improvement effect and an improvement effect in lifespan characteristics may be exhibited during battery manufacturing. In this case, the heat treatment may be performed at 130 to 150 ° C for 30 seconds to 10 minutes.

Lithium secondary battery

As an embodiment of the present invention, the lithium secondary battery includes the negative electrode described above; anode; A separator interposed between the anode and the cathode; And an electrolyte impregnated in the negative electrode, the positive electrode and the separator, and containing a lithium salt and an organic solvent, and preferably, the lithium secondary battery may be a lithium-sulfur battery containing a sulfur compound in the positive electrode.

In the present invention, the sulfur-carbon composite can be preferably used as a positive electrode active material of a lithium secondary battery.

The sulfur-carbon composite is composed of a porous carbon material and a sulfur compound.

The porous carbon material provides a skeleton in which the positive electrode active material sulfur can be immobilized uniformly and stably, and complements the electrical conductivity of sulfur, so that the electrochemical reaction can proceed smoothly.

The porous carbon material can be generally produced by carbonizing precursors of various carbon materials. The porous carbon material includes irregular pores therein, and the average diameter of the pores is in the range of 1 to 200 nm, and the porosity or porosity may range from 10 to 90% of the total volume of the porous. If the average diameter of the pores is less than the above range, impregnation of sulfur is impossible because the pore size is only at the molecular level. Conversely, when it exceeds the above range, the mechanical strength of the porous carbon is weakened, which is preferable for application in the electrode manufacturing process. Does not.

The shape of the porous carbon material may be spherical, rod-shaped, needle-shaped, plate-shaped, tubular, or bulk-type, and may be used without limitation as long as it is commonly used in lithium secondary batteries.

The porous carbon material may be either a porous structure or a high specific surface area as long as it is commonly used in the art. For example, the porous carbon material includes graphite; Graphene; Carbon blacks such as denka black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Carbon nanotubes (CNT) such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT); Carbon fibers such as graphite nanofiber (GNF), carbon nanofiber (CNF), and activated carbon fiber (ACF); And it may be at least one selected from the group consisting of activated carbon, but is not limited thereto.

The sulfur compound is composed of inorganic sulfur (S ₈ ), Li ₂ S _n (n ≥ 1), an organic sulfur compound and a carbon-sulfur polymer [(C ₂ S _x ) _n , x = 2.5 to 50, n ≥ 2] It may be one or more selected from the group. Preferably, inorganic sulfur (S ₈ ) can be used.

In the sulfur-carbon composite according to the present invention, the weight ratio of the aforementioned sulfur compound and the porous carbon material may be 9: 1 to 5: 5. If the content of the sulfur compound is less than 50% by weight, as the content of the porous carbon material increases, the amount of binder addition required in preparing the positive electrode slurry increases. The increase in the amount of the binder added eventually increases the sheet resistance of the electrode and acts as an insulator preventing electron pass, which can degrade cell performance. Conversely, when the weight ratio range is exceeded, sulfur may be aggregated between them, and it may be difficult to directly participate in the electrode reaction due to difficulty receiving electrons.

In addition, the sulfur is located on the surface as well as inside the pores of the porous carbon material, wherein less than 100%, preferably 1 to 95%, more preferably 60 to 90% of the entire outer surface of the porous carbon material is present Can be. When the sulfur is within the above range on the surface of the porous carbon material, it can exhibit the maximum effect in terms of electron transfer area and wettability of the electrolyte. Specifically, since the sulfur is thinly and evenly impregnated on the surface of the porous carbon material in the above-described range region, it is possible to increase the area of the electron transfer contact during charging and discharging. If, when the sulfur is located in the region of 100% of the surface of the porous carbon material, the porous carbon material is completely covered with sulfur, so that the wettability of the electrolyte decreases and the contact property with the conductive material contained in the electrode does not receive electron transfer and participate in the reaction. It becomes impossible.

The sulfur-carbon composite is capable of supporting a high content of sulfur due to pores of various sizes and three-dimensional interconnection in the structure and regularly aligned pores. Due to this, even if soluble polysulfide is generated by the electrochemical reaction, if it can be located inside the sulfur-carbon composite, the three-dimensional entangled structure is maintained even when the polysulfide is eluted to suppress the collapse of the anode structure. have. As a result, the lithium secondary battery including the sulfur-carbon composite has an advantage that a high capacity can be realized even at high loading.

