WO2018164517A1 - Separator for lithium secondary battery and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a separator for a lithium secondary battery and a lithium secondary battery comprising same, the separator comprising: a porous substrate; and a lithium metal layer formed on a surface of the porous substrate, wherein the lithium metal layer is formed on the outer peripheral surface of the porous substrate and has the shape of a hollow window frame.

Description

Membrane for lithium secondary battery and lithium secondary battery comprising same

[Cross-cited with Related Applications]

This application claims the benefit of priority based on Korean Patent Application No. 10-2017-0030759 dated March 10, 2017 and Korean Patent Application No. 10-2018-0027369 dated March 08, 2018. All content disclosed in the literature is included as part of this specification.

[Technical Field]

The present invention relates to a separator used in a lithium secondary battery and a lithium secondary battery comprising the same, and more particularly, to a separator for a lithium secondary battery in which a lithium metal layer is formed on one surface of a porous substrate, and a lithium secondary battery including the same. will be.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is rapidly increasing. Among them, lithium secondary batteries exhibiting 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 a non-aqueous electrolyte containing lithium salt is impregnated in an electrode assembly having a porous separator interposed between a positive electrode and a negative electrode on which an active material is coated on an electrode current collector.

The lithium secondary battery is charged / discharged only by the lithium source of the positive electrode active material of the positive electrode, and when the reversible lithium source is insufficient, the life characteristics are deteriorated. Although a technique of recycling by replenishing a lithium source through a method of injecting an additional electrolyte for a battery having a deteriorated lifespan is known, this creates a passage for additional injection into an already completed cell and reopens the passage. There is a hassle that a process such as closing is necessary.

Therefore, a lithium secondary battery including a separate lithium electrode capable of supplementing lithium when the battery degenerates has been proposed. For example, Korean Patent Publication No. 2005-0116795 discloses a secondary battery including an additional lithium electrode in addition to the positive electrode and the negative electrode. The literature discloses a secondary battery in which an additional lithium electrode is spaced apart from one or more of a positive electrode or a negative electrode by a separator, and a current collector of each electrode is exposed to the outside of the secondary battery through a terminal so that lithium is deteriorated when the battery is deteriorated. Disclosed is a method of supplying lithium ions to a positive electrode or a negative electrode by connecting at least one of a positive electrode terminal and a positive electrode terminal or a negative electrode terminal.

This method has the advantage of eliminating the trouble of creating a passageway for additional injection into the finished cell and closing the passage again, but the separate lithium electrode has a positive electrode and a negative electrode. Since the cells are stacked together to form a cell, the overall thickness of the cell increases.

On the other hand, Japanese Patent Laid-Open No. 2002-324585 has a third electrode including a metal lithium additionally in addition to the positive electrode and the negative electrode, the secondary battery of the third electrode is located away from the electrode assembly including the positive electrode and the negative electrode Is disclosed.

This method does not require the passage of additional fluids into the finished cell and the closing of the passage again, and the advantage that metal lithium does not increase the overall thickness of the cell, but metal lithium requires lithium replenishment. Since it is located on one side with a predetermined distance from the electrodes to be made, there is a disadvantage that the replenishment of lithium ions is not evenly made throughout the electrode.

Accordingly, there is a need for the development of a lithium secondary battery capable of more effectively replenishing a lithium source with no electrode, without the inconvenience of forming a separate passage for replenishing lithium, and without affecting the thickness or capacity of the battery.

The problem to be solved of the present invention is to provide a separator for a lithium secondary battery comprising a lithium metal layer that can provide a lithium source to the secondary battery deteriorated life characteristics.

Another object of the present invention is to provide a lithium secondary battery including the separator for a lithium secondary battery.

In order to solve the above problems, the present invention, a porous substrate; And a lithium metal layer formed on one surface of the porous substrate,

The lithium metal layer is formed along the outer circumferential surface of the porous substrate, and provides a separator for a lithium secondary battery having a hollow window frame.

