WO2018062882A1 - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery and, more particularly, to a lithium secondary battery, comprising: a cathode; an anode; and a separator interposed between the cathode and the anode; and an electrolyte, in which a gel polymer electrolyte is provided between the anode and the separator, and a liquid electrolyte is provided between the cathode and the separator. The lithium secondary battery according to the present invention uses the different electrolytes for the anode and the cathode, thereby improving the stability and performance of an electrode to thus enhance the performance and life span of the lithium secondary battery.

Description

Lithium secondary battery

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0127000 dated September 30, 2016 and Korean Patent Application No. 10-2017-0124872 dated September 27, 2017. All content disclosed in the literature is included as part of this specification.

The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery designed to increase the stability of a lithium metal electrode and to exhibit more excellent performance and life characteristics.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, lithium secondary batteries with high energy density and operating potential, long cycle life, and low self-discharge rate Batteries have been commercialized and widely used.

Also, as interest in environmental issues has increased recently, electric vehicles (EVs) and hybrid electric vehicles (HEVs), which can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, There is a lot of research on the back. Ni-MH secondary batteries are mainly used as power sources of such electric vehicles (EVs) and hybrid electric vehicles (HEVs). However, lithium secondary batteries of high energy density, high discharge voltage and output stability are used. Research is actively underway and some are commercialized.

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 inside. do. In such a lithium secondary battery, charging and discharging proceed while repeating a process in which lithium ions of a positive electrode are inserted into and detached from a negative electrode. The capacity of the lithium secondary battery varies depending on the type of electrode active material, but there is a need for continuous capacity increase and stability improvement.

Therefore, it is possible to occlude and release more lithium ions through alloying with lithium, and metal-based materials such as silicon (4,200 mAh / g) and tin (990 mAh / g), which exhibit high capacity characteristics, are used as the negative electrode active material. have. However, when a metal such as silicon or tin is used as the negative electrode active material, the volume expands to about four times in the process of alloying with lithium during charging and shrinks during discharge. Due to such a large volume change of the electrode repeatedly generated during charging and discharging, the active material is gradually micronized and dropped from the electrode, thereby rapidly decreasing the capacity, which causes difficulties in commercialization.

Compared to the negative electrode active material mentioned above, lithium metal has a high theoretical energy density of 3860 mAh / g and a very low standard hydrogen potential (SHE) of -3.045 V, thus enabling high capacity and high energy density batteries. In recent years, as interest in lithium-sulfur and lithium-air batteries increases, studies have been actively conducted as negative active materials of lithium secondary batteries.

However, when lithium metal is used as a negative electrode of a lithium secondary battery, lithium metal reacts with electrolytes, impurities, and lithium salts to form a solid electrolyte interphase (SEI). Such a passivation layer causes a local current density difference. It promotes the formation of dendritic dendrite by lithium metal during charging, and gradually grows during charging and discharging, causing internal short circuit between positive and negative electrodes. In addition, dendrite has a mechanically weak neck, which forms dead lithium, which loses electrical contact with the current collector during discharge, thereby reducing battery capacity and reducing cycle life. Adversely affects. Due to the heterogeneity of the redox reaction of the lithium metal negative electrode and the reactivity with the electrolyte, a lithium secondary battery using lithium metal as a negative electrode has not been put to practical use yet.

In order to solve this problem, various methods such as introducing a polymer protective layer or an inorganic solid protective layer on the lithium metal surface, increasing a lithium salt of an electrolyte solution, or introducing an appropriate additive have been studied.

For example, Korean Patent Laid-Open Publication No. 2009-0055224 discloses that the surface of an electrode can be protected from an electrolyte by forming a polyimide protective film on the surface of a lithium electrode.

In addition, the Republic of Korea Patent Publication No. 2016-0052351 discloses that by including the lithium dendrite absorbent material in the polymer protective film formed on the surface of the lithium metal to suppress the growth of lithium dendrite to improve the stability and life characteristics of the lithium secondary battery Doing.

