阅读说明：本技术 在锂金属电极的表面上形成钝化膜的锂二次电池的连续制造方法和由此制造的锂二次电池 (Method for continuously manufacturing lithium secondary battery having passivation film formed on surface of lithium metal electrode and lithium secondary battery manufactured thereby ) 是由 诸葛鍾必 催贤俊 于 2018-12-14 设计创作，主要内容包括：本发明提供一种锂二次电池的制造方法和通过该制造方法制造的锂二次电池,所述制造方法包括：(i)制备在集电器的一个表面或两个表面上形成金属锂(Li)的锂金属电极；(ii)在金属锂的表面上施加包括一种或多种锂盐、一种或多种非水有机溶剂和一种或多种添加剂的用于涂覆的电解质溶液,以形成作为稳定涂层的钝化膜；(iii)制造包括所述锂金属电极作为负极的电极组件；和(iv)将所述电极组件容纳在二次电池壳体中并注入包括一种或多种锂盐、一种或多种非水有机溶剂和一种或多种添加剂的用于注入的电解质溶液,以制造锂二次电池,其中特定材料被用作所述用于涂覆的电解质溶液的添加剂和所述用于注入的电解质溶液的添加剂,但添加剂的组成不同。(The present invention provides a method of manufacturing a lithium secondary battery and a lithium secondary battery manufactured by the manufacturing method, the manufacturing method including: (i) preparing a lithium metal electrode in which metallic lithium (Li) is formed on one surface or both surfaces of a current collector; (ii) applying an electrolyte solution for coating including one or more lithium salts, one or more non-aqueous organic solvents, and one or more additives on a surface of metallic lithium to form a passivation film as a stable coating layer; (iii) manufacturing an electrode assembly including the lithium metal electrode as a negative electrode; and (iv) accommodating the electrode assembly in a secondary battery case and injecting an electrolyte solution for injection including one or more lithium salts, one or more non-aqueous organic solvents, and one or more additives, to manufacture a lithium secondary battery, wherein specific materials are used as the additive for the coated electrolyte solution and the additive for the injected electrolyte solution, but the compositions of the additives are different.)

1. A method of manufacturing a lithium secondary battery, comprising:

(i) preparing a lithium metal electrode in which metallic lithium (Li) is formed on one surface or both surfaces of a current collector;

(ii) applying an electrolyte solution for coating including one or more lithium salts, one or more non-aqueous organic solvents, and one or more additives on a surface of the metallic lithium to form a passivation film as a stable coating layer;

(iii) manufacturing an electrode assembly including the lithium metal electrode on which the passivation film is formed as a negative electrode; and

(iv) accommodating the electrode assembly in a secondary battery case, and injecting an electrolyte solution for injection including one or more lithium salts, one or more non-aqueous organic solvents, and one or more additives to manufacture a lithium secondary battery;

wherein

The additive for the coated electrolyte solution is one or more selected from the group consisting of Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), fluoroethylene carbonate (FEC), Propane Sultone (PS), 1,3-propane sultone (PRS), vinyl sulfate (ESa), succinonitrile (sn), adiponitrile (adapionite (an)), Hexane Trinitrile (HTCN), gamma-butyrolactone (gbl)), biphenyl (biphenol (bp), Cyclohexylbenzene (CHB)), and tert-amyl benzene (TAB)),

the additive for the injected electrolyte solution is one or more selected from the group consisting of pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, ethylene glycol dimethyl ether (glyme), hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, carbon tetrachloride, trifluoroethylene, fluoroethylene carbonate (FEC), and Propane Sultone (PS), and

the additive composition of the electrolyte solution for coating is different from the additive composition of the electrolyte solution for injection.

2. The method of manufacturing a lithium secondary battery according to claim 1, wherein the composition is any one or more of a content and a kind.

3. The method for manufacturing a lithium secondary battery according to claim 1, wherein the current collector is a copper foil.

4. The method of manufacturing a lithium secondary battery according to claim 1, wherein the lithium metal is formed on one surface or both surfaces of the current collector by deposition or rolling.

