Electrode assembly and secondary battery including the same

Abstract

The electrode assembly of the present invention includes a first electrode coated with a first electrode active material layer, a second electrode coated with a second electrode active material layer, and a separator disposed between the first electrode and the second electrode. The separator includes: a porous substrate disposed between the first electrode and the second electrode and in contact with the first electrode active material layer; and a coating layer in contact with the second electrode active material layer and disposed on a surface of the porous substrate, in which a friction coefficient between the first electrode active material layer and the porous substrate and a friction coefficient between the second electrode active material layer and the coating layer correspond to each other.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2022-0118219, filed on September 19, 2022, which is hereby incorporated by reference in its entirety.

[0004] The present invention relates to an electrode assembly that improves the difference between the frictional force between a positive electrode and a separator and the frictional force between a negative electrode and a separator, and a secondary battery including the electrode assembly. Background Art

[0005] Generally, a secondary battery is a battery that can be charged and discharged, unlike a primary battery that is not rechargeable. Secondary batteries are widely used in mobile phones, notebook computers, as well as video cameras, electric vehicles, and the like.

[0006] Secondary batteries are classified into cylindrical secondary batteries in which an electrode assembly is embedded in a metal can and pouch-type secondary batteries in which an electrode assembly is embedded in a pouch.

[0007] The cylindrical secondary battery includes an electrode assembly, a can accommodating the electrode assembly, and a cap assembly mounted in an opening of the can.

[0008] The pouch-type secondary battery includes an electrode assembly and a pouch accommodating the electrode assembly, and the pouch includes an accommodating portion accommodating the electrode assembly and a sealing portion sealing the accommodating portion.

[0009] The electrode assembly has a structure in which electrodes and separators are alternately disposed therein, and the electrodes include a positive electrode and a negative electrode.

[0010] In a cylindrical type secondary battery, positive electrodes and negative electrodes are alternately disposed with a separator interposed therebetween, and then wound into a wound shape to manufacture an electrode assembly.

[0011] Here, in the cylindrical secondary battery, shrinkage and expansion occur repeatedly in the positive electrode and the negative electrode during charge and discharge. Here, friction occurs repeatedly between the positive electrode and the separator and between the negative electrode and the separator.

[0012] However, cylindrical secondary batteries have a problem in that due to the difference in friction between the positive electrode and the separator and between the negative electrode and the separator, wear and deformation occur toward the electrode with higher friction, resulting in performance problems and internal short circuits. Summary of the invention

[0013] Technical issues

[0014] An object of the present invention is to provide an electrode assembly and a secondary battery including the electrode assembly, in which the difference in friction between a positive electrode and a separator and between a negative electrode and a separator is improved, thereby preventing wear and deformation between the positive electrode and the separator and between the negative electrode and the separator, thereby preventing performance problems and internal short circuits.

[0015] Technical Solution

[0016] The electrode assembly of the present invention may include a first electrode coated with a first electrode active material layer, a second electrode coated with a second electrode active material layer, and a separator arranged between the first electrode and the second electrode, wherein the separator may include: a porous substrate, which is arranged between the first electrode and the second electrode and in contact with the first electrode active material layer; and a coating, which is in contact with the second electrode active material layer and is arranged on the surface of the porous substrate, wherein the friction coefficient between the first electrode active material layer and the porous substrate and the friction coefficient between the second electrode active material layer and the coating may correspond to each other.

[0017] The friction coefficient between the first electrode active material layer and the porous substrate and the friction coefficient between the second electrode active material layer and the coating layer may be the same.

[0018] In the separator, the porous substrate and the coating layer can be determined based on the surface roughness of the first electrode active material layer and the surface roughness of the second electrode active material layer so that the friction coefficient between the first electrode active material layer and the porous substrate and the friction coefficient between the second electrode active material layer and the coating layer correspond to each other.

[0019] The second electrode active material layer may have a surface roughness rougher than that of the first electrode active material layer, and in the separator, the porous substrate may have a surface roughness rougher than that of the coating layer, so that the friction coefficient between the first electrode active material layer and the porous substrate and the friction coefficient between the second electrode active material layer and the coating layer correspond to each other.

