Electrode assembly and lithium secondary battery including the same

Abstract

The present invention relates to an electrode assembly and a lithium secondary battery including the same. The electrode assembly includes a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and a pore closing portion. The separator is disposed between the negative electrode and the positive electrode. The width of the negative electrode active material layer is larger than the width of the positive electrode active material layer. The separator includes a separator main body portion that overlaps the positive electrode active material layer in the vertical direction, and a separator extension portion that does not overlap the positive electrode active material layer in the vertical direction and extends from the separator main body portion. The pore closing portion is disposed on one or both surfaces of the separator extension portion, and the porosity of the pore closing portion can be 1% or less.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0090558, filed on July 21, 2022, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference in their entirety.

[0002] The present invention relates to an electrode assembly including a pore closing part and a lithium secondary battery including the same.

Background Art

[0003] Recently, with the rapid progress in miniaturization and weight reduction of electronic products, electronic devices, communication devices, etc., and the increasing need for electric vehicles in relation to environmental issues, the need for improving the performance of secondary batteries used as power sources for these products is also increasing. Among them, lithium secondary batteries have received considerable attention as high-performance batteries due to their high energy density and high standard electrode potential. A lithium secondary battery generally includes a positive electrode, a negative electrode, an electrolyte, and a separator. Specifically, a lithium secondary battery can be manufactured by impregnating an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode with an electrolyte.

[0004] Specifically, referring to FIG. 1, the electrode assembly 10 includes a negative electrode 100, a positive electrode 200, and a separator 300. The negative electrode 100 includes a negative electrode current collector 110 and a negative electrode active material layer 120 disposed on the negative electrode current collector. The positive electrode 200 includes a positive electrode current collector 210 and a positive electrode active material layer 220 disposed on the positive electrode current collector. Generally, the width of the negative electrode active material layer 120 (width in the W direction) is larger than the width of the positive electrode active material layer 220 (width in the W direction).

[0005] The negative electrode active material layer 120 may include a negative electrode main body portion 120a that overlaps with the positive electrode active material layer 220 in the vertical direction R-R', and a negative electrode extension portion 120b that does not overlap with the positive electrode active material layer 220 in the vertical direction R-R' and extends from the negative electrode main body portion 120a. Since the negative electrode main body portion 120a faces the positive electrode active material layer, the charge amount of the negative electrode main body portion 120a is larger than the charge amount of the negative electrode extension portion 120b.

[0006] During the driving process of the battery, if a disconnection P occurs in any one of the negative electrodes included in the electrode assembly for some reason, the lithium ions in the electrolyte move to the negative electrode extension portion 120b, and the electrons of the negative electrode main body portion 120a move to the negative electrode extension portion 120b. The lithium ions in the electrolyte come into contact with the moved electrons in the negative electrode extension portion 120b. If such a phenomenon continues, a problem of lithium precipitation occurs in the negative electrode extension portion 120b. The precipitated lithium may short-circuit the positive electrode and the negative electrode, causing heat generation and ignition.

[0007] As a conventional technology, there are technologies such as a method for confirming whether lithium precipitation has occurred (Korean Patent Publication No. 10-2017-0023583) or a method for preventing disconnection of the negative electrode (Korean Patent Publication No. 10-2013-0050654). However, in the situation where disconnection of the negative electrode occurs, there is no effective method that can minimize lithium precipitation.

[0008] Therefore, there is a need for a new electrode assembly that can minimize the above-mentioned lithium precipitation when the negative electrode is disconnected.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] One problem to be solved by the present invention is to provide an electrode assembly capable of minimizing lithium precipitation at the negative electrode.

[0011] Another problem to be solved by the present invention is to provide a lithium secondary battery including the electrode assembly.

Means for Solving the Problems

[0012] According to one embodiment of the present invention, there is provided an electrode assembly including a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and a pore closing portion. The separator is disposed between the negative electrode and the positive electrode. The width of the negative electrode active material layer is larger than the width of the positive electrode active material layer. The separator includes a separator main body portion that overlaps the positive electrode active material layer in the vertical direction and a separator extension portion that does not overlap the positive electrode active material layer in the vertical direction and extends from the separator main body portion. The pore closing portion is disposed on one or both surfaces of the separator extension portion, and the porosity of the pore closing portion is 1% or less.

