KR20200113737A - Flexible Electrode Assembly and Manufaturing Method thereof - Google Patents

Abstract

The present invention relates to a manufacturing method of an electrode assembly applicable to a foldable device and to a secondary battery comprising the electrode assembly thereby. The electrode assembly according to the present invention is excellent in flexibility and thus is suitable for application to secondary batteries embedded in various foldable devices. In addition, it is easy to optimize even when manufacturing a thin-walled secondary battery, and it has excellent stability since there is no performance degradation due to electrode detachment.

Description

Electrode assembly with excellent flexibility and manufacturing method thereof {Flexible Electrode Assembly and Manufaturing Method thereof}

The present invention relates to a method of manufacturing an electrode assembly applicable to a foldable device, and a secondary battery including the electrode assembly according to the method.

As the price of energy sources rises due to the depletion of fossil fuels and interest in environmental pollution increases, the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life. In particular, technology development for mobile devices As the demand and demand increase, the demand for secondary batteries as an energy source is rapidly increasing.

Typically, in terms of the shape of the battery, there is a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness.In terms of materials, lithium-ion batteries with high energy density, discharge voltage, and output stability, There is high demand for lithium secondary batteries such as lithium ion polymer batteries.

In general, a secondary battery refers to a battery capable of charging and discharging unlike a primary battery that cannot be charged, and is widely used in electronic devices such as mobile phones, notebook computers, camcorders, or electric vehicles. In particular, lithium secondary batteries have an operating voltage of about 3.6V, about three times the capacity of nickel-cadmium batteries or nickel-hydrogen batteries, which are widely used as power sources for electronic equipment, and have a high energy density per unit weight. There is a trend of increasing rapidly.

These lithium secondary batteries mainly use lithium-based oxides and carbon materials as a positive electrode active material and a negative electrode active material, respectively. A lithium secondary battery includes a cell assembly in which unit cells having a structure in which a positive electrode plate and a negative electrode plate are respectively coated with such a positive electrode active material and a negative electrode plate are disposed with a separator therebetween, and an exterior material case for sealing and storing the cell assembly together with an electrolyte. Equipped.

Meanwhile, lithium secondary batteries are not only widely used as energy sources for wireless mobile devices or wearable electronic devices worn on the body, but also environmental problems such as air pollution caused by conventional gasoline vehicles and diesel vehicles that use fossil fuels. As a solution to the problem, it is also used as an energy source for electric vehicles and hybrid electric vehicles.

In order to be used as an energy source in various industrial fields, the sizes and shapes of secondary batteries are also manufactured in various designs in response to devices. In particular, a shape of a secondary battery having various designs, such as a geometric structure, an ultra-thin type, and a curved type, is required to deviate from the conventional rectangular or cylindrical structure. To this end, the secondary battery and the electrode assembly included in the secondary battery are required to have high flexibility, and for this purpose, there is a high need for a technology regarding a method of manufacturing an electrode assembly having excellent flexibility.

In this regard, Korean Laid-Open Patent Publication No. 10-2015-0050131 (Patent Document 1) discloses a stack-folding electrode assembly including a plurality of unit cells of a full cell or a bi-cell. Patent Document 1 describes an electrode assembly manufactured by disposing a plurality of unit cells on a continuous sheet-shaped separator at regular intervals and then winding them. The electrode assembly having this structure is also used in a flexible secondary battery. It is being applied. However, in the electrode assembly as described above, since the number of stacked unit cells or more are separately manufactured and spaced apart on the separator sheet at regular intervals, the manufacturing process is cumbersome and the balance between cells may be problematic.