[0020] The coating layer may include an inorganic material, and the inorganic material may be made of ceramic.

[0021] The electrode assembly of the present invention may include a first electrode coated with a first electrode active material layer, a second electrode coated with a second electrode active material layer, and a separator arranged between the first electrode and the second electrode, wherein the separator may include: a porous substrate located between the first electrode and the second electrode; a first coating layer contacting the first electrode active material layer and arranged on the surface of the porous substrate; and a second coating layer contacting the second electrode active material layer and arranged on the surface of the porous substrate, wherein the friction coefficient between the first electrode active material layer and the first coating layer and the friction coefficient between the second electrode active material layer and the second coating layer may correspond to each other.

[0022] The friction coefficient between the first electrode active material layer and the first coating layer and the friction coefficient between the second electrode active material layer and the second coating layer may be the same.

[0023] In the separator, the first coating layer and the second coating layer can be determined based on the surface roughness of the first electrode active material layer and the surface roughness of the second electrode active material layer, so that the friction coefficient between the first electrode active material layer and the first coating layer and the friction coefficient between the second electrode active material layer and the second coating layer correspond to each other.

[0024] The second electrode active material layer may have a surface roughness rougher than that of the first electrode active material layer, and in the separator, the first coating layer may have a surface roughness rougher than that of the second coating layer, so that the friction coefficient between the first electrode active material layer and the first coating layer and the friction coefficient between the second electrode active material layer and the second coating layer correspond to each other.

[0025] Each of the first coating layer and the second coating layer may include an inorganic material, and the inorganic material may be made of ceramic.

[0026] The first coating layer and the second coating layer may be made of materials having different surface roughnesses.

[0027] The first electrode may be provided as a positive electrode, and the second electrode may be provided as a negative electrode.

[0028] The porous substrate may be made of an insulating polymer film.

[0029] The polymer film may be made of any one of polyethylene, polyurethane, and polypropylene.

[0030] The ceramic may be made of any one of silicon carbide (SiC), silicon nitride (Si3n4), zirconium oxide (ZrO2), aluminum oxide (Al2O3), and boehmite (AlOOH).

[0031] The secondary battery of the present invention may include an electrode assembly.

[0032] Beneficial Effects

[0033] The electrode assembly according to the present invention may include a separator provided with a porous substrate and a coating, and the friction coefficient between the first electrode active material layer of the first electrode and the porous substrate and the friction coefficient between the second electrode active material layer of the second electrode and the coating may correspond to each other. Due to these characteristics, wear and deformation between the first electrode and the separator and between the second electrode and the separator can be prevented to solve performance problems, thereby preventing internal short circuits from occurring. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a cross-sectional view of an electrode assembly according to a first embodiment of the present invention.

[0035] Figure 2 is a table illustrating the surface roughness of the electrode assembly according to the first embodiment of the present invention.

[0036] Figure 3 is a cross-sectional view of an electrode assembly according to a second embodiment of the present invention.

[0037] Figure 4 is a cross-sectional view of a secondary battery according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings in a manner in which a person skilled in the art can easily implement the technical ideas of the present invention. However, the present invention can be embodied in different forms and should not be construed as being limited to the embodiments described herein. In the accompanying drawings, for the sake of clarity, any content that is not necessary for describing the present invention will be omitted, and in addition, the same reference numerals are used in the drawings to represent the same elements.

[0039] [Electrode Assembly According to First Embodiment of the Present Invention]

[0040] Figure 1 is a cross-sectional view of an electrode assembly according to a first embodiment of the present invention.

[0041] like Figure 1 As illustrated in FIG. 1 , the electrode assembly 10 according to the first embodiment of the present invention includes a first electrode 11 , a second electrode 12 , and a separator 13 disposed between the first electrode 11 and the second electrode 12 .

