Lithium secondary battery and method for manufacturing the same

Abstract

The present invention relates to a lithium secondary battery capable of improving the lifespan performance and high-temperature storage performance of the lithium secondary battery, and a manufacturing method thereof, wherein the lithium secondary battery comprises: a positive electrode comprising a positive electrode active material layer containing a positive electrode active material and one or more additives selected from the group consisting of butanedinitrile (SN), propane sulfone (PS), and propene sulfone (PRS); a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a gel polymer electrolyte, wherein the content of the additive is 0.2 parts by weight to 5.0 parts by weight based on 100 parts by weight of the positive electrode active material layer.

Description

TECHNICAL FIELD

[0001] This application claims priority to Korean Patent Application No. 10-2020-0121824, filed on September 21, 2020, the disclosure of which is incorporated herein by reference.

[0002] The present application relates to a lithium secondary battery and a manufacturing method thereof. BACKGROUND

[0003] Recently, due to the rapid spread of electronic devices using batteries such as mobile phones, notebook computers, electric vehicles, etc., the demand for small and lightweight secondary batteries having relatively high capacity has sharply increased. In particular, lithium secondary batteries are lightweight and have high energy density, thereby attracting attention as a driving power source for portable devices. Accordingly, research and development attempts have been actively made to improve the performance of lithium secondary batteries.

[0004] When lithium ions are intercalated / deintercalated between a cathode and an anode including an active material capable of intercalating and deintercalating lithium ions, a lithium secondary battery generates electric energy through oxidation and reduction reactions. As a cathode active material of a lithium secondary battery, a lithium transition metal oxide is used, and as an anode active material of a lithium secondary battery, lithium metal, lithium alloy, crystalline carbon, amorphous carbon, carbon composite material, etc. are used.

[0005] Generally, a lithium secondary battery is manufactured by injecting an electrolyte in a liquid state into a battery case including an electrode assembly having a cathode, an anode, and a separator wound or stacked therein. Generally, a lithium secondary battery uses an electrolyte in a liquid state, thereby uniformly maintaining the composition of the electrolyte.

[0006] On the other hand, although the electrolyte components (e.g., additives, solvents, etc.) required according to the type of the electrode (cathode or anode) are different, there is a limitation in that, since the composition of the electrolyte is uniform, a plurality of additives, solvents, etc. will be unnecessarily used to satisfy the desired battery performance. In addition, in this case, side reactions can increase due to the unnecessary plurality of additives, solvents, etc., and there is also a limitation that the price can increase due to the additional addition.

[0007] In addition, when the electrolyte components are adjusted to be different according to the type of the electrode to satisfy the desired battery performance, the solvents, additives, etc. move until the composition in the electrolyte becomes uniform, i.e., until the concentration balance is reached, due to the concentration difference of the electrolyte components, thereby there is a limitation that the battery performance deteriorates over time.

[0008] Accordingly, there is a need for a lithium secondary battery having improved lifespan performance and high-temperature storage performance, i.e., capable of maintaining the initial performance for a long time, without including unnecessary plurality of additives. SUMMARY

[0009] TECHNICAL PROBLEM

[0010] An aspect of the present application provides a lithium secondary battery and a manufacturing method thereof, which can improve the life performance and high-temperature storage performance of the lithium secondary battery.

[0011] TECHNICAL SOLUTION

[0012] According to an aspect of the present application, there is provided a lithium secondary battery including: a positive electrode including a positive electrode active material layer containing a positive electrode active material and one or more additives selected from the group consisting of butanedinitrile (SN), propane sultone (PS), and propene sultone (PRS); a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a gel polymer electrolyte, wherein the content of the additive is 0.2 parts by weight to 5.0 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0013] According to another aspect of the present application, there is provided a method of manufacturing a lithium secondary battery, the method including the steps of:

[0014] (A) preparing a positive electrode including a positive electrode active material layer containing a positive electrode active material and one or more additives selected from the group consisting of butanedinitrile (SN), propane sultone (PS), and propene sultone (PRS);

[0015] (B) inserting an electrode assembly, which is composed of the positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, into a battery case; and

[0016] (C) injecting a composition for forming a gel polymer electrolyte into the battery case into which the electrode assembly is inserted, and then curing the composition for forming a gel polymer electrolyte to prepare a gel polymer electrolyte,

[0017] wherein the content of the additive is 0.2 parts by weight to 5.0 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0018] ADVANTAGEOUS EFFECTS

[0019] The lithium secondary battery according to the present application includes a positive electrode including a positive electrode active material layer containing a specific type of additive in a specific content, and a gel polymer electrolyte, whereby the additive can be prevented from moving so as to balance the concentration balance while not including unnecessary multiple additives, so that the life performance and high-temperature storage performance are excellent.

