Positive electrode for lithium secondary battery and method for producing same

Abstract

The present invention relates to a positive electrode for a lithium secondary battery and a manufacturing method thereof, the positive electrode having a cross-sectional structure including an insulating layer and a positive electrode active material layer sequentially on a positive electrode current collector, and the insulating layer completely covers the inside edge of the positive electrode active material layer. As a result, the positive electrode is easy to control the shape of the edge (or end) of the positive electrode active material layer, and the capacity per unit area / weight of the end of the positive electrode active material layer is significantly reduced. Therefore, the positive electrode has an advantage that it is easy to control the N / P ratio when assembled with a negative electrode, and can be applied to various lithium secondary battery models.

Description

[Technical field]

[0001] The present invention relates to a positive electrode for a lithium secondary battery and a method for producing the same.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0079042 filed on June 28, 2022 and Korean Patent Application No. 10-2023-0082429 filed on June 27, 2023, and all contents disclosed in the disclosure of said Korean patent applications are incorporated herein by reference. [Background technology]

[0003] 2. Description of the Related Art In recent years, lithium secondary batteries have been widely used not only in small devices such as portable electronic devices, but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles and power storage devices.

[0004] Such a lithium secondary battery is a chargeable and dischargeable power generating element having a laminated structure of a positive electrode / separator / negative electrode, and the positive electrode generally contains a lithium metal oxide as a positive electrode active material, and the negative electrode generally contains a carbon-based negative electrode active material such as graphite. In addition, the lithium secondary battery has a configuration in which lithium ions released from the positive electrode during charging are absorbed into the carbon-based negative electrode active material of the negative electrode, and lithium ions contained in the carbon-based negative electrode active material during discharging are absorbed into the lithium metal oxide of the positive electrode, thereby repeatedly charging and discharging the battery.

[0005] One of the factors that influence the performance of a lithium secondary battery is the capacity ratio of the active materials contained in the positive electrode and the negative electrode. The capacity ratio of each electrode active material can be expressed as the N / P ratio. The N / P ratio is a value obtained by dividing the total capacity of the negative electrode calculated by taking into account the capacity per area and / or weight of the negative electrode by the total capacity of the positive electrode calculated by taking into account the capacity per area and / or weight of the positive electrode, and since it has a significant effect on the safety and capacity of the battery, it is generally adjusted to have one or more values.

[0006] However, a sliding phenomenon is induced at the ends of the electrode mixture layer containing the active material during the manufacture of the positive and negative electrodes. Therefore, it is difficult to keep the N / P ratio constant at each end of the positive and negative electrodes. In particular, if the N / P ratio is less than 1, lithium ions are not fully intercalated into the negative electrode active material during charging of the battery, but are precipitated on the surface of the negative electrode, forming dendrites. The dendrites formed in this way may induce an internal short circuit in the battery, thereby reducing the safety of the battery.

[0007] In addition, when an electrode is manufactured by slitting according to a coating pattern of an electrode mixture layer in order to improve productivity, there is a problem that a ratio inversion phenomenon frequently occurs. In order to prevent this, a method of forming a coating width of a negative electrode mixture layer wider than that of a positive electrode mixture layer has been applied in the past. However, when the negative electrode mixture layer is formed to have a wide width, there is a limitation that the amount of slurry for forming the negative electrode mixture layer increases, thereby increasing the process cost. In addition, when the negative electrode slurry is applied to a wide width on the negative electrode current collector, the tab part of the manufactured negative electrode becomes narrow, which not only causes interference problems during notching and welding of the tab, but also limits the applicable battery models because it is difficult to control the electrode position during electrode stacking such as zigzag stacking.

[0008] Therefore, there is a demand for the development of electrode technology that can be applied to various battery models while more easily controlling the N / P ratio of the positive and negative electrodes and having excellent processability and productivity. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Korean Patent Publication No. 10-2015-0028457 [Patent Document 2] Korean Patent Publication No. 10-2016-0125720 Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, an object of the present invention is to provide an electrode for a lithium secondary battery, which can easily control the N / P ratio of the positive electrode and the negative electrode, has high processability and productivity, and is applicable to various battery models, and a method for producing the same. [Means for solving the problem]

[0011] In order to solve the above-mentioned problems, in one embodiment, the present invention comprises: a positive electrode current collector, an insulating layer provided on at least one surface of the positive electrode current collector, and a positive electrode active material layer provided on the insulating layer, The insulating layer is discontinuously disposed on the positive electrode current collector based on a cross-sectional structure crossing from one side where a positive electrode tab is disposed to the other side where a positive electrode tab is not disposed, and provides an electrode for a lithium secondary battery having a structure in which the insulating layer is completely covered by the positive electrode active material layer.

[0012] In this case, the positive electrode active material layer may be divided into a flat portion located in a central region and having a constant thickness based on a cross-sectional structure crossing from one side where a positive electrode tab is disposed to the other side where the positive electrode tab is not disposed, a sliding portion located at an edge of the flat portion and having a thickness gradient, and a boundary portion located between the flat portion and the sliding portion, and the insulating layer may be located inside at least one of the sliding portion and the boundary portion.

[0013] In addition, the insulating layer may have a length of 30 mm or less based on a cross-sectional structure extending from one side where the positive electrode tab is disposed to the other side where the positive electrode tab is not disposed.

[0014] The insulating layer may have a thickness ratio of 30% or less based on the average thickness of the flat portion.

[0015] The insulating layer is made of Al 2 O 3 , Cr 2 O 3 , TiO 2, SiO 2 , ZrO 2 and Fe 2 O 3 and one or more binders selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, polyvinyl acetate, and styrene butadiene rubber.

[0016] The insulating layer may also contain 50% by weight or less of a metal oxide and 50% by weight or more of a binder.

[0017] In addition, the sliding portion of the active material layer may further include an auxiliary insulating layer on the outer side.

[0018] The auxiliary insulating layer is made of Al 2 O 3 , Cr 2 O 3 , TiO 2 , SiO 2 , ZrO 2 and Fe 2 O 3 and one or more binders selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, polyvinyl acetate, and styrene butadiene rubber, and the metal oxide and binder of the auxiliary insulating layer may be the same as or different from the metal oxide and binder contained in the insulating layer.

[0019] In one embodiment, the present invention further comprises: forming an insulating layer on at least one surface of a positive electrode current collector; forming a positive electrode active material layer on the formed insulating layer, The insulating layer is patterned along the running direction of the positive electrode current collector, is discontinuously disposed on the positive electrode current collector based on a cross-sectional structure crossing from one side where a positive electrode tab is disposed to the other side where a positive electrode tab is not disposed, and has a structure in which the insulating layer is completely covered by a positive electrode active material layer.

[0020] Here, the step of forming the insulating layer may be performed using a slot die coater, a slot nozzle coater, or a gravure coater.

[0021] The insulating layer may be formed using an insulating layer coating composition containing a metal oxide and a binder, and the insulating layer coating composition may have a viscosity of 1,000 to 10,000 cps at 25°C.

[0022] In addition, the step of forming the active material layer may be performed by a wet process using a positive electrode slurry including a positive electrode active material and a binder, or a dry process using a positive electrode film including a positive electrode active material and a binder.

[0023] Also, the step of forming the active material layer may further include forming an auxiliary insulating layer on a sliding portion of the formed active material layer.

[0024] Further, in one embodiment, the present invention provides There is provided an electrode assembly for a lithium secondary battery, comprising the above-described positive electrode of the present invention, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. Effect of the Invention

[0025] The positive electrode for a lithium secondary battery according to the present invention has a cross-sectional structure in which an insulating layer and a positive electrode active material layer are sequentially arranged on at least one surface of a positive electrode current collector, and the insulating layer is completely covered on the inner side of the edge of the positive electrode active material layer. As a result, the positive electrode is easy to control the shape of the edge (or end) of the positive electrode active material layer, and the capacity per unit area / weight of the end of the positive electrode active material layer is significantly reduced. Therefore, the positive electrode has an advantage that it is easy to control the N / P ratio when assembled with the negative electrode, and can be applied to various battery models. [Brief description of the drawings]

[0026] [Figure 1] 1A and 1B are a plan view and a cross-sectional view showing the positions and cross-sectional structures of an insulating layer and a positive electrode active material layer formed on a positive electrode current collector during the manufacture of a positive electrode in one embodiment according to the present invention. [Diagram 2] 2A and 2B are a plan view and a cross-sectional view showing a positive electrode structure produced when punching (or notching) a positive electrode current collector on which an insulating layer and an active material layer are formed as in FIG. 1. [Diagram 3] 2A and 2B are a plan view and a cross-sectional view showing a positive electrode structure produced when punching (or notching) a positive electrode current collector on which an insulating layer and an active material layer are formed as in FIG. 1. [Figure 4] 1 is a cross-sectional view illustrating a structure of a positive electrode assembly according to the present invention. [Diagram 5] 1 is a cross-sectional view illustrating a structure of a positive electrode assembly according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Since the present invention can be modified in various ways and can have various embodiments, specific embodiments are described in detail in the detailed description.

