阅读说明：本技术 锂二次电池用负极和包含所述锂二次电池用负极的锂二次电池 (Negative electrode for lithium secondary battery and lithium secondary battery comprising same ) 是由 康多暎 宋知恩 于 2019-09-05 设计创作，主要内容包括：本发明涉及一种锂二次电池用负极,其包含：锂金属层；和碳基薄膜层,其中多个多孔碳材料沿着一个水平方向排列；和包含所述锂二次电池用负极的锂二次电池。(The present invention relates to a negative electrode for a lithium secondary battery, comprising: a lithium metal layer; and a carbon-based thin film layer in which a plurality of porous carbon materials are arranged along one horizontal direction; and a lithium secondary battery comprising the negative electrode for a lithium secondary battery.)

1. An anode for a lithium secondary battery, comprising:

a lithium metal layer; and

a carbon-based thin film layer formed on at least one surface of the lithium metal layer,

wherein, in the carbon-based thin film layer, a plurality of porous carbon materials are arranged along a horizontal direction.

2. The anode for a lithium secondary battery according to claim 1, wherein the carbon-based thin film layer has a thickness of 1 μm to 20 μm.

3. The negative electrode for a lithium secondary battery according to claim 1, wherein the porous carbon material is a carbon nanotube or a carbon nanofiber.

4. The anode for a lithium secondary battery according to claim 3, wherein the porous carbon material has a diameter of 10nm to 1000 nm.

5. The anode for a lithium secondary battery according to claim 1, wherein the pore size of the carbon-based thin film layer is 1nm to 200 nm.

6. The anode for a lithium secondary battery according to claim 5, wherein the pore size of the carbon-based thin film layer is 10nm to 100 nm.

7. The negative electrode for a lithium secondary battery according to claim 1, wherein the lithium secondary battery is a lithium-sulfur battery.

8. A lithium secondary battery, comprising:

a positive electrode;

a negative electrode;

a separator interposed between the positive electrode and the negative electrode; and

an electrolyte is added to the electrolyte to form a mixture,

wherein the anode is the anode according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, wherein the lithium secondary battery is a lithium sulfur battery.

Technical Field

This application claims benefit based on priority of korean patent application No. 10-2018-0112863, filed on 20/9/2018, the entire disclosure of which is incorporated herein by reference in its entirety.

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

Background

Recently, there has been an increasing interest in energy storage technology. As its application field is expanded to energy sources for mobile phones, camcorders, notebook computers, and even electric vehicles, research and development work for electrochemical devices is being performed more and more specifically.

Electrochemical devices are the most notable field in this regard, and among them, development of secondary batteries capable of charging/discharging is a focus of attention. Recently, in developing these batteries, research and development on the design of new electrodes and batteries have been conducted in order to improve capacity density and energy efficiency.

Among the currently used secondary batteries, lithium secondary batteries developed in the early 90 s are receiving much attention because of the advantages thereof: it has a much higher operating voltage and energy density than conventional batteries such as nickel hydride batteries, nickel cadmium batteries, and lead sulfate batteries using electrolytes in the form of aqueous solutions.

In general, a lithium secondary battery has an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, which is laminated or wound, and is constructed by placing the electrode assembly in a battery case and injecting a nonaqueous electrolytic solution therein. As the negative electrode, a lithium electrode was used by attaching a lithium foil to a planar current collector.

In the case of a lithium secondary battery, the formation and removal of lithium are irregular during charge/discharge, thereby forming lithium dendrites, which results in a continuous decrease in capacity. In order to solve this problem, studies have been made on introducing a polymer protective layer or an inorganic solid protective layer into the lithium metal layer, increasing the salt concentration in the electrolyte, or applying an appropriate additive. However, in these studies, the lithium dendrite-suppressing effect was insufficient. Therefore, solving this problem by changing the lithium metal negative electrode itself or changing the battery structure may be an effective alternative.

[ Prior art documents ]

[ patent document ]

Korean patent laid-open No. 10-2013-0056731

Disclosure of Invention

[ problem ] to provide a method for producing a semiconductor device

As described above, the conventional lithium secondary battery has the following problems: the stability and life characteristics of the battery are degraded due to lithium dendrites generated on the surface of the electrode during charge/discharge. Therefore, as a result of various studies, the inventors of the present invention have completed the present invention by confirming the fact that: when a plurality of carbon-based thin film layers of porous carbon materials aligned in one horizontal direction are formed on a lithium metal layer, generation of lithium dendrites may be suppressed and life characteristics may be improved.

