KR20070109080A - Pouch type lithium rechargeable battery - Google Patents

Abstract

A pouch type lithium rechargeable battery is provided to ensure the maximum internal volume, to remove an electrolyte left in a dead space, thereby preventing an active material placed at an end of an electrode plate of an electrode assembly from coming off. A pouch type lithium rechargeable battery includes: an electrode assembly(120) having a first electrode plate with a first electrode tap, a second electrode plate with a second electrode tap, and a separator placed between the first electrode plate and the second electrode plate; and a pouch(130) which is divided into a front side(131) and a back side(132) having an electrode assembly-receiving part(135) by a lower folding line, and has an edge part in which the front side and the back side adhere to each other. The electrode assembly-receiving part is formed to have a round shape at corners in which the bottom(135a) and the sides(135b) meet.

Description

Pouch type lithium secondary battery {Pouch type Lithium Rechargeable Battery}

1 is a perspective view showing a state before a conventional pouch type lithium secondary battery is packaged.

FIG. 2 is a view of the pouch-type lithium secondary battery of FIG. 1 viewed from a direction opposite to the direction in which the electrode tabs are pulled out by degassing.

3 is a perspective view illustrating a state before packaging of a pouch-type lithium secondary battery according to an embodiment of the present invention.

FIG. 4 is a view illustrating a punch and a die used to form grooves on the back side of the pouch of the pouch-type lithium secondary battery of FIG. 3.

FIG. 5 is a view of the pouch-type lithium secondary battery of FIG. 3 viewed from the direction opposite to the direction in which the electrode tab is pulled out by the degassing process.

<Brief Description of Major Codes in Drawings>

20, 120: electrode assembly 30, 130: pouch

31, 131: front of the pouch 32, 132: rear of the pouch

35, 135, 235: groove 35a, 135a: bottom of groove

35b, 135b: sides of the grooves 36, 136: wing portions

37, 137: gas chamber 121: first electrode plate

122: second electrode plate 123: separator

127 and 227: first electrode tab 128 and 228: second electrode tab

129: insulating tape 130a: deep core

130b: heat seal layer 130c: insulating film

150: punch 160: die

The present invention relates to a pouch-type lithium secondary battery, and more specifically, to form an edge where the bottom and side of the electrode assembly accommodating portion formed on the back of the pouch in a round shape to accommodate the electrode assembly when the degassing process is carried out in the pouch bare cell By minimizing negative deformation and preventing dead spaces, the internal volume can be secured to the maximum, and the active material located at the end of the electrode plate of the electrode assembly can be dropped from the current collector by removing the electrolyte solution remaining in the dead space. It relates to a pouch-type lithium secondary battery that can prevent the thing.

In general, active rechargeable batteries are being actively researched by the development of portable electronic devices such as cell phones, notebook computers, camcorders, and the like. Examples of such secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-hydrogen batteries, and lithium secondary batteries. Among them, the lithium secondary battery has an operating voltage of 3.6 V, which is three times better than a nickel-cadmium battery or a nickel-metal hydride battery, which is widely used as a power source for portable electronic devices, and has an excellent energy density characteristic per unit weight. It is rapidly expanding.

Lithium secondary batteries use nonaqueous electrolytes because of their reactivity with lithium. This electrolyte may be a solid polymer containing lithium salts, or may be a liquid phase in which lithium salts dissociate in an organic solvent. When the lithium secondary battery is classified according to the electrolyte type, the lithium secondary battery may be classified into a lithium metal battery using a liquid electrolyte, a lithium ion battery, and a lithium ion polymer battery using a polymer electrolyte.

In the case of a completely solid lithium ion polymer battery, there is no problem of leakage of the organic electrolyte, and in the case of a gel type lithium ion polymer battery containing the organic electrolyte, a problem of leakage of the organic electrolyte may occur. However, in the case of a lithium ion polymer battery, the leakage problem of the electrolyte can be prevented in a simpler form as compared with a lithium ion battery using a liquid electrolyte. For example, a lithium ion polymer battery may use a multilayer film pouch consisting of a metal foil and one or more polymer films covering the foil in place of a metal can of a lithium ion battery.

When using a multilayer film pouch, the weight of the battery can be significantly reduced than when using a metal can. Aluminum is usually used as a metal forming a foil in a multilayer film pouch. The polymer film forming the inner layer of the pouch film protects the metal foil from the electrolyte and prevents a short between the positive electrode, the negative electrode, and the electrode tabs.

Such a pouch lithium ion battery is relatively free in shape and light in weight, which is advantageous for slimming and lightening portable electronic devices.

1 is a perspective view showing a state before a conventional pouch type lithium secondary battery is packaged.

