Method for manufacturing positive electrode, positive electrode, and lithium secondary battery comprising same

Abstract

A method for manufacturing a positive electrode according to exemplary embodiments of the present invention comprises: a process for preparing a positive electrode slurry including a positive electrode active material; and a coating process for manufacturing a preliminary positive electrode by coating a current collector with the positive electrode slurry by using a slot die, wherein a shim embedded in the slot die used in the coating process does not have a protrusion part for forming a semi-coated portion in which the coating thickness of the positive electrode slurry is relatively small.

Description

Method for manufacturing a cathode, cathode and lithium secondary battery including the same

[0001] This application claims the benefit of priority from Republic of Korea Patent Application No. 10-2023-0117828, filed on September 5, 2023.

[0002] The present invention relates to a method for manufacturing a positive electrode, a positive electrode, and a lithium secondary battery including the positive electrode, and more particularly, to a method for manufacturing a positive electrode for preventing delamination of a positive electrode active material layer, a positive electrode manufactured according to the manufacturing method, and a lithium secondary battery having excellent safety by preventing NP Ratio reversal.

[0003]

[0004] With the increasing technological development and demand for electric vehicles and energy storage systems (ESS), the demand for batteries as an energy source is rapidly increasing. Consequently, diverse research is being conducted to develop batteries that can meet these diverse needs. In particular, active research is being conducted on lithium secondary batteries, which possess high energy density and excellent lifespan and cycling characteristics as power sources for these devices.

[0005] Lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (LNCMO), and lithium transition metal phosphate are used as positive electrode active materials for lithium secondary batteries.

[0006] A positive electrode containing a lithium transition metal phosphate as a positive electrode active material has lower flexibility than a positive electrode containing lithium cobalt oxide (LCO) or lithium nickel cobalt manganese oxide (LNCMO) as a positive electrode active material, and thus has a higher possibility of detachment of the positive electrode active material layer during the notching and cutting processes, and detachment of the positive electrode active material layer may cause defects. In addition, since the flexibility of the electrode generally tends to decrease as the rolling density of the electrode increases, there has been a limit to increasing the rolling density in a positive electrode containing a lithium transition metal phosphate as a positive electrode active material.

[0007] FIG. 1 is a side view (below) of an electrode assembly according to a conventional technique and a side view (above) of a spare anode according to a conventional technique for processing an anode constituting the electrode assembly, FIG. 2 is a front view of a shim built into a slot die for applying anode slurry like the spare anode illustrated in FIG. 1 and a side view of a spare anode to which anode slurry is applied using the slot die, and FIG. 3 is a perspective view of the shim illustrated in FIG. 2.

[0008] Referring to FIG. 1, the electrode assembly (100) may include one or more units in which a separator (130) is interposed between a positive electrode (110) and a negative electrode (1200). In addition, a positive electrode tab (CT) and a negative electrode tab (AT) protrude in opposite directions, so that the upper part of the positive electrode from which the positive electrode tab (CT) protrudes face the lower part of the negative electrode, and the upper part of the negative electrode from which the negative electrode tab (AT) protrudes face the lower part of the positive electrode. However, the length of the sliding region of the positive electrode and the length of the sliding region of the negative electrode may be different from each other, and the inclined shape of the sliding region may also be various, such as an upwardly convex shape, a downwardly convex shape, a straight shape, an S shape, etc., and even if the inclined shape is the same, the inclination may be different. Accordingly, depending on the facing position of the positive / negative electrodes, a part where the NP Ratio is locally imbalanced may exist, and the imbalance of the NP Ratio may cause lithium to precipitate from the negative electrode, which may cause a safety accident such as a short circuit.

[0009] In particular, the area where the upper part of the cathode and the lower part of the anode face each other has a greater risk of local NP Ratio reversal compared to the area where the lower part of the cathode and the upper part of the anode face each other, so when coating the cathode slurry, the area scheduled for slitting, which will become the lower part of the anode, is coated with a relatively thin layer of cathode slurry.

[0010] Meanwhile, in order to improve the production rate of electrodes, there is a technology of applying electrode slurry in a wide width and slitting the electrode along a slitting line provided in the transverse center of the electrode slurry application area.

[0011] Referring to Fig. 1, a preliminary positive electrode (1) manufactured according to a conventional technique can be divided into a non-coated portion (2) on which a positive electrode active material layer is not formed, a positive electrode active material layer (4), and a semi-coated portion (6). At this time, the positive electrode active material layer (4) can be manufactured to have a width that is more than twice the transverse length of a conventional electrode, and in this case, the semi-coated portion (6) is positioned at the transverse center (Y direction) of the positive electrode active material layer (4). The thickness of the semi-coated portion (6) is relatively smaller than the thickness of the positive electrode active material layer (4), so that the positive electrode active material layer (4) and the semi-coated portion (6) form a step. And, by slitting the spare positive electrode along the slitting lines (SL1, SL3) located on the semi-coating portion (4), and assembling the electrode assembly so that the slit portion becomes the lower part of the positive electrode, the thickness of the positive electrode active material layer at the lower part of the positive electrode facing the upper part of the negative electrode is relatively thin. Referring to the lower drawing of Fig. 1, the lower part of the positive electrode (110) in the electrode assembly (100) faces the upper part of the negative electrode, and since the lower part of the positive electrode manufactured as in Fig. 1 has a relatively thin thickness, even if the upper part of the negative electrode facing the lower part of the positive electrode includes a sliding area, the risk of reversal of the NP Ratio can be reduced.

[0012] And, in order to form a semi-coated portion (6) on the reserve anode (1) as above, a slot die having a core as shown in FIGS. 2 and 3 is used to coat the anode slurry.

[0013] Referring to FIGS. 2 and 3, a core (10) built into a slot die includes a base (11), a guide (12), and a protrusion (13). The base (11) extends in a first direction (Y direction) which is the width direction of a die block (not shown), and the guide (12) and the protrusion (13) are each connected to the base (11) and extend in a direction (Z direction) perpendicular to the first direction. A plurality of flow paths (14) through which electrode slurry flows can be separated by the guide (12) and the protrusion (13). The flow path (14) provided by the guide (12) is opened in a direction horizontal to a plane in which the base (11) and a pair of die blocks are in contact. That is, the flow path (14) is a structure in which it is opened only in the flow direction of the electrode slurry, and is a structure in which three sides are closed by the base and the protrusion (13). And the above protrusion (13) has a groove (13a) through which the electrode slurry flows.

[0014] Accordingly, in the reserve positive electrode (1), a non-conductive portion (2) is formed corresponding to the guide (12), a positive electrode active material layer (4) is formed corresponding to the area from the guide (12) to the protrusion (13), and a semi-coated portion (6) is formed corresponding to the protrusion (13). The height of the semi-coated portion (6) can be adjusted by adjusting the difference between the thickness of the core (10) and the height of the groove (13a).