[0013] According to another embodiment of the present invention, there is provided a lithium secondary battery including the electrode assembly and an electrolyte.

Advantages of the Invention

[0014] According to the present invention, even if a disconnection occurs in a part of the negative electrode in the battery, the phenomenon of lithium precipitation from the end of the negative electrode can be suppressed. Thereby, a short circuit between the positive electrode and the negative electrode can be prevented, and heat generation and ignition of the battery can be suppressed.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0016] Hereinafter, in order to facilitate the understanding of the present invention, the present invention will be described in more detail.

[0017] The terms and words used in this specification and the claims shall not be construed as limited to their ordinary or dictionary meanings. In accordance with the principle that the inventor can appropriately define the concept of the terms in order to explain his invention in the best way, they should be construed in meanings and concepts consistent with the technical idea of the present invention.

[0018] The terms used in this specification are merely used to illustrate exemplary embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly has a different meaning.

[0019] In this specification, terms such as "comprising", "including" or "having" are used to specify the presence of implemented features, numbers, steps, components or combinations thereof, and should be understood not to preclude in advance the presence or possibility of addition of one or more different features, numbers, steps, components or combinations thereof.

[0020] In this specification, the porosity can be measured by a Capillary flow porometer device manufactured by Porous materials at 25°C. The measurement range of the pore diameter is 13 nm to 500 μm.

[0021] In this specification, the air permeability can be measured under the following conditions using an Oken Type Air-permeability & Smoothness Testing Controller device manufactured by ASAHI SEIKO.

[0022] Time: 6 sec Value: 500 Measure Mode: JIS (sec) Temperature: 25°C

[0023] In this specification, the thickness (or maximum thickness) can be measured by TESA-μHITE.

[0024] In this specification, the vertical direction corresponds to the R-R' direction in FIGS. 1, 2, 4, and 5. Specifically, the R direction corresponds to the upper direction and the R' direction corresponds to the lower direction.

[0025] In this specification, the 7Li-NMR measurement conditions are as follows.

[0026] 300 MHz solid-state NMR system; MAS rotation speed: 32 kHz; Spectral frequency: 116.6420 MHz; Temperature: room temperature (25°C); Chemical shift value standard: 1 M LiCl in H2O; Pulse sequence: spin echo (90°-τ1-180°-τ2); Spectral width: 500,000 Hz; Pulse length: 1) 90° pulse length 2.25 μsec, 2) 180° pulse length 4.50 μsec; Drive time (τ1): 31.25 μsec; Pulse delay: 2 sec

[0027] <Electrode Assembly> The electrode assembly according to an embodiment of the present invention includes a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and a pore closing portion. The separator is disposed between the negative electrode and the positive electrode. The width of the negative electrode active material layer is larger than the width of the positive electrode active material layer. The separator includes a separator main body portion that overlaps the positive electrode active material layer in the vertical direction and a separator extension portion that does not overlap the positive electrode active material layer in the vertical direction and extends from the separator main body portion. The pore closing portion is disposed on one or both surfaces of the separator extension portion, and the porosity of the pore closing portion can be 1% or less.

[0028] 1) Negative electrode FIG. 2 is a side cross-sectional view for explaining an electrode assembly according to an embodiment of the present invention. Referring to FIG. 2, the electrode assembly 10 can include one or more negative electrodes 100. Specifically, the electrode assembly 10 can include a plurality of negative electrodes 100.

[0029] The negative electrode 100 can include a negative electrode active material layer 120. Specifically, the negative electrode 100 includes a negative electrode current collector 110, and the negative electrode active material layer 120 can be located on one or both surfaces of the negative electrode current collector 110.

[0030] The negative electrode current collector 110 is not particularly limited as long as it is a material that does not cause a chemical change in the battery and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, alloys thereof, materials surface-treated with carbon, nickel, titanium, silver, etc. on their surfaces, or fired carbon, etc. can be used.