[0028] However, this is not intended to limit the invention to any particular embodiment, but is to be understood as including all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0029] In the present invention, the terms "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are to be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0030] In addition, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion in between. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion in between. In addition, in the present application, being "on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0031] The present invention will now be described in more detail.

[0032] <Positive electrodes for lithium secondary batteries> In one embodiment, the present invention comprises: a positive electrode current collector, an insulating layer provided on at least one surface of the positive electrode current collector, and a positive electrode active material layer provided on the insulating layer, The insulating layer is discontinuously disposed on the positive electrode current collector based on a cross-sectional structure crossing from one side where a positive electrode tab is disposed to the other side where a positive electrode tab is not disposed, and provides an electrode for a lithium secondary battery having a structure in which the insulating layer is completely covered by the positive electrode active material layer.

[0033] The electrode for a lithium secondary battery according to the present invention is an electrode applied to a lithium secondary battery, and may be a positive electrode, which is required to have a small capacity per area / per weight at the end of the active material layer, among positive and negative electrodes.

[0034] The positive electrode for lithium secondary battery includes a positive electrode active material layer provided on at least one surface of a positive electrode current collector, and an insulating layer between the positive electrode active material layer and the positive electrode current collector. In this case, the insulating layer is located in a region where the thickness of the active material layer is thin, specifically, on the edge of the active material layer, so that the N / P ratio of the electrode itself can be easily controlled. The N / P ratio has an advantage that it can be controlled even in a positive electrode manufacturing process using a coating pattern or when the manufactured positive electrodes are stacked.

[0035] FIG. 1 shows a surface view and a cross-sectional view of a positive electrode current collector on which an insulating layer and a positive electrode active material layer are formed during the production of a positive electrode according to the present invention.

[0036] 2 and 3 are cross-sectional views showing the structure of a positive electrode produced when the positive electrode current collector shown in FIG. 1 is punched (or notched).

[0037] Hereinafter, the structure of the positive electrode for a lithium secondary battery according to the present invention will be described with reference to FIGS.

[0038] The positive electrode 1 for a lithium secondary battery according to the present invention has a cross-sectional structure in which a positive electrode active material layer 30 is provided on a positive electrode current collector 10, and an insulating layer 20 is disposed between them. That is, the positive electrode 1 for a lithium secondary battery has a structure in which the insulating layer 20 and the positive electrode active material layer 30 are sequentially laminated on the positive electrode current collector 10.

[0039] At this time, the positive electrode active material layer 30 is a layer that realizes the electrical activity of the positive electrode 1, and is manufactured by applying a positive electrode slurry containing a positive electrode active material that realizes an electrochemical oxidation-reduction reaction during charging and discharging of a lithium secondary battery to at least one surface of the positive electrode current collector 10, and then drying and rolling the same. The positive electrode active material layer 30 manufactured in this manner is divided into a flat portion 31b located in a central region and maintained at a constant thickness based on a cross-sectional structure (A-A', hereinafter referred to as "cross-sectional structure A-A'") that crosses from one side A' where the positive electrode tab 50 is arranged to the other side A where the positive electrode tab 50 is not arranged, as shown in Figs. 1 to 3, a sliding portion 32 located at the edge of the flat portion and having a thickness gradient, and a boundary portion 31a located between the flat portion and the sliding portion.

[0040] Specifically, the positive electrode active material layer 30 includes a flat portion 31b having a ratio of 90% or more of the total length of the positive electrode active material layer 30 in the cross-sectional structure A-A'. The flat portion 31b refers to a region having a constant thickness and a flat surface. The flat portion 31b is a region constituting most of the positive electrode active material layer 30, and may have a length ratio of 93% or more, 95% or more, 97% or more, or 96% to 99% of the total length of the positive electrode active material layer 30. In the present invention, the length ratio of the flat portion 31b in the positive electrode active material layer 30 is adjusted to the above range, thereby making it possible to further increase the energy density of the positive electrode.

[0041] In addition, since the flat portion 31 b occupies 90% or more of the entire length of the positive electrode active material layer 30 , the average thickness of the flat portion 31 b may be similar to or the same as the average thickness of the positive electrode active material layer 30 .

[0042] In this case, the average thickness of the positive electrode active material layer 30 may be 50 μm to 500 μm, specifically, 50 μm to 400 μm, 50 μm to 300 μm, 50 μm to 200 μm, 50 μm to 150 μm, 100 μm to 300 μm, 150 μm to 450 μm, 200 μm to 400 μm, 250 μm to 500 μm, 80 μm to 190 μm, 80 μm to 140 μm, 100 μm to 250 μm, or 130 μm to 190 μm.

[0043] Further, a boundary portion 31a is located outside the flat portion 31b, and a sliding portion 32 is located outside the boundary portion 31a.

[0044] As an example, the boundary portion 31a and the sliding portion 32 may be sequentially and continuously disposed on both sides of the flat portion 31b as shown in FIG.

[0045] As another example, the boundary portion 31 a and the sliding portion 32 may be sequentially and continuously arranged only on one side of the flat portion 31 b, specifically, on the side on which the positive electrode tab 50 is provided, by punching (or notching) the positive electrode sheet performed in the positive electrode manufacturing process, as shown in FIG. 3, and only a portion of them may be present or they may not be present on the other side on which the positive electrode tab 50 is not provided.

[0046] The sliding portion 32 is located at the edge of the positive electrode active material layer 30 and refers to a region having a thickness gradient. The sliding portion 32 may have a ratio of 3% or less of the entire length of the positive electrode active material layer 30 based on the cross-sectional structure A-A'. Specifically, the sliding portion 32 has a shape in which the thickness decreases at the outer edge of the positive electrode active material layer 30 in a region adjacent to the boundary portion 31a. In consideration of the energy density of the positive electrode, the sliding portion 32 may have a ratio of 2% or less, 1% or less, 0.5% or less, 0.01% to 1%, or 0.01% to 0.5% of the entire length based on the cross-sectional structure A-A' of the positive electrode active material layer 30. In this case, the above length ratio is an overall length ratio based on the cross-sectional structure A-A' of the positive electrode active material layer 30, and when sliding portions 32 are provided on both sides of the flat portion 31b as shown in FIG. 1, the length ratio of each sliding portion may be halved to 1 / 2 of the above length ratio.

[0047] The boundary portion 31a is located between the flat portion 31b and the sliding portion 32, and is a region that forms a boundary between them. Like the flat portion 31b, the boundary portion 31a may have a constant thickness and a flat surface. The boundary portion 31a may occupy the remaining length excluding the length ratio between the flat portion 31b and the sliding portion 32. For example, the boundary portion 31a may have a ratio of less than 7%, less than 5%, less than 4%, less than 2.5%, 0.09% to 3%, or 0.5 to 1% of the total length of the positive electrode active material layer 30 based on the cross-sectional structure A-A' of the positive electrode active material layer 30. When the boundary portion 31a is provided on both sides of the flat portion 31b like the sliding portion 32, the length ratio of each boundary portion may be reduced to half of the length ratio.

[0048] Furthermore, the length of the boundary portion 31a based on the cross-sectional structure A-A' may have a ratio of 50% to 300% to the average thickness of the positive electrode active material layer 30, and specifically may have a ratio of 50% to 200%, 50% to 150%, 50% to 100%, 100% to 300%, 100% to 200%, or 150% to 300%.

[0049] Furthermore, the boundary portion 31a may have a length that is 0.8 to 1.2 times the length of the sliding portion 32 based on the cross-sectional structure A-A', and may be the same as the length of the sliding portion 32 in some cases.

