Electrode assembly, lithium secondary battery containing the same and manufacturing method thereof

Abstract

The present invention relates to an electrode assembly, a lithium secondary battery including the same, and a method for manufacturing the same. The electrode assembly comprises a separator having coating layers on both sides. By adjusting the binder content of the first coating layer of the separator facing the negative electrode to be higher than the binder content of the second coating layer disposed on the other side, high adhesion between the negative electrode and the separator can be achieved even when the lamination process is performed under milder conditions compared to conventional methods during manufacturing. Furthermore, this has the advantage of preventing degradation of battery performance due to excessive bonding between the positive electrode and the separator, as well as improving the rigidity of the battery.

Description

Technology Field

[0001] The present invention relates to an electrode assembly, a lithium secondary battery including the same, and a method for manufacturing the same. More specifically, it relates to a lithium secondary battery in which lamination is possible under mild conditions, thereby improving battery performance and rigidity, and a method for manufacturing the same. Background Technology

[0003] Recently, secondary batteries are being widely applied not only to small devices such as portable electronic devices, but also to medium and large devices such as battery packs or power storage devices for hybrid or electric vehicles. Examples of such secondary batteries include lithium-ion batteries, lithium batteries, lithium-ion capacitors, and non-aqueous electrolyte batteries such as sodium-ion batteries.

[0004] Such a secondary battery comprises an electrode assembly in which electrodes and separators are alternately stacked, and a case for housing the electrode assembly. A method for manufacturing the same includes a process for manufacturing electrodes, a process for manufacturing an electrode assembly by alternately stacking the manufactured electrodes and separators, a lamination process for thermally bonding the electrode assembly, a process for housing the electrode assembly in a case to manufacture an incomplete secondary battery, and an activation process for charging and discharging the incomplete secondary battery.

[0005] Meanwhile, the anode and cathode each have a structure comprising an anode composite layer and a cathode composite layer on a current collector. In this case, the anode composite layer includes a lipophilic binder such as polyvinylidene fluoride (PVdF), and the cathode composite layer includes a lipophilic binder such as styrene-butadiene rubber (SBR) or carboxymethylcellulose (CMC). Thus, the anode composite layer and the separator exhibit good adhesion, but the cathode composite layer exhibits weak adhesion to the separator. Accordingly, in order to achieve high adhesion between the conventional separator and the cathode, a lamination process was performed under high temperature conditions of 90°C or higher and pressure conditions exceeding 250 gf / cm².

[0006] However, since the heating devices generally used in the lamination process adopt a heat transfer method utilizing radiant heat, combining the electrodes and separators laminated under the aforementioned high temperature and pressure conditions takes a significant amount of time, resulting in reduced productivity. Furthermore, because excessive energy is applied to the anode composite layer, the wettability of the electrolyte on the anode side is reduced or the charge mobility is decreased, leading to a problem of degraded battery performance. Prior art literature

[0008] Republic of Korea Published Patent Application No. 10-2020-0067575 The problem to be solved

[0009] Accordingly, the objective of the present invention is to provide a technology that can achieve good adhesion between a cathode and a separator without performing a lamination process under high temperature and / or high pressure conditions. means of solving the problem

[0011] In order to solve the aforementioned problem,

[0012] In one embodiment of the present invention,

[0013] It includes an anode, a cathode, and a separator interposed between the anode and the cathode;

[0014] The above separator is,

[0015] A first coating layer containing a first binder and located on one surface in contact with the cathode, and

[0016] It includes a second coating layer located on one surface in contact with the positive electrode and containing a second binder,

[0017] The present invention provides an electrode assembly characterized in that the first binder content of the first coating layer is greater than the second binder content of the second coating layer.

[0018] At this time, the content of the first binder may be 10 to 40 weight% with respect to the total weight of the first coating layer, and the content of the second binder may be 5 to 20 weight% with respect to the total weight of the second coating layer.

[0019] In addition, the ratio of the content of the first binder to the content of the second binder may be 1.1 to 1.8.

[0020] In addition, the first binder and the second binder are each polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, and cyanoethylfluran It may include one or more of cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrilestyrene-butadiene copolymer, and polyimide.

[0021] In addition, the total thickness of the first coating layer and the second coating layer may be 1 μm to 50 μm.

[0022] In addition, the average thickness of the first coating layer may be the same as or thicker than the average thickness of the second coating layer.

[0023] In addition, the first coating layer and the second coating layer are each BaTiO3, Pb(Zrx,Ti1-x)O3 (PZT, 0 <x<1), Pb1-xLaxZr1-yTiyO3(PLZT, 0<x<1, 0<y<1), (1-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3(PMN-PT, 0<x<1), 하프니아(HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2, 리튬포스페이트(Li3PO4), 리튬티타늄포스페이트(LixTiy(PO4)3, 0<x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(LixAlyTiz(PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP)xOy 계열 글래스(0<x<4, 0<y<13), 리튬란탄티타네이트(LixLayTiO3, 0<x<2, 0<y<3), 리튬게르마니움티오포스페이트(LixGeyPzSw, 0<x<4, 0<y<1, 0<z<1, 0<w<5), 리튬나이트라이드(LixNy, 0<x<4, 0<y<2), SiS2 (LixSiySz, 0<x<3, 0<y<2, 0<z<4) 계열 글래스 및 P2S5(LixPySz, 0<x<3, 0<y<3, 0<z<7) 계열 글래스 중 1종 이상을 포함하는 무기 입자를 함유할 수 있다.

