Secondary batteries containing insulation

Abstract

According to one embodiment of the present invention, a secondary battery is provided comprising an electrode assembly including a positive electrode, a negative electrode, and a separator membrane, and an electrolyte, wherein the electrode assembly includes two or more unit cells and one or more insulating materials, and one or more of the one or more insulating materials are located between the two or more unit cells.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit of priority based on Korean Patent Application No. 10 - 2024 - 0003157 filed on January 8, 2024, and all the contents disclosed in the literature of the Korean patent application are included as part of this specification.

[0002] The present invention relates to a secondary battery including a heat insulating material.

Background Art

[0003] With the technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source has been rapidly increasing. In particular, secondary batteries have attracted much attention not only as an energy source for mobile devices such as mobile phones, digital cameras, notebook computers, and wearable devices, but also for power devices such as electric bicycles, electric vehicles, and hybrid electric vehicles.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, an electrolyte, an organic solvent, etc. The positive electrode generates oxygen due to an unstable structure in the charged state, and when oxygen is generated, there is a high risk of ignition. Therefore, research and development on methods to improve the safety of lithium secondary batteries have been attempted.

[0005] Among such safety evaluations of lithium secondary batteries, one of the important safety items is the thermal propagation test. Such a thermal propagation test is to confirm whether a lithium secondary battery can withstand without ignition for 5 minutes or more in module or pack units. However, in recent years, in lithium secondary batteries using Ni - rich Ni - based positive electrode active materials with increasing requirements for high capacity and high energy density, it has become difficult to pass the test, and the safety of lithium secondary batteries has become a problem.

[0006] On the other hand, in order to enhance safety, conventional methods have been developed to apply insulating material 12 between the secondary batteries 11 when manufacturing lithium secondary batteries in modules or packs, as shown in Figure 1, or similarly, to apply insulating material between modules.

[0007] However, as the capacity and energy density of individual lithium-ion batteries increase, the explosive force in a single lithium-ion battery increases, making it difficult for modules and packs to pass the aforementioned heat transfer tests. In other words, the safety of lithium-ion batteries remains a concern.

[0008] Therefore, the current situation necessitates the development of technologies that can solve these problems from the perspective of lithium-ion batteries. [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a secondary battery that can improve safety issues associated with heat propagation by suppressing heat transfer even inside the secondary battery unit when thermal runaway or ignition problems occur, thereby reducing the capacity of the secondary battery that becomes the starting point for thermal runaway or ignition. [Means for solving the problem]

[0010] A secondary battery according to one embodiment of the present invention is a secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator membrane, and an electrolyte, The electrode assembly includes two or more unit cells and one or more insulating materials. One or more of the aforementioned thermal insulation materials are characterized in that they are located between the two or more unit cells.

[0011] Here, each of the two or more unit cells may include one or more electrodes, either a positive or negative electrode, and a separator membrane. More specifically, each of the two or more unit cells may be a monocell containing either a positive or negative electrode and a separator membrane, a bicell stacked with electrodes of the same polarity at both ends, or a full cell stacked with electrodes of different polarities at both ends.

[0012] On the other hand, one or more of the one or more thermal insulation materials can be located in the middle section with respect to the stacking direction of the electrode assembly.

[0013] In one specific example, the one or more insulating materials may consist of one or more and five or fewer pieces, and more specifically, one or two pieces.

[0014] In this case, it is preferable that the one or more insulating materials are arranged at equal intervals. Therefore, if there is an odd number of insulating materials, they can be positioned so as to be arranged at equal intervals between unit cells facing each other, including the intermediate portion, with respect to the stacking direction of the electrode assembly. If there is an even number of insulating materials, they can be positioned so as to be arranged at equal intervals between unit cells facing each other.

[0015] Furthermore, the surface area of ​​each of the one or more insulating materials may be 100% to 110% of the surface area of ​​the negative electrode, and in detail, they may be positioned to completely cover the opposing electrodes, and even to cover a portion of the tabs protruding from the opposing electrodes.

[0016] Furthermore, the thickness of each of the one or more insulating materials may be 0.1 mm to 5 mm, and more specifically, 0.1 mm to 2 mm.

[0017] Each of these one or more insulating materials may include porous Si foam, silica aerogel, or a non-combustible resin containing glass fibers, and more specifically, silica aerogel may be included. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic cross-sectional view of a conventional battery module. [Figure 2] This is a schematic cross-sectional view of a secondary battery according to one embodiment of the present invention. [Figure 3] This is a schematic cross-sectional view of a secondary battery according to another embodiment of the present invention. [Figure 4] This is a partially exploded schematic diagram of an electrode assembly showing the position of the thermal insulation material according to one embodiment of the present invention. [Figure 5] This is a partial top view drawing of an electrode assembly according to one embodiment of the present invention. [Modes for carrying out the invention]

[0019] The following describes various embodiments of the present invention in detail, with reference to the attached drawings, so that those with ordinary skill in the art to which the present invention pertains can easily implement them. The present invention can be realized in a variety of different forms and is not limited to the embodiments described herein.

[0020] To clearly explain the present invention, descriptive parts have been omitted, and the same or similar reference numerals are used throughout the specification for identical or similar components.