Thus, the sulfur-loading amount of the sulfur-carbon composite according to the present invention may be 1 to 20 mg / cm ² .

The positive electrode is produced by applying and drying a composition for forming a positive electrode active material layer on a positive electrode current collector. The composition for forming the positive electrode active material layer is prepared by mixing the above-described sulfur-carbon composite with a conductive material and a binder, and then drying at 40 to 70 ° C. for 4 to 12 hours.

Specifically, in order to impart additional conductivity to the prepared sulfur-carbon composite, a conductive material may be added to the positive electrode composition. The conductive material plays a role for the electrons to move smoothly within the anode, and is not particularly limited as long as it is capable of providing excellent conductivity and a large surface area without causing chemical changes to the battery, but is preferably carbon-based. Use materials.

The carbon-based materials include natural graphite, artificial graphite, expanded graphite, graphite-based graphite, active carbon-based, channel black, furnace black, and thermal. Carbon black, such as Thermal black, Contact black, Lamp black, Acetylene black; Carbon fiber, carbon nanotubes (CNT), carbon nanostructures such as fullerene (Fullerene), and a combination thereof may be used.

In addition to the carbon-based material, metallic fibers such as a metal mesh depending on the purpose; Metallic powders such as copper (Cu), silver (Ag), nickel (Ni), and aluminum (Al); Alternatively, organic conductive materials such as polyphenylene derivatives can also be used. The conductive materials may be used alone or in combination.

In addition, in order to provide adhesion to the current collector to the positive electrode active material, a binder may be additionally included in the positive electrode composition. The binder should be well soluble in a solvent, not only should a well-constructed conductive network between the positive electrode active material and the conductive material, but also should have adequate impregnation properties of the electrolyte.

The binder applicable to the present invention may be all binders known in the art, and specifically, a fluorine resin-based binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE) ; Rubber-based binders including styrene-butadiene rubber, acrylonitrile-butadiene rubber, and styrene-isoprene rubber; Cellulose-based binders including carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, and regenerated cellulose; Poly alcohol-based binders; Polyolefin-based binders including polyethylene and polypropylene; Polyimide-based binder, polyester-based binder, silane-based binder; may be a mixture or copolymer of one or more selected from the group consisting of, but is not limited to, of course.

The content of the binder resin may be 0.5 to 30% by weight based on the total weight of the positive electrode, but is not limited thereto. When the content of the binder resin is less than 0.5% by weight, the physical properties of the positive electrode may deteriorate and the positive electrode active material and the conductive material may drop off, and when it exceeds 30% by weight, the ratio of the active material and the conductive material in the positive electrode is relatively reduced. Battery capacity can be reduced.

The solvent for preparing the positive electrode composition in a slurry state should be easy to dry, and can dissolve the binder well, but it is most preferable that the positive electrode active material and the conductive material can be maintained in a dispersed state without dissolving. When the solvent dissolves the positive electrode active material, the specific gravity of sulfur in the slurry (D = 2.07) is high, so the sulfur sinks in the slurry, and when it is coated, sulfur collects in the current collector, causing problems in the conductive network, which tends to cause problems in battery operation. have.

The solvent according to the present invention may be water or an organic solvent, and the organic solvent includes an organic solvent including one or more selected from the group consisting of dimethylformamide, isopropyl alcohol, acetonitrile, methanol, ethanol, and tetrahydrofuran. It is possible.

The positive electrode composition may be mixed by a conventional method using a conventional mixer, such as a rate mixer, a high-speed shear mixer, or a homo mixer.

The positive electrode composition may be applied to a current collector and dried in vacuum to form an positive electrode. The slurry may be coated on the current collector to an appropriate thickness depending on the viscosity of the slurry and the thickness of the anode to be formed, and may be appropriately selected within a range of 10 to 300 μm.

At this time, the method of coating the slurry is not limited, for example, doctor blade coating, dip coating, gravure coating, slit die coating, and spin coating ( Spin coating, comma coating, bar coating, reverse roll coating, screen coating, and cap coating may be performed.

The positive electrode current collector may be generally 3 to 500 μm thick, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, a conductive metal such as stainless steel, aluminum, copper, or titanium can be used, and preferably, an aluminum current collector can be used. The positive electrode current collector may be in various forms such as a film, sheet, foil, net, porous body, foam, or nonwoven fabric.

