CONJUNTO DE ELETRODOS E BATERIA SECUNDÁRIA DE LÍTIO, QUE INCLUI O MESMO

Abstract

The present invention relates to an electrode assembly comprising: an electrode stack comprising a positive electrode comprising a positive electrode active material layer, a negative electrode comprising a negative electrode active material layer, and a separator interposed between the positive electrode and the negative electrode; and at least one retaining member for winding the electrode stack in the overall width direction and retaining same. The positive electrode comprises a positive electrode sliding portion configured such that the thickness of the positive electrode active material layer decreases. The retaining member comprises a first retaining member disposed so as to overlap the positive electrode sliding portion and a second retaining member disposed so as not to overlap the sliding portion. The first retaining member is thicker than the second retaining member.

Description

[001] This application claims priority over Korean Patent Applications Numbers 10-2023-0137204, filed on October 13, 2023, and 10-2024-0138669, filed on October 11, 2024, the descriptions of which are incorporated herein by reference.

[002] The present invention relates to an electrode assembly and a secondary lithium battery, which includes the same and more specifically, to an electrode assembly, in which a uniform pressure can be transmitted to an end portion when inserted into a module, and a secondary lithium battery, which includes the same. BACKGROUND OF THE TECHNIQUE

[003] With the advancement of technology in electric vehicles, energy storage systems (ESS) or portable electronic devices, the demand for secondary lithium batteries as a power source has increased rapidly.

[004] Lithium secondary batteries are classified into a pouch type, container type and similar types, according to the material of a case to accommodate an electrode set, and the electrode set can be classified into a jelly-roll type, a stacked type, a stack and lamination type, or a stack and folding type, according to the method of preparation and the shape thereof.

[005] Among these, the bag-type secondary battery is prepared by a method of forming a cup portion by pressure work of a flexible bag film laminate, which accommodates the electrode assembly in the cup portion and sealing a sealing portion after injecting an electrolyte, and the container-type secondary battery is prepared by a method of accommodating the electrode assembly in a container formed of a metallic material, injecting Petition 870250083381, dated 09 / 16 / 2025, p. 50 / 94 2 / 31 of the electrolyte and then fitting a top cap onto an upper portion of the container to seal the container.

[006] The electrode array is a structure that includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, wherein the positive and negative electrodes are each prepared by forming a layer of active material, coating a current collector with an electrode paste, and then drying and laminating the coated current collector. In the case where the electrode is prepared by coating with the electrode paste, a sliding portion is formed in which a thickness of the active material layer is gradually decreased at an end portion of the active material layer. In a region where the sliding electrode portion is formed, as a distance between the active material layer of the positive electrode and the active material layer of the negative electrode increases and the adhesion to the separator decreases, lithium deposition (Li deposition) can easily occur.

[007] Also, a cell thickness at an end portion of the electrode array is relatively decreased due to the sliding portion, where, in a case where many cells are stacked to form a module, a thickness difference between a central portion and an end portion of the cell is increased and, as a result, as less pressure is applied to the end portion of the cell in the module, the occurrence of expansion and lithium deposition can be further increased.

[008] Furthermore, as the electrolyte is consumed as the secondary lithium battery is repeatedly charged and discharged, a quantity of the electrolyte decreases, whereby, if the quantity of electrolyte in the battery decreases, the electrolyte may not reach a portion of the electrode end to reduce electrolyte impregnability and, Petition 870250083381, dated 09 / 16 / 2025, page 51 / 94 3 / 31 As a result, the mobility of lithium ions can be decreased, causing lithium deposition (Li deposition).

[009] Recently, as lithium secondary batteries are being used as a power source for electric vehicles, a lithium secondary battery with a long overall length relative to its overall width (hereinafter referred to as a 'long cell' for convenience) is being developed, in consideration of the battery's accommodation and location space. The lithium secondary battery that has such a long cell structure is advantageous in that it can achieve a higher capacity than a conventional lithium secondary battery and has excellent space efficiency, but there is a problem in that pressure on an end portion of an electrode array near an electrode tab decreases as charging and discharging are repeated, so that the adhesion between a separator and an electrode is reduced and, as a result, lithium deposition is further intensified.

[0010] Lithium deposition is a phenomenon in which lithium moved from the positive electrode is not intercalated into the negative electrode, but is precipitated onto a surface of the negative electrode, where, if lithium deposition occurs, the corresponding portion becomes gray. Lithium deposition can not only degrade battery performance and significantly degrade long-term lifespan characteristics, but can also limit the battery's fast charging capability and result in combustion or explosion. DESCRIPTION OF THE INVENTION TECHNICAL PROBLEM

[0011] One aspect of the present invention provides an electrode assembly which is designed to allow uniform pressure transmission to the entire electrode assembly when inserted into a module, having a thicker fastening member in a Petition 870250083381, dated 09 / 16 / 2025, page 52 / 94 4 / 31 region overlapping a sliding portion of a positive electrode to compensate for a decrease in thickness at an end portion of a cell and to allow the suppression of lithium expansion and deposition, improving the adhesion between an electrode and a separator.

[0012] Another aspect of the present invention provides a secondary lithium battery in which battery performance and safety degradation due to lithium precipitation can be avoided by including the above electrode assembly. TECHNICAL SOLUTION

[0013] According to one embodiment, the present invention provides an electrode assembly comprising an electrode stack, which includes a positive electrode comprising a layer of active positive electrode material; a negative electrode comprising a layer of active negative electrode material; and a separator disposed between the positive electrode and the negative electrode, and at least one fastening member which secures the electrode stack by winding the electrode stack in a full-width direction.

[0014] In this case, the positive electrode includes a sliding portion of the positive electrode in which the thickness of the active material layer of the positive electrode decreases.

[0015] Also, the fixation member includes a first fixation member overlapping the sliding portion of the positive electrode and a second fixation member not overlapping the sliding portion, and the thickness of the first fixation member is greater than the thickness of the second fixation member.