[0050] The present invention can more accurately control the position of the insulating layer provided inside the positive electrode active material layer by controlling the length ratio of the boundary portion 31a of the positive electrode active material layer 30 as described above. As a result, the present invention can prevent the N / P ratio of the electrode assembly from decreasing to less than 1 even if the end of the positive electrode is separated from the end of the negative electrode during assembly of the positive electrode and the negative electrode.

[0051] For this purpose, an insulating layer 20 is provided on the inner edge of the positive electrode active material layer 30. At this time, the insulating layer 20 is located on the inner edge of the active material layer 30 and induces a decrease in capacity per unit area / weight at the end of the positive electrode active material layer 30 based on the cross-sectional structure A-A'. At the same time, it has a function of adjusting the inclination angle (or sliding angle) and / or shape of the sliding part 32.

[0052] Specifically, the insulating layer 20 may be selectively disposed only on the inner periphery of the positive electrode active material layer 30 based on the cross-sectional structure A-A', and may have a structure in which it is discontinuously provided on the positive electrode current collector 10 when analyzing the cross-sectional structure A-A' of the positive electrode 1. In this case, there is an advantage that the energy density of the positive electrode 1 may be higher than when the insulating layer 20 is continuously disposed on the positive electrode current collector 10 to form one layer.

[0053] In addition, the insulating layer 20 is provided on the inner edge of the positive electrode active material layer 30, and its position can be suitably adjusted to adjust the energy density of the positive electrode and the N / P ratio during electrode assembly. Specifically, the insulating layer 20 can be located inside one or more of the boundary portion 31a and the sliding portion 32 of the positive electrode active material layer 30. For example, the insulating layer 20 can be located inside the boundary portion 31a or the sliding portion 32 of the positive electrode active material layer 30, and in some cases, one insulating layer 20 can be located across the boundary portion 31a and the sliding portion 32.

[0054] 2 and 3, the electrode 1 for a lithium secondary battery according to the present invention is manufactured by sequentially stacking an insulating layer 20 and an active material layer 30 on an electrode current collector 10, followed by punching (or notching). At this time, the insulating layer 20 may be disposed on an edge of a side where a positive electrode tab 50 is located, i.e., a tab portion (A' side), among edges of the positive electrode active material layer 30 of the punched positive electrode. In addition, the insulating layer 20 may be selectively further disposed on the other side edge of the tab portion, i.e., a bottom portion (A side).

[0055] In general, lithium may be precipitated on the surface of the negative electrode end during charging and discharging of a lithium secondary battery. One of the causes of lithium precipitation occurs when the N / P ratio, which indicates the capacity per unit area / weight of the positive electrode and negative electrode included in the electrode assembly, falls below 1 at the end. Therefore, in order to suppress lithium precipitation on the surface of the negative electrode end, it is preferable to prevent the N / P ratio at the end of the electrode assembly from falling below 1.

[0056] The present invention is characterized in that an insulating layer 20 is introduced at an end of the positive electrode active material layer 30 to reduce the capacity per unit area / weight at the end of the positive electrode active material layer 30. As a result, the positive electrode 1 can maintain an N / P ratio of 1 or more at the end of the electrode assembly when assembled with a negative electrode. Here, the end of the positive electrode active material layer 30 is a portion corresponding to a side surface of the positive electrode active material layer 30 in the cross-sectional structure A-A', and is included in the sliding part 32. Therefore, the positive electrode 1 according to the present invention can include an insulating layer 20 on the inside of the sliding part 32 including the end of the positive electrode active material layer 30.

[0057] In addition, the positive electrode 1 has different average thicknesses and loading amounts of the positive electrode active material layer 30 depending on the model and product specifications of the lithium secondary battery to which the electrode assembly is applied. The average thickness and loading amount of the positive electrode active material layer 30 can be adjusted by adjusting the viscosity of the positive electrode slurry used when forming the positive electrode active material layer 30. At this time, the degree to which the positive electrode slurry is pushed outward from the edge of the applied positive electrode slurry varies depending on the viscosity (in other words, "fluidity"), so the inclination angle (or sliding angle) and shape of the sliding part 32 of the positive electrode active material layer 30 can vary depending on the viscosity. The sliding part 32 of the positive electrode active material layer 30 may cause various safety problems such as internal short circuit depending on the inclination angle and shape, so it is necessary to control the inclination angle and shape. However, there is a restriction that the inclination angle and shape of the sliding part 32 are difficult to control when the sliding part 32 is present in the tab part (A' side) where the positive electrode tab 50 is arranged. Therefore, the present invention includes an insulating layer 20 on the inner side of the boundary portion 31a of the positive electrode active material layer 30, and can adjust the inclination angle (or sliding angle) and / or shape of the sliding portion 32. The insulating layer 20 can increase the inclination angle of the sliding portion 32 on the inner side of the boundary portion 31a when forming the positive electrode active material layer 30, and can control the shape of the sliding portion 32 by shortening the length ratio of the sliding portion 32.

[0058] Therefore, the positive electrode 1 according to the present invention may include the insulating layer 20 solely on the inner side of the boundary portion 31a or the sliding portion 32 of the positive electrode active material layer 30. Preferably, the positive electrode 1 may include one insulating layer 20 on the inner side across the boundary portion 31a and the sliding portion 32, as shown in FIG.

[0059] Furthermore, the insulating layer 20 according to the present invention may have a structure in which it is completely covered by the positive electrode active material layer 30 based on the cross-sectional structure A-A' and is not exposed to the outside. Since the insulating layer 20 has such a structure, even if an electrode assembly assembly process is performed after punching (or notching) in the electrode manufacturing process, the insulating layer 20 inside the active material layer 30 can be maintained. Therefore, the positive electrode 1 of the present invention includes the insulating layer 20 completely covered by the positive electrode active material layer 30, and the loading amount or capacity per unit area / weight of the positive electrode active material layer 30 can be effectively controlled regardless of the manufacturing method or process. In addition, the positive electrode active material layer 30 has a problem in that it is difficult to control the inclination angle (or sliding angle) or shape of the sliding portion 32 when the insulating layer 20 is not completely covered by the positive electrode active material layer 30.

[0060] In addition, since the insulating layer 20 has a structure in which it is completely covered by the positive electrode active material layer 30 without reducing the energy density of the positive electrode active material layer 30, the size of the insulating layer 20 can be controlled.

[0061] Specifically, the insulating layer 20 may have a length (or width) that satisfies a predetermined range based on the cross-sectional structure A-A'. For example, the insulating layer 20 may have a length of 30 mm or less based on the cross-sectional structure A-A', specifically, a length of 0.2 to 30 mm, 0.5 to 30 mm, 1 to 30 mm, 5 to 30 mm, 10 to 30 mm, 15 to 25 mm, 5 to 20 mm, 10 to 25 mm, 1 to 20 mm, 0.5 to 5 mm, 0.5 to 10 mm, 0.2 to 1 mm, or 10 to 15 mm.

[0062] For example, when the boundary between the uncoated portion of the electrode current collector and the sliding portion 32 is clear as in FIG. 1, the sliding portion 32 may have a length of 5 to 18 mm, or 1 to 4 mm.

[0063] The length (or width) of the insulating layer 20 must be included inside the boundary portion 31a and / or the sliding portion 32, and is therefore affected by the length (or width) and thickness of the sliding portion 32. Therefore, in the present invention, the shape of the sliding portion 32 and the capacity of the positive electrode active material layer 30 can be easily controlled by adjusting the length (or width) of the insulating layer 20 within the above-mentioned range.

[0064] Furthermore, the insulating layer 20 may have a thickness of 30% or less compared to the thickness of the flat portion. Specifically, the insulating layer 20 may have a thickness of 1 to 30%, 1 to 25%, 1 to 20%, 5 to 20%, 10 to 25%, 15 to 30%, 20 to 30%, 13 to 22%, or 8 to 20% compared to the thickness of the flat portion.

[0065] By adjusting the average thickness of the insulating layer 20 to the above range, the present invention can prevent the insulating effect of the insulating layer 20 and the capacity reduction effect at the end of the positive electrode active material layer 30 from being insufficiently realized due to an extremely thin thickness. In addition, the present invention can prevent the sliding angle and / or shape control of the end of the positive electrode active material layer 30 from becoming difficult due to an excessive thickness of the insulating layer 20.

