Electrode assembly, method for manufacturing the same, secondary battery, battery pack, and means of transport

Abstract

The present invention relates to an electrode assembly in which a positive electrode, a first separator, a negative electrode, and a second separator are wound up, the negative electrode includes a negative electrode current collector and a negative electrode active material layer laminated on at least a portion of one or both sides of the negative electrode current collector, the negative electrode active material layer includes a first negative electrode active material layer located at a leading end of a winding and a second negative electrode active material layer located at a rear end of the first negative electrode active material layer, and the first negative electrode active material layer and the second negative electrode active material layer have different properties.

Description

[Technical Field]

[0001] This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0183192 filed with the Korean Intellectual Property Office on December 23, 2022, the entire contents of which are incorporated herein.

[0002] The present invention relates to an electrode assembly, a method for manufacturing the same, a secondary battery, a battery pack, and a moving device. [Background Art]

[0003] In general, a secondary battery, unlike a non-rechargeable primary battery, refers to a battery capable of being charged and discharged. Such secondary batteries are widely used in the field of advanced electronic devices such as mobile phones, notebook computers, and camcorders.

[0004] A secondary battery can secure stability through a stability test in which one surface is pressed with a crimping machine to measure an internal short circuit.

[0005] According to the shape of the battery case, secondary batteries are classified into cylindrical batteries and prismatic batteries, in which the electrode assembly is housed in a cylindrical or prismatic metal battery case, and pouch-type batteries, in which the electrode assembly is housed in a pouch-type battery case made of an aluminum laminate sheet.

[0006] Further, the electrode assembly housed in the battery case is a chargeable and dischargeable power generating element having a laminated structure of positive electrode / separator / negative electrode. It is classified into a folded-type electrode assembly (jelly roll) obtained by winding a long sheet-shaped positive electrode coated with an active material and a negative electrode with a separator interposed therebetween, and a stacked-type electrode assembly obtained by sequentially stacking a large number of positive electrodes and negative electrodes of a predetermined size with separators interposed therebetween. Among them, the jelly roll has the advantages of easy manufacture and high energy density per unit weight.

[0007] A jelly roll type electrode assembly is formed by winding together a positive electrode and a negative electrode, with a separator membrane interposed between them during the winding process. However, as the charge-discharge cycle progresses, which is repeated hundreds to thousands of times, the jelly roll type electrode assembly shrinks and expands, potentially compromising the safety of the secondary battery due to problems such as detachment of the negative electrode active material, deformation of the electrode assembly's shape, and cracking of the current collector. [Overview of the project] [Problems that the invention aims to solve]

[0008] Focusing on the aforementioned problems of the conventional technology, the present invention provides an electrode assembly and a method for manufacturing the same that prevent the detachment of electrode active material during the contraction and expansion of electrodes accompanying the charging and discharging of a secondary battery. [Means for solving the problem]

[0009] One embodiment of the present invention provides an electrode assembly in which a negative electrode, a separator membrane, and a positive electrode are wound together, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer laminated on at least a portion of one or both sides of the negative electrode current collector, and the negative electrode active material layer includes a first negative electrode active material layer located at the winding end and a second negative electrode active material layer located at the rear end of the first negative electrode active material layer, wherein the first negative electrode active material layer and the second negative electrode active material layer have different properties (physical properties).

[0010] One embodiment of the present invention provides an electrode assembly in which the first negative electrode active material layer has a smaller expansion rate than the second negative electrode active material layer.

[0011] One embodiment of the present invention provides an electrode assembly in which the first negative electrode active material layer has stronger adhesive strength than the second negative electrode active material layer.

[0012] One embodiment of the present invention provides an electrode assembly in which the stacking area of ​​the first negative electrode active material layer is 30% or less of the stacking area of ​​the second negative electrode active material layer.

[0013] One embodiment of the present invention provides a secondary battery comprising an electrode assembly, a battery case having an opening on one side for housing the electrode assembly, and a cap assembly coupled to the opening of the battery case.

[0014] One embodiment of the present invention provides a battery pack including the secondary battery.

[0015] One embodiment of the present invention provides a means of transport including the battery pack.

