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 including 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 disposed on a surface of the porous substrate and in contact with the second electrode active material layer, wherein the first electrode active material layer and the porous substrate and the second electrode active material layer and the coating layer have corresponding coefficients of friction.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0118219, filed on September 19, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an 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, and a secondary battery including the same. [Background technology]

[0003] In general, a secondary battery is a battery that can be charged and discharged, unlike a primary battery, which cannot be charged. Such secondary batteries are widely used in phones, laptops, camcorders, electric vehicles, etc.

[0004] The secondary batteries are classified into cylindrical secondary batteries in which an electrode assembly is housed in a metal can, and pouch secondary batteries in which an electrode assembly is housed in a pouch.

[0005] The cylindrical secondary battery includes an electrode assembly, a can that houses the electrode assembly, and a cap assembly that is mounted on an opening of the can.

[0006] The pouch-type secondary battery includes an electrode assembly and a pouch that houses the electrode assembly. The pouch includes a housing that houses the electrode assembly and a seal that seals the housing.

[0007] Meanwhile, the electrode assembly has a structure in which electrodes and separators are alternately arranged, and the electrodes include a positive electrode and a negative electrode.

[0008] The cylindrical secondary battery is fabricated by alternately arranging positive and negative electrodes with separators interposed therebetween and winding them into a jelly roll to form an electrode assembly.

[0009] Here, in a cylindrical secondary battery, the positive and negative electrodes repeatedly contract and expand during charging and discharging, and at this time, friction is repeatedly generated between the positive electrode and the separator, and between the negative electrode and the separator.

[0010] However, cylindrical secondary batteries have the problem that the electrode with the greater frictional force is subject to wear and bending due to the difference in frictional force between the positive electrode and separator and between the negative electrode and separator, resulting in performance problems and the problem of internal short circuits. Summary of the Invention [Problem to be solved by the invention]

[0011] An object of the present invention is to provide an electrode assembly and a secondary battery including the same, which can prevent wear and bending between the positive electrode and the separator and between the negative electrode and the separator by improving the difference in friction between the positive electrode and the separator and between the negative electrode and the separator, thereby preventing performance problems and internal short circuits. [Means for solving the problem]

[0012] 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 disposed on a surface of the porous substrate and in contact with the second electrode active material layer. The first electrode active material layer and the porous substrate and the second electrode active material layer and the coating layer may have corresponding coefficients of friction.

[0013] The coefficient of friction between the first electrode active material layer and the porous substrate and the coefficient of friction between the second electrode active material layer and the coating layer may be the same.

[0014] In the separator, the porous substrate and the coating layer may 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 coefficients between the first electrode active material layer and the porous substrate and the second electrode active material layer and the coating layer correspond to each other.

[0015] The second electrode active material layer has a surface rougher than that of the first electrode active material layer, and in the separator, the porous substrate may have a surface rougher than that of the coating layer so that the coefficients of friction between the first electrode active material layer and the porous substrate and between the second electrode active material layer and the coating layer correspond to each other.

[0016] The coating layer may include an inorganic material, and the inorganic material may be made of ceramic.

[0017] Meanwhile, an electrode assembly according to 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, wherein the separator includes a porous substrate disposed between the first electrode and the second electrode, a first coating layer in contact with the first electrode active material layer and provided on a surface of the porous substrate, and a second coating layer in contact with the second electrode active material layer and provided on a surface of the porous substrate, and the first electrode active material layer and the first coating layer may have corresponding coefficients of friction therebetween.

[0018] The coefficient of friction between the first electrode active material layer and the first coating layer and the coefficient of friction between the second electrode active material layer and the second coating layer may be the same.

[0019] The separator may have the first coating layer and the second coating layer determined based on the surface roughness of the first electrode active material layer and the surface roughness of the second electrode active material layer such that the coefficients of friction between the first electrode active material layer and the first coating layer correspond to each other.

[0020] The second electrode active material layer has a surface rougher than the first electrode active material layer, and in the separator, the first coating layer can have a surface rougher than the second coating layer so that the coefficients of friction between the first electrode active material layer and the first coating layer correspond to those between the second electrode active material layer and the second coating layer.

[0021] The first coating layer and the second coating layer may include an inorganic material, and the inorganic material may be made of ceramic.

[0022] The first coating layer and the second coating layer may be made of materials having different surface roughnesses.

[0023] The first electrode may be a positive electrode, and the second electrode may be a negative electrode.

