WO2019221410A1 - Negative electrode including electrode protective layer, and lithium secondary battery employing same - Google Patents

Negative electrode including electrode protective layer, and lithium secondary battery employing same Download PDF

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Publication number
WO2019221410A1
WO2019221410A1 PCT/KR2019/004760 KR2019004760W WO2019221410A1 WO 2019221410 A1 WO2019221410 A1 WO 2019221410A1 KR 2019004760 W KR2019004760 W KR 2019004760W WO 2019221410 A1 WO2019221410 A1 WO 2019221410A1
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Prior art keywords
metal
lithium
protective layer
negative electrode
secondary battery
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PCT/KR2019/004760
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French (fr)
Korean (ko)
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정찬엽
최정훈
장민철
손병국
오형주
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주식회사 엘지화학
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Publication of WO2019221410A1 publication Critical patent/WO2019221410A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a negative electrode including an electrode protective layer and a lithium secondary battery using the same, and more particularly, to effectively inhibit the growth of lithium dendrite in consideration of the surface energy of the metal constituting the coating layer and the activation energy of lithium.
  • the present invention relates to a negative electrode including a protective material that can be used, and a lithium secondary battery using the same.
  • the electrochemical device is the field that is receiving the most attention in this respect, and the development of a secondary battery that can be charged and discharged among them is the focus of attention, and in recent years to improve the capacity density and energy efficiency in developing such a battery R & D on the design of new electrodes and batteries is ongoing.
  • lithium secondary batteries developed in the early 1990s have higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.
  • the 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 stacked or wound, and the electrode assembly is embedded in a battery case and a nonaqueous electrolyte is injected into the lithium secondary battery. do.
  • the lithium secondary battery produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.
  • lithium metal, carbon, and the like are used as active materials for a negative electrode of a lithium secondary battery
  • lithium oxide, transition metal oxide, metal chalcogenide, conductive polymer, and the like are used as active materials for a positive electrode.
  • Most lithium secondary batteries using lithium metal as a negative electrode attach lithium foil on a copper current collector or use a lithium metal sheet itself as an electrode.
  • Lithium metal has attracted great attention as a high capacity cathode material due to its low potential and large capacity.
  • lithium metal When lithium metal is used as a negative electrode, electron density nonuniformity may occur on the surface of lithium metal due to various factors when the battery is driven.
  • the lithium dendrite in the form of twigs is formed on the surface of the electrode, so that protrusions are formed or grown on the surface of the electrode, thereby making the electrode surface very rough.
  • These lithium dendrites along with deterioration of the cell, cause severe damage to the separator and short circuit of the cell. As a result, there is a risk of explosion and fire of the battery due to an increase in the battery temperature.
  • lithium dendrites of the lithium secondary battery are precipitated on the surface of the negative electrode, thereby causing volume expansion of the cell. Accordingly, the present inventors have conducted various studies, and have found a way to solve the problem caused by the dendrite through the application of the protective material of the lithium metal negative electrode and completed the present invention.
  • an object of the present invention is to solve the problem of volume expansion of a cell due to lithium dendrite by applying a protective material of a lithium metal negative electrode, and to provide a lithium secondary battery having improved battery performance.
  • It includes a metal protective layer formed on at least one surface of the lithium metal layer,
  • the metal protective layer provides a negative electrode for a rechargeable lithium battery including a metal having a relative energy R E of greater than 0.132 according to Equation 1 below.
  • the metal protective layer comprises a metal or a metal alloy.
  • the metal protective layer includes any one or more selected from the group consisting of Al, Au, Ag, Co, Ni, Mg, Zn and alloys thereof.
  • One embodiment of the present invention is to obtain the surface energy of the metal of the equation (1) and the p-band or d-band center of the metal by the density function theory (density function theory).
  • the protective layer has a thickness of 2 to 2,000 nm.
  • the lithium metal layer is a lithium metal thin film formed on the current collector.
  • the current collector comprises any one or more selected from the group consisting of copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. will be.
  • the negative electrode provides a lithium secondary battery which is the negative electrode for the lithium secondary battery described above.
  • a metal protective layer is formed on a surface of the cathode opposite to the anode.
  • the negative electrode including the electrode protective material according to the present invention while suppressing the growth of lithium dendrites on the surface of the negative electrode and can effectively transfer lithium ions to the lithium metal electrode and excellent ion conductivity, a protective layer comprising a protective material Since it does not act as a resistive layer and does not take overvoltage during charging and discharging, it is possible to prevent performance degradation of the battery and to ensure stability when driving the battery.
  • the lithium electrode including the electrode protection material proposed in the present invention is preferably applicable as a negative electrode of a lithium secondary battery, which is a large-capacity energy storage device from most small electronic devices using a variety of devices, for example lithium metal as a negative electrode Applicable to the back.
  • FIG. 1 is a cross-sectional view of a negative electrode for a rechargeable lithium battery according to one embodiment of the present invention.
  • FIG. 2 illustrates a cross-sectional view of a negative electrode of a lithium secondary battery and an image of lithium dendrites.
  • 3 is a graph showing the diffusion energy barrier of lithium at the surface of each material.
  • FIG. 4 is a schematic view of a lithium secondary battery negative electrode having a protective layer having a protective layer that facilitates diffusion of lithium on the surface of the protective layer without forming lithium dendrites according to an embodiment of the present invention.
  • FIG. 5 shows a schematic diagram of a calculation process of lithium diffusion activation energy E a on the metal surface of the protective layer according to the present invention.
  • Figure 6 shows a schematic diagram of a slab model (slab model) of the metal or metal alloy included in the protective layer according to the present invention.
  • Figure 7 shows the density of states (DOS) of the slab model of the metal or metal alloy included in the protective layer according to the present invention.
  • the present invention includes a lithium metal layer 120 and a metal protective layer 110 formed on at least one surface of the lithium metal layer, wherein the metal protective layer is a relative energy according to Equation 1 below.
  • a negative electrode 100 for a lithium secondary battery wherein the R E value includes a metal of more than 0.132.
  • the protective layer according to the present invention includes a metal having a relative energy value of more than 0.132 in consideration of the surface energy of the metal, the lithium diffusion energy, and the metal p-band or d-band center, thereby preventing dendrite-shaped lithium precipitation.
  • the lithium secondary battery can be prevented, and at the same time, the lithium metal negative electrode is protected from the electrolyte and the electrochemical charge / discharge is more stable and the lithium secondary battery can maximize the cycle performance improvement effect.
  • the lithium metal layer, the metal protective layer, and the lithium secondary battery to which the same constitute the negative electrode for a lithium secondary battery of the present invention will be described in detail.
  • lithium metal when used as a battery negative electrode, the following problems exist.
  • a passivation layer is formed by reacting with electrolyte, water, impurities in a battery, lithium salt, and the like, which causes local current density difference to form dendritic lithium dendrite.
  • the dendrite thus formed may grow and cross the pores of the separator to cause a direct internal short circuit with the positive electrode, causing the battery to explode.
  • the lithium metal layer according to the present invention may be a lithium metal plate or a metal plate on which a lithium metal thin film is formed on a negative electrode current collector.
  • the method of forming the lithium metal thin film is not particularly limited, and a lamination method, a sputtering method, and the like, which are known metal thin film formation methods, may be used.
  • the lithium metal plate of the present invention also includes a case where a metal lithium thin film is formed on a metal plate by initial charging after assembling a battery without a lithium thin film in a current collector.
  • the negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and these It can be selected from the group consisting of a combination of.
  • the stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and the alloy may be an aluminum-cadmium alloy.
  • the non-conductive polymer or the conductive polymer surface-treated with a fired carbon, a conductive material, or the like may be used. You can also use Generally, a thin copper plate is used as the negative electrode current collector.
  • the lithium metal plate may be adjusted in width depending on the shape of the electrode to facilitate electrode production.
  • the thickness of the lithium metal plate may be 10 to 300 ⁇ m.
  • Applicant has completed the present invention by approaching this in terms of the lithium dendrite generation principle to solve the problem (see Fig. 2) related to the lithium dendrite precipitation that was pointed out as a disadvantage of the conventional lithium secondary battery.
  • lithium cations are reduced on the surface of the lithium metal in the process of charging and discharging the battery, and thus have a dendrite shape. It penetrates and contacts the positive electrode of the battery, causing a problem of internal short circuit.
  • the smaller the absolute value of the center of the p-band or d-band of the metal contained in the protective layer is advantageous in order to be a material applicable to the protective layer for preventing the growth of the dendrites generated by the accumulation of lithium atoms. This is because the electrons can be easily transferred to the ions, thereby improving reactivity with lithium ions.
  • the surface energy of the protective layer is relatively higher than that of lithium.
  • the lithium secondary battery negative electrode according to the present invention is a lithium metal layer; And a metal protective layer formed on at least one surface of the lithium metal layer,
  • the metal protective layer provides a negative electrode for a rechargeable lithium battery including a metal having a relative energy R E of greater than 0.132 according to Equation 1 below.
  • the metal protective layer may include a metal or a metal alloy.
  • the surface energy of the metal of the equation (1) and the p-band or d-band center of the metal can be obtained by the density function theory (density function theory).
  • E slab is the total energy of the slab
  • n is the number of atoms in the slab / the number of atoms of the unit cell
  • E bulk is the total energy of the bulk unit cell
  • A is the area of the slab surface.
  • GGA Generalized gradient approximation
  • PBE Perdew-Burke-Ernzerhof
  • the metal that can be applied to the protective layer of the lithium metal layer may have the outermost electrons located in the p orbitals or the d orbitals, respectively, depending on the atomic number, and when the outermost electrons of the metals are d-orbital electrons, such as transition metals, The band centers were calculated and the p-band centers were calculated when the outermost electrons of the metal, such as aluminum, were p-orbital electrons.
  • 7 shows a schematic diagram of the d-band center value of the metal applicable to the protective layer according to the density of states (DOS) of the metal slab model.
  • DOS density of states
  • FIG. 5 is a schematic diagram of calculation of lithium diffusion activation energy of a metal surface included in a protective layer according to the present invention.
  • one lithium atom is adsorbed to a surface having the lowest surface energy among various surfaces of the protective layer.
  • the energy of the initial state, transition state and final state is then optimized using the Generalized Gradient Approximation (GGA) -Perdew-Burke-Ernzerhof (PBE) and the Nudged elastic band method. Calculation of activation energy when lithium diffuses.
  • GGA Generalized Gradient Approximation
  • PBE Perdew-Burke-Ernzerhof
  • Table 1 shows the surface energy of the metals applicable to the protective layer, the lithium diffusion activation energy (E a ) of the metal surface, the absolute value of the center of the p-band or d-band of the metal and calculated according to Equation 1
  • the relative energy R E is calculated and shown.
