Electrode assembly and lithium secondary battery comprising same

Abstract

The present invention relates to an electrode assembly and a lithium secondary battery comprising the same, the electrode assembly comprising: a negative electrode comprising a negative electrode active material layer; a positive electrode including a positive electrode active material layer; a diaphragm; the diaphragm is arranged between the negative electrode and the positive electrode, and the width of the negative electrode active material layer is larger than that of the positive electrode active material layer; the separator comprises a separator main body part vertically overlapped with the positive electrode active material layer, and a separator extension part which does not vertically overlapped with the positive electrode active material layer and extends from the separator main body part; and the pore closing portion is provided on one surface or an opposite surface of the diaphragm extension portion, and an air porosity of the pore closing portion may be 1% or less.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2022-0090558, filed on Jul. 21, 2022, the disclosure of which is incorporated herein by reference.

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

[0003] In recent years, the miniaturization and lightweighting of electronic products, electronic devices and communication devices have developed rapidly, and with the significant increase in the demand for electric vehicles related to environmental issues, the demand for improving the performance of secondary batteries used as power sources for these products is also increasing. Among them, lithium secondary batteries have received widespread attention as high-performance batteries due to their high energy density and high standard electrode potential. Lithium secondary batteries are generally composed of a positive electrode, a negative electrode, an electrolyte and a separator. Specifically, a lithium secondary battery can be prepared by impregnating an electrode assembly with an electrolyte, the electrode assembly comprising a positive electrode, a negative electrode and a separator arranged between the positive electrode and the negative electrode.

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

[0005] The negative electrode active material layer 120 may include a negative electrode main body portion 120a overlapping the positive electrode active material layer 220 in the vertical direction RR' and a negative electrode extension portion 120b extending from the negative electrode main body portion 120a without overlapping the positive electrode active material layer 220 in the vertical direction RR'. 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 greater than the charge amount of the negative electrode extension portion 120b.

[0006] During the operation of the battery, if disconnection P occurs in any negative electrode included in the electrode assembly for some reason, the lithium ions in the electrolyte move to the negative electrode extension 120b, and the electrons in the negative electrode main body 120a move to the negative electrode extension 120b. The lithium ions of the electrolyte meet the moving electrons in the negative electrode extension 120b, wherein, if this phenomenon continues, the problem of lithium precipitation on the negative electrode extension 120b occurs. The precipitated lithium may short-circuit the positive and negative electrodes, and may cause heat and fire.

[0007] As prior arts, there are technologies such as a method of checking whether lithium deposition has occurred (Korean Patent Application Publication No. 10-2017-0023583) or a method of preventing negative electrode disconnection (Korean Patent Application Publication No. 10-2013-0050654), but when negative electrode disconnection occurs, there is no effective way to minimize lithium deposition.

[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.

[0009] <Prior Art Literature>

[0010] (Patent Document 1) Korean Patent Application Publication No. 10-2017-0023583

[0011] (Patent Document 2) Korean Patent Application Publication No. 10-2013-0050654 Summary of the invention

[0012] Technical issues

[0013] One aspect of the present invention provides an electrode assembly capable of minimizing lithium precipitation on a negative electrode.

[0014] Another aspect of the present invention provides a lithium secondary battery including the electrode assembly.

[0015] Technical Solution

[0016] According to one embodiment of the present invention, an electrode assembly is provided, which includes: a negative electrode, the negative electrode including a negative electrode active material layer; a positive electrode, the positive electrode including a positive electrode active material layer; a separator; and a pore closing portion, wherein the separator is arranged between the negative electrode and the positive electrode, the width of the negative electrode active material layer is greater than the width of the positive electrode active material layer, the separator includes a separator main body overlapping with the positive electrode active material layer in a vertical direction and a separator extension portion that does not overlap with the positive electrode active material layer in a vertical direction and extends from the separator main body, and the pore closing portion is arranged on one surface or both surfaces of the separator extension portion and the pore closing portion has a porosity of less than 1%.

[0017] According to another embodiment of the present invention, a lithium secondary battery is provided, the lithium secondary battery including the above electrode assembly and an electrolyte.

[0018] Beneficial Effects

[0019] According to the present invention, even if some negative electrodes in the battery are disconnected, the phenomenon of lithium precipitation on the end of the negative electrode can be suppressed. Accordingly, the short circuit between the positive electrode and the negative electrode can be prevented, and the heating and ignition of the battery can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a cross-sectional view illustrating a conventional secondary battery.