Referring to FIG. 1, the conventional pouch type lithium secondary battery includes an electrode assembly 20 and a pouch 30 accommodating the electrode assembly.

 The electrode assembly 20 is formed of a jelly roll by winding a multilayer film stacked in the order of the anode 21, the separator 23, and the cathode 22 in a spiral shape. When winding up the jelly roll, a separator is added to the electrode surface or the inner electrode surface that is exposed to the outside of the roll to prevent a short circuit between the positive electrode and the negative electrode. The formed jelly roll is placed in the groove 35 of the pouch rear surface 32. Typically, the groove 35 for accommodating the electrode assembly 20 is formed in the shape of a cuboid using a punch and a die.

In order to electrically connect the positive electrode 21 and the negative electrode 22 of the electrode assembly 20 to the outside of the pouch, electrode tabs 27 and 28 or electrode leads are formed at one side of the positive electrode 21 and the negative electrode 22. These electrode tabs 27 and 28 are formed to protrude from the jelly roll in the direction perpendicular to the direction in which the jelly roll is wound.

In addition, in order to enhance adhesion between the polymer film on the inner surface of the pouch and the metal forming the electrode tabs 27 and 28 in the pouch sealing process, the electrode tabs 27 and 28 may be contained in the polymer film surface before sealing. An insulating tape 29 may be further provided to prevent a short circuit between the pouches 30.

 The pouch 30 folds the rectangular pouch film in the middle 33 to form the front surface 31 and the rear surface 32 of the pouch 30. The back surface 32 is provided with a groove 35 through which the electrode assembly 20 can be accommodated, for example, by pressing. At this time, the groove 35 has a rectangular parallelepiped shape having an angled edge. When the groove 35 is formed, the gas chamber 37 for collecting the gas generated during the initial charging and discharging may also be formed.

Looking at the general forming process of the pouch-type lithium ion battery, first, the groove (35) is covered with the front surface 31, the rear surface 32, the electrode assembly 20 is accommodated, and then the edge of the groove 35 is fused. In this case, the electrode tabs 27 and 28 pass through one side of the pouch to be drawn out.

The electrolyte is injected into the electrode assembly 20 of the pouch bare cell in which the edge of the groove 35 is fused through an unsealed open section of the wing 36.

When the open section is fused and sealed, and the electrode assembly 20 is impregnated with an electrolyte solution, the pouch bare cell is initially charged and discharged. Then, the gas generated by the charging and discharging is filled in the gas chamber 37 extending in the wing 36.

Thereafter, a degassing process of vacuum compression is performed to remove gas filled in the pouch bare cell. After sealing the inside through the final fusion and removing the extended portion from the wings, the remaining pouch wing portion is folded to form a pouch bare cell battery.

The core pack is formed by attaching an accessory or structure such as a protective circuit module (PCM) or a positive temperature coefficient (PTC), which is not shown, to a bare cell formed by pouch sealing.

FIG. 2 is a view of the pouch-type lithium secondary battery of FIG. 1 viewed from a direction opposite to the direction in which the electrode tabs are pulled out by degassing.

When the initial charging and discharging is performed to the pouch bare cell into which the electrolyte is injected, and a degassing process of vacuum pressing to remove the gas generated by the initial charging and discharging is performed, as shown in FIG. 2, Deformation may occur in the groove 35 of the pouch back 32.

Initially, the groove 35 is formed into a punch and a die in which the bottom and side meet each other in an angular form, so that the corners in which the bottom 35a and the side 36b meet, like the form of a punch, have an angular form. The side portion of the bottom face 35a of the groove 35 having such a shape includes an angled edge, and has a high stress and a close bearing to the side surface 35b of the groove 35, thus having a large bearing force. Accordingly, the side portion of the groove bottom surface 35a may have a large resistance against external force. On the other hand, since the central portion, which has a relatively weaker stress than the side of the groove bottom surface 35a, is far from the side surface 35b of the groove 35, the bearing force is weak so that the degassing is carried out by vacuum compression to remove gas generated in the pouch bare cell. In the degassing process, the shape may not be maintained and may be concave in the inward direction of the groove 35. As a result, the dad space is generated as the central portion of the groove bottom surface 35a is recessed inwardly of the groove 35. The bottom surface 35a of the groove 35 becomes one long side portion of the completed pouch type lithium secondary battery.