[0031] The negative electrode active material layer 120 can include a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0032] Examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; metal oxides such as SiO v (0 < v < 2), SnO2, vanadium oxides, lithium vanadium oxides that can be doped and de-doped with lithium; or composites containing the metallic compound and the carbonaceous material such as Si-C composites or Sn-C composites. Any one or a mixture of two or more of these can be used. Also, a thin film of metallic lithium can be used as the negative electrode active material. Further, as the carbon material, both low-crystalline carbon and highly crystalline carbon can be used.

[0033] The negative electrode conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0034] As the negative electrode binder, general binders used in the technical field can be used, and the types thereof are not particularly limited. Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds can be used.

[0035] The negative electrode active material layer 120 can include a negative electrode main body portion 120a and a negative electrode extension portion 120b. The negative electrode main body portion 120a can overlap with the positive electrode active material layer 220 in the vertical direction R-R'. That is, the negative electrode main body portion 120a can face the positive electrode active material layer 220. The negative electrode extension portion 120b can extend from the negative electrode main body portion 120a. The negative electrode extension portion 120b can not overlap with the positive electrode active material layer 220 in the vertical direction. The negative electrode extension portion 120b can be closer to the end of the negative electrode current collector 110 than the negative electrode main body portion 120a.

[0036] 2) Positive electrode Referring to FIG. 2, the electrode assembly 10 can include one or more positive electrodes 200. Specifically, the electrode assembly 10 can include a plurality of positive electrodes 200.

[0037] The positive electrode 200 can include a positive electrode active material layer 220. Specifically, the positive electrode 200 can include a positive electrode current collector 210, and the positive electrode active material layer 220 can be located on one or both surfaces of the positive electrode current collector 210.

[0038] The positive electrode current collector 210 is not particularly limited as long as it is a material that does not cause a chemical change in the battery and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, alloys thereof, materials surface-treated with carbon, nickel, titanium, silver, etc. on these surfaces, or fired carbon, etc. can be used.

[0039] The positive electrode active material layer 220 can include a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0040] The positive electrode active material can be a commonly used positive electrode active material. Specifically, the positive electrode active material can be a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; lithium iron oxide such as LiFe3O4; Li 1+a M b O2+c can include.

[0041] More specifically, the positive electrode active material is Li 1+a M b O 2+C and includes, where M can be at least one element selected from the group consisting of Ni, Co, Mn, Fe, P, Al, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, and -0.2 ≦ a ≦ 0.2, 0 < b ≦ 2, and 0 ≦ c ≦ 2. Preferably, the a satisfies -0.1 ≦ a ≦ 0.1, and more preferably 0 ≦ a ≦ 0.1. More specifically, the Li 1+a M b O 2+C is Li 1+a [Ni p Co q M 1 r M 2 s O2 or can be the Li 1+a [Ni p Co q M 1 r M 2 s O2. In the Li 1+a [Ni p Co q M 1 r M 2 s O2, the M 1 can be at least one element of Al and Mn, and M 2can be at least one element selected from the group consisting of Fe, P, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, where 0 < p < 1, preferably 0.3 < p < 1, more preferably 0.5 < p < 1, 0 < q < 1, preferably 0 < q < 0.7, more preferably 0 < q < 0.5, 0 < r < 1, preferably 0 < r < 0.7, more preferably 0 < r < 0.5, and 0 ≤ s ≤ 0.2, preferably 0 ≤ s ≤ 0.1. The Li 1+a M b O 2+C can include at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, Li[Ni 0.5 Co 0.3 Mn 0.2 O2, Li[Ni 0.6 Co 0.2 Mn 0.2 O2, Li[Ni 0.7 Co 0.1 Mn 0.2 O2, Li[Ni 0.8 Co 0.1 Mn 0.1 O2, Li[Ni 0.9 Co 0.05 Mn 0.05 O2, LiMn2O4, LiFePO4, 0.5Li2MnO3·0.5Li[Mn 0.4 Ni 0.3 Co 0.3 O2. Preferably, the Li 1+a M b O 2+C can include any one of the above Li[Ni 0.6 Co 0.2 Mn 0.2 O2, Li[Ni 0.7 Co 0.1 Mn 0.2 O2, Li[Ni 0.8 Co 0.1 Mn 0.1 O2, Li[Ni 0.9 Co 0.05 Mn 0.05 O2.