[0016] Preferably, when the thickness of the first fixation member is Ti, the thickness of the second fixation member is T2 and the thickness of the positive electrode is Tc, the electrode assembly satisfies [Equation 1]. Petition 870250083381, dated 09 / 16 / 2025, pp. 53 / 94 5 / 31 [Equation 1] 0 < Ti - T2 < 0.5Tc

[0017] The negative electrode may include a sliding portion of the negative electrode in which a thickness of the active material layer of the negative electrode decreases, and the clamping member may overlap at least a portion of a region that corresponds to the sliding portion of the negative electrode.

[0018] A ratio (L / W) of a total length (L) to a total width (W) of the electrode stack may be 3 or more, and the ratio of the total length (L) to the total width (W) of the electrode stack may preferably be in a range of 3 to 7.

[0019] The electrode assembly according to the present invention may include from 2 to 10 clamping members, wherein, in this case, the clamping members may be arranged in horizontally symmetrical positions in a full-length direction and, preferably, the clamping members are arranged spaced apart from each other at equal intervals.

[0020] The fastening member may include a porous structure and may specifically be a tape in which an adhesive layer is formed on a surface of a base material that has a porous structure.

[0021] The fastening member can have a width of 10 mm to 50 mm.

[0022] According to another embodiment, the present invention provides a secondary lithium battery that includes the electrode assembly according to the present invention; an electrolyte; and a battery case that houses the electrode assembly and the electrolyte. In this case, the battery case may be a bag-type battery case. ADVANTAGEOUS EFFECTS

[0023] In an electrode array according to the present Petition 870250083381, dated 09 / 16 / 2025, p. 54 / 94 6 / 31 invention, since a first fixing member is arranged to overlap a region where a sliding portion of the positive electrode is formed, so that close contact between the sliding portion of the electrode and a separator is firmly maintained and, consequently, a decrease in lithium mobility due to poor interfacial adhesion between the sliding portion of the electrode and the separator can be minimized, the electrode assembly according to the present invention can prevent lithium precipitation from the sliding portion of the electrode.

[0024] Also, since a decrease in thickness at an end portion of the electrode array is compensated for by making the first clamping member, which is arranged in the region overlapping the sliding portion of the positive electrode, thicker than a second clamping member, pressure can be uniformly transmitted to the entire electrode array when inserted into a module and, consequently, the occurrence of lithium expansion and deposition due to a decrease in pressure at an end portion of a cell can be suppressed.

[0025] Furthermore, in a case where the fixing member is arranged, as in the present invention, in a long cell with a long overall length relative to the overall width, since a phenomenon of electrolyte solution reduction in the sliding portion of the electrode can be minimized, battery performance degradation can be avoided.

[0026] Thus, if the electrode assembly according to the present invention is used, excellent performance and safety can be achieved until the service life of a secondary lithium battery ends. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a top view of an electrode array. Petition 870250083381, dated 09 / 16 / 2025, p. 55 / 94 7 / 31 according to an embodiment of the present invention.

[0028] Figure 2 is a cross-sectional view of an electrode stack according to an embodiment of the present invention.

[0029] Figure 3 is a photograph showing whether or not lithium deposition occurs after 800 charge and discharge cycles of a module using an electrode array prepared in the Example.

[0030] Figure 4 is a photograph showing whether or not lithium deposition occurs after 800 charge and discharge cycles of a module using an electrode array prepared in Comparative Example 1.

[0031] Figure 5 is a photograph showing whether or not lithium deposition occurs after 800 charge and discharge cycles of a module using an electrode array prepared in Comparative Example 2. BEST WAY TO IMPLEMENT THE INVENTION

[0032] Hereafter, the present invention will be described in detail.

[0033] As a result of a significant amount of research conducted in the development of a secondary lithium battery capable of achieving excellent performance and safety until the end of the battery's service life, the present inventors have discovered that by fixing a region corresponding to a sliding portion of the positive electrode with a thick fixing member during the formation of an electrode assembly, not only can the interfacial adhesion between a sliding portion of the electrode and a separator be improved, but also pressure can be transmitted relatively uniformly to an entire cell after the assembly of a module and, consequently, battery performance degradation can be minimized until the end of the battery's service life and excellent safety can be achieved by suppressing ignition and / or explosion due to lithium deposition, thereby leading to the completion of the present invention. Petition 870250083381, dated 09 / 16 / 2025, page 56 / 94 8 / 31

[0034] Specifically, an electrode assembly according to the present invention is characterized in that it includes an electrode stack comprising a positive electrode, a negative electrode and a separator, and at least one fastening member which secures an outer surface of the electrode stack by wrapping the outer surface of the electrode stack in a full-width direction, wherein the positive electrode includes a sliding portion of the positive electrode in which a thickness of a layer of active material of the positive electrode decreases, the fastening member includes a first fastening member arranged to overlap a region that corresponds to the sliding portion of the positive electrode and a second fastening member arranged in a region that does not correspond to the sliding portion of the positive electrode, and a thickness of the first fastening member is greater than a thickness of the second fastening member.

[0035] In a case where the thickness of the first fastening member located in the region overlapping the sliding portion of the positive electrode is greater than the thickness of the second fastening member located in another region, as in the present invention, a decrease in the thickness of an end portion of the cell can be compensated for by the thickness of the first fastening member. Thus, the expansion and precipitation of lithium, which occur due to the decrease in the thickness of the end portion of the cell during module assembly, can be minimized.

[0036] Also, in a case where the first clamping member is arranged to overlap the sliding portion of the positive electrode, as in the present invention, a distance between the sliding portion of the electrode and the separator is maintained by the first clamping member, and an increase in the distance between the sliding portion of the electrode and the separator is prevented by the first clamping member, even if the charging and discharging are repeated to cause a Petition 870250083381, dated 09 / 16 / 2025, page 57 / 94 9 / 31 alteration in the volume of the active material layer of the positive electrode and / or the active material layer of the negative electrode. Consequently, since the interfacial adhesion between the separator and the electrode in an end portion of the electrode assembly and the impregnability of the electrolyte solution can be maintained even if charging and discharging are repeated, the occurrence of lithium deposition due to a decrease in lithium mobility can be suppressed.