[0022] Figure 2 is a side cross-sectional view illustrating an electrode assembly of the present invention.

[0023] Figure 3 is a plan view illustrating an electrode assembly of the present invention, wherein it is Figure 2 A top view of region C of FIG.

[0024] Figure 4 is a side cross-sectional view illustrating an electrode assembly of the present invention.

[0025] Figure 5 is a side cross-sectional view illustrating an electrode assembly of the present invention.

[0026] Figure 6 is a side cross-sectional view illustrating an electrode assembly of the present invention.

[0027] Figure 7 yes Figure 6 A view of area D observed from direction S.

[0028] Figure 8 This is a graph showing the 7Li-NMR measurement results of the lithium secondary battery of Example 1 of the present invention.

[0029] Fig. 9 This is a graph showing the 7Li-NMR measurement results of the lithium secondary battery according to Example 2 of the present invention.

[0030] Fig.10 It is a graph showing the 7Li-NMR measurement results of the lithium secondary battery of Comparative Example 1 of the present invention.

[0031] Fig.11 It is a graph showing the 7Li-NMR measurement results of the lithium secondary battery of Comparative Example 2 of the present invention.

[0032] Fig.12 It is a graph showing the 7Li-NMR measurement results of the lithium secondary battery of Comparative Example 3 of the present invention.

[0033] Fig.13 This is a photograph showing that lithium deposition occurs in the fully charged lithium secondary battery of Comparative Example 2 after the negative electrode is disconnected.

[0034] Fig.14This is a photograph showing that lithium deposition occurs in the fully charged lithium secondary battery of Comparative Example 3 after the negative electrode is disconnected. DETAILED DESCRIPTION

[0035] Hereinafter, the present invention will be described in more detail to make the present invention more clearly understood.

[0036] It should be understood that the words or terms used in this specification and claims should not be interpreted as the meanings defined in commonly used dictionaries, and it should be further understood that the words or terms should be interpreted as having meanings consistent with their meanings in the context of the prior art and the technical ideas of the present invention, on the basis that the inventor can appropriately define the meanings of the words or terms to best explain the principles of the present invention.

[0037] The terms used in this specification are only used to describe exemplary embodiments, but are not intended to limit the present invention. Unless otherwise specified, terms in the singular form may include plural forms.

[0038] It should be further understood that the terms "include", "comprises" or "has" in this specification clarify the existence of the described features, numbers, steps, elements or their combinations, but do not exclude the existence or addition of one or more other features, numbers, steps, elements or their combinations.

[0039] The porosity in this specification can be measured at 25° C. using a capillary flow porometer from Porous Materials Inc. The measurement range of the pore size is 13 nm to 500 μm.

[0040] The air permeability in this specification can be measured using an Oken type air permeability and smoothness test controller of ASAHI SEIKO CO., LTD under the following conditions.

[0041] Time: 6 seconds

[0042] Value: 500

[0043] Measuring mode: JIS (seconds)

[0044] Temperature: 25℃

[0045] The thickness (or maximum thickness) in this specification can be measured using TESA-μHITE.

[0046] The vertical direction in this specification corresponds to Figure 1 , Figure 2 , Figure 4 and Figure 5 In the R-R' direction, specifically, the R direction corresponds to the upper direction and the R' direction corresponds to the lower direction.

[0047] The 7Li-NMR measurement conditions in this specification are as follows.

[0048] 300 MHz solid-state NMR system;

[0049] MAS speed: 32 kHz;

[0050] Spectrum frequency: 116.6420 MHz;

[0051] Temperature: room temperature (25°C);

[0052] Chemical shift value standard: 1 M LiCl in H2O;

[0053] Pulse sequence: spin echo (90°-τ1-180°-τ2);

[0054] Spectrum width: 500000 Hz;

[0055] Pulse length: 1) 90° pulse length 2.25 μs, 2) 180° pulse length 4.50 μs;

[0056] Dwell time (τ1): 31.25 μs;

[0057] Pulse delay: 2 seconds

[0058] <Electrode assembly>

[0059] According to one embodiment of the present invention, an electrode assembly includes: a negative electrode, the negative electrode including a negative electrode active material layer; a positive electrode, the positive electrode including a positive electrode active material layer; a separator; and a pore closing portion, wherein the separator is arranged between the negative electrode and the positive electrode, the width of the negative electrode active material layer is greater than the width of the positive electrode active material layer, the separator includes a separator main body overlapping with the positive electrode active material layer in a vertical direction and a separator extension portion that does not overlap with the positive electrode active material layer in a vertical direction and extends from the separator main body, and the pore closing portion is arranged on one surface or both surfaces of the separator extension portion and may have a porosity of less than 1%.