[0016] One embodiment of the present invention provides a method for manufacturing an electrode assembly in which a negative electrode, a separator membrane, and a positive electrode are wound together, comprising a negative electrode manufacturing step of manufacturing the negative electrode by applying a negative electrode slurry to at least a portion of one or both sides of a negative electrode current collector, wherein the negative electrode manufacturing step comprises a first coating step of applying a first negative electrode slurry to the winding tip to manufacture a first negative electrode active material layer, and a second coating step of applying a second negative electrode slurry to the rear end of the first negative electrode active material layer to manufacture a second negative electrode active material layer, wherein the first negative electrode slurry and the second negative electrode slurry have different compositions.

[0017] One embodiment of the present invention provides a method for manufacturing an electrode assembly, wherein the first negative electrode slurry contains graphite, and the second negative electrode slurry contains graphite and silicon.

[0018] One embodiment of the present invention provides a method for manufacturing an electrode assembly, wherein the binder content of the first negative electrode slurry is greater than the binder content of the second negative electrode slurry.

[0019] One embodiment of the present invention provides a method for manufacturing an electrode assembly, wherein the negative electrode slurry is applied to one or both sides of the negative electrode current collector by an end-face coating method.

[0020] One embodiment of the present invention provides a method for manufacturing an electrode assembly, wherein the end surface coating is performed by a slot die coater, a spray coater, a gravure roll coater, or a DM coater.

[0021] One embodiment of the present invention provides a method for manufacturing an electrode assembly, wherein the end surface coating is performed by a Double Layer Slot Die coater (DLD). Effects of the Invention

[0022] The electrode assembly and the method for manufacturing the same according to an embodiment of the present invention can improve the stability of a secondary battery by stacking a plurality of active material layers having different expansion / contraction rates and adhesive strengths on one or both surfaces of a current collector to reduce deformation of the electrode assembly, prevent cracking of the electrode current collector, and thus prevent disconnection and short circuit.

[0023] Stacking an active material layer with high adhesive strength at a position adjacent to the core portion of the electrode assembly can prevent detachment of the electrode active material caused by expansion of the electrode active material. Brief Description of Drawings

[0024] [Figure 1] It is a cross-sectional view illustrating an electrode assembly according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view illustrating a negative electrode according to an embodiment of the present invention. [Figure 3] It is a flowchart illustrating steps of manufacturing a negative electrode according to an embodiment of the present invention. [Figure 4] It is a cross-sectional view illustrating a secondary battery including an electrode assembly according to an embodiment of the present invention. Mode for Carrying Out the Invention

[0025] The detailed description of the present invention is intended to fully explain the invention to a person with ordinary skill in the art. Wherever the specification says that a part "includes" a component or that a structure and shape "characterizes" a structure and shape, this does not mean that other components are excluded or other structures and shapes are excluded, unless otherwise stated.

[0026] Because the present invention can be subjected to various transformations and has various embodiments, we will present specific embodiments and explain them in detail in the detailed description. However, this is not intended to limit the scope of the invention by embodiments, and is understood to include all transformations, equivalents, or substitutes that fall within the spirit and technical scope of the present invention.

[0027] The present invention will be described in detail below with reference to the drawings. However, the drawings are for illustrative purposes only, and the scope of the present invention is not limited by the drawings.

[0028] Figure 1 is a cross-sectional view showing an electrode assembly 100 according to one embodiment of the present invention.

[0029] The electrode assembly 100 includes a positive electrode 110, a negative electrode 120, and separation membranes 130 and 140 located between the positive electrode 110 and the negative electrode 120, and is a power generation element capable of charging and discharging.

[0030] The electrode assembly 100 may include a jelly roll structure in which a first separation membrane 130, a negative electrode 120, a second separation membrane 140, and a positive electrode 110 are sequentially laminated and wound.

[0031] The positive electrode 110 may include a positive electrode current collector, a positive electrode active material portion, and a positive electrode blank portion. The positive electrode current collector is a thin metal plate with excellent conductivity, and may include, for example, aluminum (Al) foil.

[0032] The positive electrode 110 is coated with a positive electrode slurry containing positive electrode active material on one or more of the sides of the positive electrode current collector. The area coated with the positive electrode slurry is the positive electrode active material area, and the area not coated with the positive electrode slurry is the positive electrode plain area. The positive electrode plain area can be joined to the first electrode tab because it does not have a positive electrode active material layer applied to it.