[0066] In addition, the insulating layer 20 may be made of a material that has insulating properties and does not electrochemically exhibit charge / discharge capacity in order to reduce the capacity per unit area / weight at the end of the positive electrode active material layer 30. Specifically, the insulating layer 20 may have a structure in which inorganic particles exhibiting insulating properties are mixed with a binder. For example, the insulating layer 20 may be made of Al 2 O 3 , Cr 2 O 3 , TiO 2 , SiO 2 , ZrO 2 and Fe 2 O 3and one or more binders selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, polyvinyl acetate, and styrene butadiene rubber.

[0067] The metal oxide has an advantage that it can be insulating without exhibiting electrochemical capacitance, and at the same time, can realize mechanical properties similar to those of the active material layer 30. In addition, the binder has high miscibility with the binder applied to the positive electrode active material layer 30, and therefore can provide high adhesive strength with the positive electrode active material layer 30.

[0068] The insulating layer 20 may contain a metal oxide and a binder in a certain weight ratio. Specifically, the insulating layer 20 may contain 50% by weight or less of the metal oxide and 50% by weight or more of the binder.

[0069] For example, the insulating layer 20 may include 1-50%, 1-40%, 1-30%, 1-20%, or 1-10% by weight of metal oxide and 50-99%, 60-99%, 70-99%, 80-99%, or 90-99% by weight of binder.

[0070] In the present invention, by adjusting the weight ratio of the metal oxide to the binder contained in the insulating layer 20 within the above range, the adhesive strength between the insulating layer 20 and the positive electrode active material layer 30 can be improved. In addition, by adjusting the weight ratio of the metal oxide to the binder within the above range, the capacity per unit area / weight at the end of the positive electrode active material layer 30 can be reduced within a range that does not deteriorate the electrical properties of the electrode.

[0071] Furthermore, the positive electrode 1 for a lithium secondary battery according to the present invention may further include an auxiliary insulating layer 40 on the outer side of the sliding portion 32 of the positive electrode active material layer 30. The auxiliary insulating layer 40 may be disposed in a form in contact with the sliding portion of the positive electrode active material layer 30. Thus, the auxiliary insulating layer 40 may have a form provided continuously with the sliding portion of the positive electrode active material layer 30 in the cross-sectional structure of the positive electrode 1, and the side end of the sliding portion may be covered by the auxiliary insulating layer 40. Thus, the positive electrode 1 may prevent contact between the positive electrode and the negative electrode due to contraction of the separator occurring at the end of the positive electrode active material layer 30 when the battery is exposed to high temperatures. That is, the auxiliary insulating layer 40 may have a function of preventing contact between the positive electrode and the negative electrode due to contraction of the separator when the electrode assembly including the positive electrode 1 according to the present invention is exposed to high temperatures.

[0072] For this, the auxiliary insulating layer 40 may be made of a material that has low electrochemical electrical conductivity and low thermal conductivity to prevent heat generated in the positive electrode active material layer 30 from being transferred to the separator via the end while implementing insulating properties. Specifically, the auxiliary insulating layer 40 may have a structure in which inorganic particles exhibiting insulating properties and low thermal conductivity are mixed with a binder. For example, the auxiliary insulating layer 40 may be made of Al 2 O 3 , Cr 2 O 3 , TiO 2 , SiO 2 , ZrO 2 and Fe 2 O 3 and one or more binders selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, polyvinyl acetate, and styrene butadiene rubber.

[0073] In addition, the auxiliary insulating layer 40 may contain a certain weight ratio of the metal oxide and the binder. Specifically, the auxiliary insulating layer 40 may contain 50 wt % or less of the metal oxide and 50 wt % or more of the binder.

[0074] For example, the auxiliary insulating layer 40 may include 1-50%, 1-40%, 1-30%, 1-20%, or 1-10% by weight of metal oxide and 50-99%, 60-99%, 70-99%, 80-99%, or 90-99% by weight of binder.

[0075] Here, the metal oxide and binder of the auxiliary insulating layer 40 may have the same or different components and contents as those of the insulating layer 20 contained in the active material layer 30 .

[0076] Furthermore, the length (or width) of the auxiliary insulating layer 40 may satisfy a predetermined range based on the cross-sectional structure A-A'. For example, the insulating layer 20 may have a length (or width) of 30 mm or less based on the cross-sectional structure A-A', specifically, a length (or width) of 0.1 mm to 20 mm, 0.5 mm to 15 mm, 0.5 mm to 10 mm, 1 mm to 5 mm, 10 mm to 20 mm, 5 mm to 10 mm, or 3 mm to 8 mm.

[0077] In the present invention, by controlling the length (or width) of the auxiliary insulating layer 40 within the above-mentioned range, the contact area between the positive electrode active material layer 30 and the separator can be minimized, thereby preventing the separator from shrinking when exposed to high temperatures and improving the economic efficiency and processability of the manufactured positive electrode.

[0078] Meanwhile, the positive electrode active material layer 30 contains a positive electrode active material, and may further contain a conductive material, a binder, and other additives in some cases.

[0079] Specifically, the positive electrode active material is an active material capable of reversibly intercalating and deintercalating lithium ions, and may include at least one of a lithium metal composite oxide represented by the following Chemical Formula 1 and a lithium iron phosphate represented by the following Chemical Formula 2.

[0080] [Chemical formula 1] Li x [Ni y Coz Mn w M 1 v ]O u

[0081] [Chemical formula 2] Life 1-p M 2 p PO q

[0082] In the above chemical formulas 1 and 2, M 1 is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo; x, y, z, w, v, and u are within the range of 1.0≦x≦1.30, 0.6≦y<0.95, and 0.01, respectively. <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5であり、 M 2 is one or more doping elements selected from the group consisting of Ni, Co, Mn and V; p and q are 0.05≦p≦0.2 and 2≦q≦6, respectively.

[0083] For example, the lithium metal composite oxide represented by the above formula 1 is Li(Ni 0.6 Co 0.2 Mn 0.2 )O 2 , Li(Ni 0.7 Co 0.15 Mn 0.15 )O 2 , Li(Ni 0.8 Co 0.1 Mn 0.1 )O 2 , Li(Ni 0.9 Co 0.05 Mn 0.05 )O 2 , Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O 2 , Li(Ni 0.6 Co0.2 Mn 0.15 Zr 0.05 )O 2 and Li(Ni 0.7 Co 0.1 Mn 0.1 Zr 0.1 )O 2 The lithium iron phosphate represented by the above formula 2 may include one or more selected from the group consisting of LiFePO 4 etc.

[0084] The positive electrode active material may be included in an amount of 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight, based on 100 parts by weight of the positive electrode active material layer 30 as a whole.

[0085] The conductive material is used to improve the electrical performance of the positive electrode 1, and may be any conductive material commonly used in the art. Specifically, the conductive material may include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, denka black, ketjen black, super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0086] In addition, the conductive material may be included in an amount of 0.1 to 5 parts by weight, based on 100 parts by weight of the positive electrode active material layer 30 in total, and more specifically, may be included in an amount of 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight.

[0087] In addition, the binder plays a role of binding the positive electrode active material and the conductive material to each other, and may be used without any particular limitation as long as it has such a function. Specifically, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0088] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or the conductive material may be contained in an amount of 1 to 5 parts by weight, relative to 100 parts by weight of the total positive electrode active material layer 30.

[0089] Furthermore, the positive electrode 1 may be made of a positive electrode current collector 10 having high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, baked carbon, etc. may be used, and in the case of aluminum or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the positive electrode current collector may be suitably 3 to 500 μm, taking into consideration the conductivity and total thickness of the positive electrode to be manufactured.

[0090] The positive electrode for a lithium secondary battery according to the present invention has the above-mentioned configuration, and thus the capacity per unit area / per unit weight of the positive electrode active material loaded on the edge (or end) of the positive electrode active material layer can be significantly reduced. Therefore, the positive electrode has a high safety characteristic since the N / P ratio is reduced to less than 1 and lithium deposition from the negative electrode surface during charging and discharging of the lithium secondary battery can be prevented. In addition, the positive electrode has an advantage that it can be applied to various battery models since the N / P ratio can be easily controlled when assembled with the negative electrode.

