Electrode Assembly and Secondary Battery Comprising the Same

Abstract

The electrode assembly of the present invention comprises a plurality of first electrodes, a plurality of second electrodes, and a plurality of separators, wherein each of the first electrodes and the second electrodes is formed by stacking with a separator in between, and wherein the plurality of first electrodes and the plurality of second electrodes each have an electrode composite containing a binder and an electrode active material coated on a current collector, and at least one of the first electrodes has a binder different from the remaining first electrodes excluding it.

Description

Technology Field

[0001] The present invention relates to an electrode assembly and a secondary battery including the same. Background Technology

[0003] While the application of lithium-ion batteries was conventionally limited to electronic devices, it is expanding into various fields such as electric vehicles and power storage.

[0004] In the case of electric vehicles, research is underway to increase battery capacity and maximize energy density in order to extend the driving range on a single charge.

[0005] In addition, research is underway to reduce charging time compared to conventional internal combustion engine vehicles by lowering the battery's internal resistance and optimizing charging methods.

[0006] In particular, the demand to improve lifespan characteristics by lowering internal resistance and minimizing capacity degradation even with repeated use is a research objective pursued commonly regardless of the application field. Prior art literature

[0008] Republic of Korea Published Patent No. 10-2013-0111387 Republic of Korea Published Patent No. 10-2010-0118808 The problem to be solved

[0009] The present invention aims to provide an electrode assembly in which interlayer imbalance within the battery is significantly resolved in a secondary battery having a stacked structure in which unit cells of a negative electrode, a separator, and a positive electrode are repeated.

[0010] In particular, the present invention aims to provide an electrode assembly in which imbalances in reactivity due to temperature imbalances, imbalances in internal resistance, and consequent imbalances in charge states are significantly resolved.

[0011] In addition, we aim to provide an electrode assembly that significantly improves the lifespan characteristics of a secondary battery through this. means of solving the problem

[0013] One embodiment of the present invention provides an electrode assembly comprising a plurality of first electrodes, a plurality of second electrodes, and a plurality of separators, wherein each of the first electrodes and the second electrodes is formed by stacking with a separator in between, wherein the plurality of first electrodes and the plurality of second electrodes each have an electrode composite containing a binder and an electrode active material coated on a current collector, and at least one of the first electrodes has a binder different from that of the remaining first electrodes.

[0014] According to one embodiment of the present invention, the first electrode may be a negative electrode.

[0015] According to one embodiment of the present invention, the first electrode comprises an inner electrode and an outer electrode, wherein the inner electrode represents one or more first electrodes disposed inside the electrode assembly, and the outer electrode represents one or more first electrodes disposed on each side outside the inner electrode, and the inner electrode and the outer electrode may comprise different binders.

[0016] According to one embodiment of the present invention, the binder included in the external electrode may be a styrene acrylate (SA)-based binder.

[0017] According to one embodiment of the present invention, the binder included in the internal electrode may be a styrene-butadiene (SB)-based binder.

[0018] According to one embodiment of the present invention, the first electrode may be 26 or more.

[0019] According to one embodiment of the present invention, one to five external electrodes of the first electrode may be arranged on each side outside of the internal electrode.

[0020] According to one embodiment of the present invention, 3 to 20 internal electrodes may be included per external electrode.

[0021] According to one embodiment of the present invention, the first electrode may include (n+1) negative electrodes, and the second electrode may include n positive electrodes (where n is a natural number).

[0022] According to one embodiment of the present invention, at least one of the second electrodes may include a binder different from the remaining second electrodes excluding it.

[0023] According to one embodiment of the present invention, the second electrode comprises an inner electrode and an outer electrode, wherein the inner electrode represents one or more second electrodes disposed inside the electrode assembly, and the outer electrode represents one or more second electrodes disposed on each side outside the inner electrode, and the inner electrode and the outer electrode may comprise different binders.

[0024] According to one embodiment of the present invention, the electrode assembly may be one or more selected from a stacked electrode assembly having a stacked structure with a separator interposed between an anode and a cathode, a stacked / folded electrode assembly manufactured by winding unit cells positioned on a long sheet-type separator film, and a lamination / stacked electrode assembly having a bonded structure with a separator interposed between unit cells.

[0025] One embodiment of the present invention provides a secondary battery comprising the electrode assembly. Effects of the invention

[0027] The present invention can provide an electrode assembly in which interlayer imbalance within the battery is significantly resolved in a secondary battery having a stacked structure in which unit cells of a negative electrode, a separator, and a positive electrode are repeated.