[0037] Figure 1 illustrates a top view of an electrode assembly according to an embodiment of the present invention, and Figure 2 illustrates a cross-sectional view of an electrode stack according to an embodiment of the present invention. Hereafter, the present invention will be described in more detail with reference to the drawings. However, the following drawings are presented for explanatory purposes only; the scope of the present invention is not limited to this, and various modifications are possible without departing from the purpose and spirit of the present invention.

[0038] As illustrated in Figure 1, an electrode assembly 1, according to the present invention, includes an electrode stack 100 and one or more fastening members 200a and 200b which secure the electrode stack 100 by wrapping the electrode stack in a full-width direction, wherein the fastening members 200a and 200b include a first fastening member 200a overlapping a sliding portion of the positive electrode 12b and a second fastening member 200b not overlapping the sliding portion of the positive electrode 12b.

[0039] Referring to Figure 2, the electrode stack 100 includes a positive electrode 10, which includes the active material layers of positive electrode 12a and 12b, a negative electrode 20, which includes the active material layers of negative electrode 22a and 22b, and a separator 30 disposed between the positive electrode 10 and the negative electrode 20. The electrode stack 100 can be a stacked electrode stack, a Petition 870250083381, dated 09 / 16 / 2025, page 58 / 94 10 / 31 which is formed by cutting the positive electrode, the separator, and the negative electrode to a certain size and then stacking them.

[0040] The positive electrode 10, for example, can be formed in a structure in which the layers of active positive electrode material 12a and 12b are formed on one or both surfaces of a collector of positive electrode 14, wherein the layers of active positive electrode material include a central portion of positive electrode 12a, in which a thickness of the layer of active positive electrode material is kept relatively constant, and a sliding portion of positive electrode 12b, in which the thickness of the layer of active positive electrode material decreases. Also, the positive electrode 10 includes a positive electrode tab 16 for electrical connection to an external power source.

[0041] The positive electrode 10 of a secondary lithium battery is prepared by a method of applying a positive electrode paste, which is prepared by dispersing a positive electrode active material, a conductive agent and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water, onto one or both surfaces of the positive electrode collector 14, removing the solvent from the positive electrode paste by a drying process and then laminating, wherein, in a case where the layer of positive electrode active material is formed by a wet coating method as described above, a coating amount of the positive electrode paste on an end portion of the layer of positive electrode active material is reduced to form the sliding portion of the positive electrode 12b.

[0042] Like the positive electrode collector 14, several positive electrode collectors used in the technique can be used. For example, as the positive electrode collector, stainless steel, aluminum, nickel, titanium, burnt carbon, aluminum or stainless steel with treatment. Petition 870250083381, dated 09 / 16 / 2025, page 59 / 94 11 / 31 Surface coatings of carbon, nickel, titanium, silver, or similar materials may be used. The positive electrode collector can typically have a thickness of 3 µm to 500 µm, and microscopic irregularities may be formed on the collector surface to improve adhesion of the active positive electrode material. The positive electrode collector, for example, can be used in various forms, such as a film, a sheet, a foil, a mesh, a porous body, a foam body, a non-woven fabric body, and the like.

[0043] The active positive electrode material layers 12a and 12b may include an active positive electrode material, a conductive agent and a binder.

[0044] The active positive electrode material is a compound capable of reversibly intercalating and deintercalating lithium, wherein various active positive electrode materials used in the technique can be employed, and one type thereof is not specifically limited. For example, lithium iron phosphate-based oxide (e.g., LiFeI-xMxPO4, 0 <x<1), óxido à base de lítio-manganês (por exemplo, LiMnO2, LiMn2O4, etc.), óxido à base de lítio-cobalto (por exemplo, LiCoCh, etc.), óxido à base de lítio-níquel (por exemplo, LÍNÍO2, etc.), lithium-nickel-manganese based oxide (e.g., ΙϊΝίι-γMηγΟζ (where 0 <Y<1), LiMn2-zNizO4 (onde 0<Z<2)), óxido à base de lítio-níquelcobalto (por exemplo, LÍNÍ1-Y1COY1O2 (onde 0<Y1 <1)), óxido à base de lítio-manganês-cobalto (por exemplo, LiCoi-Y2MnY2O2 (onde 0<Y2<1), LiMn2-ziCoziO4 (onde 0<Z1<2)), óxido à base de lítio-níquelmanganês-cobalto (por exemplo, Li(NipiCoqiMnri)O2 (onde 0<p1<1, 0<q1 <1, 0<r1 <1, e p1+q1+r1=1) ou Li(NiP2Coq2Mnr2)O4 (onde 0<p2<2, 0<q2<2, 0<r2<2, e p2+q2+r2=2)), ou óxido de lítio-níquel-cobalto-metal de transição (M) (por exemplo, Li(NiP3Coq3Mnr3MS3)O2 (onde M é selecionado do grupo que consiste em alumínio (Al), ferro (Fe), vanádio (V), cromo (Cr), titânio (Ti), tântalo (Ta), magnésio (Mg) e molibdênio. Petition 870250083381, dated 09 / 16 / 2025, pp. 60 / 94 12 / 31 (Mo), and p3, q3, r3 and s3 are atomic fractions of each independent element, where 0 <p3<1, 0<q3<1, 0<r3<1, 0<s3<1, e p2+q2+r3+s2=1)) ou uma combinação dos mesmos pode ser utilizada como material ativo de eletrodo positivo.

[0045] The active positive electrode material may be included in an amount of 80% by weight to 99% by weight, preferably 85% by weight to 99% by weight, and more preferably 90% by weight to 99% by weight, based on the total weight of the active positive electrode material layer.