Accordingly, an object of the present invention is to provide a negative electrode for a lithium secondary battery, comprising a carbon-based thin film on a lithium metal layer; and a lithium secondary battery comprising the negative electrode for a lithium secondary battery.

[ technical solution ] A

In order to achieve the above object, the present invention provides a negative electrode for a lithium secondary battery, comprising: a lithium metal layer; and a carbon-based thin film layer formed on at least one surface of the lithium metal layer, wherein, in the carbon-based thin film layer, a plurality of porous carbon materials are arranged along one horizontal direction.

Further, the present invention provides a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte, wherein the negative electrode is the negative electrode of the present invention.

[ PROBLEMS ] the present invention

In the negative electrode for a lithium secondary battery of the present invention, the carbon-based thin film layer formed on the lithium metal layer can suppress the formation of lithium dendrites, thereby making the reactivity of the battery uniform and improving the life characteristics.

Drawings

Fig. 1 shows a structure of an embodiment of a negative electrode for a lithium secondary battery according to the present invention.

Fig. 2 is an SEM photograph of the carbon-based thin film layer of the negative electrode prepared in example 1.

Fig. 3 is an SEM photograph of the carbon-based thin film layer of the negative electrode prepared in comparative example 1.

Fig. 4 is an SEM photograph of the carbon-based thin film layer of the negative electrode prepared in comparative example 2.

Fig. 5 is an SEM photograph of the carbon-based thin film layer of the negative electrode prepared in comparative example 3.

Fig. 6 is a photograph obtained by observing the surface of the anode prepared in example 1 after 40 cycles.

Fig. 7 is a photograph obtained by observing the surface of the anode prepared in comparative example 1 after 1 cycle.

Fig. 8 is a photograph obtained by observing the surface of the anode prepared in comparative example 2 after 1 cycle.

Fig. 9 is a photograph obtained by observing the surface of the anode prepared in comparative example 3 after 1 cycle.

Fig. 10 is a photograph obtained by observing the surface of the anode prepared in comparative example 4 after 40 cycles.

Fig. 11 is a graph showing the measurement of life characteristics of the lithium sulfur battery of experimental example 2.

Detailed Description

Hereinafter, the present invention will be described in more detail.

The main cause of premature deterioration of lithium secondary batteries may be a decrease in the efficiency of the lithium negative electrode. When lithium metal is used as the negative electrode, not only the reaction is not uniform because the oxide layer (natural oxide layer) is not uniform, but also dead lithium (dead Li) is easily generated due to the growth of dendrite during lithium plating, and lithium that may participate in the reaction is consumed, thereby reducing the efficiency of the lithium negative electrode.

In order to secure uniform reactivity on the lithium surface and suppress the growth of lithium dendrite, a method of forming a protective film, a conductive host matrix (host matrix), and the like on a lithium metal layer or the like has been attempted. In the case of the protective film, high mechanical strength for suppressing lithium dendrite and high ion conductivity for transferring lithium ions are required at the same time, but the mechanical strength and the ion conductivity are in a trade-off relationship with each other, and thus it is difficult to improve both the mechanical strength and the ion conductivity at the same time. In the case of a conductive host matrix, lithium needs to be plated with lithium inside the host matrix to serve as a host, but lithium is merely accumulated on the surface of the host matrix to grow lithium dendrites.

Accordingly, the present invention is directed to provide a negative electrode for a lithium secondary battery, which can improve life characteristics of the battery by preventing growth of lithium dendrites.

Negative electrode for lithium secondary battery

The present invention relates to a negative electrode for a lithium secondary battery, comprising: a lithium metal layer; and a carbon-based thin film layer formed on at least one surface of the lithium metal layer, wherein, in the carbon-based thin film layer, a plurality of porous carbon materials are arranged along one horizontal direction.

Fig. 1 is a cross-sectional view of an anode for a lithium secondary battery according to an embodiment of the present invention.