  • the material suitable for the metal included in the protective layer applicable to the lithium metal anode according to the present invention should have a relative energy R E of greater than 0.132, which is the value of lithium metal, and among the 14 kinds of metals, It can be seen that Au, Ag, Co, Ni, Mg, Zn, and alloys thereof. Accordingly, one embodiment of the present invention consists of Al, Au, Ag, Co, Ni, Mg, Zn and alloys thereof. It may be a negative electrode for a lithium secondary battery to which a metal protective layer is applied, including any one or more selected from the group.
  • the metal protective layer according to the present invention may be formed by vacuum deposition, and more specifically any one of chemical vapor deposition (CVD), sputtering and evaporation may be used, but is not limited thereto. Do not.
  • the conditions for performing vacuum deposition can appropriately select any of the conventionally known conditions in consideration of the type of metal included in the protective layer used and the thickness of the metal protective layer to be deposited.
  • a sputtering method may be used to perform vacuum deposition of a metal material that may be applied to the protective layer according to the present invention on one surface of the lithium metal layer.
  • the protective layer provided in the present invention may have a thickness of 2 to 2,000 nm. If smaller than the above range, the function of the protective layer may be impaired, and if larger than the above range, the protective layer may act as a resistance and the performance of the battery may be deteriorated.
  • Lithium secondary battery according to the present invention can be manufactured through a known technique carried out by those skilled in the art for the remaining configuration except for the structure and characteristics of the above-described negative electrode, will be described in detail below.
  • the lithium secondary battery according to the present invention may be a secondary battery including a positive electrode, a negative electrode, and a separator interposed therebetween, the negative electrode may be the above-described negative electrode, and the metal protective layer included in the negative electrode faces the positive electrode. It can be formed on the side.
  • the positive electrode according to the present invention may be prepared in the form of a positive electrode by forming a composition comprising a positive electrode active material, a conductive material and a binder on a positive electrode current collector.
  • the conductive material is a component for further improving the conductivity of the positive electrode active material.
  • the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and Super-P; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.
  • the binder holds a positive electrode active material in a positive electrode current collector and has a function of organically connecting the positive electrode active materials.
  • a positive electrode active material for example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and carboxymethyl cellulose ( CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine Rubber or various copolymers thereof.
  • PVDF polyvinylidene fluoride
  • PVA polyvinyl alcohol
  • CMC carboxymethyl cellulose
  • EPDM ethylene-propylene-diene polymer
  • sulfonated-EPDM styrene-butadiene rubber
  • fluorine Rubber or various copolymers thereof.
  • the positive electrode current collector is the same as described above in the negative electrode current collector, and generally, a thin aluminum plate may be used for the positive electrode current collector.
  • the positive electrode composition may be coated on a positive electrode current collector using a conventional method known in the art, and for example, a spin method, a dipping method, a spray method, a roll court ), A gravure printing method, a bar court method, a die coating method, a comma coating method or a mixture thereof can be used.
  • the positive electrode and the positive electrode composition which have undergone such a coating process are then dried through evaporation of a solvent or a dispersion medium, compactness of the coating film and adhesion between the coating film and the current collector. At this time, the drying is carried out according to a conventional method, which is not particularly limited.
  • the separator according to the present invention is not particularly limited in material, and physically separates the positive electrode and the negative electrode, and has electrolyte and ion permeability, and can be used without particular limitation as long as they are commonly used as separators in electrochemical devices.
  • a porous, non-conductive or insulating material it is particularly desirable to have a low resistance to ionic migration of the electrolyte and excellent electrolyte-wetting ability.
  • a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto.
  • polyolefin-based porous membrane examples include polyethylene, polypropylene, polybutylene, polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, respectively, or a mixture thereof There is a curtain.
  • the nonwoven fabric is, for example, polyphenylene oxide, polyimide, polyamide, polycarbonate, polyethyleneterephthalate, polyethylenenaphthalate in addition to the above-described polyolefin-based nonwoven fabric.
  • Polybutyleneterephthalate, polyphenylenesulfide, polyacetal, polyethersulfone, polyetheretherketone, polyester, etc. alone or in combination
  • a nonwoven fabric formed of a polymer mixed therewith is possible, and the nonwoven fabric is a fiber form forming a porous web, and includes a spunbond or meltblown form made of long fibers.
  • the thickness of the separator is not particularly limited, but is preferably in the range of 1 to 100 ⁇ m, more preferably in the range of 5 to 50 ⁇ m. When the thickness of the separator is less than 1 ⁇ m, mechanical properties may not be maintained, and when the thickness of the separator is more than 100 ⁇ m, the separator may act as a resistance layer, thereby degrading battery performance.
  • the pore size and porosity of the separation membrane is not particularly limited, but the pore size is 0.1 to 50 ⁇ m, porosity is preferably 10 to 95%. If the pore size of the separator is less than 0.1 ⁇ m or porosity less than 10%, the separator acts as a resistive layer, mechanical properties cannot be maintained when the pore size exceeds 50 ⁇ m or porosity exceeds 95% .
  • the electrolyte applicable in the present invention may be a nonaqueous electrolyte or a solid electrolyte which does not react with lithium metal, but is preferably a nonaqueous electrolyte and includes an electrolyte salt and an organic solvent.
  • the electrolyte salt contained in the nonaqueous electrolyte is a lithium salt.
  • the lithium salt may be used without limitation those conventionally used in the lithium secondary battery electrolyte.
  • For example is the above lithium salt anion F -, Cl -, Br - , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 - , (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C - from the group consisting of -, CF 3 (CF
  • organic solvent included in the nonaqueous electrolyte those conventionally used in the lithium secondary battery electrolyte may be used without limitation.
  • carbonate compounds which are typically cyclic carbonates, linear carbonates, or mixtures thereof may be included.
  • cyclic carbonate compound examples include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and any one selected from the group consisting of halides thereof or mixtures of two or more thereof.
  • halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.
  • linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Mixtures of two or more of them may be representatively used, but are not limited thereto.
  • ethylene carbonate and propylene carbonate which are cyclic carbonates among the carbonate-based organic solvents, have high dielectric constants and can dissociate lithium salts in the electrolyte better.
  • the cyclic carbonates such as dimethyl carbonate and diethyl carbonate
  • any 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 may be used. It is not limited to this.
  • esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, ⁇ -valerolactone, ⁇ -caprolactone, ⁇ Any one or a mixture of two or more selected from the group consisting of -valerolactone and ⁇ -caprolactone may be used, but is not limited thereto.
  • the injection of the nonaqueous electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and the required physical properties of the final product. That is, it may be applied before the electrochemical device assembly or the final step of the electrochemical device assembly.
  • the lithium secondary battery according to the present invention may be a lamination (stacking) and folding (folding) process of the separator and the electrode in addition to the winding (winding) which is a general process.
  • the battery case may have a cylindrical shape, a square shape, a pouch type, or a coin type.
  • the lithium secondary battery including a negative electrode for a lithium secondary battery provided by the present invention may be a lithium metal battery, a lithium-sulfur battery or an all-solid-state battery.
  • the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention ratio, and therefore, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (HEVs). It is useful for the field of electric vehicles such as).
  • a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.
  • the battery module or battery pack includes a power tool; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.
  • EVs electric vehicles
  • PHEVs plug-in hybrid electric vehicles
  • a positive electrode was prepared using LCO (LiCoO 2 ) as the positive electrode active material.
  • a lithium metal having a thickness of 20 ⁇ m on a copper (Cu) thin film which is a negative electrode current collector having a thickness of 10 ⁇ m
  • sputtering aluminum (Al) to form an aluminum protective layer having a thickness of 20 nm on the lithium metal was manufactured by performing a roll press.
  • Lithium secondary battery was prepared by injecting a non-aqueous electrolyte solution into which LiPF 6 1.0M was added as a lithium salt.
  • a lithium secondary battery was manufactured in the same manner as in Example 1, except that the protective layer of lithium metal was not formed in Example 1.
  • a lithium secondary battery was manufactured in the same manner as in Example 1, except that indium (In) was used instead of aluminum as the protective layer in Example 1.

Abstract

The present invention pertains to: a negative electrode including an electrode protective layer; and a lithium secondary battery including same. The negative electrode including the protective layer can suppress the growth of lithium dendrites on the surface of the electrode while effectively transferring lithium ions to a lithium metal electrode, and has excellent ionic conductivity. The protective layer containing a protective material does not itself act as a resistive layer, such that overvoltage does not occur during charging and discharging. Accordingly, a degradation in battery performance is prevented, and stability during battery operation can be ensured.

Description

전극 보호층을 포함하는 음극 및 이를 적용한 리튬 이차전지Anode including an electrode protective layer and a lithium secondary battery using the same
본 출원은 2018년 5월 14일자 한국 특허 출원 제10-2018-0054785호에 기초한 우선권의 이익을 주장하며, 해당 한국 특허 출원의 문헌에 개시된 모든 내용은 본 명세서의 일부로서 포함된다.This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0054785 dated May 14, 2018, and all content disclosed in the literature of that Korean patent application is incorporated as part of this specification.
본 발명은 전극 보호층을 포함하는 음극 및 이를 적용한 리튬 이차전지에 관한 것으로, 보다 상세하게는 코팅층을 이루는 금속의 표면에너지와 리튬의 활성화 에너지를 고려하여 리튬 덴드라이트(dendrite)의 성장을 효과적으로 억제할 수 있는 보호 물질을 포함하는 음극 및 이를 적용한 리튬 이차전지에 관한 것이다.The present invention relates to a negative electrode including an electrode protective layer and a lithium secondary battery using the same, and more particularly, to effectively inhibit the growth of lithium dendrite in consideration of the surface energy of the metal constituting the coating layer and the activation energy of lithium. The present invention relates to a negative electrode including a protective material that can be used, and a lithium secondary battery using the same.
최근 에너지 저장 기술에 대한 관심이 갈수록 높아지고 있다. 휴대폰, 캠코더 및 노트북 PC, 나아가서는 전기 자동차의 에너지까지 적용분야가 확대되면서 전기화학소자의 연구와 개발에 대한 노력이 점점 구체화되고 있다.Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete.
전기화학소자는 이러한 측면에서 가장 주목을 받고 있는 분야이고 그 중에서도 충·방전이 가능한 이차전지의 개발은 관심의 초점이 되고 있으며, 최근에는 이러한 전지를 개발함에 있어서 용량 밀도 및 에너지 효율을 향상시키기 위하여 새로운 전극과 전지의 설계에 대한 연구 개발로 진행되고 있다.The electrochemical device is the field that is receiving the most attention in this respect, and the development of a secondary battery that can be charged and discharged among them is the focus of attention, and in recent years to improve the capacity density and energy efficiency in developing such a battery R & D on the design of new electrodes and batteries is ongoing.
