Title of Invention: Stacked electrode assembly with improved bending and manufacturing method thereof
Technical field
[One]
This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0168229 of 2018.12.
[2]
The present invention relates to a lamination stack type electrode assembly and a method of manufacturing the same, and to a lamination stack type electrode assembly and a method of manufacturing the same, which improves bending of the electrode assembly that may occur by an activation process.
Background
[3]
Secondary batteries can be classified in various ways according to the structure of the electrode assembly. For example, secondary batteries may be classified into a stack type structure, a wound type (jelly roll type) structure, or a stack/folding type structure. However, in the stacked structure, since the electrode units (anode, separator, and cathode) constituting the electrode assembly are stacked separately from each other, it is very difficult to precisely align the electrode assembly, and very many processes are required to produce the electrode assembly. There is a disadvantage that it is required. In addition, since the stack/folding type structure generally requires two lamination equipment and one folding equipment, the manufacturing process of the electrode assembly is very complicated. In particular, the stack/folding type structure has a disadvantage in that it is difficult to precisely align the full cells or bi-cells because the full cells or bi-cells are stacked through folding.
[4]
Accordingly, an electrode assembly of a lamination and stack type structure appeared. The lamination-and-stack type structure can be manufactured by laminating a basic unit formed by alternately stacking electrodes and separators to impart adhesion between the electrode and the separator in the basic unit, and simply stacking such basic units repeatedly. have.
[5]
On the other hand, in the secondary battery, an assembly process in which the electrode assembly is accommodated in a battery case to inject and seal the electrolyte, a pre-aging process in which the electrolyte is well wetted into electrodes and separators, and an activation process in which the battery structure is stabilized and usable. In the activation process, a secondary battery is mounted on a predetermined jig for smooth current conduction, and processing such as charging and discharging is performed under conditions necessary for activation. This is sometimes referred to as a jig formation. In a secondary battery, due to its characteristics, such an activation process must be preceded essentially in order to activate the positive electrode active material during the first cycle and to generate a stable surface film (SEI, Solid Electrolyte Interface) at the negative electrode. In addition, during the formation of the jig, in order to prevent the formation of a non-uniform SEI film due to gas generated by initial charging, pressurization may be performed simultaneously with charging.
[6]
During the above activation process, when the secondary battery is charged and discharged, the volume of the positive electrode and the negative electrode expands. In the activation process of the secondary battery to which the electrode assembly of the lamination and stack type is applied, bending or bending in the direction of the electric length of the secondary battery There was a problem with the phenomenon occurring.
[7]
4 illustrates a mechanism in which a bending phenomenon occurs during an activation process of a lamination-and-stack type electrode assembly. Referring to this, the electrode assembly of the conventional lamination-and-stack type structure is formed by simple stacking of basic units, so that no adhesive force is formed between the basic units and adjacent basic units. On the other hand, adhesion is formed between the electrode and the separator in the basic unit. This is because when the basic unit is manufactured, a lamination process is performed, and adhesion between the separator and the electrode is formed as the binder is melted by the lamination process.
[8]
When the electrode assembly of such a lamination-and-stack structure is charged, the positive and negative electrodes expand. Since the volume expansion rates of the positive and negative electrodes are different, the stress accumulates inside the basic unit, resulting in bending of the basic unit as a whole. It will happen.
[9]
On the other hand, even in the case of an electrode assembly having a lamination-and-stack structure, if the pressure is not pressed at the same time as initial charging, between the first electrode and the first separator, between the first separator and the second electrode, between the second electrode and the second separator, and basic Since the interfacial adhesion is weakened by the activation gas at all interfaces between the units, even if the positive and negative electrodes are expanded, the stress is dispersed inside the basic unit and the individual electrodes expand in the vertical direction, so the above bending phenomenon does not occur (Fig. 5). Reference).
[10]
In addition, even in the case of an electrode assembly having a lamination-and-stack structure, as shown in FIG. 6, basic units of the first electrode/first separator/second electrode/second separator/first electrode/first separator are repeatedly stacked. Since the electrode assembly of the stacked structure has a bidirectional symmetric structure with respect to the second electrode, even if the volume of the electrode is expanded, the expansion direction of the positive electrode and the negative electrode is symmetric, so that the above bending phenomenon hardly occurs. However, the electrode assembly of the lamination-and-stack type structure in which the basic units of the first electrode/first separator/second electrode/second separator are repeatedly stacked has an asymmetric expansion direction. Structural deformation such as bending occurs.
[11]
Therefore, in the case of applying a jig formation process for pressing the electrode assembly at the same time as charging to an electrode assembly having a lamination and stack structure, it is necessary to develop a technology for an electrode assembly preventing bending and a manufacturing method thereof. .