[0033] The positive electrode slurry comprises a positive electrode active material, a binder, a conductive material, a solvent, and additives. The positive electrode active material may include lithium cobalt oxide, which has a high operating voltage and excellent capacity characteristics; lithium nickel oxide, which has high reversible capacity and facilitates the realization of large-capacity batteries; lithium nickel cobalt oxide, in which part of the nickel is replaced with cobalt; lithium nickel cobalt metal oxide, in which part of the nickel is replaced with manganese, cobalt, or aluminum; lithium manganese-based oxide, which has excellent thermal stability and is inexpensive; and lithium iron phosphate, which has excellent stability.

[0034] The binder may contain one or more of the following: PVdF (Polyvinylidene fluoride) binder, NBR (Nitrile Butadiene Rubber) binder, SBR (Styrene Butadiene Rubber) binder, and CMC (carboxymethylcellulose) binder.

[0035] Figure 2 is a cross-sectional view showing a negative electrode 120 according to one embodiment of the present invention. The negative electrode 120 may include a negative electrode current collector 121, a negative electrode active material portion 122, and a negative electrode blank portion. The negative electrode current collector 121 may include a thin metal plate with excellent conductivity, such as copper (Cu) or nickel (Ni) foil.

[0036] The negative electrode 120 is formed by coating one or both sides of the negative electrode current collector 121 with a negative electrode slurry containing negative electrode active material. The negative electrode active material portion 122 is formed by coating or applying the negative electrode slurry, while the negative electrode blank portion is an area where the negative electrode current collector is exposed without being coated or applied with the negative electrode slurry. Because the negative electrode blank portion is not coated with the negative electrode slurry, it can be joined to the second electrode tab.

[0037] The first electrode tab and the second electrode tab transmit electrons collected by the current collector to the external circuit and can protrude in directions opposite to each other relative to the electrode assembly of the jelly roll structure.

[0038] The negative electrode slurry may contain a negative electrode active material, a binder, a conductive material, a solvent, and additives. The negative electrode active material may be, for example, carbon materials such as crystalline carbon, amorphous carbon, carbon composites, or carbon fibers, natural graphite, lithium metal, or lithium alloy. In this case, the negative electrode active material may further contain, for example, non-graphite-based SiO (silica) or SiC (silicon carbide) for high-capacity design.

[0039] The negative electrode active material portion 122 may include a first negative electrode active material layer 122a laminated at the winding tip adjacent to the center C of the jelly roll structure, and a second negative electrode active material layer 122b located at the rear end of the first negative electrode active material layer 122a.

[0040] The rear end of the first negative electrode active material layer 122a and the front end of the second negative electrode active material layer 122b may be in contact with each other. Here, the front ends of the first negative electrode active material layer 122a and the second negative electrode active material layer 122b refer to the ends located in the direction of the winding start point, and the rear end refers to the end opposite to the front end.

[0041] When the rear end of the first negative electrode active material layer 122a and the front end of the second negative electrode active material layer 122b are in contact, the area of ​​the blank portion of the negative electrode is minimized, preventing a decrease in the capacity of the secondary battery including the electrode assembly 100. In other words, if the rear end of the first negative electrode active material layer 122a and the front end of the second negative electrode active material layer 122b are separated, the area of ​​the blank portion of the negative electrode increases, which can lead to a decrease in the capacity of the secondary battery. Furthermore, a space may be created between the rear end of the first negative electrode active material layer 122a and the front end of the second negative electrode active material layer 122b, which can also cause problems with the winding uniformity of the electrode assembly 100.

[0042] The first negative electrode active material layer 122a and the second negative electrode active material layer 122b may have different properties (physical properties). In one embodiment, the first negative electrode active material layer 122a and the second negative electrode active material layer 122b may have different rates of deformation due to charging and discharging of the electrode assembly 100. That is, the first negative electrode active material layer 122a and the second negative electrode active material layer 122b may have different coefficients of thermal expansion.