[0024] In addition, the average particle size of the inorganic particles is 0.1㎛ to 5㎛, and the average particle size of the inorganic particles contained in the first coating layer may be smaller than the average particle size of the inorganic particles contained in the second coating layer.

[0026] Furthermore, in one embodiment of the present invention,

[0027] A step of alternately stacking positive and negative electrodes, interposing a separator between each positive and negative electrode to combine each electrode and the separator; and

[0028] The method includes the step of manufacturing an electrode assembly by laminating the combined electrode and the separator, and

[0029] The above separator is,

[0030] A first coating layer containing a first binder and located on one surface in contact with the cathode, and

[0031] It includes a second coating layer located on one surface in contact with the positive electrode and containing a second binder,

[0032] A method for manufacturing an electrode assembly is provided, characterized in that the first binder content of the first coating layer is greater than the second binder content of the second coating layer.

[0033] Here, the lamination can be performed in a temperature range of 80°C or lower.

[0034] In addition, the above lamination can be performed in a pressure range of 250 gf / ㎠ or less. Effects of the invention

[0036] The electrode assembly according to the present invention comprises a separator having coating layers on both sides, wherein the binder content of the first coating layer of the separator facing the cathode is adjusted to be higher than the binder content of the second coating layer disposed on the other side, thereby enabling high adhesion between the cathode and the separator even when the lamination process is performed under milder conditions compared to conventional methods during manufacturing, and not only can the degradation of battery performance due to excessive bonding between the anode and the separator be prevented, but the rigidity of the battery can also be improved. Brief explanation of the drawing

[0038] Figures 1 and 2 are graphs showing the impact test results of a secondary battery according to the present invention. Specific details for implementing the invention

[0039] The present invention is capable of various modifications and may have various embodiments, and specific embodiments are to be described in detail in the detailed description.

[0040] However, this is not intended to limit the invention to specific embodiments, and it should be understood that it includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0041] In the present invention, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0042] Furthermore, in the present invention, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only cases where it is "immediately above" the other part, but also cases where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only cases where it is "immediately below" the other part, but also cases where there is another part in between. Additionally, in the present application, being "placed on" may include cases where it is placed on the lower part as well as on the upper part.

[0043] In addition, in the present invention, "include as a main component" may mean including a defined component in an amount of 50% or more by weight, 60% or more by weight, 70% or more by weight, 80% or more by weight, 90% or more by weight, or 95% or more by weight with respect to the total weight. For example, "include graphite as a main component as a negative electrode active material" may mean including graphite in an amount of 50% or more by weight, 60% or more by weight, 70% or more by weight, 80% or more by weight, 90% or more by weight, or 95% or more by weight with respect to the total weight of the negative electrode active material, and in some cases, it may mean that the entire negative electrode active material is made of graphite and includes graphite in an amount of 100% by weight.

[0045] The present invention will be described in more detail below.

[0047] electrode assembly

[0048] In one embodiment of the present invention,

[0049] It includes an anode, a cathode, and a separator interposed between the anode and the cathode;

[0050] The above-mentioned separator comprises a first coating layer containing a first binder located on one side in contact with a cathode and a second coating layer containing a second binder located on one side in contact with an anode; wherein the content of the first binder in the first coating layer is greater than the content of the second binder in the second coating layer.

[0052] An electrode assembly according to the present invention comprises an anode, a cathode, and a separator interposed between the anode and the cathode. The separator is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is commonly used in the art, but specifically includes chemically resistant and hydrophobic polypropylene; polyethylene; polyethylene-propylene copolymer; and polyvinylidene fluoride (PVdF). A polymer comprising one or more of polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate copolymer, and polyethylene oxide may be used. In addition, the separator may have a porous polymer substrate form, such as a sheet or nonwoven fabric, containing the aforementioned polymer, wherein the average diameter of the pores may be 0.01 to 10 μm, and the average thickness of the separator may be 5 to 300 μm; 5 to 200 μm; or 5 to 100 μm. It may be 5~80㎛; or 10~50㎛.

[0053] In addition, the separator comprises a coating layer containing inorganic particles and a binder on both sides. Specifically, the separator comprises a first coating layer containing a first binder located on one side in contact with the cathode, and a second coating layer containing a second binder located on one side in contact with the anode.At this time, the first and second binders are not particularly limited as long as they are used in the industry as binders for separators, but specifically, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate It may include one or more of propionate (cellulose acetate propionate), cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrilestyrene-butadiene copolymer, and polyimide.

[0054] As one example, the first binder and the second binder may each contain polyvinylidene fluoride (PVdF), polyvinylidene fluoride-co-hexafluoropropylene, or polyvinylidene fluoride-co-trichloroethylene alone or in combination.

