Electrode assembly and electrochemical device including the same

Abstract

The present invention relates to an electrode assembly and an electrochemical device including the same. The electrode assembly of the present invention comprises a unit electrode and a strip-shaped separator. The separator is folded in a zigzag manner, and the unit electrode is inserted into the portion where the separator overlaps. The separator comprises a porous substrate made of a polymer material and a porous coating layer formed on the upper and lower surfaces of the porous substrate, each containing inorganic particles. The thickness (Ts) of the porous substrate gradually decreases from the center of the separator in the longitudinal direction toward both ends, the total thickness (Tc) of the porous coating layer gradually increases toward both ends, and the total thickness (Ts+Tc) is maintained constant across the entire surface of the separator.

Description

Technology Field

[0001] The present invention relates to an electrode assembly and an electrochemical device including the same, specifically a zigzag-stack type electrode assembly and a secondary battery including the same. Background Technology

[0002] Recently, interest in energy storage technology has been steadily increasing. As application fields expand to include energy for mobile phones, camcorders, laptop PCs, and even electric vehicles, efforts in battery research and development are becoming increasingly concrete. Electrochemical devices are the field receiving the most attention in this regard; in particular, driven by the recent trend toward the miniaturization and lightweighting of electronic devices, the development of rechargeable batteries—capable of small size, light weight, and high capacity—is becoming a focal point of interest.

[0003] Furthermore, secondary batteries are also classified according to the structure of the electrode assembly comprising the positive electrode, separator, and negative electrode. Representatively, they are divided into a jelly-roll (wound-type) electrode assembly, in which long sheet-type positive and negative electrodes are wound with a separator interposed, and a stack-type (laminated-type) electrode assembly, in which multiple positive and negative electrodes cut into units of a predetermined size are sequentially stacked with a separator interposed. However, these conventional electrode assemblies have several problems.

[0004] First, since the jelly-roll electrode assembly is formed by winding long sheet-type positive and negative electrodes in a dense manner to create a cylindrical or elliptical structure in cross-section, stress caused by the expansion and contraction of the electrodes during charging and discharging accumulates within the electrode assembly. When such stress accumulation exceeds a certain limit, deformation of the electrode assembly occurs. This deformation of the electrode assembly results in uneven spacing between the electrodes, causing a rapid deterioration in battery performance and threatening the safety of the battery due to internal short circuits. Additionally, since long sheet-type positive and negative electrodes must be wound, it is difficult to wind them quickly while maintaining a constant spacing between them, which leads to a problem of reduced productivity.

[0005] Second, since stacked electrode assemblies must sequentially stack multiple anode and cathode units, a separate transfer process for electrode plates is required for manufacturing the units, and since the sequential stacking process requires a lot of time and effort, there is a problem of low productivity.

[0006] Figure 1 is a cross-sectional view schematically illustrating the structure of a stacked electrode assembly.

[0007] Referring to FIG. 1, a stacked electrode assembly (1) has been developed in which a positive electrode (5) and a negative electrode (7) are stacked in a zig-zag pattern with a separator (3) in between.

[0008] A battery is manufactured by assembling an electrode assembly using the zigzag stacking method as described above and finally fixing it through a hot press process. At this time, since the heat and pressure applied during the final hot press process are applied to the entire stacked electrode assembly, the amount of heat and pressure transferred to the top and bottom parts of the electrode assembly based on the stacking direction increases, and consequently, the thickness deformation of the substrate at the top and bottom parts increases, which ultimately leads to a problem of quality defects in the electrode assembly. The problem to be solved

[0009] Therefore, the problem that the present invention aims to solve is to provide a novel structure of a separator and an electrode assembly including the same, in which thickness deformation and pore damage of the porous structure can be minimized during the manufacture of an electrode assembly using the zig-zag stacking (ZZS) method.

[0010] Specifically, the present invention aims to provide a novel structure of an electrode assembly in which thickness deformation and pore damage of the porous structure can be minimized despite heat and pressure that are particularly significantly transferred to the separator region of the uppermost bottom portion of the electrode assembly in the stacking direction that the hot press contacts during the hot pressing step for manufacturing the electrode assembly.

[0011] Thus, the purpose is to provide a separator that maintains a high dielectric breakdown voltage and has improved insulation properties, and an electrode assembly including the same. means of solving the problem

[0012] In order to solve the above problem,

[0013] According to one aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0014] According to the first embodiment,

[0015] An electrode assembly is provided, comprising a unit electrode and a strip-shaped separator, wherein the separator is folded in a zigzag manner and the unit electrode is inserted into the overlapping portion of the separator, and the separator comprises a porous substrate made of a polymer material and a porous coating layer formed on the upper and lower surfaces of the porous substrate, each containing inorganic particles, wherein the thickness (Ts) of the porous substrate gradually decreases from the center in the longitudinal direction of the separator to both ends, the total thickness (Tc) of the porous coating layer gradually increases towards both ends, and the total thickness (Ts+Tc) is maintained constant across the entire surface of the separator.

[0016] According to the second embodiment, in the first embodiment,

[0017] The thickness (Ts) of the porous substrate is maintained constant from the longitudinal centerline of the separator to a predetermined position (A) in the direction of one end and a predetermined position (A') in the direction of the opposite end, and all or at least part of the region AE from the position (A) to the end (E) and the region A'E' from the position (A') to the other end (E') are respectively positioned at the top and bottom of the stacking direction of the electrode assembly, and the thickness (Ts) of the porous substrate gradually decreases as it goes toward the end of the separator, and the total thickness (Tc) of the porous coating layer may increase as it goes toward both ends.