[0042] The positive electrode conductive material is not particularly limited as long as it does not cause a chemical change in the battery and has conductivity. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers and metal fibers; conductive tubes such as single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives can be used.

[0043] As the positive electrode binder, a general binder used in the technical field can be used, and the type thereof is not particularly limited. Examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof. Among these, one kind alone or a mixture of two or more kinds can be used.

[0044] The width of the negative electrode active material layer 120 can be larger than the width of the positive electrode active material layer 220. Here, the width means the width of the negative electrode active material or the positive electrode active material layer parallel to the W direction in FIGS. 2 and 4 to 6. Since the width of the negative electrode active material layer is larger than the width of the positive electrode active material layer, there is an effect of suppressing lithium plating during battery charging.

[0045] 3) Separator The separator 300 can separate the negative electrode 100 and the positive electrode 200 and provide a migration path for lithium ions. The separator 300 is located between the negative electrode 100 and the positive electrode 200 and can separate the negative electrode 100 and the positive electrode 200. The electrode assembly 10 can include one or more separators 300, specifically, it can also include a plurality of separators 300.

[0046] As the separator 300, generally, any separator that can be used in a lithium secondary battery can be used without particular limitation. In particular, those with low resistance to ion migration of the electrolyte and excellent electrolyte moisture retention ability are preferred. Specifically, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer (polyethylene), propylene homopolymer (polypropylene), ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. Also, a normal porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. can also be used.

[0047] In addition, the separator 300 can use the above-mentioned materials as a base material and can also include a coating layer disposed on the base material. The coating layer can include at least one of inorganic particles and polymers. The coating layer can improve heat resistance or mechanical strength. The coating layer can be a single layer or a multi-layer structure.

[0048] The separator 300 can include a separator main body portion 300a and a separator extension portion 300b. The separator main body portion 300a can overlap with the positive electrode active material layer 220 in the vertical direction R-R'. The separator main body portion 300a can face the positive electrode active material layer 220. The separator extension portion 300b can extend from the separator main body portion 300a. The separator extension portion 300b can be non-overlapping with the positive electrode active material layer 220 in the vertical direction R-R'.

[0049] 4) Pore closing portion The pore closing portion serves to suppress the phenomenon in which a large amount of lithium ions directly move to the negative electrode extension portion. Thereby, when the negative electrode is disconnected, the phenomenon in which lithium is deposited at the negative electrode extension portion can be reduced. Therefore, the problem of short circuit between the negative electrode and the positive electrode in the battery can be prevented, and heat generation and ignition of the battery can be suppressed.

[0050] The porosity of the pore closing portion can be 1% or less, specifically 0% to 1%, more specifically 0% to 0.8%, for example, 0% to 0.5%. Since the porosity of the pore closing portion is 1% or less, the amount of lithium ions directly transmitted from the electrolyte to the negative electrode extension portion can be significantly reduced, and when the negative electrode is disconnected, the phenomenon in which lithium is deposited at the negative electrode extension portion can be reduced. Conversely, when the porosity of the pore closing portion exceeds 1%, the phenomenon in which lithium ions move from the electrolyte to the negative electrode extension portion cannot be effectively suppressed, and thereby it becomes difficult to prevent the lithium deposition phenomenon at the negative electrode extension portion.

[0051] The air permeability of the pore closing part can be 1,500 sec / 100 cc or more, specifically 1,500 sec / 100 cc to 10,000 sec / 100 cc, more specifically 1,500 sec / 100 cc to 8,000 sec / 100 cc, for example, it can be 1,500 sec / 100 cc to 5,500 sec / 100 cc. When the above range is satisfied, the amount of lithium ions directly transmitted from the electrolyte to the negative electrode extension part can be significantly reduced, and when the negative electrode is disconnected, the phenomenon of lithium precipitation at the negative electrode extension part can be reduced.