In order to solve the above other problem, the present invention

It provides a method of manufacturing a separator for a lithium secondary battery comprising the step of forming an electrode active material layer by applying an electrode active material slurry comprising an electrode active material and a binder on a porous substrate.

In order to solve the above another problem, the present invention

anode; cathode; And a separator interposed between the positive electrode and the negative electrode,

The separator is a porous substrate; And a lithium metal layer formed on one surface of the porous substrate, wherein the lithium metal layer is formed along an outer circumferential surface of the porous substrate and has a hollow window frame shape.

The lithium metal layer provides a lithium secondary battery surrounding the edge of the positive electrode at a position spaced apart from the positive electrode.

The separator for a lithium secondary battery according to the present invention includes a porous substrate including a lithium metal layer on one surface, and the lithium metal layer is formed on an outer circumferential surface of the porous substrate, and is a flat layer of a window frame shape having an empty inside. When configuring a lithium secondary battery in which a positive electrode is positioned in a window frame shape formed by a metal layer, the lithium metal layer may effectively replenish lithium ions in the positive electrode when the lithium secondary battery degenerates.

1 is a view showing an example of a separator for a lithium secondary battery according to an example of the present invention.

2 is a cross-sectional view of an example of a separator for a rechargeable lithium battery according to one embodiment of the present invention.

3 is a view showing an example of a laminated form of a positive electrode, a separator and a negative electrode of a lithium secondary battery according to an example of the present invention.

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

The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. 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.

Lithium secondary battery separator according to the present invention is a porous substrate; And a lithium metal layer formed on one surface of the porous substrate, wherein the lithium metal layer is formed on an outer circumferential surface of the porous substrate, and is a planar layer having a window frame shape having an empty inside.

The porous base material included in the separator for a lithium secondary battery according to an example of the present invention is not particularly limited as long as it is a material that can be used as a separator for a lithium secondary battery, for example, an olefin polymer such as polypropylene having chemical resistance and hydrophobicity; Sheets or nonwovens made of glass fibers or polyethylene may be used. Specifically, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, poly Ethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, polyethylene, polypropylene, polybutylene, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile and polyvinylidene fluoride hexafluoropropylene aerial It may be a separator consisting of one or more selected from the group consisting of coalescing.

The porosity of the porous substrate is not particularly limited, and may be, for example, 5% to 95%, specifically 20% to 80%, more specifically 30% to 70%. When the porosity of the porous substrate is in the above range, the electrolyte may be smoothly moved to maintain proper mechanical properties without deteriorating battery performance, thereby preventing internal short circuits of the positive electrode and the negative electrode.

The porous substrate may have a thickness of 5 μm to 300 μm, specifically 10 μm to 100 μm, and more specifically 10 μm to 50 μm. When the porous substrate has a thickness in the above range, while exhibiting appropriate mechanical properties, the porous substrate itself may act as a resistive layer or may not increase the thickness of the entire lithium secondary battery.

The porous substrate may have an average pore size of 10 nm to 100 nm, specifically 10 nm to 90 nm, more specifically 30 nm to 50 nm. The pore size of the porous substrate represents the diameter of the pores measured on the surface of the porous substrate. The method of measuring the average pore size is not particularly limited, but may be measured through, for example, a graph of nitrogen adsorption isotherm and a pore size distribution.

When the average pore size of the porous substrate is in the above range, the movement of the electrolyte is smooth and battery performance is not lowered, and the mechanical properties of the porous substrate can be properly maintained.

The lithium metal layer formed on one surface of the porous substrate may include lithium metal, a lithium alloy, or a mixture thereof, and specifically may include lithium metal.

The lithium metal layer is formed on an outer circumferential surface of one surface of the porous substrate. That is, the lithium metal layer does not entirely cover one surface of the porous substrate, and the lithium metal layer is not formed inside the outer surface of the porous substrate. Therefore, the lithium metal layer has a window frame shape of which the inside is empty.

