Patent Description:
The present invention relates to an electrode assembly.

Secondary batteries, unlike primary batteries, are rechargeable, and have been widely researched and developed in recent years due to their small size and large capacity. As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing.

Secondary batteries can be classified into a coin-type battery, a cylindrical battery, a prismatic battery, and a pouch-type battery, according to the shape of the battery case. In a secondary battery, an electrode assembly mounted inside a battery case is a chargeable/dischargeable power generating element having a stacked structure comprising electrodes and separators.

The electrode assembly may be generally classified into a jelly-roll type, a stack type, and a stack-and-folding type. In the jelly-roll type, a separator is interposed between a sheet type positive electrode and a sheet type negative electrode, each of which are coated with an active material, and the entire arrangement is wound. In the stack type, a plurality of positive and negative electrodes are sequentially stacked with a separator interposed therebetween. In a stack-and-folding type, stacked unit cells are wound with a long-length separation film.

<CIT>, <CIT>, <CIT> and <CIT> relate to electrode assembly manufacturing device.

The present invention provides, among other things, an electrode assembly which has reduced deviations in adhesive force and air permeability across each layer, while still maintaining adequate adhesive force and air permeability.

The invention is as defined in the set of claims. An exemplary aspect of the present invention provides an electrode assembly. An electrode assembly according to the invention is defined in claim <NUM>.

In accordance with some aspects of the invention, the separator portions may be portions of an elongated separator sheet. Such elongated separator sheet may be folded between each separator portion such that the elongated separator sheet follows a serpentine path traversing back and forth along an orthogonal dimension orthogonal to the stacking axis to extend between each of the successive electrodes in the stack.

The electrode assembly according to exemplary aspects of the present invention is desirably capable of preventing side-effects, such as lithium (Li) precipitation in the electrode assembly and non-charging of the electrode assembly. The electrode assembly according to exemplary aspects of the present invention may also have uniform performance.

The objects, specific advantages, and novel features of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings and exemplary embodiments. In the present specification, in adding reference numbers to the constituent elements of each drawing, it should be noted that the same constituent elements are given the same number even though they are indicated on different drawings. In addition, the present invention may be implemented in several different forms and is not limited to the exemplary embodiments described herein.

<FIG> is a cross-sectional view illustrating an example of an electrode assembly according to an exemplary embodiment of the present invention. That is, referring to <FIG>, an electrode assembly <NUM> according to an exemplary embodiment of the present invention includes a stack of electrodes in which one or more first electrodes <NUM> alternates with one or more second electrodes <NUM>. Each of the electrodes in the stack are separated from one another by a separator <NUM> positioned therebetween, which may be a single elongated separator <NUM> repeatedly folded so as to follow a serpentine or zigzag path around each successive electrode.

The electrode assembly <NUM> is a chargeable/dischargeable power generating element, where the first electrode may be a positive electrode, and the second electrode may be a negative electrode. However, alternatively, the first electrode may be a negative electrode, and the second electrode may be a positive electrode. Moreover, the electrode assembly <NUM> may be provided in a form in which the outermost portion is surrounded by the separator <NUM>, e.g., by wrapping the separator around the assembled electrode assembly <NUM>, as illustrated in <FIG>. With respect to the electrodes and the separator comprising the electrode assembly, materials commonly used in the art may be used.

As discussed further herein, an "upper surface" of the electrode assembly <NUM> refers to the uppermost position of the electrode assembly <NUM> in the stacking direction of the electrode assembly, which is designated by reference numeral <NUM> in <FIG>. Thus, subsequent references to "upper surface air permeability" relate to air permeability of the separator <NUM> abutting the uppermost electrode in the electrode assembly. Likewise, subsequent references to "upper surface adhesive force" refer the adhesive force between the uppermost electrode in the electrode assembly and the abutting portion of the separator <NUM>.

Further, as discussed herein, a "lower surface" of the electrode assembly <NUM> refers to the lowermost position of the electrode assembly <NUM> in the stacking direction of the electrode assembly, which is designated by reference numeral <NUM> in <FIG>. Thus, subsequent references to "lower surface air permeability" relate to air permeability of the separator <NUM> abutting the lowermost electrode in the electrode assembly. Likewise, subsequent references to "lower surface adhesive force" refer the adhesive force between the lowermost electrode in the electrode assembly and the abutting portion of the separator <NUM>.