[0052] Referring to FIGS. 2 to 5, the pore closing part 400 can be disposed on one or both surfaces of the separator extension part 300b. Specifically, the pore closing part 400 may be disposed on the entire area of one or both surfaces of the separator extension part 300b. In this case, one end of the pore closing part 400 can be located on the same line as one end of the separator 300. That is, the pore closing part 400 can cover the upper surface and / or the lower surface of the separator extension part 300b up to the edge of the separator 300.

[0053] Referring to FIG. 2, the pore closing part 400 can be disposed on one surface of the separator extension part 300b. Specifically, the one surface of the separator extension part 300b where the pore closing part 400 is located can be located in the same direction as the surface of the separator main body part 300a (the separator main body part 300a attached to the separator extension part 300b) in contact with the positive electrode active material layer 220. When the pore closing part 400 is formed on the surface facing the positive electrode active material layer, the loss of the negative electrode loading amount can be minimized, and lithium precipitation can be suppressed.

[0054] FIG. 3 corresponds to a view of region C in FIG. 2 seen from above. Referring to FIG. 3, the pore closing part 400 can be located while surrounding the positive electrode active material layer 220.

[0055] On the one hand, referring to FIG. 4, the pore closing portion 400 can be located on one surface of the separator extension portion 300b and in the same direction as the surface of the separator main body portion 300a (the separator main body portion 300a adhered to the separator extension portion 300b) in contact with the negative electrode active material layer 120. In this case, the transfer of lithium ions existing in the pores of the separator to the negative electrode extension portion can be more effectively suppressed.

[0056] Also, referring to FIG. 5, the pore closing portion 400 can be located on both surfaces of the separator extension portion 300b. In this case, the lithium precipitation in the negative electrode extension portion can be more effectively suppressed.

[0057] Referring to FIGS. 2 to 5, the pore closing portion 400 can overlap with the negative electrode extension portion 120b in the vertical direction R-R'. Thereby, the amount of lithium ions directly transferred from the electrolyte to the negative electrode extension portion can be significantly reduced, and when the negative electrode is disconnected, the phenomenon of lithium precipitation in the negative electrode extension portion can be reduced.

[0058] Furthermore, the pore closing portion 400 can be non-overlapping with the negative electrode main body portion 120a in the vertical direction R-R'. Therefore, the movement of lithium ions generated during the normal driving process of the battery (lithium ions move from the positive electrode to the negative electrode) can be smoothly performed.

[0059] The pore closing portion can contain a polymer, for example, it can also be made of a polymer. The polymer can include at least any one selected from the group consisting of polyethylene (PE), polypropylene (PP), polyimide (PI), and polymethyl methacrylate (PMMA). Since the pore closing portion contains a polymer, the pore closing portion can be effectively adhered to the separator extension portion, and the stability of the battery can be further improved.

[0060] The polymer contained in the pore closing portion can be the same as the polymer material contained in the separator (separator main body portion, separator extension portion). For example, when the separator contains at least one of polyethylene and polypropylene, the polymer contained in the pore closing portion can also be at least one of polyethylene and polypropylene. In this case, the adhesive force between the pore closing portion and the separator extension portion increases, and the safety can be further improved.

[0061] The polymer can be contained in the pore closing portion in an amount of 15% by weight to 100% by weight, specifically 15% by weight to 50% by weight, and more specifically 15% by weight to 30% by weight. When the above range is satisfied, the porosity of the pore closing portion is easily adjusted to 1% or less.

[0062] Depending on the case, the pore closing portion can further contain inorganic particles together with the polymer. The inorganic particles can contain at least one selected from the group consisting of BaTiO3, Al2O3, ZrO2, and TiO2. Since the inorganic particles improve the heat resistance of the separator extension portion and the pore closing portion, the battery safety can be improved.

[0063] The inorganic particles can be contained in the pore closing portion in an amount of 85% by weight or less, specifically 50% by weight to 85% by weight, and more specifically 70% by weight to 85% by weight. When the above range is satisfied, the heat resistance of the pore closing portion is improved, and the porosity is easily adjusted to 1% or less.