[0060] 1) Negative electrode

[0061] Figure 2 is a side cross-sectional view illustrating an electrode assembly according to one embodiment of the present invention. Figure 2 The electrode assembly 10 may include at least one negative electrode 100 , and the electrode assembly 10 may specifically include a plurality of negative electrodes 100 .

[0062] The negative electrode 100 may include a negative electrode active material layer 120. Specifically, the negative electrode 100 includes a negative electrode collector 110, and the negative electrode active material layer 120 may be provided on one surface or both surfaces of the negative electrode collector 110.

[0063] The negative electrode current collector 110 is not particularly limited as long as it is a material that has conductivity and does not cause adverse chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel or titanium, an alloy thereof, copper, stainless steel, aluminum, nickel or titanium surface-treated with one of carbon, nickel, titanium, silver, etc., or fired carbon can be used.

[0064] The negative electrode active material layer 120 may include a negative electrode active material, a negative electrode conductive material, and a negative electrode binder.

[0065] The negative electrode active material may include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; metal substances that can form alloys with lithium such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloy, Sn alloy or Al alloy; metal oxides that can be doped and dedoped with lithium such as SiO v (0<v<2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite material containing a metal substance and a carbonaceous material such as a Si-C composite material or a Sn-C composite material, and any one thereof or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as a negative electrode active material. In addition, both low crystalline carbon and high crystalline carbon can be used as carbon materials.

[0066] The negative electrode conductive material is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, conductive materials such as the following can be used: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0067] As the negative electrode binder, a common binder used in the art can be used, and there is no particular restriction on its type. For example, the binder may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0068] The negative electrode active material layer 120 may include a negative electrode main body 120a and a negative electrode extension 120b. The negative electrode main body 120a may overlap with the positive electrode active material layer 220 in the vertical direction RR'. That is, the negative electrode main body 120a may face the positive electrode active material layer 220. The negative electrode extension 120b may extend from the negative electrode main body 120a. The negative electrode extension 120b may not overlap with the positive electrode active material layer 220 in the vertical direction. The negative electrode extension 120b may be closer to the end of the negative electrode collector 110 than the negative electrode main body 120a.

[0069] 2) Positive electrode

[0070] Reference Figure 2 The electrode assembly 10 may include at least one positive electrode 200 , and the electrode assembly 10 may specifically include a plurality of positive electrodes 200 .

[0071] The positive electrode 200 may include a positive electrode active material layer 220. Specifically, the positive electrode 200 includes a positive electrode collector 210, and the positive electrode active material layer 220 may be provided on one surface or both surfaces of the positive electrode collector 210.

[0072] The positive electrode current collector 210 is not particularly limited as long as it is a material that has conductivity and does not cause adverse chemical changes in the battery, and can use, for example: copper, stainless steel, aluminum, nickel, or titanium, their alloys, copper, stainless steel, aluminum, nickel or titanium surface-treated with one of carbon, nickel, titanium, silver, etc., or fired carbon.

[0073] The positive active material layer 220 may include a positive active material, a positive conductive material, and a positive binder.

[0074] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may include: layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds replaced with one or more transition metals; lithium iron oxide such as LiFe3O4; and Li 1+a Mb O 2+c 。