[0055] In addition, the binder content of each coating layer provided on the separator can be adjusted differently depending on the type of electrode the coating layer contacts. Specifically, the separator is characterized in that the content of the first binder contained in the first coating layer is greater than the content of the second binder contained in the second coating layer.

[0056] Generally, the anode composite layer provided on the anode contains a lipophilic binder such as polyvinylidene fluoride (PVdF), and the cathode composite layer provided on the cathode contains a lipophilic binder such as styrene-butadiene rubber (SBR) or carboxymethylcellulose (CMC). Consequently, the adhesion between the anode and the separator is good, but the adhesion between the cathode and the separator is weak. Accordingly, in order to achieve high adhesion between the cathode and the separator, a lamination process is performed under high temperature conditions of 90°C or higher and pressure conditions exceeding 250 gf / cm². However, during this process, along with the achievement of excessive adhesion between the anode and the separator, there was a problem in which the shape and size of pores on the side of the separator bonded to the anode were deformed or the porosity was reduced, thereby degrading the performance of the battery. However, the present invention has the advantage of enabling the manufacture of an electrode assembly in a lamination process performed at a temperature of 80°C or lower and a pressure of 250 gf / ㎠ or lower by adjusting the ratio of the first binder content, i.e., the content ratio, of the first coating layer located on the side in contact with the cathode among the first coating layer and the second coating layer provided on both sides of the separator to a certain range such that the second binder content ratio of the second coating layer located on the side in contact with the anode is greater.

[0057] For example, the content of the first binder may be 10 to 40 weight% with respect to the total weight of the first coating layer, more specifically 15 to 40 weight%; 20 to 30 weight%; or 15 to 25 weight%; and the content of the second binder may be 5 to 20 weight% with respect to the total weight of the second coating layer, more specifically 10 to 20 weight%; 5 to 15 weight%; or 8 to 14 weight%.

[0058] As an example, the first coating layer may have a content of 18±2 weight% of the first binder, and the second coating layer may have a content of 13±2 weight% of the second binder.

[0059] In addition, since the content of the first binder is higher than the content of the second binder, the content of the first binder (P 1st ) and the content of the second binder (P 2nd The ratio of ) (P 1st / P 2nd ) may be greater than 1, specifically greater than 1.0 and less than 2.0; 1.1 to 1.8; 1.4 to 1.8; 1.1 to 1.5; or 1.3 to 1.6.

[0060] The present invention can prevent the effect of improving adhesion between the separator and the cathode from being negligible due to a low content of the first binder by adjusting the content of each binder contained in the first coating layer and the second coating layer and their ratio to the above range, and can prevent the rigidity of the electrode assembly manufactured from being reduced due to an excessive content of the first binder.

[0061] In addition, the total thickness of the first coating layer and the second coating layer can be adjusted to satisfy a certain range. Specifically, the total thickness of the first coating layer and the second coating layer can be adjusted to 1 μm to 50 μm, and more specifically, to 5 μm to 40 μm; or to 10 μm to 35 μm. By controlling the total thickness of the first coating layer and the second coating layer to the above range, the present invention prevents the reduction of the energy efficiency of the battery caused by the excessive formation of the coating layer thickness, while preventing the failure to sufficiently achieve adhesion between the separator and the electrode due to the significantly thin thickness of the coating layer.

[0062] In addition, the average thickness of the first coating layer may be the same as or thicker than the average thickness of the second coating layer. Specifically, the average thickness of the first coating layer and the second coating layer may be the same, and in some cases, the average thickness of the first coating layer may be 1.01 to 1.50 times; 1.01 to 1.40 times; 1.01 to 1.30 times; 1.01 to 1.20 times; 1.01 to 1.10 times; or 1.05 to 1.15 times thicker than the average thickness of the second coating layer.

[0063] In addition, the first coating layer and the second coating layer contain inorganic particles along with a binder, and the inorganic particles act as spacers that maintain the physical shape of each coating layer, while suppressing thermal shrinkage of the separator when the secondary battery heats up and performing the function of preventing short circuits of the electrodes.

[0064] These inorganic particles include BaTiO3, Pb(Zrx,Ti1-x)O3 (PZT, 0 <x<1), Pb1-xLaxZr1-yTiyO3(PLZT, 0<x<1, 0<y<1), (1-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3(PMN-PT, 0<x<1), 하프니아(HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2, 리튬포스페이트(Li3PO4), 리튬티타늄포스페이트(LixTiy(PO4)3, 0<x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(LixAlyTiz(PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP)xOy 계열 글래스(0<x<4, 0<y<13), 리튬란탄티타네이트(LixLayTiO3, 0<x<2, 0<y<3), 리튬게르마니움티오포스페이트(LixGeyPzSw, 0<x<4, 0<y<1, 0<z<1, 0<w<5), 리튬나이트라이드(LixNy, 0<x<4, 0<y<2), SiS2 (LixSiySz, 0<x<3, 0<y<2, 0<z<4) 계열 글래스 및 P2S5(LixPySz, 0<x<3, 0<y<3, 0<z<7) 계열 글래스 중 1종 이상을 제1 코팅층과 제2 코팅층에 독립적으로 포함할 수 있다. 상기 무기 입자들은 전기화학적으로 안정하고, 액체 전해질 내 전해질 염의 해리를 향상시켜 전해액의 이온 전도도를 개선할 수 있는 이점이 있다.