[0024] The porous substrate may be made of an insulating polymer film.

[0025] The polymer film may be made of any one of polyethylene, polyurethane, and polypropylene.

[0026] The ceramic may be made of any one of silicon carbide (SiC), silicon nitride (Si3n4), zirconia (ZrO2), aluminum oxide (Al2O3), and boehmite (AlOOH).

[0027] Meanwhile, the secondary battery of the present invention may include the electrode assembly. [Effects of the Invention]

[0028] The electrode assembly of the present invention includes a separator having a porous substrate and a coating layer, and is characterized in that the first electrode active material layer of the first electrode and the porous substrate have a corresponding coefficient of friction, and the second electrode active material layer of the second electrode and the coating layer have a corresponding coefficient of friction. This characteristic prevents wear and bending between the first electrode and the separator, and between the second electrode and the separator, thereby resolving performance issues and preventing internal short circuits. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a cross-sectional view showing an electrode assembly according to a first embodiment of the present invention. [Figure 2] 3 is a table showing the surface roughness of the electrode assembly according to the first embodiment of the present invention. [Figure 3] FIG. 4 is a cross-sectional view showing an electrode assembly according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view showing a secondary battery according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily understand the present invention. However, the present invention may be realized in various different forms and is not limited to the embodiments described herein. In the drawings, parts that are not relevant to the description will be omitted in order to clearly explain the present invention, and similar parts will be designated by similar reference numerals throughout the specification.

[0031] [Electrode assembly according to the first embodiment of the present invention] FIG. 1 is a cross-sectional view showing an electrode assembly according to a first embodiment of the present invention.

[0032] As shown 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.

[0033] 1st electrode The first electrode 11 includes a first current collector 111 having a long sheet shape, and a first electrode active material layer 112 coated on one or both sides of the first current collector 111 .

[0034] On the other hand, 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.

[0035] Here, the first electrode active material layer 112 may be any one of LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNiMnCoO2.

[0036] 2nd electrode The second electrode 12 includes a second current collector 121 having a long sheet shape, and a second electrode active material layer 122 coated on one or both sides of the second current collector 121 .

[0037] Meanwhile, the second electrode 12 can be a negative electrode, the second current collector 121 can be a negative electrode current collector, and the second electrode active material layer 122 can be a negative electrode active material layer.

[0038] The second electrode active material layer 122 may be any one of natural graphite, artificial graphite, carbonaceous material, lithium titanium oxide (LTO), Si, Sn, Li, Zn, Mg, Cd, Ce, and Ni.

[0039] Meanwhile, the first current collector 111 and the second current collector 121 are not particularly limited as long as they do not cause chemical changes in the battery and are conductive. For example, the first current collector 111 and the second current collector 121 may be made of any one of copper, stainless steel, aluminum, nickel, titanium, and calcined carbon.

[0040] Separator The separator 13 is disposed between the first electrode 11 and the second electrode 12, and includes a porous substrate 131 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 provided on the surface of the porous substrate 131.

[0041] The porous substrate 131 may be a microporous membrane or nonwoven fabric made of a single material or a mixture of two or more materials selected from the group consisting of polyolefin resins, fluorine-based resins, polyester resins, polyacrylonitrile resins, and cellulose-based materials.

[0042] The porous substrate 131 may be made of an insulating polymer film, for example, polyethylene, polyurethane, or polypropylene.

[0043] The coating layer 132 may be an inorganic material. The inorganic material may be ceramic. For example, the ceramic may be any one of silicon carbide (SiC), silicon nitride (Si3n4), zirconia (ZrO2), aluminum oxide (Al2O3), and boehmite (AlOOH).

[0044] The electrode assembly 10 according to the first embodiment of the present invention is obtained based on the first electrode 11, second electrode 12, and separator 13 having such a structure. That is, the first electrodes 11 and second electrodes 12 are alternately arranged with the separator 13 interposed therebetween, and then wound up into a jelly roll to obtain the electrode assembly 10 according to the first embodiment of the present invention. Furthermore, a secondary battery is manufactured by housing the electrode assembly 10 according to the first embodiment of the present invention in a case 20, and the secondary battery undergoes a charge / discharge process to improve battery performance.

[0045] In this case, conventional electrode assemblies have a problem in that the electrode with the greater frictional force is subject to wear and bending due to the difference in the coefficient of friction between the first electrode and separator and between the second electrode and separator, resulting in performance problems and internal short circuits.