[0021] Furthermore, the dimensions and thicknesses of each component shown in the drawings are arbitrary for illustrative purposes, and the present invention is not necessarily limited to what is shown. In the drawings, the thicknesses are shown enlarged to clearly represent various layers and regions. In addition, in the drawings, the thicknesses of some layers and regions are shown exaggerated for illustrative purposes.

[0022] Furthermore, when a specification states that a part of it "includes" a certain component, unless otherwise specified, this means that it may include other components rather than excluding them.

[0023] Furthermore, throughout the specification, "planar view" refers to a view of the subject from above, and "cross-section" refers to a view of a cross-section obtained by cutting the subject perpendicularly, as seen from the side.

[0024] Terms such as “approximately” and “substantially” used throughout this specification are used to mean the numerical value or an approximation thereof when manufacturing and material tolerances inherent to the meaning referred to are presented, and are used to aid in the understanding of this application and to prevent dishonest infringers from unfairly exploiting disclosures that refer to exact or absolute numerical values.

[0025] The terms "length," "thickness," and "width" used in this specification shall be based on those defined in the specification.

[0026] According to one embodiment of the present invention, A secondary battery comprising a positive electrode, a negative electrode, an electrode assembly including a separator membrane, and an electrolyte, The electrode assembly includes two or more unit cells and one or more insulating materials. One or more of the aforementioned thermal insulation materials are provided in a secondary battery located between the aforementioned two or more unit cells.

[0027] Figure 2 schematically shows a cross-sectional view of a secondary battery 100 according to one embodiment, and Figure 3 schematically shows a cross-sectional view of a secondary battery 200 according to another embodiment.

[0028] Referring to Figure 2, the secondary battery 100 includes an electrode assembly containing two unit cells 110 and 120 and one insulating material 130, and an electrolyte (not shown), where the insulating material 130 is located between the unit cells 110 and 120.

[0029] Figure 2 shows an electrode assembly containing two unit cells 110 and 120 and one insulating material 130, but is not limited to this, and can have a structure containing two or more unit cells and one or more insulating materials. As another example, referring to Figure 3, the secondary battery 200 may have a structure containing an electrode assembly containing three unit cells 210, 220 and 230 and two insulating materials 231 and 232, and an electrolyte (not shown), or more.

[0030] However, for the sake of explanation, Figure 2 shows a configuration with one insulation material, and Figure 2 shows a configuration with two insulation materials, and we will explain by referring to these.

[0031] On the other hand, such a unit cell may have a structure that includes one or more electrodes selected from the group consisting of a positive electrode and a negative electrode, and a separation membrane.

[0032] Specifically, each of the unit cells may be a monocell containing either a positive or negative electrode and a separator membrane, a bicell stacked with electrodes of the same polarity at both ends, or a full cell stacked with electrodes of different polarities at both ends.

[0033] In this case, there is no limit to the number of electrodes and separation membranes stacked in a single unit cell.

[0034] Referring again to Figure 2, the unit cells 110 and 120 may each contain positive electrodes 111 and 121, negative electrodes 112 and 122, and separation membranes 113 and 123, respectively, and may be bicells stacked such that negative electrodes 112 and 122 are located at both ends.

[0035] Needless to say, the drawing shows that there is one unit cell 110 and 120 on each side of the insulation material 130, but this is for the sake of explanation, and the structure may have two or more unit cells stacked on one side with the insulation material 130 as the base. In other words, the structure may have many unit cells of one or more types selected from the group consisting of monocells, bicells, and full cells stacked on one side with the insulation material 130 as the base.

[0036] On the other hand, the insulation material, which is another component, may be included in quantities of one or more units, and more specifically, in quantities of one to five units.

[0037] If the number of batteries exceeds the aforementioned range and is greater than five, the heat insulation effect may increase, but the energy density decreases relative to the total volume of the secondary battery, which is undesirable because it increases both cost and overall volume.

[0038] Considering the aforementioned issues, more specifically, the secondary battery contains one or two insulating materials.

[0039] Therefore, while the present invention will focus on explaining Figures 2 and 3, which include one or two insulating materials, it is not limited to these, and these are representative of cases where an odd or even number of insulating materials are included.

[0040] Referring to Figure 2, the secondary battery 100 includes one insulating material 130, i.e., an odd number of insulating materials 130.

[0041] In this case, the thermal insulation material 130 is located in the middle section with respect to the stacking direction of the electrode assembly. Here, the middle section means a point where there is a difference of one or two electrodes in the number of electrodes between the state in which the same number of electrodes and separator membranes are located on both sides of the thermal insulation material 130 with respect to the stacking direction of the electrode assembly.

[0042] Thus, when the insulation material 130 is located in the middle section, the capacity of the secondary battery that participates in the reaction during thermal runaway or ignition can be reduced by half, making it more effective in suppressing heat propagation.

[0043] On the other hand, if there are three or more, odd-numbered, insulating materials can be positioned so as to be arranged at equal intervals between opposing unit cells, including the intermediate portion.

[0044] Such an evenly spaced arrangement will be explained with reference to Figure 3, which shows a diagram including two insulation materials.