These patents stabilized the surface of lithium metal to some extent but the effect is insufficient. In addition, when the battery is charged or discharged, the protective layer becomes hard or swelling occurs when contacted with the electrolyte, resulting in limitations in application to the lithium secondary battery. In addition, changing the composition of the electrolyte or adding a separate protective layer is uneconomical because it requires a lot of time and money. Therefore, there is a need for further development of a lithium secondary battery capable of improving the instability problem of the lithium metal electrode and thus improving the charge and discharge efficiency and lifespan characteristics of the lithium secondary battery.

[Preceding technical literature]

[Patent Documents]

Republic of Korea Patent Publication No. 2009-0055224 (2009.06.02), a lithium metal battery comprising a polyimide and a method of manufacturing the same

Republic of Korea Patent Publication No. 2016-0052351 (2016.05.12), a lithium metal electrode having a stable protective layer and a lithium secondary battery comprising the same

Accordingly, the present inventors have conducted various studies to solve the above problems. As a result, the efficiency and stability of the positive and negative electrodes are improved by introducing a gel polymer electrolyte or a liquid electrolyte containing the most efficient organic solvent in each of the positive and negative electrodes. It was confirmed that the performance is improved.

Accordingly, an object of the present invention is to provide a lithium secondary battery comprising a gel polymer electrolyte containing an ether solvent at a negative electrode and a liquid electrolyte containing a carbonate solvent at a positive electrode.

In order to achieve the above object, the present invention includes a positive electrode, a negative electrode and a separator and an electrolyte interposed between the positive electrode and the negative electrode, a gel polymer electrolyte between the negative electrode and the separator, a liquid electrolyte between the positive electrode and the separator It provides a lithium secondary battery comprising a.

The negative electrode is characterized in that the lithium metal or lithium alloy.

The gel polymer electrolyte is characterized in that the electrolyte solution containing an ether solvent and a lithium salt is impregnated in the polymer matrix.

The liquid electrolyte is characterized in that it comprises a carbonate solvent and a lithium salt.

In addition, the present invention comprises a cathode, a cathode and a separator interposed therebetween, a gel polymer electrolyte and a liquid electrolyte, wherein the gel polymer electrolyte comprises an ether solvent, the liquid electrolyte comprises a carbonate solvent It provides a lithium secondary battery.

The lithium secondary battery according to the present invention uses a gel polymer electrolyte containing an ether solvent as a negative electrode, and a lithium secondary battery using a liquid electrolyte containing a carbonate solvent as a positive electrode, and thus has a high output and long-term charge and discharge. A lithium secondary battery capable of satisfying efficiency and cycle characteristics can be provided.

1 is a cross-sectional view illustrating a lithium secondary battery according to one embodiment of the present invention.

2 is a graph showing the capacity characteristics of the lithium secondary battery prepared in Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in detail with reference to the drawings. 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.

Therefore, the configurations described in the drawings and embodiments described herein are only one of the most preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, various modifications that can be substituted for them at the time of the present application It should be understood that there may be equivalents and variations.

As the information and communication industry develops rapidly and the application fields of lithium secondary batteries extend from mobile phones and wireless electronic devices to electric vehicles, they can be miniaturized, light weight, thin and portable, and have high performance and high stability. Development is required.

In response to this demand, a lithium metal battery (LMB) using lithium metal as a negative electrode has been in the spotlight. Lithium metal is expected to be a negative electrode material of a high capacity lithium secondary battery because of its high energy density (3,860 mAh / g) with low oxidation / reduction potential (-3.045 V vs. standard hydrogen electrode) and low atomic weight (6.94 g / a.u.).