1 and 2 schematically show a separator for a lithium secondary battery according to an example of the present invention.

The drawings are intended to illustrate the invention but are not intended to limit the scope thereof. In the drawings of the present invention, the size of each component may be exaggerated for description, and may differ from the size actually applied.

1 is a plan view of a separator for a lithium secondary battery according to an example of the present invention, and FIG. 2 is a cross-sectional view of a separator for a lithium secondary battery according to an example of the present invention. Referring to FIG. 1, in the separator for a lithium secondary battery according to an exemplary embodiment of the present invention, a lithium metal layer 200 is formed on an outer circumferential surface of one surface of the porous substrate 100, and referring to FIG. 2, an example of the present invention. In the separator for a lithium secondary battery according to the lithium metal layer 200 is formed on the outer circumferential surface of the porous substrate 100 can be confirmed that the inside of the window frame shape is empty.

The empty interior of the window frame formed by the lithium metal layer may be a space where the anode is located. As such, when the anode is positioned in an empty interior of a window frame formed by the lithium metal layer, the lithium metal layer may surround the edge of the anode at a position spaced apart from the anode.

The thickness of the lithium metal layer may be appropriately adjusted according to the capacity of the cathode to be recovered after degeneration of the lithium secondary battery including the separator for the lithium secondary battery, and the upper limit of the thickness may be determined to be equal to or less than the thickness of the anode. For example, the lithium metal layer may have a thickness of 1 μm to 500 μm, specifically 5 μm to 100 μm, and more specifically 5 μm to 20 μm.

The lithium metal layer may have an area of 1% to 40% with respect to 100% of the area of the window frame having an empty interior, and specifically, may have an area of 2% to 20%, more specifically, 5% to 10%. Can be.

When the lithium metal layer has an area of the ratio with respect to the area of the window frame shape in which the inside is empty, the size or capacity of the positive electrode to be located inside the window frame shape when manufacturing a lithium secondary battery using the separator The lithium metal layer may include a lithium source in an amount capable of effectively replenishing lithium ions in the positive electrode when the lithium secondary battery is degenerated without affecting.

The method of forming the lithium metal layer on one surface of the porous substrate may include lamination of a film of lithium metal on one surface of the porous substrate, chemical vapor deposition (CVD), or physical vapor deposition of lithium metal. (PVD, physical vapor deposition) can be made by the method.

The forming of the lithium metal layer may be performed under a condition in which no contact between ambient moisture and oxygen is made in order to reduce the risk that lithium metal reacts with ambient moisture or air to form or explode lithium oxide. To this end, the forming of the lithium metal layer may be performed under an inert gas atmosphere, and the inert gas atmosphere may be an argon or nitrogen atmosphere.

In addition, the present invention provides a lithium secondary battery comprising the separator for a lithium secondary battery.

The lithium secondary battery is a positive electrode; cathode; And a separator for the lithium secondary battery interposed between the positive electrode and the negative electrode, wherein the lithium metal layer surrounds an edge of the positive electrode at a position spaced apart from the positive electrode.

The separator is a porous substrate; And a lithium metal layer formed on one surface of the porous substrate, wherein the lithium metal layer is formed along an outer circumferential surface of the porous substrate and has a hollow window frame.

The anode may be located in an empty interior of a window frame formed by the lithium metal layer. As such, when the anode is positioned in an empty interior of a window frame formed by the lithium metal layer, the lithium metal layer may surround the edge of the anode at a position spaced apart from the anode.

3 schematically illustrates a stacked form of a positive electrode, a separator, and a negative electrode of a lithium secondary battery according to an example of the present invention.

Referring to FIG. 3, the lithium metal layer 200 is formed on the outer circumferential surface of the porous substrate 100, and the porous substrate 100 is exposed in the inner space of the lithium metal layer 200 formed on the outer circumferential surface. The anode 300 is positioned in a space inside the lithium metal layer 200, and the cathode 400 is positioned on the other surface of the porous substrate 100.