[0042] First electrode

[0043] The first electrode 11 includes a first current collector 111 having a long sheet shape and a first electrode active material layer 112 applied on one surface or both surfaces of the first current collector 111 .

[0044] The first electrode 11 is a positive electrode, the first current collector 111 is a positive electrode current collector, and the first electrode active material layer 112 is a positive electrode active material layer.

[0045] Here, the first electrode active material layer 112 may be any one of LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiCoPO 4 , LiFePO 4 , and LiNiMnCoO 2 .

[0046] Second electrode

[0047] The second electrode 12 includes a second current collector 121 having a long sheet shape and a second electrode active material layer 122 applied on one surface or both surfaces of the second current collector 121 .

[0048] The second electrode 12 may be a negative electrode, the second current collector 121 may be a negative electrode current collector, and the second electrode active material layer 122 may be a negative electrode active material layer.

[0049] The second electrode active material layer 122 may be any one of natural graphite, artificial graphite, a carbonaceous material, a lithium-titanium composite oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, and Ni.

[0050] The first current collector 111 and the second current collector 121 are not particularly limited as long as they have conductivity without causing chemical changes in the battery. For example, the first current collector 111 and the second current collector 121 may be any one of copper, stainless steel, aluminum, nickel, titanium, and calcined carbon.

[0051] Separators

[0052] The separator 13 includes a porous substrate 131 disposed between the first electrode 11 and the second electrode 12 and in contact with the first electrode active material layer 112 , and a coating layer 132 in contact with the second electrode active material layer 122 and disposed on a surface of the porous substrate 131 .

[0053] The porous substrate 131 may be a microporous film or nonwoven fabric made of a single material or a mixture of two or more materials selected from the group consisting of polyolefin-based resins, fluorine-based resins, polyester-based resins, polyacrylonitrile resins, and cellulose-based materials.

[0054] In addition, the porous substrate 131 may be made of a polymer film having insulating properties. For example, the polymer film may be made of any one of polyethylene, polyurethane, and polypropylene.

[0055] The coating 132 may be an inorganic material. The inorganic material may be made of ceramics. For example, the ceramics may be made of any one of silicon carbide (SiC), silicon nitride (Si3n4), zirconium oxide (ZrO2), aluminum oxide (Al2O3), and boehmite (AlOOH).

[0056] The electrode assembly 10 according to the first embodiment of the present invention is obtained based on the first electrode 11, the second electrode 12 and the separator 13 having the above-mentioned structure. That is, the first electrode 11 and the second electrode 12 are alternately provided with the separator 13 interposed therebetween, and then wound into a winding shape to obtain the electrode assembly 10 according to the first embodiment of the present invention. Then, the electrode assembly 10 according to the first embodiment of the present invention is accommodated in the box 20 to manufacture a secondary battery, and the secondary battery undergoes a charging and discharging process to improve battery performance.

[0057] Here, the electrode assembly according to the related art has a problem in that due to the difference in friction coefficient between the first electrode and the separator and between the second electrode and the separator, wear and deformation occur toward the electrode having relatively large friction, thereby causing performance problems and internal short circuits.

[0058] The coefficient of friction is obtained by quantifying how easily two objects do not slide, and is expressed as μ. The coefficient of friction is a unitless integer.

[0059] In order to solve the above problem, the electrode assembly 10 according to the first embodiment of the present invention has a friction coefficient between the first electrode 11 and the separator 13 corresponding to a friction coefficient between the second electrode 12 and the separator 13 .

[0060] That is, the friction coefficient between the first electrode active material layer of the first electrode 11 and the porous substrate 131 corresponds to the friction coefficient between the second electrode active material layer of the second electrode 12 and the coating layer 132. Therefore, since there is no difference in the friction between the first electrode 11 and the separator 13 and the friction between the second electrode 12 and the separator 13, wear and deformation can be prevented, thereby preventing performance problems and internal short circuits.

