Electrode assembly, manufacturing method thereof, secondary battery, battery pack, and mobile device

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 by reference.

[0002] The present invention relates to an electrode assembly, a manufacturing method thereof, a secondary battery, a battery pack, and a means of transportation. [Background technology]

[0003] In general, a secondary battery is a battery that can be charged and discharged, unlike a primary battery that cannot be charged. Such secondary batteries are widely used in advanced electronic devices such as phones, laptops, and camcorders.

[0004] The stability of the secondary battery can be ensured by passing a stability test in which one side of the secondary battery is crimped with a crimping machine and an internal short circuit is measured.

[0005] Depending on 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 batteries, in which the electrode assembly is housed in a pouch-type battery case made of an aluminum laminate sheet.

[0006] The electrode assembly built into the battery case is a power generating element that can be charged and discharged and consists of a laminated structure of a positive electrode / separator / negative electrode, and is classified into a folding type electrode assembly (jelly roll) in which a separator is interposed between a long sheet-like positive electrode and a negative electrode coated with an active material and the electrode is wound up, and a stack type electrode assembly in which a number of positive electrodes and negative electrodes of a certain size are stacked in sequence with a separator interposed between them. Among them, the jelly roll has the advantage of being easy to manufacture and having a high energy density per weight.

[0007] The jelly roll type electrode assembly is formed by winding a positive electrode and a negative electrode, with a separator interposed between the positive electrode and the negative electrode. However, as charge and discharge cycles are repeated hundreds to thousands of times, the jelly roll type electrode assembly may contract and expand, which may cause problems such as detachment of the negative electrode active material, deformation of the electrode assembly shape, and cracks in the current collector, significantly impairing the safety of the secondary battery. Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above-mentioned problems in the prior art, the present invention provides an electrode assembly and a manufacturing method thereof that prevent detachment of an electrode active material when an electrode contracts and expands due to charging / 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, and a positive electrode are wound up, the negative electrode including 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 including 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 (physical properties).

[0010] In one embodiment of the present invention, there is provided an electrode assembly, wherein the first negative electrode active material layer has a smaller expansion coefficient than the second negative electrode active material layer.

[0011] In one embodiment of the present invention, there is provided an electrode assembly, wherein the first negative electrode active material layer has a stronger adhesive strength than the second negative electrode active material layer.

[0012] In one embodiment of the present invention, there is provided an electrode assembly, wherein a lamination area of ​​the first negative electrode active material layer is 30% or less of a lamination area of ​​the second negative electrode active material layer.

[0013] One embodiment of the present invention provides a secondary battery including the electrode assembly, a battery case having an opening on one side and 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 transportation 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, and a positive electrode are wound, the method including: 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; the negative electrode manufacturing step includes a first coating step of applying a first negative electrode slurry to a leading end of a winding to manufacture a first negative electrode active material layer; and a second coating step of applying a second negative electrode slurry to a trailing end of the first negative electrode active material layer to manufacture a second negative electrode active material layer, the first negative electrode slurry and the second negative electrode slurry having 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] In one embodiment of the present invention, a binder content of the first negative electrode slurry is greater than a binder content of the second negative electrode slurry.

[0019] In one embodiment of the present invention, the negative electrode slurry is applied to one or both sides of the negative electrode current collector by an edge coating method.

[0020] In one embodiment of the present invention, there is provided a method for manufacturing an electrode assembly, wherein the edge coating is performed by a slot die coater, a spray coater, a gravure roll coater, or a DM coater.

[0021] In one embodiment of the present invention, there is provided a method for manufacturing an electrode assembly, wherein the edge coating is performed using a double layer slot die coater (DLD). Effect of the Invention

[0022] According to an embodiment of the present invention, an electrode assembly and a manufacturing method thereof 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 sides of a current collector to reduce deformation of the electrode assembly and prevent cracks in the electrode current collector, thereby preventing disconnections and short circuits.

[0023] By laminating an active material layer with high adhesive strength at a position adjacent to the core portion of the electrode assembly, detachment due to expansion of the electrode active material can be prevented. [Brief description of the drawings]

[0024] [Figure 1] 1 is a cross-sectional view showing an electrode assembly according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a cross-sectional view showing a negative electrode according to one embodiment of the present invention. [Diagram 3] 2 is a flow chart illustrating steps for making a negative electrode according to one embodiment of the present invention. [Figure 4] 1 is a cross-sectional view showing a secondary battery including an electrode assembly according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The detailed description of the present invention is intended to fully explain the present invention to those skilled in the art. Throughout the specification, when a part is described as "comprising" a certain element or when a certain structure and shape are described as "featuring", this does not mean that other elements are excluded or that other structures and shapes are excluded, but that other elements, structures and shapes may be included, unless otherwise specified to the contrary.

