KR20190075859A - Electrode assembly for lithium battery and method of making the same - Google Patents

Abstract

The present invention provides an electrode assembly for a lithium secondary battery including a negative electrode, a separator, and a positive electrode. A lithium metal layer is coated on the entire upper surface of the negative electrode, and the lithium metal layer is to be pre-lithiated in an amount of 65-100% of the negative electrode charging capacity. The positive electrode does not include a lithium source, and the lithium metal layer is located between the negative electrode and the separator. The positive electrode does not include a lithium source, and the lithium metal layer acts as a lithium source, wherein the lithium metal layer is in contact with an electrolyte to generate lithium ions to supply lithium to the negative electrode.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode assembly for a lithium secondary battery,

The present invention relates to a lithium secondary battery electrode assembly and a manufacturing method thereof.

A lithium ion secondary battery, which is one of the lithium secondary batteries, is one in which lithium ions deintercalated from a cathode active material included in the cathode are intercalated into the cathode. 1, the lithium ion secondary battery includes a cathode 100 including an anode current collector 110 and a cathode active material layer 120 formed on at least one surface of the anode current collector; A separation membrane 200; And a positive electrode 300 including a positive electrode collector 310 and a positive electrode active material layer 320 formed on at least one surface of the positive electrode collector.

In the lithium ion secondary battery, in particular, when a lithium metal sheet is used as a negative electrode, an internal short circuit occurs due to generation of a dendrite. In order to solve such a problem, a carbonaceous material such as graphite is used as an anode active material, but the carbonaceous anode active material has a small capacity and a problem of dendrite is not completely solved.

On the other hand, in the conventional lithium ion secondary battery, selection of the material of the cathode active material is limited, and some cathode active materials have problems of material depletion and high cost. In addition, the cathode active material such as LiCoO ₂ has a low theoretical capacity.

Accordingly, the present invention provides a lithium battery system using a compound that does not contain lithium in the positive electrode active material, thereby overcoming the limitation of selection of the positive electrode active material.

Also, the present invention provides a lithium battery system in which lithium metal is used as a lithium source but no dendrite generation problem occurs.

Further, the present invention provides a lithium battery system showing a high capacity.

According to a first aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery comprising a negative electrode, a separator and a positive electrode, wherein a lithium metal layer for pre-lithizing the negative electrode is coated on the upper surface of the negative electrode, Wherein the lithium metal layer has a thickness in the range of about 235 to about 235 mu m and the amount of lithium ion that is included in the lithium metal layer and pre-lithized the negative electrode is 65% to 100% of the negative electrode charging capacity, the positive electrode does not include a lithium source, Is located between the cathode and the separator.

According to a second aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery, wherein the lithium metal layer in the first aspect is preliminarily lithiated in an amount of 80% to 100% of the capacity of the negative electrode.

According to a third aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery, wherein the lithium metal layer in the first or second aspect is a lithium metal sheet having the same size as the cathode or larger than the cathode.

According to a fourth aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery, wherein the lithium metal layer in any one of the first to third aspects has a thickness in the range of 18 탆 to 20 탆.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the positive electrode active material constituting the positive electrode active material layer is CoO ₂ ; NiO ₂ ; MnO ₂ ; Mn ₂ O ₄ ; (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1); Ni _{1 - y} Co _y O ₂ (0 <y <1); Co _{1 - y} Mn _y O ₂ (0 = y <1); Ni _1-y Mn _y O ₂ (O = y <1); (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2); Mn _{2 - z} Ni _z O ₄ (0 < z &lt;2); Mn _2-z Co _z O ₄ (0 < z &lt;2); CoPO _4; FePO _4; (Si), Sn, Ge, Pb, Cd, Zn, Bi, Al, Sb, Mg, The metal layer may include at least one selected from the group consisting of molybdenum (Mo), gallium (Ga), iron (Fe), nickel (Ni), vanadium (V), chromium (Cr), calcium (Ca), titanium (Ti), zirconium (Zr), cobalt At least one metal or alloy selected from the group consisting of niobium (Nb) and indium (In), or an oxide thereof; and a mixture of at least one selected from the group consisting of An electrode assembly is provided.