Referring to fig. 1, the negative electrode (110) for a lithium secondary battery has a structure in which a carbon-based thin film layer (112) is stacked on a lithium metal layer (111). In the figure, the carbon-based thin film layer (112) is formed on only one surface of the lithium metal layer (111), but may be formed on both surfaces.

The lithium metal layer (111) may be lithium metal or a lithium alloy. In this case, the lithium alloy contains an element capable of alloying with lithium, and specifically, the lithium alloy may Be an alloy of lithium and at least one selected from the group consisting of Si, Sn, C, Pt, Ir, Ni, Cu, Ti, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Sb, Pb, In, Zn, Ba, Ra, Ge, and Al.

The lithium metal layer (111) may be a sheet or a foil. In some cases, the lithium metal layer may have a form of depositing or coating lithium metal or lithium alloy on the current collector by a dry process, or a form of depositing or coating metal and alloy in a particle phase form by a wet process, or the like.

At this time, a method of forming the lithium metal layer (111) is not particularly limited, and may be a lamination method, a sputtering method, or the like, which is a known metal thin film forming method. Further, the lithium metal layer (111) of the present invention also includes a case where a metallic lithium thin film is formed on a metal plate by initial charging after a battery is assembled in a state where no lithium thin film is present on a current collector.

The width of the lithium metal layer (111) can be adjusted according to the shape of the electrode to easily manufacture the electrode. The thickness of the lithium metal layer (111) may be 1 μm to 500 μm, preferably 10 μm to 350 μm, and more particularly may be 50 μm to 200 μm.

Further, the lithium metal layer (111) may further include a current collector on one side thereof. Specifically, the lithium metal layer (111) may be an anode, and in this case, the current collector may be an anode current collector.

The anode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery, and may be selected from the group consisting of copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. The stainless steel may be surface treated with carbon, nickel, titanium or silver, and the alloy may be an aluminum cadmium alloy. In addition, a non-conductive polymer whose surface is treated with sintered carbon, i.e., a conductive material, a conductive polymer, or the like can be used. Generally, a thin copper foil is used as a negative electrode current collector.

In addition, the shape of the anode current collector may be in various forms, such as a film, a sheet, a foil, a mesh, a porous body, a foam, a nonwoven fabric, or the like, with or without fine irregularities on the surface.

Further, the thickness of the negative electrode current collector is 3 μm to 500 μm. If the thickness of the negative electrode current collector is less than 3 μm, the current collecting effect is reduced. On the other hand, if the thickness exceeds 500 μm, there is a problem in that workability is lowered when the battery is folded and then assembled.

In general, when lithium metal is used as the negative electrode, there are the following problems. First, when lithium is used as a negative electrode, a passivation layer is formed by reacting with an electrolyte, water, impurities in a battery, a lithium salt, etc., and the layer causes a local current density difference to form dendritic lithium dendrites. In addition, the dendrite thus formed may grow and cross the pores of the separator to cause a direct internal short circuit with the positive electrode, thereby causing an explosion phenomenon of the battery. Second, lithium is a soft metal and its mechanical strength is weak, so it is difficult to treat lithium for use without additional surface treatment.

Therefore, in the present invention, by forming the carbon-based thin film layer (112) on the surface of the lithium metal layer (111), the formation of a passivation layer and the mechanical strength can be enhanced, and particularly, the formation of dendrites can be effectively prevented.

The carbon-based thin film layer (112) of the present invention is formed on the lithium metal layer (111), and suppresses the formation of lithium dendrites by mitigating the phenomenon of uneven distribution of electrons during charge/discharge of the negative electrode (110) through the conductive surface of the carbon-based thin film layer. Thereby, a more uniform reactivity of lithium can be ensured. Accordingly, it is possible to prevent an internal short circuit of the battery, thereby improving cycle life characteristics during charge/discharge.

When carbon materials, which are the absorbing materials for lithium dendrites, contact each other and are aggregated, a conductive network is formed, whereby electrons are uniformly dispersed on the surface of the anode through the conductive network. In this case, if the pores formed by the carbon-based thin film layer are not uniform or the pores are largely formed to several tens of micrometers or more, the movement of lithium ions may not be prevented and dendrites may be formed, resulting in the degradation of the cycle characteristics of the battery. Therefore, the carbon material as the absorbing material for lithium dendrite is preferably uniformly distributed along one direction.