5. The method of manufacturing a lithium secondary battery according to claim 1, wherein the additive included in the electrolyte solution for coating is one or more selected from the group consisting of Vinylene Carbonate (VC) and fluoroethylene carbonate (FEC).

6. The method of manufacturing a lithium secondary battery according to claim 1, wherein an additive included in the electrolyte solution for coating is included at 0.1 wt% to 20 wt% based on the total weight of the electrolyte solution for coating.

7. The manufacturing method of a lithium secondary battery according to claim 1, wherein applying the electrolyte solution for coating is performed by dip coating (dip coating) or roll-to-roll coating (roll to roll coating).

8. The manufacturing method of a lithium secondary battery according to claim 1, wherein applying the electrolyte solution for coating is performed at least once.

9. The method of manufacturing a lithium secondary battery according to claim 1, wherein the passivation film is a Solid Electrolyte Interface (SEI) coating.

10. The method of manufacturing a lithium secondary battery according to claim 1, wherein the electrode assembly includes an anode, a cathode, and a separator interposed between the anode and the cathode, the anode being a lithium metal electrode having a passivation film formed thereon.

11. The method of manufacturing a lithium secondary battery according to claim 1, wherein the additive included in the electrolyte solution for injection is one or more selected from the group consisting of fluoroethylene carbonate (FEC) and Propane Sultone (PS).

12. The manufacturing method of a lithium secondary battery according to claim 1, wherein an additive included in the electrolyte solution for injection is included at 0.1 wt% to 10 wt% based on the total weight of the electrolyte solution for injection.

13. A lithium secondary battery manufactured by the manufacturing method of claim 1, wherein

A passivation film having a composition depending on the decomposition of an electrolyte solution used for coating is uniformly formed on the surface of a lithium metal electrode in which metallic lithium (Li) is formed on one surface or both surfaces of a current collector.

Technical Field

Cross Reference to Related Applications

The present application claims priority and benefit of korean patent application No. 10-2017-.

The present invention relates to a continuous manufacturing method of a lithium secondary battery in which a passivation film is formed on a surface of a lithium metal electrode, and more particularly, to a method of applying an electrolyte solution on a lithium metal electrode to form a passivation film before assembling a lithium secondary battery, and then manufacturing an electrode assembly and a lithium secondary battery, and a lithium secondary battery manufactured by the manufacturing method.

Background

As the technical development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing, and among the secondary batteries, lithium secondary batteries having high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and widely used.

In general, a lithium secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is laminated or wound and housed in a battery case, and is configured by injecting a nonaqueous electrolyte solution thereinto.

Here, as the anode, a carbon-based material having high stability is mainly used. However, despite the problems due to high chemical activity, the demand for the development of secondary batteries having high energy density is increasing with the recent steady increase in the use of mobile communication and portable electronic devices and the rapid development thereof. Therefore, the density is low (0.54 g/cm)³) And the very low standard reduction potential (-3.045V SHE: standard hydrogen electrode), the demand for lithium metal, which is the most popular material for negative electrode materials for high energy density batteries, is still increasing.

Meanwhile, the manufacturing method of the lithium metal battery has also progressed along with the manufacturing method of the lithium secondary battery using the carbon-based material accumulating the manufacturing technology of the battery. However, since the two batteries generate a difference in the formation step of the passivation film due to the difference in the anode materials, which has a decisive influence on the long-life characteristics, a fundamental change in the battery manufacturing technique is required.

In the case of the conventional carbon electrode, the carbon electrode shows a potential close to 0V (with respect to SHE) after injection of the electrolyte solution, and since the potential is higher than the reductive decomposition potential of the electrolyte solution and the additive, the passivation film cannot be formed by decomposition of the electrolyte solution and the additive only by injection of the electrolyte solution. Therefore, in the case of a carbon electrode, a passivation film is formed by applying a potential in a formation process, at which time, an aging treatment is performed for 24 hours or more at room temperature or in an atmosphere of a high temperature (40-60 ℃) so that the surface of the carbon electrode is uniformly impregnated with an electrolyte solution. Therefore, in the case of using a carbon electrode, the coating layer is formed relatively uniformly on the surface.