[0064] The maximum thickness of the pore closing portion can be 10 μm to 20 μm, specifically 12 μm to 20 μm, and more specifically 14 μm to 20 μm. When the above range is satisfied, it is possible to suppress the excessive transmission of lithium ions from the electrolyte to the negative electrode extension portion, the thickness of the pore closing portion is not excessively thick, and the thickness of the battery can be uniform as a whole.

[0065] Specifically, the pore closing portion can be composed of the base layer made of the polymer, or can also include the base layer and the reinforcing coating layer located on the base layer and containing the inorganic particles. Thereby, the heat resistance of the pore closing portion is enhanced, and the safety of the battery can be further improved.

[0066] On the other hand, the porosity and / or air permeability of the pore closing portion of the present invention can be adjusted by adjusting the porosity of the polymer constituting the pore closing portion, the type of inorganic particles, and / or the content of the polymer and inorganic particles. For example, when the pore closing portion is composed of a base layer and a reinforcing coating layer, by adjusting the type and draw ratio of the polymer in the base layer so that the porosity of the base layer is 1% or less, the porosity of the pore closing portion can be made 1% or less. Or even when the porosity of the base layer is 1% or more, by forming a coating layer with a low porosity on the surface of the base layer, the porosity of the pore closing portion can be made 1% or less.

[0067] The thickness of the base layer can be 9 μm to 15 μm, specifically 10 μm to 13 μm. The thickness of the reinforcing coating layer can be 1 μm to 5 μm, specifically 2 μm to 5 μm. When the above range is satisfied, the effect of suppressing lithium precipitation can be achieved, and the heat resistance of the pore closing portion can be effectively improved.

[0068] 5) Others The electrode assembly can further include a pore closing coating layer 500. FIG. 6 shows a cross-section of the electrode assembly, and FIG. 7 is a cross-section of the D region of the electrode assembly in FIG. 6 viewed from the S direction. Referring to FIGS. 6 and 7, the pore closing coating layer 500 exists together with the above-mentioned pore closing portion 400.

[0069] The pore-closing coating layer 500 can cover at least a part of the side surface of the negative electrode extension part 120b. Thereby, lithium ions moving from the electrolyte to the negative electrode extension part can be more effectively reduced. Thereby, when the negative electrode is disconnected, the phenomenon of lithium precipitation from the negative electrode extension part can be more effectively suppressed.

[0070] The material and structure constituting the pore-closing coating layer can be the same as the material and structure constituting the above-mentioned pore-closing part, and the description thereof is omitted.

[0071] <Lithium Secondary Battery> The lithium secondary battery according to another embodiment of the present invention can include the electrode assembly and the electrolyte of the above-described embodiment.

[0072] The electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, etc. that can be used during the manufacture of the lithium secondary battery, and is not limited thereto.

[0073] Specifically, the electrolyte can include a non-aqueous organic solvent and a metal salt.

[0074] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate.

[0075] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, can be preferably used because they are organic solvents with high viscosity, high dielectric constant, and can dissociate lithium salts well. When such cyclic carbonates are mixed and used with linear carbonates with low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte having high electrical conductivity can be produced and can be more preferably used.

[0076] The metal salt can be a lithium salt, and the lithium salt is a substance that is easily dissolved in the non-aqueous electrolyte. For example, as the anion of the lithium salt, F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and one or more selected from the group consisting of (CF3CF2SO2)2N - can be used.

[0077] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, triamide hexaline, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride for the purpose of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery.

[0078] According to still another embodiment of the present invention, there are provided a battery module including the lithium secondary battery as a unit cell and a battery pack including the same. The battery module and the battery pack include the lithium secondary battery having high capacity, high rate characteristics, and cycle characteristics, and can be used as a power source for medium and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0079] Hereinafter, preferred examples are presented to facilitate the understanding of the present invention. However, it is obvious to those skilled in the art that the examples are illustrative of the description and various changes and modifications can be made within the scope of the description and the scope of the technical idea. Needless to say, such variations and modifications belong to the scope of the appended claims.