[0061] In particular, the friction coefficient between the first electrode active material layer 112 and the porous substrate 131 may be the same as the friction coefficient between the second electrode active material layer 122 and the coating layer 132. Therefore, the electrode assembly 10 has no deviation in the friction coefficient between the first electrode active material layer 112 and the porous substrate 131 and the friction coefficient between the second electrode active material layer 122 and the coating layer 132, thereby significantly preventing the occurrence of wear and deformation.

[0062] Since it is difficult to match the friction coefficient between the first electrode active material layer 112 and the porous substrate 131 with the friction coefficient between the second electrode active material layer 122 and the coating 132, there may be an error tolerance range in the friction coefficient between the first electrode active material layer 112 and the porous substrate 131 and the friction coefficient between the second electrode active material layer 122 and the coating 132. That is, it is determined that the friction coefficient between the first electrode active material layer 112 and the porous substrate 131 and the friction coefficient between the second electrode active material layer 122 and the coating 132 within the error tolerance range correspond to each other. The error tolerance range may be 0.05 to 0.50. Preferably, the error tolerance range may be 0.1 to 0.2. Here, if the error tolerance is less than 0.05, precision machining is required, which reduces the machinability, and if the error tolerance is greater than 0.50, wear and deformation may occur as in the related art.

[0063] Reference Figure 1 In the electrode assembly 10 according to the first embodiment of the present invention, the porous substrate 131 and the coating layer 132 of the separator 13 may be determined based on the surface roughness of the first electrode active material layer 112 and the surface roughness of the second electrode active material layer 122. Therefore, the friction coefficient between the first electrode 11 and the separator 13 corresponds to the friction coefficient between the second electrode 12 and the separator 13.

[0064] As a first example, the surface of the second electrode active material layer 122 has a surface roughness coarser than that of the first electrode active material layer 112. Therefore, it is determined based on the surface roughness of the first electrode active material layer 112 and the surface roughness of the second electrode active material layer 122 that the porous substrate 131 has a surface roughness coarser than that of the coating layer 132 in the separator 13.

[0065] As a second example, the porous substrate 131 is determined based on the surface roughness of each of the first electrode active material layer 112, the second electrode active material layer 122, and the coating layer 132. In other words, the porous substrate 131 is determined so that the sum of the surface roughness of the second electrode active material layer 122 and the surface roughness of the coating layer 132 corresponds to the sum of the surface roughness of the first electrode active material layer 112 and the surface roughness of the porous substrate 131. In summary, the surface roughness of each of the first electrode active material layer 112, the second electrode active material layer 122, and the coating layer 132 is obtained, and then the porous substrate is determined so that the surface roughnesses correspond to each other.

[0066] As a third example, coating layer 132 is determined based on the surface roughness of each of first electrode active material layer 112, second electrode active material layer 122, and porous substrate 131. That is, after obtaining the surface roughness of each of first electrode active material layer 112, second electrode active material layer 122, and porous substrate 131, coating layer 132 is determined so that the surface roughnesses correspond to each other.

[0067] In the following experimental examples, the surface roughness of each of the first electrode active material layer, the second electrode active material layer, the porous substrate, and the coating layer was measured based on the arithmetic mean roughness (Ra).

[0068] As an experimental example, refer to Figure 2 , the surface roughness of the first electrode active material layer 112 was measured to be 0.1, the surface roughness of the second electrode active material layer 122 was measured to be 0.25, and the surface roughness of the porous substrate 131 in contact with the first electrode active material layer 112 was measured to be 0.3. Therefore, the coating layer 132 is made of a material having a surface roughness of 0.15.

[0069] In this way, the friction coefficient between the first electrode active material layer 112 and the porous substrate 131 corresponds to the friction coefficient between the second electrode active material layer 122 and the coating layer 132 .

[0070] Therefore, the electrode assembly 10 according to the first embodiment of the present invention can correspond to the friction coefficient between the first electrode active material layer 112 and the porous substrate 131 and the friction coefficient between the second electrode active material layer 122 and the coating 132 to prevent wear and deformation between the first electrode 11 and the separator 13 and between the second electrode 12 and the separator 13, thereby solving performance problems and preventing internal short circuits.