[0091] <Method of manufacturing electrodes for lithium secondary batteries> In one embodiment, the present invention further comprises: forming an insulating layer on a positive electrode current collector; forming a positive electrode active material layer on the formed insulating layer, The insulating layer is patterned along the running direction of the positive electrode current collector, and is discontinuously disposed on the positive electrode current collector based on a cross-sectional structure crossing from one side where the positive electrode tab 50 is disposed to the other side where the positive electrode tab 50 is not disposed, and has a structure in which the insulating layer is completely covered by the positive electrode active material layer.

[0092] The method for producing a positive electrode for a lithium secondary battery according to the present invention relates to a method for producing the positive electrode for a lithium secondary battery according to the present invention described above.

[0093] In the past, efforts were made to control the inclination angle (or sliding angle) and shape of the sliding part formed at the edge of the positive active material layer, i.e., the end of the positive active material layer, from the perspective of the safety of lithium secondary batteries. For example, a method of adjusting the shim offset or shim shape, or adjusting the gap between the electrode current collector and the coater when applying the slurry that constitutes the active material layer, was applied. However, when adjusting the shim offset or shape, there are problems in that in-line control is not possible and there is a mechanical limit for fastening when applying the shim, and the method of adjusting the gap between the electrode current collector and the coater has a limitation in that there are many gap adjustment factors depending on the slurry composition, which reduces the reliability of the manufactured active material layer.

[0094] However, the method for manufacturing a positive electrode according to the present invention has a configuration in which, before forming a positive electrode active material layer on a positive electrode current collector, an insulating layer is preemptively formed at a position corresponding to the edge of the positive electrode active material layer, and then the positive electrode active material layer is formed so as to completely cover the insulating layer formed thereafter. As a result, the manufacturing method can easily control the inclination angle (or sliding angle) and / or shape of the edge of the positive electrode active material layer while minimizing changes in the electrochemical properties of the positive electrode active material layer.

[0095] Here, the step of forming the insulating layer may be performed by any method that can form an insulating layer before forming the positive electrode active material layer, without any particular limitation. Specifically, the step may be performed by using one or more coating devices selected from the group consisting of a slot die coater, a slot nozzle coater, and a gravure coater.

[0096] The insulating layer coating composition may be made of a material that has insulating properties and does not electrochemically exhibit charge / discharge capacity in order to reduce the capacity per unit area / weight at the end of the positive electrode active material layer. Specifically, the insulating layer coating composition may be a mixture of inorganic particles exhibiting insulating properties and a binder.

[0097] For example, the insulating layer coating composition may include Al 2 O 3 , Cr 2 O 3 , TiO 2 , SiO 2 , ZrO 2 and Fe 2 O 3 and one or more binders selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, polyvinyl acetate, and styrene butadiene rubber.

[0098] The metal oxide has an advantage that it can be insulating without exhibiting electrochemical capacitance and can simultaneously have mechanical properties similar to those of the active material layer after drying. In addition, the binder has high compatibility with the binder applied to the active material layer, and therefore can provide high adhesion to the active material layer.

[0099] The insulating layer coating composition may contain a metal oxide and a binder in a certain weight ratio. Specifically, the insulating layer coating composition may contain 50 wt % or less of a metal oxide and 50 wt % or more of a binder.

[0100] By way of example, the insulating layer coating composition may include 1-50%, 1-40%, 1-30%, 1-20%, or 1-10% by weight of metal oxide and 50-99%, 60-99%, 70-99%, 80-99%, or 90-99% by weight of binder.

[0101] In the present invention, by adjusting the weight ratio of the metal oxide and the binder contained in the insulating layer coating composition within the above range, the adhesive strength between the insulating layer and the active material layer can be improved, and the capacity at the end of the active material layer can be reduced without deteriorating the electrical properties of the electrode.

[0102] The insulating layer coating composition may have a viscosity of 1,000 to 10,000 cps at 25°C, specifically, a viscosity of 1,000 to 8,000 cps, 1,000 to 5,000 cps, 1,000 to 3,000 cps, 5,000 to 10,000 cps, 3,000 to 8,000 cps, or 2,000 to 5,000 cps at 25°C.

[0103] In the present invention, by controlling the viscosity of the insulating layer coating composition to the above viscosity, the length (or width) and average thickness of the insulating layer produced can be formed to satisfy predetermined values, and thus the inclination angle and shape of the end of the positive electrode active material layer can be easily controlled.

[0104] In addition, the step of forming the active material layer may be performed by a wet process or a dry process.

[0105] For example, when the step of forming the active material layer is performed using a wet process, the step may be performed by coating a positive electrode slurry including a positive electrode active material and a binder on a positive electrode current collector having an insulating layer, and drying the coated positive electrode slurry.

[0106] In another example, when the step of forming the active material layer is performed by a dry process, the step of forming the active material layer may be performed by placing a film for a positive electrode including a positive electrode active material and a binder on a positive electrode current collector having an insulating layer, and laminating the film under pressure. In this case, the positive electrode slurry and the film for a positive electrode may include a positive electrode active material and a binder, and may further include a conductive material, other additives, and the like.

[0107] Specifically, the positive electrode active material is a positive electrode active material capable of reversibly intercalating and deintercalating lithium ions, and may include at least one of a lithium metal composite oxide represented by the following Chemical Formula 1 and a lithium iron phosphate represented by the following Chemical Formula 2.

[0108] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O u

[0109] [Chemical formula 2] Life 1-p M 2 p PO q

[0110] In the above chemical formulas 1 and 2, M 1is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo; x, y, z, w, v, and u are within the range of 1.0≦x≦1.30, 0.6≦y<0.95, and 0.01, respectively. <z≦0.5、0.01<w≦0.5、0≦v≦0.2、1.5≦u≦4.5であり、 M 2 is one or more doping elements selected from the group consisting of Ni, Co, Mn and V; p and q are 0.05≦p≦0.2 and 2≦q≦6, respectively.

[0111] For example, the lithium metal composite oxide represented by the above formula 1 is Li(Ni 0.6 Co 0.2 Mn 0.2 )O 2 , Li(Ni 0.7 Co 0.15 Mn 0.15 )O 2 , Li(Ni 0.8 Co 0.1 Mn 0.1 )O 2 , Li(Ni 0.9 Co 0.05 Mn 0.05 )O 2 , Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O 2 , Li(Ni 0.6 Co 0.2 Mn 0.15 Zr 0.05 )O 2 and Li(Ni 0.7 Co 0.1 Mn 0.1 Zr 0.1 )O 2 The lithium iron phosphate represented by the above formula 2 may include one or more selected from the group consisting of LiFePO 4 etc.

[0112] The positive electrode active material may be contained in an amount of 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight, based on 100 parts by weight of the entire positive electrode active material layer.

[0113] In addition, the conductive material is used to improve the electrical performance of the positive electrode, and may be any conductive material commonly used in the art. Specifically, the conductive material may include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, denka black, ketjen black, super P, channel black, furnace black, lamp black, thermal black, graphene, and carbon nanotubes.

[0114] The conductive material may be contained in an amount of 0.1 to 5 parts by weight, specifically 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight, relative to 100 parts by weight of the entire positive electrode active material layer.

[0115] In addition, the binder plays a role of binding the positive electrode active material and the conductive material to each other, and may be used without any particular limitation as long as it has such a function. Specifically, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0116] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or the conductive material may be contained in an amount of 1 to 5 parts by weight, relative to 100 parts by weight of the entire positive electrode active material layer.

[0117] Furthermore, the step of forming the positive electrode active material layer may further include a step of forming an auxiliary insulating layer on the outside of a sliding portion of the formed positive electrode active material layer. For example, when the step of forming the active material layer is performed by a wet process, an auxiliary insulating layer coating composition for forming the auxiliary insulating layer may be applied simultaneously with application of an electrode slurry including an electrode active material on an electrode collector, or an auxiliary insulating layer coating composition may be applied and dried successively after application of the electrode slurry, thereby forming the auxiliary insulating layer on the outside of the sliding portion of the active material layer.

[0118] As another example, when the step of forming the active material layer is performed by a dry process, a film for a positive electrode may be laminated on a positive electrode current collector on which an insulating layer is formed so that the insulating layer is completely covered, and then an auxiliary insulating layer coating composition for forming the auxiliary insulating layer may be applied to an outer end of the film for a positive electrode and dried to form the auxiliary insulating layer.