[0020] A method of manufacturing a lithium secondary battery can provide a lithium secondary battery having improved lifespan performance and high-temperature storage performance without adding or changing a specific device in a process. DETAILED DESCRIPTION

[0021] It will be understood that the words or terms used in the description and claims of the present invention should not be interpreted as limited to the meanings defined in commonly used dictionaries. It will be further understood that the words or terms should be interpreted as having a meaning consistent with their meaning in the context of the relevant field and technical ideas of the present invention, based on the principle that the inventor can appropriately define the meaning of the words or terms to best explain the present invention.

[0022] In this specification, it should be understood that the terms "include", "comprising" or "having" are intended to clarify the existence of the stated features, numbers, steps, elements or their combinations, but do not exclude the existence or addition of one or more other features, numbers, steps, elements or their combinations.

[0023] Hereinafter, the present invention will be described in more detail.

[0024] Lithium secondary battery

[0025] The lithium secondary battery according to the present invention includes: a positive electrode, the positive electrode including a positive electrode active material layer, the positive electrode active material layer containing a positive electrode active material and one or more additives selected from the following: succinonitrile (SN), propane sultone (PS) and propene sultone (PRS); a negative electrode; a separator, the separator being interposed between the positive electrode and the negative electrode; and a gel polymer electrolyte, wherein the content of the additive is 0.2 to 5.0 parts by weight based on 100 parts by weight of the positive electrode active material layer.

[0026] positive electrode

[0027] The positive electrode includes a positive electrode active material layer containing a positive electrode active material and one or more additives selected from the group consisting of succinonitrile (SN), propane sultone (PS), and propene sultone (PRS). Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer being located on at least one surface of the positive electrode current collector and containing the additive and the positive electrode active material.

[0028] The positive electrode current collector is not particularly limited as long as it has electrical conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon; or aluminum or stainless steel subjected to surface treatment with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foamed body, a nonwoven fabric body, etc.

[0029] In addition to the additive and the positive electrode active material, the positive electrode active material layer can further include a conductive material and a binder.

[0030] According to the present application, the additive can be one or more selected from the group consisting of butanedinitrile (SN), propane sultone (PS), and propene sultone (PRS), preferably butanedinitrile (SN), propane sultone (PS), and propene sultone (PRS), and more preferably butanedinitrile (SN). The additive can inhibit side reactions that can occur in the gel polymer electrolyte to reduce the generation of gas. In addition, the additive can be uniformly distributed in the thickness direction in the positive electrode active material layer without affecting the physical properties of the positive electrode. When the additive is not uniformly present in the positive electrode active material layer but is enriched on the surface of the positive electrode active material layer, there can be a problem in that the additive acts to hinder the movement of lithium ions, thereby deteriorating the mobility of lithium.

[0031] The additive can exist in a gel state. Since the additive exists only in the positive electrode active material layer and rarely moves into the gel polymer electrolyte, the lithium secondary battery according to the present application can have excellent lifespan performance. That is, the additive does not penetrate the separator and diffuse to the negative electrode but exists only in the positive electrode, thereby continuously protecting the positive electrode.

[0032] According to the present application, the content of the additive can be 0.2 parts by weight to 5.0 parts by weight, preferably 0.5 parts by weight to 3.0 parts by weight, and more preferably 1.0 parts by weight to 3.0 parts by weight, based on 100 parts by weight of the positive electrode active material layer. When the content of the additive is less than 0.2 parts by weight based on 100 parts by weight of the positive electrode active material layer, there is a problem in that the performance of the additive cannot be exhibited. When the content of the additive is greater than 5.0 parts by weight based on 100 parts by weight of the positive electrode active material layer, there is a problem in that the additive interferes with the movement of lithium ions, causing an increase in the resistance of the secondary battery. When the content of the additive is within the above range, side reactions with the electrolyte at high temperatures are inhibited, and the resistance of the secondary battery does not increase, so that the storage performance is excellent and the lifespan performance is also improved.

[0033] According to the present application, the positive electrode active material can be one or more selected from the group consisting of NCM-based positive electrode active materials, NCA-based positive electrode active materials, NCMA-based positive electrode active materials, and LiFePO4.

[0034] Specifically, the positive electrode active material can have a composition represented by the following Formula 1.

[0035] [Formula 1]

[0036] Li x [Ni a Co b M 1 c M 2 d ]O2

[0037] In the above Formula 1,

[0038] M 1 is one or more selected from the group consisting of Mn and Al,

[0039] M 2 is one or more selected from the group consisting of B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta, and W, and

[0040] 0.9≤x≤1.2, 0.5≤a<1, 0<b<0.5, 0<c<0.5, 0≤d≤0.1, and a+b+c+d=1.

[0041] a represents an atomic fraction of nickel among the metal elements other than lithium in the positive electrode active material, and a can satisfy 0.5≤a<1, 0.6≤a≤0.98, or 0.7≤a≤0.95.

[0042] b represents an atomic fraction of cobalt among the metal elements other than lithium in the positive electrode active material, and b can satisfy 0<b<0.5, 0.01≤b≤0.4, or 0.01≤b≤0.3.