Detailed description of the invention
Technical challenge
[12]
The present invention is to improve the phenomenon that the electrode assembly is bent or bent by an activation process in a lamination stacked electrode assembly.
[13]
Another object of the present invention is to improve the productivity of a battery by improving the bending phenomenon of the electrode assembly.
Means of solving the task
[14]
The electrode assembly of the present invention includes a unit stack portion in which at least one basic unit forming a four-layer structure by sequentially stacking a first electrode, a first separator, a second electrode, and a second separator is stacked, and the first A coating material having adhesive strength is applied to each surface of the first separator and the second separator, and in the unit stack portion, the basic unit is adhered to an adjacent basic unit.
[15]
In the electrode assembly according to an exemplary embodiment of the present invention, the adhesive force between the basic unit and the adjacent basic unit is equal to or greater than the adhesive force between the first electrode and the first separator in the basic unit.
[16]
In the electrode assembly according to an embodiment of the present invention, the coating material is coated on one surface of the second separator facing the second electrode and on the opposite surface, and the basic unit is coated by a coating material of the second separator. They adhere to each other.
[17]
In the electrode assembly according to an embodiment of the present invention, the coating material is formed of a mixture of inorganic particles and a binder polymer that connects and fixes the inorganic particles to each other. At this time, the inorganic particles form a densely packed structure to form interstitial volumes between the inorganic particles as a whole in the coating layer, and the inorganic particles are in the coating layer by an interstitial volume defined by the inorganic particles. It may be that a pore structure is formed.
[18]
In the electrode assembly according to an embodiment of the present invention, the difference between the thickness (d1) measured for 2 seconds under a pressure of 30 kgf and the thickness (d2) measured for 2 seconds under a pressure of 90 kgf is 100 μm or less, thereby preventing the bending phenomenon. There is.
[19]
In the electrode assembly according to an embodiment of the present invention, the first electrode is an anode, and the second electrode is a cathode.
[20]
In the electrode assembly according to an embodiment of the present invention, the basic unit is formed by repeatedly stacking the four-layer structure.
[21]
In addition, the present invention provides a method of manufacturing a secondary battery including the electrode assembly. In the method of manufacturing a secondary battery of the present invention, a first electrode, a first separator, a second electrode, and a second separator are sequentially stacked. A basic unit manufacturing step (S100) of manufacturing a basic unit forming a layer structure; Manufacturing a unit stack unit (S200) of repeatedly stacking the basic units to manufacture a unit stack unit; An assembly step (S300) of receiving the electrode assembly including the unit stack unit in a battery case and then injecting and sealing the electrolyte solution; A lamination step (S400) of bonding the second separator of the one basic unit and the first electrode of the adjacent basic unit to each other in the unit stack unit by applying heat and pressure; Includes.
[22]
In the method of manufacturing a secondary battery according to an embodiment of the present invention, the separator is coated with a coating material including a binder having adhesive force on its surface, and the temperature of the lamination step (S400) is the adhesive force of the binder. This is the temperature that is maximized.
[23]
In an embodiment of the present invention, the specific range of the temperature is 45°C to 85°C, and may be 45°C to 70°C.
[24]
In the manufacturing method according to an embodiment of the present invention, the pressure of the lamination step (S400) is 1 to 10 kgf/cm 2, and the heating and pressing time is 2 to 20 minutes.
[25]
In the manufacturing method according to an embodiment of the present invention, after the lamination step (S400), a first formation process is further included. In this case, the temperature during the first formation process is 45°C or less.
[26]
In the manufacturing method according to an embodiment of the present invention, the solvent of the electrolyte is ethyl methyl carbonate or dimethyl carbonate.
[27]
The present invention provides a secondary battery including the electrode assembly as described above, and the secondary battery has the advantage of improving productivity by preventing bending.
Effects of the Invention
[28]
In the electrode assembly of the present invention, by performing a lamination process of heating and pressing the electrode assembly before the first formation process, the separator of one basic unit and the first electrode of the other basic unit are adhered by the coating material coated on the separator. Since it is fixed, there is an effect of preventing bending of the electrode assembly that may occur during the charging and discharging process.
Brief description of the drawing
[29]
1 is a side view showing the structure of a basic unit according to an embodiment of the present invention.
[30]
2 is a side view showing the structure of a unit stack unit according to an embodiment of the present invention.
[31]
3 is a process chart showing a process of manufacturing another basic unit according to the present invention.
[32]
4 is a schematic diagram of a principle in which a bending phenomenon occurs in a conventional electrode assembly.
[33]
5 is a schematic diagram illustrating the reason why a bending phenomenon does not occur when a general activation process other than jig formation is performed for an electrode assembly having a lamination stack type structure.
[34]
6 is a schematic diagram showing a reason why a bending phenomenon does not occur in an electrode assembly different from the lamination stacked structure of the present invention.