[0046] The conductive agent is used to provide conductivity to the electrode, where any conductive agent may be used without specific limitation, provided it has adequate electron conductivity without causing adverse chemical changes in the battery. Specific examples of conductive agents may be graphite, such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fibers and carbon nanotubes; metallic powders or fibers such as copper, nickel, aluminum and silver; conductive filaments such as zinc oxide filaments and potassium titanate filaments; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one of these or a mixture of two or more of them may be used.The conductive agent can typically be included in an amount of 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, and most preferably 1% by weight to 10% by weight, based on the total weight of the positive electrode active material layer.

[0047] The binder improves the adhesion between the particles of the positive electrode active material and the adhesion between the positive electrode active material and the positive electrode collector. Specific examples of Petition 870250083381, dated 09 / 16 / 2025, pp. 61 / 94 13 / 31 binders may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, a monomeric ethylene-propylene-diene rubber (EPDM rubber), a sulfonated EPDM, a styrene-butadiene rubber (SBR), a fluorine rubber or various copolymers thereof, and any one of the same or a mixture of two or more of the same may be used. The binder can be included in an amount of 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, and more preferably 1% by weight to 10% by weight, based on the total weight of the positive electrode active material layer.

[0048] Next, the negative electrode 20 can be formed in a structure in which the layers of negative electrode active material 22a and 22b are formed on one or both surfaces of a negative electrode collector 24, wherein the layers of negative electrode active material include a central portion of negative electrode 22a, in which the thickness of the negative electrode active material layer is kept relatively constant, and a sliding portion of negative electrode 22b, in which the thickness of the negative electrode active material layer decreases. Also, the negative electrode 20 includes a negative electrode tab 26 for electrical connection to an external power source.

[0049] The negative electrode 20 of the secondary lithium battery is prepared by a method of applying a negative electrode paste, which is prepared by dispersing a negative electrode active material, a conductive agent and a binder in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water, onto one or both surfaces of the Petition 870250083381, dated 09 / 16 / 2025, pp. 62 / 94 14 / 31 Negative electrode collector 24, removing the solvent from the negative electrode paste through a drying process and then laminating, wherein, in a case where the negative electrode active material layer is formed by a wet coating method as described above, a coating amount of the negative electrode paste on an end portion of the negative electrode active material layer is reduced to form the negative electrode sliding portion 22b. Although this varies depending on the amount of negative electrode charge and coating conditions, the negative electrode sliding portion 22b is generally formed to be longer than the positive electrode sliding portion 12b.

[0050] Like the negative electrode collector, negative electrode collectors commonly used in the art can be used, and, for example, copper, stainless steel, aluminum, nickel, titanium, burnt carbon, copper or stainless steel with surface treatment of carbon, nickel, titanium, silver or similar, and an aluminum-cadmium alloy can be used. The negative electrode collector can typically have a thickness of 3 µm to 500 µm and, similar to the positive electrode collector, microscopic irregularities can be formed on the collector surface to improve the adhesion of the negative electrode active material. The negative electrode collector, for example, can be used in various forms, such as that of a film, a plate, a sheet, a mesh, a porous body, a foam body, a nonwoven fabric body and the like.

[0051] The negative electrode active material layer may include a negative electrode active material, a conductive agent, and a binder.

[0052] As the active negative electrode material, compounds capable of reversibly intercalating and deintercalating lithium, which are commonly used in the technique, can be used, and one type of Petition 870250083381, dated 09 / 16 / 2025, pp. 63 / 94 15 / 31 itself is not specifically limited. Specific examples of the negative electrode active material may be a carbonaceous material, such as artificial graphite, natural graphite, graphite-impregnated carbon fibers and amorphous carbon; a silicon-based material, such as silicon (Si), a Si-Me alloy (where Me is at least one selected from the group consisting of aluminum (Al), tin (Sn), magnesium (Mg), copper (Cu), iron (Fe), lead (Pb), zinc (Zn), manganese (Mn), chromium (Cr), titanium (Ti) and nickel (Ni)), SiOy (where 0 <y<2) e um composto de Si-C; uma película fina de lítio metálico; e um material metálico ligável com lítio, tal como Sn e Al, e qualquer um dos mesmos ou uma mistura de dois ou mais dos mesmos pode ser utilizado.

[0053] The negative electrode active material may be included in an amount of 80% by weight to 99% by weight, preferably 85% by weight to 99% by weight, and more preferably 90% by weight to 99% by weight based on the total weight of the negative electrode active material layer.

[0054] The conductive agent is used to provide conductivity to the negative electrode, where any conductive agent may be used without specific limitation, provided it has adequate electron conductivity without causing chemical changes in the battery. Specific examples of conductive agents may be graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fibers and carbon nanotubes; metallic powders or fibers, such as copper, nickel, aluminum and silver; conductive fibers, such as zinc oxide and potassium titanate fibers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of these or a mixture of two or more of these may be used. The agent conducting Petition 870250083381, dated 09 / 16 / 2025, p. 64 / 94 16 / 31 tor can typically be included in an amount of 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, and most preferably 1% by weight to 10% by weight, based on the total weight of the negative electrode active material layer.

[0055] The binder improves the adhesion between the particles of negative electrode active material and the adhesion between the negative electrode active material and the negative electrode collector. Specific examples of the binder may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, an ethylene-propylene-diene monomeric rubber (EPDM rubber), a sulfonated EPDM, a styrene-butadiene rubber (SBR), a fluorine rubber or various copolymers thereof, and any one of the same or a mixture of two or more of the same may be used.The binder can be included in an amount of 1% by weight to 30% by weight, preferably 1% by weight to 20% by weight, and more preferably 1% by weight to 10% by weight, based on the total weight of the negative electrode active material layer.