Accordingly, the carbon-based thin film layer (112) of the present invention is characterized in that a plurality of porous carbon materials are arranged in one horizontal direction.

In the present invention, the horizontal direction refers to the horizontal direction with respect to the lithium metal layer (111).

The carbon-based thin film layer includes a plurality of carbon materials aligned in one direction and horizontally oriented with the lithium metal layer.

The plurality of carbon materials contained in the carbon-based thin film layer may be, for example, carbon materials bound by a binder or carbon materials in the form of: a carbon material formed and solidified in a predetermined direction while the carbon material is rotated by electrospinning.

In the above description, the horizontal direction should be construed to include a completely horizontal direction and a direction forming an angle of 0 ° to 45 °, preferably 0 ° to 10 °, with the lithium metal layer in consideration of the manufacturing process of the carbon-based thin film layer.

In addition, even in the case of being aligned in one direction, it should be construed that some carbon materials having different directions may be contained in consideration of the manufacturing process of the carbon-based thin film layer. That is, when the carbon material has an orientation in one direction as a whole, it is understood that the case of containing some carbon materials having different directions also belongs to a state of being aligned along one direction.

The thickness of the carbon-based thin film layer may be 1 μm to 20 μm, preferably 2 μm to 8 μm. If the thickness of the carbon-based thin film layer is less than 1 μm, the internal pore structure of the carbon-based thin film layer may collapse, and the internal pores may be insufficient to inhibit the growth of lithium dendrites. If the thickness of the carbon-based thin film layer exceeds 20 μm, the thickness of the negative electrode becomes thicker, the weight may increase, and the energy density of unit volume and weight may decrease.

The porous carbon material may be carbon nanotubes or carbon nanofibers, and is preferably carbon nanotubes. The carbon nanotubes may be single-walled carbon nanotubes, double-walled carbon nanotubes, or multi-walled carbon nanotubes.

The diameter of the porous carbon material is 10nm to 1000nm, preferably 20nm to 50 nm. It is difficult to manufacture porous carbon materials with diameters less than 10 nm. If the diameter of the porous carbon material exceeds 1000nm, the effect of suppressing the generation of lithium dendrites cannot be exhibited.

In addition, since the plurality of porous carbon materials of the carbon-based thin film layer are arranged in one horizontal direction, predetermined spaces, i.e., pores of the carbon-based thin film layer, are formed between the porous carbon materials.

The size of the pores of the carbon-based thin film layer is 1nm to 200nm, preferably 10nm to 100 nm. When the porous carbon material forms a structure aligned in one horizontal direction, the pores of the carbon-based thin film layer may have a size of 1nm to 200nm, and the carbon-based thin film layer containing the porous carbon material not aligned in one direction is difficult to generate pores in the above range, and non-uniform pores of several tens of micrometers or more are generally generated. If the porosity of the carbon-based thin film layer exceeds 200nm, the effect of suppressing the growth of lithium dendrites cannot be exhibited.

Since the plurality of porous carbon materials form narrow gaps in the horizontal direction of the pore arrangement, lithium ions are plated after passing through the small pores between the porous carbon materials, and thus the surface of the lithium negative electrode can have a uniform shape even after the lithium secondary battery is charged/discharged. Therefore, the carbon-based thin film layer in which a plurality of porous carbon materials are arranged in one horizontal direction may be used as a protective layer of the lithium metal layer.

In the case of the carbon-based thin film layer in which the carbon material is aligned in one vertical direction, the manufacturing process is complicated because the carbon material must be grown on the substrate in the vertical direction by using a seed and an additional step of dispersing the anode active material in the carbon-based thin film layer is required. In addition, since the substrate cannot be removed while maintaining the structure of the vertically aligned carbon-based thin film layer, it must be used with the substrate. In this case, the substrate may be a metal containing nickel or cobalt or the like having durability capable of enduring the manufacturing process of the carbon material aligned in one vertical direction, i.e., a metal having a high specific gravity, but a lithium metal layer cannot be used because it does not have excellent durability.