According to a sixth aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery, wherein the gap in the negative electrode active material layer in any one of the first to fifth aspects is coated with a molten lithium metal do.

According to a seventh aspect of the present invention, there is provided an electrode assembly for a lithium secondary battery according to the first aspect and a lithium secondary battery including the electrolyte solution.

According to an eighth aspect of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: preparing a negative electrode by bringing a lithium metal layer into contact with a top surface of the negative electrode; Inserting a separator between the negative electrode and a positive electrode not including a lithium source, and storing the separator in a battery case; And injecting an electrolytic solution into the electrode assembly. The method for manufacturing an electrode assembly for a lithium secondary battery according to any one of the first to sixth aspects is provided.

According to a ninth aspect of the invention, in the eighth aspect, a negative pressure at the top surface 20 ℃ to a temperature of 60 ℃ range after face-to-face contact with a lithium metal to a pressure of lithium metal 1.5 cm 1 kgf to about 20 kgf range per ^second The method of manufacturing an electrode assembly for a lithium secondary battery according to claim 1, further comprising the steps of:

According to a tenth aspect of the present invention, in the eighth or ninth aspect, the method further comprises melting the lithium metal layer after bringing the lithium metal layer into contact with the upper surface of the negative electrode, Method is provided.

The present invention has the advantage of overcoming limitations such as low capacity, high cost, resource depletion, and the like of the cathode active material itself due to the absence of restrictions on the cathode active material. Particularly, since a material used as a negative electrode active material can be used for a positive electrode, a lithium battery system is provided which is driven by a completely different mechanism from the conventional one.

In addition, since the present invention solves the problem that dendrite is generated when lithium metal is used as a cathode, it has an advantage that a safety issue due to dendrite formation can be solved.

In addition, by initializing the negative electrode active material with a lithium metal layer, the initial irreversible capacity of the negative electrode can be reacted in advance before the battery is manufactured, thereby improving the initial efficiency. In addition, the N / P ratio can be easily adjusted by adjusting the amount of the lithium metal layer, thereby giving a great deal of fluidity to the cell design.

1 is a schematic cross-sectional view of an electrode assembly of a conventional lithium ion battery.
2 schematically illustrates a cross-section of an electrode assembly immediately after being assembled according to the present invention.
3 is a schematic cross-sectional view of an electrode assembly in which a lithium metal layer is removed after electrolyte injection in an electrode assembly assembled according to the present invention.

Hereinafter, embodiments and examples of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention.

It should be understood, however, that the present invention may be embodied in many different forms and is not limited to the embodiments and examples described herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout this specification, when an element is referred to as "including " an element, it is understood that the element may include other elements as well, without departing from the other elements unless specifically stated otherwise.

As used herein, the terms "about," " substantially, "and the like are used herein to refer to or approximate the numerical value of manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to prevent unauthorized exploitation by unauthorized intruders of the mentioned disclosure. Also, throughout the present specification, the phrase " step "or" step "does not mean" step for.

Throughout this specification, the term "combination thereof" included in the expression of the machine form means one or more combinations or combinations selected from the group consisting of the constituents described in the expression of the machine form, And the like.

Throughout this specification, the description of "A and / or B" means "A or B, or A and B".

According to an aspect of the present invention, there is provided a negative electrode comprising: a negative electrode including a negative electrode collector and a negative electrode active material layer formed on at least one surface of the negative electrode collector; A lithium metal layer formed on the upper surface of the cathode; Separation membrane; A positive electrode including a positive electrode collector and a positive electrode active material layer formed on at least one surface of the positive electrode collector; and the positive electrode contains no lithium source.

In the present invention, the lithium metal layer formed on the upper surface of the negative electrode is formed on the upper surface of the negative electrode in the form of a lithium metal sheet (first embodiment), a lithium metal powder (second embodiment) or a lithium metal deposition layer (third embodiment) May be loaded and formed.