[0015] However, when the preliminary positive electrode (1) including the positive electrode active material layer (4) and the semi-coated portion (6) is rolled as described above, the pressure applied by the rolling roller is more concentrated on the positive electrode active material layer (4) due to the step difference between the positive electrode active material layer (4) and the semi-coated portion (6), so the rolling density of the relatively thin semi-coated portion (6) becomes lower than the rolling density of the positive electrode active material layer (4), and this unevenness in rolling density further aggravates the detachment of the positive electrode active material layer.

[0016] Therefore, when manufacturing the positive electrode, it is necessary to develop a technology to suppress the delamination of the positive electrode active material layer.

[0017]

[0018] The technical idea of ​​the present invention aims to solve a problem by providing a method for manufacturing a positive electrode that suppresses delamination of a positive electrode active material layer, a positive electrode in which delamination of a positive electrode active material layer is minimized, and a lithium secondary battery including the same.

[0019]

[0020] According to one embodiment of the present invention, a method for manufacturing a positive electrode is provided. The method for manufacturing a positive electrode includes: a process for manufacturing a positive electrode slurry containing a positive electrode active material; and a coating process for manufacturing a preliminary positive electrode by applying the positive electrode slurry onto a current collector using a slot die; wherein a shim built into the slot die used in the coating process does not have a protrusion for forming a semi-coated portion where the positive electrode slurry is applied to a relatively thin thickness.

[0021] A method for manufacturing an anode according to one embodiment of the present invention further includes: a process of drying and rolling the preliminary anode; a process of slitting the preliminary anode along one or more slitting lines parallel to the conveying direction (MD) of the preliminary anode; and a notching and cutting process of notching an anode tab in the slit preliminary anode and cutting it to the size of a unit anode.

[0022] In one embodiment, the slot die comprises two or more die blocks; and a core interposed between the die blocks to form a slot.

[0023] In one embodiment, the core comprises a base extending in a first direction, which is the width direction of the die block; and a guide connected to the base and extending in a direction perpendicular to the first direction.

[0024] In one embodiment, the core does not have a protrusion extending in a direction perpendicular to the first direction, other than the guide.

[0025] In one embodiment, the positive electrode active material is a lithium transition metal phosphate represented by the following chemical formula 1.

[0026] [Chemical Formula 1]

[0027] Li 1+a M1 1-x M2 x (PO y-b )D b

[0028] In the above chemical formula 1

[0029] M1 is one or more elements selected from Fe, Mn, Co, Ni, Cu, Zn, and Mg,

[0030] M2 is one or more elements selected from any one of Groups 2 to 15, excluding element M1,

[0031] D is one or more selected from the group consisting of F, S and N,

[0032] -0.5≤a≤+0.5, 0≤x≤0.8, 3.95≤y≤4.05, 0≤b≤1.

[0033] In one embodiment, the positive electrode slurry comprises a positive electrode active material, a binder, and a conductive agent in a weight ratio of 94 to 99: 0.5 to 4: 0.5 to 4.

[0034] In one embodiment, after the coating process, the thickness (T) of the positive electrode active material layer measured at any point (P) selected along the transverse direction (TD) of the positive electrode P ) and the thickness T of the central part of the positive electrode active material layer C satisfies the following condition 1.

[0035] [Condition 1]

[0036] 0.975≤T P / T C ≤1.025

[0037] However, the above P is an arbitrary point selected in the flattening area excluding the sliding area at the end of the reserve anode.

[0038] In one embodiment, during the slitting process, at least one of the slitting lines is provided on the positive slurry application portion.

[0039] In one embodiment, during the slitting process, the cut surface of the slit positive electrode slurry application portion is slit so as to be perpendicular to the plane of the current collector.

[0040] According to another embodiment of the present invention, a positive electrode is provided. The positive electrode comprises a positive electrode body having a positive electrode active material layer disposed on one or both sides of the positive electrode current collector; and a positive electrode tab protruding from one side of the positive electrode body, wherein the positive electrode has a rolling density RD measured at an arbitrary point (P) selected from the lower end of the positive electrode opposite the positive electrode tab. B and rolling density average value RD A satisfies the following condition 2.

[0041] [Condition 2]

[0042] 0.975≤ RD B / RD A ≤1.025

[0043] However, the above P is an arbitrary point selected in the flattening region excluding the sliding region of the terminal end in the electric field direction of the positive electrode active material layer.

[0044] In one embodiment, the positive electrode active material layer includes a lithium transition metal phosphate represented by the chemical formula 1 as a positive electrode active material.

[0045] According to another embodiment of the present invention, a lithium secondary battery is provided. The lithium secondary battery is a lithium secondary battery having a structure in which an electrode assembly is housed inside a pouch outer case together with an electrolyte, the electrode assembly includes a positive electrode and a negative electrode, and the positive electrode includes a positive electrode main body and a positive electrode tab protruding from one side of the positive electrode main body, and a rolling density RD measured at an arbitrary point (P) selected from the lower end of the positive electrode opposite the positive electrode tab. B and rolling density average value RD A satisfies the following condition 2.

[0046] [Condition 2]

[0047] 0.975≤ RD B / RD A ≤1.025

[0048] However, the above P is an arbitrary point selected in the flattening region excluding the sliding region of the terminal end in the electric field direction of the positive electrode active material layer.

[0049] In one embodiment, the negative electrode includes a negative electrode sliding region in which the negative electrode upper portion facing the positive electrode lower portion has a thickness surface of the negative electrode active material layer inclined with respect to the negative electrode current collector plane, and a length in the electrical direction of the negative electrode sliding region may be 3 mm or less, and more preferably 1 mm or less.

[0050] In one embodiment, the slope of the cathode sliding region is greater than or equal to 0.15.

[0051] The above slope means the value of b, which is the maximum thickness of the negative active material layer in the negative sliding region, with respect to the length a in the electric field direction of the negative sliding region.

[0052]

[0053] According to one embodiment of the present invention, the positive electrode slurry is applied using a slot die equipped with a shim that does not have a protrusion for forming a semi-coated portion with a relatively thin coating thickness of the positive electrode slurry. Therefore, as the coating thickness of the positive electrode slurry is uniform after the coating process, the rolling density is also uniform, thereby preventing the delamination of the positive electrode active material layer that may be caused by uneven rolling density.

[0054] The positive electrode and lithium secondary battery according to one embodiment of the present invention have the advantage of excellent capacity characteristics due to minimized delamination of the positive electrode active material layer.

[0055]

[0056] FIG. 1 is a drawing showing a side view (below) of an electrode assembly according to a conventional technique and a side view (above) of a spare anode according to a conventional technique for processing an anode constituting the electrode assembly.