[0043] c represents an element fraction of M 1 elements among the metal elements other than lithium in the positive electrode active material, and c can satisfy 0<c<0.5, 0.01≤c≤0.4, or 0.01≤c≤0.3.

[0044] d represents an element fraction of M 2 elements among the metal elements other than lithium in the positive electrode active material, and d can satisfy 0≤d≤0.1 or 0≤d≤0.05.

[0045] The content of the positive active material can be 80 parts by weight to 99 parts by weight, more specifically 85 parts by weight to 98 parts by weight, based on 100 parts by weight of the positive active material layer. When the content is within the above content range, excellent life performance can be exhibited.

[0046] The conductive material is used to impart conductivity to the electrode, and any conductive material can be used without particular limitation, as long as it has electron conductivity and does not cause chemical changes in the battery to be constructed. Specific examples of the conductive material can include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal crack black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one of the above materials or a mixture of two or more thereof can be used. The content of the conductive material can be 1 part by weight to 30 parts by weight, based on 100 parts by weight of the positive active material layer.

[0047] The binder is used to improve the binding between the positive active material particles and the adhesion between the positive active material and the current collector. Specific examples of the binder can include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers of the above materials, and any one of the above materials or a mixture of two or more thereof can be used. The content of the binder can be 1 part by weight to 30 parts by weight, based on 100 parts by weight of the positive active material layer.

[0048] Negative electrode

[0049] The negative electrode includes a negative current collector and a negative active material layer on the negative current collector.

[0050] According to the present application, the negative electrode can not include one or more additives selected from the group consisting of butanedinitrile (SN), propane sultone (PS), and propene sultone (PRS). This is because the additive does not cause a large reaction in the negative electrode, and when the additive is included in the negative electrode, there is a problem that the resistance of the secondary battery increases. In addition, when the additive is included in the negative electrode, an unnecessary side reaction such as adsorption of the additive on the surface of the negative electrode (e.g., copper foil) can occur, and the initial resistance of the secondary battery can increase due to a decrease in the ionic conductivity of lithium ions in the negative electrode. Thus, there can be a problem that the life of the secondary battery is shortened.

[0051] The negative current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, baked carbon; copper or stainless steel subjected to surface treatment with one of carbon, nickel, titanium, silver, and the like; aluminum-cadmium alloy, and the like can be used. Furthermore, the negative current collector can generally have a thickness of 3 μm to 500 μm, and as in the case of the positive current collector, fine irregularities can be formed on the surface of the negative current collector to improve the adhesion of the negative active material. For example, the negative current collector can be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, and a nonwoven fabric body.

[0052] The negative active material layer selectively contains a binder and a conductive material in addition to the negative active material.

[0053] The negative active material layer can be prepared by coating a negative mixture material prepared by dispersing a negative active material and, optionally, a binder and a conductive material in a solvent on a negative current collector, and then drying. Alternatively, the negative active material layer can be prepared by casting a negative mixture material on a separate support, and then laminating the film peeled from the support on a negative current collector.

[0054] As the negative active material, a compound capable of reversibly intercalating and deintercalating lithium can be used. Specific examples of the negative active material can include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; (semi)metal-based materials capable of forming alloys with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; (semi)metal oxides that can be doped and not doped with lithium such as SnO, SnO2, vanadium oxides, and lithium vanadium oxides; or composite materials containing (semi)metal-based materials and carbonaceous materials such as Si-C composite materials or Sn-C composite materials, and any one of the above materials or a mixture of two or more thereof can be used. In addition, a metal lithium thin film can be used as the negative active material. Furthermore, low-crystalline carbon, high-crystalline carbon, and the like can all be used as the carbon material. Representative examples of the low-crystalline carbon can include soft carbon and hard carbon, and representative examples of the high-crystalline carbon can include irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbead, mesophase pitch, and high-temperature sintered carbon such as petroleum or coal tar pitch-derived coke. β (0 < β < 2), SnO2, vanadium oxides, and lithium vanadium oxides; or composite materials containing (semi)metal-based materials and carbonaceous materials such as Si-C composite materials or Sn-C composite materials, and any one of the above materials or a mixture of two or more thereof can be used. In addition, a metal lithium thin film can be used as the negative active material. Furthermore, low-crystalline carbon, high-crystalline carbon, and the like can all be used as the carbon material. Representative examples of the low-crystalline carbon can include soft carbon and hard carbon, and representative examples of the high-crystalline carbon can include irregular, planar, flaky, spherical, or fibrous natural graphite or artificial graphite, condensed graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesocarbon microbead, mesophase pitch, and high-temperature sintered carbon such as petroleum or coal tar pitch-derived coke.

[0055] The content of the negative active material can be 80 parts by weight to 99 parts by weight based on 100 parts by weight of the negative active material layer.