On the other hand, Korean Laid-Open Patent Publication No. 10-2017-0033516 (Patent Document 2) discloses a flexible electrode assembly using a patterned coating electrode in which a coated portion coated with an active material and a non-coated portion alternately appear on one unit electrode. . The flexible electrode assembly having a structure in which the uncoated portion is bent as in Patent Document 2 does not exhibit the cell balance problem that was problematic in Patent Document 1, and thus has an advantage of being excellent in terms of stability. However, when the coating part is bent together when the electrode assembly is bent, a defect due to electrode detachment occurs. In addition, in the case of an electrode assembly in which a number of electrodes are stacked to achieve high capacity, the range of stress applied around the bent portion is widened, so that the loss of energy density is reduced while preventing performance degradation due to electrode detachment. There is a problem that it becomes difficult to design by optimizing the width.

Korean Patent Publication No. 10-2015-0050131 Korean Patent Publication No. 10-2017-0033516

An object of the present invention is to provide a method for manufacturing an electrode assembly having excellent flexibility and a flexible electrode assembly according to the method of manufacturing an electrode assembly having excellent flexibility while preventing the problem of imbalance and stability between cells, which was a problem in the conventional electrode assembly having a flexible structure. .

In order to achieve the above object, the electrode assembly manufacturing method according to the present invention may include the following steps.

Manufacturing a positive electrode and a negative electrode formed by alternating a coating portion to which an active material is applied and an uncoated portion to which the active material is not applied;

Stacking the anode, the cathode, and a separator interposed between the anode and the cathode to form an electrode assembly;

Forming a folding portion by compressing a portion of the electrode assembly where the uncoated portion is formed;

Bending the folding part.

In this case, the width of the uncoated portion satisfies Equation 1 below with respect to the curved length of the bent folding portion.

[Equation 1]

W = S + R

(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)

On the other hand, the curved length of the folding part in Equation 1 may be approximated from the total thickness of the electrode assembly and the thicknesses of components not included in the folding part of the electrode assembly configuration. Specifically, the R value, which is the length of the curved surface of Equation 1, can be calculated in the same manner as in Equation 2 below.

[Equation 2]

R = π * (t ₁ -t ₂ ) * k

(In Equation 2, t ₁ is the thickness of the electrode assembly, t ₂ is the total thickness of components not included in the folding part of the electrode assembly, k is a constant that satisfies 0.5 ≤ k ≤ 1.5)

According to the method of manufacturing the electrode assembly, the anode and the cathode each include a non-coated portion, to which an active material is not applied, and the electrode assembly according to the present invention is bent at the uncoated portion to form a folding portion. And by making the width equal, it is possible to form the folding part efficiently.

On the other hand, as the electrode assembly is bent, the outer surfaces of the electrode assembly may face each other. Therefore, in order to improve stability, an insulating film may be additionally formed on the outer surface of the electrode assembly to further improve insulation.

That is, after the step of forming the electrode assembly, before the step of forming the folding part

It may further include forming an insulating film on the outer surface of the electrode assembly.

At this time, the insulating film may be made of the same material as the separator, and specifically, any one selected from the group consisting of polyolefin-based resin, fluorine-based resin, polyester-based resin, polyacrylonitrile resin, cellulose-based material, and copolymers thereof. Alternatively, a porous film or nonwoven fabric including a mixture of two or more may be used.

In addition to this, insulating properties and stability may be further improved by further including an insulating coating on the electrode assembly.

The electrode assembly manufactured by the above manufacturing method is an electrode assembly including one or two or more of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, respectively, and the coating part coated with the active material and the active material are not The coated uncoated portions are formed alternately, and the uncoated portions are bent to form a folding portion, and the following equation (1) is satisfied.

[Equation 1]

W = S + R

(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)

At this time, the R value of Equation 1 is characterized in that it satisfies Equation 2 below.

[Equation 2]

R = π * (t ₁ -t ₂ ) * k

(In Equation 2, t ₁ is the thickness of the electrode assembly, t ₂ is the total thickness of components not included in the folding part of the electrode assembly, k is a constant that satisfies 0.5 ≤ k ≤ 1.5)

Meanwhile, as described above, by further including the step of adding an insulating film when manufacturing the electrode assembly, the electrode assembly may have a structure further including an insulating film on the outer surface of the electrode assembly.