[0075] More specifically, the positive electrode active material may include Li 1+a M b O 2+c , where M may be at least one element selected from the following: nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), phosphorus (P), aluminum (Al), magnesium (Mg), calcium (Ca), zirconium (Zr), zinc (Zn), titanium (Ti), ruthenium (Ru), niobium (Nb), tungsten (W), boron (B), silicon (Si), sodium (Na), potassium (K), molybdenum (Mo), and vanadium (V), and -0.2 ≤ a ≤ 0.2, 0 < b ≤ 2, and 0 ≤ c ≤ 2. a may preferably satisfy -0.1 ≤ a ≤ 0.1, more preferably 0 ≤ a ≤ 0.1. Specifically, Li 1+a M b O 2+c may include Li 1+a [Ni p Co q M 1 r M 2 s O2 or may be Li 1+a [Ni p Co q M 1 r M 2 s O2. In Li 1+a [Ni p Co q M 1 r M 2 s O2, M 1 may be at least one element of Al and Mn, M 2 may be at least one element selected from Fe, P, Mg, Ca, Zr, Zn, Ti, Ru, Nb, W, B, Si, Na, K, Mo, and V, p may satisfy 0 < p < 1, preferably 0.3 < p < 1, more preferably 0.5 < p < 1, q may satisfy 0 < q < 1, preferably 0 < q < 0.7, more preferably 0 < q < 0.5, r may satisfy 0 < r < 1, preferably 0 < r < 0.7, more preferably 0 < r < 0.5, and s may satisfy 0 ≤ s ≤ 0.2, preferably 0 ≤ s ≤ 0.1. Li 1+a M b O 2+c may include at least one of the following: LiCoO2, LiNiO2, LiMnO2, Li[Ni 0.5 Co0.3 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 and 0.5Li2MnO3·0.5Li[Mn 0.4 Ni 0.3 Co 0.3 ]O2. Preferably, Li 1+a M b O 2+c May include any of the following: 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 and Li[Ni 0.9 Co 0.05 Mn 0.05 ]O2.

[0076] The positive electrode conductive material is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example, conductive materials such as the following can be used: graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; conductive tubes such as single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes; fluorocarbons; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or polyphenylene derivatives.

[0077] As the positive electrode binder, a common binder used in the art can be used, and there is no particular restriction on its type. For example, the binder may include: polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber and various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0078] The width of the negative electrode active material layer 120 may be greater than the width of the positive electrode active material layer 220. In this document, width refers to the width of the negative electrode active material layer or the positive electrode active material layer. Figure 2 and Figures 4 to 6 The width is parallel to the W direction in the graph. Since the width of the negative electrode active material layer is larger than that of the positive electrode active material layer, there is an effect of suppressing lithium plating during battery charging.

[0079] 3) Diaphragm

[0080] The separator 300 separates the negative electrode 100 from the positive electrode 200 and may provide a movement path for lithium ions. The separator 300 may be disposed between the negative electrode 100 and the positive electrode 200 to separate the negative electrode 100 from the positive electrode 200. The electrode assembly 10 may include at least one separator 300, and may specifically include a plurality of separators 300.

[0081] As the separator 300, any separator can be used without particular limitation, as long as it is commonly used in lithium secondary batteries, and in particular, a separator having high moisturizing ability for the electrolyte and low resistance to the movement of electrolyte ions is preferred. Specifically, a porous polymer film can be used, for example: a porous polymer film prepared from a polyolefin polymer such as an ethylene homopolymer (polyethylene), a propylene homopolymer (polypropylene), an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer; or a laminated structure having two or more layers thereof. In addition, a typical porous non-woven fabric can be used, such as a non-woven fabric formed from a high melting point glass fiber or a polyethylene terephthalate fiber.

[0082] In addition, the diaphragm 300 uses the above-mentioned material as a substrate, and may further include a coating disposed on the substrate. The coating may include at least one of inorganic particles and a polymer. Heat resistance or mechanical strength may be improved by the coating. The coating may have a single-layer or multi-layer structure.

[0083] The separator 300 may include a separator main body 300a and a separator extension 300b. The separator main body 300a may overlap with the positive electrode active material layer 220 in the vertical direction RR'. The separator main body 300a may face the positive electrode active material layer 220. The separator extension 300b may extend from the separator main body 300a. The separator extension 300b may not overlap with the positive electrode active material layer 220 in the vertical direction RR'.

[0084] 4) Hole closure

[0085] The pore closing portion is used to suppress the phenomenon that a large amount of lithium ions directly move to the negative electrode extension portion. Therefore, the phenomenon that lithium is precipitated on the negative electrode extension portion when the negative electrode is disconnected can be reduced. Therefore, the problem of short circuit between the negative electrode and the positive electrode in the battery can be prevented, and the heating and ignition of the battery can be suppressed.

[0086] The porosity of the pore closing portion may be 1% or less, particularly 0% to 1%, more particularly 0% to 0.8%, for example 0% to 0.5%. Because the porosity of the pore closing portion is 1% or less, the amount of lithium ions directly transferred from the electrolyte to the negative electrode extension portion can be significantly reduced, thereby reducing the phenomenon of lithium precipitation on the negative electrode extension portion when the negative electrode is disconnected. On the contrary, when the porosity of the pore closing portion is greater than 1%, the phenomenon of lithium ions moving from the electrolyte to the negative electrode extension portion may not be effectively suppressed, and therefore, it is difficult to prevent the phenomenon of lithium precipitation in the negative electrode extension portion.