[0057] FIG. 2 is a front view of a core embedded in a slot die for applying anode slurry, such as the anode substrate illustrated in FIG. 1, and a side view of a preliminary anode to which anode slurry is applied using the same.

[0058] Figure 3 is a perspective view of the deliberation shown in Figure 2.

[0059] FIG. 4 is a flowchart illustrating a method for manufacturing an anode according to exemplary embodiments of the present invention.

[0060] FIG. 5 is an exploded perspective view of a slot die according to exemplary embodiments of the present invention.

[0061] FIG. 6 is a front view of a core according to one embodiment of the present invention and a side view of a spare anode coated using a slot die having the core built in therein.

[0062] Figure 7 is a perspective view of the deliberation shown in Figure 6.

[0063] Figure 8 is a front view and a perspective view of a deaf person according to another embodiment of the present invention.

[0064] FIG. 9 is a side view of a preliminary anode coated using a slot die having a core as shown in FIG. 8.

[0065] FIG. 10 is a flowchart illustrating a method for manufacturing an anode according to exemplary embodiments of the present invention.

[0066] FIG. 11 is a drawing illustrating a slitting process according to exemplary embodiments of the present invention.

[0067] FIG. 12 is a drawing illustrating a notching and cutting process according to exemplary embodiments of the present invention.

[0068] Figure 13 is a top view of an anode according to an exemplary embodiment of the present invention.

[0069] Figure 14 is a cross-sectional view of the anode shown in Figure 13.

[0070] Fig. 15 is an enlarged view of one side of a cross-section of a cathode according to exemplary embodiments.

[0071] FIG. 16 is a drawing showing a method for manufacturing a cathode according to exemplary embodiments.

[0072] Figure 17 is a graph showing the results of calculating the thickness ratio by position of a spare anode manufactured according to an embodiment.

[0073] Figure 18 is a graph showing the results of calculating the thickness ratio by location of a spare anode manufactured according to a comparative example.

[0074] Figure 19 is a photograph of a positive electrode manufactured according to an example and a comparative example.

[0075] [Explanation of symbols]

[0076] 1,20,30: Spare anode

[0077] 510: Bipolar

[0078] 2,21,31: Mujibu

[0079] 511: Positive current collector

[0080] 4,22,32,512: Positive active material layer

[0081] 515: Positive tab

[0082] 6: Peninsular Aspirations

[0083] 10: Heart

[0084] 11: Base

[0085] 12: Guide

[0086] 13: Protrusion

[0087] 100: Electrode assembly

[0088] 110: Positive

[0089] 120: Cathode

[0090] CT: positive tab

[0091] AT: Negative tab

[0092] 200: Slot Die

[0093] 210, 310: Heart

[0094] 211,311: Base

[0095] 212,312: Guide

[0096] 220,230: Die Block

[0097] 231: Manifold

[0098] 520: Cathode

[0099]

[0100] Hereinafter, the present invention will be described in more detail to help understand the present invention.

[0101] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0102] The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

[0103] In this specification, it should be understood that the terms “include,” “comprising,” or “having” are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0104] In this specification, the transport direction (MD) of the spare anode and the full-width direction of the anode are defined as the X direction, the transverse direction (TD) of the spare anode and the full-length direction of the anode are defined as the Y direction, and the direction perpendicular to the plane obtained by the combination of the X direction and the Y direction is defined as the Z direction.

[0105]

[0106] Method for manufacturing anode

[0107] The present invention provides a method for manufacturing a positive electrode as a first embodiment.

[0108] FIG. 4 is a flowchart for explaining a method for manufacturing an anode according to exemplary embodiments of the present invention, FIG. 5 is an exploded perspective view of a slot die according to exemplary embodiments of the present invention, FIG. 6 is a front view of a core according to one embodiment of the present invention and a side view of a spare anode coated using a slot die having the core built in, and FIG. 7 is a perspective view of the core illustrated in FIG. 6.

[0109] Referring to FIG. 4, a method for manufacturing a positive electrode according to exemplary embodiments of the present invention may include a step (P110) of manufacturing a positive electrode slurry; and a coating step (P120) of applying the positive electrode slurry onto a current collector using a slot die to manufacture a preliminary positive electrode. According to the method for manufacturing a positive electrode according to exemplary embodiments of the present invention, a shim built into the slot die does not have a protrusion for forming a semi-coating portion where the positive electrode slurry has a relatively thin coating thickness. Accordingly, since the coating thickness of the positive electrode slurry is uniform after the coating process, uneven rolling density due to uneven coating thickness of the positive electrode slurry can be prevented during the rolling process. In addition, since the preliminary positive electrode manufactured according to the present invention has a uniform rolling density along the transverse direction (TD), it can prevent a delamination phenomenon of a positive electrode active material layer that may be caused by uneven rolling density during subsequent slitting, notching, and cutting processes. In particular, in the case of a positive electrode including a lithium transition metal phosphate as a positive electrode active material, the flexibility is poor compared to a positive electrode including a lithium cobalt oxide (LCO) or a lithium nickel cobalt manganese oxide (LNCMO) as a positive electrode active material, and thus the risk of detachment of the positive electrode active material layer is higher, and therefore the method for manufacturing a positive electrode according to the present invention is more useful, particularly in a positive electrode including a lithium transition metal phosphate.

[0110] The process for manufacturing the above positive electrode slurry (P110) may include a process of mixing and stirring a positive electrode active material, a binder, a conductive material, etc. in a solvent.

[0111] The above solvent is preferably a solvent capable of dispersing the positive electrode active material, binder, and conductive material to a certain level or higher.

[0112] Specific examples of the solvent include one or more selected from the group consisting of acetone, tetrahydrofuran, acetonitrile, dimethylformamide, dimethylsulfoxide, dimethylacetamide, and N-methyl-2-pyrrolidone (NMP). These solvents are non-aqueous solvents and are preferable in terms of phase stability compared to aqueous solvents.

[0113] The above positive electrode active material may include a lithium transition metal phosphate represented by the following chemical formula 1.

[0114] [Chemical Formula 1]

[0115] Li 1+a M1 1-x M2 x (PO y-b )D b

[0116] In the above chemical formula 1

[0117] M1 is one or more elements selected from Fe, Mn, Co, Ni, Cu, Zn, and Mg,

[0118] M2 is one or more elements selected from any one of Groups 2 to 15, excluding element M1,

[0119] D is one or more selected from the group consisting of F, S and N,

[0120] -0.5≤a≤+0.5, 0≤x≤0.8, 3.95≤y≤4.05, 0≤b≤1.