[0043] In one embodiment, the thickness expansion rate of the first negative electrode active material layer 122a may be 10% to 20%. Preferably, the thickness expansion rate of the first negative electrode active material layer 122a is 10% to 18%, and more preferably 10% to 15%. Furthermore, the thickness expansion rate of the second negative electrode active material layer 122b may be 15% to 30%. Preferably, the thickness expansion rate of the second negative electrode active material layer 122b is 15% to 28%, and more preferably 15% to 25%.

[0044] The first negative electrode active material layer 122a may have a lower thickness expansion coefficient than the second negative electrode active material layer 122b. The difference between the thickness expansion coefficients of the first negative electrode active material layer 122a and the second negative electrode active material layer 122b may be between 1% and 15%.

[0045] The thickness expansion ratios of the first negative electrode active material layer 122a and the second negative electrode active material layer 122b were calculated using the thickness of the secondary battery containing the electrode assembly and electrolyte according to the present invention before charging, and the electrode thickness measured after disassembly following full charging to a voltage of 4.3V.

[0046] The negative electrode 120 has a smaller radius of curvature the closer it is to the center C of the jelly roll structure, that is, the winding tip where winding begins. This causes expansion and contraction of the negative electrode active material 122 in a narrow space during charging and discharging of the electrode assembly 100, leading to a higher frequency of detachment of the negative electrode active material 122 and a problem of deformation of the jelly roll structure.

[0047] In the negative electrode 120 according to the present invention, the first negative electrode active material layer 122a located at the winding tip has a smaller thickness expansion rate than the second negative electrode active material layer 122b, and the amount of volume that expands relative to the radius of curvature and space at the winding tip and winding rear end of the jelly roll structure is similar, so deformation of the jelly roll structure can be minimized. Furthermore, at the winding tip of the negative electrode 120, the expansion volume of the first negative electrode active material layer 122a decreases, which prevents the detachment of the negative electrode active material portion 122.

[0048] Furthermore, the first negative electrode active material layer 122a has higher adhesive strength than the second negative electrode active material layer 122b, and the adhesive force between the negative electrode active material portion 122 and the negative electrode current collector 121 can be higher than the repulsive force between the negative electrode current collector 121 and the negative electrode active material portion 122 due to the expansion of the negative electrode active material portion 122.

[0049] In one embodiment, the adhesive strength of the first negative electrode active material layer 122a to the negative electrode current collector may be 15gf / 25mm to 35gf / 25mm. Preferably, the adhesive strength of the first negative electrode active material layer 122a may be 18gf / 25mm to 32gf / 25mm, and more preferably 20gf / 25mm to 30gf / 25mm. The adhesive strength of the second negative electrode active material layer 122b to the negative electrode current collector may be 5gf / 25mm to 25gf / 25mm. Preferably, the adhesive strength of the second negative electrode active material layer 122b may be 8gf / 25mm to 23gf / 25mm, and more preferably 10gf / 25mm to 20gf / 25mm.

[0050] The difference between the adhesive strength of the first negative electrode active material layer 122a and the adhesive strength of the second negative electrode active material layer 122b may be 10 to 20 gf / 25 mm.

[0051] The adhesive strength between the first negative electrode active material layer 122a and the second negative electrode active material layer 122b and the negative electrode current collector was measured by coating one surface of the negative electrode current collector with the first negative electrode active material layer 122a and the second negative electrode active material layer 122b, then attaching a 2.0 cm x 5 cm piece of double-sided tape to a glass slide, cutting the negative electrode portion containing the first negative electrode active material layer 122a and the negative electrode portion containing the second negative electrode active material layer 122b into 2.0 cm x 10 cm pieces, and attaching them to the double-sided tape with a constant force using a 2 kg roller. The negative electrode current collector was peeled off the glass slide to which the negative electrode was attached, and the 90° peel strength was measured.

[0052] Therefore, in the present invention, even with volume expansion due to the first negative electrode active material layer 122a, the first negative electrode active material layer 122a does not detach from the negative electrode current collector 121, thus preventing deformation of the jelly roll shape.

[0053] Furthermore, in the negative electrode 120 according to the present invention, the first negative electrode active material layer 122a can detach due to contraction and expansion and protrude in the direction in which the negative electrode current collector 121 or the separator membranes 130 and 140 are located, thereby preventing pressure from concentrating on the detached first negative electrode active material layer 122a and causing cracks and short circuits in the negative electrode current collector 121 or the separator membranes 130 and 140.