However, when lithium metal is used as a negative electrode, a passivation layer is formed by reacting with organic solvents, lithium salts, and impurities present in the battery, and the passivation layer causes a local current density difference to form dendritic lithium dendrite. . The lithium dendrite not only shortens the life of the lithium secondary battery but also causes short circuits and inert lithium, thereby increasing physical and chemical instability of the lithium secondary battery and negatively affecting the charge and discharge capacity. In addition, the passivation layer is thermally unstable, so that charging and discharging of the battery may be continuously progressed, or, in particular, during high temperature storage in a fully charged state, the passivation layer may be gradually collapsed by increased electrochemical energy and thermal energy. Due to the collapse of the passivation layer, side reactions in which the exposed lithium metal surface reacts directly with the electrolyte solvent and decompose continuously occur, thereby increasing the resistance of the negative electrode and decreasing the charge and discharge efficiency of the battery. In addition, the solvent of the electrolyte is consumed when the passivation layer is formed, and the lifespan of the battery is reduced due to the by-products and gases generated during various side reactions such as formation and collapse of the passivation layer and decomposition of the electrolyte.

To this end, the conventional technique used a method such as changing the composition of the electrolyte or introducing a separate protective layer on the surface of the lithium metal, but the stability of the lithium metal electrode was not effectively improved.

Accordingly, the present invention provides a lithium secondary battery including the most efficient electrolyte for each of the positive electrode and the negative electrode in order to increase the stability of the lithium metal electrode and secure the effect of improving the charge and discharge characteristics and life of the lithium secondary battery.

Specifically, the lithium secondary battery according to the present invention includes a positive electrode, a negative electrode and a separator and an electrolyte interposed between the positive electrode and the negative electrode, and comprises a gel polymer electrolyte between the negative electrode and the separator, the liquid between the positive electrode and the separator Electrolyte.

1 is a cross-sectional view illustrating a lithium secondary battery according to one embodiment of the present invention.

Referring to FIG. 1, a lithium secondary battery 100 according to an embodiment of the present invention includes a separator 40 interposed between a positive electrode 20, a negative electrode 10, and the positive electrode 20 and the negative electrode 10. The electrolyte 30 includes a gel polymer electrolyte 31 between the cathode 10 and the separator 40, and a liquid electrolyte 32 between the anode 20 and the separator 40.

In general, electrolytes applied to lithium secondary batteries include liquid electrolytes in which lithium salts are dissolved in an organic solvent, and gel polymer electrolytes in which the liquid electrolyte is impregnated in a polymer material. In the case of liquid electrolytes, the ion conductivity is high and uniformly dispersed, so that lithium ions are sufficiently diffused in the electrode, which is advantageous for high current charging, but organic membranes require the installation of separators and special protection circuits to ensure stability. Do. On the other hand, in the case of gel polymer electrolytes, organic solvents do not leak out and the membrane functions simultaneously, thus ensuring superior stability and designing a variety of shapes, but having low ionic conductivity and non-uniform dispersion compared to liquid electrolytes. Due to the characteristics, there is a problem that the lifetime characteristics are degraded. In addition, the electrolyte exhibits different characteristics depending on the type of the electrode active material, the type of the organic solvent included in the electrolyte, and the driving conditions of the battery.

Accordingly, the present invention introduces an electrolyte containing a specific organic solvent suitable for the active material used for the negative electrode and the positive electrode of the lithium secondary battery. That is, in the case of using lithium metal as the negative electrode, the negative electrode includes a gel polymer electrolyte containing an ether solvent and a positive electrode liquid electrolyte containing a carbonate solvent, thereby maximizing the advantages of each electrolyte, in particular lithium metal By improving the reaction efficiency and stability of the electrode to provide a lithium secondary battery having a more improved charge and discharge efficiency and life characteristics.

The positive electrode 20 may include a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector.

The positive electrode current collector supports the positive electrode active material layer, and is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, surface treated with carbon, nickel, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, and the like can be used.

The positive electrode current collector may form fine concavities and convexities on its surface to enhance bonding strength with the positive electrode active material, and may be used in various forms such as a film, a sheet, a foil, a mesh, a net, a porous body, a foam, and a nonwoven fabric.