2, the cathode 100 includes an anode current collector 110 and an anode active material layer 120 formed on at least one surface of the anode current collector 110. The cathode 100 may be formed of, for example, A lithium metal sheet 400; A separation membrane 200; There is provided an electrode assembly including a positive electrode current collector 310 and a positive electrode 300 including a positive electrode active material layer 320 'formed on at least one surface of the positive electrode current collector. The electrode assembly may have a structure before being brought into contact with the electrolytic solution. Unlike the cathode active material layer 320 of FIG. 1, the cathode active material layer 320 'does not include a lithium source.

In a second embodiment, the lithium metal powder may be formed by a droplet emulsion technique (DET), but is not limited thereto. The emulsion droplet process dies the lithium metal sheet into the vessel containing the silicone oil and then dissolves the lithium metal sheet at high temperature. Thereafter, the vessel is rotated to disperse the lithium metal powder. Then, the solvent is removed and lithium metal powder can be obtained through a layer separation process using hexane.

The lithium metal powder may be applied to the negative electrode active material layer in the form of a slurry by forming a slurry together with the binder, and adhesion to the active material layer may be maintained by the binder.

Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, isoprene rubber, polyimide resin, and the like. , But is not limited thereto. The lithium metal powder may be adjusted to have 800 to 1,200 parts by weight based on 100 parts by weight of the binder.

The solvent should not dissolve the lithium metal powder, and examples of the solvent include, but not limited to, triethyl phosphate. The lithium metal powder slurry is coated and dried in a conventional manner in the art, and then a lithium metal powder layer is formed on the cathode by drying.

In the third embodiment, the lithium metal may be vapor-deposited on the cathode. The deposition layer is formed on the surface of the lithium metal in the atmosphere of at least one reaction gas selected from the group consisting of nitrogen, oxygen, chlorine, carbon monoxide, carbon dioxide, and sulfur dioxide, or a silane gas and / Aluminum, or the like) is added. The lithium metal may be lithium or lithium foil deposited on a resin film base or a metal-deposited resin film base (e.g., a copper-deposited polyethylene terephthalate film), but is not limited thereto. A lithium metal foil can be generally used as a lithium evaporation source used for lithium deposition. Lithium deposition is preferably performed by thermal deposition in a vacuum atmosphere of 2 to 3 x 10 ^-6 Torr. The protective film containing various materials can be formed by adjusting the content and the content of the reaction gas. The ionization efficiency can be improved by using argon gas together with the reaction gas. For example, a nitrogen gas and an argon gas may be mixed at a volume ratio of 5: 1 to 9: 1 in order to produce a Li3N vapor deposition layer. The deposition process is preferably a method capable of vapor-depositing a lithium ion conductive material on a lithium metal, and typical examples thereof include chemical vapor deposition, thermal evaporation, plasma chemical vapor deposition, laser chemical vapor deposition, and jet vapor deposition .

After the lithium metal layer is loaded on the upper portion of the negative electrode active material layer, the lithium metal layer may be pressed downward to promote total lithization.

According to an embodiment of the present invention, there is provided a method of manufacturing a lithium secondary battery, comprising: contacting a lithium metal layer on an upper surface of a negative electrode active material layer; And melting the lithium metal layer to allow the lithium metal melt to permeate into the negative electrode active material pores.

The cathode may be heat treated at a temperature of 180 ° C or higher or 180 ° C to 220 ° C so that the lithium metal layer is melted, thereby promoting total lithium ionization. The heat treatment of the negative electrode may be performed for 1 to 5 hours or for 2 to 3 hours. This heat treatment causes the lithium metal layer to penetrate between the pores of the anode active material layer, so that the contact with the anode active material particles can be improved, and lithium ionization can be easily performed when cells are constituted and an electrolyte is injected in a subsequent process. Particularly, in the case of this heat treatment, the lithium metal layer is completely or substantially completely ionized, and unreacted products are not generated. The unreacted lithium metal acts as a cause of the side reaction in the cycle charge / discharge cycle of the cell, which may accelerate cell degeneration. If the heat treatment temperature is higher than the upper limit value, deterioration of the negative electrode active material occurs. If the heat treatment temperature is less than 180 ° C, the lithium metal layer may not be melted. If the heat treatment time is longer than the upper limit value, deterioration of the negative electrode active material occurs. If the heat treatment time is shorter than the lower limit value, the lithium metal layer is not melted.