[0018] According to the third embodiment, in the first embodiment or the second embodiment,

[0019] The region AA' from the above position (A) to the above position (A') is not located at the top and bottom of the stacking direction of the electrode assembly, and the region of the separator located at the top and bottom of the stacking direction of the electrode assembly may be such that the thickness (Ts) of the porous substrate is reduced toward the end portion of the separator.

[0020] According to the fourth embodiment, in any one of the first to third embodiments,

[0021] The porous coating layers formed on the upper and lower surfaces of the porous substrate are formed symmetrically with respect to the centerline in the longitudinal direction of the separator, so that the thickness of each porous coating layer at the same arbitrary position orthogonal to the longitudinal direction of the separator may be the same or the difference in thickness may be within 10%.

[0022] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0023] The above separator is formed to have a symmetric structure with respect to a longitudinal centerline, so that in the region AE and the region A'E', the thickness (Ts) of each porous substrate formed at any position spaced apart from the longitudinal centerline of the separator may be equal to each other or have a thickness difference of within 10%.

[0024] According to the 6th embodiment, in any one of the 1st to 5th embodiments,

[0025] The ratio (Ts / Tc) of the thickness (Ts) of the porous substrate to the total thickness (Tc) of the porous coating layer across the entire surface of the separator may be 0.5 to 5.

[0026] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0027] The ratio (Ts / Tc) of the thickness (Ts) of the porous substrate to the total thickness (Tc) of the porous coating layer at the above position (A) may be 1 to 5.

[0028] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0029] After being fixed through a hot press process at a temperature of 50°C to 110°C and a pressure of 3 MPa to 10 MPa, the thickness strain of the outermost part of the electrode assembly may be 30% or less.

[0030] According to another aspect of the present invention, electrode assemblies of the following embodiments are provided.

[0031] According to the ninth embodiment,

[0032] An electrochemical device is provided, characterized in that an electrode assembly according to any one of the first to eighth embodiments is housed in a case.

[0033] According to the 10th embodiment, in the 9th embodiment,

[0034] The above electrochemical device may be a lithium secondary battery. Effects of the invention

[0035] An electrode assembly according to one embodiment of the present invention can exhibit characteristics in which thickness deformation of the separator and pore damage of the porous structure within the separator are minimized despite heat and pressure applied to the top bottom portion in the stacking direction when fixed through a hot pressing process.

[0036] Accordingly, it is possible to demonstrate the advantage of providing an electrode assembly with excellent insulation properties. Brief explanation of the drawing

[0037] FIG. 1 is a schematic cross-sectional view of one embodiment of an electrode assembly of the ZZS method. FIG. 2 schematically illustrates the upper surface of a strip-shaped separator according to one embodiment of the present invention. FIG. 3 schematically illustrates a side view of a strip-shaped separator according to one embodiment of the present invention. FIG. 4 schematically illustrates a side view of a strip-shaped separator according to one embodiment of the present invention. FIG. 5 schematically illustrates the structure of an electrode assembly before assembly according to one embodiment of the present invention. FIG. 6 schematically illustrates a method for manufacturing an electrode assembly in one embodiment of the present invention. FIG. 7 briefly illustrates the side structure when a separator according to one embodiment of the present invention is folded in a zigzag manner. FIG. 8 briefly illustrates the side structure when a separator according to one embodiment of the present invention is folded in a zigzag manner. FIG. 9 briefly illustrates the side structure when a separator according to one embodiment of the present invention is folded in a zigzag manner. Specific details for implementing the invention

[0038] The present invention will be described in detail below.

[0039] In this specification, when a part is described as "comprising" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but may include additional components.

[0040] In this specification, terms such as “about,” “substantially,” etc., are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the stated meaning, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0041] In this specification, the description of the term "A and / or B" means "A or B, or both."

[0042] Specific terms used in the following detailed description of the invention are for convenience only and are not intended to limit the invention. Additionally, words indicating direction, such as up, down, left, right, front, back, inside, and outside, indicate directions in the referenced drawings or directions toward or away from the geometric center of the respective designated device, system, and its components.

[0043] The present invention relates to a separator for an electrochemical device and an electrode assembly including the same. Examples of the electrochemical device include a primary battery, a secondary battery, a supercapacitor, an electric double layer capacitor, etc. More specifically, the secondary battery may be a lithium-ion secondary battery.

[0044] In one embodiment of the present invention, the electrode assembly comprises a unit electrode and a strip-shaped separator, and the separator is folded in a zigzag manner and has a ZZS type electrode assembly structure in which the unit electrode is inserted into the portion where the separator overlaps.

[0045] The electrode assembly and each component included in the electrode assembly will be described in more detail below with reference to the drawings.

[0046] The above-described separator comprises a porous substrate made of a polymer material and a porous coating layer formed on the upper and lower surfaces of the porous substrate, each containing inorganic particles. The thickness (Ts) of the porous substrate gradually decreases from the center to both ends along the longitudinal direction of the separator, the total thickness (Tc) of the porous coating layer gradually increases towards both ends, and the total thickness (Ts+Tc) is maintained constant across the entire surface of the separator.

[0047] In this specification, the "length direction" of the separator indicates the direction in which two or more unit electrodes are arranged on the strip-shaped separator.

[0048] In this specification, the "stacking direction" of the electrode assembly indicates the height direction in which the unit cells are stacked when the electrode assembly is folded in a zigzag manner during assembly and a unit electrode is inserted into the portion where the separator overlaps.

[0049] In this specification, the term “thickness is maintained constant within a specific area” indicates that when the thickness at any location within a specific area is measured according to the same method, the measured thickness value is within an error range of 5% or less. Specifically, it can be expressed that the thickness is maintained constant when the deviation between thickness values ​​at any two locations within a specific area is within 5%, within 4%, within 3%, within 2%, within 1%, or 0% (i.e., no difference).