The cathode active material layer may include a cathode active material, and optionally a conductive material and a binder.

The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (0 ≦ _x ≦ 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ ; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site-type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga; 0.01 ≦ x ≦ 0.3); Formula LiMn _{2 - x} M _x O ₂ (M = Co, Ni, Fe, Cr, Zn or Ta; 0.01≤x≤0.1) or Li ₂ Mn ₃ MO ₈ (M = Fe, Co, Ni, Cu or Zn Lithium manganese composite oxide represented by; Spinel-structure lithium manganese composite oxides represented by LiNi _x Mn _{2 - x} O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like may be included, but is not limited thereto. Preferably, the positive electrode active material may be at least one selected from the group consisting of lithium cobalt oxide, lithium nickel oxide, and lithium manganese oxide. More preferably, it may be lithium cobalt oxide.

The conductive material is to improve electrical conductivity, and there is no particular limitation as long as it is an electronic conductive material that does not cause chemical change in a lithium secondary battery.

In general, carbon black, graphite, carbon fiber, carbon nanotubes, metal powder, conductive metal oxide, organic conductive materials, and the like can be used, and currently commercially available products as acetylene black series (Chevron Chemical) Chevron Chemical Company or Gulf Oil Company, etc., Ketjen Black EC series (Armak Company), Vulcan XC-72 (Cabot Company) (Cabot Company) and Super P (MMM). For example, acetylene black, carbon black, graphite, etc. are mentioned.

In addition, the cathode active material layer may further include a binder having a function of maintaining the cathode active material in the current collector for the cathode and connecting the active material. As the binder, for example, polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacryl Various kinds of binders such as polymethyl methacrylate, styrene-butadiene rubber (SBR), and carboxyl methyl cellulose (CMC) may be used.

The negative electrode 10 may include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector. Alternatively, the negative electrode 10 may be a lithium metal plate.

The negative electrode current collector is for supporting the negative electrode active material layer, and is not particularly limited as long as it has excellent conductivity and is electrochemically stable in the voltage range of the lithium secondary battery. For example, copper, stainless steel, aluminum, nickel, and titanium. , Palladium, calcined carbon, surface treated with carbon, nickel, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy and the like can be used.

The negative electrode current collector may form fine irregularities on its surface to enhance bonding strength with the negative electrode active material, and may be used in various forms such as film, sheet, foil, mesh, net, porous body, foam, and nonwoven fabric.

The thickness of the negative electrode current collector is not particularly limited and may be appropriately determined depending on the use. For example, the thickness of the current collector may be 3 to 500 ㎛, preferably 5 to 100 ㎛, more preferably 5 to 50 ㎛. When the thickness of the current collector is less than the range, the durability is lowered. On the contrary, when the thickness of the current collector is exceeded, the capacity per volume of the lithium secondary battery may be reduced.

The negative electrode active material layer may include a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reacting with lithium ions to reversibly form a lithium-containing compound, lithium metal or a lithium alloy. . The negative electrode active material layer may be in the form of a lithium metal thin film or lithium metal powder on the negative electrode current collector.

The method of forming the negative electrode active material layer is not particularly limited, and a method of forming a layer or a film commonly used in the art may be used. For example, a method such as pressing, coating or vapor deposition can be used. In addition, the case where the metal lithium thin film is formed on the metal plate by the initial charge after assembling the battery without the lithium thin film in the current collector is also included in the negative electrode 10 of the present invention.

The negative electrode active material layer or the lithium metal plate may be adjusted in width depending on the shape of the electrode to facilitate electrode production. In addition, the thickness of the negative electrode active material layer or the lithium metal plate is also not particularly limited, but may be, for example, 5 to 200 μm, and preferably 10 to 100 μm. When the thickness of the lithium metal layer falls within the above range, ion and electron transfer in the cathode may be smoothly performed.