[0054] The first negative electrode active material layer 122a may have a smaller capacity than the second negative electrode active material layer 122b. In other words, the second negative electrode active material layer 122b may have a larger capacity than the first negative electrode active material layer 122a.

[0055] The capacity of the secondary battery including the electrode assembly 100 according to the present invention may be determined by the second negative electrode active material layer 122b. Therefore, the stacking area of ​​the second negative electrode active material layer 122b must be larger than that of the first negative electrode active material layer 122a, and the stacking area of ​​the first negative electrode active material layer 122a may be 30% or less based on 100% of the total area of ​​the negative electrode active material. Preferably, the stacking area of ​​the first negative electrode active material layer 122a is 1% to 20% or less, and more preferably 5% to 15% or less.

[0056] When the area of ​​the first negative electrode active material layer 122a satisfies the aforementioned value, the electrode assembly 100 according to the present invention minimizes deformation of the electrode assembly 100, disconnection of the negative electrode current collector 121 and the separation membranes 130 and 140, and detachment of the negative electrode active material portion 122, while also providing a secondary battery with high capacity and high energy density. Furthermore, it prevents the problem of the stacking area of ​​the first negative electrode active material layer 122a becoming larger and the overall capacity of the secondary battery decreasing.

[0057] The separation membranes 130 and 140 prevent internal short circuits that may occur due to contact between the positive electrode 110 and the negative electrode 120, and may contain porous materials to facilitate the movement of ions between the electrodes.

[0058] In one embodiment, the separation membranes 130 and 140 may include a porous substrate layer. The substrate layer may include, for example, any of the materials selected from the group consisting of polyethylene (PE), polystyrene (PS), polypropylene (PP), and copolymers of polyethylene (PE) and polypropylene (PP).

[0059] In other embodiments, the separation membranes 130 and 140 may include SRS (Safety Reinforced Separator) separation membranes. That is, the separation membranes 130 and 140 may include a substrate layer made of a porous material and a coating layer formed by coating the substrate layer with a mixed slurry of inorganic particles and a binder polymer. Preferably, the coating layer contains ceramic particles and has a uniform pore structure formed by the interstitial volume between the ceramic particles, which are the active layer components, along with the pore structure contained in the separation membrane substrate itself.

[0060] The coating layer may contain ceramic particles comprising at least one selected from the group consisting of alumina, silica, TiO2, SiC, and MgAl2O4. Including such a coating layer can enhance the safety of the electrode assembly. The coating layer may further contain lithium salts.

[0061] Figure 4 is a cross-sectional view showing a secondary battery 1000 including an electrode assembly 100 according to one embodiment of the present invention. The secondary battery 1000 according to the present invention may also include an electrode assembly 100, a battery case 200, and a cap assembly 300.

[0062] The battery case 200 may be provided as a columnar structure with a space formed inside. The battery case 200 may house an electrode assembly 100 including electrodes and a separation membrane, and an electrolyte (not shown) in its internal space. The battery case 200 may have a structure with one side open (hereinafter referred to as the opening) and the other side sealed. Here, one side and the other side of the battery case 200 refer to the ends located at the top and bottom along the direction of gravity or the central axis of the battery case 200.

[0063] The upper side of the open battery case 200 may be provided with a beading portion 210 that is folded toward the center of the secondary battery 1000. Furthermore, the battery case 200 may have a crimping portion 220 above the beading portion 210. That is, the crimping portion 220 can be located at the uppermost part of the battery case 200. Here, "upper part" refers to the region from the center of the battery case 200 toward the opening.

[0064] The battery case 200 may be made of a lightweight conductive metal material such as aluminum or an aluminum alloy.

[0065] The cap assembly 300 may be coupled to the open surface of the battery case 200 and may include a top cap 310, a safety vent 320, and a current interruption element 330.

[0066] The top cap 310 is located at the top of the cap assembly 300 and may protrude away from the center of the battery case 200. The top cap 310 can act as an electrode terminal so that the protruding portion is electrically connected to the outside; for example, the top cap 310 can act as a positive terminal.