[0056] Next, separator 30 separates the negative electrode and the positive electrode and provides a path for the lithium ions to move, wherein any separator can be used as the separator, without specific limitation, provided it is typically used in a secondary lithium battery. Specifically, a porous polymer film, for example, a porous polymer film prepared from a polyolefin-based polymer, such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer, or a laminated structure having two or more layers thereof, Petition 870250083381, dated 09 / 16 / 2025, pp. 65 / 94 17 / 31 can be used as the separator. Also, a typical porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, can be used. Furthermore, a coated separator that includes a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength.

[0057] As in the present invention, in a case where the sliding portion of the electrode, in which the thickness of the active material layer decreases, is included at the ends of the positive and negative electrodes, since the separator and the active material layer of the electrode are not firmly fixed to each other in the sliding portion of the electrode, the mobility of lithium is less than that of the central portion of the electrode and, as a result, a lithium deposition phenomenon occurs, in which the lithium ions generated in the positive electrode during a discharge process are not intercalated in the negative electrode and are precipitated on a surface of the negative electrode.Also, in a case where the total length of the electrode array increases, pressure at one end of the electrode array is decreased to further reduce adhesion to the separator at the end of the electrode array, and in a case where charging and discharging are repeated to consume the electrolyte, since the electrolyte may not be in contact with the sliding portion of the electrode, battery performance degradation and the lithium deposition phenomenon may be accelerated.

[0058] Furthermore, in a case where a plurality of cells are stacked and assembled into a module, once a thickness difference between the end portion and the central portion of the cell is accumulated and further increased, the pressure is not properly transmitted to the end portion of the cell and thus lithium precipitation is further intensified. Petition 870250083381, dated 09 / 16 / 2025, pp. 66 / 94 18 / 31

[0059] The present invention is to solve such a problem, wherein, since the first fastening member 200a is arranged to overlap the sliding portion of the positive electrode 12b and the thickness of the first fastening member 200a is made greater than the thickness of the second fastening member 200b arranged in a region that does not overlap the sliding portion of the positive electrode 12b, the adhesion between the sliding portion of the positive electrode 12b and the separator 30 is improved to minimize the decrease in lithium mobility due to poor interfacial adhesion between the sliding portion of the electrode and the separator and the decrease in thickness of the cell end portion during module assembly is compensated to allow pressure to be transmitted relatively uniformly to the entire electrode assembly in the module and thus lithium expansion and precipitation can be minimized.

[0060] In this case, it is desirable that the difference between the thickness Ti of the first fastening member and the thickness T2 of the second fastening member, that is, T1-T2, satisfies [Equation 1] below. [Equation 1] < Ti-T2 < 0.5Tc

[0061] In [Equation 1], T1 is the thickness of the first clamping member, T2 is the thickness of the second clamping member, and Tce is the thickness of the positive electrode.

[0062] In a case where T1-T2 is 0 or less, there is no effect on the decrease in thickness of the end portion of the cell relative to the central portion of the cell, or the decrease in thickness may even be increased to intensify lithium deposition and, in a case where T1-T2 is greater than 0.5TC, as a thickness of a portion of the cell corresponding to the sliding portion becomes greater than the thickness of the central portion of the cell to increase the pressure on the outside of a module structure during cycles, Petition 870250083381, dated 09 / 16 / 2025, pp. 67 / 94 19 / 31 a fracture of the structure may occur due to non-uniform pressurization. T1-T2 may preferably be in a range of 0.01 Tca 0.5 Tc, more preferably 0.2 Tca 0.3 Tc.

[0063] Specifically, the thickness T1 of the first clamping member may be 0.2 to 0.5 times, preferably 0.25 to 0.45 times, and more preferably 0.3 to 0.4 times the thickness Tc of the positive electrode, and the thickness T2 of the second clamping member may be 0.05 to 0.2 times, preferably 0.1 to 0.15 times, and more preferably 0.12 to 0.14 times the thickness Tc of the positive electrode. In a case where the thicknesses of the first clamping member and the second clamping member satisfy the above ranges, the decrease in thickness of the end portion of the cell is appropriately compensated so that the pressure can be transmitted relatively uniformly to the entire electrode assembly in the module.

[0064] The thickness Tcdo of the positive electrode can vary depending on the capacity of a battery to be ultimately prepared, but, for example, it can be in a range of 100 pm to 200 pm, 120 pm to 180 pm or 140 pm to 160 pm.In this case, the thickness of the positive electrode refers to the thickness after lamination. If the thickness of the positive electrode is excessively high, the energy density of the battery may be reduced, and if the thickness of the positive electrode is excessively low, the processability of the coating of the active material layer of the positive electrode is reduced, the active material of the positive electrode may be significantly broken during electrode lamination, and as a result, a side reaction with the electrolyte solution is increased, leading to increased gas generation and degraded life characteristics.

[0065] The first fixing member 200a can be arranged to overlap at least a portion of a region that corresponds to the sliding portion of the negative electrode 22b. In a case where the Petition 870250083381, dated 09 / 16 / 2025, pp. 68 / 94 20 / 31 first fixing member 200a is arranged to overlap at least a portion of the sliding portion of the negative electrode, since both the interfacial adhesion between the positive electrode and the separator and the interfacial adhesion between the negative electrode and the separator increase, a suppression effect on lithium deposition and performance degradation can be more excellent.

[0066] A ratio (L / W) of a total length L to a total width W of the electrode stack may be 3 or more, and the ratio of the total length L to the total width W of the electrode stack may preferably be in the range of 3 to 7, more preferably 4 to 6. In this case, the total width and total length mean a length in a width direction and a length in a length direction of a component that has the largest dimension among the positive electrode, the negative electrode, and the separator that make up the electrode stack, respectively. In a case where the ratio of the total length to the total width of the electrode stack is 3 or more, there is an advantage in being able to achieve high capacity.However, in a case where the total length relative to the total width is large, as described above, since the cell pressure at the end portion in a direction of total length can be decreased, a problem may occur in which the impregnability of electrolyte at the end portion may be reduced when the electrolyte is consumed due to charging and discharging. However, in the case where the first fixing member is arranged to overlap the sliding portion of the positive electrode, as in the present invention, this problem can be solved because the pressure is maintained relatively uniformly up to the end of the electrode stack.