[0046] On the other hand, the coefficient of friction is a numerical representation of the degree of resistance to sliding between two objects, and is expressed as μ. It is a unitless positive number.

[0047] To solve the above problems, the electrode assembly 10 according to the first embodiment of the present invention has corresponding coefficients of friction between the first electrode 11 and the separator 13 and between the second electrode 12 and the separator 13.

[0048] That is, there are corresponding coefficients of friction between the first electrode active material layer of the first electrode 11 and the porous substrate 131 and between the second electrode active material layer of the second electrode 12 and the coating layer 132. As a result, there is no difference in frictional force between the first electrode 11 and the separator 13 and between the second electrode 12 and the separator 13, which prevents wear and bending, thereby solving performance problems and preventing internal short circuits.

[0049] In particular, the first electrode active material layer 112 and the porous substrate 131 may have the same coefficient of friction as the second electrode active material layer 122 and the coating layer 132. As a result, the electrode assembly 10 has no deviation in the coefficient of friction between the first electrode active material layer 112 and the porous substrate 131 and the second electrode active material layer 122 and the coating layer 132, which significantly reduces wear and deformation.

[0050] Meanwhile, because it is difficult to adjust the coefficient of friction between the first electrode active material layer 112 and the porous substrate 131 and the second electrode active material layer 122 and the coating layer 132 to correspond to each other, there may be a tolerance for the coefficient of friction between the first electrode active material layer 112 and the porous substrate 131 and between the second electrode active material layer 122 and the coating layer 132. That is, if the coefficient of friction between the first electrode active material layer 112 and the porous substrate 131 and the coefficient of friction between the second electrode active material layer 122 and the coating layer 132 fall within the tolerance for error, they are considered to correspond to each other. The tolerance for error may be 0.05 to 0.50, preferably 0.1 to 0.2. Here, if the tolerance for error is 0.05 or less, a precision process is required, resulting in poor workability, while if the tolerance for error is 0.50 or more, wear and warping may occur, as in the conventional method.

[0051] 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 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. As a result, the first electrode 11 and the separator 13 and the second electrode 12 and the separator 13 have corresponding coefficients of friction.

[0052] As a first example, the second electrode active material layer 122 has a surface rougher than the first electrode active material layer 112. Thus, the porous substrate 131 of the separator 13, which has a surface rougher than the coating layer 132, 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.

[0053] As a second example, the porous substrate 131 is determined based on the surface roughness 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 coating layer 132 corresponds to the sum of the surface roughness of the first electrode active material layer 112 and the porous substrate 131. In summary, after determining the surface roughness of the first electrode active material layer 112, the second electrode active material layer 122, and the coating layer 132, the porous substrate 131 is determined so that there is a corresponding relationship.

[0054] As a third example, the coating layer 132 is determined based on the surface roughness of the first electrode active material layer 112, the second electrode active material layer 122, and the porous substrate 131. That is, after the surface roughness of the first electrode active material layer 112, the second electrode active material layer 122, and the porous substrate 131 is determined, the coating layer 132 is determined so as to have a corresponding relationship.

[0055] Meanwhile, in the following experimental examples, the surface roughness of the first electrode active material layer, the second electrode active material layer, the porous substrate, and the coating layer is measured based on the arithmetic mean roughness (Ra).

[0056] 2, in the experimental example, 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. As a result, a material having a surface roughness of 0.15 was determined for the coating layer 132.

[0057] In this manner, the first electrode active material layer 112 and the porous substrate 131 and the second electrode active material layer 122 and the coating layer 132 may have corresponding coefficients of friction.

[0058] Therefore, in the electrode assembly 10 according to the first embodiment of the present invention, the first electrode active material layer 112 and the porous substrate 131 and the second electrode active material layer 122 and the coating layer 132 have corresponding coefficients of friction, which can prevent wear and bending 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.

[0059] In the following description of other embodiments of the present invention, the same reference numerals will be used for components having the same functions as those in the above-described embodiment, and duplicated explanations will be omitted.

[0060] [Electrode assembly according to a second embodiment of the present invention] FIG. 3 is a cross-sectional view showing an electrode assembly according to a second embodiment of the present invention.

[0061] As shown in FIG. 3, 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.

[0062] Here, the first electrode 11 and the second electrode 12 have the same configuration and function as the first electrode 11 and the second electrode 12 according to the first embodiment described above, and therefore the same reference numerals are used and redundant explanations will be omitted.