Further, the carbon-based thin film layer cannot be manufactured to have a thin thickness due to the perpendicular direction, but is generally manufactured to have a thickness of several tens of micrometers or more, and thus there are problems as follows: the thickness of the negative electrode becomes thicker, the weight increases, and the energy density per volume and weight decreases. In the case of a carbon-based thin film layer in which a plurality of porous carbon materials are arranged in one vertical direction, lithium is accumulated only on the surface of the carbon-based thin film layer as a host matrix, and the carbon-based thin film layer cannot serve as a protective layer formed on a lithium negative electrode to suppress the growth of lithium dendrites.

In the present invention, a plurality of porous carbon materials having diameters as described above are arranged in one horizontal direction to include a carbon-based thin film layer having pores as described above, thereby preventing the formation of lithium dendrites as described above and thus improving the life characteristics of the battery.

The negative electrode for a lithium secondary battery may preferably be a negative electrode for a lithium sulfur battery.

The carbon-based thin film layer (112) according to the present invention may be formed by a method selected from the group consisting of sputtering, evaporation, Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), Atomic Layer Deposition (ALD), arc discharge, and combinations thereof, and the physical vapor deposition is specifically applied.

The formation of the carbon-based thin film layer (112) by physical vapor deposition is preferred because it can form a uniform and thin carbon-based thin film layer.

Further, the physical vapor deposition is performed for 20 minutes to 120 minutes, preferably 40 minutes to 120 minutes, more preferably 40 minutes to 100 minutes, and most preferably 40 minutes to 60 minutes. If the deposition time is less than 20 minutes, the thickness of the carbon-based thin film layer is so thin that it does not act as a protective film and cracks occur. On the other hand, if the deposition time exceeds 120 minutes, the carbon-based thin film layer becomes thicker, which causes a problem of lowering the energy density.

After the deposition step, a heat treatment process may be selectively performed as needed. At this time, the heat treatment temperature may be 1200 ℃. Specifically, the heat treatment process is preferably performed by rapid thermal annealing having a temperature rise rate of rising to the heat treatment temperature at 5 ℃/minute to 300 ℃/minute. This heat treatment process can induce uniform arrangement of pores by self-assembly of the deposited carbon particles.

Lithium secondary battery

Further, the present invention relates to a lithium secondary battery comprising: a positive electrode; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte, wherein the negative electrode may be the negative electrode of the present invention described above.

The positive electrode according to the present invention may be manufactured in the form of a positive electrode by coating a composition including a positive electrode active material, a conductive material, and a binder on a positive electrode current collector.

The positive electrode active material may be based on lithium secondary electricityThe use of the bath varies and known materials are used for specific compositions. For example, the positive electrode active material may be any one of lithium transition metal oxides selected from the group consisting of lithium cobalt-based oxides, lithium manganese-based oxides, lithium copper-based oxides, lithium nickel-based oxides, and lithium manganese composite oxides and lithium nickel manganese cobalt-based oxides, and more particularly, but not limited to, Li_1+xMn_2-xO₄(where x is 0 to 0.33), such as LiMnO₃、LiMn₂O₃、LiMnO₂The lithium manganese oxide of (1); lithium copper oxide (Li)₂CuO₂) (ii) a Such as LiV₃O₈、V₂O₅、Cu₂V₂O₇Vanadium oxide of (a); from LiNi_1-xM_xO₂(wherein M is Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x is 0.01 to 0.3); from LiMn_2-xM_xO₂(wherein M is Co, Ni, Fe, Cr, Zn or Ta, and x is 0.01 to 0.1) or Li₂Mn₃MO₈(wherein M ═ Fe, Co, Ni, Cu, or Zn), or Li (Ni)_aCo_bMn_c)O₂(wherein 0)<a<1，0<b<1，0<c<1, a + b + c ═ 1) of lithium nickel manganese cobalt oxides; in addition, the positive electrode active material may be one or more selected from the group consisting of: fe₂(MoO₄)₃(ii) a Elemental sulfur, disulfide compound, organic sulfur compound, and carbon-sulfur polymer ((C)₂S_x)_n: x is 2.5 to 50, and n is more than or equal to 2); a graphite-based material; carbon black-based materials such as Super-P, DENKA carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon black; carbon derivatives such as fullerenes; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; and conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; a form produced by supporting a catalyst such as Pt or Ru on a porous carbon support, and preferably a carbon-sulfur polymer can be used.