현재 적용되고 있는 이차전지 중에서 1990년대 초에 개발된 리튬 이차전지는 수용액 전해액을 사용하는 Ni-MH, Ni-Cd, 황산-납 전지 등의 재래식 전지에 비해서 작동 전압이 높고 에너지 밀도가 월등히 크다는 장점으로 각광을 받고 있다. Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.
리튬 이차전지는 양극, 음극 및 상기 양극과 상기 음극 사이에 개재된 분리막을 포함하는 전극 조립체가 적층 또는 권취된 구조를 가지며, 이 전극 조립체가 전지케이스에 내장되고 그 내부에 비수 전해액이 주입됨으로써 구성된다. 상기 리튬 이차전지는 리튬 이온이 양극 및 음극에서 삽입/탈리될 때의 산화, 환원 반응에 의해 전기 에너지를 생산한다. The 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 stacked or wound, and the electrode assembly is embedded in a battery case and a nonaqueous electrolyte is injected into the lithium secondary battery. do. The lithium secondary battery produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.
통상 리튬 이차전지의 음극은 리튬 금속, 탄소 등이 활물질로 사용되며, 양극은 리튬 산화물, 전이금속 산화물, 금속 칼코겐 화합물, 전도성 고분자 등이 활물질로 사용된다. 이중 리튬 금속을 음극으로 사용한 리튬 이차전지는 대부분 구리 집전체 상에 리튬 호일을 부착하거나 리튬 금속 시트 자체를 전극으로 사용한다. 리튬 금속은 전위가 낮고 용량이 커서 고용량의 음극 소재로 큰 관심을 받고 있다.In general, lithium metal, carbon, and the like are used as active materials for a negative electrode of a lithium secondary battery, and lithium oxide, transition metal oxide, metal chalcogenide, conductive polymer, and the like are used as active materials for a positive electrode. Most lithium secondary batteries using lithium metal as a negative electrode attach lithium foil on a copper current collector or use a lithium metal sheet itself as an electrode. Lithium metal has attracted great attention as a high capacity cathode material due to its low potential and large capacity.
리튬 금속을 음극으로 사용할 경우 전지 구동시 여러 가지 요인으로 인하여 리튬 금속 표면에 전자 밀도 불균일화가 일어날 수 있다. 이에 전극 표면에 나뭇가지 형태의 리튬 덴드라이트가 생성되어 전극 표면에 돌기가 형성 또는 성장하여 전극 표면이 매우 거칠어진다. 이러한 리튬 덴드라이트는 전지의 성능저하와 함께 심각한 경우 분리막의 손상 및 전지의 단락(short circuit)을 유발한다. 그 결과, 전지 내 온도가 상승하여 전지의 폭발 및 화재의 위험성이 있다.When lithium metal is used as a negative electrode, electron density nonuniformity may occur on the surface of lithium metal due to various factors when the battery is driven. The lithium dendrite in the form of twigs is formed on the surface of the electrode, so that protrusions are formed or grown on the surface of the electrode, thereby making the electrode surface very rough. These lithium dendrites, along with deterioration of the cell, cause severe damage to the separator and short circuit of the cell. As a result, there is a risk of explosion and fire of the battery due to an increase in the battery temperature.
이를 해결하기 위해 현재 리튬 금속층에 폴리머 보호층 또는 무기 고체 보호층을 도입하거나, 전해액의 염의 농도를 높이거나 적절한 첨가제의 적용하는 연구가 진행되었다. 하지만 이러한 연구들의 리튬 덴드라이트 억제 효과는 미미한 실정이다. 따라서 리튬 금속 음극의 보호물질을 적용하여 문제를 해결하는 것이 효과적인 대안이 될 수 있다.In order to solve this problem, a research has been conducted to introduce a polymer protective layer or an inorganic solid protective layer to the lithium metal layer, increase the salt concentration of an electrolyte solution, or apply an appropriate additive. However, the effects of these studies on lithium dendrites are insignificant. Therefore, solving the problem by applying a protective material of the lithium metal anode may be an effective alternative.
상술한 바와 같이, 리튬 이차전지의 리튬 덴드라이트는 음극 표면에서 석출되고, 이로 인해 셀의 부피 팽창을 초래하기도 한다. 이에 본 발명자는 다각적으로 연구를 수행한 결과, 이러한 덴드라이트로 인한 문제를 리튬 금속 음극의 보호물질의 적용을 통해 해결할 수 있는 방법을 알아내고 본 발명을 완성하였다.As described above, lithium dendrites of the lithium secondary battery are precipitated on the surface of the negative electrode, thereby causing volume expansion of the cell. Accordingly, the present inventors have conducted various studies, and have found a way to solve the problem caused by the dendrite through the application of the protective material of the lithium metal negative electrode and completed the present invention.
따라서 본 발명의 목적은 리튬 금속 음극의 보호물질의 적용을 통해 리튬 덴드라이트로 인한 셀의 부피팽창 문제를 해결하고, 전지 성능이 향상된 리튬 이차전지를 제공하는 것이다.Accordingly, an object of the present invention is to solve the problem of volume expansion of a cell due to lithium dendrite by applying a protective material of a lithium metal negative electrode, and to provide a lithium secondary battery having improved battery performance.
상기 목적을 달성하기 위해, 본 발명은,In order to achieve the above object, the present invention,
리튬 금속층; 및Lithium metal layer; And
상기 리튬 금속층의 적어도 일면에 형성되는 금속 보호층을 포함하며,It includes a metal protective layer formed on at least one surface of the lithium metal layer,
상기 금속 보호층은 하기 수학식 1에 따른 상대 에너지인 RE 값이 0.132 를 초과하는 금속을 포함하는 것인 리튬 이차전지용 음극을 제공한다.The metal protective layer provides a negative electrode for a rechargeable lithium battery including a metal having a relative energy R E of greater than 0.132 according to Equation 1 below.
[수학식 1][Equation 1]
Figure PCTKR2019004760-appb-I000001
Figure PCTKR2019004760-appb-I000001
본 발명의 일 구체예는 상기 금속 보호층이 금속 또는 금속 합금을 포함하는 것이다.One embodiment of the present invention is that the metal protective layer comprises a metal or a metal alloy.
본 발명의 일 구체예는 상기 금속 보호층이 Al, Au, Ag, Co, Ni, Mg, Zn 및 이들의 합금으로 이루어진 군으로부터 선택된 어느 하나 이상을 포함하는 것이다.One embodiment of the present invention is that the metal protective layer includes any one or more selected from the group consisting of Al, Au, Ag, Co, Ni, Mg, Zn and alloys thereof.
본 발명의 일 구체예는 상기 수학식 1의 금속의 표면에너지 및 금속의 p-밴드 또는 d-밴드 중심을 범밀도 함수론(density function theory)으로 구하는 것이다.One embodiment of the present invention is to obtain the surface energy of the metal of the equation (1) and the p-band or d-band center of the metal by the density function theory (density function theory).
본 발명의 일 구체예는 상기 보호층의 두께가 2 내지 2,000 nm 인 것이다.In one embodiment of the present invention, the protective layer has a thickness of 2 to 2,000 nm.
본 발명의 일 구체예는 상기 리튬 금속층이 집전체 상에 리튬 금속 박막이 형성된 것이다.In one embodiment of the present invention, the lithium metal layer is a lithium metal thin film formed on the current collector.
본 발명의 일 구체예는 상기 집전체가 구리, 알루미늄, 스테인리스스틸, 아연, 티타늄, 은, 팔라듐, 니켈, 철, 크롬, 이들의 합금 및 이들의 조합으로 이루어진 군으로부터 선택된 어느 하나 이상을 포함하는 것이다.One embodiment of the present invention the current collector comprises any one or more selected from the group consisting of copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. will be.
또한 본 발명은, In addition, the present invention,
양극, 음극 및 이들 사이에 개재되는 분리막을 포함하는 리튬 이차전지에 있어서, 상기 음극은 상술한 리튬 이차전지용 음극인 리튬 이차전지를 제공한다.In a lithium secondary battery comprising a positive electrode, a negative electrode and a separator interposed therebetween, the negative electrode provides a lithium secondary battery which is the negative electrode for the lithium secondary battery described above.
본 발명의 일 구체예는 상기 음극이 양극과 대향하는 면에 금속 보호층이 형성된 것이다.In one embodiment of the present invention, a metal protective layer is formed on a surface of the cathode opposite to the anode.
본 발명에 따른 전극 보호물질을 포함하는 음극은, 음극 표면에서 리튬 덴드라이트가 성장하는 것을 억제하는 동시에 리튬 이온을 리튬 금속 전극으로 효과적으로 전달할 수 있고 이온 전도성이 우수하여, 보호물질을 포함하는 보호층 자체가 저항층으로 작용하지 않아 충방전시 과전압이 걸리지 않으므로 전지의 성능 저하를 방지하고 및 전지 구동시 안정성을 확보할 수 있다.The negative electrode including the electrode protective material according to the present invention, while suppressing the growth of lithium dendrites on the surface of the negative electrode and can effectively transfer lithium ions to the lithium metal electrode and excellent ion conductivity, a protective layer comprising a protective material Since it does not act as a resistive layer and does not take overvoltage during charging and discharging, it is possible to prevent performance degradation of the battery and to ensure stability when driving the battery.
따라서, 본 발명에서 제시한 전극 보호물질을 포함하는 리튬 전극은 리튬 이차전지의 음극으로 바람직하게 적용 가능하며, 이는 다양한 장치, 일례로 리튬 금속을 음극으로 사용한 대부분의 소형 전자기기에서부터 대용량 에너지 저장 장치 등에 적용 가능하다.Therefore, the lithium electrode including the electrode protection material proposed in the present invention is preferably applicable as a negative electrode of a lithium secondary battery, which is a large-capacity energy storage device from most small electronic devices using a variety of devices, for example lithium metal as a negative electrode Applicable to the back.
도 1은 본 발명의 일 실시예에 따른 리튬 이차전지용 음극의 단면도이다.1 is a cross-sectional view of a negative electrode for a rechargeable lithium battery according to one embodiment of the present invention.
도 2는 리튬 이차전지의 음극의 단면도 및 리튬 덴드라이트 이미지를 나타낸 것이다.2 illustrates a cross-sectional view of a negative electrode of a lithium secondary battery and an image of lithium dendrites.
도 3은 각 물질의 표면에서 리튬의 확산 에너지 장벽을 나타낸 그래프이다.3 is a graph showing the diffusion energy barrier of lithium at the surface of each material.