The separator 40 is used to physically separate both electrodes in the lithium secondary battery of the present invention. If the separator 40 is used as a separator in a lithium secondary battery, the separator 40 may be used without particular limitation, and particularly, has low resistance to ion migration of the electrolyte. At the same time, it is preferable that the electrolyte moisture storage ability be excellent.

The separator 40 may be made of a porous substrate, and the porous substrate may be used as long as it is a porous substrate that is typically used in an electrochemical device. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used. It doesn't happen.

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 One membrane may be mentioned.

Examples of the nonwoven fabrics include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and the like, in addition to the polyolefin nonwoven fabric; Polyamides such as polyacetal and aramid; Polycarbonate; Polyimide; Polyetheretherketone; Polyethersulfone; Polyphenylene oxide; Polyphenylenesulfide; Polytetrafluoroethylene; Polyvinylidene fluoride; Poly (vinyl chloride); Polyacrylonitrile; Cellulose; Nylon; Poly (p-phenylene benzobisoxazole); Glass; ceramic; And nonwoven fabrics formed of ionically conductive glass-ceramic or the like, alone or in combination thereof. The structure of the nonwoven fabric may be a spunbond nonwoven fabric or a melt blown nonwoven fabric composed of long fibers.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm.

The pore size and pore present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

The electrolyte 30 includes lithium ions, and is used to generate an electrochemical oxidation or reduction reaction at the positive electrode and the negative electrode, and includes a gel polymer electrolyte 31 and a liquid electrolyte 32.

The gel polymer electrolyte 31 is included between the anode 10 and the separator 40, and an electrolyte solution including an ether solvent and a lithium salt is impregnated in the polymer matrix.

The ether solvent serves as a medium through which ions involved in the electrochemical reaction of the lithium secondary battery can move. Particularly, in the lithium secondary battery 100 according to the present invention, when the ether solvent is included, the lithium secondary battery 100 has high efficiency with lithium metal used for the negative electrode 10, thereby increasing dissociation of ions, thereby more smoothly conducting ions. Can be.

The ether solvent is dimethyl ether, diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, 1,3 -Dioxolane, 4-methyldioxolane, 1,4-dioxane, 3,5-dimethyl isoxazole, 2,5-dimethylfuran, furan, 2-methylfuran, tetrahydrofuran and 2-methyltetrahydrofuran It may include one or more selected from the group consisting of. Preferably the ether solvent is selected from the group consisting of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether and 1,3-dioxolane It may be one or more. More preferably, it may be at least one selected from the group consisting of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and 1,3-dioxolane.

The lithium salt is dissolved together with the ether solvent to form an electrolyte solution. At this time, the lithium salt acts as a source of lithium ions in the battery to enable the operation of the basic lithium secondary battery.

The lithium salt may be used without limitation as long as it is conventionally used in the lithium secondary battery electrolyte. For example, LiCl, LiBr, LiFSI, LiI, LiClO ₄ , LiAlO _{4 ,} LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, LiC ₄ F ₉ SO ₃ , chloroborane lithium, lower aliphatic lithium carbonate, lithium phenyl borate and the like can be used. .

The concentration of the lithium salt is 0.2 to 2 M, depending on several factors such as the exact composition of the electrolyte solvent mixture, the solubility of the salt, the conductivity of the dissolved salt, the charging and preconditioning of the cell, the operating temperature and other factors known in the lithium battery art. For example, it may be 0.6 to 2 M, more specifically 0.7 to 1.7 M. When the concentration of the lithium salt is less than 0.2 M, the conductivity of the electrolyte may be lowered, and thus the performance of the electrolyte may be lowered. When the lithium salt is used, the viscosity of the electrolyte may be increased to reduce the mobility of lithium ions.

In addition, the lithium salt-containing electrolyte solution contains, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphate for the purpose of improving charge / discharge characteristics and flame retardancy. Triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. It may also be added. In some cases, in order to impart nonflammability, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. Carbonate), PRS (Propene sultone) may be further included. In addition, additives such as vinylene carbonate (VC) and vinyl ethylene carbonate may be further included to improve cycle characteristics and high temperature safety of the battery.