Therefore, the lithium secondary battery of the present invention may preferably be a lithium sulfur battery.

The conductive material serves to further improve the conductivity of the positive electrode active material. As non-limiting examples, graphite such as natural graphite or artificial graphite; carbon black-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, and the like.

The positive electrode may further include a binder for binding the positive electrode active material and the conductive material and for binding to a current collector. The binder may comprise a thermoplastic resin or a thermosetting resin. For example, polyethylene, polypropylene, Polytetrafluoroethylene (PTEE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer and the like can be used alone or in combination thereof, but is not limited thereto and any binder that can be used in the art is possible.

The positive electrode current collector is the same as the negative electrode current collector described above, and generally a thin plate of aluminum may be used for the positive electrode current collector.

The positive electrode as described above can be prepared by a conventional method. Specifically, the positive electrode may be prepared by coating a composition for forming a positive electrode active material layer, which is prepared by mixing a positive electrode active material, a conductive material and a binder in an organic solvent or water, on a current collector, drying it, and optionally compression-molding it on the current collector to improve the electrode density. At this time, as the organic solvent, a solvent which can uniformly disperse the positive electrode active material, the binder, and the conductive material and is easily evaporated is preferably used. Specifically, acetonitrile, methanol, ethanol, tetrahydrofuran, isopropanol, or the like can be used as the organic solvent.

The composition for forming the positive electrode active material layer may be coated on the positive electrode current collector using a conventional method known in the art, and for example, various methods such as a dip coating method, a spray coating method, a roll coating method, a gravure printing method, a bar coating method, a die coating method, a comma coating method, or a combination thereof may be used.

The positive electrode and the composition for forming the positive electrode active material layer after the coating process are subjected to evaporation of the solvent and the dispersion medium, densification of the coating film, and adhesion between the coating film and the current collector through the subsequent drying process. At this time, the drying is performed according to a conventional method and is not particularly limited.

A conventional separator may be interposed between the positive electrode and the negative electrode. The separator is a physical separator having a function of physically separating electrodes, and may be used without particular limitation as long as it is used as a conventional separator, and in particular, a separator having low resistance to ion migration in an electrolytic solution and excellent impregnation ability to the electrolytic solution is preferable.

In addition, the separator enables transfer of lithium ions between the cathode and the anode while separating or insulating the cathode and the anode from each other. The separator may be made of a porous, non-conductive or insulating material. The separator may be a separate member such as a film, or a coating layer added to the positive electrode and/or the negative electrode.

Examples of the polyolefin-based porous film that can be used as the separator may be a film formed solely of any one polymer selected from polyolefin-based polymers such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene and ultrahigh-molecular-weight polyethylene, polypropylene, polybutene and polypentene, or may be a film formed of a polymer mixture thereof.

Examples of the nonwoven fabric that can be used as the separator are nonwoven fabrics formed of polymers of polyphenylene ether, polyimide, polyamide, polycarbonate, polyester such as polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyether sulfone, polyether ether ketone, etc., alone or in a mixture thereof. Such nonwoven fabrics include nonwoven fabrics in the form of fibers forming a porous web, i.e., spunbond nonwoven fabrics or meltblown nonwoven fabrics composed of long fibers.

The thickness of the separator is not particularly limited, but is preferably 1 μm to 100 μm, more preferably 5 μm to 50 μm. If the thickness of the separator is less than 1 μm, mechanical properties cannot be maintained. If the thickness of the separator exceeds 100 μm, the separator acts as a resistance layer, thereby deteriorating the performance of the battery.

The pore size and porosity of the separator are not particularly limited, but it is preferable that the pore size is 0.1 to 50 μm and the porosity is 10 to 95%. The separator acts as a resistive layer if the separator has a pore size of less than 0.1 μm or a porosity of less than 10%. If the separator has a pore size of more than 50 μm or a porosity of more than 95%, the mechanical properties cannot be maintained.

The electrolyte of the lithium secondary battery may be an aqueous electrolyte or a nonaqueous electrolyte as an electrolyte containing a lithium salt, specifically, a nonaqueous electrolyte composed of an organic solvent electrolyte and a lithium salt. In addition, an organic solid electrolyte or an inorganic solid electrolyte may be included, but is not limited thereto.