[0065] In addition, the average particle size of the inorganic particles may be smaller than the average thickness of each coating layer containing them, specifically having an average particle size of 0.1 μm to 5 μm, and the average particle size of the inorganic particles contained in the first coating layer may be smaller than the average particle size of the inorganic particles contained in the second coating layer.

[0066] As one example, the average particle size of the inorganic particles contained in the first coating layer may be 0.1 μm to 2 μm; 0.1 μm to 1 μm; or 0.5 μm to 0.9 μm, and the average particle size of the inorganic particles contained in the second coating layer may be 1 μm to 5 μm; 1 μm to 4 μm; 1.5 μm to 3 μm; or 2 μm to 4 μm.

[0067] The present invention can not only further improve the adhesion between each electrode and the separator by controlling the average particle size of the inorganic particles contained in the first coating layer and the second coating layer, respectively, to the above range, but also improve the rigidity of the manufactured battery.

[0069] Meanwhile, the above-mentioned anode comprises an anode composite layer manufactured by applying, drying, and pressing an anode active material onto an anode current collector, and may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0070] Here, the positive electrode active material is a material capable of causing an electrochemical reaction on a positive electrode current collector and may include one or more of lithium metal oxides represented by the following Chemical Formula 1 and Chemical Formula 2, which are capable of reversibly intercalating and deintercalating lithium ions:

[0071] [Chemical Formula 1]

[0072] Li x [Ni y Co z Mn w M 1 v ]O2

[0073] [Chemical Formula 2]

[0074] LiM 2 p Mn (2-p) O4

[0075] In the above Chemical Formulas 1 and 2,

[0076] M 1It is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0077] x, y, z, w, and v are 1.0≤x≤1.30, 0.5≤y<1, 0, respectively. <z≤0.3, 0<w≤0.3, 0≤v≤0.1이되, y+z+w+v=1이고,

[0078] M 2 is Ni, Co, or Fe, and

[0079] p is 0.05≤p≤0.6.

[0081] The lithium metal oxides represented by the above chemical formulas 1 and 2 are materials containing high amounts of nickel (Ni) and manganese (Mn), respectively, and when used as cathode active materials, they have the advantage of being able to stably supply high capacity and / or high voltage electricity.

[0082] In this case, LiNi is used as the lithium metal oxide represented by the above chemical formula 1. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.15 Al 0.05 O2, LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 The lithium metal oxide represented by the above chemical formula 2 may include O2, etc., and is LiNi 0.7 Mn 1.3 O4; LiNi 0.5 Mn 1.5 O4; LiNi0.3 Mn 1.7 It may include O4, etc., and can be used alone or in combination.

[0083] In addition, the above-mentioned positive electrode may be used as a positive electrode current collector that has high conductivity without causing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. may be used, and in the case of aluminum or stainless steel, surface-treated materials such as carbon, nickel, titanium, silver, etc. may be used. Furthermore, the average thickness of the above-mentioned current collector may be appropriately applied in the range of 3 to 500 μm, taking into consideration the conductivity and total thickness of the manufactured positive electrode.

[0084] In addition, the above-mentioned cathode, like the anode, comprises a cathode composite layer manufactured by applying, drying, and pressing a cathode active material onto a cathode current collector, and may optionally further include a conductive material, a binder, other additives, etc., as needed.

[0085] The above-mentioned cathode active material may include carbon materials and silicon materials. Specifically, the carbon material refers to a material having carbon atoms as its main component, and such carbon materials may include one or more selected from the group consisting of natural graphite, artificial graphite, expanded graphite, non-graphitized carbon, carbon black, acetylene black, and Ketjen black. In addition, the silicon material refers to a material having silicon atoms as its main component, and such silicon materials may include silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), or silicon dioxide (SiO2) alone or in combination. When silicon monoxide (SiO) and silicon dioxide (SiO2) are uniformly mixed or composited as silicon (Si)-containing materials and included in the cathode composite layer, they may be represented as silicon oxide (SiOq, provided that 0.8≤q≤2.5).

[0086] In addition, the silicon material may be included in an amount of 1 to 20 weight% with respect to the total weight of the negative electrode active material, and specifically, may be included in an amount of 3 to 10 weight%; 8 to 15 weight%; 13 to 18 weight%; or 2 to 8 weight%. The present invention can maximize the energy density of the battery by controlling the content of the silicon material to the above-mentioned content range.

[0087] In addition, the above-mentioned negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. may be used, and in the case of copper or stainless steel, surface-treated carbon, nickel, titanium, silver, etc. may be used. Furthermore, the average thickness of the above-mentioned negative electrode current collector can be appropriately applied in the range of 1 to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode being manufactured.