[0050] In this specification, the term “thickness gradually increases within a specific region” indicates that when thickness is measured in the same way according to a certain direction within a specific region, the thickness value increases continuously or discontinuously. The rate at which the thickness value increases may be maintained constant within an error range of 5% or may change discontinuously, but preferably, “thickness gradually increases within a specific region” may indicate that the thickness value increases continuously at a constant rate.

[0051] In this specification, the term “thickness gradually decreases within a specific region” indicates that when thickness is measured in the same way according to a certain direction within a specific region, the thickness value decreases continuously or discontinuously. The rate at which the thickness value decreases may be maintained constant within an error range of 5% or may vary discontinuously, but preferably, “thickness gradually decreases within a specific region” may indicate that the thickness value decreases continuously at a constant rate.

[0052] In this specification, the "thickness" of each component may represent a value measured according to a known method for measuring the thickness of a battery separator, unless otherwise defined.

[0053] According to one embodiment, the thickness of the separator and / or porous substrate may be a value measured using a known thickness gauge. For example, the thickness gauge may use the VL-50S product from Mitutoyo, but is not limited thereto.

[0054] According to another embodiment, the thickness of the separation membrane and / or porous substrate may be measured through an SEM image of a cross- section of the separation membrane and / or porous substrate.

[0055] In one embodiment of the present invention, the thickness of the porous substrate may be measured by a method of measuring after removing the porous coating layer from the separator. For example, the thickness of the remaining porous substrate may be measured after removing the porous coating layer using a solvent capable of dissolving the porous coating layer included in the separator, or after peeling off the porous coating layer using a tape.

[0056] In one embodiment of the present invention, the thickness of the porous coating layer may be measured by the difference value of the thickness of the porous substrate measured according to the above after measuring the thickness of the separator, but the measurement method is not limited thereto.

[0057] In one embodiment of the present invention, the strip-shaped separator is a long strip-shaped separator having a predetermined width, specifically a rectangular separator having an aspect ratio of 1 or more. More specifically, the separator may have a length of about 1,000 mm or more.

[0058] FIG. 2 schematically illustrates the upper surface of a strip-shaped separator according to one embodiment of the present invention. Referring to FIG. 2, the separator (10) may be divided into an upper region (X), a lower region (Y) located at the top or bottom relative to the stacking direction when folded in a ZZS manner during the manufacture of an electrode assembly, and an inner region (Z) located between the upper region and the lower region.

[0059] FIG. 3 schematically illustrates a side view of a strip-shaped separator according to one embodiment of the present invention. Referring to FIG. 3, the separator (10) comprises a porous substrate (11) and a porous coating layer (12) formed on each of the upper and lower surfaces of the porous substrate. In this specification, for convenience of explanation, the thickness of the porous substrate is denoted as Ts, and the total thickness of the porous coating layer is denoted as Tc. At this time, the total thickness (Tc) of the porous coating layer represents the sum of the thickness (Tc1) of the porous coating layer formed on one surface of the porous substrate and the thickness (Tc2) of the porous coating layer formed on the other surface.

[0060] Referring to FIG. 3, the thickness (Ts) of the porous substrate of the separator (10) gradually decreases from the central portion (10a) in the longitudinal direction to both ends, the total thickness (Tc) of the porous coating layer gradually increases to both ends, and the total thickness (Ts+Tc) is maintained constant across the entire surface of the separator.

[0061] FIG. 4 schematically illustrates a side view of a strip-shaped separator according to one embodiment of the present invention. Referring to FIG. 4, the separator includes a region (AA') in which the thickness (Ts) of a porous substrate is maintained constant from a longitudinal center (10a) to a predetermined position (101) in the direction of one end (103) and to a predetermined position (102) in the direction of the opposite end (104). Additionally, the separator includes a region AE in which the thickness (Ts) of the porous substrate gradually decreases as it moves from the position (101) toward the one end (103), and a region A'E' in which the thickness (Ts) of the porous substrate gradually decreases as it moves from the position (102) toward the opposite end (103).

[0062] FIG. 5 schematically illustrates the structure of an electrode assembly (30) before assembly, wherein unit electrodes (20a, 20b) are arranged on a strip-shaped separator (10) according to one embodiment of the present invention. Referring to the figure, a plurality of first unit electrodes are arranged side by side on one side of the separator at a predetermined spacing. Considering that the separator must be folded so that each folded side covers the front surface of the unit electrode, the spacing between each unit electrode is preferably wider than the width of the first unit electrode. Meanwhile, a plurality of second unit electrodes may be arranged in the same shape on the other side of the separator. At this time, the first unit electrodes and the second unit electrodes may be arranged staggered so that they do not overlap at all when viewed from the side. When arranged staggered as described above, it is preferable that the adjacent first electrode and the second electrode be spaced at a predetermined spacing to ensure a gap sufficient for the separator to be folded. When arranged as described above, an electrode assembly having a structure in which the first electrode and the second electrode are stacked with the separator interposed therebetween can be obtained when the separator is folded. The first unit electrode and the second unit electrode have opposite polarities to each other; for example, the first unit electrode may be a positive electrode and the second unit electrode may be a negative electrode, or vice versa.

[0063] FIG. 6 schematically illustrates a method for manufacturing an electrode assembly in one embodiment of the present invention. Referring to FIG. 6, a separator (10) is folded in a zigzag manner, and unit electrodes (20a, 20b) are inserted into the overlapping portions of the separator so that the separator and the unit electrodes are stacked, and after the insertion of the unit electrodes, the stacked structure is pressed to manufacture a ZZS type electrode assembly. When pressure is applied to the electrode assembly (30), the pressure applied to the uppermost region (40a) and the lowermost region (40b) is relatively greater than that applied to the inner region, so that deformation of the separator in the uppermost region (40a) and / or the lowermost region (40b) may be caused, so the present invention may introduce a new structure to the porous substrate and the porous coating layer present in the uppermost region (X) and / or the lowermost region (Y).