The separator interposed between the positive electrode and the negative electrode separates or insulates the positive electrode and the negative electrode from each other and enables transport of lithium ions between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material. The separator is an insulator having high ion permeability and mechanical strength, and may be an independent member such as a thin film or a film, or a coating layer added to the anode and / or the cathode. In addition, when a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The pore diameter of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 300 μm, and as the separator, a glass electrolyte, a polymer electrolyte, or a ceramic electrolyte may be used. For example, olefin-based polymers such as chemically and hydrophobic polypropylene, sheets or non-woven fabrics made of glass fiber or polyethylene, or the like are used. Typical examples currently on the market include the Celgard series (Celgard ^R 2400, 2300 Hoechest Celanese Corp.), polypropylene separator (manufactured by Ube Industries Ltd. or Pall RAI), and polyethylene series (Tonen or Entek).

The solid electrolyte separator may contain less than about 20% by weight of a non-aqueous organic solvent, and in this case, may further include an appropriate gel-forming compound to reduce the fluidity of the organic solvent. Representative examples of such gel-forming compounds include polyethylene oxide, polyvinylidene fluoride, and polyacrylonitrile.

The negative electrode, the positive electrode and the electrolyte impregnated in the separator are lithium salts and non-aqueous electrolytes containing lithium salts. The electrolytes include non-aqueous organic solvents, organic solid electrolytes, and inorganic solid electrolytes.

The lithium salt of the present invention is a material that is soluble in a non-aqueous organic solvent, for example, LiSCN, LiCl, LiBr, LiI, LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiClO ₄ , LiAlCl ₄ , Li (Ph) ₄ , LiC (CF ₃ SO ₂ ) ₃ , LiN (FSO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (SFO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , lithium chloroborane, lower aliphatic lithium carboxylate, lithium 4-phenyl borate, lithium imide, and combinations thereof One or more may be included.

The concentration of the lithium salt is 0.2 to 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 conditions for charging and discharging the cell, the working temperature and other factors known in the lithium battery field. Specifically, it may be 0.6 to 2 M, more specifically 0.7 to 1.7 M. When used below 0.2 M, the conductivity of the electrolyte may be lowered, resulting in deterioration of electrolyte performance, and when used above 2 M, the viscosity of the electrolyte may increase and mobility of lithium ions (Li ⁺ ) may decrease.

The non-aqueous organic solvent should dissolve a lithium salt well, and as the non-aqueous organic solvent of the present invention, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, di Ethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, 4-methyl-1,3-dioxene, diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trime Non-proton such as methoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, ethyl propionate Organic solvent It may be used, and the organic solvent may be one or a mixture of two or more organic solvents.

Examples of the organic solid electrolyte include, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and ionic dissociation. Polymers containing groups and the like can be used.

As the inorganic solid electrolyte, for example, 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 Li nitrides such as SiO ₄ -LiI-LiOH, Li ₃ PO4-Li ₂ S-SiS ₂ , halides, sulfates, and the like can be used.

In the electrolyte of the present invention, for the purpose of improving charge / discharge characteristics, flame retardance, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme (glyme), hexaphosphate triamide, nitro Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. may be added. . In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, or carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-ethylene) carbonate), PRS (Propene sultone), FPC (Fluoro-propylene carbonate), and the like.

The electrolyte may be used as a liquid electrolyte, or may be used in the form of a solid electrolyte separator. When used as a liquid electrolyte, a physical separator having a function of physically separating electrodes further includes a separator made of porous glass, plastic, ceramic, or polymer.

Hereinafter, a preferred embodiment is provided to help the understanding of the present invention, but the following examples are only illustrative of the present invention, and it is apparent to those skilled in the art that various changes and modifications are possible within the scope and technical scope of the present invention. It is no wonder that such variations and modifications fall within the scope of the appended claims.

[Example]

Preparation of cathode

[Example 1]

A lithium metal having a thickness of 40 μm was prepared. On the lithium metal, a negative electrode was prepared by depositing indium metal for 10 minutes using a DC sputter (manufactured by LG Chemical) under conditions of process pressure of 10 mTorr, sputter power of 200 W, and sample rotation speed of 5 rpm.

[Example 2]

The negative electrode prepared in Example 1 was heated in an oven at 145 ° C for 1 minute to prepare an alloyed negative electrode.

[Example 3]

A cathode was prepared in the same manner as in Example 1, except that the deposition time of indium metal was adjusted to 30 seconds.