[0056] The binder is a component that contributes to the binding between the conductive material, the active material, and the current collector, and is generally added in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the negative active material layer. Examples of the binder can include: polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, various copolymers of the above materials, and the like.

[0057] The conductive material is a component for further improving the conductivity of the negative active material, and can be added in an amount of 10 parts by weight or less, preferably 5 parts by weight or less, based on 100 parts by weight of the negative active material layer. The conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal crack black; conductive fibers such as carbon fibers and metal fibers; fluorinated carbon; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive materials such as polyphenylene derivatives, and the like, can be used.

[0058] Separator

[0059] The separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. In particular, it is preferable that the separator have excellent moisture retention with respect to the electrolyte and have low resistance to the movement of ions in the electrolyte.

[0060] According to the present application, the separator can be a porous polymer film. For example, a porous polymer film manufactured using a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer; or a laminated structure of two or more layers of the above porous polymer films can be used.

[0061] The separator is not a gel-type separator, thereby having the advantage that no special device or change in the currently used process is required to manufacture the secondary battery, which does not incur additional costs.

[0062] Gel polymer electrolyte

[0063] The gel polymer electrolyte is an electrolyte containing a polymer whose fluidity is inhibited, and can have a phase angle δ value of greater than or equal to 45°, specifically greater than or equal to 60°, which is one of indexes for measuring the viscoelasticity of a material. In this case, because the fluidity of the electrolyte is low, the movement of the additive is limited, so that the additive can continuously be enriched in the positive electrode, thereby continuously protecting the positive electrode.

[0064] The gel polymer electrolyte can include a polymer and a lithium salt.

[0065] The polymer can be a cured product of a curable polymer such as a thermosetting polymer, a photocurable polymer, an electron beam-curable polymer, etc. For example, the polymer can be a cured product of an acrylic polymer having a weight average molecular weight (Mw) of 1,000 to 10,000.

[0066] Any compound can be used as the lithium salt without particular limitation, as long as it can provide lithium ions used in a lithium secondary battery. Specifically, as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. can be used. The lithium salt can be used in a concentration range of 0.1 M to 2.0 M. When the concentration of the lithium salt is in the above range, the electrolyte has proper conductivity and viscoelasticity, thereby exhibiting excellent performance, and lithium ions can move effectively.

[0067] To improve the life performance of the battery, suppress the decrease in the capacity of the battery, and improve the discharge capacity of the battery, the gel polymer electrolyte can further include one or more electrolyte additives, for example: halogenated alkylene carbonate compounds (such as difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (glycol) dimethyl ether, hexamethylphosphoramide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted azolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, etc.

[0068] As described above, the lithium secondary battery according to the present application exhibits excellent life performance and excellent high-temperature storage performance, thereby being applicable to: portable devices such as mobile phones, laptop computers, and digital cameras; and the electric vehicle field such as a hybrid electric vehicle (HEV).

[0069] Therefore, a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module can be provided.

[0070] The battery module or battery pack can be used as a power source for a large-sized device, for example, one or more of: a power tool; an electric vehicle, such as an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); or a power storage system.

[0071] The outer shape of the lithium secondary battery of the present application is not particularly limited, but can be: a cylindrical shape, a square shape, a pouch shape, a coin shape, etc. using a can.

[0072] The lithium secondary battery according to the present application can be used in a battery cell used as a power source for a small-sized device, and can also be preferably used as a unit cell of a large-sized battery module including a plurality of battery cells.

[0073] Method for manufacturing lithium secondary battery

[0074] The method of manufacturing a lithium secondary battery according to the present application includes the following steps:

[0075] (A) preparing a positive electrode including a positive electrode active material layer containing a positive electrode active material and one or more additives selected from the group consisting of butanedinitrile (SN), propane sulfone (PS), and propene sulfone (PRS);

[0076] (B) inserting an electrode assembly into a battery case, the electrode assembly being composed of the positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; and

[0077] (C) injecting a composition for forming a gel polymer electrolyte into the battery case into which the electrode assembly is inserted, and then curing the composition for forming a gel polymer electrolyte to prepare a gel polymer electrolyte.

[0078] The content of the additive is 0.2 parts by weight to 5.0 parts by weight, based on 100 parts by weight of the positive electrode active material layer.

[0079] The lithium secondary battery according to the present application can be manufactured by the method for manufacturing a lithium secondary battery.

[0080] Hereinafter, each step of the method of manufacturing a lithium secondary battery will be described in detail.

[0081] Step (A)

[0082] Step (A) is a step of preparing a positive electrode including a positive electrode active material layer containing a positive electrode active material and one or more additives selected from the group consisting of butanedinitrile (SN), propane sultone (PS), and propene sultone (PRS).