The electrode assembly may be used in various types of lithium secondary batteries. Specifically, the electrode assembly according to the present invention may be used in the manufacture of a conventional stack-folding electrode assembly, and has excellent flexibility when manufactured as a flexible secondary battery, and has excellent stability against stress caused by repeated bending. do.

The electrode assembly according to the present invention has excellent flexibility and is suitable for manufacturing a flexible secondary battery. In particular, it is easy to apply to secondary batteries embedded in various types of foldable devices. In addition, it is easy to design even when manufacturing a secondary battery having a thin thickness, and since there is little performance degradation due to electrode detachment, stability is very excellent.

On the other hand, it can also be used to manufacture a conventional stack-folding type electrode assembly. In this case, unlike the conventional method in which a plurality of unit cells must be manufactured in response to the number of folding, one foldable unit electrode is stacked. It can be easily manufactured just by itself. Accordingly, it is possible to improve an imbalance phenomenon between cells, which is a disadvantage of the stack-folding electrode assembly according to the conventional method.

1 schematically shows the structure of a stack-folding electrode assembly according to the prior art.
2 schematically shows the structure of an electrode assembly according to the prior art manufactured by stacking electrodes of a conventional bendable shape.
3 is a conceptual diagram showing a manufacturing mode of a unit electrode according to the present invention.
4 is a diagram sequentially illustrating a manufacturing and bending process of an electrode assembly according to an embodiment of the present invention.
5 shows an electrode assembly structure according to another embodiment of the present invention.
6 shows a structure of an electrode assembly according to still another embodiment of the present invention.
FIG. 7 shows an embodiment of a stack-folding electrode assembly manufactured using the electrode assembly structure of FIG. 4.
FIG. 8 shows an embodiment of a flexible electrode assembly manufactured using the electrode assembly structure of FIG. 4.

Terms used in the present specification and claims are not limited to their usual or dictionary meanings and should not be interpreted, and that the inventor can appropriately define the concept of terms in order to describe his own invention in the best way. Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of the invention. Therefore, the configuration shown in the embodiments described in the present specification is only one of the most preferred embodiments of the present invention, and does not represent all the technical spirit of the present invention, and various equivalents that can replace them at the time of the present application And it should be understood that there may be variations.

In the entire specification of the present application, when a certain part is said to be ``connected'' with another part, this includes not only ``directly connected'' but also ``electrically connected'' with another element interposed therebetween. .

Throughout this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, actions, elements, parts, or combinations thereof described in the specification, but one or more other It is to be understood that the presence or addition of features, numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance the possibility of being excluded. Further, when a part such as a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the case where the other part is "directly above" but also the case where there is another part in the middle. Conversely, when a part such as a layer, film, region, plate, etc. is said to be "under" another part, this includes not only the case where the other part is "directly below", but also the case where there is another part in the middle. In addition, in the present application, the term "over" may include not only the upper part but also the lower part.

The terms "about" and "substantially" used throughout this specification are used as meanings at or close to the numerical values when manufacturing and material tolerances specific to the stated meanings are presented, and are accurate to aid understanding of the present application. Or absolute figures are used to prevent unfair use of the stated disclosure by unconscionable infringers.

In the entire specification of the present application, the term "combination(s) thereof" included in the expression of the Makushi form means one or more mixtures or combinations selected from the group consisting of the constituent elements described in the expression of the Makushi form, It means to include at least one selected from the group consisting of the above components.

In the entire specification of the present application, the term "curved surface length" means the length of the longer side of the outer peripheral surface of the curved portion when the object is bent to the maximum. For example, in the present invention, "the length of the curved surface of the folding part" means the length of the outer surface when the folding part 140 of the electrode assembly is bent to the maximum as shown in FIG. 4C.

In the present invention, the length of the curved surface of the folding portion is calculated in advance before manufacturing the electrode assembly and reflected in the width of the uncoated portion of the electrode. Specifically, the length (W) of the width of the electrode uncoated portion of the present invention can be calculated according to Equation 1 below.