Best mode for carrying out the invention
[35]
Terms used in the present specification and claims are not limited to their usual or dictionary meanings and should not be interpreted, and that the inventor can appropriately define the concept of terms in order to describe his own invention in the best way Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of ​​the invention. Therefore, the configuration shown in the embodiments described in the present specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical spirit of the present invention, and various equivalents that can replace them at the time of the present application And it should be understood that there may be variations.
[36]
[37]
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[38]
The electrode assembly according to an embodiment of the present invention includes a unit stack portion in which at least one basic unit forming a four-layer structure is stacked by sequentially stacking a first electrode, a first separator, a second electrode, and a second separator. And a coating material having adhesive strength is applied to each surface of the first and second separators, and the basic unit is adhered to an adjacent basic unit.
[39]
In the electrode assembly according to an embodiment of the present invention, a plurality of basic units are not simply repeatedly stacked, but an electrode assembly in which a plurality of basic units are stacked is heated and pressurized under a temperature condition in which the adhesion of the coating material coated on the separator is maximized. The lamination process is performed so that the separator of one basic unit and the first electrode of the adjacent basic unit are bonded to each other, so that each interface between the basic unit and the adjacent basic unit is bonded.
[40]
[41]
In the electrode assembly according to the present invention, the basic unit is formed by alternately stacking electrodes and separators. At this time, the electrode and the separator are stacked by the same number. For example, as shown in FIG. 1, the basic unit 110a may be formed by stacking two electrodes 111 and 113 and two separators 112 and 114. At this time, the anode and the cathode can naturally face each other through the separator. When the basic unit is formed in this way, an electrode (see electrode 111 in Figs. 1 and 2) is positioned at one end of the basic unit, and a separator (referred to at 114 in Figs. 1 and 2) is located at the other end of the basic unit. Separation membrane) is located.
[42]
The present invention has a basic feature in that a unit stack portion can be formed by repeatedly stacking one type of basic unit or by stacking two or more types of basic unit in a predetermined order. In order to implement such characteristics, the basic unit may have the following structure.
[43]
First, the basic unit may be formed by sequentially stacking a first electrode, a first separator, a second electrode, and a second separator. More specifically, the basic unit bodies 110a and 110b include the first electrode 111, the first separator 112, the second electrode 113, and the second separator 114 from the upper side to the lower side as shown in FIG. The first electrode 111, the first separator 112, the second electrode 113, and the second separator 114 may be sequentially stacked and formed from the lower side to the upper side. In this case, the first electrode 111 and the second electrode 113 are opposite electrodes. For example, if the first electrode 111 is an anode, the second electrode 113 is a cathode.
[44]
In this way, when the first electrode, the first separator, the second electrode, and the second separator are sequentially stacked to form a basic unit, as shown in FIG. 2 through a manufacturing step (second step) of the unit stack unit to be described later, The unit stack portion 100a may be formed by repeatedly stacking the basic unit 110a.
[45]
Referring to Figure 3, looks at the process of manufacturing the basic unit of the present invention. First, a first electrode material 121, a first separator material 122, a second electrode material 123, and a second separator material 124 are prepared. Here, the first separator material 122 and the second separator material 124 may be the same material. Then, the first electrode material 121 is cut into a predetermined size through the cutter C1, and the second electrode material 123 is also cut into a predetermined size through the cutter C2. Then, the first electrode material 121 is stacked on the first separator material 122, and the second electrode material 123 is stacked on the second separator material 124.
[46]
Then, it is preferable to bond the electrode material and the separator material to each other in the laminators L1 and L2. By such adhesion, a basic unit in which the electrode and the separator are integrally bonded can be manufactured. The method of bonding may vary. The laminators L1 and L2 apply pressure or pressure and heat to the material for bonding. Such adhesion makes it easier to laminate the basic unit when manufacturing the unit stack unit. In addition, such adhesion is advantageous for alignment of basic units. After such adhesion, the first separator material 122 and the second separator material 124 are cut into a predetermined size through the cutter C3, so that the basic unit body 110a may be manufactured. During this process, the end of the separator is not bonded to the end of the adjacent separator.
[47]
In this way, in the basic unit, the electrode may be adhered to the adjacent separator. Or it can be seen that the separator is adhered to the electrode. At this time, it is preferable that the electrode is entirely adhered to the separator from the side facing the separator. This is because the electrode can be stably fixed to the separator. Typically, the electrode is smaller than the separator.
[48]
For this, an adhesive can be applied to the separator. However, in order to use the adhesive in this way, it is necessary to apply the adhesive in a mesh or dot form over the adhesive surface. This is because reactive ions such as lithium ions cannot pass through the separator if the adhesive is applied to the entire adhesive surface. Therefore, if an adhesive is used, even if the electrode can be adhered to the separator as a whole (ie, over the entire adhesive surface), it is difficult to completely adhere the electrode as a whole.