[0045] Referring to Figure 3, the secondary battery 200 includes two insulating materials 231 and 232, i.e., an even number of insulating materials, and each of these two insulating materials 231 and 232 is located between the unit cells 210, 220, and 230.

[0046] In this case, the thermal insulation materials 231 and 232 are positioned so as to be arranged at equal intervals between the unit cells 210, 220, and 230 that face each other. That is, each of the thermal insulation materials 231 and 232 can be formed so that their intervals (b) are the same. Furthermore, the electrode assembly may be evenly divided into three sections (a=b=c) based on the stacking direction, with the thermal insulation materials 231 and 232 placed between them.

[0047] In other words, since it is preferable to minimize the capacity of the insulating material in the event of thermal runaway or ignition within the secondary battery to prevent heat transfer, it is preferable to position the insulating material in the evenly divided portions to reduce its capacity to 1 / n.

[0048] Therefore, if an odd number of insulation materials are included, it is preferable that at least one insulation material be located in the middle section.

[0049] Furthermore, it is preferable that the insulating material be able to perform its function regardless of where thermal runaway or ignition occurs in the components. Generally, thermal runaway and ignition in secondary batteries occur due to short circuits between the positive and negative electrodes, oxygen generation due to side reactions between the positive electrode and the electrolyte, and lithium dendrite formation at the negative electrode. Therefore, it is preferable to form the insulating material with a surface area that can prevent these occurrences.

[0050] In this case, since the negative electrode is generally manufactured to be larger than the positive electrode, it is preferable that the insulating material has a surface area of ​​100% to 120%, more specifically 100% to 110%, of the surface area of ​​the negative electrode.

[0051] To explain this in more detail, Figure 4 shows a partially exploded perspective view of the secondary battery 100, and Figure 5 shows a partial perspective top view of the secondary battery 100.

[0052] Referring to Figures 4 and 5, the surface area (Si) of the insulating material 130 may be the same as or larger than the surface area (Sa) of the negative electrode 112 facing it across the separation membrane 113, and it can be positioned to cover it completely. That is, if it has the same surface area (Si=Sa) as the negative electrode 112, it can be positioned to cover the entire remaining part of the negative electrode 112 excluding the tab 112a, and if it is larger, it can be positioned to cover the entire negative electrode 112 and a part of the tab 112a of the negative electrode 112.

[0053] If the size exceeds the aforementioned range and is smaller than the negative electrode, problems such as short circuits occurring at the negative electrode end cannot be effectively prevented, and heat propagation occurs through the end. If the size is too wide, the overall volume increases, leading to problems such as increased manufacturing costs. Therefore, it is preferable to satisfy the aforementioned range.

[0054] Furthermore, referring again to Figure 2, the thickness (t) of the insulation material 130 may be 0.1 mm to 5 mm, more specifically 0.1 mm to 2 mm, and even more specifically 0.1 mm to 1 mm.

[0055] If the thickness exceeds the aforementioned range, it may increase the overall volume of the secondary battery, and if it is too thin, the heat insulation effect intended by this invention cannot be effectively obtained, which is undesirable.

[0056] Such thermal insulation materials may each include porous Si foam, silica aerogel, or a non-combustible resin containing glass fibers, and more specifically, silica aerogel, and more specifically, they may be composed of these.

[0057] In this case, the porous Si foam may have a porosity of 50% to 95% by volume, and more specifically, 60% to 90% by volume. Furthermore, the average diameter of these pores can be approximately 100 nm to 100 μm, and more specifically, 500 nm to 10 μm.

[0058] The porosity of the porous Si foam can be measured in accordance with ASTM D4641 using AUTOSORBiQ series (manufacturer: Quantachrome). The average diameter of the pores was measured by magnifying the sample surface 2,500 times using a scanning electron microscope (FE-SEM) (Hitachi S-4800 Scanning Electron Microscope). After that, among the surface pores confirmed in an arbitrarily sampled range (horizontal 10 μm or more, vertical 15 μm or more) within the measured photograph, the length of the major axis was measured as the size of the pores. The number of measurements was at least 10 or more, and the average value of the pore sizes obtained after the measurement was determined.

[0059] Such a porous Si foam can be manufactured by foaming silicon (Si), and is not limited as long as it is a conventionally known method.

[0060] The silica aerogel is a highly porous solid material and has an irregular network structure. Here, the porosity of the silica aerogel may be 90% to 99.9% by volume, specifically 95% to 99.9% by volume, and more specifically 97% to 99% by volume.

[0061] Also, the average diameter of these pores may be 1 nm to 100 nm, specifically 5 nm to 50 nm, and more specifically 5 nm to 10 nm.

[0062] At this time, the porosity and the average pore diameter of the silica aerogel can be analyzed by the amount of nitrogen adsorption / desorption at a partial pressure (0.11 < p / po < 1) using a Micrometrics ASAP 2010 instrument.

[0063] The method for producing the silica aerogel can be produced by a method of drying under supercritical conditions by the sol-gel method, and is not limited as long as it is a production method known in the art.

[0064] The aforementioned non-combustible resin containing glass fibers is in the form of a glass fiber reinforcement coated with non-combustible resin, in which case the non-combustible resin and glass fibers are included in a ratio of 30:70 to 80:20 by weight, and more specifically, 40:60 to 70:30.