[0028] In particular, the present invention can provide an electrode assembly in which imbalances in reactivity due to temperature imbalances, imbalances in internal resistance, and resulting imbalances in charge states are significantly resolved.

[0029] In addition, the present invention can provide an electrode assembly that significantly improves the lifespan characteristics of a secondary battery. Brief explanation of the drawing

[0031] FIG. 1 illustrates a stacked structure within an electrode assembly according to one embodiment of the present invention. Specific details for implementing the invention

[0032] The expression "comprising" as used in this specification should be understood as an open-ended term implying the possibility of including other embodiments.

[0033] As used herein, the terms "preferred" and "preferably" refer to embodiments of the invention that can provide certain advantages under certain conditions. However, other embodiments may also be preferred under the same or different conditions. Additionally, the mention of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

[0035] Generally, lithium secondary batteries have a structure in which unit cells of a negative electrode, a separator, and a positive electrode are repeatedly stacked.

[0036] Generally, battery capacity increases as the number of stacked electrodes increases. However, increasing the number of stacked electrodes also increases the likelihood of interlayer imbalance within the battery. In particular, there are issues regarding imbalances in reactivity, internal resistance, or charge states caused by temperature imbalances. Repeated use of the battery without resolving these imbalances leads to the rapid degradation of specific electrodes, consequently shortening the battery's lifespan.

[0037] To solve the problem of such imbalance, the present invention can resolve it by placing electrodes containing different types of binders within an electrode assembly.

[0038] More preferably, the problem of imbalance can be resolved by arranging electrodes containing different types of binders separately inside and outside the electrode assembly.

[0040] Below, an electrode assembly for resolving the above-mentioned imbalance problem will be described in detail.

[0041] An electrode assembly according to one embodiment of the present invention includes a plurality of first electrodes, a plurality of second electrodes, and a plurality of separators.

[0042] As an example, the first electrode may be a negative electrode and the second electrode may be a positive electrode. As another example, the second electrode may be a negative electrode and the first electrode may be a positive electrode.

[0043] The above separator separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions, and can be used without special restrictions as long as it is used as a separator in a secondary battery. Specifically, as the above separator, a porous polymer film, such as a porous polymer film made of a polyolefin-based polymer like 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 thereof may be used.

[0044] An electrode assembly according to one embodiment of the present invention is formed by stacking each of the first electrode and the second electrode with a separator in between.

[0045] The plurality of first electrodes and the plurality of second electrodes each include an electrode composite containing a binder and an electrode active material coated on a current collector.

[0046] The current collector may be a conductive foil, film, sheet, net, porous body, or nonwoven fabric, for example, a metal foil, film, sheet, net, porous body, or nonwoven fabric. Specifically, the current collector may be, for example, a foil, film, or sheet containing stainless steel, aluminum, nickel, titanium, copper, or aluminum. The surface of the current collector may be treated with a surface treatment using carbon, nickel, titanium, or silver, and may have fine irregularities formed on it. These irregularities may help improve adhesion to the active layer. The method of forming the irregularities by roughening the surface of the current collector is not particularly limited, and known methods such as mechanical polishing, electrolytic polishing, or chemical polishing may be applied. The thickness of the current collector is not particularly limited and can be set within an appropriate range considering mechanical strength, productivity, or battery capacity.

[0047] The above binder is a component that assists in the bonding of the active material and the conductive material, and in the bonding to the current collector, and is typically added in an amount of 1 to 30 weight percent based on the total weight of the mixture containing the positive active material. Examples of such binders include, as previously mentioned, polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butylene rubber, fluororubber, and various copolymers.

[0048] The above electrode active material refers to a negative electrode active material in the case of a negative electrode, and a positive electrode active material in the case of a positive electrode.

[0049] The above-mentioned negative electrode active material is carbon such as non-graphitizable carbon, graphite-based carbon, etc.; Li x Fe2O3(0≤x≤1), LixWO2(0≤x≤1), Sn xMe 1-x Me y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, and 3 elements of the periodic table, halogens; 0 <x≤1; 1≤y≤3; 1≤z≤8) 등의 금속 복합 산화물; 리튬 금속; 리튬 합금; 규소계 합금; 주석계 합금; SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5등의 금속 산화물; 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등이 사용될 수 있으나, 이에 한정되는 것은 아니다.

[0050] The above-mentioned cathode active material is a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, Li2MnO3, LiMnO2, etc.; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, Cu2V2O7, etc.; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 ~ 0.3); chemical formula LiMn 2-x M x Examples include but are not limited to lithium manganese complex oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which part of the Li of the chemical formula is substituted with alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3, etc.