[49]
Alternatively, the entire electrode may be adhered to the separator through a separator including a coating layer having adhesive force. The separator may include a porous separator substrate such as a polyolefin-based separator substrate, and a porous coating layer that is entirely coated on one or both sides of the separator substrate. In this case, the coating layer may be formed of a mixture of inorganic particles and a binder polymer that connects and fixes the inorganic particles to each other.
[50]
Here, the inorganic particles can improve the thermal stability of the separation membrane. That is, the inorganic particles can prevent the separation membrane from shrinking at high temperatures. And the binder polymer can improve the mechanical stability of the separator by fixing the inorganic particles. In addition, the binder polymer may adhere the electrode to the separator. Since the binder polymer is distributed throughout the coating layer, unlike the above-described adhesive, adhesion may occur on the entire adhesive surface without a gap. Therefore, if such a separator is used, the electrode can be more stably fixed to the separator. In order to reinforce such adhesion, the laminator described above may be used.
[51]
However, the inorganic particles may form a densely packed structure to form interstitial volumes between the inorganic particles as a whole in the coating layer. At this time, a pore structure may be formed in the coating layer by the interstitial volume defined by the inorganic particles. Due to such a pore structure, even if a coating layer is formed on the separator, lithium ions can pass through the separator well. For reference, the interstitial volume defined by the inorganic particles may be blocked by a binder polymer depending on the location.
[52]
Here, the filling structure may be described as a structure such as a glass bottle containing gravel. Therefore, when inorganic particles form a filling structure, an interstitial volume between inorganic particles is not formed locally in the coating layer, but an interstitial volume between inorganic particles is formed in the coating layer as a whole. Accordingly, as the size of the inorganic particles increases, the size of the pores due to the interstitial volume also increases. Due to such a charging structure, lithium ions can smoothly pass through the separator on the entire surface of the separator.
[53]
[54]
The unit stack portion of the present invention is formed by repeatedly stacking the basic units, and an interface between the basic units and adjacent basic units is adhered.
[55]
As described above, in the electrode assembly of the conventional lamination and stack type structure, adhesion is formed between the electrode and the separator in the basic unit, but since the unit stack is formed by simple lamination of the basic unit, the adhesion between the basic units Not formed. When the formation process including charging and pressing on the electrode assembly of this structure is performed, the first electrode and the second electrode expand. Since the volume expansion rates of the first and second electrodes are different, the basic As stress accumulates inside the unit, a bending phenomenon occurs in which the basic unit is bent as a whole.
[56]
Accordingly, the present invention maximizes the adhesion of the coating material applied to the surface of the separator by heating and pressing the electrode assembly prior to the formation process, and bonding between the basic unit and the basic unit, so that the anode and the cathode are expanded by the subsequent formation process Even so, since the positive electrode and the negative electrode are continuous, the stress caused by volume expansion of the electrode is relieved and the direction of expansion is canceled, so that bending of the electrode assembly does not occur.
[57]
As described above, the coating material is formed of a mixture of inorganic particles and a binder polymer that connects and fixes the inorganic particles to each other, and the coating material may be applied to the first and second separators, respectively. In an embodiment of the present invention, the first separator is coated with the coating material on both surfaces facing the first electrode and the second electrode, and the second separator includes one surface facing the second electrode, and The coating material is coated on the opposite side.
[58]
The binder polymer contained in the coating material exhibits adhesive strength by heating, and since the temperature at which the adhesive strength is maximized is different for each type of binder polymer, the optimum temperature during the heating and pressing process of the electrode assembly of the present invention is the adhesive strength of the binder polymer. This maximized temperature would be desirable.
[59]
In the electrode assembly of the present invention, adhesion is imparted to the interface between the basic units by the coating material, and the adhesion between the basic units and the adjacent basic units in the unit stack portion is, in the basic unit, the first electrode and the first It is characterized by being equal to or greater than the adhesive strength between the separators.
[60]
This is because the interface between the first separator and the first electrode in the basic unit (referred to as the lami surface) is adhered by the coating material already applied to the separator during the manufacturing process of the basic unit, so that the electrolyte is not well impregnated. Prior to the heating and pressurization process (lamination process) of, the adhesion between the basic unit and the basic unit was not achieved.Since the electrolyte is well impregnated between the basic unit and the basic unit, adhesion is well formed by the subsequent heating and pressing process. Because. Accordingly, in the electrode assembly of the present invention, the adhesion between the basic units and the adjacent basic units in the unit stack part is equal to or greater than the adhesive force between the first electrode and the first separator in the basic unit.
[61]
[62]
Hereinafter, a method of manufacturing a secondary battery including the electrode assembly of the present invention will be described in detail.