The heat treatment may be performed after the lithium metal layer is coated on the negative electrode active material layer.

In one embodiment of the present invention, at least a part of the air gap formed in the negative electrode active material layer by the heat treatment is provided with a cathode coated with a lithium melt.

The lithium metal sheet of the electrode assembly contacts the electrolyte solution and generates lithium ions in the lithium metal sheet. Therefore, when the electrode assembly is in contact with the electrolyte solution and after a predetermined time has elapsed, It completely disappears. 3, the electrode assembly includes a cathode 100 including a cathode current collector 110 and a cathode active material layer 120 'formed on at least one surface of the cathode current collector; A separation membrane 200; And a positive electrode 300 including a positive electrode current collector 310 and a positive electrode active material layer 320 &quot; formed on at least one surface of the positive electrode current collector.

The anode active material layer 120 'of FIG. 3 is characterized in that it is lithiated as compared with the anode active material layer 120 of FIG. The positive electrode active material layer 320 '' of FIG. 3 differs from the positive electrode active material layer 320 'of FIG. 3 in that lithium ions are not present in the positive electrode active material layer 320' because the positive electrode active material included in the positive active material layer 320 ' Lithium ions migrated from the cathode 100 are present.

In the present invention, the negative electrode may be formed by dispersing a negative electrode active material, a conductive material, a binder polymer and, if necessary, additives in a solvent to form an anode active material slurry and coating the slurry on at least one surface of the negative electrode current collector.

The negative electrode active material is not particularly limited as long as it is commonly used in the art.

The negative electrode active material may be a carbon-based compound as a non-limiting example. Concretely, low-crystalline carbon and high-crystalline carbon may be used. Examples of the low-crystalline carbon include soft carbon and hard carbon, and highly crystalline carbon includes natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon Fired carbon such as mesophase pitch based carbon fiber, mesocarbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes can be used. Specifically, natural graphite Is preferable in that reversible insertion and removal of lithium ions are possible while maintaining the structural and electrical properties. The carbon-based compound is a negative electrode active material, which permits reversible insertion and removal of lithium ions while maintaining structural and electrical properties, but has a disadvantage in that a battery having a small capacity and high energy density can not be manufactured.

The negative electrode active material may be, without limitation, a metal or an alloy, or an oxide thereof. Specifically, the negative electrode active material may be selected from the group consisting of Si, Sn, Ge, Pb, Cd, Zn, Bi, Al, Magnesium, magnesium, gallium, iron, nickel, vanadium, chromium, calcium, titanium, zirconium, At least one metal or alloy selected from the group consisting of cobalt (Co), noble metal (Nb) and indium (In), or an oxide thereof may be used.

The binder polymer is not particularly limited as long as it is a component that assists in bonding between the active material and the conductive material and bonding to the current collector. Examples of the binder polymer include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC) Polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, polyvinyl chloride, polyvinylpyrrolidone, polyvinylpyrrolidone, Various copolymers and the like. An aqueous binder such as styrene-butadiene rubber or carboxymethylcellulose is preferably used for the negative electrode.

The binder polymer may ordinarily be contained in an amount of 1 to 30% by weight based on the total weight of the mixture including the negative electrode active material.

The conductive material is not particularly limited as long as it can be generally used in the art, and examples thereof include synthetic graphite, natural graphite, carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, carbon fiber, , Aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, iridium, Polythiophene, polyacetylene, polypyrrole, or a combination thereof. In general, a carbon black-based conductive material may be used.

The conductive material may be typically contained in an amount of 0 to 30% by weight based on the total weight of the mixture including the anode active material.

As the additive, a filler that suppresses the expansion of the electrode may be used. The filler is not particularly limited as long as it is a fibrous material without causing chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The negative electrode current collector generally has a thickness of 3 to 500 탆, and is not particularly limited as long as it is commonly used in the art, and examples thereof include copper foil, nickel foil, stainless steel foil, titanium foil, Nickel foams, copper foams, polymeric substrates coated with conductive metals, or combinations thereof.