[0119] By applying the auxiliary insulating layer coating composition in the above manner, the present invention can prevent the positive electrode slurry applied on the positive electrode current collector from being pushed out to the uncoated area, which causes the inclination angle of the sliding part to become lower.

[0120] When the step of forming the active material layer is performed by a wet process, it may be performed in a manner commonly used in the art. Specifically, it may be performed using one or more coating devices selected from the group consisting of a slot die coater, a slot nozzle coater, and a gravure coater.

[0121] Meanwhile, the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention may further include a punching step after the step of forming an active material layer or the step of forming an auxiliary insulating layer on a sliding portion of the active material layer.

[0122] In this case, the punching step may punch the electrode such that the insulating layer disposed on the bottom is completely covered by the active material layer as shown in FIG. 2, or may punch the electrode such that the insulating layer disposed on the bottom is partially notched to expose an end of the insulating layer as shown in FIG. 3.

[0123] The method for manufacturing an electrode for a lithium secondary battery according to the present invention has the above-mentioned configuration, and thus can realize a cross-sectional structure in which an insulating layer and a positive electrode active material layer are sequentially formed on a positive electrode current collector, and the insulating layer is completely covered on the inner edge of the positive electrode active material layer. As a result, the capacity per unit area / weight of the positive electrode active material loaded on the edge (or end) of the positive electrode active material layer is significantly reduced. Therefore, the positive electrode has an advantage that it is easy to control the N / P ratio when assembling with a negative electrode, and can be applied to various battery models.

[0124] <Electrode assembly for lithium secondary battery> Furthermore, the present invention provides an electrode assembly for a lithium secondary battery, comprising the electrode according to the present invention described above.

[0125] The electrode assembly for a lithium secondary battery according to the present invention has a structure including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the positive electrode includes the positive electrode according to the present invention. The positive electrode included in the electrode assembly has the same structure as the positive electrode described above, and therefore a detailed description thereof will be omitted.

[0126] 4 and 5 are cross-sectional views showing a schematic structure of the electrode assembly. Referring to FIG. 4 and FIG. 5, the electrode assembly according to the present invention may have a structure including an anode 200 and a cathode 100 according to the present invention, with a separator 300 provided therebetween. The cathode 100 includes a cathode current collector 110, an insulating layer 120 provided on the cathode current collector, and a cathode active material layer 130 provided on the insulating layer. The active material layer 130 includes a flat portion having a constant thickness and located in a central region based on a cross-sectional structure A-A' crossing from one side where the cathode tab 50 is disposed to the other side where the cathode tab 50 is not disposed, a sliding portion located at an edge of the flat portion and having a thickness gradient, and a boundary portion located between the flat portion and the sliding portion. Here, the insulating layer 120 may have a structure in which it is located inside any one or more of the sliding portion and the boundary portion of the active material layer and is completely covered by them.

[0127] The positive electrode 100 having such a structure has an advantage that the capacity per unit area / weight of the positive electrode active material loaded on the edge (or end) of the positive electrode active material layer 130 is significantly reduced, and the N / P ratio is easily controlled when assembled with the negative electrode 200, so that it can be applied to various battery models. In addition, an electrode assembly including the same is highly unlikely to have an N / P ratio that falls below 1, so that it is possible to effectively prevent safety issues caused by lithium deposition on the negative electrode surface during charging and discharging of a lithium secondary battery.

[0128] In addition, the positive electrode 100 may further include an auxiliary insulating layer 140 on the outer side of the sliding portion of the positive electrode active material layer 130. In this case, the auxiliary insulating layer 140 may be disposed in contact with the sliding portion of the positive electrode active material layer 130. Thus, the auxiliary insulating layer 140 may have a shape provided continuously with the sliding portion of the positive electrode active material layer 130 in the cross-sectional structure of the positive electrode 100, and the side end of the sliding portion may be hidden by the auxiliary insulating layer 140. Thus, when the battery is exposed to high temperatures, the positive electrode 100 may prevent contact between the positive electrode 100 and the negative electrode 200 due to contraction of the separator 300 occurring at the end of the positive electrode active material layer 130.

[0129] The negative electrode 200, like the positive electrode 100, includes a negative electrode active material layer 220 containing a negative electrode active material on at least one surface of a negative electrode current collector 210.

[0130] The negative electrode active material layer 220 includes a carbon-based negative electrode active material as a negative electrode active material to realize electrical activity through a reversible oxidation-reduction reaction during charging and discharging of the battery.

[0131] The carbon-based negative electrode active material refers to a material mainly composed of carbon atoms, and may include graphite. The graphite may include at least one of natural graphite and artificial graphite.

[0132] For example, the carbon-based negative electrode active material may include mixed graphite obtained by mixing natural graphite and artificial graphite. In this case, the mixed graphite may be a mixture of natural graphite and artificial graphite in a weight ratio of 10-50:50-90 or 10-30:70-90. By adjusting the content ratio of natural graphite and artificial graphite as described above, the mixed graphite can prevent a decrease in adhesive strength between the negative electrode current collector 210 and the negative electrode active material layer 220 due to less than 10 parts by weight of natural graphite relative to the total weight, and can prevent a decrease in charge / discharge capacity of the negative electrode due to more than 50 parts by weight of natural graphite.

[0133] The carbon-based negative electrode active material is not particularly limited in shape, but preferably has the shape of a spherical graphite granule formed by the aggregation of a plurality of flake graphite. Examples of flake graphite include natural graphite and artificial graphite, as well as mesophase calcined carbon (bulk mesophase) made from tar pitch as a raw material, and graphitized cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.). In particular, the carbon-based negative electrode active material is preferably one assembled using a plurality of natural graphites having high crystallinity. One graphite granule may be formed by the aggregation of 2 to 100 flake graphite particles, preferably 3 to 20 flake graphite particles.

[0134] In addition, the carbon-based negative electrode active material has an average particle size (D50 Specifically, the average particle size (D) may be 0.5 μm to 15 μm, 0.5 μm to 10 μm, 5 μm to 20 μm, 10 μm to 20 μm, 12 μm to 18 μm, 2 μm to 7 μm, 0.5 μm to 5 μm, or 1 μm to 3 μm. 50 ) can be shown.

[0135] The average particle size of the carbon-based negative electrode active material may be advantageously small to maximize the degree of disorder in the expansion direction of each particle so as to prevent the expansion of the particles due to charging of lithium ions. However, if the particle size of the graphite is less than 0.5 μm, a large amount of binder may be required due to the increase in the number of particles per unit volume. On the other hand, if the maximum particle size exceeds 20 μm, the expansion becomes intense, and the adhesion between the particles and the current collector decreases due to repeated charging and discharging, so that the cycle characteristics may be significantly reduced.

[0136] The negative electrode 200 may include a predetermined silicon-based negative electrode active material in the negative electrode active material layer 220 together with the carbon-based negative electrode active material. The silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and may be silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), or silicon dioxide (SiO 2 The silicon-based negative electrode active material may contain silicon monoxide (SiO) and silicon dioxide (SiO 2 ) are uniformly mixed or composited and contained in the negative electrode active material layer 220, they are treated as silicon oxide (SiO q , where 0.8≦q≦2.5).

[0137] In addition, the negative electrode active material may be included in an amount of 85 parts by weight or more based on the total weight of the negative electrode active material layer 220, specifically, 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more.

[0138] In addition, the silicon-based negative electrode active material may be included in an amount of 0.1 to 30% by weight based on the total weight of the negative electrode active material, specifically, 0.5 to 20% by weight, 1 to 9% by weight, 5 to 15% by weight, 3 to 7% by weight, 11 to 19% by weight, 13 to 17% by weight, 15 to 20% by weight, 10 to 30% by weight, 20 to 30% by weight, 15 to 25% by weight, or 9 to 22% by weight. The present invention can improve the charge capacity per unit mass while reducing the lithium consumption amount and irreversible capacity loss during initial charge and discharge of the lithium secondary battery by adjusting the content of the carbon-based negative electrode active material and the silicon-based negative electrode active material contained in the negative electrode active material within the above range. In addition, the volume change of the negative electrode active material layer 220 during charge and discharge of the lithium secondary battery can be minimized to improve the structural stability of the negative electrode active material layer 220, thereby extending the life of the lithium secondary battery.