[63]
The manufacturing method of a secondary battery of the present invention includes a basic unit manufacturing step (S100) of manufacturing a basic unit in which a first electrode, a first separator, a second electrode, and a second separator are sequentially stacked to form a four-layer structure; Manufacturing a unit stack unit (S200) of repeatedly stacking the basic units to manufacture a unit stack unit; An assembly step (S300) of receiving the electrode assembly including the unit stack unit in a battery case and then injecting and sealing the electrolyte solution; A lamination step (S400) of bonding the second separator of the one basic unit and the first electrode of the adjacent basic unit to each other in the unit stack unit by applying heat and pressure; Includes.
[64]
Since the basic unit manufacturing step (S100) and the unit stack unit manufacturing step (S200) have been described above, details after the stack unit manufacturing step will be described in detail.
[65]
The assembling step (S300) includes inserting the electrode assembly manufactured above into a battery case and then introducing an electrolyte. In some cases, storing a secondary battery assembled so that the electrolyte can be well impregnated in the first electrode, the first separator, the second electrode, and the second separator for a predetermined period of time at room temperature and pressure (pre-aging). It may further include.
[66]
The lamination step (S400) is a step of imparting adhesion between the basic unit constituting the unit stack unit and the adjacent basic unit, and the adhesion of the binder included in the coating material applied to the first separator is formed by heating and pressing. Bonds between units.
[67]
Therefore, the temperature of the lamination step is preferably adjusted by appropriately selecting a temperature at which the adhesive strength of the binder is maximized in consideration of the physical properties of the binder. Specifically, the temperature of the lamination step may be 45°C to 85°C, but is not limited thereto. In an embodiment of the present invention, the temperature of the lamination step is preferably 45°C to 70°C.
[68]
If the lamination temperature is too low, it is difficult to achieve the object of the present invention because adhesion between the basic unit and the adjacent basic unit is not sufficiently applied.If the lamination temperature is too high, the adhesive strength of the binder is rather reduced, and the coating material layer containing the binder becomes It may peel off from, which is not preferable.
[69]
The pressure of the lamination step S400 may be selected within an appropriate numerical range in consideration of the thickness of the electrode assembly, the electrode, and the physical properties of the binder coated on the separator. Specifically, it may be 1 to 10 kgf/cm 2, preferably 2 to 6 kgf/cm 2, and more preferably 3 to 5 kgf/cm 2. When the pressure is less than 1 kgf/cm 2, the pressure is insufficient, so adhesion between the basic unit and the basic unit may be insufficient, making it difficult to achieve the object of the present invention. When the pressure exceeds 10 kgf/cm 2, the pressure is too high. It is not preferable because it is strong and can damage the electrode assembly.
[70]
The pressing time of the lamination step (S400) may be 2 to 20 minutes, more preferably 5 to 15 minutes. The pressing time may be appropriately selected within the above range in consideration of the thickness of the electrode assembly and the physical properties of the binder coated on the separator.
[71]
The lamination step (S400) according to an embodiment of the present invention is performed before the initial formation process. In the present invention, the formation process should be understood as a concept including an initial charge in which a state of charge (SOC) is partially charged or fully charged in order to stabilize the structure of the electrode.
[72]
Through the initial charging step, lithium ions from the lithium transition metal oxide used as the positive electrode are transferred to the carbon electrode used as the negative electrode. At this time, the lithium ions are highly reactive and react with the carbon negative electrode to react with Li 2 CO 3 , LiO, A compound such as LiOH is produced, and an SEI film is formed on the surface of the negative electrode by the compound. The SEI film is a non-conductor formed when the amount of ion migration of the battery increases, and when the SEI film is formed, it prevents lithium ions and other substances from reacting at the negative electrode during subsequent battery charging. In addition, the SEI film can function as a kind of ion tunnel, and serves to pass only lithium ions. After the SEI film is formed, since lithium ions do not react with the negative electrode or other materials, the amount of lithium ions is reversibly maintained, and charging and discharging of the lithium secondary battery is reversibly maintained, thereby improving battery life. In addition, even when the SEI film is left at a high temperature or when charging and discharging is repeatedly performed, it is not easily collapsed, so that a change in the thickness of the battery occurs less.
[73]
In the case of performing the initial charging, a large amount of side reaction gas may be generated, so that the SEI film may not be uniformly formed according to the flow of the side reaction gas. To solve this problem, a process of initially charging and pressing the secondary battery may be performed. The pressurization may be performed using a jig or the like, but any means capable of pressurizing the secondary battery is not limited thereto. The pressurization may be applied to the battery cell at 100 gf/cm 2 to 500 kgf/cm 2.
[74]
Since the volume of the first electrode and the second electrode is expanded by the formation process, the lamination step (S400) is preferably performed before the first formation process or the first formation process in order to achieve the object of the present invention.