However, unlike the carbon electrode, the lithium metal electrode shows a potential close to-3.04V (with respect to SHE) after the injection of the electrolyte solution, and since the potential is lower than the reductive decomposition potential of the electrolyte solution and the additive, a passivation film is immediately generated by the reductive decomposition of the electrolyte solution and the additive through contact with the lithium metal, almost simultaneously with the injection of the electrolyte solution.

Therefore, unlike the external portion of the battery, which is impregnated with the electrolyte solution and forms the passivation film immediately after the injection of the electrolyte solution, the inside of the battery is impregnated with the electrolyte solution after aging (aging) for a certain period of time and simultaneously forms the passivation film, thereby causing a difference in physical properties of the passivation film, such as composition, thickness, and density, due to a sequential change between the inside and the outside of the battery.

The difference in physical properties of the passivation film causes an imbalance in current density during charge and discharge, resulting in local generation and growth of lithium dendrites, which is a major cause of reduction in the life span of metal batteries.

Therefore, as a method for avoiding this problem, introduction of a novel electrolyte solvent, an additive, and the like has been proposed, but this problem has not been fundamentally solved.

Further, in the case of adding various additives as a method for solving the problems, there are still problems to be solved, for example, among various additives, there are some additives which are good in the characteristics of forming a passivation film but leave components having large side effects on the subsequent battery performance when the residual amount thereof remains in an electrolyte solution, thereby deteriorating the performance of a secondary battery.

Therefore, there is a high demand for a technique capable of forming a uniform passivation film even on the surface of a lithium metal electrode while preventing the performance degradation of a lithium secondary battery.

Disclosure of Invention

Technical problem

The present invention has been made in an effort to provide a continuous manufacturing method of a lithium secondary battery having advantages of solving the above-mentioned problems of the conventional art and technical objects required in the past.

The inventors of the present application repeated extensive studies and various experiments, and as a result, confirmed that, in the case where an electrolyte solution including an additive favorable to the properties of a passivation film is first applied on a lithium metal electrode to form a passivation film before an electrode assembly and a lithium secondary battery are assembled, and the electrode assembly and the lithium secondary battery are manufactured using the lithium metal electrode on which the passivation film is formed, even a uniform passivation film can be formed on the surface of the lithium metal electrode, and deterioration in the performance of the lithium secondary battery can be prevented according to the additive included in the electrolyte solution when the lithium secondary battery is assembled, as described below, and completed the present invention.

Technical scheme

Accordingly, an exemplary embodiment of the present invention provides a method of manufacturing a lithium secondary battery, including:

(i) preparing a lithium metal electrode in which metallic lithium (Li) is formed on one surface or both surfaces of a current collector;

(ii) applying an electrolyte solution for coating including one or more lithium salts, one or more non-aqueous organic solvents, and one or more additives on a surface of metallic lithium to form a passivation film as a stable coating layer;

(iii) manufacturing an electrode assembly including a lithium metal electrode having a passivation film formed thereon as a negative electrode; and (iv) accommodating the electrode assembly in a secondary battery case, and injecting an electrolyte solution for injection including one or more lithium salts, one or more non-aqueous organic solvents, and one or more additives to manufacture a lithium secondary battery;

wherein

The additive for the coated electrolyte solution is one or more selected from the group consisting of Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), fluoroethylene carbonate (FEC), Propane Sultone (PS), 1,3-propane sultone (PRS), vinyl sulfate (ESa), succinonitrile (sn), adiponitrile (adapteronitrile (an)), Hexanetrione (HTCN), gamma-butyrolactone (gbl), biphenyl (bp), Cyclohexylbenzene (CHB)), and tert-amylbenzene (tert-amyl),

the additive for the injected electrolyte solution is one or more selected from the group consisting of pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme (glyme), hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, carbon tetrachloride, trifluoroethylene, fluoroethylene carbonate (FEC), and Propane Sultone (PS), and

the additive composition of the electrolyte solution for coating is different from the additive composition of the electrolyte solution for injection.