The anode and the lithium metal layer may be spaced apart by a distance corresponding to 20% to 12,000% when the thickness of the anode is 100%, specifically 40% to 6,000%, more specifically 100% to 3,000% It may be spaced apart.

The positive electrode and the lithium metal layer may be spaced apart in a certain distance range based on the thickness of the positive electrode, and when the distance is too close, the positive electrode and the lithium metal layer may contact each other during use of the lithium secondary battery. When the distance is too long, the lithium replenishment effect from the lithium metal layer to the cathode may be reduced. Therefore, when the positive electrode and the lithium metal layer are spaced apart by a distance corresponding to the range based on the thickness of the positive electrode, supplying a lithium source after deterioration of the lithium secondary battery while maintaining a stable state of separation between the positive electrode and the lithium metal layer The process can be done effectively.

In addition, the distance between the anode and the lithium metal layer may be 10 ㎛ to 10 mm, specifically 20 ㎛ to 5 mm, more specifically 50 ㎛ to 2 mm. When the separation distance between the positive electrode and the lithium metal layer is within the above range, the separation state between the positive electrode and the lithium metal layer may be stably maintained, and the lithium source supply process after deterioration of the lithium secondary battery may be effectively performed.

In one example of the present invention, the positive electrode and the lithium metal layer may satisfy both the separation distance based on the thickness of the positive electrode and the separation distance according to a specific length value.

In the present invention, the space between the positive electrode and the lithium metal layer means that there is no direct contact surface or contact point between the positive electrode and the lithium metal layer.

On the other hand, in general, the negative electrode of the lithium secondary battery has a larger area than the positive electrode, and the lithium metal layer included in the lithium secondary battery according to an example of the present invention may have an area smaller than the area difference between the negative electrode and the positive electrode.

The lithium metal layer has an area smaller than the area difference between the negative electrode and the positive electrode, and is formed on the outer circumferential surface of the porous substrate of the separator so that it is not necessary to adjust the size or shape of the positive electrode according to the size or shape of the lithium metal layer. Does not affect the capacity of the positive electrode.

The lithium metal layer may have an area of 1% to 40% with respect to 100% of the area of the anode, and specifically, may have an area of 2% to 20%, more specifically 5% to 10%.

When the lithium metal layer has an area of the ratio with respect to the area of the positive electrode, the lithium metal layer is effectively lithium on the positive electrode during degeneration of the lithium secondary battery without affecting the capacity of the positive electrode included in the lithium secondary battery. It may include an amount of lithium source that can replenish ions.

The capacity of the lithium metal layer may be appropriately adjusted according to the capacity of the positive electrode, the capacity of the lithium metal layer is 5% to 60% of the capacity of the positive electrode, specifically 10% to 50%, More specifically, it may be adjusted to have a dose of 20% to 40%.

The lithium metal layer may be connected to a lithium electrode terminal exposed to the outside of the lithium secondary battery. The lithium electrode terminal may be electrically connected to the anode to allow lithium ions to be supplied from the lithium metal layer to the cathode.

That is, the lithium secondary battery may include a positive electrode terminal, a negative electrode terminal, and a lithium electrode terminal connected to the lithium metal layer exposed to the outside of the lithium secondary battery. When the lithium secondary battery is degenerated, the lithium The lithium secondary battery can be recycled by connecting the positive electrode terminal and the positive electrode terminal and supplying lithium ions to the positive electrode by a current flowing between the lithium electrode and the positive electrode.

Since the lithium metal layer surrounds the periphery of the positive electrode, transfer of lithium ions from the lithium metal layer to the positive electrode may be more effectively performed.

The positive electrode can be prepared by conventional methods known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, a binder, a conductive material, and a dispersant in a positive electrode active material, and then applying (coating) to a current collector of a metal material, compressing, and drying the positive electrode to prepare a positive electrode. have.