[Equation 1]

W = S + R

(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)

Hereinafter, the present invention will be described in detail with reference to the drawings.

1 is a form of a stack-folding electrode assembly according to a conventional method. 1, in order to manufacture a stack-folding type electrode assembly, a folding direction is indicated by an arrow, and a folding point is indicated by a dotted line. 1 is a bi-cell, and as shown in the figure, if folding starts from the right end, the anode 11 located at the top of the bi-cell is about the width of one bi-cell so that it can contact the separator 14. There are areas where the bi-cell is not placed.

After that, if the folding process is performed continuously at the point indicated by the dotted line in the direction of the arrow, all bicells are wrapped by a separator, and a separator is interposed between adjacent bicells, and the bicells correspond to each other in a stacked form. You will have a stack-folding structure that is arranged to be (stack-folding). However, it is obvious to those skilled in the art that the width between the bi-cells should gradually increase as cells are sequentially stacked in the stack-folding process as described above, but those skilled in the art understand that in FIG. 1, it is illustrated at uniform intervals for convenience of expression. shall.

However, in the stack-folding electrode assembly as described above, since each bicell can be arranged according to the width and height of the bicell, it is not difficult to design the spacing between each bicell, but the bicell must be manufactured and disposed. An imbalance between cells may be a problem. In addition, although the structure shown in FIG. 1 is easy to manufacture a stack-folding type electrode assembly, it is not suitable as an electrode assembly for manufacturing a flexible secondary battery.

FIG. 2 shows a structure of a flexible electrode assembly composed of a coating portion 21 and an uncoated portion 22 according to a conventional method. In the center of FIG. 2, a folding portion 23 made of a non-coated portion is formed, and the central portion of the folding portion is bent to have flexibility. However, in the case of an electrode assembly in which a plurality of electrodes are stacked, if the folding part 23 is bent in a state where the length of the folding part 23 is insufficient as shown in FIG. 2, not only the folding part 23 but also the coating part 21 are bent together. An external force acts on the electrode mixture of the coating part 21, and as a result, electrode detachment may occur.

The electrode assembly of the present invention is a further improvement of the structure of FIG. 2. The electrode assembly of the present invention predicts the degree of bending of the folding part in advance at the electrode manufacturing step and design the width of the uncoated part accordingly, prevents electrode detachment and performance degradation that may occur due to the uncoated part width is too short, and the width of the uncoated part is excessive. Energy density loss caused by lengthening can be prevented.

In this regard, an embodiment of a unit electrode used in the electrode assembly according to the present invention is shown in FIG. 3. The width and length of the folding part in FIG. 3 are adjusted according to the curved length of the folding part when manufacturing the electrode assembly, and the thickness of the intended electrode assembly, the thickness of the electrode assembly excluding the materials forming the folding part, the thickness of the separator, the bicell stack structure, and/or It is set in the electrode manufacturing step according to the quantity and the like.

The method of manufacturing an electrode assembly according to the present invention may include the following steps, which will be described in more detail with reference to FIG. 4.

4 is a conceptual diagram showing a manufacturing process of the electrode assembly 100 according to the manufacturing method of the present invention.

First, a positive electrode 110 and a negative electrode 120 formed by alternating a coating portion coated with an active material and an uncoated portion not coated with the active material are manufactured. The width of the uncoated portion is adjusted according to the length of the curved surface of the outer surface of the folding portion as in the description of FIG. 3 and may be specifically calculated according to Equation 1 below.

[Equation 1]

W = S + R

(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)

The length (W) of the width of the uncoated portion in Equation 1 reflects the curved length (R) of the folding portion, but is corrected by a tolerance value (S) according to the amount of the electrode mixture applied to the coating portion.

Unlike the positive and negative current collectors, separators, and pouch materials, the electrode mixture layer including an active material, a conductive material, a binder, an additive, etc., spreads in a direction perpendicular to the external force when an external force acts after application and drying. For example, when forming an electrode mixture layer of high loading, or when manufacturing an electrode assembly by stacking a plurality of electrodes coated with the electrode mixture, or when repeatedly bending the electrode assembly after manufacturing, it is applied as an external force acts. The electrode mixture spreads sideways. Accordingly, as the amount of application of the electrode mixture increases and the thickness of the electrode mixture layer appears, it is necessary to correct the width and length of the uncoated portion by increasing the tolerance value.