[0087] The air permeability of the pore-closing portion may be 1500 sec / 100 cc or more, particularly 1500 sec / 100 cc to 10000 sec / 100 cc, more particularly 1500 sec / 100 cc to 8000 sec / 100 cc, for example 1500 sec / 100 cc to 5500 sec / 100 cc. When the above range is satisfied, the amount of lithium ions directly transferred from the electrolyte to the negative electrode extension portion can be significantly reduced, so that the phenomenon of lithium precipitation on the negative electrode extension portion when the negative electrode is disconnected can be reduced.

[0088] Reference Figures 2 to 5 , the hole closing portion 400 may be provided on one surface or both surfaces of the diaphragm extension portion 300b. Specifically, the hole closing portion 400 may be provided on the entire area of ​​one surface or both surfaces of the diaphragm extension portion 300b. In this case, one end of the hole closing portion 400 may be provided on the same line as one end of the diaphragm 300. That is, the hole closing portion 400 may cover the upper surface and / or the lower surface of the diaphragm extension portion 300b up to the edge of the diaphragm 300.

[0089] Reference Figure 2, the pore closing portion 400 may be provided on one surface of the separator extension portion 300b, specifically, one surface of the separator extension portion 300b provided with the pore closing portion 400 may be provided in the same direction as the surface of the separator main body portion 300a (the separator main body portion 300a attached to the separator extension portion 300b) in contact with the positive electrode active material layer 220. In the case where the pore closing portion 400 is formed on the surface facing the positive electrode active material layer, lithium precipitation can be suppressed while minimizing the loss of negative electrode loading.

[0090] Figure 3 Corresponds to Figure 2 A top view of region C. Figure 3 , the pore closing portion 400 may be disposed around the positive electrode active material layer 220 .

[0091] Reference Figure 4 , the pore closing portion 400 is provided on one surface of the separator extension portion 300b, wherein it may be provided in the same direction as the surface of the separator main body portion 300a (the separator main body portion 300a attached to the separator extension portion 300b) in contact with the negative electrode active material layer 120. In this case, the transfer of lithium ions present in the pores of the separator to the negative electrode extension portion can be more effectively suppressed.

[0092] In addition, refer to Figure 5 , the pore closing portion 400 may be provided on both surfaces of the separator extension portion 300b. In this case, lithium deposition on the negative electrode extension portion may be more effectively suppressed.

[0093] Reference Figures 2 to 5 The pore closing portion 400 may overlap the negative electrode extension portion 120b in the vertical direction RR′. Therefore, since the amount of lithium ions directly transferred from the electrolyte to the negative electrode extension portion can be significantly reduced, the phenomenon of lithium precipitation on the negative electrode extension portion when the negative electrode is disconnected can be reduced.

[0094] In addition, the pore closing portion 400 may not overlap the negative electrode main body portion 120a in the vertical direction RR'. Thus, the movement of lithium ions (lithium ions from the positive electrode to the negative electrode) occurring during normal operation of the battery may be smoothly performed.

[0095] The pore-closing portion may include a polymer, for example, may be formed of a polymer. The polymer may include at least one selected from polyethylene (PE), polypropylene (PP), polyimide (PI) and polymethyl methacrylate (PMMA). Because the pore-closing portion includes a polymer, the pore-closing portion can be effectively attached to the diaphragm extension portion, thereby further improving the stability of the battery.

[0096] The polymer contained in the hole closing part may be the same as the polymer material contained in the diaphragm (diaphragm main body, diaphragm extension). For example, when the diaphragm contains at least one of polyethylene and polypropylene, the polymer contained in the hole closing part may also be at least one of polyethylene and polypropylene. In this case, because the adhesion between the hole closing part and the diaphragm extension part is increased, the safety can be further improved.

[0097] The content of the polymer in the pore-closing portion may be 15 to 100 wt %, particularly 15 to 50 wt %, and more particularly 15 to 30 wt %. When the above range is satisfied, the porosity of the pore-closing portion may be easily adjusted to 1% or less.

[0098] In some cases, the pore-closing portion may further include inorganic particles in addition to the polymer. The inorganic particles may include at least one selected from 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 may be improved.

[0099] The content of the inorganic particles in the pore-closing portion may be 85 wt % or less, particularly 50 wt % to 85 wt %, and more particularly 70 wt % to 85 wt %. When the above range is satisfied, the porosity can be easily adjusted to 1% or less while improving the heat resistance of the pore-closing portion.