Therefore, the finished pouch type lithium secondary battery having grooves formed with angled corners among the pouch type lithium secondary batteries having the same thickness has a groove due to the dead space of the long side portion generated in the degassing process during the process of forming the pouch type lithium secondary battery. The internal volume of (35) is relatively reduced, resulting in a decrease in the overall volume. As a result, the conventional pouch type lithium secondary battery having a small internal volume of the groove at a limited thickness cannot receive as much electrolyte as a dead space. For this reason, in a pouch-type lithium secondary battery having a limited thickness, it is difficult to maximize the capacity of the battery.

Further, in the vacuum pressing process for removing gas generated in the pouch bare cell, since the center portion of the groove bottom face 35a is recessed inwardly of the groove 36, the edge portion of the side of the groove bottom face 35a is relatively It has a bulge. As a result, the electrolyte injected into the pouch bare cell may remain in the corner portion of the raised side. The remaining electrolyte solution is more likely to float than the middle portion of the electrode plate among the active materials applied to the electrode plate of the electrode assembly, so that the bonding strength is weak, and the electrode assembly is impregnated with the active material at the end portion of the electrode plate that is overexposed to the remaining electrolyte solution. There is a problem that the bonding strength with the whole can be reduced and the active material can be peeled off from the electrode current collector.

The present invention has been made to solve the problems described above, an object of the present invention is to form a rounded corner of the bottom and side of the electrode assembly receiving portion formed on the back of the pouch in the form of a round degassing process to the pouch bare cell Active material located at the end of the electrode plate of the electrode assembly by minimizing deformation of the electrode assembly accommodating portion to prevent dead space from occurring, thereby ensuring maximum internal volume and removing electrolyte solution remaining in the dead space. It is to provide a pouch-type lithium secondary battery that can prevent the fall.

Pouch-type lithium secondary battery according to an embodiment of the present invention for achieving the above object is a first electrode plate with a first electrode tab, a second electrode plate with a second electrode tab and the first electrode plate and An electrode assembly having a separator positioned between the second electrode plates; And a front side and a back side having an electrode assembly accommodating portion and separated by a lower fold line, and having a pouch having an edge portion in which the front side and the rear side are in close contact with each other. It is characterized in that it is formed to have a round shape.

The bottom surface of the electrode assembly accommodating portion may be positioned upward in an outward direction of the rear surface from the side portion to the central portion.

The corner may be in the form of a round having a radius of curvature of 2-3 mm.

The electrode assembly accommodating part of the back side of the pouch may be formed by using a punch and a die having a round shape at an outer side of an edge where the bottom and side meet.

The active material layers of the first and second electrode plates may have styrene-butadiene rubber as a binder.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

3 is a perspective view illustrating a state before a pouch-type lithium secondary battery is packaged according to an embodiment of the present invention, and FIG. 4 is used to form grooves on the rear surface of the pouch-type lithium secondary battery of FIG. 3. Figure showing punches and dies being.

Referring to FIG. 3, a pouch-type lithium secondary battery according to an embodiment of the present invention includes an electrode assembly 120 and a pouch 130 accommodating the electrode assembly 120.

The electrode assembly 120 may include any one of a positive electrode active material and a negative electrode active material, for example, a first electrode plate 121 coated with a positive electrode active material, another one of a positive electrode active material and a negative electrode active material, for example, a negative electrode active material coated. Located between the second electrode plate 122, the first electrode plate 121 and the second electrode plate 122 to prevent short (short) of the first electrode plate 121 and the second electrode plate 122 It consists of a separator 123 which enables only movement of lithium ions. Here, as the binder of the active material, styrene-butadiene rubber, which has a lower bonding strength than polyvinylidene fluoride (PVDF) but is advantageous in capacity, is used.

In addition, a first electrode tab 127, which is generally made of aluminum (Al) and protrudes for a predetermined length, serves as a positive electrode tab is bonded to the first electrode plate 121. The second electrode plate 122 is generally made of a nickel (Ni) material, but the second electrode tab 128, which protrudes a predetermined length to serve as a negative electrode tab, is bonded. However, in the present invention, the above material is limited. no. In addition, the insulating tape 129 may be further provided to prevent a short circuit between the first electrode tab 127 and the second electrode tab 128 and the pouch 130. In addition, the first electrode tab 127 and the second electrode tab 128 are drawn out through one side of the pouch 130, and the first electrode tab 127 and the second electrode tab 128 are removed. ) Is electrically connected to a protection circuit module (not shown). In addition, upper and lower insulating plates (not shown) may be further attached to upper and lower portions of the electrode assembly 120 to prevent the electrode assembly 120 from contacting the pouch 130.