The tolerance value may be adjusted within the range of 0.1 to 2 mm, and it is preferable to increase the tolerance value in proportion to this, as the electrode mixture layer appears thicker or the number of stacked electrodes increases. However, when the tolerance value is less than 0.1 mm, the electrode mixture partially spreading to the side may be detached due to the influence of external force, and when it exceeds 2 mm, the uncoated portion becomes longer than necessary, which is not preferable because the energy density is lowered.

The anode 110, the cathode 120, and the separator 130 interposed therebetween are stacked together to form an electrode assembly having a shape as shown in FIG. 4A.

Next, as shown in (b) of FIG. 4, the part including the separator 140 and the uncoated part is compressed to form the folding part 140.

Thereafter, when the folding part 140 is bent, the electrode assembly may be completely bent as shown in (c) of FIG. 4. At this time, a high external force acts as the folding portion is bent to the maximum. Since the coating portions of the anode and the cathode are not bent and are hardly affected by external force, electrode detachment does not occur even with repeated bending.

In the pressing and folding process, a lamination roller may be used, and specifically, it may be performed by attaching an electrode and a separator by setting parameter values of temperature, pressure, and speed. In the folding process, the electrode assembly manufactured in the bi-cell lamination step is placed on the unfolding separator at a certain interval, and then rotated using a gripper to fix it.

As another embodiment, two uncoated portions may be formed as shown in FIG. 5. Accordingly, two folding parts may be formed, and such an electrode assembly may be bent in the form of a stack-folding electrode assembly as shown in FIG. 7, and may be formed in the form of a'Z'-shaped flexible electrode assembly as shown in FIG. It is possible. The width of the uncoated portion is set based on the curved length of the outer circumferential surface of the folding portion in the state where the folding portion is bent at the maximum, so that even when the folding portion is bent in any shape, stability can be maintained without detaching the electrode.

As another embodiment, it is possible to have a high loading electrode assembly structure as shown in FIG. 6. As the number of electrodes and separators stacked as shown in FIG. 6 increases, the thickness of the electrode assembly increases, and thus, the width of the uncoated portion must be increased to prevent electrode detachment due to bending. However, as described above, the width of the uncoated part is set by predicting the length of the curved part of the folding part in advance, and additionally, in the case of the high-loading electrode mixture, by applying a relatively high tolerance value to correct it, it has excellent flexibility and stability without trial and error. It is possible to manufacture this highly flexible electrode assembly.

Meanwhile, the length of the curved surface of Equation 1 may be calculated according to the total thickness of the electrode assembly and the total thickness of materials forming the folding part. Specifically, the curved surface length R value can be calculated by the same method as in Equation 2 below.

[Equation 2]

R = π * (t ₁ -t ₂ ) * k

(In Equation 2, t ₁ is the thickness of the electrode assembly, t ₂ is the total thickness of components not included in the folding part of the electrode assembly, k is a constant that satisfies 0.5 ≤ k ≤ 1.5)

In Equation 2, t ₁ is the thickness of the electrode assembly including all of the electrode mixture, the positive electrode, the negative electrode, the separator, and the outer insulating film, and t ₂ is a configuration that is not included in the folding part like the electrode mixture layer among the components of the electrode assembly. It is the sum of all the thicknesses of the fields. That is, in Equation 2, the expected thickness of the folding part formed when manufacturing the electrode assembly can be obtained by (t ₁ -t ₂ ).

On the other hand, the folding part must have stability and high flexibility so that electrode detachment does not occur even with repeated bending. This can be achieved by making the length of the folding part sufficiently long, but if the length of the folding part is too long, the energy density is lowered, which is not preferable.