[0083] According to the present application, the above-mentioned step (A) can include:

[0084] i) preparing a composition for forming a positive electrode active material layer including a positive electrode active material and one or more additives selected from the group consisting of butanedinitrile (SN), propane sultone (PS), and propene sultone (PRS); and

[0085] ii) coating the composition for forming a positive electrode active material layer on a current collector, followed by drying the coated composition to form a positive electrode active material layer.

[0086] In the present application, during the manufacture of a positive electrode, an additive is added to a composition for forming a positive electrode active material layer, so that the additive can exist in a solid state in the manufactured positive electrode.

[0087] Specifically, a positive electrode active material layer can be prepared by coating a composition for forming a positive electrode active material layer prepared by dispersing an additive, a positive electrode active material, and optionally a binder and a conductive material in a solvent on a positive electrode current collector, and then drying and roll-pressing.

[0088] The positive electrode active material, the binder, and the conductive material have been described above in the description of the lithium secondary battery according to the present application, and thus detailed description thereof will be omitted. Hereinafter, only the remaining ingredients will be described in detail.

[0089] The solvent can be a solvent generally used in the art, and can be dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl pyrrolidone (NMP), acetone, water, or the like. Any one of the above solvents or a mixture of two or more thereof can be used. The amount of the solvent used is just enough in that the solvent can dissolve or disperse the positive electrode active material, the binder, and the conductive material, and thereafter has a viscosity that can exhibit excellent thickness uniformity during coating for manufacturing a positive electrode, if the coating thickness and the manufacturing yield of the slurry are taken into account.

[0090] Further, in another method, a positive electrode can be manufactured by casting a composition for forming a positive electrode active material layer on a separate support, and then laminating a film obtained by peeling off from the support on a positive electrode current collector.

[0091] Step (B)

[0092] Step (B) is a step of inserting an electrode assembly composed of a cathode, an anode, and a separator interposed between the cathode and the anode into a battery case.

[0093] The anode can be manufactured by the same method as the cathode except that the anode active material is used instead of the cathode active material.

[0094] The separator has been described above in the description of the lithium secondary battery according to the present application, and thus a detailed description thereof will be omitted.

[0095] Step (C)

[0096] Step (C) is a step of injecting a composition for forming a gel polymer electrolyte into the battery case into which the electrode assembly is inserted, and then curing the composition for forming a gel polymer electrolyte to prepare a gel polymer electrolyte.

[0097] When the composition for forming a gel polymer electrolyte is injected into the battery case into which the electrode assembly is inserted, the additive included in the cathode active material layer can be dissolved and liquefied in the solvent included in the composition for forming a gel polymer electrolyte until the composition for forming a gel polymer electrolyte is cured. Further, after the composition for forming a gel polymer electrolyte is cured, the additive dissolved in the solvent can exist in a gel state. On the other hand, the present application uses a gel polymer electrolyte instead of a liquid electrolyte, so that the movement of the additive is limited, thereby allowing the additive to continuously be enriched in the cathode, thereby continuously protecting the cathode. That is, even when the additive included in the cathode active material layer is dissolved in the solvent included in the composition for forming a gel polymer electrolyte, the additive can exist only in the cathode without penetrating the separator and diffusing to the anode.

[0098] The composition for forming a gel polymer electrolyte can include a curable polymer, a non-aqueous organic solvent, and a lithium salt.

[0099] The curable polymer can be a thermosetting polymer, a photocurable polymer, an electron beam-curable polymer, or the like. For example, the curable polymer can be an acrylic polymer having a weight average molecular weight (Mw) of 1,000 to 10,000.

[0100] Any non-aqueous organic solvent can be used as the non-aqueous organic solvent without particular limitation, as long as it can be used as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the non-aqueous organic solvent, an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; an ether-based solvent such as dibutyl ether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; an aromatic hydrocarbon-based solvent such as benzene and fluorobenzene; a carbonate-based solvent such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); an alcohol-based solvent such as ethanol and isopropanol; a nitrile such as R-CN (wherein R is a linear, branched, or cyclic C2 to C20 hydrocarbon group and can include a double bond, an aromatic ring, or an ether bond); an amide such as dimethylformamide; a dioxolane such as 1,3-dioxolane; or a sulfolane can be used. Among the above-mentioned solvents, a carbonate-based solvent is preferred, and more preferably a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate). In this case, when the cyclic carbonate and the linear carbonate are mixed at a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte solution can be excellent.

[0101] Any compound can be used as the lithium salt without particular limitation, as long as it can provide lithium ions used in the lithium secondary battery. Specifically, as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, and the like can be used. The lithium salt can be used at a concentration in the range of 0.1 M to 2.0 M. When the concentration of the lithium salt is in the above range, the electrolyte has proper conductivity and viscoelasticity, thereby exhibiting excellent performance, and lithium ions can move effectively.

[0102] Preferred Embodiments

[0103] Hereinafter, embodiments of the present application will be described in detail so that those skilled in the art can easily practice the present application. However, the present application can be embodied in many different forms and is not limited to the embodiments set forth herein.