In the present invention, a lithium source is interposed between the anode active material layer and the separator, and the lithium source may be a lithium metal sheet, a lithium metal powder, or a lithium metal deposition layer. Lithium metal sheet is preferable to lithium metal powder in terms of cost competitiveness and oxidation stability.

The lithium metal layer has a larger size than the negative electrode, and can have a thickness in the range of 15 mu m to 300 mu m or a thickness in the range of 20 mu m to 100 mu m. If the lithium metal layer is thinner than the lower limit, it is too thin to be handled. If the lithium metal layer is thicker than the upper limit, the diffusion distance becomes far away, and lithium ions generated from the lithium metal layer can not sufficiently enter into the negative electrode active material.

The separator according to the present invention may be an insulating porous thin film interposed between an anode and a cathode and having high ion permeability and mechanical strength. Specifically, the separation membrane may be formed of a polyolefin such as polypropylene, which is chemically resistant and hydrophobic; A composite separator in which a ceramic layer is formed on at least one surface of a porous polymer substrate such as polyolefin; A sheet or a nonwoven fabric made of glass fiber, polyethylene or the like can be used. The pore diameter of such a separation membrane is generally 0.01 to 10 mu m, and the thickness may be generally 5 to 300 mu m.

The positive electrode of the present invention may be formed by forming a positive electrode active material slurry by dispersing a positive electrode active material, a conductive material, a binder polymer and, if necessary, an additive in a solvent, and coating the positive electrode active material slurry on at least one surface of the positive electrode current collector .

The cathode active material is characterized in that a transition metal oxide can be used and does not contain lithium. Non-limiting _{examples, CoO 2, NiO 2, MnO} 2, Mn 2 O 4, (Ni a Co b Mn c) O 2 (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), Ni 1 - y Co y O 2 (0 <y <1), Co 1 - y Mn y O 2 (0 = y <1), Ni 1 - y Mn y O 2 (O = _{y <1), (Ni a} Co b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), Mn 2 - z Ni z O may be a _{z Co z O 4 (0 <} z <2), CoPO 4 FePO ₄ and at least one mixture selected from the group consisting of _{- 4 (0 <z <2} ), Mn 2.

As the cathode active material, compounds usable as an anode active material, that is, soft carbon, hard carbon, natural graphite, Kish graphite, pyrolytic carbon Mesophase pitch based carbon fibers, mesocarbon microbeads, mesophase pitches, petroleum or coal tar pitch derived cokes; (Si), Sn, Ge, Pb, Cd, Zn, Bi, Al, Sb, Mg, (Mo), Ga, Fe, Ni, V, Cr, Ca, Ti, Zr, Co, ), Noble metal (Nb), and indium (In), or an oxide thereof may be used.

The binder polymer used for the anode is not particularly limited as long as it is a component that assists in bonding of the active material and the conductive material and bonding to the current collector. Examples of the binder polymer include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC) , Starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, Fluorine rubber, various copolymers, and the like.

The conductive material used for the anode is not particularly limited as long as it can be generally used in the art as well as the cathode. For example, artificial graphite, natural graphite, carbon black, acetylene black, ketjen black, denka black, A metal such as aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, Ruthenium, platinum, iridium, titanium oxide, polyaniline, polythiophene, polyacetylene, polypyrrole, or a combination thereof may be used. In general, carbon black-based conductive materials are often used.

The cathode current collector generally has a thickness of 3 탆 to 500 탆, and is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, surfaces of copper, stainless steel, aluminum, nickel, titanium, sintered carbon or aluminum or stainless steel surface-treated with carbon, nickel, titanium or silver may be used.

In the present invention, cathode lithium ionization does not require a separate step. According to the present invention, the lithium metal layer is brought into contact with the upper surface of the anode in a total lithiating process using a lithium metal, and then the temperature and pressure applied during lamination, for example, At a temperature in the range of 1 kgf to 20 kgf per 1.5 cm &lt; ² &gt; of the lithium metal layer, the lithium metal layer can sufficiently come into contact with the negative electrode active material layer.