Here, the "additive composition" refers to any one or more of the content and the kind of the additive, and means a concept in which the kind and/or the content of the additive included in the electrolyte solution for coating is different from the kind and/or the content of the additive included in the electrolyte solution for injection, that is, all cases except the case where the kind and the content are the same, such as a case where the kind of the additive included in the electrolyte solution for coating and the kind of the additive included in the electrolyte solution for injection are different from each other, a case where the kind of the additive is the same but the content of the additive is different from each other, a case where some kinds of the additive are the same but other kinds of the additive are different from each other, or a case where various additives are the same but the content of some additives is different.

Therefore, according to the present invention, unlike the electrolyte solution for injection contained in the case during the assembly of the battery, the composition of the electrolyte solution for coating applied on the lithium metal electrode to form the passivation film can be then arbitrarily determined, whereby the electrolyte solution for coating can exhibit excellent effects in forming the passivation film; however, since an additive that may cause problems, such as when the residual amount thereof remains in an electrolyte solution used during the operation of the lithium secondary battery, may be used, a passivation film having excellent quality may be formed. Furthermore, subsequently, the material is not included in the electrolyte solution for injection, thereby preventing the performance degradation of the lithium secondary battery caused by the material.

As described above, the electrolyte solution for coating may include an additive that exerts advantageous characteristics when forming a passivation film, and for example, may include a material as described above, however, specifically, the additive may be one or more selected from the group consisting of succinonitrile (sn), adiponitrile (an), Hexanetrinitrile (HTCN), gamma-butyrolactone (gbl), Propane Sultone (PS), 1,3-propane sultone (PRS), Vinylene Carbonate (VC), and fluoroethylene carbonate (FEC), and more specifically, the additive may be VC and FEC.

These materials VC, SN, AN, HTCN, PS, PRS, GBL, and FEC cause a reductive decomposition reaction at a high potential with respect to a solvent when forming a passivation film, thereby forming a passivation film, and therefore, when these materials are used as a composition of a passivation film, AN effect of suppressing the decomposition reaction of the solvent and forming a dense passivation film can be exhibited. However, when FEC and VC are included in an electrolyte solution injected at the time of assembling a lithium secondary battery, they have a problem of increased swelling caused by gas generated during high-temperature storage even in the case where FEC remains in a large amount and VC remains in a trace amount.

Therefore, according to the present invention, these materials may preferably be included in the electrolyte solution for coating, and then may not be included or may be included in a smaller content in the electrolyte solution for injection.

Here, the additive may be included at 0.1 to 20 wt%, specifically 0.5 to 10 wt%, more specifically 1 to 5 wt%, based on the total weight of the electrolyte solution for coating.

When the content of the additive is too small to exceed this range, a passivation film having excellent performance may not be formed, and when the content of the additive is too large, the additive may function as a resistance, and thus is not preferable.

Meanwhile, applying the electrolyte solution for coating may be performed by dip coating (dip coating) or roll to roll coating (roll coating).

Here, the dip coating is a method of directly dipping a lithium metal electrode having metallic lithium (Li) formed on one surface or both surfaces of a current collector in an electrolyte solution for coating.

Here, since the lithium metal electrode is continuously manufactured in a sheet shape, it is possible to continuously perform along with the manufacturing process of the lithium metal electrode by designing the lithium metal electrode tab to be dip-coated by a water bath containing an electrolyte solution for coating.

This method is illustrated in fig. 1.

Referring to fig. 1, a lithium metal electrode 110 having metallic lithium 112 formed on both surfaces of a copper current collector 111 is transported in a sheet form by rollers 121, 122, and 123. Here, the second roller 122 is immersed in a water tank 130 filled with an electrolyte solution 131 for coating to apply the electrolyte solution 131 for coating on the lithium metal electrode 110 moving along the rollers 121, 122, and 123.