In order to secure the flexibility and stability of the electrode assembly while maintaining the energy density at a high level, it is preferable that the outer outer peripheral surface of the folding part of the present invention has a semicircular arc shape. Accordingly, the length of the long side of the outer peripheral surface of the folding part, that is, the length of the outer curved surface may be expressed as π * (t ₁ -t ₂ ).

However, as shown in FIG. 4, the electrode assembly and the folding part inevitably have different thicknesses. Therefore, the folding part cannot appear in a complete semicircle shape, and accordingly, the length of the curved surface needs to be corrected.

In this case, when the difference between the thickness of the electrode assembly and the folding part is large according to the ratio of t ₁ and t ₂ , the k value of Equation 2 may be largely adjusted to correct it. However, if the k value is less than 0.5, not only the folding part but also the electrode mixture layer may be affected by bending, and if the k value exceeds 1.5, the width of the uncoated part becomes longer and thus energy density decreases. It is desirable to be internal.

In addition, according to the method of manufacturing an electrode assembly of the present invention, the positive electrode and the negative electrode each include an uncoated portion to which an active material is not applied, and the electrode assembly according to the present invention is bent at the uncoated portion to form a folding portion. By making the uncoated portion position and width the same, it is possible to efficiently form the folding portion.

On the other hand, as the electrode assembly is bent, the outer surfaces of the electrode assembly may face each other. Therefore, in order to improve stability, an insulating film may be additionally formed on the outer surface of the electrode assembly to further improve insulation.

In other words. After the step of forming the electrode assembly and before the step of forming the folding part, the step of forming an insulating film on the outer surface of the electrode assembly may be further included.

At this time, the insulating film may be made of the same material as the separator, and specifically, any one selected from the group consisting of polyolefin-based resin, fluorine-based resin, polyester-based resin, polyacrylonitrile resin, cellulose-based material, and copolymers thereof. Alternatively, a porous film or nonwoven fabric including a mixture of two or more may be used.

In addition to this, insulating properties and stability may be further improved by further including an insulating coating on the electrode assembly. Specifically, in the case of insulating coating, particulate ceramic materials such as AL ₂ O ₃ and ZrO may be used and suspended in each dispersible solvent using an aqueous or non-aqueous binder, and applied on the insulating film of the electrode assembly. In addition, it is also possible to additionally attach a tape made of a chemical resistant material such as imide or CPP on the insulating film.

The electrode assembly manufactured by the above manufacturing method is an electrode assembly including one or two or more of a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, respectively, and the coating part coated with the active material and the active material are not The coated uncoated portions are formed alternately, and the uncoated portions are bent to form a folding portion, and the following equation (1) is satisfied.

[Equation 1]

W = S + R

(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)

At this time, the R value of Equation 1 is characterized in that it satisfies Equation 2 below.

[Equation 2]

R = π * (t ₁ -t ₂ ) * k

(In Equation 2, t ₁ is the thickness of the electrode assembly, t ₂ is the total thickness of components not included in the folding part of the electrode assembly, k is a constant that satisfies 0.5 ≤ k ≤ 1.5)

Meanwhile, by further including the step of adding an insulating film as described above, the electrode assembly may have a structure further including an insulating film on the outer surface of the electrode assembly.

By adding the insulating layer, the risk of occurrence of an internal short circuit can be further lowered and the flexibility and durability of the folding portion can be further improved. Accordingly, the flexible secondary battery including the electrode assembly according to the present invention is characterized by excellent flexibility and excellent stability against stress caused by repeated bending.

In addition, the folding part is composed of a non-coated part and a separator to which an active material is not applied, or an insulating film optionally included, and since the compartment is separated from the active material application part, sufficient buffer against external shock during the manufacturing process or use of the battery It can exhibit an action, and stability can be maintained with little reduction in battery capacity even under repeated bending stress.