The electrode assembly may be housed in an outer case together with an electrolyte to form a lithium secondary battery.

The electrolytic solution includes conventional electrolytic components such as an organic solvent and an electrolyte salt.

The electrolyte salt is a salt having the same structure as A ⁺ B ^- , wherein A ⁺ includes an alkali metal cation such as Li ⁺ , Na ⁺ , K ⁺ , or a combination thereof and B ^- includes PF ₆ ^- , BF ₄ ^{-, Cl -, Br -,} I -, ClO 4 -, AsF 6 -, CH 3 CO 2 -, CF 3 SO 3 -, N (CF 3 SO 2) 2 -, C (CF 2 SO 2) 3 - Or an ion consisting of a combination of these. In particular, a lithium salt is preferable. For example, LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _2, or a mixture thereof can be used.

The organic solvent may be a solvent commonly known in the art, for example, a cyclic carbonate system with or without a halogen substituent; Linear carbonate system; Ester-based, nitrile-based, phosphate-based solvents, or mixtures thereof. For example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, (NMP), ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, acetic acid Methyl, ethyl acetate, propyl acetate, pentyl acetate, methyl propionate, ethyl propionate, ethyl propionate and butyl propionate or mixtures thereof.

The pre-lithization of the present invention is characterized in that no further processing is required. When the electrode assembly of the present invention is housed in a battery case and an electrolyte is injected, lithium ions are discharged from the lithium metal layer due to the electrolytic solution and intercalated into the cathode. The lithium metal layer can generate lithium ions in an amount corresponding to 50 to 110% or 65 to 100% or 80 to 100% of the negative electrode capacity, and thus generated lithium ions can be inserted into the negative electrode. When the lithium metal layer is less than the lower limit value, the capacity of the lithium secondary battery itself decreases because there is no lithium source in the cathode active material. When the lithium metal layer is larger than the upper limit value, all lithium ions are not ionized, Lithium remains in the metal state, causing side reactions and adversely affecting the cell (cell), accelerating cycle degeneration.

The lithium secondary battery according to an embodiment of the present invention is not limited to the outer shape or the case, but may be a cylindrical shape, a square shape, a pouch shape, a coin shape, or the like using a can.

In addition, the lithium secondary battery according to an embodiment of the present invention may include all conventional lithium secondary batteries such as a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited by these Examples and Experimental Examples. The embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example  One

&Lt; Preparation of negative electrode &

A negative electrode was prepared by adding 92 wt% of natural graphite (BTR), 3 wt% of Denka black, 3.5 wt% of styrene-butadiene rubber (SBR) and 1.5 wt% of carboxymethyl cellulose (CMC) A mixture slurry was prepared. The prepared negative electrode mixture slurry was coated on one surface of the copper collector, dried and rolled to obtain a negative electrode for a lithium secondary battery having a charge capacity of 4.2 mAh / cm 2 and a discharge capacity of 3.9 mAh / cm 2.

&Lt; Application of lithium on the cathode &

A lithium metal sheet having the same size as the cathode and having a thickness of 20 탆 was coated on the entire upper surface of the above-prepared negative electrode with a lithium metal layer, and a flat plate horizontally positioned on the upper surface of the negative electrode was moved downward to produce 500 kPa / 1.5 cm ² ).

&Lt; Production of both batteries >

MnO ₂ (Sigma Aldrich) not containing a lithium source was prepared as an anode.

The negative electrode prepared above and MnO ₂ (Sigma Aldrich) not containing the lithium source were used as a counter electrode (anode), a polyolefin separator was interposed therebetween, and the resultant was housed in a battery case, and ethylene carbonate (EC) Ethyl carbonate (DEC) in a volume ratio of 50:50 was injected into a solvent containing 1 M LiPF ₆ dissolved therein to prepare coin-like batteries. At this time, from the point of time when the electrolyte is injected, the lithium metal sheet applied to the upper surface of the negative electrode is ionized into the negative electrode, and the negative electrode is filled up to 98.5% of the capacity of the negative electrode.