[0051] The first electrode and the second electrode may further include a conductive material, which is typically added in an amount of 1 to 30 weight percent based on the total weight of the mixture containing the positive electrode active material. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and examples may be used, such as graphite, such as natural graphite or artificial graphite; carbon black, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; conductive fibers, such as carbon fiber or metal fiber; metal powders, such as carbon fluoride, aluminum, or nickel powder; conductive whiskey, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials, such as polyphenylene derivatives.

[0052] In an electrode assembly according to one embodiment of the present invention, at least one of the first electrodes comprises a binder different from the remaining first electrodes. By arranging electrodes comprising such different types of binders within the electrode assembly, the present invention can resolve the problem of interlayer imbalance within the battery as described above and significantly improve the lifespan characteristics of the battery.

[0053] As a more preferred example, the first electrode may be a negative electrode. By arranging a negative electrode containing different types of binders in such a way within an electrode assembly, the present invention can resolve the problem of interlayer imbalance within the battery as described above and significantly improve the lifespan characteristics of the battery.

[0054] According to one embodiment of the present invention, the first electrode may include an inner electrode and an outer electrode. Here, the inner electrode refers to one or more first electrodes disposed inside the electrode assembly, and the outer electrode refers to one or more first electrodes disposed on each side outside the inner electrode.

[0055] According to one embodiment of the present invention, the inner electrode and the outer electrode may include different binders. By arranging electrodes containing such different types of binders separately inside and outside the electrode assembly, the present invention can resolve the problem of interlayer imbalance within the battery as described above and significantly improve the lifespan characteristics of the battery.

[0056] As a more desirable example, the first electrode may be a negative electrode, and the present invention can resolve the problem of interlayer imbalance within the battery and significantly improve the lifespan characteristics of the battery by arranging negative electrodes containing different types of binders separately inside and outside the electrode assembly.

[0057] As a more desirable example, the binder included in the external electrode may be a styrene acrylate (SA)-based binder.

[0058] In addition, as a more desirable example, the binder included in the internal electrode may be a styrene-butadiene (SB)-based binder.

[0059] Among the binders for electrodes of lithium-ion batteries, styrene acrylate (SA)-based binders have high swelling properties in the electrolyte and low internal resistance. On the other hand, styrene butadiene (SB)-based binders have excellent binding strength, low swelling properties in the electrolyte, and good lifespan characteristics.

[0060] In this way, by using a styrene butadiene (SB)-based binder with good lifespan characteristics as an internal electrode binder and a styrene acrylate (SA)-based binder with good resistance characteristics as an external electrode binder, it is possible to provide a secondary battery with significantly improved lifespan characteristics as well as battery performance.

[0061] As a more desirable example, the first electrode may be 26 or more, 30 or more, 35 or more, or 40 or more. Generally, the capacity of a lithium-ion battery increases as the number of stacked electrodes increases; however, the more stacked electrodes there are, the higher the likelihood of causing interlayer imbalance within the battery.

[0062] The present invention can significantly improve battery performance by using a large number of electrodes to increase the capacity of the battery while resolving interlayer imbalance within the battery.

[0063] As a more preferred example, the external electrodes of the first electrode may be arranged in 1 to 5, 1 to 4, 1 to 3, or 1 to 2 places on each outer side of the internal electrode. Within the above numerical range, the capacitance can be increased, and the resistance increase rate and thickness increase rate can be reduced.

[0064] As a more preferred example, the number of internal electrodes per external electrode may be 3 or more, 5 or more, 7 or more, 9 or more, 11 or more, or 13 or more, and may be 20 or fewer or 15 or fewer. More preferably, when the number of internal electrodes per external electrode is 7 or more, the capacitance can be increased and the resistance increase rate and thickness increase rate can be lowered.

[0065] According to one embodiment of the present invention, the first electrode may include (n+1) negative electrodes, and the second electrode may include n positive electrodes. As an example, negative electrodes are arranged at the outermost edges of both sides within an electrode assembly, and positive electrodes and separators are arranged in that order inside, so that the number of negative electrodes is one more than the number of positive electrodes.

[0066] According to one embodiment of the present invention, one or more of the second electrodes may include a binder different from the remaining second electrodes. In this case, the first electrode and the second electrode within the electrode assembly both include binders different from each other.