[0121] According to a specific embodiment of the present invention, the lithium transition metal phosphate may be at least one selected from the group consisting of M1 being Fe and M2 being Al, Mg, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y. Specifically, the lithium transition metal phosphate may be lithium iron phosphate (LiFePO4).

[0122] The above binder may be any binder polymer typically used in electrodes without limitation. For example, various types of binder polymers such as polyvinylidene fluoride-hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, styrene butadiene rubber (SBR), and carboxyl methyl cellulose (CMC) may be used.

[0123] Such binders may be included in an amount of 0.1 to 30 wt%, specifically 0.1 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the solid content in the positive electrode slurry.

[0124] There is no particular limitation on the above conductive material as long as it is an electronically conductive material that does not cause a chemical change in an electrochemical device. Specifically, the conductive material may be carbon black, graphite, carbon fiber, carbon nanotube, metal powder, conductive metal oxide, organic conductive material, etc., and products currently sold as conductive materials include acetylene black series (Chevron Chemical Company or Gulf Oil Company products, etc.), Ketjen Black EC series (Armak Company product), Vulcan XC-72 (Cabot Company product), and Super P (MMM product).

[0125] The above-mentioned conductive material may be included in an amount of 0.1 to 30 wt%, specifically 0.1 to 10 wt%, and more specifically 0.5 to 5 wt%, based on the solid content in the positive electrode slurry.

[0126] According to a specific embodiment of the present invention, the positive electrode slurry may include a positive electrode active material, a binder, and a conductive agent in a weight ratio of 94 to 99: 0.5 to 4: 0.5 to 4, more specifically, a weight ratio of 95 to 98.5: 1 to 4: 0.5 to 3, and more specifically, a weight ratio of 95.5 to 98: 1.5 to 3.5: 1 to 3. In the solid content of the positive electrode slurry, when the weight ratio of the positive electrode active material, the binder, and the conductive agent satisfies the above numerical range, a positive electrode having excellent capacity, adhesiveness, and electrical characteristics can be manufactured.

[0127] The above coating process (P120) is a process of coating the positive electrode slurry on the current collector to a predetermined coating thickness.

[0128] In exemplary embodiments, the transverse length of the anode slurry application portion in the coating process (P120) may be twice the longitudinal length of the anode to be manufactured. By applying the anode slurry in such a wide width and then slitting the center thereof, the productivity of anode manufacturing can be improved.

[0129] According to the present invention, in order to ensure that the electrode slurry has a uniform coating thickness along the transverse direction (TD, Y direction) of the preliminary positive electrode (20), the shim (210) built into the slot die (200) is characterized in that it does not have a protrusion for forming a semi-coating portion in which the coating thickness of the positive electrode slurry is relatively thin.

[0130] Referring to FIGS. 5 to 7, a slot die (200) according to one embodiment may include a pair of die blocks (220, 230); and a shim (210) interposed between the die blocks (220, 230) to form a slot. FIG. 5 illustrates a slot die having two die blocks, but the present invention is not limited thereto, and the number of die blocks may be two or more. Specifically, two die blocks may be required to apply a single electrode slurry, and three or more die blocks may be required to apply two or more electrode slurries.

[0131] The die blocks (220, 230) above have a shape of a pyramid that is symmetrical to each other, and are assembled so that one side corresponding to the bottom of the pyramid faces each other. At this time, it is preferable that the die blocks (220, 230) surround the outer surface of the shim (210) and are larger than one side of the shim. The shim (210) can be interposed between two die blocks (220, 230), and these can be fastened to each other by a plurality of bolt members. A pair of die blocks (220, 230) are spaced apart from each other by the thickness of the shim (210), so that a flow path (214) is formed inside the slot die (200).

[0132] At least one of the two die blocks may be provided with a manifold (231) for accommodating a certain volume of positive electrode slurry, and the manifold (231) may be connected to an external positive electrode slurry supply unit (not shown). The positive electrode slurry stored in the manifold (231) flows inside the slot die (200) along the flow path (214) and is discharged to the outside through a discharge port (not shown). This discharge port is formed thin and long, and a current collector positioned at the bottom of the slot die (200) moves at a certain speed, so that the positive electrode slurry can be widely and uniformly applied to the substrate.

[0133] Referring to FIGS. 6 and 7, the core (210) includes a base (211) extending in a first direction (Y direction) which is the width direction of the die blocks (220, 230); and a guide (212) connected to the base (211) and extending in a direction (Z direction) perpendicular to the first direction. The guide (212) may extend in the flow direction (Z direction) of the positive electrode slurry. A non-coated portion (21) is formed corresponding to the guide (212), and a positive electrode tab may be formed in the non-coated portion (21). In the drawing, the core (210) is illustrated in a structure in which a pair of guides (212) are positioned at both ends of the base (211), but the number of guides is not limited thereto. The thicknesses of the guides (212) on the one side are mutually the same.

[0134] FIG. 8 is a front view and a perspective view of a core according to another embodiment of the present invention, and FIG. 9 is a side view of a preliminary positive electrode coated using a slot die having the core illustrated in FIG. 8 built in. Referring to these drawings, the core (310) includes a base (311); and three guides (312) connected to the base and extending in a direction perpendicular to the first direction (Y direction). Among the three guides, two guides are located at both ends of the base (311), and the remaining one is structured to be located at the center of the base (311). A non-coated portion (31) may be formed corresponding to the three guides (312).

[0135] As described above, the core (210, 310) does not have a protrusion extending in a direction perpendicular to the first direction (Y-axis direction) other than the guide (212, 312). When the positive electrode slurry is applied using a slot die having such a core (210, 310) built in, a relatively thin semi-coated portion of the positive electrode slurry is not formed, and as illustrated in FIGS. 6 and 9, the positive electrode slurry can be applied uniformly along the transverse direction (Y-direction) of the spare positive electrode (20, 30).

[0136] According to one embodiment of the present invention, after the coating process (P120), the thickness (T) of the positive electrode active material layer measured at any point (P) selected along the transverse direction (TD) of the positive electrode P ) and the thickness T of the central part of the positive electrode active material layer C can satisfy the following condition 1.

[0137] [Condition 1]

[0138] 0.975≤T P / T C ≤1.025

[0139] However, the above P is an arbitrary point selected in the flattening region excluding the sliding region of the terminal end in the electric field direction of the positive electrode active material layer.

[0140] As described above, according to the coating process (P120) according to the present invention, the thickness of the positive electrode slurry applied is uniform, so that the rolling density of the positive electrode active material layer in the subsequent rolling process also becomes uniform, and thus the delamination phenomenon of the positive electrode active material layer that may be caused by a deviation in the rolling density can be suppressed.