[0139] Meanwhile, the negative electrode active material layer 220 may further include, in addition to the carbon-based negative electrode active material as the main component, a conductive material, a binder, and other additives, if necessary.

[0140] The conductive material may include one or more of carbon black such as acetylene black and ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0141] For example, the negative electrode active material layer 220 may contain carbon black, carbon nanotubes, carbon fibers, etc., alone or in combination, as a conductive material.

[0142] At this time, the content of the conductive material may be 0.1 to 10 parts by weight, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, 2 to 6 parts by weight, or 0.5 to 2 parts by weight, based on 100 parts by weight of the total negative electrode active material layer. By controlling the content of the conductive material within the above range, the present invention can prevent a decrease in charge capacity due to an increase in the resistance of the negative electrode caused by a low content of the conductive material, and can prevent a decrease in charge capacity due to a decrease in the content of the negative electrode active material caused by an excessive amount of the conductive material, or a decrease in rapid charge characteristics due to an increase in the loading amount of the negative electrode active material layer 220.

[0143] In addition, the binder may be suitably used as a component that assists in bonding between the negative electrode active material and the conductive material and the current collector, within a range that does not reduce the electrical properties of the electrode. Specifically, the binder may include any one or more selected from the group consisting of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber (SBR), and fluororubber.

[0144] The content of the binder may be 0.1 to 10 parts by weight, specifically 0.1 to 8 parts by weight, 0.1 to 5 parts by weight, 0.1 to 3 parts by weight, or 2 to 6 parts by weight, based on 100 parts by weight of the total negative electrode active material layer 220. By controlling the content of the binder contained in the negative electrode active material layer 220 within the above range, the present invention can prevent a decrease in adhesive strength of the negative electrode active material layer 220 due to a low content of the binder, or a decrease in electrical properties of the electrode due to an excessive amount of the binder.

[0145] Furthermore, the average thickness of the negative electrode active material layer 220 may be 100 μm to 300 μm, specifically 100 μm to 250 μm, 100 μm to 250 μm, or 130 μm to 190 μm, and the average thickness may be the same as the average thickness of the flat region. By adjusting the average thickness of the negative electrode active material layer 220 to the above range, the present invention can improve the high-rate charge / discharge performance and energy density of a battery including the negative electrode.

[0146] The negative electrode current collector 210 is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and may be, for example, copper, stainless steel, nickel, titanium, calcined carbon, etc., and in the case of copper or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, etc. The average thickness of the negative electrode current collector 210 may be preferably 1 to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0147] The separator 300 is an insulating thin film having high ion permeability and mechanical strength, and is not particularly limited as long as it is a commonly used material in the art. Specifically, the separator 300 may include at least one polymer selected from polypropylene, polyethylene, and polyethylene-propylene copolymers, which are chemically resistant and hydrophobic. The separator 300 may have a porous polymer substrate such as a sheet or nonwoven fabric including the above-mentioned polymer, and may have a composite separator formed by coating organic or inorganic particles on the porous polymer substrate with an organic binder. The separator 300 may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0148] Meanwhile, the electrode assembly according to the present invention is not particularly limited, but may be applied to a lithium secondary battery having a configuration that may include a stack type, a zigzag type, or a zigzag stack type electrode assembly. For example, the electrode assembly according to the present invention may be applied to a zigzag type lithium secondary battery or a zigzag stack type lithium secondary battery.

[0149] The zigzag type lithium secondary battery and / or the zigzag stack type lithium secondary battery have the advantage of being highly productive and highly usable in terms of energy density since unit cells of the lithium secondary battery can be packed at high density in a limited space.

[0150] The present invention will now be described in more detail with reference to examples and experimental examples.

[0151] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0152] <Examples 1 to 10 and Comparative Examples 1 to 2. Production of Positive Electrodes for Lithium Secondary Batteries> An aluminum thin plate (length 20 cm, width 20 cm, thickness 10 μm) was prepared, and an insulating layer coating composition, a positive electrode slurry, and an auxiliary insulating layer coating composition were each prepared.

[0153] Specifically, the insulating layer coating composition and the auxiliary insulating layer coating composition each contain aluminum oxide (Al 2 O 3 30 parts by weight of PVDF and 70 parts by weight of PVDF were weighed and mixed uniformly to prepare the insulating layer coating composition and the auxiliary insulating layer coating composition, respectively, having a solid content of 3 to 10%.

[0154] The positive electrode slurry contains LiNi 0.7 Co 0.1 Mn 0.2 O 2 97.5 parts by weight of the positive electrode slurry, 1 part by weight of carbon nanotubes as a conductive material, and 1.5 parts by weight of PVDF as a binder were weighed and mixed with N-methylpyrrolidone to prepare the positive electrode slurry. At this time, the solid content of the prepared positive electrode slurry was about 65%.

[0155] Then, the insulating layer coating composition was first patterned on the prepared aluminum sheet, and the aluminum sheet on which the insulating layer coating composition was continuously applied was simultaneously coated with the positive electrode slurry and the auxiliary insulating layer coating composition. Then, it was dried in a vacuum oven at 120°C and rolled. The rolled electrode sheet was punched to manufacture a positive electrode for a lithium secondary battery in which an insulating layer was formed on the boundary portion of the positive electrode active material layer and on the inside of the sliding portion, as shown in FIG. 2.

[0156] At this time, the flat portion included in the positive electrode active material layer was formed so that the total length was about 27 cm based on the cross-sectional structure A-A'. The average thickness of the flat portion was about 120 μm based on the cross-sectional structure A-A', and the lengths of the sliding portion and the boundary portion were 5 mm and 5 mm, respectively, based on the cross-sectional structure A-A'. When the auxiliary insulating layer was formed, the length of the auxiliary insulating layer was 5 mm based on the cross-sectional structure A-A'. The length and average thickness of the insulating layer included inside the sliding portion and the presence or absence of the formation of the auxiliary insulating layer are as shown in Table 1.

[0157] [Table 1]

[0158] <Example 11. Production of positive electrode for lithium secondary battery> A positive electrode for a lithium secondary battery was manufactured in the same manner as in Example 1, except that an insulating layer was formed only on the inside of the sliding portion of the positive electrode active material layer. At this time, the length of the insulating layer provided on the positive electrode was 2 mm, and the height was 2 μm.

[0159] <Experimental Example> In order to evaluate the performance of the positive electrode produced according to the present invention, the following experiment was carried out.

[0160] a) Measuring the inclination angle of the sliding part Scanning electron microscope (SEM) photographs were taken of the cross sections of the positive electrodes produced in Examples 1 to 11 and Comparative Examples 1 and 2, and the inclination angle (or sliding angle) of the sliding portion of the active material layer was measured. The results are shown in Table 2 below.

[0161] b) Evaluation of the N / P ratio of the electrode assembly and the lithium deposition phenomenon A negative electrode active material in which natural graphite and artificial graphite were mixed in a weight ratio of 1:1 was prepared, and 97 parts by weight of the negative electrode active material and 3 parts by weight of styrene butadiene rubber (SBR) were mixed with water to form a slurry, which was then cast onto a copper sheet (length 150 cm, width 22 cm, and thickness 10 μm), dried in a vacuum oven at 130°C, and rolled to manufacture a negative electrode. In this case, the average thickness and capacity per unit area of ​​the negative electrode active material layer of the manufactured negative electrode were adjusted to be the same as the average thickness and capacity per unit area of ​​the positive electrode active material layer of the positive electrode. In addition, the length and height of the boundary and sliding parts of the negative electrode active material layer were adjusted to be the same as the length and height of the boundary and sliding parts of the positive electrode active material layer.

[0162] Five negative electrodes and five positive electrodes prepared in Examples 1 to 11 and Comparative Examples 1 to 2 were alternately arranged and stacked with a polypropylene separator having a thickness of 18 μm interposed therebetween to prepare an electrode assembly. At this time, the negative electrodes were assembled such that the sliding part of the negative active material layer was located about 2 mm outside the sliding part of the positive active material layer based on the cross-sectional structure A-A'.