[0067] The top cap 310 may be joined to the edge of the top cap 310 and the sealing gasket 340, but the sealing gasket 340 may be located inside the crimping portion 220 of the battery case 200. The sealing gasket 340 can increase the sealing force between the top cap 310 and the battery case 200.

[0068] The top cap 310 may include a projection extending upward, an edge that contacts and connects with the sealing gasket 340, and a first connecting portion that connects the projection and the edge.

[0069] The safety vent 320 is located below the top cap 310 and may be electrically connected to the top cap 310. At least a portion of the surface of the safety vent 320 facing the top cap 310 may be in contact with the top cap 310. The safety vent 320 may be in contact with the top cap 310 for a certain length from its end, and the portion excluding the contact length may be located at a certain distance from the top cap 310. Alternatively, the portion of the safety vent 320 that is in contact with the top cap 310 may be coupled to the sealing gasket 340.

[0070] The safety vent 320 can increase its separation distance from the top cap 310 as it moves from the area in contact with the top cap 310 towards the center of the safety vent 320.

[0071] The safety vent 320 may include a contact portion that contacts the top cap 310, a central portion located in the center of the safety vent 320 that contacts the current interruption element, and a second connecting portion that connects the contact portion and the central portion. The safety vent 320 may also have bent portions (or notches) in the portions where the contact portion and the second connecting portion, and the second connecting portion and the central portion, come into contact.

[0072] In one embodiment, the end of the safety vent 320 may be positioned perpendicular to the axial direction of the battery case 200. In this case, the top cap 310 may also be positioned perpendicular to the axial direction of the battery case 200, similar to the safety vent 320. That is, the safety vent 320 and the top cap 310 can be positioned horizontally.

[0073] In another embodiment, the safety vent 320 may be provided such that its ends are bent to wrap around the outer circumferential surface of the top cap 310.

[0074] In the secondary battery 1000 according to the present invention, the electrode assembly 100 housed inside the battery case 200 reacts with the electrolyte, generating gas and heat, which causes the internal pressure to rise.

[0075] When the pressure inside the secondary battery 1000 rises, the safety vent 320 is subjected to a force towards the top cap 310, causing the bent portion to rupture and the gas inside the secondary battery 1000 to be released.

[0076] The current interruptive device (CID) 330 is located below the safety vent 320 and may be connected to the safety vent 320 in some respects.

[0077] The current interruption element 330 will disconnect from the safety vent 320 and interrupt the current if the safety vent 320 ruptures due to an increase in the internal pressure of the secondary battery 1000.

[0078] More specifically, the current interruption element 330 may include a central portion connected to the safety vent 320, a connecting portion protruding in the direction of the safety vent 320, an edge portion excluding the connecting portion, and a coupling portion connecting the connecting portion and the edge portion. Multiple coupling portions may be provided, and these coupling portions may be spaced apart from each other.

[0079] When the safety vent 320 is distorted in the direction in which the top cap 310 is positioned, the joint can break, and the connecting portion can be separated from the edge. That is, the connecting portion separates in the direction of the top cap 310 while still connected to the safety vent 320.

[0080] The CID gasket 350 encloses the edge of the current interruption element 330, electrically separating the edge and joint of the current interruption element 330 (excluding the connecting portion) from the safety vent 320.

[0081] The battery pack according to the present invention may include one or more of the aforementioned secondary batteries. More specifically, the battery pack includes a structure in which the secondary battery is contained in a pack housing.

[0082] Furthermore, the battery pack has high output and high capacity.

[0083] According to one embodiment of the present invention, a means of transport including the aforementioned battery pack is provided. The means of transport according to this embodiment is superior in terms of stability and safety because it uses the aforementioned battery pack having high output / high capacity.

[0084] The method for manufacturing an electrode assembly according to the present invention may include a negative electrode manufacturing step (S10), a positive electrode manufacturing step (S20), and a winding step (S30) for winding the negative electrode, separation membrane, and positive electrode.

[0085] Figure 3 is a flowchart of the negative electrode manufacturing step (S10) according to one embodiment of the present invention. In the negative electrode manufacturing step (S10), the negative electrode is manufactured by applying the negative electrode slurry to at least a portion of one or both sides of the negative electrode current collector.