[75]
In this case, the temperature during the formation process may be 45°C or less. During the first formation process, if the temperature exceeds 45℃, the binder contained in the coating material applied to the separator creates adhesion and can bond the basic unit adjacent to the basic unit, so be sure to heat it before the first formation process. Since there is no need to perform the pressing process, the manufacturing method of the present invention may be particularly usefully applied when the temperature during the first formation process must be set to 45° C. or less.
[76]
After performing the lamination and formation process as described above, at least one of an aging process, a degassing process, and a formation process may be additionally included.
[77]
[78]
Hereinafter, examples will be described in detail to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.
[79]
[80]
Manufacturing Example 1
[81]
Manufacture of anode
[82]
A positive electrode mixture slurry was prepared by adding 96.25% by weight of LiCoO 2 as a positive electrode active material, 1.5% by weight of carbon black as a conductive material, and 2.25% by weight of PVDF as a binder to N-methyl-2 pyrrolidone (NMP) as a solvent. The positive electrode mixture slurry was coated on an aluminum (Al) thin film having a thickness of 12 μm, which is a positive electrode plate, and dried to prepare a positive electrode, followed by roll press.
[83]
Preparation of cathode
[84]
A negative electrode mixture by adding 96% by weight of carbon powder as an anode active material, 3% by weight of carbon black as a conductive material, and 1% by weight of polyvinylidene fluoride (PVdF) as a binder to N-methyl-2 pyrrolidone (NMP) A slurry was prepared. The negative electrode mixture slurry was coated on a 10 μm thick copper (Cu) thin film as a negative electrode plate and dried to prepare a negative electrode, followed by roll press.
[85]
[86]
Preparation of basic unit
[87]
A separator coated with a coating material including binder A on both sides of a polyolefin separator was prepared, and the anode/the separator/the cathode/the separator were prepared with a basic unit using the laminator shown in FIG. 3.
[88]
The binder A is a PVdF-HFP copolymer having a molecular weight of 410 to 450 Kg/mol (a polymer material with an HFP content of 15 mol% or more and a Tm of 140 degrees or less compared to PVdF), a molecular weight of 250 to 300 kg/mol, and a Tm of 160°C. It is a mixture with the above PVDF-CTFE copolymer.
[89]
Assembly steps
[90]
The three basic units were stacked to make a unit stack, and the unit stack was accommodated in a pouch case of a laminate sheet of CPP/aluminum/nylon. Ethyl methyl carbonate electrolyte containing LiPF 6 was injected and the pouch outer material was thermally fused to complete the assembly of the secondary battery.
[91]
[92]
Manufacturing Example 2
[93]
In Preparation Example 1, the assembly of the secondary battery was completed in the same manner as in Preparation Example 1, except that the type of the binder included in the coating material applied to the separator was changed to Binder B.
[94]
The binder B is a PVdF-HFP copolymer having a molecular weight of about 380 to 400 Kg/mol (a polymer material having an HFP content of 8 mol% or less and a Tm of 150°C or higher compared to PVdF), a molecular weight of 250 to 300 kg/mol, and a Tm of 160 It is a mixture with PVDF-CTFE copolymer which is higher than or equal to ℃.
[95]
[96]
Manufacturing Example 3
[97]
The assembly of the secondary battery was completed in the same manner as in Preparation Example 1, except that the solvent of the electrolyte was changed to dimethyl carbonate in the assembly step of Preparation Example 1.
[98]
[99]
Comparative Example 1
[100]
After aging the assembled secondary battery of Preparation Example 1 at room temperature for about 72 hours, the pouch containing the electrode assembly was mounted on a pressing jig and pressed at a temperature of 25° C. for 11 minutes at a pressure of 5 kgf/cm 2. Thereafter, the secondary battery was charged while being pressurized at a pressure of 5kgf/cm2 at room temperature, and then fully discharged.
[101]
[102]
Examples 1 to 5
[103]
After aging the assembled secondary battery of Preparation Example 1 at room temperature for about 72 hours, the pouch in which the electrode assembly was embedded was mounted on a pressurizing jig at a pressure of 5kgf/cm2, 45°C, 50°C, 55°C, 60°C. , Pressurized for 11 minutes at each temperature of 65 ℃. Thereafter, the secondary battery was charged while being pressurized at a pressure of 5kgf/cm2 at room temperature, and then fully discharged.
[104]
[105]
Comparative Example 2
[106]
After aging the assembled secondary battery of Preparation Example 1 at room temperature for about 72 hours, the pouch containing the electrode assembly was mounted on a pressing jig and pressed at a temperature of 70° C. for 11 minutes at a pressure of 5 kgf/cm 2. Thereafter, the secondary battery was charged while being pressurized at a pressure of 5kgf/cm2 at room temperature, and then fully discharged.