The current collector of the metallic material is a highly conductive metal, and is a metal to which the slurry of the positive electrode active material can easily adhere, and is particularly limited as long as it has high conductivity without causing chemical change in the battery in the voltage range of the battery. For example, surface treated with carbon, nickel, titanium, silver, or the like on the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel may be used. In addition, fine concavities and convexities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. The current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, and may have a thickness of 3 to 500 μm.

In the method of manufacturing a lithium secondary battery of the present invention, the positive electrode active material is, for example, lithium cobalt oxide (LiCoO ₂ ); Lithium nickel oxide (LiNiO ₂ ); Li [Ni _a Co _b Mn _c M ¹ _d ] O ₂ (wherein M ¹ is any one selected from the group consisting of Al, Ga, and In or two or more elements thereof, and 0.3 ≦ a <1.0, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.1, a + b + c + d = 1); Li (Li _e M ² _{fe-f '} M ³ _f' ) O _{2 - g} A _g (wherein 0≤e≤0.2, 0.6≤f≤1, 0≤f'≤0.2, 0≤g≤0.2 , M ² includes at least one selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn and Ti, M ³ is 1 selected from the group consisting of Al, Mg and B At least one species, and A is at least one species selected from the group consisting of P, F, S and N), or a compound substituted with one or more transition metals; _{Li 1 + h Mn 2 - h} O 4 ( wherein 0≤h≤0.33), LiMnO _3, the lithium manganese oxide such as LiMn ₂ O _3, LiMnO _2; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , Cu ₂ V ₂ O _7, and the like; Formula ^{_{LiNi 1 - i M 4 i O}} 2 Ni site type lithium nickel oxides represented by (wherein, M = ^4, and Co, Mn, Al, Cu, Fe, Mg, B or Ga, 0.01≤i≤0.3); Formula LiMn _{2 - j} M ⁵ _j O ₂ (wherein M ⁵ = Co, Ni, Fe, Cr, Zn or Ta, 0.01 ≦ j ≦ 0.1) or Li ₂ Mn ₃ M ⁶ O ₈ (wherein M ⁶ = Fe, Co, Ni, Cu or Zn) lithium manganese composite oxide; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; LiFe ₃ O ₄ , Fe ₂ (MoO ₄ ) _3, etc. may be mentioned, but is not limited thereto.

Solvents for forming the positive electrode include organic solvents such as N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), acetone, dimethyl acetamide or water, and these solvents alone or in combination of two or more. Can be mixed and used. The amount of the solvent used is sufficient to dissolve and disperse the positive electrode active material, the binder, and the conductive material in consideration of the coating thickness of the slurry and the production yield.

The binder may be polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinylidenefluoride), polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM , Styrene butadiene rubber (SBR), fluorine rubber, poly acrylic acid, and polymers in which hydrogen thereof is replaced with Li, Na, or Ca, or Various kinds of binder polymers such as various copolymers can be used.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, farnes black, lamp black and thermal black; Conductive fibers such as carbon fibers and metal fibers; Conductive tubes such as carbon nanotubes; Metal powders such as fluorocarbon, aluminum and nickel powders; 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 dispersant may be an aqueous dispersant or an organic dispersant such as N-methyl-2-pyrrolidone.

The negative electrode may be manufactured by a conventional method known in the art, and for example, a negative electrode active material slurry is prepared by mixing and stirring the negative electrode active material and additives such as a binder and a conductive material, and then applying the same to a negative electrode current collector and drying it. After compression can be prepared.