[0089] secondary battery

[0090] In addition, the present invention provides a secondary battery comprising the electrode assembly described above.

[0092] The secondary battery according to the present invention has a configuration comprising an electrode assembly, an electrolyte, and a case in which the electrode assembly and the electrolyte are housed. In this case, the electrode assembly includes the electrode assembly of the present invention described above, which not only prevents degradation of battery performance but also has the advantage of improving the rigidity of the battery.

[0093] Since the above electrode assembly is identical to the configuration described above, a detailed description will be omitted.

[0094] In addition, the above electrolyte may include a lithium salt-containing electrolyte. The lithium salt-containing electrolyte may consist of an electrolyte and a lithium salt, and the electrolyte may use a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, etc.

[0095] Specifically, the above lithium salt can be applied without particular limitation as long as it is used in the industry for non-aqueous electrolytes. Specifically, the above lithium salt is LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl 10 It may include one or more selected from the group consisting of LiPF6, LiFSI, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, and (CF3SO2)2NLi.

[0096] In addition, the above-mentioned non-aqueous organic solvent can be applied without particular limitation as long as it is used in the industry for non-aqueous electrolytes. Specifically, as the above-mentioned non-aqueous organic solvent, for example, aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate (EC), propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfranc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, and ethyl propionate may be used. there is.

[0097] In addition, the non-aqueous solvent used in the present invention may be used as a single type, or two or more types may be mixed in any combination or ratio according to the intended use. Among these, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethylmethyl carbonate are particularly preferred in terms of electrochemical stability against oxidation and reduction and chemical stability against reaction with heat or solutes.

[0098] Meanwhile, the above electrolyte composition may further include additives in addition to the basic components described above. As long as it does not impair the essence of the present invention, additives generally used in the non-aqueous electrolyte of the present invention may be added in any proportion. Specifically, examples include compounds having an overcharge prevention effect, a negative electrode film formation effect, and a positive electrode protection effect, such as cyclohexylbenzene, biphenyl, t-butylbenzene, vinylene carbonate, vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate, propanesulfone, succinonitrile, and dimethylvinylene carbonate. In addition, it is also possible to use an electrolyte for a non-aqueous electrolyte battery by pseudo-solidifying it with a gelling agent or a cross-linking polymer, as in the case of use in a non-aqueous electrolyte battery called a lithium polymer battery.

[0100] Method for manufacturing an electrode assembly

[0101] Furthermore, in one embodiment of the present invention,

[0102] A step of alternately stacking positive and negative electrodes, interposing a separator between each positive and negative electrode to combine each electrode and the separator; and

[0103] The method includes the step of manufacturing an electrode assembly by laminating the combined electrode and the separator, and

[0104] The above separator is,

[0105] A first coating layer containing a first binder and located on one surface in contact with the cathode, and

[0106] It includes a second coating layer located on one surface in contact with the positive electrode and containing a second binder,

[0107] A method for manufacturing an electrode assembly is provided, characterized in that the first binder content of the first coating layer is greater than the second binder content of the second coating layer.

[0109] The method for manufacturing an electrode assembly according to the present invention relates to the method for manufacturing an electrode assembly described above, wherein an electrode assembly can be manufactured by alternately stacking an anode and a cathode, interposing a separator between the stacked anodes and cathodes to laminate them, and then performing lamination of the combined electrodes and the separator.

[0110] Specifically, the above manufacturing method includes the step of alternately stacking a positive electrode and a negative electrode, interposing a separator between each positive electrode and a negative electrode, and combining each electrode and the separator.

[0111] At this time, the separator comprises coating layers containing inorganic particles and a binder on both sides. Specifically, the separator comprises a first coating layer containing a first binder located on one side in contact with the cathode, and a second coating layer containing a second binder located on one side in contact with the anode. The binder content of each coating layer provided on the separator can be adjusted differently depending on the type of electrode the coating layer contacts. Specifically, the separator is characterized in that the content of the first binder contained in the first coating layer is greater than the content of the second binder contained in the second coating layer.

[0112] Generally, the anode composite layer provided on the anode contains a lipophilic binder such as polyvinylidene fluoride (PVdF), and the cathode composite layer provided on the cathode contains a lipophilic binder such as styrene-butadiene rubber (SBR) or carboxymethylcellulose (CMC). Consequently, the adhesion between the anode and the separator is good, but the adhesion between the cathode and the separator is weak. Accordingly, in order to achieve high adhesion between the cathode and the separator, a lamination process is performed under high temperature conditions of 90°C or higher and pressure conditions exceeding 250 gf / cm². However, during this process, along with the achievement of excessive adhesion between the anode and the separator, there was a problem in which the shape and size of pores on the side of the separator bonded to the anode were deformed or the porosity was reduced, thereby degrading the performance of the battery. However, the present invention has the advantage of enabling the manufacture of an electrode assembly in a lamination process performed at a temperature of 80°C or lower and a pressure of 250 gf / ㎠ or lower by adjusting the ratio of the first binder content, i.e., the content ratio, of the first coating layer located on the side in contact with the cathode among the first coating layer and the second coating layer provided on both sides of the separator to a certain range such that the second binder content ratio of the second coating layer located on the side in contact with the anode is greater.