As another method, roll-to-roll coating is a method in which a lithium metal electrode is not directly passed through an electrolyte solution, but a portion of a roll is immersed in an electrolyte solution for coating, and a portion of the roll, which is not immersed in the electrolyte solution, is in contact with the lithium metal electrode, thereby indirectly applying the electrolyte solution on the roll to the lithium metal electrode.

This method is illustrated in fig. 2.

Referring to fig. 2, a lithium metal electrode 210 having metallic lithium 212 formed on both surfaces of a copper current collector 211 is transported in a sheet form by rollers 221, 222, and 223. Here, in the water tanks 230 and 240 filled with the electrolyte solutions 231 and 241 for coating, the coating rollers 224 and 225 for coating are disposed wherein one side of the rollers is immersed in the electrolyte solutions 231 and 241 and the other side of the rollers is in contact with the lithium metal electrode 210.

Here, the electrolyte solutions 231 and 241 for coating are drawn by the rotation of the coating rollers 224 and 225, and the electrolyte solutions 231 and 241 for coating on the coating rollers 224 and 225 may be applied on the surface of the lithium metal electrode 210.

Through this process, the electrolyte solution for coating may be applied on one surface or both surfaces of the lithium metal electrode, and thus, a passivation film is immediately generated on the surface of the lithium metal electrode by reductive decomposition of the solvent and additives of the electrolyte solution for coating due to the low potential characteristic of the lithium metal electrode. Therefore, the number of applications of the electrolyte solution is not limited, and may be applied at least once, and thus, a passivation film having a multilayer structure of a desired degree may be formed.

Here, the passivation film may be a Solid Electrolyte Interface (SEI) coating.

The inventors of the present application found that, according to the manufacturing method, an electrolyte solution for coating may be set to conditions favorable only for coating layer formation, separately from an electrolyte solution for injection that is injected later when assembling a lithium secondary battery, thereby enabling formation of a passivation film having excellent characteristics, thereby suppressing non-uniform generation and growth of lithium dendrites, thereby enabling manufacture of a lithium secondary battery having high charge-discharge efficiency and having excellent life characteristics. In addition, it was confirmed that a minimum amount of additives was added to the electrolyte solution for injection, thereby solving the problem of deterioration in performance of the lithium secondary battery, which may be problematic later.

As described above, the electrolyte solution for injection may include one or more lithium salts, one or more non-aqueous electrolyte solutions, and one or more additives, except that: the additive composition is different from that of the electrolyte solution used for coating.

That is, as described above, the electrolyte solution for injection does not include an additive having conditions favorable for forming a passivation film but may cause deterioration in the performance of the lithium secondary battery when a residual amount of the additive remains during the operation of the lithium secondary battery, but may include an additive species that may exert beneficial effects during the operation of the lithium secondary battery.

For example, the electrolyte solution for injection may include additives for improving charge and discharge characteristics, flame retardancy, and the like, and may include, for example, the above-described materials, and specifically, may include one or more selected from the group consisting of fluoroethylene carbonate (FEC) and Propane Sultone (PS).

When fluoroethylene carbonate (FEC) is included at an appropriate content, battery performance does not deteriorate, and further, FEC is preferable because it functions as a preferable coating forming agent for battery operation, having the effect of improving life characteristics, and Propane Sultone (PS) is preferable because it suppresses side reactions occurring in the positive electrode during high-temperature storage, thereby improving high-temperature storage characteristics.

However, as omitted from the example of the additive for injection, a material such as Vinylene Carbonate (VC) deteriorates high-temperature storage characteristics by remaining in a slight amount, and therefore, is not included in the electrolyte solution for injection.

The additive included in the electrolyte solution for injection may be included at 0.1 to 10% by weight, specifically 0.5 to 7% by weight, more specifically 0.5 to 5% by weight, based on the total weight of the electrolyte solution for injection.

When the content of the additive is too large to exceed this range, the additive may act as a resistance or even affect the high-temperature storage characteristics, and thus is not preferable, and when the content of the additive is too small, for example, the improved life characteristics and high-temperature storage characteristics exhibited by including the additive may not be expected, which is also not preferable.