As the lithium salt, a lithium salt conventionally used in an electrolyte for a lithium secondary battery may be used without limitation. The anion of the lithium salt may, for example, comprise a compound selected from the group consisting of F^-、Cl^-、Br^-、I^-、NO₃ ^-、N(CN)₂ ^-、BF₄ ^-、ClO₄ ^-、PF₆ ^-、(CF₃)₂PF₄ ^-、(CF₃)₃PF₃ ^-、(CF₃)₄PF₂ ^-、(CF₃)₅PF^-、(CF₃)₆P^-、CF₃SO₃ ^-、CF₃CF₂SO₃ ^-、(CF₃SO₂)₂N^-、(FSO₂)₂N^-、CF₃CF₂(CF₃)₂CO^-、(CF₃SO₂)₂CH^-、(SF₅)₃C^-、(CF₃SO₂)₃C^-、CF₃(CF₂)₇SO₃ ^-、CF₃CO₂ ^-、CH₃CO₂ ^-、SCN^-And (CF)₃CF₂SO₂)₂N^-Any one of the group consisting of, or a combination of two or more thereof.

As the organic solvent contained in the nonaqueous electrolytic solution, an organic solvent generally used in an electrolytic solution for a lithium secondary battery can be used without limitation, and for example, an ether, an ester, an amide, a chain carbonate, a cyclic carbonate, or the like can be used alone or in combination of two or more thereof. Among them, cyclic carbonates, chain carbonates, or a mixture thereof may be representatively contained as the carbonate compound.

Specific examples of the cyclic carbonate compound may be at least one selected from the group consisting of Ethylene Carbonate (EC), Propylene Carbonate (PC), 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentylene carbonate, 2, 3-pentylene carbonate, vinylene carbonate, vinyl ethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of such halides are, but not limited to, fluoroethylene carbonate (FEC) and the like.

Further, specific examples of the chain carbonate compound may include, but are not limited to, at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, Ethyl Methyl Carbonate (EMC), propyl methyl carbonate and propyl ethyl carbonate, or a mixture of two or more thereof.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among carbonate-based organic solvents, are highly viscous organic solvents having a high dielectric constant, and thus, lithium salts in the electrolyte can be more easily dissociated. If such cyclic carbonate is mixed with chain carbonate having low viscosity and low dielectric constant (such as dimethyl carbonate and diethyl carbonate) in an appropriate ratio, an electrolytic solution having higher conductivity can be produced.

Further, the ether in the organic solvent may be, but not limited to, at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether and ethylpropyl ether, or a mixture of two or more thereof.

Examples of the ester of the organic solvent may include, but are not limited to, at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, γ -valerolactone, γ -caprolactone, σ -valerolactone and-caprolactone, or a mixture of two or more thereof.

The injection of the nonaqueous electrolytic solution may be performed at an appropriate stage in the manufacturing process of the electrochemical device according to the manufacturing process and desired properties of the final product. That is, the injection of the nonaqueous electrolytic solution may be performed before the electrochemical device is assembled or at the final stage of the assembly of the electrochemical device.

In the case of the lithium secondary battery according to the present invention, a lamination or stacking and folding process of the separator and the electrode may be performed in addition to a winding process, which is a general process. Further, the battery case may be a cylinder type, a corner post type, a pouch type, a coin type, or the like.

In this case, the lithium secondary battery may be classified into various types of batteries such as a lithium sulfur battery, a lithium air battery, a lithium oxide battery, and a lithium all-solid battery according to the types of cathode materials and separators used, into a cylinder type, a rectangular type, a coin type, a pouch type, etc. according to the shape, and into a block type and a thin film type according to the size. The structure and preparation method of these batteries are well known in the art, and thus a detailed description thereof is omitted.

Modes for carrying out the invention

Hereinafter, preferred embodiments of the present invention will be described to facilitate understanding of the present invention. However, it will be apparent to those skilled in the art that the following embodiments are merely illustrative of the present invention and various changes and modifications may be made within the scope and spirit of the present invention, and such changes and modifications are within the scope of the appended claims.

< production of lithium-sulfur Battery >