[0026] Since the present invention can be modified in various ways and can have various embodiments, a specific embodiment will be presented and described in detail in the detailed description. However, this is not intended to limit the content of the invention according to the embodiment, and it is understood that the present invention includes all modifications, equivalents, or alternatives included in 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 illustrating the present invention and the scope of the present invention is not limited by the drawings.

[0028] FIG. 1 is a cross-sectional view of 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 separators 130 and 140 disposed between the positive electrode 110 and the negative electrode 120, and is a power generating element capable of charging and discharging.

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

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

[0032] The positive electrode 110 is formed by coating at least one of both sides of a positive electrode current collector with a positive electrode slurry containing a positive electrode active material, the region coated with the positive electrode slurry being a positive electrode active material portion, and the region not coated with the positive electrode slurry being a positive electrode uncoated portion. The positive electrode uncoated portion is not coated with a positive electrode active material layer, and therefore can be bonded to a first electrode tab.

[0033] The positive electrode slurry includes a positive electrode active material, a binder, a conductive material, a solvent, and an additive. The positive electrode active material may include lithium cobalt oxide having a high working voltage and excellent capacity characteristics, lithium nickel oxide having a high reversible capacity and easily realizing a large-capacity battery, lithium nickel cobalt oxide in which nickel is partially substituted with cobalt, lithium nickel cobalt metal oxide in which nickel is partially substituted with manganese, cobalt, or aluminum, lithium manganese-based oxide which is excellent in thermal stability and inexpensive, and lithium iron phosphate which is excellent in stability.

[0034] The binder may include one or more of a PVdF (Polyvinylidene fluoride) binder, an NBR (Nitrile Butadiene Rubber) binder, an SBR (Styrene Butadiene Rubber) binder, and a CMC (carboxymethylcellulose) binder.

[0035] 2 is a cross-sectional view showing a negative electrode 120 according to an 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 uncoated portion. The negative electrode current collector 121 may include a metal thin plate having excellent electrical conductivity, such as a copper (Cu) or nickel (Ni) foil.

[0036] The negative electrode 120 is formed by coating one or both sides of a negative electrode current collector 121 with a negative electrode slurry containing a negative electrode active material, the negative electrode active material part 122 is formed by coating or spreading the negative electrode slurry, and the negative electrode uncoated part is a region where the negative electrode current collector is exposed without being coated or spread with the negative electrode slurry. Since the negative electrode uncoated part is not coated with the negative electrode slurry, it can be bonded to a second electrode tab.

[0037] The first and second electrode tabs transmit electrons collected in the current collector to an external circuit, and may protrude in opposite directions from the electrode assembly of the jelly roll structure.

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

[0039] The negative electrode active material part 122 may include a first negative electrode active material layer 122a laminated at the winding leading end 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 ends refer to the ends opposite to the front ends.

[0041] 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 come into contact with each other, thereby minimizing the area of ​​the negative electrode uncoated portion and preventing a decrease in the capacity of the secondary battery including the electrode assembly 100. That is, 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 spaced apart, the area of ​​the negative electrode uncoated portion increases, which may cause a problem of a decrease in the capacity of the secondary battery. In addition, a space may be generated 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 may cause a problem in 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. In one embodiment, the first negative electrode active material layer 122a and the second negative electrode active material layer 122b may have different deformation rates 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 thermal expansion coefficients.

[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 may be 10% to 18%, more preferably 10% to 15%. And, 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 may be 15% to 28%, more preferably 15% to 25%.

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

[0045] The thickness expansion rate of the first negative electrode active material layer 122a and the second negative electrode active material layer 122b was calculated using the thickness of a secondary battery including the electrode assembly and the electrolyte according to the present invention before charging and the thickness of the electrode measured after disassembling the secondary battery after full charging to a voltage of 4.3 V.

[0046] The negative electrode 120 has a smaller radius of curvature at the end of the winding where winding begins, which is closer to the center C of the jelly roll structure. This causes the negative electrode active material part 122 to expand and contract in a narrow space during charging and discharging of the electrode assembly 100, resulting in a high frequency of the negative electrode active material part 122 falling off and deformation of the jelly roll structure.