An electrolytic solution having the composition described above is impregnated into a polymer matrix and cured to prepare a gel polymer electrolyte.

The polymer matrix should have an internal space in which the electrolyte solution may be impregnated, and the mechanical strength should be maintained even if the electrolyte solution is impregnated therein and should not be dissolved in the electrolyte solution. In addition, the polymer matrix is excellent in the lithium ion dissociation ability, but should exhibit a strong binding force with the separator 40 and the negative electrode 10, for this purpose, the material and the hydrophobicity of the separator 40 and the negative electrode 10 There must be affinity.

The polymer matrix is selected from the group consisting of polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylchloride, polyvinylidene fluoride, polymethylmethacrylate, poly (meth) acrylate, polysiloxane and polyphosphazene It may include one or more kinds.

The gel polymer electrolyte 31 is impregnated with an electrolyte solution containing an ether solvent and a lithium salt in the polymer matrix, and then gelled by irradiation with heat or light. In this case, thermally decomposable to promote gelation by heat or light. An initiator or a photodegradable initiator may be further added.

Specific examples of the thermally decomposable initiators include peroxide initiators, ester-based and azo-based initiators, and the photodegradable initiators may be used. In this case, the thermally decomposable initiator or the photodegradable initiator is added in an amount of 0.5 to 7 parts by weight based on 100 parts by weight of the polymer matrix.

The liquid electrolyte 32 is included between the anode 20 and the separator 40 and includes a carbonate solvent and a lithium salt.

In the present invention, high voltage stability can be ensured by using a liquid electrolyte containing a carbonate-based solvent between the anode 20 and the separator 40.

The carbonate solvent may be ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 2,3-pentylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, It may include one or more selected from the group consisting of methylpropyl carbonate and ethylpropyl carbonate. Preferably, the carbonate solvent may be at least one selected from the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and dipropyl carbonate. More preferably, it may be one or more selected from the group consisting of ethylene carbonate, dimethyl carbonate and diethyl carbonate.

The lithium salt is as described above in the gel polymer electrolyte 31.

Accordingly, the present invention includes a positive electrode, a negative electrode and a separator interposed therebetween, a gel polymer electrolyte and a liquid electrolyte, wherein the gel polymer electrolyte includes an ether solvent, and the liquid electrolyte includes a carbonate solvent. It includes a lithium secondary battery.

As described above, the lithium secondary battery 100 according to the embodiment of the present invention includes a gel polymer electrolyte 31 between the negative electrode 10 and the separator 40, and the positive electrode 20 and the separator 40. It contains a liquid electrolyte 32 in between. In this case, the gel polymer electrolyte 31 includes an ether solvent, and the liquid electrolyte 32 includes a carbonate crab solvent. In this case, by using an ether solvent in the negative electrode 10, the reaction efficiency with lithium metal as the negative electrode active material can be improved, and the direct reaction with the electrolyte is minimized by using a gel type polymer electrolyte and the metal eluted from the positive electrode. The stability of the lithium metal electrode can be improved because ions can be prevented from moving to the cathode or metal can be reduced from being deposited at the cathode. In addition, the use of a carbonate-based solvent in the positive electrode 20 can ensure high voltage stability and solve the problem of increasing the internal resistance, and the reaction area between the liquid electrolyte and the positive electrode active material becomes uniform and wide, thereby enabling an effective electrochemical reaction. Accordingly, the charging and discharging efficiency and lifespan of the lithium secondary battery can be improved, and the capacity characteristics of the battery are excellent even when charged at a high voltage as well as a general voltage.

Preparation of the lithium secondary battery having the above-described configuration is not particularly limited in the present invention, it can be manufactured through a known method.