[0067] Specifically, the electrode stack according to the present invention may have a total width of 50 mm to 200 mm, of Petition 870250083381, dated 09 / 16 / 2025, pp. 69 / 94 21 / 31 preferably from 70 mm to 200 mm, and more preferably from 70 mm to 150 mm, and may have a total length of 200 mm to 1,000 mm, preferably from 300 mm to 800 mm, and more preferably from 400 mm to 600 mm.

[0068] Fixing members 200a and 200b may include a porous structure. In a case where the fixing members include a porous structure, since the electrolyte can be impregnated into the electrode stack by passing through the fixing member, a reduction in the electrolyte impregnability of the electrode stack due to the fixing member can be avoided. Specifically, fixing members 200a and 200b may be a finishing tape in which an adhesive layer is formed on a surface of a polymer-based material layer with a porous structure, but are not limited to this. The polymer material, for example, may be polyethylene terephthalate (PET), polyvinyl chloride (PVC) or polyethylene (PE), but is not limited to this.

[0069] It is desirable that the clamping members 200a and 200b have a width in the full width direction of the electrode stack of approximately 10 mm to 50 mm or approximately 20 mm to 40 mm. If the widths of the clamping members 200a and 200b are excessively large, since an external surface area of ​​the electrode stack 100, which is covered by the clamping members 200a and 200b, is increased to decrease a contact area with the electrolyte, the impregnability of the electrolyte may be reduced, and if the widths of the clamping members 200a and 200b are excessively small, an effect of the electrode stack clamping may be reduced.

[0070] The electrode assembly according to the present invention may include from 2 to 10 clamping members, preferably from 2 to 8 clamping members and, more preferably, from 3 to 7 clamping members. In this case, the clamping members may be arranged in position Petition 870250083381, dated 09 / 16 / 2025, pp. 70 / 94 22 / 31 horizontally symmetrical positions in the direction of the total length and, preferably, the fixing members can be arranged spaced apart from each other at equal intervals. In a case where a plurality of fixed members is included and arranged as described above, an electrode stack that has a long cell structure with a large length can be firmly fixed, and pressure variation depending on the position of the electrode stack can be avoided.

[0071] Next, a secondary lithium battery according to the present invention will be described.

[0072] The secondary lithium battery according to the present invention includes the electrode assembly according to the present invention; an electrolyte; and a battery case that houses the electrode assembly and the electrolyte. As the electrode assembly has been described above, only the remaining components will be described below.

[0073] The secondary lithium battery according to the present invention can be prepared by a method of accommodating the electrode assembly in the battery case, then injecting the electrolyte and sealing the battery case.

[0074] In this case, the battery box, for example, could be a pouch-type battery box.

[0075] A bag-type battery case may include a barrier layer, a base material layer disposed on one surface of the barrier layer, a sealing layer disposed on another surface of the barrier layer, and at least one recessed cup portion in one direction.

[0076] Specifically, the bag-type battery case can be prepared by a method of forming a cup portion that has a recessed shape in one direction, inserting a flexible bag film laminate, in which a base material layer, a barrier layer and a sealing layer are sequentially applied. Petition 870250083381, dated 09 / 16 / 2025, pp. 71 / 94 23 / 31 laminated, in a pressure forming device, and stretching of the bag film laminate by applying pressure to a partial region of the bag film laminate with a punch.

[0077] In this case, the base material layer is arranged as an outermost layer of the bag-type battery case to protect the electrode assembly from external impacts and to electrically isolate the electrode assembly.

[0078] The base material layer may be formed from a polymer material and, for example, may be formed from at least one polymer material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, Nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate and Teflon.

[0079] The base material layer may have a single-layer structure or it may have a multi-layer structure in which different polymer films are laminated. In a case where the base material layer has a multi-layer structure, an adhesive layer may be placed between the polymer films.

[0080] For example, the base material layer may have a laminated structure of a polyethylene terephthalate (PET) film and a Nylon film. In this case, it is desirable that the Nylon film be arranged on one side of the barrier layer, i.e., an inner side, and the polyethylene terephthalate film be arranged on one side of the bag surface.

[0081] Because polyethylene terephthalate has excellent durability and electrical insulation properties, the durability and insulation properties are excellent when the PET film is applied to the surface side. However, with regard to the PET film, as the adhesion to a thin aluminum alloy film that constitutes Petition 870250083381, dated 09 / 16 / 2025, pp. 72 / 94 24 / 31 tui the barrier layer is weak and the stretching behavior is also different, delamination between the base material layer and the barrier layer can occur during a forming process and a problem can occur in which the barrier layer may not be stretched uniformly to reduce plasticity, when the PET film is placed on the barrier layer side. In contrast, since the Nylon film has a stretching behavior similar to that of the thin aluminum alloy film that constitutes the barrier layer, an effect of improving plasticity can be obtained when the Nylon film is placed between the polyethylene terephthalate and the barrier layer.

[0082] The polyethylene terephthalate film can have a thickness of 5 µm to 20 µm, preferably 5 µm to 15 µm and, more preferably, 7 µm to 15 µm, and the Nylon film can have a thickness of 10 µm to 40 µm, preferably 10 µm to 35 µm and, more preferably, 15 µm to 25 µm. When the thicknesses of the polyethylene terephthalate film and the Nylon film meet the above ranges, the plasticity and rigidity after forming are excellent.

[0083] The base material layer can have a total thickness of 10 µm to 60 µm, preferably 20 µm to 50 µm, and most preferably 30 µm to 50 µm. In a case where the base material layer has a multi-layer structure, the thickness is a thickness that includes the adhesive layer. When the base material layer meets the above range, the durability, insulation properties, and plasticity are excellent. If the base material layer is excessively thin, the durability may be reduced and the base material layer may be damaged during the forming process, and if the base material layer is excessively thick, the plasticity may be reduced, the total thickness of the bag may be increased, and the accommodation space of the Petition 870250083381, dated 09 / 16 / 2025, pp. 73 / 94 25 / 31 battery capacity can be reduced to lower energy density.