[0065] Here, the non-combustible resin may be one or more selected from the group consisting of polyester, polyamide, polyethersulfone, polyetherimide, polyimide, polyamideimide, polyamidesiloxane, polyurethane, polystyrene, polycarbonate, and polymethyl methacrylate.

[0066] The thermal conductivity of such insulation materials may be, for example, 0.02 W / m·K to 0.5 W / m·K, more specifically 0.03 W / m·K to 0.1 W / m·K, and even more specifically 0.04 W / m·K to 0.07 W / m·K.

[0067] If the range is larger than the aforementioned range, sufficient thermal insulation cannot be obtained.

[0068] In this case, the thermal conductivity was evaluated according to the ISO 2207-2 standard of the TPS Corporation Hot Disk method. The measurement model may also be the TPS 3500.

[0069] On the other hand, other components of a secondary battery include: The positive electrode may have a structure that includes a positive electrode current collector and a positive electrode active material layer formed on one or both sides of the positive electrode current collector.

[0070] Here, the positive electrode current collector is not particularly limited as long as it is conductive without inducing a chemical change in the battery. For example, the current collector can be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc.

[0071] The positive electrode current collector can have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to increase the adhesive force to the positive electrode active material layer. For example, it is used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabrics, etc.

[0072] The positive electrode active material layer contains a positive electrode active material and can contain a conductive material, a binder, and other additives as required.

[0073] The positive electrode active material is not limited as long as it is a compound capable of reversible intercalation and deintercalation of lithium. Specifically, it can include a lithium metal oxide containing one or more metals such as cobalt, manganese, nickel, or aluminum and lithium. More specifically, the positive electrode active material can include a nickel-based lithium transition metal oxide represented by the following Chemical Formula 1.

[0074] [Chemical Formula 1] Li 1+x Ni a Co b Mn c M 1-(a+b+c) O2 In the above formula, M is one or more selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, 0 ≦ x ≦ 0.5, 0.6 ≦ a < 1, 0 < b < 0.4, 0 < c < 0.4.

[0075] Furthermore, the positive electrode active material includes lithium-manganese-based oxides (such as LiMnO2, LiMn2O4, etc.), lithium-cobalt-based oxides (such as LiCoO2, etc.), lithium-nickel-based oxides (such as LiNiO2, etc.), lithium-nickel-manganese-based oxides (such as Li 1+x’ Ni 1-Y Mn Y O2 (where -0.5 ≦ x' ≦ 0.5, 0 < Y < 1), Li 1+x’’ Mn 2-Z Ni ZO4 (where -0.5 ≤ x'' ≤ 0.5, 0 < Z < 2, etc.), lithium-nickel-cobalt-based oxide (e.g., Li 1+x’’’ Ni 1-Y1 Co Y1 O2 (where -0.5 ≤ x''' ≤ 0.5, 0 < Y1 < 1, etc.), lithium-manganese-cobalt-based oxide (e.g., Li 1+x’’’’ Co 1-Y2 Mn Y2 O2 (where -0.5 ≤ x'''' ≤ 0.5, 0 < Y2 < 1), Li 1+x’’’’’ Mn 2-Z1 Co Z1 O4 (where -0.5 ≤ x''''' ≤ 0.5, 0 < Z1 < 2, etc.), lithium-nickel-manganese-cobalt-based oxide (e.g., Li 1+a1 (Ni p Co q Mn r )O2 (where -0.5 ≤ a1 ≤ 0.5, 0 < p < 1, 0 < q < 1, 0 < r < 1, p + q + r = 1) or Li 1+a2 (Ni p1 Co q1 Mn r1 O4 (where -0.5 ≤ a2 ≤ 0.5, 0 < p1 < 2, 0 < q1 < 2, 0 < r1 < 2, p1 + q1 + r1 = 2, etc.), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li 1+a3 (Ni p2 Co q2 Mn r2 Ms2O2 (where M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg, and Mo, and a3, p2, q2, r2, and s2 are the atomic fractions of the respective independent elements, -0.5 ≤ a3 ≤ 0.5, 0 < p2 < 1, 0 < q2 < 1, 0 < r2 < 1, 0 < s2 < 1, p2 + q2 + r2 + s2 = 1, etc.), lithium iron phosphate (e.g., Li 1+a4 Fe 1-p3 M p3 (PO 4-b4 X b4(Here, M is one or more selected from Al, Mg, and Ti, and X is one or more selected from F, S, and N, with -0.5 ≤ a4 ≤ 0.5, 0 ≤ p3 ≤ 0.5, 0 ≤ b4 ≤ 0.1), and so on, and one or more of these compounds may be included.

[0076] The positive electrode active material may be present in an amount of 60% to 98% by weight, preferably 80% to 98% by weight, and more preferably 90% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0077] The conductive material is a component for further improving the conductivity of the positive electrode active material, and such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery. Examples of such materials include carbon powder such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black; graphite powder such as natural graphite, artificial graphite, or graphite with a highly developed crystalline structure; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon powder; conductive powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0078] The conductive material may be included in an amount of 0.1% to 20% by weight, more specifically 0.5% to 10% by weight, or more specifically 0.5% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0079] The binder is a component that helps to bond the conductive material, the positive electrode active material, and the positive electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0080] Typically, the binder may be included in an amount of 0.5% to 20% by weight, more specifically 0.5% to 10% by weight, or more specifically 0.5% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0081] Furthermore, the aforementioned other additives may further include, for example, fillers as components that suppress expansion. The filler is not particularly limited as long as it can suppress the expansion of the electrodes without inducing a chemical change in the battery, and for example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fibers and carbon fibers; etc. can be used.