In addition, the shape of the lithium secondary battery of the present invention is not particularly limited, and can be in various shapes such as cylindrical, stacked, coin type, etc., which can operate as a battery.

In addition, the present invention provides a battery module including the lithium secondary battery as a unit cell, and provides a battery pack including the battery module.

The battery pack may be used as a power source for medium and large devices that require high temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-to-large device include a power tool that is driven by an electric motor; Electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; Electric motorcycles including electric bicycles (E-bikes) and electric scooters (Escooters); Electric golf carts; Power storage systems and the like, but is not limited thereto.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the appended claims.

Production Example : Li Of Li Symmetrical  Produce

[Production Example 1]

A lithium metal thin film having a thickness of 20 μm was used as the negative electrode. The electrolyte was prepared by dissolving lithium bisfluoro sulfonyl imide (LiFSI) at a concentration of 1 M in an organic solvent consisting of 1,3-dioxolane and ethylene glycol dimethyl ether (DOL: DME = 1: 1 (volume ratio)).

A Li / Li symmetric cell was prepared using the cathode and the electrolyte.

[Production Example 2]

In Preparation Example 1, 1M concentration of lithium hexafluoro phosphate (LiPF ₆ ) was dissolved in an organic solvent consisting of ethylene carbonate, diethyl carbonate, and dimethyl carbonate (EC: DEC: DMC = 1: 2: 1 (volume ratio). A lithium / li symmetric cell was prepared in the same manner as in Preparation Example 1, except that 2 wt% of VC was added thereto.

Example  And Comparative example

Example 1

After preparing a positive electrode active material slurry consisting of 95% by weight, 2.5% by weight and 2.5% by weight of LiCoO ₂ as a positive electrode active material, Super P as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, the positive electrode active material slurry Was coated on an aluminum current collector and then dried to prepare a positive electrode.

A lithium metal thin film having a thickness of 20 μm was used as the negative electrode.

100 μl of an electrolyte solution containing 1 M of lithium bisfluoro sulfonyl imide (LiFSI) dissolved in an organic solvent composed of dioxolane and ethylene glycol dimethyl ether (DOL: DME = 1: 1 (volume ratio)) was placed on the surface of the negative electrode. It was impregnated into a polymer matrix formed of ethoxylated trimethylol propanetriacrylate (ETPTA) and cured to form a gel polymer electrolyte on the surface of the negative electrode.

The electrode assembly was manufactured by placing the gel polymer electrolyte to face the anode and the cathode to face each other, and then interposing an ion conductive glass-ceramic (manufactured by Ohara, Japan) between the anode and the cathode as a separator.

After inserting the electrode assembly into a coin cell, lithium hexafluoro phosphate (LiPF ₆ ) at a concentration of 1M in an organic solvent consisting of dimethyl carbonate (EC: DEC: DMC = 1: 2: 1 (volume ratio)) between the anode and the separator. The lithium secondary battery was manufactured by dissolving and inject | pouring the electrolyte solution which added 2 weight% of VC, and sealing it completely.

Comparative Example 1

An organic solvent composed of ethylene glycol dimethyl ether (DOL: DME = 1: 1 (volume ratio)) after inserting an electrode assembly having an ion conductive glass-ceramic separator interposed between the same anode and cathode as Example 1 in a coin cell. 100 µl of an electrolyte in which lithium bisfluoro sulfonyl imide (LiFSI) was dissolved at a concentration of 1 M was injected. Then, a lithium secondary battery was manufactured by completely sealing.

Comparative Example 2

After inserting the electrode assembly with an ion conductive glass-ceramic separator between the same anode and cathode as in Example 1 in the coin cell, the organic consisting of dimethyl carbonate (EC: DEC: DMC = 1: 2: 1 (volume ratio)) Lithium hexafluoro phosphate (LiPF ₆ ) at a concentration of 1 M was dissolved in a solvent, and 100 μl of an electrolyte solution containing 2 wt% of VC was injected, and then a lithium secondary battery was prepared by completely sealing.