[0086] In one embodiment, when the negative electrode slurry is applied to only one surface of the negative electrode current collector, the negative electrode manufacturing step (S10) may include the step of applying the negative electrode slurry to one surface of the negative electrode current collector.

[0087] In another embodiment, when the negative electrode slurry is applied to both sides of the negative electrode current collector, the negative electrode manufacturing step (S10) may include the steps of applying the negative electrode slurry to one side of the negative electrode current collector and applying the negative electrode slurry to the other side of the negative electrode current collector.

[0088] In other words, the method for applying the negative electrode slurry in the negative electrode manufacturing stage (S10) can be an end-face coating method.

[0089] The end face coating method allows for coating or applying a negative electrode slurry to one or both sides of the negative electrode current collector using a slot die coater, spray coater, gravure roll coater, or DM coater.

[0090] The negative electrode manufacturing step (S10) may include a first coating step (S11) in which a first negative electrode slurry is applied to the winding tip to produce a first negative electrode active material layer, and a second coating step (S12) in which a second negative electrode slurry is applied to the trailing end of the first negative electrode active material layer to produce a second negative electrode active material layer.

[0091] Therefore, the negative electrode manufacturing step (S10) according to the present invention can be performed by coating one or both sides of the negative electrode current collector with negative electrode slurry using an end face coating method, and the end face coating method may include a method of coating or applying negative electrode slurry to one or both sides of the negative electrode current collector using a double layer slot die coater (DLD).

[0092] Furthermore, the anode manufacturing step (S10) may further include a step of controlling the coating of the first anode slurry and the second anode slurry by controlling a double-layer slot die coater.

[0093] The double-layer slot die coater 10 may include a discharge section 11 from which a negative electrode slurry is discharged. The discharge section 11 may include a first discharge port 11a from which a first negative electrode slurry 12a is discharged and a second discharge port 11b from which a second negative electrode slurry 12b is discharged. It may further include a first negative electrode slurry supply section that supplies the first negative electrode slurry 12a to the first discharge port 11a and a second negative electrode slurry supply section that supplies the second negative electrode slurry 12b to the second discharge port 11b, and may further include a control unit that controls the first and second negative electrode slurry supply sections.

[0094] The negative electrode manufacturing step (S10) may include the steps of: the control unit controlling the first negative electrode slurry supply unit to supply the first negative electrode slurry to the first discharge port; the negative electrode current collector moving so that the first negative electrode slurry discharged from the first discharge port is applied to one surface of the negative electrode current collector; the control unit controlling the first negative electrode slurry supply unit to stop supplying the first negative electrode slurry; the control unit controlling the second negative electrode slurry supply unit to supply the second negative electrode slurry to the second discharge port; and the negative electrode current collector moving so that the second negative electrode slurry is applied to the rear end of the first negative electrode slurry.

[0095] The first negative electrode slurry and the second negative electrode slurry may have different compositions. The negative electrode slurry may contain a negative electrode active material, a binder, a conductive material, a solvent, and additives.

[0096] The first negative electrode slurry contains graphite as the negative electrode active material, while the second negative electrode slurry may contain graphite plus one or more of silicon, silica, and silicon carbide as the negative electrode active material. By containing only graphite as the negative electrode active material in the first negative electrode slurry, the expansion rate of the negative electrode active material is reduced during charging / discharging, preventing the negative electrode active material from detaching from the negative electrode current collector. Furthermore, by including one or more of silicon, silica, and silicon carbide as the negative electrode active material in the second negative electrode slurry, the effect of enabling a high-capacity design can be achieved.

[0097] Furthermore, the binder content of the first negative electrode slurry may be higher than that of the second negative electrode slurry. The first negative electrode slurry has a higher binder content, which can increase the adhesive strength with the negative electrode current collector.

[0098] Therefore, the first negative electrode slurry with increased adhesive strength has a smaller radius of curvature of the jelly roll structure and a higher density of negative electrode slurry. Consequently, the expansion volume of the negative electrode active material is larger during charging / discharging of the electrode assembly, which prevents the problem of the negative electrode active material frequently detaching from the negative electrode current collector.

