Patent ID: 12244038

DETAILED DESCRIPTION

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. Further, in describing the present invention, detailed descriptions of related known technologies that may unnecessarily obscure the gist of the present invention will be omitted.

FIG.1is a cross-sectional view illustrating an example of an electrode assembly according to an exemplary embodiment of the present invention. That is, referring toFIG.1, an electrode assembly10according to an exemplary embodiment of the present invention includes a stack of electrodes in which one or more first electrodes11alternates with one or more second electrodes12. Each of the electrodes in the stack are separated from one another by a separator14positioned therebetween, which may be a single elongated separator14repeatedly folded so as to follow a serpentine or zigzag path around each successive electrode.

The electrode assembly10is 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 assembly10may be provided in a form in which the outermost portion is surrounded by the separator14, e.g., by wrapping the separator around the assembled electrode assembly10, as illustrated inFIG.1. 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 assembly10refers to the uppermost position of the electrode assembly10in the stacking direction of the electrode assembly, which is designated by reference numeral2inFIG.2. Thus, subsequent references to “upper surface air permeability” relate to air permeability of the separator14abutting 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 separator14.

Further, as discussed herein, a “lower surface” of the electrode assembly10refers to the lowermost position of the electrode assembly10in the stacking direction of the electrode assembly, which is designated by reference numeral3inFIG.2. Thus, subsequent references to “lower surface air permeability” relate to air permeability of the separator14abutting 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 separator14.

Finally, as discussed herein, the “middle” of the electrode assembly10refers to a middle position between the upper surface and the lower surface of the electrode assembly10in the stacking direction of the electrode assembly, as designated by reference numeral1inFIG.2. For example, when an electrode assembly10formed of nine electrodes and viewed from the side, as inFIG.2, 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 separator14abutting 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 separator14.

Referring toFIGS.3and4, an apparatus100for manufacturing an electrode assembly according to an exemplary embodiment of the present invention includes a stack table110; a separator supply unit120for supplying a separator14; a first electrode supply unit130for supplying a first electrode11; a second electrode supply unit140for supplying a second electrode12; a first electrode stack unit150for stacking the first electrode11on the stack table110; a second electrode stack unit160for stacking the second electrode12on the stack table110; and a press unit180for bonding the first electrode11, the separator14, and the second electrode12to each other. Further, the apparatus100for manufacturing the electrode assembly according to the exemplary embodiment of the present invention may include a holding mechanism170for fixing the stack (comprising the first electrode(s)11, the second electrode(s)12, and the separator14) to the stack table110as the stack is being assembled.

The separator supply unit120may have a passage through which the separator14passes towards the stack table110. In particular, the separator supply unit120may include a separator heating unit121defining the passage through which the separator14passes towards the stack table110. As shown inFIG.8, the separator heating unit121may include a pair of bodies121a, each of which may be in the form of a square block, and the bodies121amay be spaced apart by a distance defining one of the dimensions of the passage through which the separator14passes. At least one or both of the bodies121amay further include a separator heater121bfor heating the respective body121a, and thereby transferring heat to the separator14.

The separator supply unit120may further include a separator roll122on which the separator14is wound. Thus, the separator14wound on the separator roll122may be gradually unwound and pass through the formed passage to be supplied to the stack table110.

The first electrode supply unit130may include a first electrode roll133on which the first electrode11is wound in the form of a sheet, a first cutter134for cutting the first electrode11at regular intervals to form the first electrodes11having a predetermined size when the first electrode11is unwound and supplied from the first electrode roll133, a first conveyor belt135for moving the first electrode11cut by the first cutter134, and a first electrode supply head136for picking up (e.g., via vacuum suction) the first electrode11transferred by the first conveyor belt135and seating the first electrode11on a first electrode seating table131.

The second electrode supply unit140may include a second electrode seating table141on which the second electrode12is seated before being stacked on the stack table110by the second electrode stack unit160. The second electrode supply unit140may further include a second electrode roll143on which the second electrode12is wound in the form of a sheet, a second cutter144for cutting the second electrode12at regular intervals to form the second electrode12of a predetermined size when the second electrode12is unwound and supplied from the second electrode roll143, a second conveyor belt145for moving the second electrode121cut by the second cutter144, and a second electrode supply head146for picking up (e.g., via vacuum suction) the second electrode12transferred by the second conveyor belt145and seating the second electrode on the second electrode seating table141.