도 4는 본 발명의 일 실시예에 따라 리튬 덴드라이트가 형성되지 않고 보호층의 표면에서 리튬의 확산을 용이하게 하는 보호층이 형성된 리튬 이차전지 음극의 모식도를 나타낸 것이다.4 is a schematic view of a lithium secondary battery negative electrode having a protective layer having a protective layer that facilitates diffusion of lithium on the surface of the protective layer without forming lithium dendrites according to an embodiment of the present invention.
도 5는 본 발명에 따른 보호층의 금속 표면에서의 리튬 확산 활성화 에너지(Ea)의 계산 과정에 관한 모식도를 나타낸 것이다.5 shows a schematic diagram of a calculation process of lithium diffusion activation energy E a on the metal surface of the protective layer according to the present invention.
도 6은 본 발명에 따른 보호층에 포함되는 금속 또는 금속 합금의 슬래브 모델(slab model)의 모식도를 나타낸 것이다.Figure 6 shows a schematic diagram of a slab model (slab model) of the metal or metal alloy included in the protective layer according to the present invention.
도 7은 본 발명에 따른 보호층에 포함되는 금속 또는 금속 합금의 슬래브 모델의 DOS(density of states)를 나타낸 것이다.Figure 7 shows the density of states (DOS) of the slab model of the metal or metal alloy included in the protective layer according to the present invention.
이하, 본 발명이 속하는 기술 분야에서 통상의 지식을 가진 자가 용이하게 실시할 수 있도록 첨부한 도면을 참고로 하여 상세히 설명한다. 그러나 본 발명은 여러 가지 상이한 형태로 구현될 수 있으며, 본 명세서에 한정되지 않는다.Hereinafter, with reference to the accompanying drawings to be easily carried out by those skilled in the art will be described in detail. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the scope of the present invention.
도면에서는 본 발명을 명확하게 설명하기 위해서 설명과 관계없는 부분을 생략하였고, 명세서 전체를 통해 유사한 부분에 대해서는 유사한 도면 부호를 사용하였다. 또한, 도면에서 표시된 구성요소의 크기 및 상대적인 크기는 실제 축척과는 무관하며, 설명의 명료성을 위해 축소되거나 과장된 것일 수 있다.In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification. In addition, the size and relative size of the components shown in the drawings are not related to the actual scale, may be reduced or exaggerated for clarity of description.
본 명세서 및 청구범위에 사용된 용어나 단어는 통상적이거나 사전적인 의미로 한정해서 해석되어서는 아니되며, 발명자는 그 자신의 발명을 가장 최선의 방법으로 설명하기 위해 용어의 개념을 적절하게 정의할 수 있다는 원칙에 입각하여 본 발명의 기술적 사상에 부합하는 의미와 개념으로 해석되어야만 한다.The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.
본 발명은 도 1에 도시된 바와 같이, 리튬 금속층(120) 및 상기 리튬 금속층의 적어도 일면에 형성되는 금속 보호층(110)을 포함하며, 상기 금속 보호층은 하기 수학식 1에 따른 상대 에너지인 RE 값이 0.132 를 초과하는 금속을 포함하는 것인 리튬 이차전지용 음극 (100)을 제공한다. As shown in FIG. 1, the present invention includes a lithium metal layer 120 and a metal protective layer 110 formed on at least one surface of the lithium metal layer, wherein the metal protective layer is a relative energy according to Equation 1 below. Provided is a negative electrode 100 for a lithium secondary battery, wherein the R E value includes a metal of more than 0.132.
[수학식 1][Equation 1]
Figure PCTKR2019004760-appb-I000002
Figure PCTKR2019004760-appb-I000002
본 발명에 따른 보호층은 금속의 표면에너지와 리튬 확산 에너지 및 금속의 p-밴드 또는 d-밴드 중심을 고려한 상대 에너지 값이 0.132를 초과하는 금속을 포함함으로써 덴드라이트(dendrite) 형상의 리튬 석출을 막을 수 있고, 동시에 전해액 등으로부터 리튬 금속 음극을 보호하여 전기화학적인 충/방전이 보다 안정적이고 사이클 성능 개선 효과가 극대화된 리튬 이차전지를 구현할 수 있다.The protective layer according to the present invention includes a metal having a relative energy value of more than 0.132 in consideration of the surface energy of the metal, the lithium diffusion energy, and the metal p-band or d-band center, thereby preventing dendrite-shaped lithium precipitation. The lithium secondary battery can be prevented, and at the same time, the lithium metal negative electrode is protected from the electrolyte and the electrochemical charge / discharge is more stable and the lithium secondary battery can maximize the cycle performance improvement effect.
이하 본 발명의 리튬 이차전지용 음극을 구성하는 리튬 금속층, 금속 보호층 및 이를 적용한 리튬 이차전지에 대하여 상세히 설명한다.Hereinafter, the lithium metal layer, the metal protective layer, and the lithium secondary battery to which the same constitute the negative electrode for a lithium secondary battery of the present invention will be described in detail.
리튬 금속층Lithium metal layer
일반적으로 리튬 금속을 전지 음극으로 이용하는 경우 다음과 같은 문제가 존재한다. 첫째, 리튬은 알칼리 금속으로서 물과 폭발적으로 반응하므로 일반적인 환경에서 제조 및 이용이 어렵다. 둘째, 리튬을 음극으로 사용할 경우 전해질이나 물, 전지 내의 불순물, 리튬염 등과 반응하여 부동태층을 만들게 되고, 이 층은 국부적인 전류밀도 차이를 초래하여 수지상의 리튬 덴드라이트를 형성시킨다. 또한, 이렇게 형성된 덴드라이트는 성장하여 분리막의 공극 사이를 넘어 양극과 직접적인 내부 단락을 일으킬 수 있으므로 전지가 폭발하는 현상을 초래하게 된다. 셋째, 리튬은 부드러운 금속이며 기계적 강도가 약해서 추가적인 표면처리 없이 사용하기엔 취급성이 매우 떨어진다.In general, when lithium metal is used as a battery negative electrode, the following problems exist. First, lithium is an alkali metal and explosively reacts with water, making it difficult to manufacture and use in a general environment. Second, when lithium is used as a negative electrode, a passivation layer is formed by reacting with electrolyte, water, impurities in a battery, lithium salt, and the like, which causes local current density difference to form dendritic lithium dendrite. 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, causing the battery to explode. Third, lithium is a soft metal and its mechanical strength is low, so its handling is very poor for use without additional surface treatment.
본 발명에 따른 리튬 금속층은 리튬 금속판이거나, 음극 집전체 상에 리튬 금속 박막이 형성된 금속판일 수 있다. 이때 리튬 금속 박막의 형성방법은 특별히 제한되지 않으며, 공지의 금속박막 형성방법인 라미네이션법, 스퍼터링법 등이 이용될 수 있다. 또한, 집전체에 리튬 박막이 없는 상태로 전지를 조립한 후 초기 충전에 의해 금속판 상에 금속 리튬 박막이 형성되는 경우도 본 발명의 리튬 금속판에 포함된다.The lithium metal layer according to the present invention may be a lithium metal plate or a metal plate on which a lithium metal thin film is formed on a negative electrode current collector. At this time, the method of forming the lithium metal thin film is not particularly limited, and a lamination method, a sputtering method, and the like, which are known metal thin film formation methods, may be used. The lithium metal plate of the present invention also includes a case where a metal lithium thin film is formed on a metal plate by initial charging after assembling a battery without a lithium thin film in a current collector.
상기 음극 집전체는 전지에 화학적 변화를 유발하지 않으면서 높은 도전성을 가지는 것이라면 특히 제한하지 않으며, 구리, 알루미늄, 스테인리스스틸, 아연, 티타늄, 은, 팔라듐, 니켈, 철, 크롬, 이들의 합금 및 이들의 조합으로 이루어진 군으로부터 선택될 수 있다. 상기 스테인리스스틸은 카본, 니켈, 티탄 또는 은으로 표면 처리될 수 있으며, 상기 합금으로는 알루미늄-카드뮴 합금을 사용할 수 있고, 그 외에도 소성 탄소, 도전재로 표면 처리된 비전도성 고분자, 또는 전도성 고분자 등을 사용할 수도 있다. 일반적으로 음극 집전체로는 구리 박판을 적용한다. The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and these It can be selected from the group consisting of a combination of. The stainless steel may be surface-treated with carbon, nickel, titanium, or silver, and the alloy may be an aluminum-cadmium alloy. In addition, the non-conductive polymer or the conductive polymer surface-treated with a fired carbon, a conductive material, or the like may be used. You can also use Generally, a thin copper plate is used as the negative electrode current collector.
상기 리튬 금속판은 전극 제조에 용이하도록 전극 형태에 따라 폭이 조절될 수 있다. 리튬 금속판의 두께는 10 내지 300 ㎛일 수 있다.The lithium metal plate may be adjusted in width depending on the shape of the electrode to facilitate electrode production. The thickness of the lithium metal plate may be 10 to 300 μm.
금속 보호층Metal protective layer
본 출원인은 기존의 리튬 이차 전지의 단점으로 지적되던 리튬 덴드라이트 석출에 관한 문제(도 2 참조)를 해결하고자 이를 리튬 덴드라이트 생성원리의 측면에서 접근하여 본 발명을 완성하게 되었다.Applicant has completed the present invention by approaching this in terms of the lithium dendrite generation principle to solve the problem (see Fig. 2) related to the lithium dendrite precipitation that was pointed out as a disadvantage of the conventional lithium secondary battery.
일반적으로 리튬 이차전지에서 리튬 금속 음극의 표면에 보호층이 없는 경우, 전지의 충방전 과정에서 리튬 양이온이 리튬 금속의 표면에서 환원되면서 덴드라이트 형상을 가지는 등, 비정상적인 형상으로 석출되어 전지의 분리막을 뚫고 전지의 양극과 접촉하여 내부 단락을 일으키는 문제점이 있다.In general, in a lithium secondary battery, when there is no protective layer on the surface of the lithium metal negative electrode, lithium cations are reduced on the surface of the lithium metal in the process of charging and discharging the battery, and thus have a dendrite shape. It penetrates and contacts the positive electrode of the battery, causing a problem of internal short circuit.