- Cathode charging capacity = 4.2 mAh / cm ²

- Theoretical capacity of lithium metal sheet = 2068 mAh / cm ³

- Capacity of lithium metal sheet = Theoretical capacity of lithium metal sheet x Thickness = 2068 (mAh / cm ³ ) x 0.002 cm = 4.136 mAh / cm ²

- amount of total lithium ionized lithium ion based on anode charge capacity = capacity of lithium metal sheet / anode charge capacity x 100 = 4.136 mAh / cm ² /4.2 mAh / cm ² x 100 = 98.5%

No lithium metal was present between the cathode and the separator after 5 hours of the injection of the electrolyte.

Example  2

Except that the lithium metal sheet coated on the cathode in Example 1 was changed to a thickness of 18 탆 to form a lithium metal layer. At this time, the lithium metal sheet applied to the upper surface of the negative electrode is ionized into the negative electrode from the point of time when the electrolyte is injected, and the negative electrode is filled up to 88.6% of the capacity of the negative electrode. No lithium metal was present between the cathode and the separator after 5 hours of the injection of the electrolyte.

That is, the amount of lithium ion included in the lithium metal layer and pre-lithizing the negative electrode was 88.6% of the negative electrode charging capacity. This was calculated by the formula of Example 1.

Comparative Example  One

Except that the lithium metal sheet coated on the cathode in Example 1 was changed to a thickness of 10 mu m to form a lithium metal layer. At this time, from the point of time when the electrolyte is injected, the lithium metal sheet applied to the upper surface of the negative electrode is ionized into the negative electrode, and it is filled up to 49% of the negative electrode charging capacity.

No lithium metal was present between the cathode and the separator after 5 hours of the injection of the electrolyte.

That is, the amount of lithium ion included in the lithium metal layer and pre-lithizing the negative electrode was 49% of the negative electrode charging capacity. This was calculated by the formula of Example 1.

Comparative Example  2

Except that the lithium metal sheet coated on the cathode in Example 1 was changed to a thickness of 350 mu m to form a lithium metal layer. At this time, the lithium metal sheet applied to the upper surface of the negative electrode is ionized into the negative electrode from the point of time when the electrolyte is injected into the negative electrode, and 100% of the capacity of the negative electrode is charged and excess lithium is present in the form of metal. That is, the amount of lithium ions included in the lithium metal layer and pre-lithizing the negative electrode was 1600% of the negative electrode charging capacity. This was calculated by the formula of Example 1.

<Cycle charge / discharge test>

The charge and discharge cycle tests were performed on both the coin-type batteries manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 by using an electrochemical charging / discharging device. During discharging, current was applied at a current density of 0.5 C-rate up to a voltage of 0.3 V, and the battery was charged to a voltage of 3.0 V at the same current density upon charging. The first cycle discharge capacity and the 50th cycle discharge capacity were measured and are shown in Table 1.

The first cycle discharge capacity (mAh) The 50th cycle discharge capacity (mAh) Capacity retention rate (%) Example 1 3.7 3.3 89.1 Example 2 3.5 3.1 88.5 Comparative Example 1 1.6 1.1 68.8 Comparative Example 2 3.9 2.7 69.2

From Table 1, the first cycle discharge capacity was 3.7 mAh and the third cycle discharge capacity was 3.3 mAh and 3.1 mAh, respectively, in Example 1 and Example 2, respectively. This is because although the lithium metal sheets of Examples 1 and 2 did not include lithium in the cathode active materials of Examples 1 and 2, lithium metal sheets were preliminarily lithium-added to the electrolyte solution and entered the cathode, It is proved that it is widely used as a reversible capacity, and as a result, excellent cycle performance can be exhibited.

On the other hand, the capacity of Comparative Example 1 was lower than that of Examples 1 and 2. This is because the lithium metal sheet is thin and the lithium is converted into lithium by the lithium ion in the cathode, and the reversible capacity is lowered.