[0104] Examples and Comparative Examples

[0105] Example 1

[0106] LiNi0.8 Co 0.1 Mn 0.1 O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and butyrolactone (SN) were mixed in a weight ratio of 93:2:2:3 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode. At this time, butyrolactone contained in the positive active material layer was present in a solid state.

[0107] Artificial graphite, carbon black (Super P, Timcal), a conductive material, and a PVdF binder as a negative active material were mixed in a weight ratio of 96:1:3 in an N-methylpyrrolidone solvent to prepare a composition for forming a negative active material, and the composition was coated on one surface of a copper current collector, dried at 120°C, and then roll-pressed to manufacture a negative electrode.

[0108] A solution in which 1.0 M of LiPF6 was contained in a non-aqueous organic solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) were mixed in a weight ratio of 30:70, based on 100 parts by weight of the non-aqueous organic solvent, was mixed with 5 parts by weight of an acrylic polymer having a weight average molecular weight of 3,000 to prepare a composition for forming a gel polymer electrolyte.

[0109] A porous polyethylene separator was interposed between the positive electrode and the negative electrode manufactured as described above to manufacture an electrode assembly, and the electrode assembly was placed inside a battery case. Thereafter, the composition for forming a gel polymer electrolyte was injected into the case, and the composition for forming a gel polymer electrolyte was thermally cured at 40°C to form a gel polymer electrolyte, thereby manufacturing a lithium secondary battery. At this time, butyrolactone contained in the positive active material layer of the lithium secondary battery was present in a gel state.

[0110] Example 2

[0111] A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi 0.8 Co 0.1 Mn 0.1 O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and butyrolactone (SN) were mixed in a weight ratio of 95.5:2:2:0.5 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode. At this time, butyrolactone contained in the positive active material layer was present in a solid state.

[0112] Example 3

[0113] A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8 Co 0.1 Mn 0.1 O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 93:2:2:3 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and a lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material.

[0114] Example 4

[0115] A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material, and a composition for forming a positive active material was prepared by mixing LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and butyrolactone (BN) in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent. 0.8 Co 0.1 Mn 0.1 O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 93:2:2:3 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and a lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material.

[0116] Comparative Example 1

[0117] A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material, and a composition for forming a positive active material was prepared by mixing LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and butyrolactone (BN) in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent. 0.8 Co 0.1 Mn 0.1 O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 93:2:2:3 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and a lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material.

[0118] Comparative Example 2

[0119] A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material, and a composition for forming a positive active material was prepared by mixing LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and butyrolactone (BN) in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent. 0.8 Co 0.1 Mn 0.1 O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 93:2:2:3 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and a lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material.

[0120] Comparative Example 3

[0121] A lithium secondary battery was manufactured in the same manner as in Example 1, except that LiNi0.8Co0.1Mn0.1O2was used as the positive active material, and a composition for forming a positive active material was prepared by mixing LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal), a conductive material, a PVdF binder, and butyrolactone (BN) in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent. 0.8 Co 0.1 Mn 0.1A lithium secondary battery was manufactured in the same manner as in Example 1, except that O2, carbon black (Super P, Timcal) conductive material, PVdF binder and succinonitrile (SN) were mixed in an N-methylpyrrolidone solvent at a weight ratio of 86:2:2:10 to prepare a composition for forming a positive electrode active material.

[0122] Comparative Example 4

[0123] In addition to LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that O2, carbon black (Super P, Timcal) conductive material, PVdF binder and succinonitrile (SN) were mixed in an N-methylpyrrolidone solvent in a weight ratio of 95.9:2:2:0.1 to prepare a composition for forming a positive electrode active material.

[0124] Comparative Example 5

[0125] LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, carbon black (Super P, Timcal) conductive material and PVdF binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 96:2:2 to prepare a composition for forming a positive electrode active material, and the composition was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode.

[0126] Artificial graphite as a negative electrode active material, carbon black (Super P, Timcal) conductive material and PVdF binder were mixed in an N-methylpyrrolidone solvent in a weight ratio of 96:1:3 to prepare a composition for forming a negative electrode active material, and the composition was coated on one surface of a copper current collector, dried at 120°C, and then roll-pressed to manufacture a negative electrode.

[0127] In a solution in which 1.0 M LiPF6 was contained in a non-aqueous organic solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) mixed in a weight ratio of 30:70, 1 part by weight of succinonitrile was mixed based on 100 parts by weight of the non-aqueous organic solvent to prepare an electrolyte.

[0128] A porous polyethylene separator was interposed between the positive electrode and the negative electrode manufactured as described above to manufacture an electrode assembly, and the electrode assembly was placed in a battery case. Thereafter, an electrolyte was injected into the case to manufacture a lithium secondary battery.

[0129] Comparative Example 6

[0130] LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal) conductive material, PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition for forming a positive active material was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode. 0.8 Co 0.1 Mn 0.1 LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal) conductive material, PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition for forming a positive active material was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode.