기존에는 리튬 이차 전지의 문제점인 리튬 덴드라이트의 문제를 해결하기 위해 보호층에서의 리튬 확산에너지만을 고려하여 인듐 금속 등을 적용한 In-Li Hybrid 전극 등을 제안하였다. (도 3)Conventionally, in order to solve the problem of lithium dendrites, which is a problem of lithium secondary batteries, an In-Li hybrid electrode using indium metal or the like is proposed in consideration of only lithium diffusion energy in a protective layer. (Figure 3)
그러나 리튬이 리튬 금속 보호층 표면에서 확산할 때 그 활성화에너지(Ea)가 낮으면 보호층 표면에서 리튬의 이동이 쉬워 덴드라이트 성장을 막을 수 있지만, 음극 표면에서 계속적인 리튬의 석출을 고려한다면 보호층 물질의 리튬과의 반응성과 보호층 표면에너지도 중요한 인자가 된다. 전해질을 통해 이동해 온 리튬 이온이 보호층에 포함된 금속 물질로부터 전자를 받아 리튬 금속으로 잘 환원되어야 하며, 환원으로 석출된 리튬 원자가 리튬 음극이 아닌 보호층의 표면에 먼저 흡착되기 위해서는 보호층에 포함된 금속 표면에너지가 리튬 금속 음극의 표면에너지 보다 높아야 하기 때문이다. (도 4)However, when lithium diffuses from the surface of the lithium metal protective layer, if its activation energy (E a ) is low, the movement of lithium on the surface of the protective layer is easy to prevent dendrite growth, but considering continuous precipitation of lithium on the surface of the negative electrode, The reactivity of the protective layer material with lithium and the protective layer surface energy are also important factors. Lithium ions that have migrated through the electrolyte must receive electrons from the metal material contained in the protective layer and be reduced to lithium metal. The lithium atoms deposited by reduction are included in the protective layer in order to be first adsorbed onto the surface of the protective layer instead of the lithium negative electrode. This is because the surface energy of the metal should be higher than that of the lithium metal anode. (Figure 4)
따라서 리튬 원자들이 쌓여서 생성되는 덴드라이트의 성장을 방지하기 위한 보호층에 적용 가능한 물질이 되기 위해서는 보호층에 포함된 금속의 p-밴드 혹은 d-밴드 중심의 절대값이 작을 수록 유리하며, 이는 리튬이온에 전자를 쉽게 전달할 수 있어 리튬 이온과의 반응성이 우수해질 수 있기 때문이다. 또한 환원된 리튬 금속이 보호층의 표면에 우선 흡착하기 위해서는 보호층의 표면에너지가 리튬의 표면에너지 보다 상대적으로 높은 것이 유리하며 흡착된 리튬이 보호층의 금속 표면에서 확산을 할 때 그 활성화에너지(Ea) 값이 낮을수록 리튬의 확산이 용이하게 된다. Therefore, the smaller the absolute value of the center of the p-band or d-band of the metal contained in the protective layer is advantageous in order to be a material applicable to the protective layer for preventing the growth of the dendrites generated by the accumulation of lithium atoms. This is because the electrons can be easily transferred to the ions, thereby improving reactivity with lithium ions. In addition, in order for the reduced lithium metal to adsorb to the surface of the protective layer first, it is advantageous that the surface energy of the protective layer is relatively higher than that of lithium. When the adsorbed lithium diffuses from the metal surface of the protective layer, the activation energy ( The lower the value of E a ), the easier the diffusion of lithium.
따라서 본 발명에 따른 리튬 이차전지용 음극은 리튬 금속층; 및 상기 리튬 금속층의 적어도 일면에 형성되는 금속 보호층을 포함하며,Therefore, the lithium secondary battery negative electrode according to the present invention is a lithium metal layer; And a metal protective layer formed on at least one surface of the lithium metal layer,
상기 금속 보호층은 하기 수학식 1에 따른 상대 에너지인 RE 값이 0.132 를 초과하는 금속을 포함하는 것인 리튬 이차전지용 음극을 제공한다.The metal protective layer provides a negative electrode for a rechargeable lithium battery including a metal having a relative energy R E of greater than 0.132 according to Equation 1 below.
[수학식 1][Equation 1]
Figure PCTKR2019004760-appb-I000003
Figure PCTKR2019004760-appb-I000003
이때, 상기 금속 보호층은 금속 또는 금속 합금을 포함할 수 있다.In this case, the metal protective layer may include a metal or a metal alloy.
본 발명의 일 실시예에 있어서, 상기 수학식 1의 금속의 표면에너지 및 금속의 p-밴드 또는 d-밴드 중심은 범밀도 함수론(density function theory)으로 구할 수 있다.In one embodiment of the present invention, the surface energy of the metal of the equation (1) and the p-band or d-band center of the metal can be obtained by the density function theory (density function theory).
먼저 금속의 표면에너지를 구하기 위해 금속 slab 모델을 형성한 뒤 하기의 식에 따라 계산을 진행하였다.First, a metal slab model was formed to obtain the surface energy of the metal, and then the calculation was performed according to the following equation.
[수학식 2][Equation 2]
Figure PCTKR2019004760-appb-I000004
Figure PCTKR2019004760-appb-I000004
도 6은 본 발명에 따른 보호층에 포함된 금속의 슬래브(slab) 모델에 관한 것으로, 상기 수학식 2에서 Eslab는 slab의 총 에너지, n은 slab 내의 원자수/ 유닛셀의 원자수, Ebulk는 벌크 유닛 셀의 총 에너지, 그리고 A는 slab 표면의 면적이다.6 is related to a slab model of a metal included in a protective layer according to the present invention, in which E slab is the total energy of the slab, n is the number of atoms in the slab / the number of atoms of the unit cell, E bulk is the total energy of the bulk unit cell, and A is the area of the slab surface.
범밀도 함수론 기반의 계산에서 보호층에 포함된 금속의 표면 slab 구조의 최적화를 수행하기 위해 일반 기울기 근사(GGA, generalized gradient approximation)-PBE(Perdew-Burke-Ernzerhof)를 사용하였으며, 상기 최적화된 금속 slab를 이용하여 보호층에 포함된 금속의 표면에너지 및 p-밴드 또는 d-밴드 중심값을 역시 상기 일반 기울기 근사를 사용하여 계산하였다. 리튬 금속층의 보호층에 적용될 수 있는 금속은 원자번호에 따라 최외각 전자가 각각 p 오비탈 또는 d 오비탈에 위치할 수 있으며, 이때 전이금속처럼 상기 금속의 최외각 전자가 d-오비탈 전자인 경우에는 d-밴드 중심값을 계산하였고, 알루미늄같이 금속의 최외각 전자가 p-오비탈 전자인 경우에는 p-밴드 중심값을 계산하였다. 도 7은 본 발명에 따른 보호층에 적용 가능한 금속의 d-밴드 중심값을 금속 slab 모델의 density of states(DOS)에 따라 그 모식도를 나타낸 것이다.Generalized gradient approximation (GGA) -Perdew-Burke-Ernzerhof (PBE) was used to perform optimization of the surface slab structure of the metals included in the protective layer in calculations based on the density density function. The slab was used to calculate the surface energy and p-band or d-band center values of the metals included in the protective layer using the general slope approximation as well. The metal that can be applied to the protective layer of the lithium metal layer may have the outermost electrons located in the p orbitals or the d orbitals, respectively, depending on the atomic number, and when the outermost electrons of the metals are d-orbital electrons, such as transition metals, The band centers were calculated and the p-band centers were calculated when the outermost electrons of the metal, such as aluminum, were p-orbital electrons. 7 shows a schematic diagram of the d-band center value of the metal applicable to the protective layer according to the density of states (DOS) of the metal slab model.
도 5는 본 발명에 따른 보호층에 포함된 금속 표면의 리튬 확산 활성화 에너지의 계산에 관한 모식도로써, 본 발명에서는 상기 보호층의 다양한 표면 중 표면에너지가 가장 낮은 표면에 리튬 원자 한 개를 흡착시킨 다음 초기 상태, 전이 상태, 최종 상태의 에너지를 상기의 일반 기울기 근사(GGA, generalized gradient approximation)-PBE(Perdew-Burke-Ernzerhof)를 사용하여 구조의 최적화를 수행하고, NEB 법(Nudged elastic band method)으로 리튬이 확산할 때의 활성화에너지를 계산하였다.FIG. 5 is a schematic diagram of calculation of lithium diffusion activation energy of a metal surface included in a protective layer according to the present invention. In the present invention, one lithium atom is adsorbed to a surface having the lowest surface energy among various surfaces of the protective layer. The energy of the initial state, transition state and final state is then optimized using the Generalized Gradient Approximation (GGA) -Perdew-Burke-Ernzerhof (PBE) and the Nudged elastic band method. Calculation of activation energy when lithium diffuses.
표 1은 상기 보호층에 적용할 수 있는 금속들의 표면에너지, 금속 표면의 리튬 확산 활성화 에너지(Ea), 금속의 p-밴드 또는 d-밴드 중심의 절대값 및 이를 상기 수학식 1에 따라 계산한 상대에너지인 RE를 계산하여 나타낸 것이다.Table 1 shows the surface energy of the metals applicable to the protective layer, the lithium diffusion activation energy (E a ) of the metal surface, the absolute value of the center of the p-band or d-band of the metal and calculated according to Equation 1 The relative energy R E is calculated and shown.
Ea[eV]E a [eV] 표면에너지[eV/Å2]Surface energy [eV / Å 2 ] |p- or d-band center|[eV]| p- or d-band center | [eV] RE R E
SnSn 0.2880.288 0.0140.014 12.5312.53 0.0040.004
SbSb 0.1550.155 0.0370.037 3.1973.197 0.0750.075
InIn 0.0950.095 0.0190.019 9.0159.015 0.0220.022
AlAl 0.0370.037 0.0490.049 1.3591.359 0.9740.974
AuAu 0.0370.037 0.0300.030 1.6851.685 0.4810.481
AgAg 0.020.02 0.0330.033 1.9161.916 0.8610.861
CoCo 0.0130.013 0.1160.116 1.3351.335 6.6846.684
NiNi 0.0110.011 0.1050.105 0.9210.921 10.36410.364
MgMg 0.0090.009 0.0340.034 0.0420.042 89.94789.947
ZnZn 0.0080.008 0.0110.011 4.1944.194 0.3280.328
Li [ref.]Li [ref.] 0.0140.014 0.030.03 16.293 [s-band center]16.293 [s-band center] 0.1320.132
상기 표 1에 따르면 본 발명에 따른 리튬 금속 음극에 적용 가능한 보호층에 포함되는 금속으로 적합한 물질은 상기 상대에너지인 RE 값이 리튬 금속의 값인 0.132 보다 커야 하고, 상기 14 종의 금속 중 Al, Au, Ag, Co, Ni, Mg, Zn 및 이들의 합금이 이에 해당됨을 알 수 있다.따라서 본 발명의 일 실시예는 Al, Au, Ag, Co, Ni, Mg, Zn 및 이들의 합금으로 이루어진 군으로부터 선택된 어느 하나 이상을 포함하는 것을 특징으로 하는 금속 보호층이 적용된 리튬 이차전지용 음극일 수 있다.According to Table 1, the material suitable for the metal included in the protective layer applicable to the lithium metal anode according to the present invention should have a relative energy R E of greater than 0.132, which is the value of lithium metal, and among the 14 kinds of metals, It can be seen that Au, Ag, Co, Ni, Mg, Zn, and alloys thereof. Accordingly, one embodiment of the present invention consists of Al, Au, Ag, Co, Ni, Mg, Zn and alloys thereof. It may be a negative electrode for a lithium secondary battery to which a metal protective layer is applied, including any one or more selected from the group.