Finally, as discussed herein, the "middle" of the electrode assembly <NUM> refers to a middle position between the upper surface and the lower surface of the electrode assembly <NUM> in the stacking direction of the electrode assembly, as designated by reference numeral <NUM> in <FIG>. For example, when an electrode assembly <NUM> formed of nine electrodes and viewed from the side, as in <FIG>, the "middle" position relates to the position of the fifth electrode in the stack. Thus, subsequent references to "middle air permeability" relate to air permeability of the separator <NUM> abutting the middle electrode in the electrode assembly. Likewise, subsequent references to "middle adhesive force" refer the adhesive force between the middle electrode in the electrode assembly and the abutting portion of the separator <NUM>.

Referring to <FIG> and <FIG>, an apparatus <NUM> for manufacturing an electrode assembly according to an exemplary embodiment of the present invention includes a stack table <NUM>; a separator supply unit <NUM> for supplying a separator <NUM>; a first electrode supply unit <NUM> for supplying a first electrode <NUM>; a second electrode supply unit <NUM> for supplying a second electrode <NUM>; a first electrode stack unit <NUM> for stacking the first electrode <NUM> on the stack table <NUM>; a second electrode stack unit <NUM> for stacking the second electrode <NUM> on the stack table <NUM>; and a press unit <NUM> for bonding the first electrode <NUM>, the separator <NUM>, and the second electrode <NUM> to each other. Further, the apparatus <NUM> for manufacturing the electrode assembly according to the exemplary embodiment of the present invention may include a holding mechanism <NUM> for fixing the stack (comprising the first electrode(s) <NUM>, the second electrode(s) <NUM>, and the separator <NUM>) to the stack table <NUM> as the stack is being assembled.

The separator supply unit <NUM> may have a passage through which the separator <NUM> passes towards the stack table <NUM>. In particular, the separator supply unit <NUM> may include a separator heating unit <NUM> defining the passage through which the separator <NUM> passes towards the stack table <NUM>. As shown in <FIG>, the separator heating unit <NUM> may include a pair of bodies 121a, each of which may be in the form of a square block, and the bodies 121a may be spaced apart by a distance defining one of the dimensions of the passage through which the separator <NUM> passes. At least one or both of the bodies 121a may further include a separator heater 121b for heating the respective body 121a, and thereby transferring heat to the separator <NUM>.

The separator supply unit <NUM> may further include a separator roll <NUM> on which the separator <NUM> is wound. Thus, the separator <NUM> wound on the separator roll <NUM> may be gradually unwound and pass through the formed passage to be supplied to the stack table <NUM>.

The first electrode supply unit <NUM> may include a first electrode roll <NUM> on which the first electrode <NUM> is wound in the form of a sheet, a first cutter <NUM> for cutting the first electrode <NUM> at regular intervals to form the first electrodes <NUM> having a predetermined size when the first electrode <NUM> is unwound and supplied from the first electrode roll <NUM>, a first conveyor belt <NUM> for moving the first electrode <NUM> cut by the first cutter <NUM>, and a first electrode supply head <NUM> for picking up (e.g., via vacuum suction) the first electrode <NUM> transferred by the first conveyor belt <NUM> and seating the first electrode <NUM> on a first electrode seating table <NUM>.

The second electrode supply unit <NUM> may include a second electrode seating table <NUM> on which the second electrode <NUM> is seated before being stacked on the stack table <NUM> by the second electrode stack unit <NUM>. The second electrode supply unit <NUM> may further include a second electrode roll <NUM> on which the second electrode <NUM> is wound in the form of a sheet, a second cutter <NUM> for cutting the second electrode <NUM> at regular intervals to form the second electrode <NUM> of a predetermined size when the second electrode <NUM> is unwound and supplied from the second electrode roll <NUM>, a second conveyor belt <NUM> for moving the second electrode <NUM> cut by the second cutter <NUM>, and a second electrode supply head <NUM> for picking up (e.g., via vacuum suction) the second electrode <NUM> transferred by the second conveyor belt <NUM> and seating the second electrode on the second electrode seating table <NUM>.

The first electrode stack unit <NUM> may be structured to stack the first electrode <NUM> on the stack table <NUM>. The first electrode stack unit <NUM> may include a first suction head <NUM> and a first moving unit <NUM>. The first suction head <NUM> may pick up the first electrode <NUM> seated on the first electrode seating table <NUM> via vacuum suction through one or more vacuum suction ports (not shown) formed on a bottom surface of the first suction head <NUM>, and then the first moving unit <NUM> may move the first suction head <NUM> to the stack table <NUM> so as to allow the first suction head <NUM> to stack the first electrode <NUM> on the stack table <NUM>.

