KR20220107518A - Secondary Battery - Google Patents

Abstract

A secondary battery according to an embodiment of the present invention includes: an electrode assembly including a first electrode plate, a second electrode plate having a polarity different from that of the first electrode plate, and a separator between the first electrode plate and the second electrode plate; an electrolyte; a case for accommodating the electrode assembly and the electrolyte; and an adhesive layer positioned on the outer surface of the electrode assembly or the corresponding inner surface of the case, wherein an adhesive includes α,β-unsaturated dicarboxylic acid-modified polyolefin.

Description

Secondary Battery

The present invention relates to a secondary battery.

A secondary battery is generally configured by accommodating an electrode assembly and an electrolyte in a case, and installing a cap plate in the case. An electrode tab, a positive terminal, etc. are connected to the electrode assembly, which is exposed or protruded to the outside through the cap plate. The electrode assembly of the secondary battery may be configured in a jelly-roll form by winding a stack of a positive electrode plate, a negative electrode plate and a separator, or a stack type by stacking a plurality of positive electrode plates, negative electrode plates and separators. .

As the range of application of the secondary battery to mobile devices is widened, the case where the device employing the secondary battery is dropped frequently occurs in various use environments. In this case, the battery installed in the device may be damaged by the impact when the product is dropped, which may cause a short circuit, smoke, or ignition. In particular, in the case of a polymer battery, since a pouch is used as an exterior material, it is easy to deform, and the movement of the electrode assembly inside the pouch is large when it is dropped, so it is easy to collide inside the case of the mobile device and cause a short circuit. Therefore, a method is required to minimize the movement of the electrode assembly and prevent the electrode assembly from colliding inside the case, and a technology for integrating them with the exterior material by applying an adhesive resin or tape to the surface of a jelly-roll or stack is being developed. .

However, since the conventional adhesive material does not provide sufficient adhesive strength, a material with enhanced adhesive strength is required. In particular, when the battery case and the electrode assembly are bonded in the presence of an electrolyte, the adherends must be adhered to each other in a state in which the adhesive has absorbed the organic solvent, so the adhesive material requires low electrolyte absorption and high adhesion. In addition, it is requested to develop a technology for an adhesive material having excellent initial adhesion and excellent adhesion retention at high temperatures so that battery stability can be maintained even after exposure to high temperature environments.

The present invention provides a secondary battery having excellent impact strength and high temperature stability.

A secondary battery according to an embodiment of the present invention is an electrode assembly including a first electrode plate, a second electrode plate having a polarity different from that of the first electrode plate, and a separator between the first electrode plate and the second electrode plate ; electrolyte; a case accommodating the electrode assembly and the electrolyte; and an adhesive layer positioned on the outer surface of the electrode assembly or on the corresponding inner surface of the case, wherein the adhesive comprises α,β-unsaturated dicarboxylic acid-modified polyolefin, and the α,β-unsaturated dicarboxylic acid-modified The polyolefin satisfies at least one of the following formulas (I) and (II).

(I): a/b ≥ 0.2

In the above formula,

a is the absorption intensity of the α,β-unsaturated dicarboxylic acid (the difference in transmittance between the maximum peak near 1,715 cm ^-1 and the baseline),

b is the absorption intensity of α,β-unsaturated dicarboxylic acid anhydride (the difference in transmittance between the maximum peak near 1,780 cm ^-1 and the baseline),

The baseline is a line connecting the transmittance of 1,550 cm ^-1 and 1,950 cm ^-1 ,

(II): (a/1.8 + b)/c ≥ 0.05

In the above formula,

a and b are the same as defined in formula (I) above,

c is the absorption intensity of the polyolefin (the difference in transmittance between the maximum peak near 2,915 cm ^-1 and the baseline),

The baseline is the predecessor of the transmittances of 2,400 cm ^-1 and 3,750 cm ^-1 .

An embodiment of the present invention provides a secondary battery having excellent impact strength and high temperature stability.

1 is a view showing an adhesive application form according to an embodiment of the present invention.
2 is a view showing an adhesive application form according to another embodiment of the present invention.

Examples of the present invention are provided to more completely explain the present invention to those of ordinary skill in the art, and the following examples may be modified in various other forms, and the scope of the present invention is as follows It is not limited to an Example. Rather, these examples are provided so that this disclosure will be more thorough and complete, and will fully convey the spirit of the invention to those skilled in the art.

The terminology used herein is used to describe specific embodiments, not to limit the present invention. As used herein, the singular form may include the plural form unless the context clearly dictates otherwise.