The first electrode stack unit150may be structured to stack the first electrode11on the stack table110. The first electrode stack unit150may include a first suction head151and a first moving unit153. The first suction head151may pick up the first electrode11seated on the first electrode seating table131via vacuum suction through one or more vacuum suction ports (not shown) formed on a bottom surface of the first suction head150, and then the first moving unit153may move the first suction head151to the stack table110so as to allow the first suction head151to stack the first electrode11on the stack table110.

The second electrode stack unit160may also be structured to stack the second electrode12on the stack table110. The second electrode stack unit160may have the same structure as that of the foregoing first electrode stack unit150. In such case, the second electrode stack unit160may include a second suction head161and a second moving unit163. The second suction head161may pick up the second electrode12seated on the second electrode seating table141via vacuum suction. The second moving unit163may then move the second suction head161to the stack table110so as to allow the second suction head161to stack the second electrode12on the stack table110.

The stack table110may be rotatable so as to rotate between positions facing the first electrode stack unit150and the second electrode stack unit160. As the stack table110rotates, the holding mechanism170may hold the stack being assembled (comprising the first electrode11, the second electrode12, and the separator14) in order to secure the position of the stack relative to the stack table110. For example, the holding mechanism170may apply downward pressure to the upper surface of the stack to press it towards the stack table110. The holding mechanism170may include, for example, a first holder171and a second holder172to fix opposing sides of the first electrode11or the second electrode12. The holders171,172may each be in the form of one or more clamps or other clamping mechanisms.

Thus, in operation, the first electrode11is supplied from the first electrode supply unit130to the first electrode stack unit150, the first electrode stack unit150stacks the first electrode11on the upper surface of the separator14stacked on the stack table110. The holding mechanism170then presses down on the upper surface of the first electrode11to secure the position of the first electrode11on the stack table110. Thereafter, the stack table110is rotated in the direction of the second electrode stack unit160while the separator14is continuously supplied so as to cover the upper surface of the first electrode11. Meanwhile, the second electrode12is supplied from the second electrode supply unit140and is stacked by the second electrode stack unit160on a portion of the separator14where the separator14covers the upper surface of the first electrode11. Then the holding mechanism170releases the upper surface of the first electrode11and then presses down on the upper surface of the second electrode12to secure the position of the stack S being built vis-a-vis the stack table110.

Thereafter, by repeating the process of stacking the first electrode11and the second electrode12, the stack S in which the separator14is zig-zag-folded and positioned between each of the successive first and second electrodes11,12may 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 unit180, which applies heat and pressure to the stack by advancing heated pressing blocks181and182towards 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 toFIG.7, 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 way 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 unit180, 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 40 sec/100 ml, 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 120 sec/100 ml, 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 40 sec/100 ml to 120 sec/100 ml.

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 may each independently be in a range from 80 sec/100 ml to 120 sec/100 ml.

In accordance with the present invention, the method for measuring the air permeability of the separator is not particularly limited, and the air permeability may be measured by using a method commonly used in the art. For example, a Gurley type Densometer (No. 158) 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 100 ml (or 100 cc) of air to pass through the separator of 1 square inch under a pressure of 0.05 MPa at room temperature (i.e., 20° C. to 25° C.).

According to exemplary embodiments of the present invention, the middle air permeability of the electrode assembly may be in a range from 70 sec/100 ml to 85 sec/100 ml, preferably from 75 sec/100 ml to 85 sec/100 ml.

According to exemplary embodiments of the present invention, the upper surface air permeability of the electrode assembly may be in a range from 80 sec/100 ml to 120 sec/100 ml, preferably from 80 sec/100 ml to 110 sec/110 ml, more preferably from 80 sec/100 ml to 100 sec/100 ml.

According to exemplary embodiments of the present invention, the lower surface air permeability of the electrode assembly may be in a range from 80 sec/100 ml to 120 sec/100 ml, preferably from 80 sec/100 ml to 110 sec/110 ml, more preferably from 80 sec/100 ml to 100 sec/100 ml.