[107]
[108]
Comparative Examples 3 to 4
[109]
After aging the assembled secondary battery of Preparation Example 2 at room temperature for about 72 hours, the pouch containing the electrode assembly was mounted on a pressurizing jig for 11 minutes at each temperature of 55°C and 60°C at a pressure of 5kgf/cm2. Pressurized. Thereafter, the secondary battery was charged while being pressurized at a pressure of 5kgf/cm2 at room temperature, and then fully discharged.
[110]
[111]
Examples 6 to 8
[112]
After aging the assembled secondary battery of Preparation Example 2 at room temperature for about 72 hours, the pouch containing the electrode assembly was mounted on a pressurizing jig, and at a pressure of 5kgf/cm2, each temperature of 65℃, 70℃, and 75℃ Pressurized for 11 minutes. Thereafter, the secondary battery was charged while being pressurized at a pressure of 5kgf/cm2 at room temperature, and then fully discharged.
[113]
[114]
Example 9
[115]
After aging the assembled secondary battery of Preparation Example 3 at room temperature for about 72 hours, the pouch containing the electrode assembly was mounted on a pressing jig and pressed at a temperature of 55°C for 11 minutes at a pressure of 5 kgf/cm 2. Thereafter, the secondary battery was charged while being pressurized at a pressure of 5kgf/cm2 at room temperature, and then fully discharged.
[116]
[117]
Comparative Example 5
[118]
After aging the assembled secondary battery of Preparation Example 1 for about 72 hours at room temperature, the secondary battery was charged under pressure of 1 kgf/cm 2 at room temperature and then fully discharged.
[119]
[120]
Comparative Example 6
[121]
After aging the assembled secondary battery of Preparation Example 1 for about 72 hours at room temperature, the secondary battery was charged while pressing at room temperature with a pressure of 10 kgf/cm 2, and then fully discharged.
[122]
[123]
Experimental Example 1-Measurement of wet (WET) adhesion after filling
[124]
For each of the secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 4, the pouch was opened to take out the electrode assembly. Thereafter, a sample for measuring adhesion was collected from the electrode assembly, and immediately adhered to the slide glass. Peel Off was performed at an angle of 90 degrees and a speed of 10 mm/min to measure adhesion, and the results are shown in Table 1.
[125]
[Table 1]
division bookbinder Temperature during lamination (℃) Adhesion (gf/20mm)
Comparative Example 1 A 25 0
Example 1 45 25
Example 2 50 35
Example 3 55 41
Example 4 60 20.5
Example 5 65 9
Comparative Example 2 70 One
Comparative Example 3 B 55 2
Comparative Example 4 60 2
Example 6 65 4
Example 7 70 25
Example 8 75 3.8
[126]
As shown in Table 1, the temperature at which adhesion is maximized varies according to the type of binder included in the coating material applied to the separator. The binder of Preparation Example 1 exhibited maximum adhesion when lamination at 55°C, and the binder of Preparation Example 2 exhibited maximum adhesion at 70°C. Therefore, in the lamination process of the present invention, the temperature condition is preferably selected in consideration of the adhesion performance according to the temperature of the binder.
[127]
[128]
Experimental Example 2 Measurement of wet adhesion according to electrolyte
[129]
Twenty secondary batteries prepared as in Examples 3 and 9 were prepared, and the pouch was opened to take out the electrode assembly in the pouch. Thereafter, a sample for measuring adhesion was taken, and immediately adhered to the slide glass. The adhesion was measured by performing Peel Off at an angle of 90 degrees and a speed of 10 mm/min to the interface between the anode and the separator in the basic unit (this is referred to as lami surface adhesion). The measurement of such adhesion was carried out in the same manner for the interface between the basic unit and the basic unit (this is referred to as stack surface adhesion). When the Peel Off, in order to prevent damage to the adhesion of the sample, the Peel Off test was performed by holding the electrode and the separator together, and the adhesion measurement results are shown in Table 2 below.
[130]
[Table 2]
menstruum Adhesion (gf/20mm)
Ramie noodles Stack side
Example 3 Ethyl methyl carbonate 30~41 38-50
Example 9 Dimethyl carbonate 46~56 50-60
[131]
In the electrode assembly of the present invention, after charging, an adhesive force between the basic unit and the adjacent basic unit (stack surface) is formed, and the magnitude of this adhesive force is similar to or greater than the adhesive force between the electrode and the separator in the basic unit (lamy surface). . As described above, in the electrode assembly of the present invention, adhesive force is formed between the basic unit and the adjacent basic unit through a heating and pressing process before the formation process, so that the positive electrode and the negative electrode constituting the electrode assembly are continuous, so even if there is an electrode expansion due to charging, The stress of the expansion of the electrode is relieved, and the direction of expansion is lost, so that bending of the electrode assembly may be prevented.