본 발명에 따른 금속 보호층은 진공증착에 의해 형성될 수 있으며, 보다 구체적으로는 화학기상증착(CVD), 스퍼터링(sputtering) 및 이베퍼레이션(evaporation) 중 어느 하나를 이용할 수 있으나, 이제 제한되지 않는다. 진공증착을 수행하는 조건은 사용되는 보호층에 포함되는 금속의 종류 및 증착되는 금속 보호층의 두께를 고려하여 종래 공지인 임의의 조건을 적절히 선택할 수 있다. 일례로, 스퍼터링(sputtering) 방법을 이용하여 리튬 금속층의 일면에 본 발명에 따른 보호층에 적용될 수 있는 금속 물질의 진공 증착을 수행할 수 있다.The metal protective layer according to the present invention may be formed by vacuum deposition, and more specifically any one of chemical vapor deposition (CVD), sputtering and evaporation may be used, but is not limited thereto. Do not. The conditions for performing vacuum deposition can appropriately select any of the conventionally known conditions in consideration of the type of metal included in the protective layer used and the thickness of the metal protective layer to be deposited. For example, a sputtering method may be used to perform vacuum deposition of a metal material that may be applied to the protective layer according to the present invention on one surface of the lithium metal layer.
본 발명에서 제공하는 보호층은 그 두께가 2 내지 2,000 nm 일 수 있다. 만약 상기 범위보다 작을 경우, 보호층의 기능이 떨어질 수 있고, 상기 범위보다 클 경우에는 보호층이 저항으로 작용하여 전지의 성능이 저하될 수 있기 때문에, 상기 범위에서 적절히 선택할 수 있다.The protective layer provided in the present invention may have a thickness of 2 to 2,000 nm. If smaller than the above range, the function of the protective layer may be impaired, and if larger than the above range, the protective layer may act as a resistance and the performance of the battery may be deteriorated.
리튬 이차전지Lithium secondary battery
본 발명에 따른 리튬 이차전지는 전술한 음극의 구조 및 특성을 제외한 나머지 구성에 대해서는 통상의 당업자가 실시하는 공지된 기술을 통하여 제조 가능하며, 이하 구체적으로 설명한다.Lithium secondary battery according to the present invention can be manufactured through a known technique carried out by those skilled in the art for the remaining configuration except for the structure and characteristics of the above-described negative electrode, will be described in detail below.
본 발명에 따른 리튬 이차전지는 양극, 음극 및 이들 사이에 개재되는 분리막을 포함하는 이차 전지일 수 있고, 상기 음극은 전술한 음극일 수 있으며, 상기 음극에 포함된 금속 보호층은 양극과 대향하는 면에 형성될 수 있다.The lithium secondary battery according to the present invention may be a secondary battery including a positive electrode, a negative electrode, and a separator interposed therebetween, the negative electrode may be the above-described negative electrode, and the metal protective layer included in the negative electrode faces the positive electrode. It can be formed on the side.
본 발명에 따른 양극은 양극 활물질, 도전재 및 바인더를 포함하는 조성물을 양극 집전체에 제막하여 양극의 형태로 제조할 수 있다.The positive electrode according to the present invention may be prepared in the form of a positive electrode by forming a composition comprising a positive electrode active material, a conductive material and a binder on a positive electrode current collector.
상기 양극 활물질은 비제한적인 예로 LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiaCobMnc)O2(0<a<1, 0<b<1, 0<c<1, a+b+c=1), LiNi1-yCoyO2, LiCo1-yMnyO2, LiNi1-yMnyO2(O≤y<1), Li(NiaCobMnc)O4(0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn2-zNizO4, LiMn2-zCozO4(0<z<2), LiCoPO4 및 LiFePO4로 이루어진 군에서 선택되는 어느 하나 또는 이들 중 2종 이상의 혼합물을 사용할 수 있다. 또한, 이러한 산화물(oxide) 외에 황화물(sulfide), 셀렌화물(selenide) 및 할로겐화물(halide) 등도 사용할 수 있다. 더욱 바람직한 예에서, 상기 양극 활물질은 고출력 전지에 적합한 LiCoO2일 수 있다.Examples of the positive electrode active material include, but are not limited to, LiCoO 2 , LiNiO 2 , LiMnO 2 , LiMn 2 O 4 , Li (Ni a Co b Mn c ) O 2 (0 <a <1, 0 <b <1, 0 <c < 1, a + b + c = 1), LiNi 1-y Co y O 2 , LiCo 1-y Mn y O 2 , LiNi 1-y Mn y O 2 (O ≦ y <1), Li (Ni a Co b Mn c ) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2-z Ni z O 4 , LiMn 2-z Co z O Any one selected from the group consisting of 4 (0 <z <2), LiCoPO 4 and LiFePO 4 or a mixture of two or more thereof may be used. In addition to these oxides, sulfides, selenides and halides may also be used. In a more preferred example, the positive electrode active material may be LiCoO 2 suitable for a high power battery.
상기 도전재는 양극 활물질의 도전성을 더욱 향상시키기 위한 성분으로서, 비제한적인 예로, 천연 흑연이나 인조 흑연 등의 흑연; 카본블랙, 아세틸렌 블랙, 케첸 블랙, 채널 블랙, 퍼네이스 블랙, 램프 블랙, 서머 블랙, Super-P 등의 카본블랙; 탄소 섬유나 금속 섬유 등의 도전성 섬유; 불화 카본, 알루미늄, 니켈 분말 등의 금속 분말; 산화아연, 티탄산 칼륨 등의 도전성 위스커; 산화티탄 등의 도전성 금속 산화물; 폴리페닐렌 유도체 등의 도전성 소재 등이 사용될 수 있다.The conductive material is a component for further improving the conductivity of the positive electrode active material. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and Super-P; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.
상기 바인더는 양극 활물질을 양극 집전체에 유지시키고, 양극 활물질들 사이를 유기적으로 연결해주는 기능을 가지는 것으로서, 예컨대 폴리비닐리덴플로라이드(PVDF), 폴리비닐알코올(PVA), 카르복시메틸셀룰로우즈(CMC), 전분, 히드록시프로필셀룰로오즈, 재생 셀룰로오즈, 폴리비닐피롤리돈, 테트라플루오로에틸렌, 폴리에틸렌, 폴리프로필렌, 에틸렌-프로필렌-디엔 폴리머(EPDM), 술폰화-EPDM, 스티렌-부타디엔 고무, 불소 고무 또는 이들의 다양한 공중합체 등을 들 수 있다.The binder holds a positive electrode active material in a positive electrode current collector and has a function of organically connecting the positive electrode active materials. For example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and carboxymethyl cellulose ( CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine Rubber or various copolymers thereof.
상기 양극 집전체는 상기 음극 집전체에서 전술한 바와 같으며, 일반적으로 양극 집전체는 알루미늄 박판이 이용될 수 있다.The positive electrode current collector is the same as described above in the negative electrode current collector, and generally, a thin aluminum plate may be used for the positive electrode current collector.
상기 양극 조성물을 양극 집전체 상에 당업계에 알려진 통상의 방법을 이용하여 코팅할 수 있으며, 예를 들면 스핀(spin)법, 딥핑(dipping)법, 스프레이(spray)법, 롤 코트(roll court)법, 그라비아 인쇄법, 바코트(bar court)법, 다이(die) 코팅법, 콤마(comma) 코팅법 또는 이들의 혼합 방식 등 다양한 방식을 이용할 수 있다.The positive electrode composition may be coated on a positive electrode current collector using a conventional method known in the art, and for example, a spin method, a dipping method, a spray method, a roll court ), A gravure printing method, a bar court method, a die coating method, a comma coating method or a mixture thereof can be used.
이와 같은 코팅 과정을 거친 양극 및 양극 조성물은 이후 건조 과정을 통해 용매나 분산매의 증발, 코팅막의 조밀성 및 코팅막과 집전체와의 밀착성 등이 이루어진다. 이때 건조는 통상적인 방법에 따라 실시되며, 이를 특별히 제한하지 않는다.The positive electrode and the positive electrode composition which have undergone such a coating process are then dried through evaporation of a solvent or a dispersion medium, compactness of the coating film and adhesion between the coating film and the current collector. At this time, the drying is carried out according to a conventional method, which is not particularly limited.
본 발명에 따른 분리막은 특별히 그 재질을 한정하지 않으며, 양극과 음극을 물리적으로 분리하고, 전해질 및 이온 투과능을 갖는 것으로서, 통상적으로 전기화학소자에서 분리막으로 사용되는 것이라면 특별한 제한 없이 사용 가능하나, 다공성이고 비전도성 또는 절연성인 물질로서, 특히 전해액의 이온 이동에 대하여 저저항이면서 전해액 함습 능력이 우수한 것이 바람직하다. 예컨대 폴리올레핀계 다공성 막(membrane) 또는 부직포를 사용할 수 있으나, 이에 특별히 한정되는 것은 아니다.The separator according to the present invention is not particularly limited in material, and physically separates the positive electrode and the negative electrode, and has electrolyte and ion permeability, and can be used without particular limitation as long as they are commonly used as separators in electrochemical devices. As a porous, non-conductive or insulating material, it is particularly desirable to have a low resistance to ionic migration of the electrolyte and excellent electrolyte-wetting ability. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto.
상기 폴리올레핀계 다공성 막의 예로는, 고밀도 폴리에틸렌, 선형 저밀도 폴리에틸렌, 저밀도 폴리에틸렌, 초고분자량 폴리에틸렌과 같은 폴리에틸렌, 폴리프로필렌, 폴리부틸렌, 폴리펜텐 등의 폴리올레핀계 고분자를 각각 단독으로 또는 이들을 혼합한 고분자로 형성한 막을 들 수 있다.Examples of the polyolefin-based porous membrane, polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, respectively, or a mixture thereof There is a curtain.