The second electrode stack unit <NUM> may also be structured to stack the second electrode <NUM> on the stack table <NUM>. The second electrode stack unit <NUM> may have the same structure as that of the foregoing first electrode stack unit <NUM>. In such case, the second electrode stack unit <NUM> may include a second suction head <NUM> and a second moving unit <NUM>. The second suction head <NUM> may pick up the second electrode <NUM> seated on the second electrode seating table <NUM> via vacuum suction. The second moving unit <NUM> may then move the second suction head <NUM> to the stack table <NUM> so as to allow the second suction head <NUM> to stack the second electrode <NUM> on the stack table <NUM>.

The stack table <NUM> may be rotatable so as to rotate between positions facing the first electrode stack unit <NUM> and the second electrode stack unit <NUM>. As the stack table <NUM> rotates, the holding mechanism <NUM> may hold the stack being assembled (comprising the first electrode <NUM>, the second electrode <NUM>, and the separator <NUM>) in order to secure the position of the stack relative to the stack table <NUM>. For example, the holding mechanism <NUM> may apply downward pressure to the upper surface of the stack to press it towards the stack table <NUM>. The holding mechanism <NUM> may include, for example, a first holder <NUM> and a second holder <NUM> to fix opposing sides of the first electrode <NUM> or the second electrode <NUM>. The holders <NUM>, <NUM> may each be in the form of one or more clamps or other clamping mechanisms.

Thus, in operation, the first electrode <NUM> is supplied from the first electrode supply unit <NUM> to the first electrode stack unit <NUM>, the first electrode stack unit <NUM> stacks the first electrode <NUM> on the upper surface of the separator <NUM> stacked on the stack table <NUM>. The holding mechanism <NUM> then presses down on the upper surface of the first electrode <NUM> to secure the position of the first electrode <NUM> on the stack table <NUM>. Thereafter, the stack table <NUM> is rotated in the direction of the second electrode stack unit <NUM> while the separator <NUM> is continuously supplied so as to cover the upper surface of the first electrode <NUM>. Meanwhile, the second electrode <NUM> is supplied from the second electrode supply unit <NUM> and is stacked by the second electrode stack unit <NUM> on a portion of the separator <NUM> where the separator <NUM> covers the upper surface of the first electrode <NUM>. Then the holding mechanism <NUM> releases the upper surface of the first electrode <NUM> and then presses down on the upper surface of the second electrode <NUM> to secure the position of the stack S being built vis-a-vis the stack table <NUM>. Thereafter, by repeating the process of stacking the first electrode <NUM> and the second electrode <NUM>, the stack S in which the separator <NUM> is zig-zag-folded and positioned between each of the successive first and second electrodes <NUM>, <NUM> may be formed.

After the components of the electrode assembly are stacked, the electrode assembly may undergo one or more heat press operations. In particular, the electrode assembly may be moved to the press unit <NUM>, which applies heat and pressure to the stack by advancing heated pressing blocks <NUM> and <NUM> towards one another with the stack positioned therebetween. As a result, the components of the stack (i.e., the electrodes and separator) are thermally bonded to one another, so as to desirably prevent the completed electrode assembly from falling apart or the components of the electrode assembly from shifting their positions within the stack.

The heat press operations applied to the electrode assembly may include a primary heat press operation and a secondary heat press operation. The primary heat press relates to an operation after the first electrode(s) and the second electrode(s) are alternately stacked between the folded separators to define a stack, where the stack is gripped with a gripper, and then the stack is heated and pressed. The secondary heat press operation relates to an operation after the primary heat press operation, in which the gripping of the stack by the gripper is ceased and the stack is once more heated and pressed.

Referring to <FIG>, the method may first include a stack process of assembling a stack (stack cell) on a stack table by alternately stacking the first electrode and the second electrode on the separator, where the separator is continuously supplied and sequentially folded over a previously-stacked one of the first and second electrodes before a subsequent one of the first and second electrodes is stacked. After the stack process, the stack may be moved away from the stack table. During such time, the separator is pulled, and, after the separator is pulled for a predetermined length, the separator is cut. Thereafter, the predetermined length of he cut end of the separator is wound around the stack cell. The movement of the stack away from the stack table may be accomplished by the gripper, which is desirably a movable component that can grip the stack on the stack table and then move the stack to the press unit <NUM>, where the heat press operations are performed. The primary heat press operation is then performed in a state in which the wound stack cell is gripped with the gripper. After the primary heat press operation is completed, the grip of the stack cell by the gripper is released. After the gripper is removed, the secondary heat press operation is performed. When the secondary heat press operation is completed, the finished electrode assembly may be complete.