[0113] For example, the content of the first binder may be 10 to 40 weight% with respect to the total weight of the first coating layer, more specifically 15 to 40 weight%; 20 to 30 weight%; or 15 to 25 weight%; and the content of the second binder may be 5 to 20 weight% with respect to the total weight of the second coating layer, more specifically 10 to 20 weight%; 5 to 15 weight%; or 8 to 14 weight%.

[0114] In addition, the step of combining the electrode and the separator may be configured such that the electrode and the separator are stacked to form a single cell consisting of one electrode and one separator, a mono-cell in which a separator is interposed between the positive and negative electrodes, or a bi-cell in which two separators are interposed between three electrodes having different polarities of adjacent electrodes, and the mono-cell and bi-cell may be stacked in such a way that a separator is additionally added to the other side of the electrode that does not face the separator interposed between the electrodes.

[0115] As an example, the step of combining the electrode and the separator can be performed by alternately stacking the anode and cathode, such as anode-separator-cathode-separator-anode-separator, so that a plurality of bicells are provided within the electrode assembly, and interposing the separator between them.

[0116] In addition, the above manufacturing method includes a step of manufacturing an electrode assembly by laminating a combined electrode and a separator. This step involves bonding a laminate in which an anode, a cathode, and a separator are combined by applying heat and pressure. In this case, the heat and pressure may be applied selectively, or, depending on the circumstances, simultaneously or continuously. Here, the heat and pressure applied to the laminate in which an anode, a cathode, and a separator are combined may have lower values ​​than those under conventional conditions.

[0117] As one example, the lamination may be performed in a temperature range of 80°C or lower, specifically in a temperature range of 10°C to 80°C; 25°C to 80°C; 40°C to 80°C; 60°C to 80°C; 40°C to 70°C; 45°C to 65°C; or 50°C to 65°C.

[0118] As another example, the lamination can be performed in a pressure range of 250 gf / ㎠ or less, specifically in a pressure range of 50 to 250 gf / ㎠; 100 to 250 gf / ㎠; 200 to 250 gf / ㎠; 50 to 200 gf / ㎠; 50 to 190 gf / ㎠; 50 to 150 gf / ㎠; 150 to 250 gf / ㎠; 100 to 200 gf / ㎠; 80 to 150 gf / ㎠; or 50 to 120 gf / ㎠.

[0119] The manufacturing method according to the present invention, by performing lamination under the temperature and / or pressure conditions described above, can not only achieve high adhesion between the anode and the separator; and between the cathode and the separator, but also enable excellent performance and rigidity of the manufactured battery.

[0121] The present invention will be explained in more detail below through examples and experimental examples.

[0122] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0124] Preparation Examples 1-6. Preparation of separators for secondary batteries

[0125] Polyvinylidene fluoride (PVdF) was added to acetone as a binder and dissolved at 50°C for about 12 hours or more to prepare a polymer solution. Inorganic particles, mixed with Al2O3 powder and BaTiO3 powder in a weight ratio of 9:1, were added to the prepared polymer solution, and the inorganic particles were crushed and dispersed using a ball mill method for about 12 hours or more to prepare a slurry for the first coating layer.

[0126] Separately, a slurry for the second coating layer was prepared by performing the same method as above, and the content ratio of the binder contained in the slurry for the first coating layer and the slurry for the second coating layer based on the weight of each coating layer and the average particle size of the inorganic particles are shown in Table 1 below.

[0127] A polyethylene porous membrane (Asahi ND209) with a thickness of 30 μm was prepared, and a slurry for a first coating layer and a slurry for a second coating layer were sequentially applied to and dried on both sides of the prepared porous membrane, respectively, to manufacture a separator for a secondary battery in which a first coating layer and a second coating layer were formed on each side. At this time, the average thickness of the first coating layer and the second coating layer is as shown in Table 1 below.

[0128] First coating layer Second coating layer 1st binder content Average particle size of inorganic particles average thickness Second binder content Average particle size of inorganic particles average thickness Preparation Example 1 20 wt% 0.9±0.01㎛ 10㎛ 15 wt% 2±0.01㎛ 10㎛ Preparation Example 2 20 wt% 0.9±0.01㎛ 20㎛ 15 wt% 2±0.01㎛ 10㎛ Preparation Example 3 20 wt% 2±0.01㎛ 10㎛ 15 wt% 1±0.01㎛ 10㎛ Preparation Example 4 20 wt% 0.9±0.01㎛ 15㎛ 15 wt% 2±0.01㎛ 40㎛ Preparation Example 5 40 wt% 0.9±0.01㎛ 10㎛ 15 wt% 2±0.01㎛ 10㎛ Preparation Example 6 5 wt% 0.9±0.01㎛ 10㎛ 15 wt% 2±0.01㎛ 10㎛ Preparation Example 7 15 wt% 0.9±0.01㎛ 15㎛ 15 wt% 2±0.01㎛ 10㎛

[0130] Examples 1–4 and Comparative Examples 1–4. Preparation of electrode assemblies

[0131] LiNi with a particle size of 5㎛ as a cathode active material 0.8 Co 0.1 Mn 0.05 Al 0.05 O4 was prepared, and a slurry was formed by mixing it with N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 as a carbon-based conductive agent and binder, and then casting it onto an aluminum foil, drying it in a vacuum oven at 120°C, and rolling it to produce an anode.