[0141] FIG. 10 is a flowchart illustrating a method for manufacturing an anode according to exemplary embodiments of the present invention. Referring to FIG. 10, a method for manufacturing an anode according to an embodiment of the present invention may further include a step (P130) of drying and rolling the preliminary anode after the coating step (P120); a step (P140) of slitting the preliminary anode along one or more slitting lines parallel to the transport direction (MD) of the preliminary anode; and a notching and cutting step (P150) of notching an anode tab in the slitted preliminary anode and cutting it to the size of a unit anode.

[0142] In one embodiment, the notching and cutting (P150) from the coating process (P120) can be performed as a continuous roll-to-roll process.

[0143] The above drying and rolling process (P130) may include a drying process for drying the positive electrode slurry applied to the preliminary positive electrode and a rolling process for pressing the dried positive electrode to a predetermined thickness. The method of the above drying and rolling process is not particularly limited and may be performed by a method generally well known in secondary battery electrode processes.

[0144] In one embodiment, the drying process can be performed by transporting the spare anode in a drying furnace having a hot air spray nozzle configured to spray hot air on the spare anode and / or a heater configured to irradiate radiant heat on the spare anode; and an internal space for transporting the spare anode. In addition, the rolling process can be performed by roll-pressing the spare anode using a rolling roller.

[0145] The above slitting process (P140) may be a process of cutting the spare anode (20) along a slitting line parallel to the transport direction of the spare anode. Fig. 11 is a drawing illustrating a slitting process according to exemplary embodiments of the present invention. Referring to Fig. 11, for one spare anode (20, 30), there may be one slitting line (SL) or two or more. The number of slitting lines (SL) may vary depending on the number of anode slurry application portions. Specifically, if there is one anode slurry application portion, there may be one slitting line (SL1) as in (a) of Fig. 11, and if there are two anode slurry application portions, there may be three slitting lines (SL1, SL2, SL3) as in (b) of Fig. 11. In the above slitting process (P140), at least one slitting line may be provided on the anode slurry application portion (22, 32). As a non-limiting example, the slitting line (SL1, SL3) may be provided in the transverse (Y-direction) central portion of the positive electrode slurry application portion (22, 32). Since the slitting line (SL1, SL3) provided on the positive electrode slurry application portion is parallel to the transport direction (X-direction) of the spare positive electrode (20), when slitting is performed along the slitting line, the positive electrode slurry application portion is divided into two along the transport direction (X-direction).

[0146] In the above slitting process (P140), the cut surface of the slit positive electrode slurry-coated portion is slit so as to be perpendicular to the plane of the current collector. The meaning of perpendicularity includes not only cases where the internal angle formed by the cut surface of the positive electrode slurry-coated portion and the plane of the current collector is 90 degrees, but also cases where the internal angle is almost close to 90 degrees. Since such a positive electrode does not include a sliding region, it has the advantage of excellent capacity characteristics of the positive electrode.

[0147] The above-described notching and cutting process (P150) may be a process of forming an electrode tab from a slitted preliminary positive electrode and cutting it into the size and shape of a unit positive electrode. Fig. 12 is a drawing illustrating a notching and cutting process according to exemplary embodiments of the present invention. Referring to Fig. 12, an electrode tab may be formed by notching along a notching line (dotted line) formed on a non-conductive portion (21), and a unit positive electrode (510) may be obtained by cutting along a cutting line (dotted line) located on a positive electrode active material layer (22).

[0148] In the method for manufacturing a positive electrode according to the present invention, since the thickness of the positive electrode slurry applied in the coating process (P120) is uniform, the rolling density of the positive electrode active material layer after rolling is also uniform. Therefore, when a physical external force by a cutter is applied to the positive electrode active material layer in the notching and cutting process (P50), the detachment of the positive electrode active material layer that may occur due to differences in mechanical strength can be suppressed.

[0149]

[0150] anode

[0151] The present invention provides a positive electrode for a lithium secondary battery as a second embodiment.

[0152] FIG. 13 is a top view of an anode according to an exemplary embodiment of the present invention, and FIG. 14 is a cross-sectional view of the anode illustrated in FIG. 13.

[0153] Referring to these drawings, a positive electrode (510) according to an exemplary embodiment of the present invention may include a positive electrode body (513) in which a positive electrode active material layer (512) is arranged on one side or both sides of the positive electrode current collector (511); and a positive electrode tab (515) protruding from one side of the positive electrode body (513).

[0154] Referring to FIG. 14, the positive electrode upper portion (512T) where the positive electrode tab (515) is located in the positive electrode (510) has a shape in which the thickness surface of the positive electrode active material layer (512) is inclined to the plane of the positive electrode current collector (511), and the positive electrode lower portion (512B) at a position facing the positive electrode tab (515) in the positive electrode main body (513) has a thickness surface of the positive electrode active material layer that can be perpendicular to the plane of the positive electrode current collector (511).

[0155] Referring to FIGS. 11 and 12, when the positive electrode active material layer (22, 32) is cut along the slitting line (SL1, SL3), the cut surface becomes the lower end (512B) of the positive electrode. When slitting, the slitting is performed in a direction perpendicular to the plane of the current collector (21, 31), so the thickness plane of the positive electrode active material layer at the lower end (512B) of the positive electrode cannot but be perpendicular to the plane of the positive electrode current collector.

[0156] According to one embodiment, the anode (510) has a rolling density RD measured at an arbitrary point (P) selected from the anode lower portion (512B) opposite the anode tab (515). B and rolling density average value RD A can satisfy the following condition 2.

[0157] [Condition 2]

[0158] 0.975≤ RD B / RD A ≤1.025

[0159] Here, the above P is an arbitrary point selected in the flattening region excluding the sliding region of the terminal end in the electric field direction of the positive electrode active material layer.

[0160] According to the conventional technology, since the semi-coated portion (6) of the preliminary anode (1) is relatively thin as illustrated in FIG. 1, it receives less pressing force during the rolling process. Therefore, the rolling density of the semi-coated portion (6) of the anode substrate (1) is relatively small. However, as illustrated in FIG. 1, when the center of the semi-coated portion (6) is slit, the cross-section of the semi-coated portion becomes the lower part of the anode, so the rolling density of the lower part of the anode according to the conventional technology has a value of ±5% or more compared to the average value of the anode rolling density.

[0161] However, since the above condition 2 of the anode according to the present invention is satisfied, the rolling density RD of the anode lower part (512B) B The value is the rolling density average RD A Compared to the conventional positive electrode, the rolling density is uniform at a level of ±2.5% or less, and the ability to suppress detachment of the positive electrode active material layer during slitting, notching, and cutting processes is superior to that of the conventional positive electrode.

[0162] In one embodiment, the positive electrode active material layer (512) may include a lithium transition metal phosphate represented by the following chemical formula 1 as a positive electrode active material, and specifically, the lithium transition metal phosphate may be included in an amount of 80 wt% or more, more specifically 90 wt% or more, and more specifically 95 wt% to 100 wt% based on the total weight of the positive electrode active material.