[0082] The negative electrode may have a structure that includes a negative electrode current collector and a negative electrode active material layer formed on one or both sides of the negative electrode current collector, and the negative electrode active material layer may further include electrode materials such as conductive materials and binders as described for the positive electrode, in addition to the negative electrode active material.

[0083] The negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface treatments with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used.

[0084] The negative electrode current collector can typically have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities may be formed on the surface of the negative electrode current collector to strengthen the bonding force of the negative electrode active material. For example, it can be used in a variety of forms such as films, sheets, foils, nets, porous materials, foams, and nonwoven fabrics.

[0085] The negative electrode active material may include at least one selected from the group consisting of lithium metal, carbon materials capable of reversibly intercalating / deintercalating lithium ions, metals, alloys of these metals with lithium, metal composite oxides, materials capable of doping and dedoping lithium, and transition metal oxides.

[0086] As a carbon material capable of reversibly intercalating / deintercalating lithium ions, any carbon-based negative electrode active material commonly used in lithium-ion secondary batteries can be used without particular limitations. Typical examples include crystalline carbon, amorphous carbon, or a combination of both. Examples of crystalline carbon include graphite such as amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, while examples of amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, and calcined coke.

[0087] The aforementioned metals, or alloys of these metals with lithium, are metals selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn, or alloys of these metals with lithium.

[0088] Examples of the aforementioned metal composite oxides include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, and Li x Fe2O3 (0 ≤ x ≤ 1), Lix WO₂ (0 ≤ x ≤ 1) and Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1, 2, 3 elements of the periodic table, halogen; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8) are selected from the group consisting of used.

[0089] As substances capable of doping and undoping lithium, Si, SiO x (0 < x ≤ 2), Si-Y alloy (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO₂, Sn-Y (where Y is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), etc. can be mentioned, and also, at least one of these can be mixed with SiO₂ and used. As the element Y, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof are selected from the group consisting of.

[0090] ​​​​​​​​When the negative electrode uses metal itself without including a negative electrode mixture layer, it can be manufactured by physically bonding, rolling, or vapor-depositing the metal onto the metal thin film itself or onto the negative electrode current collector. The vapor deposition method can be either electro-deposition or chemical vapor deposition.

[0093] For example, the metal bonded / rolled / deposited onto the metal thin film itself or the negative electrode current collector may include one metal or an alloy of two metals selected from the group consisting of lithium (Li), nickel (Ni), tin (Sn), copper (Cu), and indium (In).

[0094] The separation membrane can be any type commonly used as a separation membrane in lithium secondary batteries, and is particularly preferred if it has low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity.

[0095] For example, as the separation membrane, a porous polymer film containing polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. Alternatively, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used as the separation membrane.

[0096] Alternatively, it may be an SRS (Safety Reinforced Separator) separation membrane in which a coating layer containing a binder and inorganic particles is formed on one or both sides of a polymer substrate as described above.

[0097] The electrolyte may be a lithium non-aqueous electrolyte, and the lithium non-aqueous electrolyte may contain a lithium salt and a non-aqueous organic solvent.

[0098] In this case, the lithium salt is used as a medium for transferring ions within a lithium secondary battery. The lithium salt is, for example, Li as a cation. + It includes, and as an anion, F - Cl - , Br - , I - NO3 - , N(CN)2 - BF4 - ClO4 - B 10 Cl 10 - AlCl4 - AlO2 - PF6 - CF3SO3 - CH3CO2 - CF3CO2 - AsF6 - SbF6 - CH3SO3 - , (CF3CF2SO2)2N - (CF3SO2)2N - , (FSO2)2N - BF2C2O4 - BC4O8 - PF4C2O4 - PF2C4O8 - (CF3)2PF4 - (CF3)3PF3 - (CF3)4PF2 - (CF3)5PF - (CF3)6P - , C4F9SO3 - CF3CF2SO3 - CF3CF2(CF3)2CO - (CF3SO2) 2CH - CF3(CF2)7SO3 - and SCN - At least one of the following groups can be selected.

[0099] Specifically, the lithium salts are LiCl, LiBr, LiI, LiBF4, LiClO4, and LiB 10 Cl 10It may contain a single substance or a mixture of two or more substances selected from the group consisting of LiAlCl4, LiAlO2, LiPF6, LiCF3SO3, LiCH3CO2, LiCF3CO2, LiAsF6, LiSbF6, LiCH3SO3, LiFSI (Lithium bis(fluorosulfonyl)imide, LiN(SO2F)2), LiBETI (lithium bis(perfluoroethanesulfonyl)imide, LiN(SO2CF2CF3)2, and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, LiN(SO2CF3)2), but it is preferable to include Li(N(SO2CF3)2) due to its superior stability.