[0064] An electrode assembly according to one aspect of the present invention maintains a constant overall thickness across the front surface of the separator, thereby maintaining the spacing at which unit electrodes are arranged across the front surface of the electrode assembly and the folding spacing during assembly of the electrode assembly. At the same time, as the thickness of the porous substrate gradually decreases toward both ends of the separator and the thickness of the porous coating layer formed on the upper and lower surfaces of the porous substrate gradually increases, the heat resistance and impact resistance of the uppermost and lowermost parts relative to the stacking direction of the electrode assembly are improved when heat and / or pressure are applied through the outermost part during the manufacture of the electrode assembly, thereby minimizing deformation of the thickness and porosity of the central and outermost parts relative to the stacking direction of the electrode assembly.

[0065] In one embodiment of the present invention, at least a portion of the region AA' may be disposed within the X region and / or the Y region.

[0066] FIG. 7 briefly illustrates the side structure when a separator according to one embodiment of the present invention is folded in a zigzag manner. Referring to FIG. 7, when a predetermined position (101) is positioned within the uppermost region (X) such that the thickness of the porous substrate begins to decrease toward the end portion, spaced apart from the longitudinal center of the separator (10), and a predetermined position (102) such that the thickness of the porous substrate begins to decrease toward the opposite end portion is positioned within the lowermost region (Y), a portion of the region AA' may be positioned in the uppermost region (X) and the lowermost region (Y).

[0067] In another embodiment of the present invention, the region AA' is not placed in the uppermost region (X) and lowermost region (Y) based on the stacking direction of the electrode assembly, and it may be preferable that all or at least part of the region AE and region A'E' is placed in the X region and Y region.

[0068] Specifically, since the Z region is a region that is relatively less affected by heat and / or pressure compared to the X and Y regions when heat and / or pressure are applied during the manufacture of the electrode assembly, it is preferable that the region AA' be the same as the Z region or be located within the Z region. That is, the X region is included within the AE region, and the Y region may be included in the A'E' region.

[0069] FIG. 8 briefly illustrates the side structure when a separator according to another embodiment of the present invention is folded in a zigzag manner. Referring to FIG. 8, position A is a predetermined position (101) where the thickness of the porous substrate begins to decrease as it approaches the end portion of the separator, and is located at the inner end of the uppermost region (X) based on the stacking direction of the electrode assembly, and position A' is a predetermined position (102) where the thickness of the porous substrate begins to decrease as it approaches the opposite end portion, and is located at the inner end of the lowermost region (Y) based on the stacking direction of the electrode assembly, so that the entirety of the region AE coincides with the X region and the entirety of the region A'E coincides with the Y region.

[0070] FIG. 9 briefly illustrates the side structure when a separator according to another embodiment of the present invention is folded in a zigzag manner. Referring to FIG. 9, position A is a predetermined position (101) where the thickness of the porous substrate begins to decrease as it approaches the end portion of the separator, and is positioned inwardly at a predetermined distance from the uppermost region (X) based on the stacking direction of the electrode assembly, and position A' is a predetermined position (102) where the thickness of the porous substrate begins to decrease as it approaches the opposite end portion, and is positioned inwardly at a predetermined distance from the lowermost region (Y) based on the stacking direction of the electrode assembly, so that a part of each of the regions AE and A'E may each include the regions X and Y, respectively.

[0071] In one embodiment of the present invention, the region AA' may be included for example with a length of 10% to 90%, 15% to 80%, 20% to 60%, or 20% to 50% based on the total length of the separator. Accordingly, the region AE and the region A'E' may each be included at the end portion of the separator such that the length excluding the region AA' from the total length is the total length of the region AE and the region A'E'.

[0072] In one embodiment of the present invention, the lengths of region AE and region A'E' may each be the same. That is, the lengths of region AE and region A'E' may each include an equal length of the total length of the separator excluding region AA'.

[0073] In one embodiment of the present invention, the lengths of the region AE and the region A'E' may be different, and it may be preferable to assemble the electrode assembly such that the longer region is located at the bottom end of the stacking direction of the electrode assembly in order to minimize shape deformation during the hot pressing process.

[0074] In one embodiment of the present invention, the region AE and the region A'E' may exhibit the effect of preventing or reducing shape deformation caused by high temperature and high pressure during the hot pressing process when assembling electrodes by reducing the thickness (Ts) of the porous substrate and increasing the total thickness (Tc) of the porous coating layer toward the end portion of the separator, but the effect of the present invention is not limited thereto.

[0075] In one embodiment of the present invention, the porous coating layers formed on the upper and lower surfaces of the porous substrate may be formed symmetrically with respect to the central portion in the longitudinal direction of the separator.

[0076] Referring to FIGS. 3 and 4, when a porous coating layer formed on the upper surface of the porous substrate is named the first porous coating layer and a porous coating layer formed on the lower surface of the porous substrate is named the second porous coating, the first porous coating layer and the second porous coating layer may be formed in a shape that is line-symmetric with respect to the thickness direction centerline (10b) of the porous substrate.

[0077] Specifically, the porous coating layers formed on the upper and lower surfaces of the porous substrate are formed symmetrically with respect to the centerline in the thickness direction of the separator, so that the thickness of each porous coating layer at the same arbitrary position orthogonal to the length direction of the separator may be the same or have a thickness difference of within 10%.

[0078] For example, the thickness (Tc1) of the first porous coating layer and the thickness (Tc2) of the second porous coating layer located on an imaginary line perpendicular to the longitudinal direction of the separator at any location on the porous substrate may be the same, or if different, the difference in thickness may be within 10%.