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 1 below.
Upper surface air permeability≥Lower surface air permeability≥Middle air permeability  [Equation 1]

The values of air permeability in Equation 1 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 5 gf/20 mm to 75 gf/20 mm.

In the present invention, a method for measuring adhesive force of the separator is not particularly limited. 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 55 mm and a length of 20 mm, 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 90° peel test at a speed of 100 mm/min pursuant to the testing method set forth in ASTM-D6862. That is, an edge of the separator is pulled upwardly at 90° relative to the slide glass at a speed of 100 mm/min so as to peel the separator away from the electrode along the width direction of the sample (i.e., peeling from 0 mm to 55 mm).

According to exemplary embodiments of the present invention, the middle adhesive force of the electrode assembly may be in a range from 5 gf/20 mm to 35 gf/20 mm, preferably from 5 gf/20 mm to 15 gf/20 mm.

According to exemplary embodiments of the present invention, the upper surface adhesive force of the electrode assembly may be in a range from 5 gf/20 mm to 75 gf/20 mm, preferably from 6 gf/20 mm to 30 gf/20 mm.

According to exemplary embodiments of the present invention, the lower surface adhesive force of the electrode assembly may be in a range from 5 gf/20 mm to 75 gf/20 mm, preferably from 9 gf/20 mm to 30 gf/20 mm.

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 10 gf/20 mm to 35 gf/20 mm, preferably from 10 gf/20 mm to 20 gf/20 mm.

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 3 sec/100 ml to 15 sec/100 ml.

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 1.56 kV to 1.8 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 100%, it is possible to provide an electrode assembly in which the thicknesses of all electrodes are 70% to 120% 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 8.2 mm 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 0.013 mm to 0.035 mm.

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 of the present invention, 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. Various different implementations may be made by those of ordinary skill in the art within the technical spirit of the present invention.

1) Example 1

19 positive electrode sheets, 20 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 39 electrodes.

After assembling the stack, a primary heat press operation was performed by gripping the stack with the gripper and pressing for 15 seconds while heating the stack under a temperature condition of 70° C. and a pressure condition of 1.91 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 70° C. (temperature condition), and a pressure of 2.71 Mpa (pressure condition) was applied to the stack with the heated pressing block for 10 seconds (press time), thus resulting in the electrode assembly of Example 1.

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

2) Examples 2 and 3

Electrode assemblies of Examples 2 and 3 were manufactured in the same manner as in Example 1, except that the method was performed under the temperature conditions, pressure conditions, and press time represented in Table 1 below.

TABLE 1Primary heat pressTemperaturePressure conditionconditionPress area (314.57 cm2)Press time(° C.)TonfMPa(s)Example 17061.9115Example 2Example 3Secondary heat pressTemperaturePressure conditionconditionPress area (554.1 cm2)Press time(° C.)TonfMPa(s)Example 17052.7110Example 26042.1720Example 38042.1720

3) Comparative Examples 1 to 7

Electrode assemblies of Comparative Examples 1 to 7 were manufactured in the same manner as in Example 1, except that the primary heat press operation was performed under the temperature conditions, pressure conditions, and press time represented in Table 2 below, and the secondary heat press operation was not performed.

TABLE 2Primary heat pressTemperaturePressure conditionconditionPress areaPress time(° C.)TonfMPa(s)Comparative7061.9115Example 1Comparative8061.9115Example 2Comparative8082.548Example 3Comparative8082.5415Example 4Comparative9061.9115Example 5Comparative9082.548Example 6Comparative9082.545Example 7Secondary heat press (not performed)TemperaturePressure conditionconditionPress area (554.1 cm2)Press time(° C.)TonfMPa(s)Comparative————Example 1Comparative————Example 2Comparative————Example 3Comparative————Example 4Comparative————Example 5Comparative————Example 6Comparative————Example 7

4) Experimental Example 1—Thickness Measurement

The maximum thicknesses, minimum thicknesses, and average thicknesses of the electrodes configuring the electrode assemblies of Examples 1 to 3 and Comparative Example 1, 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 is lowered and came into contact with the lower plate was set as 0 mm. 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 90 kgf over the area of the electrodes for 3 seconds, after which the plate thickness was measured. In Example 1, the area to which the 90 kgf was applied was 554.1 cm2.