[0163] The outer side (i.e., the boundary and sliding part of the negative active material layer) based on the boundary between the flat part and the boundary part of the negative active material layer inserted into the fabricated electrode assembly was defined as the "end of the electrode assembly", and the capacity per unit area (N / P ratio) of the end of the electrode assembly was measured. Specifically, in order to calculate the capacity per unit area (N / P ratio), (1) a natural logarithm graph regression equation was derived that shows the position of any point of the boundary and sliding part of the positive active material layer included in the end of the electrode assembly based on the cross-sectional structure A-A'. Then, (2) the area of ​​the negative active material layer and the positive active material layer that are in contact with each other at the end of the electrode assembly was calculated by integration, and the capacity per unit area (N / P ratio) was calculated by subtracting the area of ​​the insulating layer at that position.

[0164] The electrode assembly was then inserted into a pouch case and an electrolyte was injected. The electrolyte consisted of LiPF as a lithium salt in an organic solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7. 6 A liquid electrolyte containing added . The pouch case with the electrolyte injected was sealed to prepare a pouch-type lithium secondary battery, which was then charged in 0.33C CC (Constant Current) mode until the voltage reached 4.8V while maintaining the temperature at 45°C. The battery was then discharged in 0.33C CC (Constant Current) mode until the voltage reached 2.5V, and then further discharged in CV (Constant Voltage) mode until the current value decreased to 0.05% of the initial current value to activate the lithium secondary battery.

[0165] After that, the same charge and discharge cycle was repeated 3,000 times, and then the lithium secondary battery was disassembled and the electrode assembly was visually observed to check whether lithium metal was precipitated. The results are shown in Table 2.

[0166] C) Evaluation of battery energy density The pouch-type lithium secondary batteries were manufactured in the same manner as the lithium secondary batteries manufactured previously, and the manufactured lithium secondary batteries were charged and discharged to analyze the energy per unit volume. At this time, the charge and discharge proceeded between 2.5V and 4.2V, and the charge was measured by CC / CV and the discharge was measured by CC. The C-rate measurement standard was the energy at 3C when 1C was set to 60A, and the relative comparison of each measured energy density was made based on the energy density of Example 1, and is shown in Table 2.

[0167] [Table 2]

[0168] It can be seen that the positive electrode for a lithium secondary battery according to the present invention has a high energy density because it is easy to control the angle and / or shape of the sliding portion included in the edge of the active material layer, and it is easy to adjust the N / P ratio of the electrode assembly.

[0169] Specifically, it was shown that the positive electrodes produced in Examples 1 to 8 and 10 had a high inclination angle of the sliding part of 75° or more (specifically, about 80° or more or about 84° or more). In addition, it was confirmed that the N / P ratio of the lithium secondary batteries including these was maintained at 1 or more, and lithium did not precipitate from the negative electrode during charging and discharging. However, it was confirmed that the positive electrodes of Examples 8 and 10 had a high thickness of the insulating layer, making it difficult to control the shape of the positive electrode active material layer end, i.e., the sliding part, and a lifting phenomenon occurred during assembly of the electrode assembly.

[0170] It was also confirmed that the lithium secondary battery including the positive electrode produced in the examples had excellent energy density.

[0171] From these results, it can be seen that the positive electrode for a lithium secondary battery according to the present invention includes an insulating layer and a positive electrode active material layer sequentially on a positive electrode current collector, and has a cross-sectional structure in which the insulating layer completely covers the inside edge of the positive electrode active material layer, making it easy to control the shape of the edge (or end) of the positive electrode active material layer, significantly reducing the capacity per unit area / weight of the end of the positive electrode active material layer, and making it easy to control the N / P ratio of the electrode assembly.

[0172] Although the present invention has been described above with reference to preferred embodiments thereof, it will be understood that a person skilled in the art or having ordinary knowledge in the art may make various modifications and variations to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0173] Therefore, the technical scope of the present invention is not limited to the contents described in the Summary of the Invention of the specification, but is defined by the claims. [Explanation of symbols]

[0174] 1: Positive electrode for lithium secondary batteries 10: Electrode current collector 20: Insulating layer 30: Active material layer 31a: Boundary part 31b: Flat part 32: Sliding section 40: Auxiliary insulating layer 50: Plain section 100: Positive electrode 110: Positive electrode current collector 120: Positive electrode insulating layer 130: Positive electrode active material layer 140: Positive electrode auxiliary insulating layer 200: Negative electrode 210: Negative electrode current collector 220: Negative electrode active material layer C: Coating direction of insulating layer and active material layer S: Cutting line during punching (or notching)

Claims

1. a positive electrode current collector, an insulating layer provided on at least one surface of the positive electrode current collector, and a positive electrode active material layer provided on the insulating layer, the insulating layer is discontinuously disposed on the positive electrode current collector based on a cross-sectional structure crossing from one side where a positive electrode tab is disposed to the other side where a positive electrode tab is not disposed, and has a structure in which the insulating layer is completely covered by the positive electrode active material layer.

2. The positive electrode active material layer is divided into a flat portion located in a central region and having a constant thickness based on a cross-sectional structure crossing from one side where the positive electrode tab is disposed to the other side where the positive electrode tab is not disposed, a sliding portion located at an edge of the flat portion and having a thickness gradient, and a boundary portion located between the flat portion and the sliding portion, The positive electrode for a lithium secondary battery according to claim 1 , wherein the insulating layer is located inside at least one of the sliding portion and the boundary portion.

3. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the insulating layer has a length of 30 mm or less based on a cross-sectional structure extending from one side where the positive electrode tab is disposed to the other side where the positive electrode tab is not disposed.

4. The positive electrode for a lithium secondary battery according to claim 2 , wherein the insulating layer has a thickness ratio of 30% or less based on the average thickness of the flat portion.

5. The insulating layer is A ２ O ３ , Cr ２ O ３ , TiO ２ , SiO ２ , ZrO ２ and Fe ２ O ３ and one or more metal oxides selected from the group consisting of 2. The positive electrode for a lithium secondary battery according to claim 1, comprising one or more binders selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride copolymers, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, polyvinyl acetate, and styrene butadiene rubber.

6. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the insulating layer comprises 50% by weight or less of a metal oxide and 50% by weight or more of a binder.

7. 3. The positive electrode for a lithium secondary battery according to claim 2, wherein the sliding portion of the positive electrode active material layer further comprises an auxiliary insulating layer on an outer side based on a cross-sectional structure crossing from one side where the positive electrode tab is disposed to the other side where the positive electrode tab is not disposed.

8. The auxiliary insulating layer is A ２ O ３ , Cr ２ O ３ , TiO ２ , SiO ２ , ZrO ２ and Fe ２ O ３ and one or more metal oxides selected from the group consisting of 8. The positive electrode for a lithium secondary battery according to claim 7, comprising one or more binders selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride copolymers, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, polyvinyl acetate, and styrene butadiene rubber.

9. forming an insulating layer on at least one surface of a positive electrode current collector; forming a positive electrode active material layer on the formed insulating layer, the insulating layer is patterned along a running direction of the positive electrode current collector, is discontinuously disposed on the positive electrode current collector based on a cross-sectional structure crossing from one side where a positive electrode tab is disposed to the other side where a positive electrode tab is not disposed, and has a structure in which the insulating layer is completely covered by the positive electrode active material layer.

10. 10. The method of claim 9, wherein the forming of the insulating layer is performed using a slot die coater, a slot nozzle coater, or a gravure coater.

11. The insulating layer is formed using an insulating layer coating composition comprising a metal oxide and a binder; The method for producing a positive electrode for a lithium secondary battery according to claim 9, wherein the insulating layer coating composition has a viscosity of 1,000 to 10,000 cps at 25°C.

12. The step of forming the positive electrode active material layer comprises: a wet process using a cathode slurry containing a cathode active material and a binder; or The method for producing a positive electrode for a lithium secondary battery according to claim 9, which is carried out by a dry process using a film for a positive electrode containing a positive electrode active material and a binder.

13. 10. The method of claim 9, wherein the forming of the positive electrode active material layer further comprises forming an auxiliary insulating layer on a sliding portion of the formed active material layer.

14. 10. An electrode assembly for a lithium secondary battery comprising the positive electrode for the lithium secondary battery according to claim 1, a negative electrode, and a separator disposed between the positive electrode and the negative electrode for the lithium secondary battery.

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