[0163] [Chemical Formula 1]

[0164] Li 1+a M1 1-x M2 x (PO y-b )D b

[0165] In the above chemical formula 1

[0166] M1 is one or more elements selected from Fe, Mn, Co, Ni, Cu, Zn, and Mg,

[0167] M2 is one or more elements selected from any one of Groups 2 to 15, excluding element M1,

[0168] D is one or more selected from the group consisting of F, S and N,

[0169] -0.5≤a≤+0.5, 0≤x≤0.8, 3.95≤y≤4.05, 0≤b≤1.

[0170] A positive electrode comprising the lithium transition metal phosphate as a positive electrode active material has a higher possibility of delamination of the positive electrode active material layer compared to a positive electrode comprising lithium cobalt oxide (LCO) or lithium nickel cobalt manganese oxide (LNCMO) as a positive electrode active material. Therefore, the present invention, which uniformizes the rolling density of a positive electrode, may be more useful in terms of the delamination rate of the positive electrode when the positive electrode comprises the lithium transition metal phosphate as a positive electrode active material.

[0171]

[0172] lithium secondary battery

[0173] The present invention provides a lithium secondary battery as a third embodiment.

[0174] A lithium secondary battery according to exemplary embodiments of the present invention is a lithium secondary battery having a structure in which an electrode assembly is housed inside a pouch outer case together with an electrolyte, wherein the electrode assembly includes a positive electrode and a negative electrode, and the positive electrode may specifically include the positive electrode according to the present invention.

[0175] Specifically, the anode includes an anode body and an anode tab protruding from one side of the anode body, and the rolling density RD measured at an arbitrary point (P) selected from the lower part of the anode opposite the anode tab B and rolling density average value RD A can satisfy the following condition 2.

[0176] [Condition 2]

[0177] 0.975≤ RD B / RD A ≤1.025

[0178] Here, the above P is an arbitrary point selected in the flattening region excluding the sliding region of the terminal end in the electric field direction of the positive electrode active material layer.

[0179] Since the positive electrode according to the present invention satisfies the above condition 2 and has a uniform rolling density along the electric field direction (Y direction) of the positive electrode, the detachment of the positive electrode active material layer is minimized during the slitting, notching, and cutting processes, and the lithium secondary battery according to the present invention has excellent energy density.

[0180] According to one embodiment of the present invention, the negative electrode includes a negative electrode sliding region in which the thickness surface of the negative electrode active material layer is inclined with respect to the negative electrode current collector plane, and the length in the electrical direction of the negative electrode sliding region may be 3 mm or less.

[0181] In the past, in order to reduce the risk of NP Ratio reversal in the area where the lower part of the positive electrode and the upper part of the negative electrode face each other, the thickness of the positive active material layer at the lower part of the positive electrode was intentionally designed to be relatively thin.

[0182] However, since the thickness of the positive electrode active material layer at the lower portion of the positive electrode according to the present invention is the same as or similar to the thickness of the positive electrode active material layer at a portion other than the lower portion of the positive electrode, in order to reduce the risk of NP Ratio reversal, it is necessary to design the negative electrode capacity of the upper portion of the negative electrode facing the lower portion of the positive electrode to be large.

[0183] In particular, the upper portion of the negative electrode facing the lower portion of the positive electrode includes a negative electrode sliding region in which the thickness plane of the negative electrode active material layer is inclined with respect to the plane of the negative electrode current collector. Therefore, in order to design a large negative electrode capacity, it is desirable to minimize the length in the electrical direction of the negative electrode sliding region.

[0184] According to one embodiment of the present invention, the cathode may have a length in the electrical direction of the cathode sliding region at the upper end of the cathode of 3 mm or less, preferably 2 mm or less, more preferably 1 mm or less, and most preferably 0.5 mm or less.

[0185] The length of the sliding region of a conventional cathode in the electrical direction is on the order of 5 mm to 10 mm, but the length of the sliding region of the cathode according to the present invention is very short compared to that of a conventional cathode.

[0186] The method for manufacturing the above cathode is not particularly limited.

[0187] Fig. 15 is an enlarged view of one side of a cross-section of a cathode according to exemplary embodiments. In one embodiment, the cathode (520) can be manufactured by manufacturing a composition for dam coating, and applying a composition for dam coating (522D) to both edges in the transverse direction (TD, Y direction) of the cathode slurry application portion (522A), thereby manufacturing a cathode with a short length of the cathode sliding region (522S) as described above. The composition for dam coating (522D) acts as a dam at both edges in the transverse direction (TD) of the cathode slurry application portion, thereby suppressing the cathode slurry from flowing down in the transverse direction, and thus controlling the length of the sliding region in the full-length direction to be short.

[0188] FIG. 16 is a drawing showing a method for manufacturing a negative electrode according to exemplary embodiments. Referring to FIG. 16, a method for manufacturing a negative electrode according to an embodiment of the present invention may include a step (P210) of attaching an adhesive tape (525) to a current collector (521); a step (P220) of applying a negative electrode slurry (522) to a predetermined portion of a maintenance portion; a drying step (P230); a step (P240) of peeling and removing the adhesive tape (525) from the current collector; and a rolling step (P250).

[0189] According to a method for manufacturing a negative electrode according to exemplary embodiments of the present invention, an adhesive tape is attached to the edge of a predetermined portion of a holding portion where a negative electrode slurry is to be applied, and while the adhesive tape is attached to a current collector, an electrode slurry is applied and dried, and then the adhesive tape is peeled off. When the adhesive tape is peeled off, the negative electrode active material layer formed on the adhesive tape is removed together, so that a cross-section of the negative electrode active material layer from which the adhesive tape is peeled off forms a perpendicular angle with respect to the plane of the current collector, and therefore the length of the sliding region of the negative electrode active material layer is significantly reduced.

[0190] In one embodiment, the adhesive tape may have a characteristic in which the adhesive strength is reduced by passing through the drying step (P230). In this case, the adhesive tape has a reduced adhesive strength during the drying step, and becomes peelable after drying, allowing for easy removal of the adhesive tape. Therefore, there is no need to perform a separate cutting process to remove the adhesive tape.

[0191] In another example, the adhesive tape may be a pressure-sensitive adhesive tape. Pressure-sensitive adhesive tapes have a relatively low adhesive strength, and thus, during the peeling and removal step of the adhesive tape, the phenomenon of the electrode active material being detached due to the peeling force of the adhesive tape can be minimized. The adhesive strength of the adhesive tape may be specifically 20 gf / inch or less, preferably 15 gf / inch or less, and more preferably 10 gf / inch or less.