[Comparative Example 1]

A cathode was prepared in the same manner as in Example 1, except that indium metal was not deposited.

Experimental Example  1: Observation of the surface of the cathode 1

When the lithium-indium alloy was made through deposition, the following experiment was conducted to simulate the situation of the negative electrode during charging after discharge occurred.

First, using an indium foil of 40 μm and a lithium foil of 35 μm, assembling in the order of indium foil / separator / lithium foil, and then injecting the electrolyte solution to assemble the coin cell, Li plating was performed with an indium electrode. . At this time, the current density was 0.8 mA. The results are photographed with a shape measurement laser microscope (KEYENCE) and shown in FIG. 1. Referring to FIG. 1, a Li-In alloy was formed, and when the surface shape was observed, it exhibited a round shape unlike the conventional dendritic growth.

Experimental Example  2: Analysis of the surface after discharge of the battery

Sulfur-carbon composite: Conductive material: Binder = After preparing a slurry at a weight ratio of 90: 5: 5 and applying it to a current collector of 20 μm thick aluminum foil, dried in an oven at 80 ° C. for 30 minutes, and then rolled to roll the anode. It was prepared. At this time, carbon black was used as the conductive material, and styrene-butadiene rubber and carboxymethyl cellulose were used as the binder. Thereafter, polyethylene was used as the separator. Here, lithium secondary battery coin cells were prepared using the negative electrodes prepared in Examples 1 to 3 and Comparative Example 1.

At this time, the coin cell was an electrolyte prepared by dissolving 1 M LiFSI, 1% LiNO ₃ in an organic solvent composed of diethylene glycol dimethyl ether and 1,3-dioxolane (DECDME: DOL = 6: 4 (volume ratio)). .

Thereafter, the produced coin cell was discharged after 48h rest. The results are taken with a shape measuring laser microscope (KEYENCE) and shown in FIG. 2. As shown in FIG. 2, in the case of Comparative Example 1 (upper photo in FIG. 2), a hole through which lithium escaped after discharge was shown to show an uneven surface shape, whereas in Example 1 (lower photo in FIG. 2), discharge After that, it was confirmed that the indium surface remained smooth and the surface shape was more evenly formed.

Experimental Example  3: Early battery Charge / discharge  Result 1

Of the coin cells prepared in Experimental Example 2, an initial charge / discharge test was performed on a battery manufactured using the negative electrode of Example 1 and Comparative Example 1 using a charge / discharge measuring device. Specifically, 0.1C charging and discharging 2.5 times, 0.2C / 0.2C charging and discharging 3 times, and then proceeded under the conditions of 0.3C / 0.5C charging and discharging. The results obtained at this time are shown in FIGS. 3 to 5.

Specifically, FIG. 3 is the first discharge profile of Comparative Example 1 and Example 1, FIG. 4 is the second discharge profile of Comparative Example 1 and Example 1, and FIG. 5 is a result of evaluation of life characteristics of Comparative Example 1 and Example 1 to be.

Referring to FIG. 3, In is deposited, an overvoltage occurs in Example 1 during initial discharge, but referring to FIG. 4, it can be seen that the overvoltage is improved from the second charge / discharge. As a result, it was confirmed through FIG. 5 that the life characteristics of Example 1 were improved compared to Comparative Example 1.

Experimental Example  4: Observation of the surface of the cathode 2

The surfaces of the cathodes prepared in Example 2 and Comparative Example 1 were photographed using a shape measurement laser microscope (KEYENCE) and are shown in FIG. 6. As shown in FIG. 6, when comparing the surfaces of Example 2 (the upper photograph in FIG. 6) and Comparative Example 1 (the lower photograph in FIG. 6), it can be confirmed that the lithium surface alloying in Example 2 was evenly caused. .

Experimental Example  5: Initial battery Charge / discharge  Result 2

Among the coin cells prepared in Experimental Example 2, an initial charge / discharge test was performed on a battery prepared using the negative electrode of Example 2 and Comparative Example 1 using a charge / discharge measuring device. Specifically, 0.1C charging and discharging 2.5 times, 0.2C / 0.2C charging and discharging 3 times, and then proceeded under the conditions of 0.3C / 0.5C charging and discharging. The results obtained at this time are shown in FIGS. 7 to 8.

Specifically, FIG. 7 is the first discharge profile of Comparative Example 1 and Example 2, and FIG. 8 is a result of evaluation of life characteristics of Comparative Example 1 and Example 2.