[0071] Hereinafter, in the description of another embodiment of the present invention, constituent elements having the same functions as those of the above-mentioned embodiment have been given the same reference numerals in the drawings, and thus repeated description will be omitted.

[0072] [Electrode assembly according to a second embodiment of the present invention]

[0073] Figure 3 is a cross-sectional view of an electrode assembly according to a second embodiment of the present invention.

[0074] like Figure 3 As illustrated in FIG. 1 , the electrode assembly 10 according to the second embodiment of the present invention includes a first electrode 11 coated with a first electrode active material layer 112 , a second electrode 12 coated with a second electrode active material layer 122 , and a separator 13 disposed between the first electrode 11 and the second electrode 12 .

[0075] Here, the first electrode 11 and the second electrode 12 have the same structure and function as those of the first electrode 11 and the second electrode 12 according to the first embodiment described above, and thus are given the same reference numerals, and thus repeated description will be omitted.

[0076] Separators

[0077] The separator 13 includes a porous substrate 131 disposed between the first electrode 11 and the second electrode 12 , a first coating layer 133 in contact with the first electrode active material layer 112 and disposed on the surface of the porous substrate 131 , and a second coating layer 134 in contact with the second electrode active material layer 122 and disposed on the surface of the porous substrate 131 .

[0078] The porous substrate 131 has the same structure and function as the porous substrate 131 according to the first embodiment described above, and is therefore given the same reference numerals, and thus repeated description will be omitted.

[0079] Each of the first coating layer 133 and the second coating layer 134 may include an inorganic material, and the inorganic material may be made of ceramics. For example, the ceramic may be made of any one of silicon carbide (SiC), silicon nitride (Si3n4), zirconium oxide (ZrO2), aluminum oxide (Al2O3), and boehmite (AlOOH).

[0080] Here, the electrode assembly 10 according to the second embodiment of the present invention has a friction coefficient between the first electrode active material layer 112 and the first coating layer 133 corresponding to a friction coefficient between the second electrode active material layer 122 and the second coating layer 134 .

[0081] In particular, the electrode assembly 10 according to the second embodiment of the present invention may have the same friction coefficient between the first electrode active material layer 112 and the first coating layer 133 and the friction coefficient between the second electrode active material layer 122 and the second coating layer 134 .

[0082] It is difficult to make the friction coefficient between the first electrode active material layer 112 and the first coating 133 and the friction coefficient between the second electrode active material layer 122 and the second coating 134 match correspondingly. Of course, even if the friction coefficients are matched, precision machining is required, which reduces the machinability. Therefore, there may be an error tolerance range in the friction coefficient between the first electrode active material layer 112 and the first coating 133 and the friction coefficient between the second electrode active material layer 122 and the second coating 134. That is, it is determined that the friction coefficient between the first electrode active material layer 112 and the first coating 133 and the friction coefficient between the second electrode active material layer 122 and the second coating 134 within the error tolerance range correspond to each other. The error tolerance range may be 0.05 to 0.50. Preferably, the error tolerance range may be 0.1 to 0.2.

[0083] Based on the surface roughness of each of the first electrode active material layer 112, the second electrode active material layer 122, the first coating layer 133 and the second coating layer 134, the electrode assembly 10 according to the second embodiment of the present invention has a friction coefficient between the first electrode active material layer 112 and the first coating layer 133 corresponding to a friction coefficient between the second electrode active material layer 122 and the second coating layer 134.

[0084] That is, the first coating layer 133 and the second coating layer 134 may be set to have the same surface roughness or may be set to have different surface roughnesses based on the surface roughness of the first electrode active material layer 112 and the surface roughness of the second electrode active material layer 122. Therefore, the friction coefficient between the first electrode active material layer 112 and the first coating layer 133 and the friction coefficient between the second electrode active material layer 122 and the second coating layer 134 may be determined to correspond to each other.