In addition, a chalcogenide compound is used as the positive electrode active material, and examples thereof include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1- X} Co _X O ₂ (0 <x <1), and LiMnO ₂ . Composite metal oxides are used. As the negative electrode active material, carbon (C) -based materials, Si, Sn, tin oxides, composite tin alloys, transition metal oxides, lithium metal nitrides, or lithium metal oxides are used. In addition, in general, the positive electrode plate is made of aluminum (Al), the negative electrode plate is made of copper (Cu), the separator is generally used polyethylene (PE) or polypropylene (PP), but in the present invention It does not limit the material.

Meanwhile, in the present invention, the direction in which the first electrode tab 127 and the second electrode tab 128 of the pouch-type lithium secondary battery are drawn out is assumed to be an "upper" direction.

The pouch 130 forms a front surface 131 and a rear surface 132 coupled with the front surface 131 by folding the middle 133 of the pouch film. The rear surface 132 is formed with a groove 135 through which the electrode assembly 120 can be accommodated through press processing. Here, the groove 135 of the pouch rear surface 132 according to the present invention has a corner where the bottom face 135a and the side surface 135b of the groove 135 meet each other, unlike a groove formed in an angled rectangular parallelepiped shape in a conventional pouch lithium secondary battery. It is formed to have a convex round shape when viewed in the outward direction. In order to form such a groove 135, as shown in Fig. 4, a punch 150 and a die 160 having a convex round shape in which the edge where the bottom face and the side meet are seen in the outward direction are used. . On the other hand, when the groove 135 is formed, a gas chamber 137 for collecting the gas generated during the initial charge and discharge may be formed together.

The pouch 130 is made of a core portion 130a made of a metal material such as aluminum (Al), a heat seal layer 130b formed on the upper surface of the core portion, and an insulating film 130c formed on the lower surface of the core portion. Is done. The heat seal layer 130b serves as an adhesive layer using a modified polypropylene, for example, a polymer resin, such as CPP (Casted Poly propylene), and the insulating film 130c is formed of a resin material such as nylon (nylon) or polyethylene terephthalate (PET). It may be, but is not limited to the structure and material of the pouch 130.

The electrode assembly 120 having the above structure is wound in one direction in a state where the first electrode plate 121, the separator 123, and the second electrode plate 122 are disposed. The electrode assembly 120 wound in the shape of a jelly roll is mounted on the rear surface 132 of the pouch 130 provided with the groove 135. At this time, ends of the first electrode tab 127 and the second electrode tab 128 drawn from the electrode plates 121 and 122 of the electrode assembly 120 are exposed to the outside of the pouch 130 to be sealed. The exposed first and second electrode tabs 127 and 128 are electrically connected to a protection circuit module (not shown) installed for the safety of the battery.

After the electrode assembly 120 is mounted, heat fusion is performed along the edge of the groove 135 of the pouch 130 in close contact with the front surface 131 of the pouch covering the rear surface 132.

Electrolyte is injected into the electrode assembly 120 of the pouch bare cell in which the edge of the groove 135 is fused through an unsealed open section of the wing 136.

When the open section is fused and sealed, and the electrolyte assembly is impregnated with the electrode assembly 120, initial charging and discharging are performed on the pouch bare cell. Then, the gas generated by the charging and discharging is filled in the gas chamber 137 extending in the wing portion 136.

Thereafter, a degassing process of vacuum pressing is performed to remove gas filled in the pouch bare cell. After sealing the inside through the final fusion and removing the extended portion from the wing portion 136, the remaining pouch wing portion is folded to form a pouch bare cell battery.

The core pack is formed by attaching an accessory or structure such as a protective circuit module (PCM) or a positive temperature coefficient (PTC), which is not shown, to a bare cell formed by pouch sealing.

FIG. 5 is a view of the pouch-type lithium secondary battery of FIG. 3 viewed from the direction opposite to the direction in which the electrode tab is pulled out by the degassing process.

As shown in FIG. 5, the pouch-type lithium secondary battery according to the exemplary embodiment of the present invention, which has undergone the initial charging and discharging process and the degassing process, has a groove bottom surface 135a and a groove on the rear surface of the pouch 132. The corner where the side 135b meets has a groove 135 in the form of a convex round when viewed from the outside.

In the completed pouch-type lithium secondary battery, the groove bottom surface 135a constituting the long side portion is formed of a side portion and a center portion located upward from the inside of the pouch rear surface 132 from the side portion, and the surface extending from the side portion to the center portion is flat. Is in the form of a close round.

The pouch-type lithium secondary battery completed through the degassing process as described above has a round shape close to flat as follows.