When the temperature, pressure, and time conditions disclosed herein are not satisfied, the components of the electrode assembly may not be properly adhered together, which can result in the electrode assembly falling apart or the components of the electrode assembly shifting their positions within the assembly, particularly when the electrode assembly is moved before being inserted into a battery case. A problem may also occur in which the air permeability of the separator is excessively high.

On the other hand, when the heat press operations disclosed herein are performed (including satisfying the respective pressure, temperature, and time conditions), an electrode assembly may be manufactured without the need to individually heat and/or press each level of the electrode assembly (i.e., heating and/or pressing each electrode and separator pair at each step of the process) in order to bond the components together. Such individual heat pressing at each level can detrimentally cause the effects of the heat and/or pressure to accumulate in the lower separators in the stack, since the already-stacked layers will experience the heat and/or pressure of each application. That can negatively impact such portions of separator by, for example, reducing porosity (and air permeability). In contrast, the present invention allows the entire electrode assembly to be simultaneously bonded, which improves uniformity, among other things. It is thus possible to simultaneously achieve both an appropriate level of adhesive force between the electrodes and also achieve a separator having an appropriate amount of air permeability, all while minimizing damage to the unit electrode.

In the present application, the "air permeability" of the electrode assembly refers to the air permeability of the separator component of the electrode assembly. In addition, unless specifically stated, the "air permeability" means air permeability of all separators comprising the electrode assembly, where the air permeability of each separator may be independently the same or different.

In general, when the air permeability is less than <NUM> sec/<NUM>, the speed of lithium ion movement in the separator is increased, but there can be a problem in that the safety of the electrode assembly may be rapidly reduced, and there can also be a problem in that the speed of the lithium ion movement in the electrode(s) in the electrode assembly may not correspond to the speed of the lithium ion movement in the separator. Further, when the air permeability is greater than <NUM> sec/<NUM>, the speed of lithium ion movement in the separator is lowered, which may reduce efficiency and performance of charging and discharging cycles. Thus, regardless of position within the electrode assembly, the separator desirably has an air permeability in a range from <NUM> sec/<NUM> to <NUM> sec/<NUM>.

The electrode assembly according to the present invention preferably has higher air permeability than electrode assemblies in the related art, thereby increasing the safety of the electrode assembly. Specifically, the upper surface air permeability and the lower surface air permeability of the electrode assembly according to the present invention are in a range from <NUM> sec/<NUM> to <NUM> sec/<NUM>.

As recited in claim <NUM>, for measuring the air permeability of the separator, a Gurley type Densometer (No. <NUM>) manufactured by Toyoseiki may be used according to the JIS Gurley measurement method of the Japanese industrial standard. That is, the air permeability of the separator may be obtained by measuring the time it takes for <NUM> (or <NUM> cc) of air to pass through the separator of <NUM> square inch, equivalent to <NUM> square centimeters, under a pressure of <NUM> MPa at room temperature (i.e., <NUM> to <NUM>).

According to exemplary embodiments of the present invention, the middle air permeability of the electrode assembly may be in a range from <NUM> sec/<NUM> to <NUM> sec/<NUM>, preferably from <NUM> sec/<NUM> to <NUM> sec/<NUM>.

According to the present invention, the upper surface air permeability of the electrode assembly is in a range from <NUM> sec/<NUM> to <NUM> sec/<NUM>, preferably from <NUM> sec/<NUM> to <NUM> sec/<NUM>, more preferably from <NUM> sec/<NUM> to <NUM> sec/<NUM>.

According to the present invention, the lower surface air permeability of the electrode assembly is in a range from <NUM> sec/<NUM> to <NUM> sec/<NUM>, preferably from <NUM> sec/<NUM> to <NUM> sec/<NUM>, more preferably from <NUM> sec/<NUM> to <NUM> sec/<NUM>.

According to exemplary embodiments of the present invention, the lower surface air permeability may be less than or equal to the upper surface air permeability. In addition, the middle air permeability may be less than or equal to the lower surface air permeability.