Referring to FIG. 7, it was confirmed that the overvoltage of Example 2 was improved as the lithium-indium alloy was formed. As a result, it was confirmed through FIG. 8 that the life characteristics of Example 2 were improved compared to Comparative Example 1.

Experimental Example  6: Surface observation of cathode 3

Of the coin cells prepared in Experimental Example 2, the batteries prepared using the negative electrode of Example 3 and Comparative Example 1 were analyzed for surface shape at 20% charge after 20 cycles. Specifically, the surface of the cathode is photographed with a shape measurement laser microscope (KEYENCE) and shown in FIG. 9. As shown in Fig. 9,

As a result, in the case of Comparative Example 1 (upper photograph of FIG. 9), a portion in which the dendrite of the acicular was grown exists, while in Example 3 (lower photograph of FIG. 9), it was confirmed that the dendritic of the acicular was not observed.

Experimental Example  7: Early in the battery Charge / discharge  Result 3

Of the coin cells prepared in Experimental Example 2, an initial charge / discharge test was performed on a battery manufactured using the negative electrode of Example 3 and Comparative Example 1 using a charge / discharge measuring device. Specifically, 0.1C charging and discharging 2.5 times, 0.2C / 0.2C charging and discharging 3 times, and then proceeded under the conditions of 0.3C / 0.5C charging and discharging. The results obtained at this time are shown in FIGS. 10 to 11.

Specifically, FIG. 10 is a first discharge profile of Comparative Example 1 and Example 3, and FIG. 11 is a result of evaluation of life characteristics of Comparative Example 1 and Example 3.

Referring to FIG. 10, it was confirmed that the overvoltage of Example 3 was greatly improved as the lithium-indium alloy was formed. As a result, through FIG. 11, it was confirmed that Example 3 was charged and discharged with a capacity as high as 100 mAh / g, and the lifespan characteristics of Example 3 were improved compared to Comparative Example 1, and Example 3 exhibited high lithium efficiency. It was confirmed that it had.

Claims (15)

Lithium metal layer; And
A negative electrode for a lithium secondary battery comprising indium (In) on at least a portion of the interior and surface of the lithium metal layer. According to claim 1,
The lithium metal layer comprises an indium-lithium alloy, a negative electrode for a lithium secondary battery. According to claim 1,
The indium is contained in 0.1 to 20% by weight compared to lithium metal, lithium secondary battery negative electrode. The negative electrode of claim 1; anode; And electrolyte; lithium secondary battery comprising a. The method of claim 4,
The lithium secondary battery is a lithium secondary battery, characterized in that it contains sulfur in the positive electrode. The method of claim 4,
The lithium secondary battery having a loading amount of sulfur of 5 mAh / cm ² or more. According to claim 1,
The porous carbon material is at least one selected from the group consisting of graphite, graphene, carbon black, carbon nanotubes, carbon fibers, and activated carbon, lithium secondary battery. (A) preparing a lithium metal layer; And
(B) depositing indium on the lithium metal layer; A method of manufacturing a negative electrode for a lithium secondary battery comprising a. The method of claim 8,
(c) heat treatment of the lithium metal layer on which indium is deposited; further comprising, a method of manufacturing a negative electrode for a lithium secondary battery. The method of claim 8,
The lithium metal layer is a thickness of 1 to 500㎛, the method of manufacturing a negative electrode for a lithium secondary battery. The method of claim 8,
The deposition of step (b) is performed by any one or more methods selected from the group consisting of physical vapor deposition, chemical vapor deposition, and atomic layer deposition, lithium secondary. Method for manufacturing a negative electrode for a battery. The method of claim 11,
The vapor deposition method is performed under the conditions of a process pressure of 0.1 to 100 mTorr, a method of manufacturing a negative electrode for a lithium secondary battery. The method of claim 11,
The vapor deposition method is performed under the condition of sputter power (Sputter power) 50 to 500W, a method for manufacturing a negative electrode for a lithium secondary battery. The method of claim 11,
The vapor deposition method is performed under the conditions of sample rotation speed (Sample rotation speed) 1 to 50 rpm, a method for manufacturing a negative electrode for a lithium secondary battery. The method of claim 9,
The heat treatment is performed for 30 seconds to 10 minutes at 130 to 150 ℃, the method of manufacturing a negative electrode for a lithium secondary battery.

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