[0192] The above negative electrode can be manufactured by applying a negative electrode slurry containing a negative electrode active material onto a negative electrode current collector and drying it. The negative electrode slurry can be manufactured by mixing and stirring a negative electrode active material, a binder, and a conductive material together in a solvent, and may optionally further include additives such as fillers.

[0193] The negative electrode current collector is a metal having high conductivity and to which the negative electrode slurry can easily adhere, and any metal that is non-reactive within the voltage range of the battery can be used. Specifically, copper, stainless steel, aluminum, nickel, titanium, sintered carbon; stainless steel surface-treated with carbon, nickel, titanium or silver; aluminum-cadmium alloy; non-conductive polymer surface-treated with a conductive material; or conductive polymer can be used. In addition, the bonding strength of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and the negative electrode current collector can be used in various forms such as a film, sheet, foil, net, porous body, foam, or non-woven fabric.

[0194] The above negative active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO x (0 < x < 2), SnO2, vanadium oxide, lithium vanadium oxide, and other metal oxides capable of doping and dedoping lithium; or composites containing the above metallic compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, and any one or a mixture of two or more of these may be used. A metallic lithium thin film may also be used as the negative electrode active material.

[0195] The above negative active material may be included in an amount of about 80 wt% to 99.5 wt% or 88 wt% to 99 wt% relative to the total weight of the negative active material layer, but the content is not limited thereto.

[0196] The above binder is not particularly limited as long as it is a component that assists in the bonding of the negative electrode active material and the conductive material and the bonding to the current collector, and examples thereof include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, and various copolymers.

[0197] The above binder may typically be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0198] The conductive material is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, and the like; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0199] The above-mentioned conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the negative electrode active material layer.

[0200] The above filler is optionally used as a component that suppresses expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, olefin polymers such as polyethylene and polypropylene; fibrous materials such as glass fiber and carbon fiber can be used.

[0201] According to one embodiment of the present invention, the slope of the negative electrode sliding region may be 0.15 or more. Here, the slope refers to the value of b, which is the maximum thickness of the negative electrode active material layer of the negative electrode sliding region with respect to the length a in the electric field direction of the negative electrode sliding region. The slope of the negative electrode sliding region being 0.15 or more is a very large level compared to the slope of a conventional negative electrode sliding region, and as the slope of the negative electrode sliding region has the above range, the risk of reversal of the NR Ratio can be reduced.

[0202] The lithium secondary battery of the present invention can be manufactured using conventional methods known in the art. For example, it can be manufactured by inserting a separator between the positive and negative electrodes and injecting an electrolyte.

[0203] The above separator can be any porous substrate typically used as a separator in lithium secondary batteries. Examples include, but are not limited to, a polyolefin-based porous membrane or non-woven fabric. In particular, one having low resistance to electrolyte ion movement and excellent electrolyte moisture retention capacity is preferred.

[0204] Examples of the above polyolefin porous membrane include a membrane formed from a single or mixed polymer of polyolefin polymers such as polyethylene, polypropylene, polybutylene, polypentene, etc., such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene.

[0205] The above nonwoven fabric may include, in addition to polyolefin-based nonwoven fabrics, nonwoven fabrics formed from polymers such as polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalene, either singly or in combination. The structure of the nonwoven fabric may be a spunbond nonwoven fabric composed of long fibers or a meltblown nonwoven fabric.

[0206] The thickness of the porous substrate is not particularly limited, but may be 5 to 50 μm, and the pore size and pore content present in the porous substrate are also not particularly limited, but may be 0.01 to 50 μm and 10 to 95%, respectively.

[0207] Meanwhile, in order to improve the mechanical strength of the separator composed of the porous substrate and to suppress short circuits between the anode and cathode, a porous coating layer including inorganic particles and a binder polymer may be further included on at least one side of the porous substrate.

[0208] Meanwhile, in the lithium secondary battery, the electrolyte may include an organic solvent and lithium salt commonly used in electrolytes, and is not particularly limited.

[0209] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC) can be used.

[0210] Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.

[0211] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the lithium salt be included in the electrolyte at a concentration of approximately 0.6 mol% to 2 mol%.

[0212] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0213] The lithium secondary battery of the present invention can be manufactured by forming an electrode assembly by placing a separator between the positive and negative electrodes, placing the electrode assembly in the pouch-shaped outer material, and then injecting an electrolyte. Alternatively, the electrode assembly can be manufactured by stacking the electrode assembly, impregnating it with an electrolyte, and placing the resulting product in a battery case and sealing it.

[0214] The lithium secondary battery according to the present invention has excellent discharge capacity, output characteristics, and safety, and is therefore useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in electric vehicles such as energy storage systems (ESS) and hybrid electric vehicles (HEVs).

[0215]

[0216] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and are not intended to limit the scope of the present invention.

[0217]

[0218] Example

[0219] Lithium transition metal phosphate with an average particle size D 50 This 1.0 μm, single-structure primary particle, LiFePO4, carbon nanotubes (CNTs) as a conductive material, and polyvinylidene fluoride (PVdF) with a weight-average molecular weight (Mw) of 630,000 g / mol as a fluorinated binder were introduced into N-methylpyrrolidone (NMP) solvent. A positive electrode slurry was prepared by mixing at 2500 rpm for 90 minutes using a homo-disperse.

[0220] In the above positive electrode slurry, lithium transition metal phosphate, conductive material, and fluorine-based binder were present in a weight ratio of 96.5:1.0:2.5, and the solid content of the positive electrode slurry was 62 wt%.

[0221] The anode slurry was applied to a 20 μm thick aluminum film at a concentration of 600 mg / 25 cm2. At this time, the anode slurry was applied using a slot die with a built-in core as shown in Fig. 6.

[0222] The preliminary anode coated with the above anode slurry was dried and rolled, and slit along a slitting line (SL1) extending from the transverse direction (TD) center of the anode slurry coated portion along the transport direction of the preliminary anode, as shown in Fig. 11 (a). The slit preliminary anode was notched with electrode tabs and cut to the size of a unit electrode, as shown in Fig. 12, thereby completing the manufacture of the anode.

[0223]

[0224] Comparative example

[0225] In the coating process of the positive electrode slurry, the positive electrode slurry was coated using a slot die with a built-in core as shown in FIG. 3, and in the slitting process, the preliminary positive electrode was slit along the slitting line in the center of the semi-coated portion as shown in FIG. 1, except that the positive electrode was manufactured in the same manner as in the above example.

[0226]

[0227] Experimental Example 1: Measurement of the thickness ratio of the anode

[0228] The thickness T of the positive electrode active material layer measured at multiple points along the transverse direction (TD) in each of the above examples and comparative examples P Wow, the thickness T of the central part of the positive electrode active material layer C Measure the above T C The above T for values P The thickness ratio, which is the ratio of the values, was calculated and the results are shown in Fig. 17 (Example) and Fig. 18 (Comparative Example).