[0100] The maximum thickness of the pore-closing portion may be in the range of 10 μm to 20 μm, particularly 12 μm to 20 μm, and more particularly 14 μm to 20 μm. When the above range is satisfied, excessive transfer of lithium ions from the electrolyte to the negative electrode extension portion can be suppressed, and because the thickness of the pore-closing portion is not too large, the thickness of the entire battery can be uniform.

[0101] Specifically, the pore-closing portion may be composed of a base layer formed of a polymer, or may include a base layer and a reinforcing coating layer disposed on the base layer and including inorganic particles. Therefore, the heat resistance of the pore-closing portion may be enhanced to further improve the safety of the battery.

[0102] 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 amount of the polymer and the inorganic particles. For example, in the case where the pore-closing portion is composed of a base layer and a reinforcing coating, the porosity of the base layer can be adjusted to less than 1% by adjusting the type of polymer or the degree of stretching of the base layer. In addition, even in the case where the porosity of the base layer is more than 1%, the porosity of the pore-closing portion can be adjusted to less than 1% by forming a coating with low porosity on the surface of the base layer.

[0103] The thickness of the base layer may be 9 μm to 15 μm, specifically 10 μm to 13 μm. The thickness of the reinforcement coating layer may be 1 μm to 5 μm, specifically 2 μm to 5 μm. When the above range is met, the heat resistance of the pore-closing portion can be effectively improved while achieving the effect of suppressing lithium precipitation.

[0104] 5) Others

[0105] The electrode assembly may further include a pore-closing coating 500 . Figure 6 shows a cross section of an electrode assembly, Figure 7 is observed from direction S Figure 6 A cross section of a region D of an electrode assembly. Figure 6 and Figure 7 In addition to the pore-closing portion 400 , a pore-closing coating 500 is also provided.

[0106] The pore-closing coating 500 may cover at least a portion of the side surface of the negative electrode extension 120b. Therefore, the lithium ions moving from the electrolyte to the negative electrode extension may be more effectively reduced. Therefore, the phenomenon of lithium precipitation on the negative electrode extension when the negative electrode is disconnected may be more effectively suppressed.

[0107] Since the structure and material constituting the pore-closing coating layer may be the same as the structure and material constituting the above-mentioned pore-closing portion, a description thereof will be omitted.

[0108] <Lithium Secondary Battery>

[0109] A lithium secondary battery according to another embodiment of the present invention may include the electrode assembly of the above embodiment and an electrolyte.

[0110] The electrolyte may be an organic liquid electrolyte or an inorganic liquid electrolyte that can be used to prepare a lithium secondary battery, but the present invention is not limited thereto.

[0111] Specifically, the electrolyte may include a nonaqueous organic solvent and a metal salt.

[0112] Examples of the nonaqueous organic solvent may be aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0113] In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in carbonate-based organic solvents, have high dielectric constants as high-viscosity organic solvents, thereby dissociating lithium salts well, so the cyclic carbonates can be preferably used, and when the cyclic carbonates are mixed with low-viscosity, low-dielectric-constant straight-chain carbonates such as dimethyl carbonate and diethyl carbonate in an appropriate ratio, an electrolyte with high conductivity can be prepared, so the cyclic carbonates can be more preferably used.

[0114] As the metal salt, a lithium salt can be used, and the lithium salt is a material that is easily soluble in a non-aqueous electrolyte, wherein as the anion of the lithium salt, for example, at least one selected from the following can be used: 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 (CF3CF2SO2)2N - .

[0115] In order to improve the life characteristics of the battery, prevent the battery capacity from decreasing, and improve the discharge capacity of the battery, the electrolyte may further contain at least one additive such as the following on the basis of containing the above electrolyte components: halogenated alkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted Oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride.

[0116] According to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the battery module are provided. Because the battery module and the battery pack include the secondary battery having high capacity, high rate capability and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium and large devices selected from the following: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles and power storage systems.

[0117] In the following, preferred examples are given to help better understand the present invention, but the following examples are only presented in a manner of illustrating the present invention. It is obvious to those skilled in the art that various modifications and changes are possible within the scope and technical spirit of the present invention, and such modifications and changes fall within the scope of the claims contained herein.