Further, the electrolyte solution for coating and the electrolyte solution for injection include one or more lithium salts, and one or more non-aqueous organic solvents, the compositions of which may be the same or different from each other, and may be appropriately selected from the following examples.

The lithium salt is a material that is easily soluble in the nonaqueous electrolyte solution, and as the lithium salt, for example, LiCl, LiBr, LiI, LiClO can be used₄、LiBF₄、LiB₁₀Cl₁₀、LiPF₆、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiAlCl₄、CH₃SO₃Li、CF₃SO₃Li、(CF₃SO₂)₂NLi, lithium chloroborane, lithium lower aliphatic carbonate, lithium 4-phenylboronate, imide, or the like.

As the non-aqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, or the like can be used.

Hereinafter, other constituent elements will be described.

The lithium metal electrode may be manufactured by depositing metallic lithium or rolling a lithium foil on one surface or both surfaces of a planar-form current collector. Here, the current collector may be specifically a copper foil.

The copper foil may be generally manufactured to have a thickness of 3 to 50 μm, and the lithium metal formed on the copper foil may be formed to have a thickness of 1 to 300 μm, for example.

The electrode assembly may be manufactured by including a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode, the negative electrode being a lithium metal electrode having a passivation film formed thereon.

Here, the structure of the electrode assembly is not limited, and the electrode assembly may be: a laminate-type electrode assembly in which a positive electrode, a separator, and a negative electrode are punched into unit electrodes and laminated; a jelly-roll type electrode assembly in which a positive electrode, a separator, and a negative electrode sheet are laminated and wound; or a stacking and folding type electrode assembly in which unit electrodes are arranged on a separator in the form of a sheet and wound.

The positive electrode may include all conventional manufacturing methods and constituent elements of the positive electrode.

Specifically, the positive electrode may be manufactured by applying a mixture of the positive electrode active material, the conductive material, and the binder on the positive electrode current collector and drying the mixture, and if necessary, a filler may be further added to the mixture.

The positive electrode current collector is generally manufactured to have a thickness of 3 to 500 μm. The positive electrode current collector and the extended current collector portion are not particularly limited as long as they do not cause chemical changes in the battery and have high conductivity, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, and the like may be used. The cathode current collector and the extended current collector portion may be formed with fine protrusions and depressions on the surface to improve the adhesion of the cathode active material, and may be formed in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a non-woven fabric.

The positive active material may include: such as lithium cobalt oxide (LiCoO)₂) Or lithium nickel oxide (LiNiO)₂) Such layered compounds or compounds substituted with one or more transition metals; from the formula Li_1+xMn_2-xO₄(wherein x is 0-0.33), LiMnO₃、LiMn₂O₃Or LiMnO₂Lithium manganese oxide of the formula; lithium copper oxide (Li)₂CuO₂) (ii) a Vanadium oxides, such as LiV₃O₈、LiFe₃O₄、V₂O₅、Cu₂V₂O₇(ii) a From the formula LiNi_1-xM_xO₂(wherein M ═ Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x ═ 0.01 to 0.3) represents a Ni site-type lithium nickel oxide; represented by the chemical formula 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); LiMn₂O₄Wherein the chemical formulaWherein Li is partially substituted with alkaline earth metal ions; a disulfide compound; fe₂(MoO₄)₃(ii) a From the chemical formula LiFe_xMn_yCo_zPO₄(wherein x, y, z ≧ 0, and x + y + z ═ 1), but not limited thereto.

The conductive material is generally added in an amount of 1 to 30 wt% based on the total weight of the mixture including the cathode active material. The conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity, and for example, there may be used: graphite, such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, or summer black; conductive fibers such as carbon fibers or metal fibers; metal powders such as carbon fluoride powder, aluminum powder, or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives; or the like.

The binder is a component that facilitates the binding of the active material with a conductive material and the like and with a current collector, and is generally added in an amount of 1 to 30 wt% based on the total weight of the mixture including the cathode active material. Examples of binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, and the like.