[0084] The barrier layer serves to ensure the mechanical strength of the bag-type battery case, blocking the entry and exit of gas or moisture from the outside of the secondary battery and preventing electrolyte leakage.

[0085] The barrier layer may be formed from a metallic material and, for example, may be formed from a thin film of aluminum alloy. In this case, the thin film of aluminum alloy may include aluminum and a metallic element other than aluminum, for example, at least one selected from the group consisting of iron (Fe), copper (Cu), chromium (Cr), manganese (Mn), nickel (Ni), magnesium (Mg), silicon (Si) and zinc (Zn).

[0086] The barrier layer may have a thickness of 40 pm to 100 pm, more preferably 50 pm to 80 pm, and most preferably 60 pm to 80 pm. In a case where the thickness of the barrier layer satisfies the above range, plasticity is improved to increase the depth of formation of the cup portion, or the occurrence of cracking and / or pinholes is reduced, even when forming two cups, so that the resistance to external tension after formation is improved.

[0087] The sealing layer is joined by heat compression to seal the bag-type battery case, where it is placed over an inner layer of the battery case.

[0088] Since the sealing layer is a surface in contact with the electrolyte and the electrode assembly after the pocket is formed, it must have insulating and corrosion-resistant properties and, since the sealing layer must completely seal the interior to block the movement of material between the inside and outside, it must have high sealing properties.

[0089] The sealing layer can be made of a material of Petition 870250083381, dated 09 / 16 / 2025, pp. 74 / 94 26 / 31 polymer and, for example, may be formed from at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, Nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate and Teflon, and among these, it is particularly preferable to include polypropylene (PP), which has excellent mechanical properties, such as tensile strength, stiffness, surface hardness, wear resistance and heat resistance, and chemical properties, such as corrosion resistance.

[0090] More specifically, the sealing layer may include polypropylene, cast polypropylene (CPP), acid-modified polypropylene, a polypropylene-butylene-ethylene copolymer, or a combination thereof.

[0091] The sealing layer may have a single-layer structure or it may have a multi-layer structure, including two or more layers formed from different polymer materials.

[0092] The sealing layer may have a total thickness of 60 µm to 100 µm, preferably 60 µm to 90 µm, and most preferably 70 µm to 90 µm. If the thickness of the sealing layer is excessively thin, the sealing durability and insulation properties may be reduced, and if the thickness of the sealing layer is excessively thick, the flexibility may be reduced and the total thickness of the bag film laminate may be increased, and the volumetric energy density may be reduced.

[0093] Next, the electrolyte serves to move lithium ions generated by an electrochemical reaction of the electrode during the charging and discharging of the secondary battery, in which various electrolytes for a lithium secondary battery, which are known in the art, can be used, and the types thereof are not specifically limited.

[0094] For example, the electrolyte may include an organic solvent. Petition 870250083381, dated 09 / 16 / 2025, pp. 75 / 94 27 / 31 and a lithium salt.

[0095] Any organic solvent may be used as an organic solvent without specific limitation, provided that it can function as a medium through which the ions involved in an electrochemical reaction of the battery can move.Specifically, an ester-based solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; an ether-based solvent, such as dibutyl ether or tetrahydrofuran; a ketone-based solvent, such as cyclohexanone; an aromatic hydrocarbon-based solvent, such as benzene and fluorobenzene; a carbonate-based solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethylmethyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); an alcohol-based solvent, such as ethyl alcohol and isopropyl alcohol; nitriles, such as R-CN (where R is a linear, branched or cyclic C2-C20 hydrocarbon group and may include an aromatic double-bonded ring or ether linkage); Amides, such as dimethylformamide; dioxolanes, such as 1,3-dioxolane; or sulfolanes can be used as organic solvents.Among these solvents, a carbonate-based solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) that has high ionic conductivity and a high dielectric constant, which can increase the battery's charge / discharge performance, and a low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable.

[0096] Lithium salt can be used without specific limitation, provided it is a compound capable of supplying lithium ions used in the secondary lithium battery. Specifically, LiPFe, LÍCIO4, LiAsFe, LiBF4, LiSbF6, LÍAIO4, LiAICk, LÍCF3SO3, LÍC4F9SO3, UN(C2F5SO3)2, Petition 870250083381, dated 09 / 16 / 2025, pp. 76 / 94 28 / 31 LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, Lil, or LiB(C2O4)2 can be used as lithium salts. Lithium salts can be used in a concentration range of 0.1 M to 5.0 M, preferably 0.1 M to 3.0 M. If the lithium salt concentration is within the above range, the electrolyte can have appropriate conductivity and viscosity, excellent electrolyte performance can be achieved, and lithium ions can effectively move.

[0097] In order to improve battery life characteristics, suppress a reduction in battery capacity and improve battery discharge capacity, an additive may also be included in the electrolyte, in addition to the electrolyte components.

[0098] The present invention will now be described in more detail, according to specific examples. Example

[0099] A positive electrode measuring 70 mm x 500 mm, a negative electrode measuring 75 mm x 505 mm, and a separator measuring 80 mm x 510 mm were prepared and stacked in the order of positive electrode / separator / negative electrode to form an electrode stack.

[00100] In this case, the positive electrode was prepared by coating both surfaces of an aluminum current collector that has a thickness of 12 µm and a length of 500 mm with a positive electrode paste, so that the total length of a layer of active positive electrode material was 490 mm, and then drying and laminating the coated aluminum current collector, and sliding portions of positive electrode with a length of 8 mm were formed on both end portions of the layer of active positive electrode material, and a total thickness of the positive electrode was 162 µm.