[0047] In the negative electrode 120 according to the present invention, the first negative active material layer 122a located at the winding front end has a smaller thickness expansion rate than the second negative active material layer 122b, and the radius of curvature and the amount of volume expanded relative to the space at the winding front end and the winding rear end of the jelly roll structure are similar, so that deformation of the jelly roll structure can be minimized. Also, the expansion volume of the first negative active material layer 122a at the winding front end of the negative electrode 120 is reduced, so that the detachment of the negative active material part 122 can be prevented.

[0048] In addition, the first negative electrode active material layer 122a has a higher adhesive strength than the second negative electrode active material layer 122b, and the adhesive force between the first negative electrode active material layer 122a and the negative electrode current collector 121 can be made 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 15 gf / 25 mm to 35 gf / 25 mm. Preferably, the adhesive strength of the first negative electrode active material layer 122a may be 18 gf / 25 mm to 32 gf / 25 mm, more preferably 20 gf / 25 mm to 30 gf / 25 mm. And, the adhesive strength of the second negative electrode active material layer 122b to the negative electrode current collector may be 5 gf / 25 mm to 25 gf / 25 mm. Preferably, the adhesive strength of the second negative electrode active material layer 122b may be 8 gf / 25 mm to 23 gf / 25 mm, more preferably 10 gf / 25 mm to 20 gf / 25 mm.

[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 of the first negative electrode active material layer 122a and the second negative electrode active material layer 122b to the negative electrode current collector was measured by coating one side of the negative electrode current collector with the first negative electrode active material layer 122a and the second negative electrode active material layer 122b, attaching a 2.0 cm x 5 cm double-sided tape to a glass slide, cutting the negative electrode portion including the first negative electrode active material layer 122a and the negative electrode portion including the second negative electrode active material layer 122b into a size of 2.0 cm x 10 cm, and attaching them to the double-sided tape by applying a certain force with a 2 kg roller. The negative electrode current collector was peeled off from the glass slide to which the negative electrode was attached, and the 90° peel strength was measured.

[0052] Therefore, in the negative electrode 120 according to the present invention, even if the first negative electrode active material layer 122a expands in volume, the first negative electrode active material layer 122a does not detach from the negative electrode current collector 121, so that deformation of the jelly roll shape can be prevented.

[0053] In addition, in the negative electrode 120 according to the present invention, the first negative electrode active material layer 122a may detach due to contraction and expansion and protrude in the direction in which the negative electrode current collector 121 or the separators 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 separators 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 a 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 second negative electrode active material layer 122b must have a larger lamination area than the first negative electrode active material layer 122a, and the lamination area of ​​the first negative electrode active material layer 122a may be 30% or less based on the total area of ​​the negative electrode active material being 100%. Preferably, the lamination area of ​​the first negative electrode active material layer 122a may be 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 above numerical value, the electrode assembly 100 according to the present invention can provide a secondary battery with high capacity and high energy density while minimizing deformation of the shape of the electrode assembly 100, disconnection between the negative electrode current collector 121 and the separators 130 and 140, and detachment of the negative electrode active material part 122. In addition, it can prevent a problem that the total capacity of the secondary battery is reduced due to an increase in the stacking area of ​​the first negative electrode active material layer 122a.

[0057] The separators 130 and 140 serve to prevent an internal short circuit that may occur due to contact between the positive electrode 110 and the negative electrode 120, and may include a porous material to facilitate the movement of ions between the electrodes.

[0058] In an embodiment, the separators 130 and 140 may include a substrate layer made of a porous material. The substrate layer may include, for example, any one selected from the group consisting of polyethylene (PE), polystyrene (PS), polypropylene (PP), and a copolymer of polyethylene (PE) and polypropylene (PP).

[0059] In another embodiment, the separation membranes 130, 140 may include a safety reinforced separator (SRS) separation membrane. That is, the separation membranes 130, 140 may include a substrate layer of a porous material and a coating layer formed by applying a mixed slurry of inorganic particles and a binder polymer to be coated on the substrate layer. Preferably, the coating layer has a uniform pore structure formed by the interstitial volume between the ceramic particles, which are active layer components, as well as the pore structure contained in the separation membrane substrate itself, including ceramic particles.

[0060] The coating layer may include ceramic particles including at least one selected from the group consisting of alumina, silica, TiO2, SiC, and MgAl2O4. By including such a coating layer, the safety of the electrode assembly can be enhanced. The coating layer may further include a lithium salt.