The filler is a component that suppresses the expansion of the positive electrode and is selectively used, and the filler is not particularly limited as long as it does not cause a chemical change in the battery and is a fibrous material, and for example, it is possible to use: olefin polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers.

The separator is interposed between the positive electrode and the negative electrode, and uses an insulating thin film having high ion permeability and mechanical strength. The pore size of the separator is generally 0.01 to 10 μm, and the thickness is generally 5 to 300. mu.m. As the separator, for example, olefin polymers such as chemical-resistant and hydrophobic polypropylene; a sheet or nonwoven fabric made of glass fiber, polyethylene, or the like; and a separator made of a fabric coated on the surface with a ceramic, an adhesive, or a mixed layer of a ceramic and an adhesive. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrode assembly thus manufactured is accommodated in a secondary battery case, which may be a pouch-type battery case composed of an aluminum laminate sheet, or a prismatic or cylindrical battery case composed of a metal can.

After the electrode assembly is received in the secondary battery case, an electrolyte solution for injection may be injected through the injection port.

The present invention provides a lithium secondary battery manufactured by the method, and particularly, a lithium secondary battery according to the method may include a lithium metal electrode on one surface or both surfaces of which metallic lithium is formed on a current collector, on the surface of which a passivation film having a composition depending on decomposition of an electrolyte solution for coating is uniformly formed.

Drawings

Fig. 1 is a schematic view of an application method of an electrolyte solution for coating according to an exemplary embodiment of the present invention.

Fig. 2 is a schematic view of an application method of an electrolyte solution for coating according to another exemplary embodiment of the present invention.

Detailed Description

Hereinafter, the present invention will be described with reference to embodiments according to the present invention, however, for better understanding of the present invention, the scope of the present invention is not limited thereto.

< example 1>

Metallic lithium (thickness: 20 μm) was rolled on a current collector (thickness: 10 μm) composed of copper to manufacture a lithium metal negative electrode sheet. The lithium metal negative electrode sheet was immersed in an electrolyte solution for coating by the method shown in fig. 1 to form a passivation film on the surface. In this case, the amount of the solvent to be used,as the composition of the electrolyte solution for coating, 1M LiPF was used₆A liquid electrolyte solution dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, diethyl carbonate in a ratio of 1:2:1 including FEC (10 wt%) and VC (2 wt%) as additives.

The lithium metal negative electrode was punched and used as a negative electrode.

Mixing Co precursor and Li₂CO₃Mixing and sintering at 940 ℃ for 10 hours in a furnace (kiln) to prepare LiCoO for use as a positive electrode active material₂And PVdF as a binder and Super-P as a conductive material. The positive electrode active material, the binder and the conductive material were sufficiently mixed in NMP so that the weight ratio was 95:2.5:2.5, and the mixture was applied on an Al foil having a thickness of 12 μm (loading: 4 mAh/cm)²) The positive electrode was manufactured by drying at 130 ℃ and rolling so that the electrode porosity was 30%.

A positive electrode, a negative electrode, a polyethylene film (Celgard, thickness: 12 μ M) as a separator, and 1M LiPF thereof as an electrolyte solution for injection were used₆A liquid electrolyte solution dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate including FEC (5 wt%) and PS (2 wt%) additives in a ratio of 1:2:1 was contained in a pouch-type case, thereby manufacturing a lithium secondary battery.

< example 2>

A lithium secondary battery was manufactured in the same manner as in example 1, except that: a passivation film was formed on a lithium metal negative electrode sheet by the method shown in fig. 2, and as a composition of an electrolyte solution for coating, 1M LiPF was used₆A liquid electrolyte solution dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a ratio of 1:2:1 including FEC (10 wt%) and VC (2 wt%) as additives.

< comparative example 1>

A lithium secondary battery was manufactured in the same manner as in example 1, except that: the lithium metal sheet on which the passivation film was not formed was punched and used as a negative electrode.