[0100] In addition to these, lithium salts commonly used as electrolytes in lithium secondary batteries may be used without restriction.

[0101] The lithium salt can be appropriately modified within a range of normal use, but in order to obtain the optimal effect of forming a protective film to prevent corrosion on the electrode surface, it may be included in the electrolyte at a concentration of 0.5 M to 3 M, more specifically, 1 M to 2.5 M, and more specifically, 1 M to 2 M. When the concentration of the lithium salt satisfies the above range, the effect of improving the cycle characteristics of the lithium secondary battery during high-temperature storage is sufficient, the viscosity of the electrolyte is appropriate, and the electrolyte impregnation is improved.

[0102] The aforementioned non-aqueous organic solvent is not limited as long as it can minimize decomposition due to oxidation reactions during the charging and discharging process of the lithium secondary battery and can exhibit the desired properties together with the additive. For example, carbonate-based organic solvents, ether-based organic solvents, or ester-based organic solvents can be used individually or in combination of two or more types, and in particular, carbonate-based organic solvents can be used.

[0103] Of the aforementioned organic solvents, the carbonate-based organic solvent may include at least one of cyclic carbonate-based organic solvents and linear carbonate-based organic solvents. Specifically, the cyclic carbonate-based organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate, and fluoroethylene carbonate (FEC). Specifically, it may include a mixed solvent of ethylene carbonate having a high dielectric constant and propylene carbonate having a relatively lower melting point compared to ethylene carbonate.

[0104] Furthermore, the linear carbonate-based organic solvent may contain at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, as a solvent having low viscosity and low dielectric constant, and more specifically, it may contain dimethyl carbonate.

[0105] The ether-based organic solvent may be one selected from the group consisting of ethylene glycol dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, and ethyl propyl ether, or a mixture of two or more of these, but is not limited to these.

[0106] The ester-based organic solvent mentioned above is at least one selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents.

[0107] The linear ester-based organic solvents mentioned above are typically selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate-propyl propionate, and butyl propionate, or mixtures of two or more of these, but are not limited to these.

[0108] The cyclic ester organic solvent may, but is not limited to, one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone, or a mixture of two or more of these.

[0109] Among the ester solvents mentioned above, cyclic carbonate compounds can be preferably used because they have a high dielectric constant as high-viscosity organic solvents and effectively dissociate lithium salts in the electrolyte. Furthermore, when such cyclic carbonate compounds are mixed with low-viscosity, low-dielectric-constant linear carbonate compounds and linear ester compounds such as dimethyl carbonate and diethyl carbonate in appropriate proportions, an electrolyte with high electrical conductivity can be produced, and this mixture can be used even more preferably.

[0110] Furthermore, the lithium non-aqueous electrolyte may further contain functional additives, which may be included to prevent negative electrode collapse from being induced in high-power environments, and to further improve low-temperature high-rate discharge characteristics, high-temperature stability, overcharge prevention, and swelling improvement effects during high-temperature storage.

[0111] Specifically, the functional additive may include, as a typical example, one or more functional additives selected from the group consisting of sultone compounds, sulfite compounds, sulfone compounds, sulfate compounds, halogen-substituted carbonate compounds, nitrile compounds, cyclic carbonate compounds, phosphate compounds, borate compounds, and lithium salt compounds.

[0112] The sultone compound may be at least one compound selected from the group consisting of 1,3-propanesultone (PS), 1,4-butanesultone, ethensortone, 1,3-propensultone (PRS), 1,4-butensultone, and 1-methyl-1,3-propensultone, and may be included in an amount of 0.3% to 5% by weight, specifically 1% to 5% by weight, based on the total weight of the electrolyte. If the content of the sultone compound in the electrolyte exceeds 5% by weight, an excessively thick film may be formed on the electrode surface, potentially causing increased resistance and output degradation. The resistance due to the excess additive also increases, degrading the output characteristics.

[0113] The sulfite compound mentioned above includes one or more compounds selected from the group consisting of ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, 4,5-dimethylpropylene sulfite, 4,5-diethylpropylene sulfite, 4,6-dimethylpropylene sulfite, 4,6-diethylpropylene sulfite, and 1,3-butylene glycol sulfite, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0114] The sulfone compound may be one or more compounds selected from the group consisting of divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0115] The sulfate compound may be ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyltrimethylene sulfate (MTMS), and may be present in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0116] Furthermore, the halogen-substituted carbonate compound may be fluoroethylene carbonate (FEC), and may be included in an amount of 5% by weight or less based on the total weight of the electrolyte. If the content of the halogen-substituted carbonate compound in the electrolyte exceeds 5% by weight, the swelling performance of the cell may deteriorate.

[0117] Furthermore, the nitrile compounds include at least one compound selected from the group consisting of succinonitrile, adiponitrile (Adn), acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.

[0118] The cyclic carbonate compound may be vinylene carbonate (VC) or vinylethylene carbonate, and may be included in an amount of 3% by weight or less based on the total weight of the electrolyte. If the content of the cyclic carbonate compound in the electrolyte exceeds 3% by weight, the cell swelling suppression performance may deteriorate.