That is, the magnitude of the upper surface air permeability, the lower surface air permeability, and the middle air permeability may satisfy Equation <NUM> below.

The values of air permeability in Equation <NUM> relate to the air permeability of the separators in the electrode assembly after the completion of the heating and pressing steps.

According to exemplary embodiments of the present invention, the adhesive force between the separator and the electrodes at any of the positions in the electrode assembly (i.e., upper surface, middle, and lower surface) may be in a range from <NUM> gf/<NUM> to <NUM> gf/<NUM> (<NUM>. 049N/<NUM> to <NUM>. 735N/<NUM>, wherein 1gf is equivalent to <NUM>.

As recited in the claims, a method for measuring adhesive force of the separator is according to the testing method set forth in ASTM D6862. For example, samples of the lower portion, the middle portion, and the upper portion of the electrode assembly may be separated from the stack. Such samples may include a positive electrode and a separator or a negative electrode and a separator. The samples, which may have a width of <NUM> and a length of <NUM>, are each adhered to a respective slide glass with the electrode being positioned on the adhesive surface of the slide glass. The samples are then each tested by performing a <NUM>° peel test at a speed of <NUM>/min pursuant to the testing method set forth in ASTM-D6862. That is, an edge of the separator is pulled upwardly at <NUM>° relative to the slide glass at a speed of <NUM>/min so as to peel the separator away from the electrode along the width direction of the sample (i.e., peeling from <NUM> to <NUM>).

According to exemplary embodiments of the present invention, the middle adhesive force of the electrode assembly may be in a range from <NUM> gf/<NUM> to <NUM> gf/<NUM>, preferably from <NUM> gf/<NUM> to <NUM> gf/<NUM>.

According to exemplary embodiments of the present invention, the upper surface adhesive force of the electrode assembly may be in a range from <NUM> gf/<NUM> to <NUM> gf/<NUM>, preferably from <NUM> gf/<NUM> to <NUM> gf/<NUM>.

According to exemplary embodiments of the present invention, the lower surface adhesive force of the electrode assembly may be in a range from <NUM> gf/<NUM> to <NUM> gf/<NUM>, preferably from <NUM> gf/<NUM> to <NUM> gf/<NUM>.

According to exemplary embodiments of the present invention, the lower surface adhesive force and the upper surface adhesive force may be greater than the middle adhesive force.

According to exemplary embodiments of the present invention, the adhesive force between the positive electrode and the separator and the adhesive force between the negative electrode and the separator may be the same as or may be different from each other.

According to exemplary embodiments of the present invention, a deviation between the middle adhesive force of the electrode assembly and either the upper surface adhesive force or the lower surface adhesive force of the electrode assembly may be in a range from <NUM> gf/<NUM> to <NUM> gf/<NUM>, preferably from <NUM> gf/<NUM> to <NUM> gf/<NUM>.

According to exemplary embodiments of the present invention, a deviation between the middle air permeability of the electrode assembly and either the upper surface air permeability or the lower surface air permeability of the electrode assembly may be in a range from <NUM> sec/<NUM> to <NUM> sec/<NUM>.

When the air permeability and adhesive force conditions described above are satisfied, it may preferably make cleaning and process handling easy, and it may also make wetting of the separator by the electrolyte easier, so that an electrode assembly having uniform performance may be manufactured. In addition, side-effects, such as lithium (Li) precipitation in the electrode assembly and non-charging of the electrode assembly, may be prevented.

A withstand voltage of the electrode assembly of the present invention may be in a range from <NUM> kV to <NUM> kV. The electrode assembly of the present invention is manufactured by the method of manufacturing the electrode assembly including the primary heat press operation and the secondary heat press operation, which may result in both excellent adhesive force and excellent withstand voltage compared to the case where only the primary heat press operation is performed.

According to the exemplary embodiment of the present invention, when it is assumed that a thickness of the uppermost electrode is <NUM>%, it is possible to provide an electrode assembly in which the thicknesses of all electrodes are <NUM>% to <NUM>% of the thickness of the uppermost electrode.

According to the exemplary embodiment of the present invention, the minimum thickness of the electrode of the electrode assembly may be <NUM> or more.

According to the exemplary embodiment of the present invention, a thickness deviation of the electrodes of the electrode assembly may be in a range from <NUM> to <NUM>.