[0131] Comparative Example 7

[0132] LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal) conductive material, PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition for forming a positive active material was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode. 0.8 Co 0.1 Mn 0.1 LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal) conductive material, PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition for forming a positive active material was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode.

[0133] Comparative Example 8

[0134] LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal) conductive material, PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition for forming a positive active material was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode. 0.8 Co 0.1 Mn 0.1 LiNi0.8Co0.1Mn0.1O2, carbon black (Super P, Timcal) conductive material, PVdF binder, and propane sultone (PS) were mixed in a weight ratio of 89:2:2:7 in an N-methylpyrrolidone solvent to prepare a composition for forming a positive active material, and the composition for forming a positive active material was coated on one surface of an aluminum current collector, dried at 130°C, and then roll-pressed to manufacture a positive electrode.

[0135] Thereafter, succinonitrile (SN) was dissolved in an N-methylpyrrolidone solvent at 5% by weight, coated on the surface of the positive electrode, and then dried to form a coating layer.

[0136] Artificial graphite as a negative active material, carbon black (Super P, Timcal) conductive material, and PVdF binder were mixed in a weight ratio of 96:1:3 in an N-methylpyrrolidone solvent to prepare a composition for forming a negative active material, and the composition was coated on one surface of a copper current collector, dried at 120°C, and then roll-pressed to manufacture a negative electrode.

[0137] A solution in which 1.0 M of LiPF6is contained in a non-aqueous organic solvent in which ethylene carbonate (EC) and ethylmethyl carbonate (EMC) are mixed at a weight ratio of 30:70, based on 100 parts by weight of the non-aqueous organic solvent, 5 parts by weight of an acrylic polymer having a weight average molecular weight of 3,000 is mixed in, to prepare a composition for forming a gel polymer electrolyte.

[0138] A porous polyethylene separator is interposed between the positive electrode and the negative electrode manufactured as described above, to manufacture an electrode assembly, and the electrode assembly is placed in a battery case. Thereafter, the composition for forming a gel polymer electrolyte is injected into the case, and the composition for forming a gel polymer electrolyte is heat-cured at 40°C to form a gel polymer electrolyte, thereby manufacturing a lithium secondary battery.

[0139] Experimental examples

[0140] Experimental Example 1: Evaluation of gas generation increase rate and resistance increase rate after high-temperature storage

[0141] Each of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 8 was charged to 4.2 V and the volume thereof was measured. Each of the secondary batteries was left to stand at 60°C for 4 weeks, and the volume of each of the secondary batteries was measured. The increase rate of the volume after the standing at 60°C with respect to the volume before the standing at 60°C is shown in Table 1 below as the gas generation increase rate.

[0142] In addition, each of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 8 was charged to 4.2 V, discharged to SOC 50% at room temperature, and then instantaneously discharged at 2.5 C for 10 seconds, to measure the amount of change in voltage. The charging voltage was divided by the current, to confirm the resistance of each of the secondary batteries. Each of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 8 was charged to 4.2 V, and then left to stand at 60°C for 4 weeks. The resistance of each of the secondary batteries was confirmed in the same manner. The increase rate of the resistance after the standing at 60°C with respect to the resistance before the standing at 60°C is shown in Table 1 below.

[0143] [Table 1]

[0144] Gas generation increase rate (%) Resistance increase rate (%) Example 1 1.8 9.3 Example 2 2.5 9.8 Example 3 2.0 9.5 Example 4 2.2 9.6 Comparative example 1 2.8 10.2 Comparative example 2 1.5 12.7 Comparative example 3 1.4 15.3 Comparative example 4 2.8 10.5 Comparative example 5 2.7 10.2 Comparative example 6 1.8 13.1 Comparative example 7 2.0 13.2 Comparative example 8 1.7 12.2

[0145] Referring to Table 1 above, it can be confirmed that each of the secondary batteries of Examples 1 to 4, based on 100 parts by weight of the positive electrode active material layer, has a content of 3 parts by weight to 0.5 parts by weight of malononitrile, propane sultone or propene sultone, has excellent high-temperature storage performance, compared to the secondary battery of Comparative Example 1 not containing malononitrile and the secondary battery of Comparative Example 4 based on 100 parts by weight of the positive electrode active material layer, a content of 0.1 parts by weight of malononitrile. That is, it can be confirmed that both the gas generation increase rate and the resistance increase rate after high-temperature storage are low. In particular, it can be confirmed that the high-temperature storage performance of the secondary battery of Example 1 is significantly excellent. On the contrary, each of the secondary batteries of Comparative Examples 2, 3, 6 and 7, which contain an excessive amount of malononitrile, propane sultone or propene sultone, has a significantly high resistance increase rate because the additives interfere with the movement of lithium ions. In addition, it can be confirmed that the secondary battery of Comparative Example 5, which uses an electrolyte containing malononitrile and in a liquid state, has poor high-temperature storage performance.