Initially, the groove 135 for accommodating the electrode assembly 120 is formed of a punch having rounded corners at which the bottom and side meet, so that the corner at which the groove bottom 135a and the groove side 135b meet also has a round shape. . The side portion of the bottom surface 135a of the groove 135 having such a shape includes rounded corners, so that the stress of the side surface of the bottom surface of the groove in the conventional pouch lithium secondary battery has an angled corner. Accordingly, the side portion of the groove bottom surface 135a does not differ much from the center portion of the groove bottom surface 135a having weak stress in stress. Thus, the sides and the center of the pouch groove bottom surface 135a are deformed in a substantially similar form to the force generated when vacuum compression is performed on the pouch bare cell to remove gas generated in the charge and discharge process of the pouch bare cell. . Therefore, the side and center portion of the pouch groove bottom surface 135a which has undergone the degassing process may maintain the shape that the pouch groove 135a had during the initial molding, or the side surface of the groove bottom surface 135a and the pouch rear surface 132 than the side portions. ), The central portion located above the inner side in the outward direction becomes substantially flat, so that the pouch-type lithium secondary battery has a bottom face 135a of a round groove close to flat. Here, the side of the groove bottom surface 135a has a rounded corner having a radius of curvature of 2-3 mm. The bottom surface 135a of the groove 135 becomes one long side portion of the completed pouch type lithium secondary battery.

As described above, the pouch-type lithium secondary battery of the present invention has a long side portion having a round shape close to flat, so that the dead space generated as long as the central portion of the long side portion concave inward in the conventional pouch-type lithium secondary battery having the same thickness can be removed. Can be. As a result, the pouch-type lithium secondary battery according to the exemplary embodiment of the present invention can secure the maximum internal volume at a limited thickness. As a result, more electrolyte can be injected and the capacity of the battery can be ensured.

In addition, the pouch-type lithium secondary battery according to an embodiment of the present invention has a long side portion having a round shape close to flat, and the raised edge portion of the long side portion is removed from the conventional pouch-type lithium secondary battery. The remaining electrolyte solution can be removed. In the present invention, the binder used to form the active material layer of the electrode plate is weak, but the binding strength between the electrode plate base material and the active material layer is weak by using Styrene Butadiene Rubber (SBR) for high capacity. Due to the removal of the electrolyte solution in which the active material most prone at the end of the electrode plate of the electrode assembly is removed, excessive exposure to the electrolyte may be prevented, thereby preventing the active material from being removed at the end of the electrode plate.

As described above, the pouch-type lithium secondary battery according to the embodiment of the present invention is formed in the electrode assembly accommodating portion having a rounded corner where the bottom and the rear face meet on the back of the pouch, the round form close to flat after the degassing process of the pouch bare cell By having one long side portion, the dead space generated by the long side portion recessed in the conventional pouch type lithium secondary battery can be reduced. For this reason, the pouch-type lithium secondary battery according to the embodiment of the present invention can ensure the maximum internal volume. As a result, more electrolyte can be injected and the capacity of the battery can be increased.

In addition, the pouch-type lithium secondary battery according to the embodiment of the present invention has a long side portion having a round shape close to flat, so that the raised edge portion of the long side portion of the conventional pouch-type lithium secondary battery is removed and remains on the raised edge portion. The electrolyte can be removed. Accordingly, the active material at the end portion of the electrode plate may be prevented from being excessively exposed to the remaining electrolyte solution and peeled from the electrode current collector.

As described above, the present invention is not limited to the specific preferred embodiments described above, and any person having ordinary skill in the art to which the present invention pertains without departing from the gist of the present invention claimed in the claims. Various modifications are possible, of course, and such changes are within the scope of the claims.

Claims (5)

An electrode assembly including a first electrode plate having a first electrode tab, a second electrode plate having a second electrode tab, and a separator positioned between the first electrode plate and the second electrode plate; And A pouch type lithium secondary battery comprising a front surface and a back side having an electrode assembly accommodating portion and separated by a lower fold line, and having a pouch having an edge portion in which the front side and the rear side are in close contact. The electrode assembly accommodating portion is a pouch-type lithium secondary battery, characterized in that the outer side of the bottom and the side of the edge meets the round shape. The method of claim 1, The bottom surface of the electrode assembly accommodating portion is a pouch type lithium secondary battery, characterized in that located in the upper direction toward the outer side of the rear toward the central portion. The method of claim 1, The corner is a pouch-type lithium secondary battery, characterized in that the round shape having a radius of curvature of 2 to 3mm. The method of claim 1,  The electrode assembly accommodating part of the back side of the pouch is a pouch type lithium secondary battery, characterized in that the outer side of the edge meets the round (punch) and the die (die) is formed using a punch (die). The method of claim 1, Pouch-type lithium secondary battery, characterized in that the active material layer of the first and second electrode plate has a styrene-butadiene rubber (Styrene Butadiene Rubber) as a binder.

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