[0132] Separately, artificial graphite was prepared as a negative electrode active material, and 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene-butadiene rubber (SBR) were mixed with water to form a slurry, cast onto a copper foil, dried in a vacuum oven at 130°C, and then rolled to manufacture a negative electrode.

[0133] A monocell-type electrode assembly was manufactured by interposing a separator prepared in the manufacturing example between the anode and cathode obtained above and on their outermost surface, and performing lamination (moving speed: 50~300 mm / min) by heating and pressurizing under the temperature and pressure conditions shown in Table 2 below. At this time, the separator was interposed between the anode and cathode such that a first coating layer was positioned on one surface in contact with the cathode.

[0134] Types of separators temperature enter Example 1 Separator of Preparation Example 1 65±2℃ 180 gf / ㎠ Example 2 Separator of Preparation Example 2 65±2℃ 180 gf / ㎠ Example 3 Separator of Preparation Example 3 65±2℃ 180 gf / ㎠ Example 4 Separator of Preparation Example 4 65±2℃ 180 gf / ㎠ Example 5 Separator of Preparation Example 5 65±2℃ 180 gf / ㎠ Comparative Example 1 Separator of Preparation Example 6 65±2℃ 180 gf / ㎠ Comparative Example 2 Separator of Preparation Example 7 65±2℃ 180 gf / ㎠ Comparative Example 3 Separator of Preparation Example 6 85±2℃ 300 gf / ㎠ Comparative Example 4 Separator of Preparation Example 7 85±2℃ 300 gf / ㎠

[0136] Experimental Example.

[0137] To evaluate the performance of the electrode assembly according to the present invention, the following experiment was performed.

[0139] a) Evaluation of the adhesion of the electrode assembly

[0140] The adhesion strength between the separator and the outermost cathode was measured for each electrode assembly prepared in the examples and comparative examples. Specifically, the separator bonded to the anode surface of the electrode assembly was fixed to a glass plate with double-sided tape, and only the separator bonded to the cathode surface was peeled using a tensile testing machine at a speed of 100 mm / min and an angle of 90°, and the peeling strength was measured in real time. The results are shown in Table 3 below.

[0142] b) Impact assessment of secondary batteries

[0143] Each electrode assembly prepared in the examples and comparative examples was inserted into a pouch case, and a liquid electrolyte containing LiPF6 as a lithium salt was injected into an organic solvent mixed with EC (Ethylene Carbonate) and EMC (Ethyl Methyl Carbonate) in a volume ratio of 3:7, and then the case was sealed to produce a secondary battery.

[0144] The fabricated secondary batteries were charged to an SOC of 100%. Then, the change in voltage over time was measured while applying an external force to the injected secondary batteries; a case with no change in voltage was evaluated as a pass, and a case where the voltage decreased by 0.1V or more was evaluated as a failure. At this time, the external force was applied by pressing the surface of the pouch cell using a 9kg weight, and the measurement results are shown in Figure 1 and Table 3.

[0146] c) Performance evaluation of secondary batteries

[0147] Each electrode assembly prepared in the examples and comparative examples was inserted into a pouch case, and a liquid electrolyte containing LiPF6 as a lithium salt was injected into an organic solvent mixed with EC (Ethylene Carbonate) and EMC (Ethyl Methyl Carbonate) in a volume ratio of 3:7, and then the case was sealed to produce a secondary battery.

[0148] Then, after the activation charge / discharge of each secondary battery was performed twice at 0.2C / 0.5C, a charge / discharge experiment was conducted once each with a standard charge / discharge current density of 0.5C / 0.2C, a charge termination voltage of 4.8V (Li / graphite), and a discharge termination voltage of 3.0V (Li / graphite).

[0149] The capacity of the activated secondary battery was measured by performing charge and discharge at 25℃ and 70mAh / 3mAh, and the results are shown in Table 3 below.

[0150] Cathode-separator adhesion Impact test Charge / Discharge Capacity Example 1 109 N / m passing 884 mAh Example 2 117 N / m passing 881 mAh Example 3 96 N / m passing 880 mAh Example 4 103 N / m passing 878 mAh Example 5 95 N / m passing 875 mAh Comparative Example 1 81 N / m failure 879 mAh Comparative Example 2 85 N / m failure 877 mAh Comparative Example 3 98 N / m passing 842 mAh Comparative Example 4 102 N / m passing 837 mAh

[0152] As shown in Table 3 above, it can be seen that the electrode assembly according to the present invention not only has excellent adhesion between the negative electrode and the separator, but also has excellent rigidity and allows lamination under mild conditions, thereby exhibiting high charge / discharge capacity.