[0080] Examples and Comparative Examples Example 1 (1) Manufacture of the electrode assembly On a part of both sides of the porous polyethylene separator, a pore-closed portion with a porosity of 0.5% and an air permeability of 5,500 sec / 100 cc was formed. Specifically, the pore-closed portion was manufactured by coating both sides of a base layer made of polyethylene (with a thickness of 12 μm) with a reinforcing coating layer containing Al2O3 at a thickness of 3 μm. After assembling the electrode assembly, the pore-closed portion configured as described above was placed on the surface of the separator that does not overlap with the positive electrode active material layer (i.e., the separator extension part), and a separator with a pore-closed portion formed was manufactured.

[0081] Next, a negative electrode including a copper current collector and a negative electrode active material layer disposed on both sides of the copper current collector was prepared. The negative electrode active material layer contains a mixture of artificial graphite and natural graphite as the negative electrode active material, a mixture of styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as the negative electrode binder, and carbon black as the negative electrode conductive material.

[0082] Also, a positive electrode including an aluminum current collector and a positive electrode active material layer disposed on both sides of the aluminum current collector was prepared. The positive electrode active material layer contains Li[Ni 0.6 Co 0.2 Mn 0.2 O2 as the positive electrode active material, polyvinylidene fluoride (PVdF) as the positive electrode binder, and carbon black as the positive electrode conductive material.

[0083] Three negative electrodes and two positive electrodes prepared as described above were laminated with a separator having a pore-closed portion interposed therebetween to manufacture an electrode assembly with a negative electrode / separator / positive electrode / separator / negative electrode / separator / positive electrode / separator / negative electrode structure. Then, the negative electrodes were electrically connected to each other using negative electrode tabs, and the positive electrodes were electrically connected to each other using positive electrode tabs.

[0084] (2) Manufacture of a lithium secondary battery After placing the electrode assembly in the battery case, an electrolyte was injected into the battery case to impregnate the electrode assembly with the electrolyte. Thereafter, the battery case was sealed. The electrolyte contains a non-aqueous solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2 and lithium hexafluorophosphate (1 mol of LiPF6).

[0085] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that pore-closed portions having a porosity of 0.1% and an air permeability of 10,000 sec / 100 cc or more were formed on a part of both surfaces of the porous polyethylene separator.

[0086] Comparative Example 1 A lithium secondary battery was manufactured in the same manner as in Example 1, except that a separator without pore-closed portions formed thereon was used.

[0087] Comparative Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that pore-closed portions having a porosity of 3% and an air permeability of 1,500 sec / 100 cc were formed on a part of both surfaces of the porous polyethylene separator.

[0088] Comparative Example 3 A lithium secondary battery was manufactured in the same manner as in Example 1, except that pore-closed portions having a porosity of 10% and an air permeability of 1,500 sec / 100 cc were formed on a part of both surfaces of the porous polyethylene separator.

[0089] Experimental Example 1: Confirmation of Lithium Deposition Possibility 7Li-NMR evaluation was performed on the negative electrode extension portions of the examples and comparative examples. Specifically, at 25°C, CC / CV charging was performed at 1 / 3C up to 4.2V, and the battery was fully charged with a 5% current cut. Next, the negative electrode located at the bottom of the electrode assembly was separated from the tab and the negative electrode was disconnected.

[0090] Thereafter, after leaving the battery for 60 minutes, a 2.5V CC discharge was performed at 1 / 3C. After the discharge, in order to confirm the possibility of lithium precipitation, the battery was fully charged at 4.2V CC / CV (5% current cut-off) at 1 / 3C at 25°C.

[0091] Thereafter, the disconnected negative electrode was separated, and 7Li-NMR evaluation was performed on the negative electrode extension.

[0092] The 7Li-NMR measurement conditions are as follows.