The negative electrode active material includes amorphous carbon or crystalline carbon, and specifically, carbon such as non-graphitized carbon and graphite carbon; Li _u Fe ₂ O ₃ (0 ≦ _u ≦ ₁ ), Li _v WO ₂ (0 ≦ _v ≦ ₁ ), SnxMe _1-x Me ' _y O _z (Me: Mn, Fe, Pb, Ge; Me': Al Metal complex oxides such as B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen, 0 <x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , GeO, GeO ₂ , Bi ₂ O ₃ , Bi ₂ O ₄ , And oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The binder may be used to bind the negative electrode active material particles to maintain the molded body, and is not particularly limited as long as it is a conventional binder used in preparing a slurry for the negative electrode active material. For example, the non-aqueous binder may be polyvinyl alcohol, carboxymethyl cellulose, or hydroxy. Propylene cellulose, diacetylene cellulose, polyvinylchloride, polyvinylpyrrolidone, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyethylene or polypropylene, and the like, and acrylic resin as an aqueous binder. Any one or a mixture of two or more selected from the group consisting of ronitrile-butadiene rubber, styrene-butadiene rubber and acrylic rubber can be used. Aqueous binders are economical and environmentally friendly compared to non-aqueous binders, are harmless to the health of workers, and have excellent binding effects compared to non-aqueous binders. Preferably styrene-butadiene rubber may be used.

The binder may be included in less than 10% by weight in the total weight of the slurry for the negative electrode active material, specifically, may be included in 0.1% by weight to 10% by weight. If the content of the binder is less than 0.1% by weight, the effect of using the binder is insignificant and undesirable. If the content of the binder is more than 10% by weight, the capacity per volume may decrease due to the decrease in the relative content of the active material due to the increase in the content of the binder. not.

The conductive material is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black and summer black; 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; Or conductive materials such as polyphenylene derivatives. The conductive material may be used in an amount of 1% by weight to 9% by weight based on the total weight of the slurry for the negative electrode active material.

The negative electrode current collector used for the negative electrode according to an embodiment of the present invention may have a thickness of 3 ㎛ to 500 ㎛. The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, gold, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver and the like, aluminum-cadmium alloy and the like can be used. In addition, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The thickener may be used all thickeners conventionally used in lithium secondary batteries, for example, carboxymethyl cellulose (CMC).

A lithium salt which can be included as an electrolyte used in the present invention can be used without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example the lithium salt of the anion is ^{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 -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO ^₂ may be any one selected from the group consisting of _{^{-, CH 3 CO 2 -,}} SCN - , and _{(CF 3 CF 2 SO 2)} 2 N.

In the electrolyte solution used in the present invention, as the organic solvent included in the electrolyte solution, those conventionally used in the electrolyte for secondary batteries may be used without limitation, and typically propylene carbonate (PC), ethylene carbonate (ethylene carbonate, EC ), Diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane , Vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, any one selected from the group consisting of, or mixtures of two or more thereof may be representatively used. Specifically, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, may be preferably used because they have high dielectric constants to dissociate lithium salts in the electrolyte, and may be preferably used in such cyclic carbonates. When a low viscosity, low dielectric constant linear carbonate such as ethyl carbonate is mixed and used in an appropriate ratio, an electrolyte having high electrical conductivity can be prepared, and thus it can be used more preferably.

Optionally, the electrolyte solution stored according to the present invention may further include additives such as an overcharge inhibitor included in a conventional electrolyte solution.

The lithium secondary battery may be a stack type or a stack and folding type.

The external shape of the lithium secondary battery is not particularly limited, but may be cylindrical, square, pouch type or coin type using a can.

The lithium secondary battery may be used in a battery cell used as a power source of a small device, and may be a unit cell of a battery module including a plurality of battery cells or a medium / large battery module used in a medium-large device.

Preferred examples of the medium-to-large device include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and electric power storage systems.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples, but the present invention is not limited to these Examples and Experimental Examples. Embodiments according to the present invention can be modified in many different forms, the scope of the invention should not be construed as 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.

Example 1

<Production of Separator>

A lithium metal layer was formed by pressing a 2 mm wide and 20 μm thick lithium metal onto the outer circumferential surface of a 30 μm thick porous separator having a polypropylene / polyethylene / polypropylene structure having a size of 4 cm × 5 cm to form a window frame. In this case, when the lithium metal layer surrounds a 3 cm × 4 cm sized anode, lithium metal is attached so that the distance from the anode is 2 mm apart, and a terminal for electrical connection is formed on the lithium metal layer.