[0099] In one embodiment, the binder content of the first negative electrode slurry may be 0.5 wt% to 3 wt% based on the total content of the first negative electrode slurry (100 wt%). Preferably, the first negative electrode slurry is 0.6 wt% to 2 wt%, and more preferably 0.7 wt% to 1.5 wt%.

[0100] While preferred embodiments of the present invention have been described above with reference to those skilled in the art, it will be understood that various modifications and changes can be made to the present invention without departing from the spirit and scope of the invention as set forth in the following claims. [Explanation of symbols]

[0101] 1000 secondary battery 100 electrode assembly 110 Positive electrode 120 negative electrode 121 Negative electrode current collector 122 Negative electrode active material section 122a First negative electrode active material layer 122b Second negative electrode active material layer 130 First separation membrane 140 Second separation membrane 200 Battery Case 210 Beading section 220 Crimping section 300 Cap Assembly 310 Top Cap 320 Safety Vent 330 Current interruption element 340 Sealing Gasket 350 CID Gasket 10 Double Layer Slot Die Coater 11 Discharge part 11a 1st discharge port 11b 2nd discharge port 12a First negative electrode slurry 12b Second negative electrode slurry

Claims

1. An electrode assembly in which a positive electrode, a first separator membrane, a negative electrode, and a second separator membrane are wound together, The negative electrode includes a negative electrode current collector and a negative electrode active material layer laminated on at least a portion of one or both sides of the negative electrode current collector. The negative electrode active material layer includes a first negative electrode active material layer located at the winding tip and a second negative electrode active material layer located at the rear end of the first negative electrode active material layer. The first negative electrode active material layer has a smaller thickness expansion coefficient than the second negative electrode active material layer. The first negative electrode active material layer contains a negative electrode active material consisting solely of graphite. The second negative electrode active material layer contains a negative electrode active material comprising graphite and one or more of silicon or silica. The aforementioned thickness expansion rate is calculated using the thickness of the secondary battery, including the electrode assembly and electrolyte, before charging, and the electrode thickness measured after disassembly following full charging to a voltage of 4.3V.

2. The electrode assembly according to claim 1, wherein the adhesive force between the first negative electrode active material layer and the negative electrode current collector is greater than the adhesive force between the second negative electrode active material layer and the negative electrode current collector.

3. The electrode assembly according to claim 1, wherein the stacking length of the first negative electrode active material layer is 30% or less based on 100% of the total length of the negative electrode current collector.

4. An electrode assembly according to any one of claims 1 to 3, A battery case with an opening on one side for housing the electrode assembly, A secondary battery comprising a cap assembly that is coupled to the opening of the battery case.

5. A battery pack including the secondary battery described in claim 4.

6. A means of transport including the battery pack described in claim 5.

7. A method for manufacturing an electrode assembly in which a negative electrode, a separation membrane, and a positive electrode are wound together, The process includes a negative electrode manufacturing step of applying a negative electrode slurry to at least a portion of one or both sides of a negative electrode current collector to manufacture the negative electrode, The negative electrode manufacturing step includes a first coating step of applying a first negative electrode slurry to the winding tip to produce a first negative electrode active material layer, and a second coating step of applying a second negative electrode slurry to the rear end of the first negative electrode active material layer to produce a second negative electrode active material layer. The first negative electrode slurry contains a negative electrode active material consisting solely of graphite. A method for manufacturing an electrode assembly, wherein the second negative electrode slurry contains a negative electrode active material comprising graphite and one or more of silicon or silica.

8. The method for manufacturing an electrode assembly according to claim 7, wherein the binder content of the first negative electrode slurry is greater than the binder content of the second negative electrode slurry.

9. The method for manufacturing an electrode assembly according to claim 7, wherein the application of the negative electrode slurry is performed by applying the negative electrode slurry to one or both sides of the negative electrode current collector using an end-face coating method.

10. The method for manufacturing an electrode assembly according to claim 9, wherein the end face coating method is performed by a slot die coater, a spray coater, a gravure roll coater, or a DM coater.

11. The method for manufacturing an electrode assembly according to claim 9, wherein the end face coating method is performed by coating with a double-layer slot die coater (DLD).

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