[0229] Referring to these drawings, it can be confirmed that the preliminary positive electrode according to the embodiment has a uniform thickness of the positive electrode active material layer with a thickness ratio value of 1 regardless of the location. On the other hand, the preliminary positive electrode according to the comparative example has a thickness ratio distribution of 0.8 to 1 depending on the location, so it can be predicted that a deviation in the rolling density will occur during rolling due to a deviation in the thickness of the positive electrode active material layer.

[0230]

[0231] Experimental Example 2: Observation of the desorption of the anode

[0232] Whether or not the positive electrode active material layer detached from the positive electrode of the above examples and comparative examples was visually observed, and the photographs are shown in Fig. 19. Referring to Fig. 19, in the positive electrode of the examples, the rolling density was uniform, so the positive electrode active material layer did not detach during the notching and cutting processes. On the other hand, in the positive electrode of the comparative example, it can be confirmed that the positive electrode active material layer detached from a portion with a relatively low rolling density due to the non-uniform rolling density.

[0233] As described above, the positive electrode manufactured according to the embodiment of the present invention is expected to have a higher capacity than a conventional positive electrode because the detachment of the positive electrode active material layer is minimized during the notching and cutting processes.

Claims

1. A process for manufacturing a cathode slurry containing a cathode active material; and A coating process for manufacturing a preliminary positive electrode by applying the positive electrode slurry onto a current collector using a slot die; The shim built into the slot die used in the above coating process is A method for manufacturing an anode, characterized in that the anode slurry does not have a protrusion for forming a semi-coated portion with a relatively thin coating thickness.

2. In claim 1, The process of drying and rolling the above-mentioned preliminary anode; A process of slitting the reserve anode along one or more slitting lines parallel to the transport direction (MD) of the reserve anode; and A method for manufacturing an anode, further comprising a notching and cutting process of notching an anode tab in a slitted spare anode and cutting it to the size of a unit anode; 3. In claim 1, The above slot die, Two or more die blocks; and A method for manufacturing an anode including a core interposed between the above die blocks to form a slot.

4. In claim 3, The above planted, a base extending in a first direction, which is the width direction of the die block; and A method for manufacturing an anode including a guide connected to the base and extending in a direction perpendicular to the first direction.

5. In claim 4, The above planted, A method for manufacturing an anode having no protrusion extending in a direction perpendicular to the first direction, in addition to the above guide.

6. In claim 1, A method for manufacturing a positive electrode, characterized in that the positive electrode active material is a lithium transition metal phosphate represented by the following chemical formula 1. [Chemical Formula 1] Li 1+a M1 1-x M2 x (PO y-b D) b In the above chemical formula 1 M1 is one or more elements selected from Fe, Mn, Co, Ni, Cu, Zn, and Mg, M2 is one or more elements selected from any one of Groups 2 to 15, excluding element M1, D is one or more selected from the group consisting of F, S and N, -0.5≤a≤+0.5, 0≤x≤0.8, 3.95≤y≤4.05, 0≤b≤1.

7. In claim 1, A method for manufacturing a positive electrode, wherein the positive electrode slurry comprises a positive electrode active material, a binder, and a conductive agent in a weight ratio of 94 to 99: 0.5 to 4: 0.5 to 4.

8. In claim 1, After the above coating process, The thickness (T) of the positive electrode active material layer measured at an arbitrary point (P) selected along the transverse direction (TD) of the above-mentioned positive electrode P ) and the thickness T of the central part of the positive electrode active material layer C A method for manufacturing a positive electrode satisfying the following condition 1. [Condition 1] 0.975≤T P / T C ≤1.025 However, the above P is an arbitrary point selected in the flattening area excluding the sliding area at the end of the reserve anode.

9. In claim 2, A method for manufacturing an anode, characterized in that, during the above slitting process, at least one of the slitting lines is provided on the anode slurry application portion.

10. In claim 2, A method for manufacturing a positive electrode, characterized in that, in the above slitting process, the cut surface of the slit positive electrode slurry application portion is slit so as to be perpendicular to the plane of the current collector.

11. A positive electrode comprising a positive electrode body having a positive electrode active material layer disposed on one or both sides of the positive electrode current collector; and a positive electrode tab protruding from one side of the positive electrode body. Rolling density RD measured at an arbitrary point (P) selected from the lower part of the anode opposite to the above anode tab B and rolling density average value RD A is a positive electrode that satisfies the following condition 2. [Condition 2] 0.975≤ RD B / RD A ≤1.025 However, the above P is an arbitrary point selected in the flattening region excluding the sliding region of the terminal end in the electric field direction of the positive electrode active material layer.

12. In claim 11, The above positive electrode active material layer is a positive electrode including a lithium transition metal phosphate represented by chemical formula 1 as a positive electrode active material. [Chemical Formula 1] Li 1+a M1 1-x M2 x (PO y-b D) b In the above chemical formula 1 M1 is one or more elements selected from Fe, Mn, Co, Ni, Cu, Zn, and Mg, M2 is one or more elements selected from any one of Groups 2 to 15, excluding element M1, D is one or more selected from the group consisting of F, S and N, -0.5≤a≤+0.5, 0≤x≤0.8, 3.95≤y≤4.05, 0≤b≤1.

13. A lithium secondary battery having a structure in which an electrode assembly is stored inside a pouch outer material together with an electrolyte, The above electrode assembly includes a positive electrode and a negative electrode, The above anode is, It includes a positive electrode body and a positive electrode tab protruding from one side of the positive electrode body, Rolling density RD measured at an arbitrary point (P) selected from the lower part of the anode opposite to the above anode tab B and rolling density average value RD A A lithium secondary battery satisfying the following condition 2. [Condition 2] 0.975≤ RD B / RD A ≤1.025 However, the above P is an arbitrary point selected in the flattening region excluding the sliding region of the terminal end in the electric field direction of the positive electrode active material layer.

14. In claim 13, The above cathode is, The upper part of the cathode facing the lower part of the anode, The thickness plane of the negative electrode active material layer includes a negative electrode sliding region inclined with respect to the negative electrode current collector plane, A lithium secondary battery, characterized in that the length of the cathode sliding region in the electrical direction is 3 mm or less.

15. In claim 13, A lithium secondary battery wherein the length of the negative electrode sliding region in the electrical direction is 1 mm or less.

16. In claim 13, A lithium secondary battery having a slope of the above-mentioned negative electrode sliding region of 0.15 or more. The above slope means the value of b, which is the maximum thickness of the negative active material layer in the negative sliding region, with respect to the length a in the electric field direction of the negative sliding region.

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