[0079] More specifically, the difference in thickness between the first porous coating layer and the second porous coating layer may be within 10%, within 8%, within 5%, within 4%, within 3%, within 2%, within 1%, or 0% (i.e., identical).

[0080] In one embodiment of the present invention, the separator may be formed to have a symmetrical structure with respect to the longitudinal center (10a).

[0081] In one embodiment of the present invention, the separator may be formed to have a symmetric structure with respect to a longitudinal centerline (10a) and a thickness centerline (10b). Referring to FIG. 6, the region AE from the predetermined position (101) to the end (103) and the region A'E' from the opposite predetermined position (102) to the opposite end (104) may be formed to have a symmetric structure with respect to a longitudinal centerline (10a) and a thickness centerline (10b).

[0082] Specifically, in the region AE and region A'E', the thickness (Ts) of each porous substrate formed at any position spaced apart from the longitudinal centerline (10a) of the separator may be equal to each other or have a thickness difference of within 10%.

[0083] More specifically, in the region AE and the region A'E', the thickness (Ts) of each porous substrate formed at any position spaced apart from the longitudinal centerline (10a) of the separator may have a difference of within 10%, within 8%, within 5%, within 4%, within 3%, within 2%, within 1%, or 0% (i.e., the same).

[0084] In one embodiment of the present invention, the ratio (Ts / Tc) of the thickness (Ts) of the porous substrate to the total thickness (Tc) of the porous coating layer over the entire surface of the separator may be 0.5 to 5. Specifically, the ratio (Ts / Tc) may be 0.8 to 3, 1 to 2, or 1 to 1.8. In the electrode assembly, as the thickness (Ts) of the porous substrate gradually decreases and the total thickness (Tc) of the porous coating layer gradually increases toward the end portion in the longitudinal direction of the separator, the ratio (Ts / Tc) may exhibit a decreasing trend toward the end portion in the longitudinal direction of the separator.

[0085] In another embodiment of the present invention, the ratio (Ts / Tc) of the thickness (Ts) of the porous substrate to the total thickness (Tc) of the porous coating layer at position (A) may be 1 to 5. Specifically, the ratio (Ts / Tc) at position (A) may be 1 to 3, 1 to 2, or 1.5 to 1.8. In the electrode assembly, as described above, the region (AA') from position (A) to position (A') is a region where the thickness (Ts) of the porous substrate is maintained constant, and the ratio (Ts / Tc) at position (A) may represent the maximum value of the ratio (Ts / Tc) across the entire surface of the separator.

[0086] In one embodiment of the present invention, the porous substrate refers to a substrate having a plurality of pores formed therein, which acts as a porous ion-conducting barrier that blocks electrical contact between a cathode and an anode while allowing ions to pass through. The pores are structured to be interconnected, allowing gas or liquid to pass from one side of the substrate to the other. As such a porous substrate, a porous polymer film containing a thermoplastic resin may be used to provide a shutdown function. Here, the shutdown function refers to a function that prevents thermal runaway of the battery by blocking the movement of ions when the battery temperature rises, by causing the thermoplastic resin to melt and close the pores of the porous substrate. As the thermoplastic resin, a thermoplastic resin with a melting point of less than 200°C is suitable, and polyolefin is particularly preferred.

[0087] In one embodiment of the present invention, the porosity of the porous substrate may be, for example, 30% to 90%, 35% to 80%, 40% to 70%, 40% to 60%, or 40% to 50%. The porosity of the porous substrate may represent a value measured by, for example, the formula [true density - density of porous substrate / true density * 100 (%)] of the material included in the porous substrate.

[0088] In one embodiment of the present invention, the thickness of the porous substrate is not particularly limited as long as it satisfies the range of the ratio (Ts / Tc) described above, but may be, for example, 5 to 300 μm.

[0089] In one embodiment of the present invention, the porous coating layer is formed on the upper and lower surfaces of the porous substrate, respectively, and comprises inorganic particles. The inorganic particles within the porous coating layer are packed in a dense state and may have a plurality of micropores resulting from the interstitial volume formed between the inorganic particles.

[0090] In one embodiment of the present invention, the porous coating layer may further comprise a binder resin, such that the inorganic particles have all or at least a portion of their surface coated by the binder resin. In this case, the inorganic particles are surface-bonded and / or point-bonded via the binder resin. For example, the inorganic particles and the binder resin in the porous coating layer may be included in a weight ratio of 95:5 to 50:50.

[0091] In one embodiment of the present invention, the inorganic particles may be used without particular limitation as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). Non-limiting examples of such inorganic particles include BaTiO3, Pb(Zr,Ti)O3 (PZT), and Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 Examples include O3-PbTiO3 (PMN-PT), hafnia (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, SiC, and TiO2, and one or more of these may be included.

[0092] In one embodiment of the present invention, when a binder resin is included in the porous coating layer, the binder resin may include, for example, a polyvinylidene fluoride-based resin (PVdF-based resin). In one embodiment of the present invention, the PVdF-based resin may include one or more of a homopolymer of vinylidene fluoride (i.e., polyvinylidene fluoride), a copolymer with a monomer capable of copolymerizing with vinylidene fluoride, and a mixture thereof. In one embodiment of the present invention, the monomer may be, for example, a fluorinated monomer and / or a chlorinated monomer. Non-limiting examples of the fluorinated monomer include vinyl fluoride; trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); and hexafluoropropylene (HFP). Perfluoro(alkylvinyl) ethers such as perfluoro(methylvinyl) ether (PMVE), perfluoro(ethylvinyl) ether (PEVE), and perfluoro(propylvinyl) ether (PPVE); perfluoro(1,3-dioxol); and perfluoro(2,2-dimethyl-1,3-dioxol) (PDD), etc., and one or more of these may be included.