[0067] According to one embodiment of the present invention, the second electrode may include an inner electrode and an outer electrode. Here, the inner electrode represents one or more second electrodes disposed inside the electrode assembly, and the outer electrode represents one or more second electrodes disposed on each side outside the inner electrode.

[0068] According to one embodiment of the present invention, the inner electrode and the outer electrode of the second electrode may include different binders. In this case, both the first electrode and the second electrode within the electrode assembly include different binders in the inner and outer electrodes.

[0069] As an example, the first electrode is a cathode and the second electrode is an anode, and both the cathode and the anode within the electrode assembly may include binders that are different from each other in the inner and outer electrodes.

[0070] According to one embodiment of the present invention, the electrode assembly may be one or more selected from a stacked electrode assembly having a stacked structure with a separator interposed between an anode and a cathode, a stacked / folded electrode assembly manufactured by winding unit cells positioned on a long sheet-type separator film, and a lamination / stacked electrode assembly having a bonded structure with a separator interposed between unit cells.

[0071] One embodiment of the present invention provides a secondary battery comprising the electrode assembly.

[0072] The above secondary battery is structured such that the electrode assembly capable of charging and discharging is embedded in a battery case while impregnated with an ion-containing electrolyte.

[0073] The above secondary battery is preferably a lithium secondary battery with high energy density, discharge voltage, and output stability.

[0074] Other components and manufacturing methods of the above-mentioned secondary battery are known in the art, and a detailed description thereof is omitted in this specification.

[0076] The present invention will be described in more detail below through examples. These examples are merely illustrative of the present invention, and therefore the scope of the present invention should not be interpreted as being limited by these examples.

[0078] [Preparation Example 1] Preparation of a binder

[0079] Manufacture of Binder A

[0080] Butadiene (52g), styrene (46g), and acrylic acid (2g) were added to water containing sodium lauryl sulfate (0.5g) as an emulsifier and potassium persulfate as a polymerization initiator. These were mixed and polymerized at 70°C for about 5 hours to produce styrene-butadiene binder A with a number average particle size of 200 nanometers and a solid content of 40%.

[0081] Manufacture of Binder B

[0082] Butiaacrylate (60g), styrene (30g), acrylic acid (7g), acrylamide (1g), and glycidyl methacrylate (2g) were added to water containing sodium lauryl sulfate (0.5g) as an emulsifier and potassium persulfate as a polymerization initiator. These were mixed and polymerized at 70°C for about 5 hours to produce a styrene-butadiene binder b with a number average particle size of 200 nanometers and a solid content of 40%.

[0084] [Preparation Example 2] Preparation of an electrode

[0085] Preparation of cathode a

[0086] A conductive material dispersion was prepared by mixing a 1% sodium carboxymethyl cellulose (CMC) solution (100g) with a conductive material (1.5g) and stirring for 1 hour. Natural graphite and distilled water were added to the conductive material dispersion and stirred for 1 hour to prepare a binder-free slurry. Binder A prepared in the above example was added to the binder-free slurry and stirred for 30 minutes to prepare a slurry containing binder A.

[0087] A slurry containing the binder A is applied to both sides of a 10-micron copper foil at a cross-sectional area of ​​8 mg / cm² 2 A cathode a containing binder A was prepared by coating both sides with a loading and drying, then rolling to 115 microns.

[0088] Preparation of cathode b

[0089] A cathode b was manufactured in the same manner as the method for manufacturing a cathode a, except that binder B was added to the binder-free slurry to produce a slurry containing binder B and a cathode b containing binder B.

[0091] [Preparation Example 3] Preparation of a pouch-type cell

[0092] A 36Ah pouch-type cell was fabricated by using the above-prepared cathode a and cathode b alone or in combination [Table 1 below]. The same cathode was used alone without distinguishing between the inside and outside.

[0093] The above pouch-type cell is configured such that a total of 32 negative electrodes and 31 positive electrodes are paired with each other, and its structure is as shown in FIG. 1.

[0094] In the structure of Fig. 1, the first cathode is numbered in the order of stacking with the first cathode as cathode 1, and the last cathode becomes cathode 32.

[0096] [Example 1]

[0097] Cathodes 1 and 32 were treated with cathode b, and the other cathodes were treated with cathode a.

[0098] [Example 2]

[0099] Cathodes 1, 32, 2, and 31 were treated with cathode b, and the other cathodes were treated with cathode a.

[0100] [Example 3]

[0101] Cathodes 1, 32, 2, 31, 3 and 30 were treated with cathode b, and the other cathodes were treated with cathode a.