[0153] Specifically, it was confirmed that the secondary batteries of the embodiments according to the present invention not only achieve an adhesion force of 95 N / m or more between the negative electrode and the separator, but also exhibit excellent rigidity, so no voltage drop occurs even when an external force is applied during an impact test. In addition, since lamination is performed under lower temperature and pressure conditions compared to conventional conditions, the porosity of the positive-side separator is excellent, and thus the secondary batteries exhibited a high capacity of 875 mAh or more during charging and discharging.

[0154] On the other hand, the secondary batteries of the comparative examples exhibited low adhesion between the negative electrode and the separator and a tendency for low voltage during impact testing because lamination was not sufficiently performed under lower temperature and pressure conditions compared to conventional conditions. Furthermore, when the secondary batteries of the comparative examples underwent a high-temperature and high-pressure lamination process to achieve strong adhesion between the negative electrode and the separator, the pores of the positive-side separator were damaged despite containing the same electrode active material as the secondary batteries of the examples, resulting in a capacity of less than 850 mAh during charge and discharge.

[0155] From these results, it can be seen that the electrode assembly according to the present invention comprises a separator having coating layers on both sides, wherein the binder content of the first coating layer of the separator facing the cathode is adjusted to be higher than the binder content of the second coating layer disposed on the other side, thereby enabling high adhesion between the cathode and the separator even when the lamination process is performed under milder conditions compared to conventional methods during manufacturing, and not only can the degradation of battery performance due to excessive bonding between the anode and the separator be prevented, but the rigidity of the battery can also be improved.

[0157] Although the present invention has been described above with reference to preferred embodiments, those skilled in the art or those with ordinary knowledge in the art will understand that various modifications and changes can be made to the present invention without departing from the spirit and technical scope of the invention as described in the claims set forth below.

[0158] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be determined by the claims.

Claims

Claim 1 An electrode assembly comprising an anode, a cathode, and a separator interposed between the anode and the cathode; wherein the separator comprises a first coating layer located on one surface in contact with the cathode and containing a first binder, and a second coating layer located on one surface in contact with the anode and containing a second binder, wherein the content of the first binder in the first coating layer is greater than the content of the second binder in the second coating layer, the content of the first binder is 20% to 30% by weight with respect to the total weight of the first coating layer, and the content of the second binder is 13±2% by weight with respect to the total weight of the second coating layer, and each of the first binder and the second binder comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 An electrode assembly according to claim 1, wherein the total thickness of the first coating layer and the second coating layer is 1 μm to 50 μm. Claim 6 An electrode assembly according to claim 1, characterized in that the average thickness of the first coating layer is equal to or thicker than the average thickness of the second coating layer. Claim 7 In claim 1, the first coating layer and the second coating layer are each BaTiO3, Pb(Zrx,Ti1-x)O3 (PZT, 0 <x<1), Pb1-xLaxZr1-yTiyO3(PLZT, 0<x<1, 0<y<1), (1-x)Pb(Mg1 / 3Nb2 / 3)O3-xPbTiO3(PMN-PT, 0<x<1), 하프니아(HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, TiO2, 리튬포스페이트(Li3PO4), 리튬티타늄포스페이트(LixTiy(PO4)3, 0<x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(LixAlyTiz(PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP)xOy 계열 글래스(0<x<4, 0<y<13), 리튬란탄티타네이트(LixLayTiO3, 0<x<2, 0<y<3), 리튬게르마니움티오포스페이트(LixGeyPzSw, 0<x<4, 0<y<1, 0<z<1, 0<w<5), 리튬나이트라이드(LixNy, 0<x<4, 0<y<2), SiS2 (LixSiySz, 0<x<3, 0<y<2, 0<z<4) 계열 글래스 및 P2S5(LixPySz, 0<x<3, 0<y<3, 0<z<7) 계열 글래스 중 1종 이상을 포함하는 무기 입자를 함유하는 전극 조립체. Claim 8 An electrode assembly according to claim 7, wherein the average particle size of the inorganic particles is 0.1㎛ to 5㎛, and the average particle size of the inorganic particles contained in the first coating layer is smaller than the average particle size of the inorganic particles contained in the second coating layer. Claim 9 A step of alternately stacking positive and negative electrodes, interposing a separator between each positive and negative electrode, and combining each electrode and separator; A method for manufacturing an electrode assembly comprising the step of laminating a combined electrode and a separator, wherein the separator comprises a first coating layer containing a first binder located on one surface in contact with a cathode and a second coating layer containing a second binder located on one surface in contact with an anode, wherein the first binder content of the first coating layer is greater than the second binder content of the second coating layer, the first binder content is 20% to 30% by weight with respect to the total weight of the first coating layer, and the second binder content is 13±2% by weight with respect to the total weight of the second coating layer, and each of the first binder and the second binder comprises one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, and polyvinylidene fluoride-trichloroethylene. Claim 10 In claim 9, the lamination is performed in a temperature range of 80°C or lower, in a method for manufacturing an electrode assembly. Claim 11 In claim 9, a method for manufacturing an electrode assembly in which lamination is performed in a pressure range of 250 gf / ㎠ or less.

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