On the other hand, in the case of Comparative Example 2 in which the lithium metal sheet was used in a thickness of 350 mu m, the first cycle discharge capacity was larger than that in Examples 1 and 2. However, the 50th cycle discharge capacity was lower than in Examples 1 and 2. In the case of Comparative Example 2, since the lithium metal sheet thicker than those of Examples 1 and 2 was applied to the negative electrode, the total lithium ionization was increased and the first cycle discharge capacity was increased. At this time, the lithium metal sheet was too thick, And some of the lithium remained in the metal state, causing side reactions, which adversely affected the cell (cell) and accelerated cycle degeneration.

Claims (10)

1. An electrode assembly for a lithium secondary battery comprising a cathode, a separator and an anode,
A lithium metal layer for pre-lithizing the cathode is applied to the upper surface of the cathode,
Wherein the lithium metal layer has a thickness in the range of 14 [mu] m to 235 [mu] m,
The amount of lithium ions included in the lithium metal layer and pre-lithizing the negative electrode is 65% to 100% of the negative electrode charging capacity,
The anode does not contain a lithium source,
Wherein the lithium metal layer is located between the cathode and the separator
Electrode assemblies for lithium secondary batteries.
The method according to claim 1,
Wherein an amount of lithium ions included in the lithium metal layer and pre-lithizing the negative electrode is 80% to 100% of the negative electrode charging capacity.
The method according to claim 1,
Wherein the lithium metal layer is a lithium metal sheet having a size equal to or larger than that of the negative electrode.
The method of claim 1, wherein
Wherein the lithium metal layer has a thickness in the range of 18 占 퐉 to 20 占 퐉.
The method according to claim 1,
Wherein the positive electrode comprises: a current collector; And a positive electrode active material layer disposed on at least one surface of the current collector, wherein the positive electrode active material layer comprises CoO ₂ ; NiO ₂ ; MnO ₂ ; Mn ₂ O ₄ ; (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1); Ni _{1 - y} Co _y O ₂ (0 <y <1); Co _{1 - y} Mn _y O ₂ (0 = y <1); Ni _{1 - y} Mn _y O ₂ (O = y <1); (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2); Mn _{2 - z} Ni _z O ₄ (0 < z &lt;2); Mn _{2 - z} Co _z O ₄ (0 < z &lt;2); CoPO _4; FePO _4; (Si), Sn, Ge, Pb, Cd, Zn, Bi, Al, Sb, Mg, The metal layer may include at least one selected from the group consisting of molybdenum (Mo), gallium (Ga), iron (Fe), nickel (Ni), vanadium (V), chromium (Cr), calcium (Ca), titanium (Ti), zirconium (Zr), cobalt At least one metal or alloy selected from the group consisting of niobium (Nb) and indium (In), or an oxide thereof; and a mixture of at least one selected from the group consisting of Electrode assembly.
The method according to claim 1,
The negative electrode comprising: a current collector; And a negative electrode active material layer disposed on at least one side of the current collector, wherein the gap in the negative electrode active material layer is covered with a melt of lithium metal.
7. A lithium secondary battery comprising the electrode assembly for a lithium secondary battery according to any one of claims 1 to 6 and an electrolyte solution.
In the method for producing a lithium secondary battery,
Preparing a negative electrode by bringing a lithium metal layer into contact with the upper surface of the negative electrode;
Inserting a separator between the negative electrode and a positive electrode not including a lithium source, and storing the separator in a battery case; And
Injecting an electrolyte;
The method of manufacturing an electrode assembly for a lithium secondary battery according to any one of claims 1 to 6,
9. The method of claim 8,
Lithium secondary cell electrode to the step of pressing at a pressure of lithium metal 1.5 cm ² 1 kgf to about 20 kgf range sugar at a temperature of after-person contact with the lithium metal layer in contact with the cathode upper surface 20 ℃ to 60 ℃ range, characterized in that it further comprises &Lt; / RTI &gt;
9. The method of claim 8,
And melting the lithium metal layer after bringing the lithium metal layer into contact with the upper surface of the cathode in a face-to-face manner.

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