[0093] In one embodiment of the present invention, the PVdF-based resin may be used such that its Tm is 140°C or lower in terms of adhesive strength during heat bonding. To this end, the PVdF-based resin may include a copolymer of vinylidene fluoride units and other monomers copolymerizable with vinylidene fluoride units. Examples of such copolymers include PVDF-TrFE, PVDF-TFE, PVDF-CTFE, and PVDF-HFP, and may include one or more of these.

[0094] Meanwhile, in addition to the PVDF-based resin, the binder resin may further include a (meth)acrylic polymer resin if necessary. The above (meth)acrylic polymer contains (meth)acrylic acid esters as monomers, and non-limiting examples thereof include (meth)acrylic polymers containing butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-oxyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, and tetradecyl (meth)acrylate as monomers.

[0095] In one embodiment of the present invention, the separator may be manufactured by applying the inorganic particles or a slurry for forming an inorganic coating layer containing the binder resin and inorganic particles onto a porous substrate and drying the solvent and / or the binder resin to integrally form a porous coating layer on the porous substrate. The method of manufacturing the separator may be applied without limitation as long as the porous coating layer is formed on the upper and lower surfaces of the porous substrate, respectively, and a separator of the shape described above can be obtained, and is not limited to a specific manufacturing method.

[0096] In one embodiment of the present invention, the thickness of the porous coating layer is not particularly limited as long as it satisfies the range of the ratio (Ts / Tc) described above, but may be, for example, 3 to 50 μm.

[0097] The electrode assembly according to the present invention comprises a separator having the shape described above, and comprises one or more pairs of unit electrodes spaced apart on the separator.

[0098] In one embodiment of the present invention, the unit electrode may be a conventional anode and / or cathode used in an electrochemical device, and the anode and cathode may each have an electrode active material coated on a current collector, and their size or shape is not particularly limited.

[0099] When the above electrode is a positive electrode, the positive electrode active material may be, for example, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide combining these, or a mixture of two or more of these, but is not limited thereto.

[0100] When the above electrode is a negative electrode, the negative electrode active material may be, for example, lithium metal or lithium alloy, soft carbon, hard carbon, natural graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, petroleum or coal tar pitch-derived cokes, or a mixture of two or more of these, but is not limited thereto.

[0101] The electrode assembly according to the present invention having the above-described structure can exhibit an excellent shape retention rate of the electrode assembly because the heat resistance and impact resistance of the electrode assembly are excellently improved even when pressure is applied in the stacking direction of the electrode assembly through a hot press process.

[0102] In one embodiment of the present invention, the thickness deformation rate of the outermost part of the electrode assembly may be 30% or less after being fixed through a hot press process at a temperature of 50°C to 110°C and a pressure of 3 MPa to 10 MPa.

[0103] In another embodiment of the present invention, the hot press process may specifically be performed at a temperature of 50°C to 110°C and a pressure of 3 MPa to 10 MPa, and the thickness deformation rate of the outermost part of the electrode assembly after being fixed through the hot press process may be 30% or less.

[0104] In the present specification, the thickness strain of the outermost part of the electrode assembly after being fixed through a conventional method for fixing the electrode assembly, such as the hot press process, can be expressed as a value derived according to the formula [(thickness before press - thickness after press) / thickness before press * 100(%)] by measuring the thickness of the electrode assembly before and after fixing.

[0105] In another embodiment of the present invention, the thickness deformation rate of the outermost part of the electrode assembly after being fixed through a conventional method for fixing the electrode assembly, such as the hot press process, may specifically be 30% or less, 25% or less, 20% or less, or 15% or less. More specifically, the thickness deformation rate of the outermost part of the electrode assembly after being fixed through the hot press process may be 0% or more, 5% or more, or 10% or more, to 15% or less, for example, 11% to 12%.

[0106] In one embodiment of the present invention, in representing the thickness strain rate before and after fixation, the outermost part of the electrode assembly may represent a region in which the thickness (Ts) of the porous substrate in the separator gradually decreases and the total thickness (Tc) of the porous coating layer gradually increases.

[0107] In another embodiment of the present invention, in indicating the thickness strain before and after fixation, the outermost part of the electrode assembly may represent all or at least part of the aforementioned region AE and region A'E'.

[0108] In another embodiment of the present invention, the thickness deformation rate of the innermost part of the electrode assembly after being fixed through a conventional method for fixing the electrode assembly, such as the hot process, can specifically be 15% or less.

[0109] In one embodiment of the present invention, when indicating the thickness strain rate before and after fixation, the innermost part of the electrode assembly may represent a region where the thickness (Ts) of the porous substrate in the separator is maintained at a constant level.

[0110] In another embodiment of the present invention, in indicating the thickness strain before and after fixation, the innermost part of the electrode assembly may represent all or at least part of the region (AA') described above.

[0111] In the present invention, by including a separator having the above-described shape, the electrode assembly can exhibit the effect of improving the dielectric breakdown voltage of the battery, increasing the dielectric breakdown voltage, and reducing the short-circuit occurrence rate (Hi-pot failure rate) even under high voltage conditions.

[0112] The above dielectric breakdown voltage refers to the maximum voltage that an insulator can withstand, and dielectric breakdown means that when a voltage is applied to an insulator, if the voltage exceeds a certain value, the insulator is destroyed and loses its insulating performance.

[0113] The above dielectric breakdown voltage can be measured, for example, using an AC / DC / IR Hi-Pot tester. For example, a stainless steel mesh and a porous substrate are hot-press bonded under conditions of 90°C, 4 MPa, and 1 sec, and then the DC current is set to 0.5 mA and the voltage is set to 100 V / s (voltage 3 kV, ramp-up time 3 s). When the experiment begins, the measurement is completed when a short circuit occurs as the voltage rises, and the voltage at that time is defined as the dielectric breakdown voltage.