[0063] Separator 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 provided 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 provided on the surface of the porous substrate 131.

[0064] Meanwhile, the porous substrate 131 has the same configuration and function as the porous substrate 131 according to the first embodiment, and therefore the same reference numerals are used and redundant description will be omitted.

[0065] The first coating layer 133 and the second coating layer 134 include an inorganic material, which may be made of ceramic. For example, the ceramic may be made of any one of silicon carbide (SiC), silicon nitride (Si3n4), zirconia (ZrO2), aluminum oxide (Al2O3), and boehmite (AlOOH).

[0066] Here, in the electrode assembly 10 according to the second embodiment of the present invention, the friction coefficients between the first electrode active material layer 112 and the first coating layer 133 and the friction coefficients between the second electrode active material layer 122 and the second coating layer 134 correspond to each other.

[0067] In particular, the electrode assembly 10 according to the second embodiment of the present invention may have the same coefficient of friction between the first electrode active material layer 112 and the first coating layer 133 and between the second electrode active material layer 122 and the second coating layer 134.

[0068] Meanwhile, it is difficult to adjust the coefficient of friction between the first electrode active material layer 112 and the first coating layer 133 and the coefficient of friction between the second electrode active material layer 122 and the second coating layer 134 so that they correspond to each other. Even if the coefficients of friction are adjusted, precision machining is required, resulting in poor workability. Therefore, there may be an allowable error range between the coefficients of friction between the first electrode active material layer 112 and the first coating layer 133 and between the second electrode active material layer 122 and the second coating layer 134. That is, it is determined that the coefficient of friction between the first electrode active material layer 112 and the first coating layer 133 and the coefficient of friction between the second electrode active material layer 122 and the second coating layer 134 correspond to each other within the allowable error range. The allowable error range may be 0.05 to 0.50, preferably 0.1 to 0.2.

[0069] Meanwhile, in the electrode assembly 10 according to the second embodiment of the present invention, the coefficients of friction between the first electrode active material layer 112 and the first coating layer 133 and between the second electrode active material layer 122 and the second coating layer 134 are determined to correspond to each other based on the surface roughness 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.

[0070] That is, the first coating layer 133 and the second coating layer 134 may be determined to have the same surface roughness or different surface roughnesses based on the surface roughnesses of the first electrode active material layer 112 and the second electrode active material layer 122. As a result, the coefficients of friction between the first electrode active material layer 112 and the first coating layer 133 and between the second electrode active material layer 122 and the second coating layer 134 may be determined accordingly.

[0071] 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 rougher than the first electrode active material layer 112, the first coating layer 133 and the second coating layer 134 of the separator 13 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 rougher than the second coating layer 134 such that the coefficients of friction between the first electrode active material layer 112 and the first coating layer 133 and between the second electrode active material layer 122 and the second coating layer 134 correspond to each other.

[0072] As a second example, the second coating layer 134 is determined based on the surface roughness of the first electrode active material layer 112, the second electrode active material layer 122, and the first coating layer 133. In other words, the second coating layer 134 can be determined so that the sum of the surface roughness of the first electrode active material layer 112 and the first coating layer 133 corresponds to the sum of the surface roughness of the second electrode active material layer 122 and the second coating layer 134. In summary, after determining the surface roughness 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 there is a corresponding relationship.

[0073] As a third example, the first coating layer 133 may be determined based on the surface roughness of the first electrode active material layer 112, the second electrode active material layer 122, and the second coating layer 134. That is, after the surface roughness of the first electrode active material layer 112, the second electrode active material layer 122, and the second coating layer 134 is determined, the first coating layer 133 is determined so as to have a corresponding relationship.

[0074] Meanwhile, 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, in the electrode assembly 10, different materials may be selected for 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, and the friction coefficients may be determined to correspond to each other.

[0075] Therefore, in the electrode assembly 10 according to the second embodiment of the present invention, the first electrode active material layer 112 and the first coating layer 133 have a corresponding coefficient of friction, and the second electrode active material layer 122 and the second coating layer 134 have a corresponding coefficient of friction. This prevents wear and bending between the first electrode and the separator 13 and between the second electrode and the separator 13, and as a result, prevents performance problems and internal short circuits.

[0076] [Secondary battery according to a third embodiment of the present invention] FIG. 4 is a cross-sectional view showing a secondary battery according to a third embodiment of the present invention.