[0119] The phosphate compound may be one or more compounds selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium difluorophosphate, tetramethyltrimethylsilyl phosphate, trimethylsilyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, and tris(trifluoroethyl) phosphate, and may be present in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0120] The borate compound mentioned above may include lithium oxalyl difluoroborate, and may be present in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0121] The lithium salt compound is a compound different from the lithium salt contained in the lithium non-aqueous electrolyte, and includes one or more compounds selected from the group consisting of LiPO2F2, LiODFB, LiBOB (lithium bisoxalate borate (LiB(C2O4)2) and LiBF4), and can be included in an amount of 3% by weight or less based on the total weight of the electrolyte.

[0122] The functional additive may be a mixture of two or more types, and may be present in an amount of 20% by weight or less, specifically 0.1% to 10% by weight, based on the total weight of the lithium non-aqueous electrolyte. If the content of the functional additive exceeds 20% by weight, excessive side reactions may occur in the lithium non-aqueous electrolyte during battery charging and discharging. In particular, it may not decompose sufficiently at high temperatures and remain unreacted or precipitated in the lithium non-aqueous electrolyte at room temperature. This may result in side reactions that reduce the lifespan or resistance characteristics of the lithium metal battery.

[0123] <Example 1> LiNi 0.8 Co 0.1 Mn 0.1 O2, carbon black as a conductive material, and PVdF as a binder were mixed in a weight ratio of 94:3:3 under NMP conditions to produce a slurry. Then, the slurry was coated to a thickness of 70 μm on both sides of a 20 μm thick Al current collector and dried, and the mixture was rolled to a total positive electrode thickness of 120 μm to produce a positive electrode.

[0124] A slurry was prepared by mixing natural graphite as the negative electrode active material, carbon black as the conductive material, styrene-butadiene rubber (SBR) as the binder, and carboxymethylcellulose (CMC) as the thickener with water in a weight ratio of 95:1:3:1. Then, the slurry was coated onto both sides of a 10 μm thick Cu current collector to a thickness of 90 μm each and dried, and the material was rolled to produce a negative electrode with a total positive electrode thickness of 130 μm.

[0125] Furthermore, as a separation membrane, an SRS separation membrane was prepared (a 15 μm thick polypropylene substrate with a 5 μm thick coating layer on both sides, each layer consisting of a mixture of Al2O3 and PVdF in a weight ratio of 80:20).

[0126] Using the positive electrode, negative electrode, and separator membrane, a separator membrane / negative electrode / separator membrane / positive electrode was laminated to produce a unit cell. After laminating 15 such unit cells, an additional unit cell made of separator membrane / negative electrode / separator membrane was laminated, and then a thermal insulation material 1 (porous Si foam, 3 mm thick, 0.07 W / m·K) the size of the negative electrode was laminated on top. Subsequently, 15 more unit cells of separator membrane / negative electrode / separator membrane / positive electrode and one unit cell of separator membrane / negative electrode / separator membrane were laminated again, and then the outside of the electrode assembly was taped with PET tape.

[0127] The electrode assemblies manufactured in this manner were placed together with the electrolyte in a pouch case, sealed, and used to produce a secondary battery.

[0128] In this experiment, the electrolyte used was prepared by dissolving LiPF6 in a non-aqueous organic solvent having a composition of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 30:70 (volume ratio), to a concentration of 1.0 M, and then adding 3% by weight of vinylene carbonate (VC).

[0129] After charging at 0.1C for 3 hours to activate at 30% SOC, aging and degassing were performed, followed by CC / CV charging at 0.33C to 4.2V (100% SOC).

[0130] <Example 2> A secondary battery was manufactured in the same manner as in Example 1, except that a thermal insulation material 2 (silica aerogel, 1 mm thick, 0.04~0.05 W / m·K) the size of the negative electrode was used as the thermal insulation material.

[0131] <Example 3> A secondary battery was manufactured in the same manner as in Example 1, except that a thermal insulation material 3 (glass fiber + polyamide resin (50:50 wt%), 0.2 mm thick, 0.05 W / m·K) the size of the negative electrode was used as the thermal insulation material.

[0132] <Comparative Example 1> In the above-mentioned Example 1, an insulating material 2 (silica aerogel, 1 mm thick, 0.04~0.05 W / m·K) the size of the negative electrode was used as the insulating material, and an electrode assembly was manufactured by sequentially stacking 15 unit cells of separation membrane / negative electrode / separation membrane / positive electrode, 1 unit cell of separation membrane / negative electrode / separation membrane, and again 15 unit cells of separation membrane / negative electrode / separation membrane / positive electrode, and 1 unit cell of separation membrane / negative electrode / separation membrane, and a secondary battery was manufactured in the same manner as in Example 1, except that the insulating material 2 was positioned between the electrode assembly and the pouch case.

[0133] <Comparative Example 2> In the above-described embodiment 1, a secondary battery was manufactured in the same manner as in embodiment 1, but without inserting the heat insulating material 1.