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

[0062] The battery case 200 may have a columnar structure with a space formed therein. The battery case 200 may accommodate an electrode assembly 100 including an electrode and a separator, and an electrolyte (not shown) in the internal space. The battery case 200 may have a structure in which one side is open (hereinafter, referred to as an opening) and the other side is sealed. Here, the 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] A side surface of the upper part of the open battery case 200 may be provided with a beading part 210 that is folded toward the center of the secondary battery 1000. The battery case 200 may also be provided with a crimping part 220 on the upper side of the beading part 210. That is, the crimping part 220 may be located at the uppermost part of the battery case 200. Here, the upper part refers to a region from the center of the battery case 200 toward the opening part.

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

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

[0066] The top cap 310 may be located at the top of the cap assembly 300 and may protrude in a direction opposite to the center of the battery case 200. The top cap 310 may serve as an electrode terminal such that the protruding portion is electrically connected to the outside, for example, the top cap 310 may serve as a positive electrode terminal.

[0067] The top cap 310 may have an edge and a sealing gasket 340 bonded thereto, 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 protrusion protruding upward, a rim that contacts and is coupled with the sealing gasket 340, and a first connecting portion that connects the protrusion and the rim.

[0069] The safety vent 320 may be located at a lower portion of the top cap 310 and electrically connected to the top cap 310. At least a portion of a surface of the safety vent 320 facing the top cap 310 may contact the top cap 310. The safety vent 320 may contact the top cap 310 at a certain length from an end thereof, and a portion other than the contact length may be located at a certain distance from the top cap 310. In addition, the portion of the safety vent 320 that contacts the top cap 310 may be coupled to the sealing gasket 340.

[0070] The safety vent 320 may be spaced apart from the top cap 310 from the area in contact with the top cap 310 toward 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 that is located at the center of the safety vent 320 and that contacts the current interrupting element, and a second connecting portion that connects the contact portion and the central portion. The safety vent 320 may have bent portions (or notches) at the portions where the contact portion and the second connecting portion and the second connecting portion and the central portion contact each other.

[0072] In one embodiment, the safety vent 320 may be provided with an end perpendicular to the axial direction of the battery case 200. In this case, the top cap 310 may be provided 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 may be positioned horizontally.

[0073] In other embodiments, the safety vent 320 may be provided with a folded end that wraps around the outer periphery 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, resulting in an increase in internal pressure.

[0075] When the pressure inside the secondary battery 1000 increases, the safety vent 320 receives a force in the direction of the top cap 310, and the bent portion bursts, allowing the gas inside the secondary battery 1000 to be discharged.

[0076] A current interruptive device (CID) 330 may be located below the safety vent 320 and at least a portion of the CID may be coupled to the safety vent 320 .

[0077] When the safety vent 320 bursts due to an increase in the internal pressure of the secondary battery 1000, the current interrupting element 330 is separated from the safety vent 320 to interrupt the current.

[0078] More specifically, the current interruption device 330 may include a connection portion having a central portion connected to the safety vent 320 and protruding in a direction toward the safety vent 320, an edge portion excluding the connection portion, and a coupling portion connecting the connection portion and the edge portion. A plurality of coupling portions may be provided, and the plurality of coupling portions may be located spaced apart from each other.

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

[0080] The CID gasket 350 wraps around the edge of the current interrupting element 330 and can electrically isolate the edges and joints other than the connection parts of the current interrupting element 330 from the safety vent 320 .

[0081] A battery pack according to the present invention may include one or more of the secondary batteries described above. In particular, the battery pack includes a structure in which the secondary battery is contained in a pack housing.

[0082] The battery pack has high output and high capacity.

[0083] According to an embodiment of the present invention, there is provided a vehicle including the battery pack described above. The vehicle according to the embodiment uses the battery pack having high output / capacity, and therefore has excellent stability and safety.

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

[0085] 3 is a flow chart showing a negative electrode manufacturing step (S10) according to an embodiment of the present invention, in which a negative electrode slurry is applied to at least a portion of one or both sides of a negative electrode current collector to manufacture a negative electrode.

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

[0088] That is, in the negative electrode preparation step (S10), the negative electrode slurry may be applied by edge coating.

[0089] The end surface coating method may involve coating or applying the negative electrode slurry to one or both surfaces of the negative electrode current collector using a slot die coater, a spray coater, a gravure roll coater, or a DM coater.