상기 부직포는 전술한 폴리올레핀계 부직포 외에 예컨대, 폴리페닐렌옥사이드(polyphenyleneoxide), 폴리이미드(polyimide), 폴리아미드(polyamide), 폴리카보네이트(polycarbonate), 폴리에틸렌테레프탈레이트(polyethyleneterephthalate), 폴리에틸렌나프탈레이트(polyethylenenaphthalate), 폴리부틸렌테레프탈레이트(polybutyleneterephthalate), 폴리페닐렌설파이드(polyphenylenesulfide), 폴리아세탈(polyacetal), 폴리에테르설폰(polyethersulfone), 폴리에테르에테르케톤(polyetheretherketone), 폴리에스테르(polyester) 등을 각각 단독으로 또는 이들을 혼합한 고분자로 형성한 부직포가 가능하며, 이러한 부직포는 다공성 웹(web)을 형성하는 섬유 형태로서, 장섬유로 구성된 스펀본드(spunbond) 또는 멜트블로운(meltblown) 형태를 포함한다.The nonwoven fabric is, for example, polyphenylene oxide, polyimide, polyamide, polycarbonate, polyethyleneterephthalate, polyethylenenaphthalate in addition to the above-described polyolefin-based nonwoven fabric. , Polybutyleneterephthalate, polyphenylenesulfide, polyacetal, polyethersulfone, polyetheretherketone, polyester, etc., alone or in combination A nonwoven fabric formed of a polymer mixed therewith is possible, and the nonwoven fabric is a fiber form forming a porous web, and includes a spunbond or meltblown form made of long fibers.
상기 분리막의 두께는 특별히 제한되지는 않으나, 1 내지 100 ㎛ 범위가 바람직하며, 더욱 바람직하게는 5 내지 50 ㎛ 범위이다. 상기 분리막의 두께가 1 ㎛ 미만인 경우에는 기계적 물성을 유지할 수 없으며, 100 ㎛를 초과하는 경우에는 상기 분리막이 저항층으로 작용하게 되어 전지의 성능이 저하된다.The thickness of the separator is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm. When the thickness of the separator is less than 1 μm, mechanical properties may not be maintained, and when the thickness of the separator is more than 100 μm, the separator may act as a resistance layer, thereby degrading battery performance.
상기 분리막의 기공 크기 및 기공도는 특별히 제한되지는 않으나, 기공 크기는 0.1 내지 50 ㎛이고, 기공도는 10 내지 95%인 것이 바람직하다. 상기 분리막의 기공 크기가 0.1 ㎛ 미만이거나 기공도가 10% 미만이면 분리막이 저항층으로 작용하게 되며, 기공 크기가 50 ㎛를 초과하거나 기공도가 95%를 초과하는 경우에는 기계적 물성을 유지할 수 없다.The pore size and porosity of the separation membrane is not particularly limited, but the pore size is 0.1 to 50 ㎛, porosity is preferably 10 to 95%. If the pore size of the separator is less than 0.1 ㎛ or porosity less than 10%, the separator acts as a resistive layer, mechanical properties cannot be maintained when the pore size exceeds 50 ㎛ or porosity exceeds 95% .
본 발명에서 적용 가능한 전해질은 리튬 금속과 반응하지 않는 비수 전해액 또는 고체 전해질이 가능하나 바람직하게는 비수 전해질이고, 전해질 염 및 유기 용매를 포함한다.The electrolyte applicable in the present invention may be a nonaqueous electrolyte or a solid electrolyte which does not react with lithium metal, but is preferably a nonaqueous electrolyte and includes an electrolyte salt and an organic solvent.
상기 비수 전해액에 포함되는 전해질 염은 리튬염이다. 상기 리튬염은 리튬 이차전지용 전해액에 통상적으로 사용되는 것들이 제한 없이 사용될 수 있다. 예를 들어 상기 리튬염의 음이온으로는 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- 및 (CF3CF2SO2)2N-로 이루어진 군으로부터 선택 또는 이들 중 2종 이상을 포함할 수 있다.The electrolyte salt contained in the nonaqueous electrolyte is a lithium salt. The lithium salt may be used without limitation those conventionally used in the lithium secondary battery electrolyte. For example is the above lithium salt anion F -, Cl -, Br - , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 - , (CF 3 SO 2) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, ( CF 3 SO 2) 3 C - from the group consisting of -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and (CF 3 CF 2 SO 2) 2 N It may include a selection or two or more of these.
상기 비수 전해액에 포함되는 유기 용매로는 리튬 이차전지용 전해액에 통상적으로 사용되는 것들을 제한 없이 사용할 수 있으며, 예를 들면 에테르, 에스테르, 아미드, 선형 카보네이트, 환형 카보네이트 등을 각각 단독으로 또는 2종 이상 혼합하여 사용할 수 있다. 그 중에서 대표적으로는 환형 카보네이트, 선형 카보네이트, 또는 이들의 혼합물인 카보네이트 화합물을 포함할 수 있다.As the organic solvent included in the nonaqueous electrolyte, those conventionally used in the lithium secondary battery electrolyte may be used without limitation. Can be used. Among them, carbonate compounds which are typically cyclic carbonates, linear carbonates, or mixtures thereof may be included.
상기 환형 카보네이트 화합물의 구체적인 예로는 에틸렌 카보네이트(ethylene carbonate, EC), 프로필렌 카보네이트(propylene carbonate, PC), 1,2-부틸렌 카보네이트, 2,3-부틸렌 카보네이트, 1,2-펜틸렌 카보네이트, 2,3-펜틸렌 카보네이트, 비닐렌 카보네이트, 비닐에틸렌 카보네이트 및 이들의 할로겐화물로 이루어진 군에서 선택되는 어느 하나 또는 이들 중 2종 이상의 혼합물이 있다. 이들의 할로겐화물로는 예를 들면, 플루오로에틸렌 카보네이트(fluoroethylene carbonate, FEC) 등이 있으며, 이에 한정되는 것은 아니다.Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and any one selected from the group consisting of halides thereof or mixtures of two or more thereof. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.
또한 상기 선형 카보네이트 화합물의 구체적인 예로는 디메틸 카보네이트(DMC), 디에틸 카보네이트(DEC), 디프로필 카보네이트, 에틸메틸 카보네이트(EMC), 메틸프로필 카보네이트 및 에틸프로필 카보네이트로 이루어진 군에서 선택되는 어느 하나 또는 이들 중 2종 이상의 혼합물 등이 대표적으로 사용될 수 있으나, 이에 한정되는 것은 아니다.In addition, specific examples of the linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Mixtures of two or more of them may be representatively used, but are not limited thereto.
특히, 상기 카보네이트계 유기 용매 중 환형 카보네이트인 에틸렌 카보네이트 및 프로필렌 카보네이트는 고점도의 유기 용매로서 유전율이 높아 전해질 내의 리튬염을 보다 더 잘 해리시킬 수 있으며, 이러한 환형 카보네이트에 디메틸 카보네이트 및 디에틸 카보네이트와 같은 저점도, 저유전율 선형 카보네이트를 적당한 비율로 혼합하여 사용하면 보다 높은 전기 전도율을 갖는 전해액을 만들 수 있다.In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, have high dielectric constants and can dissociate lithium salts in the electrolyte better. The cyclic carbonates, such as dimethyl carbonate and diethyl carbonate By using a low viscosity, low dielectric constant linear carbonate mixed in an appropriate ratio it can be made an electrolyte having a higher electrical conductivity.
또한, 상기 유기 용매 중 에테르로는 디메틸 에테르, 디에틸 에테르, 디프로필 에테르, 메틸에틸 에테르, 메틸프로필 에테르 및 에틸프로필 에테르로 이루어진 군에서 선택되는 어느 하나 또는 이들 중 2종 이상의 혼합물을 사용할 수 있으나, 이에 한정되는 것은 아니다.In addition, as the ether in the organic solvent, any 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 may be used. It is not limited to this.
그리고 상기 유기 용매 중 에스테르로는 메틸 아세테이트, 에틸 아세테이트, 프로필 아세테이트, 메틸 프로피오 네이트, 에틸 프로피오네이트, 프로필 프로피오네이트, γ-부티로락톤, γ-발레로락톤, γ-카프로락톤, σ-발레로락톤 및 ε-카프로락톤으로 이루어진 군에서 선택되는 어느 하나 또는 이들 중 2종 이상의 혼합물을 사용할 수 있으나, 이에 한정되는 것은 아니다.And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ Any one or a mixture of two or more selected from the group consisting of -valerolactone and ε-caprolactone may be used, but is not limited thereto.
상기 비수 전해액의 주입은 최종 제품의 제조 공정 및 요구 물성에 따라, 전기화학소자의 제조 공정 중 적절한 단계에서 행해질 수 있다. 즉, 전기화학소자 조립 전 또는 전기화학소자 조립 최종 단계 등에서 적용될 수 있다.The injection of the nonaqueous electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and the required physical properties of the final product. That is, it may be applied before the electrochemical device assembly or the final step of the electrochemical device assembly.
본 발명에 따른 리튬 이차전지는 일반적인 공정인 권취(winding) 이외에도 세퍼레이터와 전극의 적층(lamination, stack) 및 접음(folding) 공정이 가능하다. 그리고, 상기 전지케이스는 원통형, 각형, 파우치(pouch)형 또는 코인(coin)형 등이 될 수 있다. 또한 본 발명에서 제공하는 리튬 이차전지용 음극을 포함하는 리튬 이차전지는 리튬 금속전지, 리튬-황 전지 또는 전고체 전지일 수 있다.The lithium secondary battery according to the present invention may be a lamination (stacking) and folding (folding) process of the separator and the electrode in addition to the winding (winding) which is a general process. The battery case may have a cylindrical shape, a square shape, a pouch type, or a coin type. In addition, the lithium secondary battery including a negative electrode for a lithium secondary battery provided by the present invention may be a lithium metal battery, a lithium-sulfur battery or an all-solid-state battery.
상기와 같이 본 발명에 따른 리튬 이차전지는 우수한 방전 용량, 출력 특성 및 용량 유지율을 안정적으로 나타내기 때문에, 휴대전화, 노트북 컴퓨터, 디지털 카메라 등의 휴대용 기기, 및 하이브리드 전기자동차(hybrid electric vehicle, HEV) 등의 전기 자동차 분야 등에 유용하다.As described above, the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention ratio, and therefore, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (HEVs). It is useful for the field of electric vehicles such as).
이에 따라, 본 발명의 다른 일 구현예에 따르면, 상기 리튬 이차전지를 단위 셀로 포함하는 전지 모듈 및 이를 포함하는 전지팩이 제공된다. 상기 전지모듈 또는 전지팩은 파워 툴(power tool); 전기자동차(electric vehicle, EV), 하이브리드 전기자동차, 및 플러그인 하이브리드 전기자동차(plug-in hybrid electric vehicle, PHEV)를 포함하는 전기차; 또는 전력 저장용 시스템 중 어느 하나 이상의 중대형 디바이스 전원으로 이용될 수 있다.Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided. The battery module or battery pack includes a power tool; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); Or it can be used as a power source for any one or more of the system for power storage.