When the thicknesses of the electrodes comprising the electrode assembly are small and the thickness deviations between the electrodes are small, the electrode assembly may tend to be more structurally stable and more stable in use. As a result, , it is beneficially possible to manufacture an electrode assembly in which the thicknesses of the electrodes comprising the electrode assembly are small and the thickness deviations between the electrodes are small.

Although the present invention has been described in detail through specific exemplary embodiments, the present invention is not limited thereto and the scope of the invention is defined by the appended claims.

<NUM> positive electrode sheets, <NUM> negative electrode sheets, and an elongated separator were supplied to the stack table from the respective positive electrode supply unit, negative electrode supply unit, and separator supply unit.

More specifically, the positive electrode and the negative electrode were supplied after being cut from a positive electrode sheet and a negative electrode sheet, respectively, and the separator was supplied in the form of an elongated separator sheet. Thereafter, the supplied separator was folded while rotating the stack table and stacking the positive electrodes and the negative electrode as described above. A holding mechanism was used to press down on and stabilize the stack, which resulted in a stack including <NUM> electrodes.

After assembling the stack, a primary heat press operation was performed by gripping the stack with the gripper and pressing for <NUM> seconds while heating the stack under a temperature condition of <NUM> and a pressure condition of <NUM> MPa.

After the primary heat press operation, the gripper was released from the stack and the secondary heat press operation was performed, in which a pressing block was heated to a temperature of <NUM> (temperature condition), and a pressure of <NUM> Mpa (pressure condition) was applied to the stack with the heated pressing block for <NUM> seconds (press time), thus resulting in the electrode assembly of Example <NUM>.

In the process of manufacturing the electrode assembly, the above-described disclosure may be applied.

Electrode assemblies of Examples <NUM> and <NUM> were manufactured in the same manner as in Example <NUM>, except that the method was performed under the temperature conditions, pressure conditions, and press time represented in Table <NUM> below.

Electrode assemblies of Comparative Examples <NUM> to <NUM> were manufactured in the same manner as in Example <NUM>, except that the primary heat press operation was performed under the temperature conditions, pressure conditions, and press time represented in Table <NUM> below, and the secondary heat press operation was not performed.

The air permeability of the electrode assemblies of Examples <NUM> to <NUM> and Comparative Example <NUM> was evaluated.

Specifically, after collecting the separators in the electrode assemblies of Examples <NUM> to <NUM>, and Comparative Example <NUM>, the separators were cut to prepare separator samples having a size of <NUM> X <NUM> (width X length). After that, the separator samples were washed with acetone.

Air permeability of Examples <NUM> to <NUM> and Comparative Example <NUM> were measured by measuring the time it took for <NUM> (or <NUM> cc) of air to pass through the separator of <NUM> square inch at room temperature and under the pressure condition of <NUM> MPa by using a Gurley type Densometer (No. <NUM>) from Toyoseiki in accordance with the JIS Gurley measurement method of the Japanese industrial standard.

The results are represented in Table <NUM>.

From the results of Table <NUM>, it was confirmed that the upper surface air permeability and the lower surface air permeability of the electrode assembly according to the present invention were each independently <NUM> sec/<NUM> or more. Further, it was confirmed that the upper surface air permeability and the lower surface air permeability of the electrode assembly according to the present invention did not exceed <NUM> sec/<NUM>. That is, it could be confirmed that the electrode assembly according to the present invention has an appropriate level of air permeability for use as an electrode assembly.

In addition, it was confirmed that the air permeability deviation between each location was less than <NUM> sec/<NUM>, which was considered to be substantially uniform.

On the other hand, in the case of Comparative Example <NUM>, the deviation in air permeability between each location was smaller than that of the Example, but it could be confirmed that the upper surface air permeability and the lower surface air permeability were each independently less than <NUM> sec/<NUM>, so that safety was lower than that of the electrode assembly according to the present invention. It is believed that this is because only the primary heat press operation was performed.

The electrode assemblies of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were disassembled and analyzed to measure upper surface, lower surface, and middle adhesive force. Specifically, adhesive force between the negative electrode and the separator located at the lowermost end of the stack was measured. Additionally, adhesive force between the negative electrode and the separator located at the uppermost end of the stack was measured. Finally, adhesive force between the negative electrode and the separator located at a middle location along the stacking direction of the stack was measured.