<Production of Lithium Secondary Battery>

A positive electrode mixture slurry was prepared by adding 94% by weight of LiNiMnCoO ₂ as a positive electrode active material, 3% by weight of carbon black as a conductive agent, and 3% by weight of PVdF as a binder to N-methyl-2 pyrrolidone (NMP) as a solvent. . The positive electrode mixture slurry was coated and dried on a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, and then roll-rolled to prepare a positive electrode having a thickness of about 70 μm.

The cathode was cut into 3 cm × 4 cm in size and positioned inside the lithium metal layer of the porous separator prepared above, whereby the distance between the lithium metal surrounding the anode and the anode was 2 mm, After contacting the graphite cathode on the other side of the porous separator, 1M LiPF ₆ dissolved electrolyte was injected into a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 30:70. Was prepared.

Example 2

When the lithium metal layer is formed in Example 1, when the lithium metal layer surrounds a cathode having a size of 3 cm × 4 cm, lithium metal is attached so that a distance from the anode is separated by 1 mm, and the anode is attached to the porous separator. The separation membrane and the lithium secondary battery in the same manner as in Example 1, except that the distance between the lithium metal surrounding the positive electrode and the positive electrode was 1 mm while the lithium metal layer was not formed inside. Was prepared.

Example 3

A separator and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the lithium metal layer was formed to have a width of 1 mm and a thickness of 20 μm in Example 1.

Example 4

A separator and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the lithium metal layer was formed to have a width of 3 mm and a thickness of 20 μm in Example 1.

Example 5

<Production of Separator>

A lithium metal layer was formed by pressing a lithium metal having a width of 2 mm and a thickness of 20 μm on the outer circumferential surface of a 30 μm thick porous separator having a polypropylene / polyethylene / polypropylene structure having a size of 5.5 cm × 6.5 cm to form a window frame. At this time, when the lithium metal layer surrounds a 3 cm × 4 cm size of the positive electrode was attached to the lithium metal so that the distance from the positive electrode can be spaced by 10 mm.

<Production of Lithium Secondary Battery>

The cathode prepared in the same manner as in Example 1 was cut into a size of 3 cm × 4 cm and positioned inside the lithium metal layer of the porous separator prepared above, where the lithium metal and the anode surrounding the anode and A lithium secondary battery was manufactured in the same manner as in Example 1, except that the distance was set to 10 mm.

Comparative Example 1

In Example 1, except that a porous membrane having a thickness of 30 μm having a polypropylene / polyethylene / polypropylene structure having a size of 4 cm × 5 cm was used in place of the separator in which the lithium metal layer was formed, the same method as in Example 1 A lithium secondary battery was prepared.

Comparative Example 2

<Production of Lithium Secondary Battery>

A positive electrode mixture slurry was prepared by adding 94% by weight of LiNiMnCoO ₂ as a positive electrode active material, 3% by weight of carbon black as a conductive agent, and 3% by weight of PVdF as a binder to N-methyl-2 pyrrolidone (NMP) as a solvent. . The positive electrode mixture slurry was coated and dried on an aluminum (Al) thin film, which is a positive electrode current collector having a thickness of about 20 μm, and then roll rolled to prepare a positive electrode.

The anode was cut into a size of 3 cm × 4 cm to be in contact with one side of a porous separator having a thickness of 30 μm of a polypropylene / polyethylene / polypropylene structure having a size of 4 cm × 5 cm, and the graphite cathode was brought into contact with the other side of the porous separator. Next, a lithium metal having a width of 3 mm, a length of 5 mm, and a thickness of 20 μm was fixed to the Al thin film by using a roll press on the other surface (Al thin film) of the surface on which the positive electrode mixture layer of the positive electrode was formed, and then fixed by using a roll press. An electrolyte in which 1 M LiPF ₆ was dissolved was injected into a solvent in which (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 30:70 to prepare a lithium secondary battery.