[0077] A secondary battery 1 according to a third embodiment of the present invention has a structure including the electrode assembly 10 according to the first embodiment or the electrode assembly 10 according to the second embodiment.

[0078] That is, the secondary battery 1 according to the third embodiment of the present invention includes an electrode assembly 10 and a case 20 that houses the electrode assembly 10, as shown in FIG.

[0079] Here, the electrode assembly 10 has the same configuration and function as the electrode assembly 10 according to the first embodiment or the electrode assembly 10 according to the second embodiment.

[0080] Therefore, the secondary battery 1 according to the third embodiment of the present invention can improve safety by improving the difference in frictional force between the positive electrode and the separator 13 and between the negative electrode and the separator 13.

[0081] Although the electrode assembly according to the present invention has been described above with reference to the drawings illustrating the same, the present invention is not limited to the above-described embodiments and drawings, and various modifications can be made by those skilled in the art within the scope of the claims. [Explanation of symbols]

[0082] 1 Secondary battery 10 Electrode assembly 11 1st electrode 111 First current collector 112 First electrode active material layer 12 2nd electrode 121 Second current collector 122 Second electrode active material layer 13 Separator 131 Porous substrate 132 Coating Layer 133 First coating layer 134 Second coating layer 20 cases

Claims

1. 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 is a porous substrate disposed between the first electrode and the second electrode and in contact with the first electrode active material layer; a coating layer in contact with the second electrode active material layer and provided on the surface of the porous substrate; The electrode assembly has a corresponding coefficient of friction between the first electrode active material layer and the porous substrate and between the second electrode active material layer and the coating layer.

2. The electrode assembly of claim 1 , wherein a coefficient of friction between the first electrode active material layer and the porous substrate and a coefficient of friction between the second electrode active material layer and the coating layer are the same.

3. 2. The electrode assembly of claim 1, wherein the separator has a porous substrate and a coating layer determined based on a surface roughness of the first electrode active material layer and a surface roughness of the second electrode active material layer such that a coefficient of friction between the first electrode active material layer and the porous substrate corresponds to a coefficient of friction between the second electrode active material layer and the coating layer.

4. the second electrode active material layer has a surface rougher than the first electrode active material layer, 4. The electrode assembly according to claim 3, wherein in the separator, the porous substrate has a surface roughness greater than that of the coating layer such that a coefficient of friction between the first electrode active material layer and the porous substrate corresponds to a coefficient of friction between the second electrode active material layer and the coating layer.

5. The electrode assembly of claim 1 , wherein the coating layer includes an inorganic material, and the inorganic material is made of ceramic.

6. 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 is a porous substrate disposed between the first electrode and the second electrode; a first coating layer provided on the surface of the porous substrate and in contact with the first electrode active material layer; a second coating layer in contact with the second electrode active material layer and provided on the surface of the porous substrate; The electrode assembly has a corresponding coefficient of friction between the first electrode active material layer and the first coating layer and between the second electrode active material layer and the second coating layer.

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

8. 7. The electrode assembly of claim 6, wherein the separator has the first coating layer and the second coating layer determined based on a surface roughness of the first electrode active material layer and a surface roughness of the second electrode active material layer such that a coefficient of friction between the first electrode active material layer and the first coating layer corresponds to a coefficient of friction between the second electrode active material layer and the second coating layer.

9. the second electrode active material layer has a surface rougher than the first electrode active material layer, 9. The electrode assembly according to claim 8, wherein in the separator, the first coating layer has a surface roughness greater than that of the second coating layer such that a coefficient of friction between the first electrode active material layer and the first coating layer corresponds to a coefficient of friction between the second electrode active material layer and the second coating layer.

10. the first coating layer and the second coating layer contain an inorganic material; The electrode assembly according to claim 6 , wherein the inorganic material is made of ceramic.

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 a positive electrode and the second electrode is 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 of claim 13, wherein the polymer film is made of any one of polyethylene, polyurethane, and polypropylene.

15. The ceramics include silicon carbide (SiC), silicon nitride (Si ３ n ４ ), zirconia (ZrO ２ ), aluminum oxide (Al ２ O ３ 11. The electrode assembly according to claim 5 or 10, comprising one of: SiO2 (SiO2), SiO2 (SiO2), and boehmite (AlOOH).

16. A secondary battery comprising the electrode assembly according to claim 1 or 6.

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