Meanwhile, the insulating film may be an insulating thin film having high ion permeability and mechanical strength, and may be made of the same material as the separator. Specifically, the insulating film may be a porous support, and more specifically, a polyolefin-based resin (for example, polyethylene, polypropylene, polybutylene, polypentene, etc.), a fluorine-based resin (for example, polyvinylidene fluoride or poly). Tetrafluoroethylene, etc.), polyester resins (eg, polyethylene terephthalate or polybutylene terephthalate, etc.), polyacrylonitrile resins, cellulose materials, and any selected from the group consisting of copolymers thereof It may be a porous film including one or a mixture of two or more, a nonwoven fabric, or a laminated structure of two or more layers.

Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited by the following examples. The embodiments of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art.

Example 1

An electrode assembly having a thickness of 3 mm was prepared.

<Production of anode>

As a positive electrode active material, 95% by weight of LiCoO ₂ , 2.5% by weight of Super-P (conductive agent), and 2.5% by weight of PVdF (binder) were added to NMP (Nmethyl-2-pyrrolidone) as a solvent to prepare a positive electrode mixture slurry.

Subsequently, the positive electrode active material was pattern-coated so that one uncoated part was formed on both sides of the aluminum foil, followed by drying and pressing to prepare a positive electrode.

At this time, in order to calculate the width of the uncoated portion, the R value was first calculated by Equation 2 below.

[Equation 2]

R = π * (t ₁ -t ₂ ) * k

(In Equation 2, t ₁ is the thickness of the electrode assembly, t ₂ is the total thickness of components not included in the folding part of the electrode assembly, k is a constant that satisfies 0.5 ≤ k ≤ 1.5)

The uncoated width (W) was derived by substituting the R value that satisfies Equation 2 in Equation 1 below.

[Equation 1]

W = S + R

(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)

Preparation of cathode

An anode mixture slurry was prepared by adding 95% by weight of artificial graphite, 2.5% by weight of Super-P (conductive agent), and 2.5% by weight of PVdF (binder) as an anode active material to NMP as a solvent. Subsequently, the negative active material was pattern-coated so that one uncoated part was formed on both sides of the copper foil, followed by drying and pressing to prepare a negative electrode. The position and width of the uncoated portion were the same as those of the anode.

Manufacturing of electrode assembly

The current collector in which the positive and negative electrodes are integrally formed is bent so as to have a zigzag shape in a vertical cross section along the perforated portion. Subsequently, Celgard ^TM was interposed by a separator at the interface between the negative electrode and the positive electrode facing each other by the above bending, and then folded.

Thereafter, the bent current collector portion was cut to manufacture a superimposed electrode assembly, and then, it was built into a battery case and an electrolyte was injected to manufacture a battery. At this time, the lengths (W) of t ₁ , t ₂ , k, R, S and width of the uncoated part of Equations 1 and 2 are shown in Table 1 below.

Example 2

An electrode assembly having a thickness of 3 mm of the electrode assembly was prepared. The manufacturing method of the positive electrode, the negative electrode, and the electrode assembly was the same as in Example 1, but the S value of Equation 1 was applied differently. At this time, the lengths (W) of t ₁ , t ₂ , k, R, S and width of the uncoated part of Equations 1 and 2 are shown in Table 1 below.

Comparative Example 1

An electrode assembly was manufactured in the same manner as in Example 1, except that the R value calculated by Equation 2 was not corrected to the S value. At this time, the values of t ₁ , t ₂ , k, R, S, W of Equations 1 and 2 and the length of the width of the uncoated part are shown in Table 1 below.

<Experimental Example>

The values of each variable in Examples 1 and 2 and Comparative Example 2 are shown in Table 1 below.

division t ₁ (mm) t ₂ (mm) k R(mm) S(mm) W(mm) Example 1 3 0.5 0.5 3.925 0.1 4.025 Example 2 3 0.5 0.5 3.925 0.2 4.125 Comparative Example 1 3 0.5 0.5 3.925 0.0 3.925