[0090] The negative electrode manufacturing step (S10) may include a first coating step (S11) of applying a first negative electrode slurry to a leading end of the winding to manufacture a first negative electrode active material layer, and a second coating step (S12) of applying a second negative electrode slurry to a trailing end of the first negative electrode active material layer to manufacture a second negative electrode active material layer.

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

[0092] Also, the negative electrode preparing step (S10) may further include controlling application of the first negative electrode slurry and the second negative electrode slurry by controlling a double layer slot die coater.

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

[0094] The negative electrode manufacturing step (S10) may include a step of: the control unit controlling a first negative electrode slurry supply unit to supply the first negative electrode slurry to a first outlet; the negative electrode current collector moving so that the first negative electrode slurry discharged from the first outlet is applied to one side 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 outlet; and the negative electrode current collector moving so that the second negative electrode slurry is applied to a 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 include a negative electrode active material, a binder, a conductive material, a solvent, and an additive.

[0096] The first negative electrode slurry may contain graphite as the negative electrode active material, and the second negative electrode slurry may contain graphite and one or more of silicon, silica, and silicon carbide as the negative electrode active material. The first negative electrode slurry contains only graphite as the negative electrode active material, which reduces the expansion rate of the negative electrode active material during charging / discharging, thereby preventing the negative electrode active material from falling off the negative electrode current collector. The second negative electrode slurry contains one or more of silicon, silica, and silicon carbide as the negative electrode active material, which can provide an effect of enabling a high capacity design.

[0097] The first negative electrode slurry may have a higher binder content than the second negative electrode slurry, and the first negative electrode slurry may have a higher adhesive strength with the negative electrode current collector.

[0098] Therefore, the first negative electrode slurry with increased adhesive strength has a small radius of curvature of the jelly roll structure and a large density of the negative electrode slurry, which prevents the negative electrode active material from frequently falling off the negative electrode current collector due to a large expansion volume of the negative electrode active material during charging / discharging of the electrode assembly.

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

[0100] While the present invention has been described above with reference to preferred embodiments, it will be understood that those skilled in the art can make various modifications and variations to the present invention without departing from the spirit and scope of the present 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, a negative electrode, and a second separator are wound, 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 surfaces 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 the winding, and a second negative electrode active material layer located at a trailing end of the first negative electrode active material layer, The first negative electrode active material layer and the second negative electrode active material layer have different properties.

2. The electrode assembly of claim 1 , wherein the first negative electrode active material layer has a thickness expansion coefficient smaller than that of the second negative electrode active material layer.

3. The electrode assembly of claim 1 , wherein the first negative electrode active material layer has a stronger adhesive strength than the second negative electrode active material layer.

4. The electrode assembly of claim 1 , wherein a lamination length of the first negative electrode active material layer is 30% or less based on a total length of the negative electrode current collector (100%).

5. An electrode assembly according to any one of claims 1 to 4; a battery case having an opening on one side and housing the electrode assembly; a cap assembly coupled to the opening of the battery case.

6. A battery pack comprising the secondary battery according to claim 5.

7. A means of transportation including the battery pack according to claim 6.

8. A method for manufacturing an electrode assembly in which a negative electrode, a separator, and a positive electrode are wound, comprising the steps of: a negative electrode preparation step of coating a negative electrode slurry on at least a portion of one or both sides of a negative electrode current collector to prepare the negative electrode; The negative electrode manufacturing step includes a first coating step of coating a first negative electrode slurry on a leading end of a winding sheet to manufacture a first negative electrode active material layer, and a second coating step of coating a second negative electrode slurry on a trailing end of the first negative electrode active material layer to manufacture a second negative electrode active material layer, The first negative electrode slurry and the second negative electrode slurry have different compositions.

9. The method of claim 8 , wherein the first negative electrode slurry contains graphite and the second negative electrode slurry contains graphite and silicon.

10. The method of claim 8 , wherein the first negative electrode slurry has a binder content greater than a binder content of the second negative electrode slurry.

11. The method of claim 8 , wherein the negative electrode slurry is applied to one or both sides of the negative electrode current collector by an edge coating method.

12. The method of claim 11, wherein the edge coating is performed by using a slot die coater, a spray coater, a gravure roll coater, or a DM coater.

13. The method of claim 11, wherein the edge coating is performed by a double layer slot die coater (DLD).

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