[0102] [Example 4]

[0103] Cathodes 1, 32, 2, 31, 3, 30, 4, and 29 were treated with cathode b, and the other cathodes were treated with cathode a.

[0104] [Comparative Example 1]

[0105] Cathode a was applied to all 32 cathodes.

[0106] [Comparative Example 2]

[0107] Cathode b was applied to all 32 cathodes.

[0109] The above examples and comparative examples are described in Table 1 below.

[0111] Cathode 1, 32 Cathode 2, 31 Cathode 3, 30 Cathode 4, 29 Cathode 5-28 Example 1 cathode b cathode a cathode a cathode a cathode a Example 2 cathode b cathode b cathode a cathode a cathode a Example 3 cathode b cathode b cathode b cathode a cathode a Example 4 cathode b cathode b cathode b cathode b cathode a Comparative Example 1 cathode a cathode a cathode a cathode a cathode a Comparative Example 2 cathode b cathode b cathode b cathode b cathode b

[0113] [Experimental Example]

[0114] The resistance of the above-mentioned manufactured cell was measured by discharging it at a current of 150A for 10 seconds at SOC 50%.

[0115] The thickness was measured by applying a 90 Kgf load for 10 seconds using a flat plate thickness gauge.

[0116] In a 25℃ constant temperature chamber, the cycle of charging to 4.15V at 36A in CC / CV mode and discharging to 3.0V in CC mode at 36A current was repeated 1,000 times. During this time, a rest period of 20 minutes was given between charging and discharging, and the ratio of the 1,000th discharge capacity to the first cycle discharge capacity was recorded.

[0117] After 1000 cycles, the resistance was measured and the thickness was measured after setting the SOC to 50%.

[0119] The above measurement results are listed in Table 2 below.

[0121] SOC50% 10-second discharge resistance (mΩ) After 1000 cycles volume(%) Resistance increase rate (%) Thickness increase rate (%) Example 1 1.20 94 0 2 Example 2 1.14 94 0 2 Example 3 1.3 90 1 5 Example 4 1.13 89 3 6 Comparative Example 1 1.12 87 6 7 Comparative Example 2 1.10 85 10 8

[0123] Referring to Table 2 above, it can be seen that the capacitance, resistance increase rate, and thickness increase rate are significantly improved in Example 1, in which two negative electrodes b are applied to the external electrodes out of a total of 32 electrodes, and in Example 2, in which four negative electrodes b are applied to the external electrodes.

Claims

Claim 1 An electrode assembly comprising a plurality of first electrodes, a plurality of second electrodes, and a plurality of separators, wherein each first electrode and a second electrode are formed by stacking with a separator in between, wherein the plurality of first electrodes and the plurality of second electrodes each have an electrode composite containing a binder and an electrode active material coated on a current collector, and at least one of the first electrodes has a binder different from the remaining first electrodes excluding it, and the first electrodes include an inner electrode and an outer electrode, wherein the inner electrode represents one or more first electrodes disposed inside the electrode assembly, and the outer electrode represents one or more first electrodes disposed on each side outside the inner electrode, and the inner electrode and the outer electrode have different binders, and the binder included in the outer electrode is a styrene acrylate (SA)-based binder. Claim 2 An electrode assembly according to claim 1, wherein the first electrode is a negative electrode. Claim 3 delete Claim 4 delete Claim 5 An electrode assembly according to claim 1, wherein the binder included in the internal electrode is a styrene-butadiene (SB)-based binder. Claim 6 An electrode assembly according to claim 1, wherein the first electrode has 26 or more electrodes. Claim 7 An electrode assembly according to claim 1, wherein 1 to 5 external electrodes are arranged on each side outside of the internal electrode. Claim 8 An electrode assembly according to claim 1, wherein each external electrode comprises 3 to 20 internal electrodes. Claim 9 An electrode assembly according to claim 1, wherein the first electrode comprises (n+1) negative electrodes and the second electrode comprises n positive electrodes, and n is a natural number. Claim 10 An electrode assembly according to claim 1, wherein at least one of the second electrodes comprises a binder different from the remaining second electrodes excluding the first. Claim 11 An electrode assembly according to claim 1, comprising one or more selected from a stacked electrode assembly having a stacked structure with a separator interposed between an anode and a cathode, a stacked / folded electrode assembly manufactured by winding unit cells positioned on a long sheet-type separator film, and a lamination / stacked electrode assembly having a bonded structure with a separator interposed between unit cells. Claim 12 A secondary battery comprising the electrode assembly of claim 1.

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