Stability test

After manufacturing a battery cell using the electrode assembly according to Examples 1 and 2 and Comparative Example 1, the initial capacity was measured, and then the battery cell was repeatedly bent. The capacity of the battery cell was measured every 2000 times, 4000 times, 6000 times, 8000 times, and 100,000 times of bending times, and the capacity retention rate (%) for the initial capacity was calculated, and the results are shown in Table 2 below.

division 2000 times 4000 times 6000 times 8000 times 10000 times Example 1 95.03 94.89 94.83 94.56 94.33 Example 2 94.81 94.72 94.64 94.33 94.17 Comparative Example 1 95.28 93.22 90.44 89.33 87.69

Results and Discussion

As shown in Table 2, in the case of Examples 1 and 2 in which the width of the uncoated portion was set within the range of the W value derived according to Equations 1 and 2, the capacity retention rate was excellent even after 10,000 bending tests compared to Comparative Example 2. You can see that it is maintained.

10: electrode assembly of the prior art
11: anode
12: cathode
13: first separation membrane
14: second separator
20: electrode assembly of the prior art
21: coating
22: no branch
23: folding part
100: electrode assembly
110: anode
120: cathode
130: separator
140: folding part

Claims (10)

Manufacturing a positive electrode and a negative electrode formed by alternating a coating portion to which an active material is applied and an uncoated portion to which the active material is not applied;
Stacking the anode, the cathode, and a separator interposed between the anode and the cathode to form an electrode assembly;
Forming a folding portion by compressing a portion of the electrode assembly where the uncoated portion is formed;
Including; bending the folding portion;
The width of the uncoated portion satisfies Equation 1 below with respect to the length of the curved surface of the bent folding portion.
[Equation 1]
W = S + R
(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)
The method of claim 1,
The method of manufacturing an electrode assembly, characterized in that the R value of Equation 1 satisfies Equation 2 below.
[Equation 2]
R = π * (t ₁ -t ₂ ) * k
(In Equation 2, t ₁ is the thickness of the electrode assembly, t ₂ is the total thickness of components not included in the folding part of the electrode assembly, k is a constant that satisfies 0.5 ≤ k ≤ 1.5)
The method of claim 1,
The method of manufacturing an electrode assembly, characterized in that the position and width of the uncoated portions respectively formed on the positive and negative electrodes are the same.
The method of claim 1,
Between the step of forming the electrode assembly and the step of forming the folding part,
The method of manufacturing an electrode assembly, further comprising forming an insulating film on the outer surface of the laminate.
The method of claim 4,
The insulating film is a porous film or a nonwoven fabric including any one or a mixture of two or more selected from the group consisting of polyolefin resin, fluorine resin, polyester resin, polyacrylonitrile resin, cellulose material, and copolymers thereof. A method of manufacturing an electrode assembly, characterized in that.
The method of claim 1,
The method of manufacturing an electrode assembly, further comprising: applying an insulating coating to the laminate.
An electrode assembly comprising one or two or more of an anode, a cathode, and a separator interposed between the anode and the cathode, respectively,
On the positive and negative electrodes, a coating portion coated with an active material and an uncoated portion without an active material are formed alternately,
The uncoated portion is bent to form a folding portion,
An electrode assembly, characterized in that it satisfies Equation 1 below.
[Equation 1]
W = S + R
(In Equation 1, W is the length of the plain width (mm), R is the length of the curved surface of the folding part (mm), and S is a correction value reflecting the tolerance according to the coating amount of the electrode mixture in the coating part, and 0.1 ≤ S ≤ It is a value that satisfies 2.0)
The method of claim 7,
An electrode assembly, characterized in that the R value of Equation 1 satisfies Equation 2 below.
[Equation 2]
R = π * (t ₁ -t ₂ ) * k
(In Equation 2, t ₁ is the thickness of the electrode assembly, t ₂ is the total thickness of components not included in the folding part of the electrode assembly, k is a constant that satisfies 0.5 ≤ k ≤ 1.5)
The method of claim 7,
The electrode assembly further comprises an insulating film on the outer surface of the electrode assembly.
A lithium secondary battery comprising the electrode assembly of claim 7.

Images