[00101] Also, the negative electrode was prepared by coating am Petition 870250083381, dated 09 / 16 / 2025, pp. 77 / 94 29 / 31 based on the surfaces of a copper current collector that has a thickness of 8 µm and a length of 505 mm with a negative electrode paste so that a total length of a layer of active negative electrode material was 495 mm and then, drying and laminating the coated copper current collector, and sliding portions of negative electrode with a length of 10 mm were formed on both end portions of the layer of active negative electrode material, and a total thickness of the negative electrode was 215 µm.

[00102] Next, two first fixation members and four second fixation members were wrapped around an outer surface of the electrode stack in a full-width direction to prepare an electrode set. In this case, both ends of the first fixation member were positioned to be located 5 mm away from both end portions of the electrode stack, and the second fixation members were positioned at equal intervals between the first fixation members. A finishing tape (PET, Daehyun ST) with a width of 30 mm and a thickness of 47 µm was used as the first fixation member, and a finishing tape (PET, Daehyun ST) with a width of 30 mm and a thickness of 22 µm was used as the second fixation member. COMPARATIVE EXAMPLE 1

[00103] An electrode array was prepared in the same manner as in the Example, except that the first clamping member was not used, and six second clamping members were wrapped around an outer surface of the electrode stack in a full-width direction to prepare the electrode array. COMPARATIVE EXAMPLE 2

[00104] A set of electrodes was prepared in the same way Petition 870250083381, dated 09 / 16 / 2025, pp. 78 / 94 30 / 31 as in the Example, except that both ends of the first fixation member were arranged to be located 30 mm away from both end portions of the electrode stack, and three second fixation members were used. EXPERIMENTAL EXAMPLE 1

[00105] A secondary lithium battery cell was prepared by housing each of the electrode sets prepared in the example and comparative examples in a bag-type battery case, in which thin films of Nylon / polyethylene terephthalate / aluminum / polypropylene alloy were sequentially laminated and a cup portion was formed, injecting an electrolyte solution and then sealing the bag-type battery case.

[00106] Then, after a stack of four lithium secondary battery cells was defined as a set and a total of four sets were stacked on a polyurethane block, a polyurethane block was stacked as a top layer to prepare a cell-block set composed of 16 lithium secondary batteries and 5 polyurethane blocks, and the cell-block set was inserted into a module frame to prepare a module. After charging the lithium secondary battery module at 0.33 C at 4.22 V and discharging the lithium secondary battery module at 0.33 C at 2.5 V were defined as a cycle and 800 cycles of charging and discharging were repeated, the electrode stack was separated and visually confirmed whether lithium deposition had occurred or not.

[00107] The measurement results are shown in Table 1 and Figures 3 to 5 below. A case where lithium deposition was not visually observed was indicated as O, and a case where lithium deposition was observed was indicated as X. [Table 1] Petition 870250083381, dated 09 / 16 / 2025, pp. 79 / 94 31 / 31 Whether lithium deposition occurred or not Example 1 Comparative Example 2 Comparative Example

[00108] According to [Table 1], it can be confirmed that lithium deposition does not occur in the secondary lithium battery using the electrode array from the Example, but lithium deposition did occur in the secondary lithium batteries using the electrode arrays from Comparative Examples 1 and 2. DESCRIPTION OF SYMBOLS / REFERENCE NUMBERS 1: Electrode Set 10: Positive Electrode 20: Negative Electrode 30: Separator 100: Electrode Stack 200a: First Fixing Member 200b: Second Fixing Member 300: Electrolyte

Claims

1. An electrode assembly, characterized in that it comprises: an electrode stack comprising a positive electrode that includes a layer of active positive electrode material; a negative electrode that includes a layer of active negative electrode material; and a separator disposed between the positive electrode and the negative electrode; and at least one fastening member which secures the electrode stack by wrapping the electrode stack in a full-width direction, wherein the positive electrode comprises a sliding portion of the positive electrode in which a thickness of the active positive electrode material layer decreases, the fastening member comprises a first fastening member overlapping the sliding portion of the positive electrode and a second fastening member not overlapping the sliding portion of the positive electrode, and a thickness of the first fastening member is greater than a thickness of the second fastening member.

2. Electrode assembly according to claim 1, characterized in that, when the thickness of the first clamping member is Ti, the thickness of the second clamping member is T2, and the thickness of the positive electrode is Tc, the electrode assembly satisfies [Equation 1]. [Equation 1] 0 < Ti - T2 < 0.5Tc 3. Electrode assembly, according to claim 1, characterized in that the negative electrode comprises a sliding portion of the negative electrode in which a thickness of the layer of active material of the negative electrode decreases. Petition 870250083381, dated 09 / 16 / 2025, page 81 / 94 2 / 3 4. Electrode assembly according to claim 3, characterized in that the first clamping member overlaps at least a portion of a region corresponding to the sliding portion of the negative electrode.

5. Electrode array according to claim 1, characterized in that the ratio (L / W) of the total length (L) to the total width (W) of the electrode stack is 3 or more.

6. Electrode array according to claim 1, characterized in that the ratio of the total length (L) to the total width (W) of the electrode stack is in the range of 3 to 7.

7. Electrode assembly, according to claim 1, characterized in that the electrode assembly comprises from 2 to 10 clamping members, and the clamping members are arranged in horizontally symmetrical positions along the entire length.

8. Electrode assembly according to claim 7, characterized in that the clamping members are arranged at equal intervals from each other.

9. Electrode assembly according to claim 1, characterized in that the fixation member comprises a porous structure.

10. Electrode assembly according to claim 1, characterized in that the fastening member is a tape in which an adhesive layer is formed on the surface of a base material having a porous structure.

11. Electrode assembly, according to claim 1, characterized in that the fixing member has a width of 10 mm to 50 mm.

12. Secondary lithium battery, characterized in that it comprises the electrode assembly, as defined in any one of claims 1 to 11; an electrolyte; and a battery case that houses the electrode assembly and the electrolyte.

13. Secondary lithium battery, according to claim 12, characterized in that the battery case is a pouch-type battery case.

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