이하, 본 발명을 구체적으로 설명하기 위해 실시예를 들어 상세하게 설명하기로 한다. 그러나 본 발명에 따른 실시예는 여러 가지 다른 형태로 변형될 수 있으며, 본 발명의 범위가 아래에서 상술하는 실시예에 한정되는 것으로 해석되어서는 아니 된다. 본 발명의 실시예는 당업계에서 평균적인 지식을 가진 자에게 본 발명을 보다 완전하게 설명하기 위해서 제공되는 것이다.Hereinafter, the present invention will be described in detail with reference to Examples. However, the embodiment according to the present invention may be modified in 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 more completely explain the present invention to those skilled in the art.
<실시예 1> 알루미늄(Al) 보호층이 형성된 리튬 이차전지 제조Example 1 Manufacture of Lithium Secondary Battery with Aluminum (Al) Protection Layer
양극 활물질로 LCO(LiCoO2)를 사용하여 양극을 제조하였다. N-메틸피롤리돈(NMP)을 용매로, LCO : 슈퍼-피(Super-P) : PVDF = 95 : 2.5 : 2.5 중량비로 혼합하여 슬러리를 제조, 450mg/25cm2로 로딩하고, 두께 12㎛의 알루미늄 호일에 코팅하여 70㎛ 두께의 양극을 제조하였다.A positive electrode was prepared using LCO (LiCoO 2 ) as the positive electrode active material. A slurry was prepared by mixing N-methylpyrrolidone (NMP) with a solvent, LCO: Super-P: PVDF = 95: 2.5: 2.5 by weight, and loaded to 450 mg / 25 cm 2 , having a thickness of 12 μm. Coated on an aluminum foil to prepare a positive electrode having a thickness of 70㎛.
두께 10 ㎛의 음극 집전체인 구리(Cu) 박막에 두께 20㎛의 리튬 금속을 위치시키고, 알루미늄(Al)을 스퍼터링(sputtering)하여 두께 20 nm의 알루미늄 보호층을 리튬 금속 상에 형성한 후, 롤 프레스(roll press)를 실시하여 음극을 제조하였다.After placing a lithium metal having a thickness of 20 μm on a copper (Cu) thin film, which is a negative electrode current collector having a thickness of 10 μm, sputtering aluminum (Al) to form an aluminum protective layer having a thickness of 20 nm on the lithium metal, The negative electrode was manufactured by performing a roll press.
상기 양극 및 음극 사이에 두께 20㎛의 폴리에틸렌 분리막을 개재시킨 다음, 전해질로서 에틸렌카보네이트(EC): 에틸메틸카보네이트(EMC) = 3:7 (v/v)의 부피비로 혼합하여 제조한 비수전해액 용매에 리튬염으로 LiPF6 1.0M를 첨가한 비수성 전해액을 주입하여 리튬 이차 전지를 제조하였다.A nonaqueous electrolyte solvent prepared by interposing a polyethylene separator having a thickness of 20 μm between the positive electrode and the negative electrode, and then mixing them in a volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3: 7 (v / v) as an electrolyte. Lithium secondary battery was prepared by injecting a non-aqueous electrolyte solution into which LiPF 6 1.0M was added as a lithium salt.
<비교예 1> 리튬 보호층이 형성되지 않은 리튬 이차전지 제조Comparative Example 1 Manufacture of Lithium Secondary Battery Without Lithium Protective Layer
상기 실시예 1에서 리튬 금속의 보호층을 형성하지 않은 것을 제외하고 상기 실시예 1의 과정과 동일하게 하여 리튬 이차전지를 제조하였다.A lithium secondary battery was manufactured in the same manner as in Example 1, except that the protective layer of lithium metal was not formed in Example 1.
<비교예 2> 인듐(In) 보호층이 형성된 리튬 이차전지 제조Comparative Example 2 Manufacture of Lithium Secondary Battery with Indium (In) Protective Layer
상기 실시예 1에서 보호층으로 알루미늄대신 인듐(In)을 사용한 것을 제외하고 상기 실시예 1의 과정과 동일하게 하여 리튬 이차전지를 제조하였다.A lithium secondary battery was manufactured in the same manner as in Example 1, except that indium (In) was used instead of aluminum as the protective layer in Example 1.
<실험예> 전지 성능 평가Experimental Example Battery Performance Evaluation
상기 실시예 1 및 비교예 1 내지 2에서 제조된 각 전지에 대하여 성능 평가를 수행하였다. 이때, 충전 및 방전 조건은 다음과 같다.Performance evaluation was performed for each of the batteries prepared in Example 1 and Comparative Examples 1 and 2. At this time, the charging and discharging conditions are as follows.
충전: 율속 0.2C, 전압 4.25V, CC/CV (5% current cut at 1C)Charge rate 0.2C, voltage 4.25V, CC / CV (5% current cut at 1C)
방전: 율속 0.5C, 전압 3V, CCDischarge: Rate 0.5C, Voltage 3V, CC
상기 조건으로 사이클을 반복하면서 전지의 초기 용량과 대비하여 방전용량이 80%에 도달했을 때의 사이클 수를 측정하였으며, 그 결과를 하기 표 2에 나타내었다.The number of cycles when the discharge capacity reached 80% compared to the initial capacity of the battery while repeating the cycle under the above conditions was measured, the results are shown in Table 2 below.
초기 용량대비 80% 시점의 사이클 수Cycles at 80% of initial capacity
실시예 1Example 1 7373
비교예 1Comparative Example 1 1212
비교예 2Comparative Example 2 3636
상기 표 2에 나타난 바와 같이, 비교예 1 및 2의 경우 덴드라이트 성장 억제 능력이 감소되어 전지의 성능이 감소한 반면에, 실시예 1에 따른 금속 보호층을 적용한 리튬 이차전지의 경우 보호층을 형성하지 않거나(비교예 1) d-밴드 중심의 값이 큰 인듐(In) 보호층을 적용한 경우(비교예 2)보다 전지의 성능이 크게 향상된 것을 알 수 있었다.As shown in Table 2, in Comparative Examples 1 and 2, the performance of the battery was decreased due to the decrease in the dendrite growth suppression ability, whereas the protective layer was formed in the lithium secondary battery to which the metal protective layer according to Example 1 was applied. (Comparative Example 1) It was found that the performance of the battery was significantly improved compared with the case of applying an indium (In) protective layer having a large d-band center value (Comparative Example 2).
[부호의 설명][Description of the code]
100: 리튬 이차전지용 음극100: negative electrode for lithium secondary battery
110: 금속 보호층110: metal protective layer
120: 리튬 금속층120: lithium metal layer

Claims (9)

  1. 리튬 금속층; 및Lithium metal layer; And
    상기 리튬 금속층의 적어도 일면에 형성되는 금속 보호층을 포함하며,It includes a metal protective layer formed on at least one surface of the lithium metal layer,
    상기 금속 보호층은 하기 수학식 1에 따른 상대 에너지인 RE 값이 0.132 를 초과하는 금속을 포함하는 것인 리튬 이차전지용 음극.Wherein the metal protective layer is a negative electrode for a lithium secondary battery containing a metal having a relative energy R E value of more than 0.132 according to the following equation (1).
    [수학식 1][Equation 1]
    Figure PCTKR2019004760-appb-I000005
    Figure PCTKR2019004760-appb-I000005
  2. 제1항에 있어서, The method of claim 1,
    상기 금속 보호층은 금속 또는 금속 합금을 포함하는 것을 특징으로 하는 리튬 이차전지용 음극.The metal protective layer is a lithium secondary battery negative electrode comprising a metal or a metal alloy.
  3. 제1항에 있어서, The method of claim 1,
    상기 금속 보호층은 Al, Au, Ag, Co, Ni, Mg, Zn 및 이들의 합금으로 이루어진 군으로부터 선택된 어느 하나 이상을 포함하는 것을 특징으로 하는 리튬 이차전지용 음극.The metal protective layer is any one or more selected from the group consisting of Al, Au, Ag, Co, Ni, Mg, Zn, and alloys thereof.
  4. 제1항에 있어서, The method of claim 1,
    상기 수학식 1의 금속의 표면에너지 및 금속의 p-밴드 또는 d-밴드 중심은 범밀도 함수론(density function theory)으로 구하는 것을 특징으로 하는 리튬 이차전지용 음극.The surface energy of the metal of Equation 1 and the center of the p-band or d-band of the metal is obtained by the density function theory (density function theory), the anode for a lithium secondary battery.
  5. 제1항에 있어서,The method of claim 1,
    상기 보호층의 두께는 2 내지 2,000 nm 인 것을 특징으로 하는 리튬 이차전지용 음극.The thickness of the protective layer is a lithium secondary battery negative electrode, characterized in that 2 to 2,000 nm.
  6. 제1항에 있어서,The method of claim 1,
    상기 리튬 금속층은 집전체 상에 리튬 금속 박막이 형성된 것인 리튬 이차전지용 음극.The lithium metal layer is a negative electrode for a lithium secondary battery is a lithium metal thin film formed on the current collector.
  7. 제6항에 있어서,The method of claim 6,
    상기 집전체는 구리, 알루미늄, 스테인리스스틸, 아연, 티타늄, 은, 팔라듐, 니켈, 철, 크롬, 이들의 합금 및 이들의 조합으로 이루어진 군으로부터 선택된 어느 하나 이상을 포함하는 것을 특징으로 하는 리튬 이차전지용 음극.The current collector may be any one or more selected from the group consisting of copper, aluminum, stainless steel, zinc, titanium, silver, palladium, nickel, iron, chromium, alloys thereof, and combinations thereof. cathode.
  8. 양극, 음극 및 이들 사이에 개재되는 분리막을 포함하는 리튬 이차전지에 있어서,In a lithium secondary battery comprising a positive electrode, a negative electrode and a separator interposed therebetween,
    상기 음극은 제1항 내지 제7항 중 어느 한 항의 리튬 이차전지용 음극인 리튬 이차전지.The negative electrode is a lithium secondary battery which is a negative electrode for a lithium secondary battery of any one of claims 1 to 7.
  9. 제8항에 있어서,The method of claim 8,
    상기 음극은 양극과 대향하는 면에 금속 보호층이 형성된 것을 특징으로 하는 리튬 이차전지.The negative electrode is a lithium secondary battery, characterized in that the metal protective layer is formed on the surface facing the positive electrode.
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