[132]
[133]
Experimental Example 3-Confirmation of bending
[134]
For each of the secondary batteries of Examples 2 to 4 and Comparative Examples 5 and 6, the pouch was opened to take out the electrode assembly. After applying a force of 30 kgf to the electrode assembly for 2 seconds, the thickness of the electrode assembly was measured (d1). Thereafter, a force of 90 kgf was applied for 2 seconds, and the thickness of the electrode assembly was measured (d2). The difference between d1 and d2 was measured, and the results are shown in Table 3. As the thickness difference increases, the bending phenomenon is intensified, and when the thickness difference is 0, it means that no bending has occurred.
[135]
[Table 3]
division Lamination conditions Thickness difference (㎛)
Temperature(℃) Pressure (kgf/㎠)
Example 2 50 5 100
Example 3 55 5 0
Example 4 60 5 0
Comparative Example 5 25 One 200
Comparative Example 6 25 10 320
[136]
Referring to Table 3, each electrode assembly according to Examples 2 to 4 of the present invention has a thickness difference of 100 μm or less, so that no bending phenomenon has occurred, or even if bending occurs, it is difficult to check with the naked eye. On the other hand, before the formation process, it was confirmed that the difference in thickness of each electrode assembly of Comparative Examples 5 and 6 in which only pressurization was performed without heating was 200 μm or more, and the bending phenomenon was intensified compared to the above examples.
[137]
Therefore, in order to prevent the bending of the electrode assembly, it is preferable to perform a lamination process in which the electrode assembly is heated and pressurized to an appropriate temperature before the formation process to form adhesion of the interface (stack surface) between the basic unit and the basic unit Will do.
Claims
[Claim 1]
A first electrode, a first separator, a second electrode, and a second separator are sequentially stacked to include a unit stack portion in which at least one basic unit forming a four-layer structure is stacked, wherein the first separator and the second separator are An electrode assembly, characterized in that a coating material having adhesion is applied to each surface, and in the unit stack portion, the basic unit is adhered to an adjacent basic unit.
[Claim 2]
The electrode assembly of claim 1, wherein an adhesive force between the basic unit and an adjacent basic unit is equal to or greater than an adhesive force between the first electrode and the first separator in the basic unit.
[Claim 3]
The method of claim 1, wherein the second separator is coated with the coating material on one surface facing the second electrode and the opposite surface, and the basic units are adhered to each other by a coating material of the second separator. Electrode assembly.
[Claim 4]
The electrode assembly according to claim 1, wherein a difference between the thickness (d1) measured for 2 seconds under a pressure of 30 kgf and the thickness (d2) measured for 2 seconds under a pressure of 90 kgf is 100 μm or less.
[Claim 5]
The electrode assembly of claim 1, wherein the first electrode is an anode, and the second electrode is a cathode.
[Claim 6]
The electrode assembly of claim 1, wherein the basic unit is formed by repeatedly stacking the four-layer structure.
[Claim 7]
A method of manufacturing a secondary battery including the electrode assembly of claim 1, wherein a basic unit manufacturing step of manufacturing a basic unit in which a first electrode, a first separator, a second electrode, and a second separator are sequentially stacked to form a four-layer structure. (S100); Manufacturing a unit stack unit (S200) of repeatedly stacking the basic units to manufacture a unit stack unit; An assembly step (S300) of receiving the electrode assembly including the unit stack unit in a battery case and then injecting and sealing the electrolyte solution; A lamination step (S400) of bonding the second separator of the one basic unit and the first electrode of the adjacent basic unit to each other in the unit stack unit by applying heat and pressure; Method of manufacturing a secondary battery comprising a.
[Claim 8]
The secondary battery according to claim 7, wherein a coating material including a binder having adhesive strength is coated on the surface of the separator, and the temperature of the lamination step (S400) is a temperature at which adhesion of the binder is maximized. Method of manufacturing.
[Claim 9]
The method of claim 8, wherein the temperature of the lamination step (S400) is 45°C to 85°C.
[Claim 10]
The method of claim 8, wherein the temperature of the lamination step (S400) is 45°C to 70°C.
[Claim 11]
The method of claim 7, wherein the lamination step (S400) has a pressure of 1 to 10 kgf/cm 2, and a heating and pressurizing time of 2 to 20 minutes.
[Claim 12]
8. The method of claim 7, wherein after the lamination step (S400), a primary formation process is performed.
[Claim 13]
The method of claim 11, wherein the temperature during the primary formation process is 45°C or less.
[Claim 14]
The method of claim 7, wherein the solvent of the electrolyte is ethyl methyl carbonate or dimethyl carbonate.
[Claim 15]
A secondary battery comprising the electrode assembly according to any one of claims 1 to 6.