[0085] As a first example, in the electrode assembly 10 according to the second embodiment of the present invention, when the second electrode active material layer 122 has a surface roughness coarser than that of the first electrode active material layer 112, in the separator 13, the first coating layer 133 and the second coating layer 134 are determined based on the surface roughness of the first electrode active material layer 112 and the surface roughness of the second electrode active material layer 122. That is, the first coating layer 133 has a surface roughness coarser than that of the second coating layer 134, so that the friction coefficient between the first electrode active material layer 112 and the first coating layer 133 and the friction coefficient between the second electrode active material layer 122 and the second coating layer 134 correspond to each other.

[0086] As a second example, the second coating layer 134 is determined based on the surface roughness of each of the first electrode active material layer 112, the second electrode active material layer 122, and the first coating layer 133. That is, the second coating layer 134 may be determined so that the sum of the surface roughnesses of the first electrode active material layer 112 and the first coating layer 133 and the sum of the surface roughnesses of the second electrode active material layer 122 and the second coating layer 134 correspond to each other. In summary, after obtaining the surface roughness of each of the first electrode active material layer 112, the second electrode active material layer 122, and the first coating layer 133, the second coating layer 134 is determined so that the surface roughnesses correspond to each other.

[0087] As a third example, the first coating layer 133 may be determined based on the surface roughness of each of the first electrode active material layer 112, the second electrode active material layer 122, and the second coating layer 134. That is, after obtaining the surface roughness of each of the first electrode active material layer 112, the second electrode active material layer 122, and the second coating layer 134, the first coating layer 133 is determined so that the surface roughnesses correspond to each other.

[0088] In the electrode assembly 10 according to the second embodiment of the present invention, the first coating layer 133 and the second coating layer 134 may be made of any one of materials having different surface roughnesses. That is, the electrode assembly 10 may be determined such that the friction coefficients correspond to each other by selecting different materials of the first coating layer 133 and the second coating layer 134 based on the surface roughnesses of the first electrode active material layer 112 and the second electrode active material layer 122.

[0089] Therefore, the electrode assembly 10 according to the second embodiment of the present invention has a friction coefficient between the first electrode active material layer 112 and the first coating layer 133 corresponding to a friction coefficient between the second electrode active material layer 122 and the second coating layer 134. Therefore, wear and deformation between the first electrode and the separator 13 and between the second electrode and the separator 13 can be prevented, and thus, performance problems and internal short circuits can be prevented.

[0090] [Secondary battery according to third embodiment of the present invention]

[0091] Figure 4 is a cross-sectional view of a secondary battery according to a third embodiment of the present invention.

[0092] The secondary battery 1 according to the third embodiment of the present invention has a structure including the electrode assembly 10 according to the first embodiment or the battery assembly 10 according to the second embodiment described above.

[0093] That is to say, Figure 4As illustrated in FIG. 1 , a secondary battery 1 according to a third embodiment of the present invention includes an electrode assembly 10 and a case 20 accommodating the electrode assembly 10 .

[0094] Here, the electrode assembly 10 has the same structure and function as the electrode assembly 10 according to the first embodiment or the battery assembly 10 according to the second embodiment described above.

[0095] Therefore, the secondary battery 1 according to the third embodiment of the present invention can improve safety by improving the difference between the frictional force between the positive electrode and the separator 13 and the frictional force between the negative electrode and the separator 13 .

[0096] Although the electrode assembly according to the present invention has been described above with reference to the exemplary drawings, those skilled in the art may make various changes and modifications thereto without departing from the scope and spirit of the present invention as set forth in the appended claims.