< comparative example 2>

A lithium secondary battery was manufactured in the same manner as in example 1, except that: as the composition of the electrolyte solution for injection, 1M LiPF was used₆And a liquid electrolyte solution dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a ratio of 1:2:1 without additives.

< comparative example 3>

A lithium secondary battery was manufactured in the same manner as in example 1, except that: a lithium metal sheet on which a passivation film was not formed was punched and used as a negative electrode, and as an electrolyte solution for injection, 1M LiPF was used₆A liquid electrolyte solution dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a ratio of 1:2:1 including FEC (10 wt%), VC (2 wt%), and PS (2 wt%) as additives.

< comparative example 4>

A lithium secondary battery was manufactured in the same manner as in example 1, except that: as the composition of the electrolyte solution for injection, 1M LiPF was used₆A liquid electrolyte solution dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a ratio of 1:2:1 including VC (2 wt%) as an additive.

< test example 1>

The lithium secondary batteries manufactured according to examples 1 and 2 and comparative example 1 were charged and discharged twice at 0.2C in the range of 3V to 4.3V to measure initial discharge capacity and discharge efficiency, and the results are shown in table 1 below. Thereafter, the 100 th discharge capacity and the retention rate with respect to the first discharge capacity were calculated by charging at 0.1C and discharging at 0.5C 100 times, and the results are shown in table 1 below.

(Table 1)

	Discharge capacity/discharge efficiency	100 th (%)
			Example 1	1174mAh,99.95％	1033mAh(87％)
Example 2	1172mAh,99.94％	1020mAh(87％)
			Comparative example 1	1178mAh,99.88％	233mAh(20％)
Comparative example 2	1174mAh,99.93％	0mAh(0％)

Referring to table 1, it can be confirmed that the lithium secondary battery manufactured by forming a passivation film on a lithium metal electrode according to the present invention suppresses the non-uniform generation and growth of lithium dendrites, thus improving charge and discharge efficiency, thereby improving life characteristics of the battery, while the lithium secondary battery on which no passivation film is formed or the lithium secondary battery on which a passivation film is formed but no additive is used in an electrolyte solution for injection has significantly reduced life characteristics.

< test example 2>

The lithium secondary batteries manufactured according to examples 1 and 2 and comparative examples 2 to 4 were charged and discharged at 0.2C in the range of 3V to 4.3V and the capacity was confirmed, and then the lithium secondary batteries were recharged to 4.3V at 0.2C and left at a temperature of 60℃ for 21 days. The thickness and swelling ratio were measured, and the results are shown in table 2 below.

(Table 2)

Referring to table 2, it can be confirmed that in the embodiment in which the passivation film is formed using the additive so that the characteristics of the passivation film are excellent and then the additive is not included in the electrolyte solution for injection, the swelling problem, which may cause a problem during high-temperature storage of the lithium secondary battery, is solved, whereas in comparative examples 3 and 4 in which the additive such as VC for forming the passivation film having excellent characteristics is included in the electrolyte solution for injection, the swelling problem during high-temperature storage is serious due to gas generation caused by the residual amount of the additive.

Based on the above description, one of ordinary skill in the art to which the present invention pertains may make various applications and modifications within the scope of the present invention.

Industrial applicability

As described above, the method of manufacturing a lithium secondary battery according to the present invention includes, before assembling an electrode assembly and a lithium secondary battery, first applying an electrolyte solution for coating including an additive favorable to the property of a passivation film on a lithium metal electrode to form a passivation film, and manufacturing the electrode assembly and the lithium secondary battery using the lithium metal electrode on which the passivation film is formed, thereby being capable of forming a uniform passivation film on the surface of the lithium metal electrode. Accordingly, the non-uniform generation and growth of lithium dendrites of the manufactured lithium secondary battery is suppressed, and thus the charge and discharge efficiency is improved, thereby having an effect of contributing to an improvement in the life of the battery.

In addition, additives that may cause problems during the operation of the lithium secondary battery are not included in the electrolyte solution for injection, thereby preventing the deterioration of the performance of the lithium secondary battery.