[0093] 300MHz solid-state NMR system MAS rotation speed: 32kHz Spectral frequency: 116.6420MHz Temperature: room temperature (25°C) Chemical shift value standard: 1M LiCl of H2O Pulse sequence: spin echo (90°-τ1-180°-τ2) Spectral width: 500,000Hz Pulse length: 1) 90° pulse length 2.25μsec, 2) 180° pulse length 4.50μsec Drive time (Dwell time) (τ1): 31.25μsec Pulse delay: 2sec

[0094] Figure 8 shows the results of 7Li-NMR for the disconnected negative electrode of the lithium secondary battery of Example 1, Figure 9 shows the results of 7Li-NMR for the disconnected negative electrode of the lithium secondary battery of Example 2, Figure 10 shows the results of 7Li-NMR for the disconnected negative electrode of the lithium secondary battery of Comparative Example 1, Figure 11 shows the results of 7Li-NMR for the disconnected negative electrode of the lithium secondary battery of Comparative Example 2, and Figure 12 shows the results of 7Li-NMR for the disconnected negative electrode of the lithium secondary battery of Comparative Example 3.

[0095] The peak corresponding to lithium precipitation in 7Li-NMR is found in the region of 240 ppm to 270 ppm. Referring to FIGS. 8 and 9, it can be seen that in the lithium secondary batteries of Examples 1 and 2, lithium precipitation did not occur and no peak corresponding to lithium precipitation was found. On the other hand, referring to FIGS. 10 to 12, it can be seen that in the case of the lithium secondary batteries of Comparative Examples 1 to 3, a peak corresponding to lithium precipitation occurs.

[0096] Also, FIGS. 13 and 14 are photographs showing the states of the fully charged lithium secondary batteries of Comparative Examples 2 and 3 after disconnection of the negative electrode, respectively. Referring to FIGS. 12 and 13, it can be confirmed that lithium precipitation occurred in the lithium secondary batteries of Comparative Examples 2 and 3 where the porosity of the pore closing portion exceeded 1%.

Explanation of Reference Signs

[0097] 10 Electrode Assembly 100 Negative Electrode 110 Negative Electrode Current Collector 120 Negative Electrode Active Material Layer 200 Positive Electrode 210 Positive Electrode Current Collector 220 Positive Electrode Active Material Layer 300 Separator 300a Separator Main Body Portion 300b Separator Extension Portion 400 Pore Closing Portion 120a Negative Electrode Main Body Portion 120b Negative Electrode Extension Portion 500 Pore Closing Coating Layer

Claims

1. a negative electrode including a negative electrode active material layer, a positive electrode including a positive electrode active material layer, a separator, and a pore closing portion, wherein the separator is disposed between the negative electrode and the positive electrode, the width of the negative electrode active material layer is larger than the width of the positive electrode active material layer, the separator includes a separator main body portion that overlaps the positive electrode active material layer in the vertical direction and a separator extension portion that does not overlap the positive electrode active material layer in the vertical direction and extends from the separator main body portion, the pore closing portion is disposed on one or both surfaces of the separator extension portion, the porosity of the pore closing portion is 1% or less, an electrode assembly.

2. The electrode assembly according to claim 1, wherein the pore closing portion is disposed over the entire area of one or both surfaces of the separator extension portion.

3. The electrode assembly according to claim 1, wherein one end of the pore closing portion is located on the same line as one end of the separator.

4. the negative electrode active material layer includes a negative electrode main body portion that overlaps the positive electrode active material layer in the vertical direction and a negative electrode extension portion that does not overlap the positive electrode active material layer in the vertical direction and extends from the negative electrode main body portion, The electrode assembly according to claim 1, wherein the pore closing portion overlaps the negative electrode extension portion in the vertical direction.

5. the pore closing portion contains a polymer, The electrode assembly according to claim 1, wherein the polymer contains at least one selected from the group consisting of polyethylene, polypropylene, polyimide, and polymethyl methacrylate.

6. The electrode assembly according to claim 5, wherein the pore closing portion further contains inorganic particles.

7. The electrode assembly according to claim 1, wherein the air permeability of the pore closing portion is 1,500 sec / 100 cc or more.

8. The electrode assembly according to claim 1, wherein the maximum thickness of the pore closing portion is 10 μm to 20 μm.

9. the electrode assembly further includes a pore closing layer, the pore closing layer covers at least a part of the side surface of the negative electrode extension portion, The electrode assembly according to claim 4, wherein the porosity of the pore closing layer is 1% or less.

10. A lithium secondary battery including the electrode assembly according to claim 1 and an electrolyte.

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