[0118] Examples and Comparative Examples

[0119] Example 1

[0120] (1) Preparation of electrode assembly

[0121] A pore-closing portion having a porosity of 0.5% and an air permeability of 5500 sec / 100 cc was formed on a portion of both surfaces of a porous polyethylene separator. Specifically, the pore-closing portion was prepared by coating a 3 μm thick reinforcing coating layer containing Al2O3 on both surfaces of a base layer (12 μm thick) formed of polyethylene, and a separator having a pore-closing portion formed thereon was prepared by a method in which the pore-closing portion constructed as described above was arranged on a surface of the separator that did not overlap with the positive electrode active material layer after assembling the electrode assembly (i.e., the separator extension portion).

[0122] Next, a negative electrode including a copper current collector and a negative electrode active material layer disposed on both surfaces of the copper current collector was prepared. The negative electrode active material layer included a mixture of artificial graphite and natural graphite as a negative electrode active material, a mixture of styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as a negative electrode binder, and carbon black as a negative electrode conductive material.

[0123] In addition, a positive electrode including an aluminum current collector and a positive electrode active material layer provided on both surfaces of the aluminum current collector was also prepared. The positive electrode active material layer included Li[Ni 0.6 Co 0.2 Mn 0.2 ]O2, polyvinylidene fluoride (PVdF) as a positive electrode binder, and carbon black as a positive electrode conductive material.

[0124] An electrode assembly having a structure of negative electrode / separator / positive electrode / separator / negative electrode / separator / positive electrode / separator / negative electrode is prepared by stacking the three negative electrodes and two positive electrodes prepared above, while disposing a separator having a pore closing portion formed thereon between the negative electrode and the positive electrode. Then, the negative electrodes are electrically connected to each other using the negative electrode tabs, and the positive electrodes are electrically connected to each other using the positive electrode tabs.

[0125] (2) Preparation of lithium secondary batteries

[0126] After the electrode assembly is placed in the battery case, an electrolyte is injected into the battery case to impregnate the electrode assembly with the electrolyte. Thereafter, the battery case is sealed. The electrolyte comprises a non-aqueous solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2 and lithium hexafluorophosphate (1 M LiPF6).

[0127] Example 2

[0128] A lithium secondary battery was prepared in the same manner as in Example 1, except that pore-closing portions having a porosity of 0.1% and an air permeability of 10000 sec / 100 cc or more were formed on a portion of both surfaces of the porous polyethylene separator.

[0129] Comparative Example 1

[0130] A lithium secondary battery was prepared in the same manner as in Example 1 except that a separator on which the pore-closing portion was not formed was used.

[0131] Comparative Example 2

[0132] A lithium secondary battery was prepared in the same manner as in Example 1, except that pore-closing portions having a porosity of 3% and an air permeability of 1500 sec / 100 cc were formed on a portion of both surfaces of the porous polyethylene separator.

[0133] Comparative Example 3

[0134] A lithium secondary battery was prepared in the same manner as in Example 1, except that pore-closing portions having a porosity of 10% and an air permeability of 1500 sec / 100 cc were formed on a portion of both surfaces of the porous polyethylene separator.

[0135] Experimental Example 1: Confirmation of Lithium Precipitation

[0136] The negative electrode extensions of the examples and comparative examples were subjected to 7Li-NMR evaluation. Specifically, 4.2 V constant current / constant voltage (CC / CV) charging was performed at 1 / 3 C, 25° C. to fully charge the battery, with a current cutoff of 5%. Thereafter, the negative electrode at the bottom of the electrode assembly was separated from the tab, thereby disconnecting the corresponding negative electrode.

[0137] Thereafter, the battery was left to stand for 60 minutes and then CC-discharged to 2.5 V at 1 / 3 C. After the discharge, in order to confirm the occurrence of lithium deposition, 4.2 V CC / CV charging (current cutoff 5%) was performed at 1 / 3 C, 25° C. to fully charge the battery.

[0138] Thereafter, the disconnected negative electrode was separated to perform 7Li-NMR evaluation on the negative electrode extension portion.

[0139] 7Li-NMR measurement conditions are as follows.