[0097] [Description of Reference Signs]

[0098] 1: Secondary battery

[0099] 10: Electrode assembly

[0100] 11: First electrode

[0101] 111: First current collector

[0102] 112: Second electrode active material layer

[0103] 12: Second electrode

[0104] 121: Second current collector

[0105] 122: Second electrode active material layer

[0106] 13: Separator

[0107] 131: Porous substrate

[0108] 132: Coating

[0109] 133: First coating

[0110] 134: Second coating

[0111] 20: Box

Claims

1. An electrode assembly comprising a first electrode coated with a first electrode active material layer, a second electrode coated with a second electrode active material layer, and a separator disposed between the first electrode and the second electrode, in, The separator comprises: a porous substrate disposed between the first electrode and the second electrode and in contact with the first electrode active material layer; and a coating layer, the coating layer being in contact with the second electrode active material layer and being disposed on the surface of the porous substrate, The friction coefficient between the first electrode active material layer and the porous substrate and the friction coefficient between the second electrode active material layer and the coating layer correspond to each other.

2. The electrode assembly according to claim 1, wherein: The friction coefficient between the first electrode active material layer and the porous substrate is the same as the friction coefficient between the second electrode active material layer and the coating layer.

3. The electrode assembly according to claim 1, wherein: In the separator, the porous substrate and the coating are determined based on the surface roughness of the first electrode active material layer and the surface roughness of the second electrode active material layer, so that the friction coefficient between the first electrode active material layer and the porous substrate and the friction coefficient between the second electrode active material layer and the coating correspond to each other.

4. The electrode assembly according to claim 3, wherein: The second electrode active material layer has a surface roughness coarser than that of the first electrode active material layer, and In the separator, the porous substrate has a surface roughness coarser than that of the coating layer so that a friction coefficient between the first electrode active material layer and the porous substrate and a friction coefficient between the second electrode active material layer and the coating layer correspond to each other.

5. The electrode assembly according to claim 1, wherein: The coating comprises an inorganic material, and The inorganic material is made of ceramics.

6. An electrode assembly comprising a first electrode coated with a first electrode active material layer, a second electrode coated with a second electrode active material layer, and a separator disposed between the first electrode and the second electrode, in, The separator comprises: a porous substrate, wherein the porous substrate is located between the first electrode and the second electrode; a first coating layer that contacts the first electrode active material layer and is disposed on a surface of the porous substrate; and a second coating layer, the second coating layer being in contact with the second electrode active material layer and disposed on the surface of the porous substrate, The friction coefficient between the first electrode active material layer and the first coating layer and the friction coefficient between the second electrode active material layer and the second coating layer correspond to each other.

7. The electrode assembly according to claim 6, wherein: The friction coefficient between the first electrode active material layer and the first coating layer is the same as the friction coefficient between the second electrode active material layer and the second coating layer.

8. The electrode assembly according to claim 6, wherein: In the separator, the first coating layer and the second coating layer are determined based on the surface roughness of the first electrode active material layer and the surface roughness of the second electrode active material layer, so that the friction coefficient between the first electrode active material layer and the first coating layer and the friction coefficient between the second electrode active material layer and the second coating layer correspond to each other.

9. The electrode assembly according to claim 8, wherein: The second electrode active material layer has a surface roughness coarser than that of the first electrode active material layer, and In the separator, the first coating layer has a surface roughness coarser than that of the second coating layer so that a friction coefficient between the first electrode active material layer and the first coating layer and a friction coefficient between the second electrode active material layer and the second coating layer correspond to each other.

10. The electrode assembly according to claim 6, wherein: Each of the first coating layer and the second coating layer includes an inorganic material, and The inorganic material is made of ceramics.

11. The electrode assembly according to claim 6, wherein: The first coating layer and the second coating layer are made of materials having different surface roughnesses.

12. The electrode assembly according to claim 1 or 6, wherein: The first electrode is set as a positive electrode, and the second electrode is set as a negative electrode.

13. The electrode assembly according to claim 1 or 6, wherein: The porous substrate is made of an insulating polymer film.

14. The electrode assembly according to claim 13, wherein: The polymer film is made of any one of polyethylene, polyurethane, and polypropylene.

15. The electrode assembly according to claim 5 or 10, wherein: The ceramic is made of any one of silicon carbide (SiC), silicon nitride (Si3n4), zirconium oxide (ZrO2), aluminum oxide (Al2O3), and boehmite (AlOOH). 16 . A secondary battery comprising the electrode assembly according to claim 1 .

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