[0114] In addition, the evaluation of the above short-circuit occurrence rate (Hi-Pot failure rate) can be measured by identifying the voltage exhibited by the bottom 1% of specimens exhibiting low dielectric breakdown voltage through Weibull distribution analysis among the total number of specimens tested.

[0115] In one embodiment of the present invention, the dielectric breakdown voltage of the porous substrate located at the outermost part of the electrode assembly after being fixed through a conventional method for fixing the electrode assembly, such as the hot press process, can be 800 kV / mm or higher.

[0116] In another embodiment of the present invention, the dielectric breakdown voltage of the porous substrate present at the outermost part of the electrode assembly after being fixed through a conventional method for fixing the electrode assembly, such as the hot press process, may specifically show a value of 1,000 kV / mm or more or 1,500 kV / mm or more.

[0117] In one embodiment of the present invention, the electrochemical element is a case in which the electrode assembly described above is housed.

[0118] In one embodiment of the present invention, the case may be one that is conventionally used as a battery case, and is not particularly limited in its external shape according to the use of the battery. For example, the case may be a cylindrical, prismatic, pouch, or coin type using a can.

[0119] Once the electrode assembly described above is completed, it can be housed in a case and sealed in a conventional manner to manufacture an electrochemical device, wherein the electrochemical device may be, for example, a lithium secondary battery.

[0121] The present invention will be described in more detail below through examples, but the following examples are intended to illustrate the invention and the scope of the invention is not limited thereto.

[0123] Example 1

[0124] [Manufacturing of Separator Membranes]

[0125] A separation membrane was manufactured according to the following method.

[0126] Porosity in each composition was measured according to the formula [(true density of the applied material - density of the corresponding composition) / true density * 100 (%)].

[0127] The thickness of each component was measured using a thickness gauge (Mitutoyo, VL-50S).

[0128] Manufacture of porous substrate

[0129] A porous substrate for use in a separator was prepared according to a known method by mixing three types of polyethylene polymers and polypropylene polymers with different molecular weights and an antioxidant in appropriate proportions. The three types of polyethylene polymers used were PE 40 (Mw 400,000 g / mol), PE 90 (Mw 900,000 g / mol), and PE 150 (Mw 1,500,000 g / mol), and the polypropylene polymer was PP 35 (Mw 350,000 g / mol). The porosity of the prepared porous substrate was 45%.

[0130] The above porous substrate has an overall width of 350 mm and a length of 1 m, and the thickness measured at both ends is 12 μm each, and the thickness gradually increases from both ends to a point 0.3 m in the longitudinal direction, and then maintains a thickness of 15 μm from the point 0.3 m.

[0131] Preparation of porous coating layer

[0132] An inorganic coating slurry was prepared by mixing a PVDF-HFP binder (Mw 500,000 g / mol, HFP 15 wt%) and inorganic particles in a weight ratio of 80:20 in a suitable solvent.

[0133] The inorganic coating slurry prepared above was applied to the entire surface of the porous substrate by a dip coating method and dried according to a humidification separation method to form porous coating layers on the upper and lower surfaces of the porous substrate prepared above.

[0134] The porous coating layers formed on the upper and lower surfaces, respectively, were manufactured such that the thickness measured at both ends was 6 μm, the thickness gradually decreased from both ends to a point 0.3 m in the longitudinal direction, and then maintained a thickness of 4.5 μm from the point 0.3 m.

[0135] Thus, a separation membrane was manufactured with a total thickness of 24 μm maintained uniformly across the entire surface.

[0136] [Manufacturing of Electrode Assembly]

[0137] An electrode assembly was manufactured using the separator prepared above. Specifically, 17 positive electrodes and 16 negative electrodes were arranged intersectingly on the upper and lower surfaces of the separator. At this time, the points where the positive electrode ends are located on one side and the points where the negative electrode ends are located on the other side were spaced apart so that the horizontal spacing in the plane is 3 mm, and they were arranged intersectingly. Lithium cobalt oxide (LCO) was used as the positive electrode active material, and graphite was used as the negative electrode active material (N / P ratio > 100).

[0139] Comparative Example 1

[0140] [Manufacturing of Separator Membranes]

[0141] Manufacture of porous substrate

[0142] A porous substrate was prepared according to the same method as in Example 1, except that it was formed with a uniform thickness of 15 μm without any change in thickness along the entire length direction.

[0143] Preparation of porous coating layer

[0144] A porous coating layer was formed according to the same method as in Example 1, except that it was formed with a constant thickness of 4.5 μm without any change in thickness along the entire length direction, and accordingly, a separation membrane with a constant thickness of 24 μm was manufactured.

[0145] [Manufacturing of Electrode Assembly]

[0146] In addition to using the separator prepared above, an electrode assembly was prepared according to the same method as in Example 1.

[0148] [Evaluation of Thickness Change Rate During Hot Press Process]

[0149] The electrode assemblies of Example 1 and Comparative Example 1 prepared above were each fixed by hot pressing at 90°C and a pressure of 6.5 MPa for 6 seconds. At this time, the thickness strain in each region before and after hot pressing was measured, and the results are shown in Table 1 below.

[0150] The thickness of the separator membrane after pressing was measured using a thickness gauge (Mitutoyo, VL-50S), and the thickness of the porous substrate was measured using the same thickness gauge after peeling off the porous coating layer from the separator membrane using tape and determining the thickness of the remaining porous substrate. In this case, the thickness of the porous substrate was verified using the thickness value obtained from the SEM image of the cross-section of the separator membrane prior to the peeling of the porous coating layer.

[0151] In Table 1 below, the innermost part represents a region where the thickness of the porous substrate is maintained at a constant level, and the outermost part represents a region where the thickness of the porous substrate decreases towards both ends.