Experimental Example  One. Symmetrical  Performance evaluation

The symmetric cells prepared in Preparation Examples 1 and 2 were charged and discharged at 83% DOD (depth of discharge) and 1C charge and discharge conditions. After the charge and discharge, the cycle efficiency (%) was measured, and the results are shown in Table 1 below.

	Li cycle efficiency (%)
Preparation Example 1	99.42
Preparation Example 2	94.64

Referring to Table 1, when the negative electrode is a lithium metal, it can be seen that the Li efficiency is increased than in the case of the preparation example 2 using a carbonate solvent when the ether-based solvent as in Preparation Example 1.

Experimental Example  2. Performance Evaluation of Lithium Secondary Battery

The lithium secondary battery (battery capacity 4.6mAh) manufactured in the above Examples and Comparative Examples was charged at 55 ° C. until a constant current of 4.6 V was reached at 0.7 C, and then charged at a constant voltage of 4.6 V. Charging was terminated when the charging current became 0.275 mA. After 10 minutes, 0.5 C It discharged until it became 3.0V by constant current. After 50 cycles of charging and discharging, the battery capacity was measured and shown in FIG. 2.

2, in the case of the lithium secondary battery of Example 1, it can be seen that there is no change in capacity even at high voltage up to 25 cycles. In comparison, in Comparative Example 1, the capacity was drastically decreased at the same time as charging and discharging started, and in Comparative Example 2, the capacity was rapidly decreased after 13 cycles. Therefore, it can be seen that the lithium secondary battery according to the present invention exhibits excellent capacity characteristics even in a high voltage range.

[Description of the code]

100: lithium secondary battery 10: negative electrode

20: anode 30: electrolyte

31: gel polymer electrolyte 32: liquid electrolyte

40: separator

Lithium secondary battery according to the present invention to improve the battery performance and life by including the most efficient electrolyte to each of the negative electrode and the positive electrode to enable high capacity, high stability and long life of the lithium secondary battery.

Claims (8)

1. A positive electrode, a negative electrode and a separator and an electrolyte interposed between the positive electrode and the negative electrode,

   It comprises a gel polymer electrolyte between the cathode and the separator,

   Lithium secondary battery comprising a liquid electrolyte between the positive electrode and the separator.
2. The method of claim 1,

   The negative electrode is a lithium secondary battery, characterized in that the lithium metal or lithium alloy.
3. The method of claim 1,

   The gel polymer electrolyte is a lithium secondary battery, characterized in that an electrolyte solution containing an ether solvent and a lithium salt is impregnated in the polymer matrix.
4. The method of claim 3,

   The ether solvent is dimethyl ether, diethyl ether, dibutyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, 1,3 -Dioxolane, 4-methyldioxolane, 1,4-dioxane, 3,5-dimethyl isoxazole, 2,5-dimethylfuran, furan, 2-methylfuran, tetrahydrofuran and 2-methyltetrahydrofuran Lithium secondary battery, characterized in that at least one selected from the group consisting of.
5. The method of claim 3,

   The polymer matrix is selected from the group consisting of polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylchloride, polyvinylidene fluoride, polymethylmethacrylate, poly (meth) acrylate, polysiloxane and polyphosphazene A lithium secondary battery, characterized in that at least one.
6. The method of claim 1,

   The liquid electrolyte is a lithium secondary battery comprising a carbonate-based solvent and a lithium salt.
7. The method of claim 6,

   The carbonate solvent is ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 2,3-pentylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dipropyl carbonate, Lithium secondary battery, characterized in that at least one member selected from the group consisting of methylpropyl carbonate and ethylpropyl carbonate.
8. An anode, a cathode, and a separator, a gel polymer electrolyte, and a liquid electrolyte interposed therebetween,

   The gel polymer electrolyte includes an ether solvent,

   The liquid electrolyte is a lithium secondary battery comprising a carbonate-based solvent.

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