[0146] In addition, it can be confirmed that the secondary battery of Comparative Example 8, which does not contain malononitrile in the positive electrode active material layer but coats malononitrile on the surface of the positive electrode active material layer, has poor high-temperature storage performance.

[0147] Experimental Example 2: Evaluation of initial charge / discharge capacity and capacity retention rate

[0148] For each of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 8, the initial charge / discharge capacity and the capacity retention rate were evaluated.

[0149] Each lithium secondary battery was charged at a constant current of 0.1 C until the voltage reached 4.2 V at 25°C, and then discharged at a constant current of 0.1 C until the voltage reached 2.5 V. The initial charge / discharge capacity value is shown in Table 2.

[0150] In addition, in the range of 2.5 to 4.2 V, a charge / discharge cycle was repeated 100 times at a constant current of 0.33 C at 45°C to measure the capacity of the lithium secondary battery, and the ratio of the capacity of the 1st cycle to the capacity of the 100th cycle was shown as the capacity retention rate in Table 2.

[0151] [Table 2]

[0152]

[0153] Referring to Table 2, it can be confirmed that each of the secondary batteries of Examples 1 to 4 has a significantly excellent capacity retention rate compared to each of the secondary batteries of Comparative Examples 1 to 8. This is because, in the case of each of the secondary batteries of Examples 1 to 4, the gas generated due to a side reaction is reduced, so that the resistance reduction caused by the gas is reduced.

[0154] Accordingly, it can be seen that the lithium secondary battery according to the present application includes a cathode in which the content of a specific type of additive is 0.2 parts by weight to 5.0 parts by weight based on 100 parts by weight of a cathode active material layer and a gel polymer electrolyte, thereby preventing the movement of the additive to balance the concentration balance while not including an unnecessarily large number of additives, so that the life performance and high-temperature storage performance of the battery are excellent.

[0155] Further, it can be seen that the method of manufacturing a lithium secondary battery according to the present application can provide a lithium secondary battery having improved life performance and high-temperature storage performance without adding or changing a specific device in the process.

Claims

1. A lithium secondary battery, comprising: a positive electrode including a positive electrode active material layer containing a positive electrode active material and one or more additives selected from succinonitrile, propanesultone, and propenesultone; a negative electrode; a separator interposed between the positive electrode and the negative electrode; and a gel polymer electrolyte, in, based on 100 parts by weight of the positive electrode active material layer, the content of the additive is 0.2 to 5.0 parts by weight, the additive is uniformly distributed in the positive electrode active material layer in the thickness direction.

2. The lithium secondary battery according to claim 1, wherein Based on 100 parts by weight of the positive electrode active material layer, the content of the additive is 0.5 to 3.0 parts by weight.

3. The lithium secondary battery according to claim 1, wherein The positive electrode active material has a composition represented by the following formula 1: [Formula 1] Li x [Ni a Co b M 1 c M 2 d ]O2 wherein, in the above formula 1, M 1 is one or more selected from Mn and Al, M 2 is one or more selected from B, Mg, Ca, Ti, V, Cr, Fe, Zn, Ga, Y, Zr, Nb, Mo, Ta and W, and 0.9 ≤ x ≤ 1.2, 0.5 ≤ a < 1, 0 < b < 0.5, 0 < c < 0.5, 0 ≤ d ≤ 0.1 and a + b + c + d = 1.

4. The lithium secondary battery according to claim 1, wherein The negative electrode does not contain the additive.

5. The lithium secondary battery according to claim 1, wherein The separator is a porous polymer membrane.

6. The lithium secondary battery according to claim 1, wherein The gel polymer electrolyte has a phase angle δ of 45° or more.

7. A method for manufacturing a lithium secondary battery, the method comprising the following steps: (A) Preparing a positive electrode including a positive electrode active material layer containing a positive electrode active material and one or more additives selected from succinonitrile, propanesultone, and propenesultone; (B) Inserting an electrode assembly into a battery case, the electrode assembly being composed of the positive electrode, the negative electrode, and a separator interposed between the positive electrode and the negative electrode; and (C) Injecting a composition for forming a gel polymer electrolyte into the battery case into which the electrode assembly is inserted, and then curing the composition for forming a gel polymer electrolyte to prepare a gel polymer electrolyte, in, based on 100 parts by weight of the positive electrode active material layer, the content of the additive is 0.2 to 5.0 parts by weight, the additive is uniformly distributed in the positive electrode active material layer in the thickness direction.

8. The method according to claim 7, wherein: Based on 100 parts by weight of the positive electrode active material layer, the content of the additive is 0.5 to 3.0 parts by weight.

9. The method according to claim 7, wherein: [[ID= ​ ​ 10. The method according to claim 7, wherein: ​ 11. The method according to claim 7, wherein: ​

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