[0140] 300 MHz solid-state NMR system;

[0141] MAS speed: 32 kHz;

[0142] Spectrum frequency: 116.6420 MHz;

[0143] Temperature: room temperature (25°C);

[0144] Chemical shift value standard: 1 M LiCl in H2O;

[0145] Pulse sequence: spin echo (90°-τ1-180°-τ2);

[0146] Spectrum width: 500000 Hz;

[0147] Pulse length: 1) 90° pulse length 2.25 μs, 2) 180° pulse length 4.50 μs;

[0148] Dwell time (τ1): 31.25 μs;

[0149] Pulse delay: 2 seconds

[0150] Figure 8 This is the 7Li-NMR result after the negative electrode of the lithium secondary battery of Example 1 is disconnected. Fig. 9 This is the 7Li-NMR result of the lithium secondary battery of Example 2 after the negative electrode is disconnected. Fig.10 This is the 7Li-NMR result of the lithium secondary battery of Comparative Example 1 after the negative electrode is disconnected. Fig.11 This is the 7Li-NMR result of the lithium secondary battery of Comparative Example 2 after the negative electrode is disconnected. Fig.12 This is the 7Li-NMR result of the lithium secondary battery of Comparative Example 3 after the negative electrode was disconnected.

[0151] In 7Li-NMR, a peak corresponding to lithium precipitation was found in the range of 240 ppm to 270 ppm. Figure 8 and Fig. 9 , since lithium precipitation did not occur in the lithium secondary batteries of Examples 1 and 2, it is understood that no peak corresponding to lithium precipitation was found. Figures 10 to 12 , regarding the lithium secondary batteries of Comparative Examples 1 to 3, it can be understood that a peak corresponding to lithium precipitation appears.

[0152] also, Fig.13 and Fig.14 are photographs showing the states of the fully charged lithium secondary batteries of Comparative Examples 2 and 3 after the negative electrodes are disconnected. Fig.12 and Fig.13 It can be confirmed that lithium precipitation occurs in the lithium secondary batteries of Comparative Examples 2 and 3 in which the porosity of the pore-closed portion is greater than 1%.

[0153] <Description of Reference Numerals>

[0154] 10: Electrode assembly

[0155] 100: Negative electrode

[0156] 110: Negative electrode current collector

[0157] 120: Negative electrode active material layer

[0158] 200: Positive

[0159] 210: Positive electrode collector

[0160] 220: Positive electrode active material layer

[0161] 300: Diaphragm

[0162] 300a: Diaphragm body

[0163] 300b: Diaphragm extension

[0164] 400: Hole closure

[0165] 120a: Negative electrode main body

[0166] 120b: Negative electrode extension

[0167] 500: Pore Closure Coating

Claims

1. An electrode assembly, comprising: A negative electrode, the negative electrode comprising a negative electrode active material layer; a positive electrode, the positive electrode comprising a positive electrode active material layer; Diaphragm; and The hole closure part, The separator is disposed between the negative electrode and the positive electrode. The width of the negative electrode active material layer is greater than the width of the positive electrode active material layer, The separator includes a separator main body portion overlapping with the positive electrode active material layer in a vertical direction and a separator extension portion extending from the separator main body portion without overlapping with the positive electrode active material layer in the vertical direction, and The hole closing portion is provided on one surface or both surfaces of the diaphragm extension portion, and The pore-closing portion has a porosity of 1% or less. 2 . The electrode assembly according to claim 1 , wherein the pore closing portion is provided over the entire area of ​​one surface or both surfaces of the separator extending portion. 3 . The electrode assembly according to claim 1 , wherein one end of the pore closing portion is disposed on the same line as one end of the separator.

4. The electrode assembly according to claim 1, wherein the negative electrode active material layer includes a negative electrode main body portion overlapping with the positive electrode active material layer in a vertical direction and a negative electrode extension portion extending from the negative electrode main body portion without overlapping with the positive electrode active material layer in a vertical direction, and The pore closing portion overlaps the negative electrode extending portion in a vertical direction.

5. The electrode assembly according to claim 1, wherein the pore-closing portion comprises a polymer, The polymer comprises at least one selected from the group consisting of polyethylene, polypropylene, polyimide and polymethyl methacrylate. The electrode assembly according to claim 5 , wherein the pore-closing portion further comprises inorganic particles. 7 . The electrode assembly according to claim 1 , wherein the pore-closing portion has an air permeability of 1500 sec / 100 cc or more. 8 . The electrode assembly according to claim 1 , wherein a maximum thickness of the pore-closing portion is in the range of 10 μm to 20 μm.

9. The electrode assembly according to claim 4, further comprising a pore-closing coating, wherein the pore-closing coating covers at least a portion of a side surface of the negative electrode extension, and The pore-closing coating has a porosity of 1% or less.

10. A lithium secondary battery comprising: The electrode assembly according to claim 1, and Electrolytes.

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