[0152] division Internal strain (%) Outermost strain (%) Strain of the total thickness of the separation membrane Strain of porous substrate thickness Strain of the total thickness of the separation membrane Strain of porous substrate thickness Comparative Example 1 9.9 8.7 21.6 18.9 Example 1 10.1 9.0 11.8 9.1

[0153] As confirmed in Table 1 above, the change in the innermost part before and after hot pressing was similar between Comparative Example 1 and Example 1, but it was confirmed that the electrode assembly of Example 1, which includes a separator in which the thickness of the porous substrate gradually decreases and the thickness of the porous coating layer gradually increases towards both ends at the top and bottom ends based on the stacking direction of the electrode assembly, showed a significantly reduced strain in the outermost part.

[0155] [Evaluation of Electrode Assembly Durability]

[0156] In order to measure the thickness strain as described above, the dielectric breakdown voltage was measured using the porous substrates according to Example 1 and Comparative Example 1, in which the porous coating layer was removed through a taping process, and the results are shown in Table 2 below.

[0157] The dielectric breakdown voltage was measured using an AC / DC / IR Hi-Pot tester. Specifically, a porous substrate was bonded to a stainless steel mesh by hot pressing at 90°C, 4 MPa, and 1 second, and then the DC current was set to 0.5 mA and the ramp-up time to 100 V / s (Voltage 6 kV, ramp-up time 6 s), and the voltage was evaluated by measuring the voltage at which a short circuit occurred.

[0158] The dielectric breakdown voltage represents the result measured on the outermost porous substrate of the electrode assembly.

[0159] Dielectric breakdown voltage (V) of the outermost porous substrate Comparative Example 1 719 Example 1 1756

[0160] As confirmed in Table 2 above, the dielectric breakdown voltage of Example 1 was found to be much better than that of Comparative Example 1, which was inferred to be due to the special structure of the separator in Example 1, which lowered the pore damage rate of the porous substrate even after the hot press process.

[0161] Although the present invention has been described above with reference to embodiments and drawings, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above content. Explanation of the symbols

[0163] 1: Electrode assembly 3: Separator 5: Anode 7: Cathode 10: Separator 11: Porous substrate 12: Porous coating layer 10a: Longitudinal center of the separator 10b: Center in the thickness direction of the separator 20a: Cathode 20b: Anode 30: Electrode assembly 40: Pressing process of the electrode assembly 40a: Top region of the electrode assembly 40b: Bottom region of the electrode assembly 101: Position A 102: Location A' 103: Location E 104: Position E' X: Topmost region based on stacking direction Y: Bottommost region relative to stacking direction Z: Inner region relative to stacking direction Ts: Thickness of the porous substrate Tc1, Tc2: Thickness of the porous coating layer

Claims

Claim 1 It comprises a unit electrode and a strip-shaped separator, wherein the separator is folded in a zigzag manner and the unit electrode is inserted into the overlapping portion of the separator, and the separator comprises a porous substrate made of a polymer material and a porous coating layer formed on the upper and lower surfaces of the porous substrate, each containing inorganic particles, wherein the thickness (Ts) of the porous substrate is maintained constant from the longitudinal centerline of the separator to a predetermined position (A) in the direction of one end and a predetermined position (A') in the direction of the opposite end, wherein all or at least part of the region AE from the position (A) to the one end (E) and the region A'E' from the position (A') to the other end (E') are respectively positioned at the uppermost and lowermost ends of the electrode assembly based on the stacking direction, wherein the thickness (Ts) of the porous substrate gradually decreases as it approaches the end portion of the separator, and the total thickness (Tc) of the porous coating layer increases as it approaches both end portions, and the entire surface of the separator An electrode assembly characterized by maintaining a constant thickness (Ts+Tc). Claim 2 delete Claim 3 An electrode assembly according to claim 1, wherein the region AA' from position (A) to position (A') is not positioned at the uppermost and lowermost ends of the stacking direction of the electrode assembly, and the region of the separator positioned at the uppermost and lowermost ends of the stacking direction of the electrode assembly is characterized in that the thickness (Ts) of the porous substrate is reduced toward the end portion of the separator. Claim 4 An electrode assembly according to claim 1, wherein the porous coating layers formed on the upper and lower surfaces of the porous substrate are formed symmetrically with respect to the centerline in the longitudinal direction of the separator, and the thickness of each of the porous coating layers at any same arbitrary position orthogonal to the longitudinal direction of the separator is equal to each other or the difference in thickness is within 10%. Claim 5 An electrode assembly according to claim 1, wherein the separator is formed to have a symmetric structure with respect to a longitudinal centerline, and wherein, in the region AE and the region A'E', the thickness (Ts) of each porous substrate formed at any position spaced apart by the same distance from the longitudinal centerline of the separator is equal to each other or the difference in thickness is within 10%. Claim 6 An electrode assembly according to claim 1, characterized in that the ratio (Ts / Tc) of the thickness (Ts) of the porous substrate to the total thickness (Tc) of the porous coating layer across the entire surface of the separator is 0.5 to 5. Claim 7 An electrode assembly according to claim 1, characterized in that the ratio (Ts / Tc) of the thickness (Ts) of the porous substrate to the total thickness (Tc) of the porous coating layer at position (A) is 1 to 5. Claim 8 An electrode assembly according to any one of claims 1 and claims 3 to 7, characterized in that the thickness deformation rate of the outermost part of the electrode assembly is 30% or less after being fixed through a hot press process at a temperature of 50℃ to 110℃ and a pressure of 3MPa to 10MPa. Claim 9 An electrochemical device characterized by an electrode assembly according to claim 1 being housed in a case. Claim 10 An electrochemical device according to claim 9, characterized in that the electrochemical device is a lithium secondary battery.

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