In each of the separated electrode assemblies, the negative electrode and the separator sampled had a width of <NUM> and a length of <NUM>. The sampled sample was adhered to the slide glass with the electrode being positioned on the adhesive surface of the slide glass. After that, the slide glass with the sample was mounted to the adhesive force measuring device and tested by performing a <NUM>° peel test at a speed of <NUM>/min pursuant to the testing method set forth in ASTM-D6862. That is, an edge of the separator was pulled upwardly at <NUM>° relative to the slide glass at a speed of <NUM>/min so as to peel the separator away from the electrode along the width direction of the sample (i.e., peeling from <NUM> to <NUM>). After discounting any initial significant fluctuations, the values for applied force per sample width (in grams/mm) were measured while the separator was peeled away from the electrode.

The results are represented in Table <NUM> below.

In addition, the withstand voltages of the electrode assemblies of Examples <NUM> to <NUM> and Comparative Examples <NUM> to <NUM> were also measured.

Investigating the results of Table <NUM>, it was confirmed that the adhesive force of Examples <NUM> to <NUM> was superior to that of Comparative Example <NUM>, in which only the primary heat press operation was performed under conditions similar to those of the Examples.

In addition, investigating the results of Table <NUM>, it was confirmed that the withstand voltage of Examples <NUM> to <NUM>, in which the primary heat press operation was performed under higher temperature and higher pressure conditions than those of the Comparative Examples had a range of <NUM> kV or more and <NUM> kV or less.

That is, the electrode assembly of the present invention has excellent adhesive force and, at the same time, has a withstand voltage suitable for use as an electrode assembly. In that regard, a withstand voltage of <NUM> kV or less was confirmed.

It is believed that this is because the electrode assembly of the present invention was manufactured by the manufacturing method including both the primary and secondary heat press operations.

After charging the electrode assemblies of Example <NUM> and Comparative Example <NUM> was completed, the electrode assemblies were disassembled to check whether lithium (Li) was precipitated. The results are represented in <FIG> and <FIG>.

In the case of the electrode assembly of Comparative Example <NUM>, it was confirmed that lithium (Li) was precipitated upon disassembly after the electrode assembly was completely charged as illustrated in <FIG>.

In the case of the electrode assembly of Example <NUM>, it was confirmed that lithium (Li) was not precipitated upon disassembly after the electrode assembly was completely charged, as illustrated in <FIG>.

Through Experimental Examples <NUM> to <NUM>, it could be confirmed that the electrode assembly according to the present invention has an appropriate withstand voltage while also having excellent stability and adhesive force, and it is possible to prevent side-effects, such as lithium (Li) precipitation in the electrode assembly and non-charging of the electrode assembly.

The maximum thicknesses, minimum thicknesses, and average thicknesses of the electrodes comprising the electrode assemblies of Examples <NUM> to <NUM> and Comparative Example <NUM>, as well as the thickness deviations of the electrodes, were measured by using a plate thickness measurement device equipped with a load cell.

In particular, the thickness when the upper plate of the plate thickness measurement device was lowered and came into contact with the lower plate was set as <NUM>. Then, the electrode assembly of which the thickness was to be measured was placed inside the plate thickness measurement device, and the plate was further lowered by applying a pressing force of <NUM> kgf (<NUM>. 6N) over the area of the electrodes for <NUM> seconds, after which the plate thickness was measured. In Example <NUM>, the area to which the <NUM> kgf (<NUM>. 6N) was applied was <NUM><NUM>.

From the results of Table <NUM>, it could be confirmed that, in the electrode assembly according to the present invention, the thickness of the electrodes were small, and there was an appropriate amount of thickness deviation between the electrodes.

Claim 1:
An electrode assembly (<NUM>), comprising:
a plurality of electrodes (<NUM>, <NUM>) arranged in a stack along a stacking axis with a respective separator portion (<NUM>) positioned between each of the electrodes in the stack, the plurality of electrodes (<NUM>, <NUM>) including a top one of the plurality of electrodes positioned at a top of the stack along the stacking axis and including a bottom one of the plurality of electrodes positioned at a bottom of the stack along the stacking axis, and the separator portions (<NUM>) including a top one of the separator portions abutting the top electrode and including a bottom one of the separator portions abutting the bottom electrode,
characterized in that
the top separator portion and the bottom separator portion each have a value of air permeability measured according to the JIS Gurley measurement method of the Japanese industrial standard from <NUM> sec/<NUM> to <NUM> sec/<NUM> per <NUM> square centimeter, equivalent to <NUM> square inch, of the respective separator portion at a pressure of <NUM> MPa and at room temperature.