Separation distance between anode and lithium metal layer Area ratio of the lithium metal layer (based on 100% of the area of the anode) Capacity ratio of lithium metal layer (100% of anode area) Example 1 2 mm 20% 30% Example 2 1 mm 20% 30% Example 3 2 mm 10% 15% Example 4 2 mm 30% 45% Example 5 10 mm 20% 30% Comparative Example 1 - - - Comparative Example 2 - - 30%

Experimental Example

The lithium secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 and 2 were charged / discharged at 1C / 1C at 25 ° C., respectively. After confirming that the capacity retention ratio is 70% after 200 cycles, the lithium secondary batteries of Examples 1 to 5 and Comparative Example 2 are electrically connected to each other using terminals formed on the lithium metal of the lithium metal layer formed on the separator. After discharging was further discharged by applying a current. Thereafter, the lithium secondary batteries of Examples 1 to 5 and Comparative Example 2 were charged / discharged at 1C / 1C at 25 ° C., respectively, to confirm capacity retention rates after 100 cycles.

Capacity maintenance rate after 200 cycles Capacity maintenance rate after additional 100 cycles Example 1 70.5% 78.6% Example 2 70.3% 79.2% Example 3 70.5% 66.2% Example 4 70.1% 79.5% Example 5 70.6% 60.1% Comparative Example 1 70.5% 57.3% Comparative Example 2 70.4% 57.5%

Referring to Table 2, the smaller the distance between the lithium metal layer of the positive electrode and the separator, the higher the capacity retention rate after the additional discharge using lithium metal, and the higher the content of the inserted lithium metal, the higher the capacity retention rate after the additional discharge. On the other hand, when lithium metal is placed on the back of the positive electrode current collector as in Comparative Example 2, the degree of improvement in capacity retention of Comparative Example 1 in which the additional discharge was not made even after the additional discharge using the lithium metal was insignificant. This is because the supply of lithium source to the anode was not smooth.

Claims (9)

Porous substrates; And a lithium metal layer formed on one surface of the porous substrate, The lithium metal layer is formed along the outer circumferential surface of the porous substrate, the inside of the hollow secondary battery, the separator for a lithium secondary battery. The method of claim 1, The lithium metal layer has a thickness of 1 μm to 500 μm, a separator for a lithium secondary battery. The method of claim 1, The lithium metal layer has an area of 1% to 40% with respect to 100% of the area of the window frame shape of the hollow inside, the separator for a lithium secondary battery. anode; cathode; And a separator interposed between the positive electrode and the negative electrode, The separator is a porous substrate; And a lithium metal layer formed on one surface of the porous substrate, wherein the lithium metal layer is formed along an outer circumferential surface of the porous substrate and has a hollow window frame shape. The lithium metal layer surrounds the edge of the positive electrode at a position spaced apart from the positive electrode. The method of claim 4, wherein The positive electrode and the lithium metal layer are spaced apart by a distance corresponding to 20% to 12,000% when the thickness of the positive electrode 100%. The method of claim 4, wherein The positive electrode and the lithium metal layer are 10 μm to 10 mm apart from the lithium secondary battery. The method of claim 4, wherein The lithium metal layer has an area of 1% to 40% with respect to 100% of the area of the positive electrode. The method of claim 4, wherein The lithium secondary battery, the capacity of the lithium metal layer has a capacity of 5% to 60% with respect to 100% of the capacity of the positive electrode. The method of claim 4, wherein The lithium secondary battery includes a positive electrode terminal, a negative electrode terminal and a lithium electrode terminal connected to the lithium metal layer exposed to the outside of the lithium secondary battery, The lithium secondary battery which connects the said lithium terminal and the said positive electrode terminal, and supplies lithium ion to the said positive electrode by the electric current which flows between the said lithium electrode and the said positive electrode.

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