The results are represented in Table 3.

TABLE 3Thickness (mm)MaximumMinimumAverage(Max)(Min)(AVG)DeviationExample 18.2668.2378.2560.029Example 28.2658.2518.2580.014Example 38.2378.2058.2160.032Comparative8.3578.3498.3520.008Example 1

From the results of Table 3, 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.

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.

5) Experimental Example 2—Evaluation of Air Permeability

The air permeability of the electrode assemblies of Examples 1 to 3 and Comparative Example 1 was evaluated.

Specifically, after collecting the separators in the electrode assemblies of Examples 1 to 3, and Comparative Example 1, the separators were cut to prepare separator samples having a size of 5 cm×5 cm (width×length). After that, the separator samples were washed with acetone.

Air permeability of Examples 1 to 3 and Comparative Example 1 were measured by measuring the time it took for 100 ml (or 100 cc) of air to pass through the separator of 1 square inch at room temperature and under the pressure condition of 0.05 MPa by using a Gurley type Densometer (No. 158) from Toyoseiki in accordance with the JIS Gurley measurement method of the Japanese industrial standard.

The results are represented in Table 4.

TABLE 4Air permeability (sec/100 ml)Upper surfaceMiddleLower surfaceDeviationExample 188768411.1Example 288758712.3Example 31018410017.4Comparative7674773.0Example 1

From the results of Table 4, 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 80 sec/100 ml 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 120 sec/100 ml. 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 20 sec/100 ml, which was considered to be substantially uniform.

On the other hand, in the case of Comparative Example 1, 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 80 sec/100 ml, 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 was performed differently from the manufacturing process of the electrode assembly of the present invention.

6) Experimental Example 3—Adhesive Force Evaluation and Withstand Voltage Evaluation

The electrode assemblies of Examples 1 to 3 and Comparative Examples 1 to 7 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 55 mm and a length of 20 mm. 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 90° peel test at a speed of 100 mm/min pursuant to the testing method set forth in ASTM-D6862. That is, an edge of the separator was pulled upwardly at 90° relative to the slide glass at a speed of 100 mm/min so as to peel the separator away from the electrode along the width direction of the sample (i.e., peeling from 0 mm to 55 mm). 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 5 below.

TABLE 5Negative electrode adhesive force (gf/20 mm)Upper surfaceMiddleLower surfaceDeviationExample 119.810.821.510.7Example 211.17.114.37.2Example 325.312.022.413.3Comparative9.85.811.25.5Example 1Comparative15.66.915.88.9Example 2Comparative14.55.616.510.9Example 3Comparative19.59.021.212.2Example 4Comparative19.513.824.210.4Example 5Comparative15.67.225.918.7Example 6Comparative30.712.625.118.1Example 7

In addition, the withstand voltages of the electrode assemblies of Examples 1 to 3 and Comparative Examples 1 to 7 were also measured.

The results are represented in Table 6 below.

TABLE 6Withstand voltage (kV)Example 11.58Example 21.56Example 31.58Comparative Example 11.82Comparative Example 21.51Comparative Example 31.49Comparative Example 41.47Comparative Example 51.48Comparative Example 61.45Comparative Example 71.45

Investigating the results of Table 5, it was confirmed that the adhesive force of Examples 1 to 3 was superior to that of Comparative Example 1, 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 6, it was confirmed that the withstand voltage of Examples 1 to 3, 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 1.56 kV or more and 1.8 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 1.8 kV or less was confirmed.

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

7) Experimental Example 4

After charging the electrode assemblies of Example 1 and Comparative Example 1 was completed, the electrode assemblies were disassembled to check whether lithium (Li) was precipitated. The results are represented inFIGS.5and6.

In the case of the electrode assembly of Comparative Example 1, it was confirmed that lithium (Li) was precipitated upon disassembly after the electrode assembly was completely charged as illustrated inFIG.5.

In the case of the electrode assembly of Example 1, it was confirmed that lithium (Li) was not precipitated upon disassembly after the electrode assembly was completely charged, as illustrated inFIG.6.

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

Through Experimental Examples 1 to 3, 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 is possible to prevent side-effects, such as lithium (Li) precipitation in the electrode assembly and non-charging of the electrode assembly.