[0134] <Experimental Example 1> Thermocouples were attached to the center of the flat surface of each secondary battery manufactured in Example 1, and a stacked cell was manufactured by stacking four secondary batteries using double-sided tape. A heater (120 mm x 60 mm) was then placed on top of the first secondary battery. A thermocouple was attached between the heater and the first secondary battery, and the heater was secured with PI tape. After inserting 10T superwool insulation material (600 mm x 80 mm) into the bottom plate of the module modeling jig, the stacked cell was placed inside the module modeling jig, and 10T superwool (insulation material 600 mm x 80 mm) was inserted between the stacked cell and the jig. A gasket was then placed on the bottom plate of the jig, and the top plate of the jig was fastened with bolts and nuts.

[0135] A heat transfer test was conducted by raising the heater temperature at a rate of 5°C / sec to induce thermal runaway in the first secondary battery. The voltage of the secondary batteries was measured using a Datalogger, and the time required from when the first secondary battery reached V=0 to when the fourth secondary battery reached V=0 was measured. The results are shown in Table 1 below.

[0136] The same tests were also performed on the secondary batteries manufactured in Examples 2-3 and Comparative Examples 1-2.

[0137] [Table 1]

[0138] Examining Table 1 above, it can be confirmed that when thermal insulation material is applied inside the secondary battery as in the present invention, heat propagation is delayed compared to Comparative Example 2, in which thermal insulation material was not applied inside the secondary battery.

[0139] On the other hand, referring to Example 2 and Comparative Example 1, which use the same material for insulation, it can be confirmed that applying the insulation material to the middle part of the electrode assembly enables even better suppression of heat propagation compared to applying it to the outside.

[0140] Furthermore, it was confirmed that the insulation effect relative to the thickness of the insulation material manufactured from silica aerogel or a combination of glass fiber and non-combustible resin was even superior to that of porous silicone foam. Needless to say, the combination of glass fiber and non-combustible resin has low thermal conductivity and its thickness can be reduced, but it was found that the insulation effect also decreases as the thickness decreases. Therefore, it was found that when using an insulation material manufactured from silica aerogel with a thickness of about 1 mm, the heat propagation delay effect is the best even if the decrease in energy density is not large.

[0141] Although preferred embodiments of the present invention have been described in detail above with reference to the drawings and examples, the scope of the present invention is not limited thereto. Various modifications and improvements by those skilled in the art, utilizing the basic concepts of the present invention as defined in the claims below, also fall within the scope of the present invention. [Industrial applicability]

[0142] According to the present invention, the secondary battery has one or more insulating materials inserted inside, which not only has the effect of suppressing heat transfer inside the secondary battery, but also, because the one or more insulating materials are located between two or more unit cells, even if thermal runaway or ignition occurs inside the secondary battery due to the inserted insulating materials, heat transfer between unit cells within a single secondary battery can be prevented, thereby reducing the capacity at which thermal runaway or ignition occurs, and thus is effective in reducing explosive force and further improving safety. [Explanation of Symbols]

[0143] 11: Electrode 12: Insulation 100, 200: Secondary battery 110, 120, 210, 220, 230: Unit cells 130, 231, 232: Insulation

Claims

1. A secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator membrane, and an electrolyte, The electrode assembly includes two or more unit cells and one or more insulating materials. One or more of the aforementioned thermal insulation materials are secondary batteries located between the two or more unit cells.

2. The secondary battery according to claim 1, wherein each of the two or more unit cells includes one or more electrodes, which are positive and negative electrodes, and a separator membrane.

3. The secondary battery according to claim 2, wherein each of the two or more unit cells is a monocell including a positive electrode or a negative electrode and a separator membrane, a bicell stacked such that electrodes of the same polarity are located at both ends, or a full cell stacked such that electrodes of different polarities are located at both ends.

4. The secondary battery according to any one of claims 1 to 3, wherein one or more of the one or more thermal insulation materials are located in the intermediate part with respect to the stacking direction of the electrode assembly.

5. The secondary battery according to claim 1, wherein the number of the one or more insulating materials is five or less.

6. The secondary battery according to claim 1, wherein, when there is an odd number of the one or more insulating materials, the insulating materials are arranged at equal intervals between unit cells facing each other, including an intermediate portion, with reference to the stacking direction of the electrode assembly.

7. The secondary battery according to claim 1, wherein, when there is an even number of the one or more insulating materials, the insulating materials are arranged at equal intervals between unit cells facing each other.

8. The secondary battery according to claim 1, wherein the one or more thermal insulation materials include one or two.

9. The secondary battery according to claim 1, wherein the surface area of ​​each of the one or more insulating materials is 100% to 110% of the surface area of ​​the negative electrode.

10. The secondary battery according to claim 1, wherein the one or more heat insulating materials are positioned to completely cover the opposing electrodes.

11. The secondary battery according to claim 10, wherein the one or more heat insulating materials are positioned to cover a portion of the tabs protruding from the opposing electrodes.

12. The secondary battery according to claim 1, wherein the thickness of each of the one or more insulating materials is 0.1 mm to 5 mm.

13. The secondary battery according to claim 12, wherein the thickness of each of the one or more insulating materials is 0.1 mm to 2 mm.

14. The secondary battery according to claim 1, wherein the one or more thermal insulation materials each include porous Si foam, silica aerogel, or a non-combustible resin containing glass fibers.

15. The secondary battery according to claim 14, wherein the one or more insulating materials include silica aerogel.

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