As used herein, the term “and/or” includes any one and any combination of one or more of the listed items. In the present specification, "connected" means not only when member A and member B are directly connected, but also when member A and member B are indirectly connected by interposing member C between member A and member B. Also, as used herein, “comprise, include” and/or “comprising, including” refer to the referenced shapes, numbers, steps, actions, members, elements and/or groups thereof. It specifies the presence and does not preclude the presence or addition of one or more other shapes, numbers, movements, members, elements and/or groups.

Although the terms first, second, etc. are used herein to describe various members, parts, regions, layers and/or parts, these members, parts, regions, layers, and/or parts are limited by these terms, so that It is self-evident that These terms are used only to distinguish one member, component, region, layer or portion from another region, layer or portion. Accordingly, a first member, component, region, layer, or portion discussed below may refer to a second member, component, region, layer or portion without departing from the teachings of the present invention.

A secondary battery according to an embodiment of the present invention includes an electrode assembly, an electrolyte, a case accommodating the electrode assembly and the electrolyte, and an adhesive layer positioned on an outer surface of the electrode assembly or a corresponding inner surface of the case.

electrode assembly

The electrode assembly includes a first electrode plate, a second electrode plate having a polarity different from that of the first electrode plate, and a separator between the first electrode plate and the second electrode plate. The electrode assembly may have a jelly-roll shape in which a first electrode plate, a separator, and a second electrode plate are sequentially wound. Also, the electrode assembly may have a stack shape in which a plurality of first electrode plates, second electrode plates, and separators are stacked.

In an embodiment, the first electrode plate may act as an anode, and the second electrode plate may have a cathode having a polarity opposite to that of the first electrode plate. Each of the first electrode plate and the second electrode plate includes a coated portion in which an active material is applied to a current collector of a metal plate and an uncoated portion formed of an exposed current collector because the active material is not applied thereto. The uncoated region may be respectively formed at different ends of the first electrode plate and the second electrode plate to be wound, and serve as a passage for current flow between each electrode and the outside.

The first electrode plate as the positive electrode may be formed of a metal foil such as aluminum, and both surfaces of the coating portion of the first electrode plate are coated with an active material having a lithium-based oxide as a main component. The second electrode plate serving as the negative electrode may be formed of a metal foil such as copper, and both surfaces of the coating portion of the second electrode plate are coated with an active material having a carbon material as a main component.

The separator is positioned between the first electrode plate and the second electrode plate to prevent a short circuit and to enable the movement of ions. The separator may include a porous substrate and a coating layer formed on at least one surface of the porous substrate. The porous substrate may be made of polyethylene (PE), polypropylene (PP), or a composite film of polyethylene (PE) and polypropylene (PP).

adhesive layer

According to an embodiment of the present invention, the adhesive layer is located on the outer surface of the electrode assembly or the inner surface of the case corresponding to the electrode assembly. For example, the adhesive layer may be formed by applying an adhesive to the outer surface of the electrode assembly or to the inner surface of a case corresponding to the electrode assembly. As another example, the adhesive layer may be formed by forming an adhesive in the form of a film and then inserting the adhesive film between the electrode assembly and the case.

According to an embodiment of the present invention, the adhesive may be applied to the entire outer surface of the electrode assembly, or may be applied to at least one side of the front or rear surface of the electrode assembly. As an example, the adhesive may be applied to the outermost positive electrode substrate surface of the electrode assembly, and as another example, the adhesive may be applied to at least one side of the upper or lower portion of the electrode assembly. As another example, the adhesive may be applied to at least one side of the width of both sides of the electrode assembly. According to another embodiment of the present invention, the adhesive is a polygonal, circular or oval planar figure; straight, diagonal, curved or zigzag linear; Alternatively, it may be applied in the form of at least one or more of a dot array.

For example, as shown in FIG. 1 , the adhesive may be applied to the front or back surface of the electrode assembly in a planar figure (square) shape. As another example, as shown in FIG. 2 , the adhesive may be applied to the inner surface of the case 120 corresponding to the electrode assembly 110 in the form of a dot array.

The thickness of the adhesive layer is not particularly limited, but may be about 5 to 10 μm. The adhesive may be applied using a brush, roller, or spray, and may be applied using a Comma Coater, a Gravure Coater, a Die Coater, a Spray Coater, or an Electro-Spin Coater. Any coater that can be controlled with a thin film such as Spinning Coater) can be used.

The application area ratio of the adhesive is not particularly limited, but for example, the application area of the adhesive is 25% or more of the height direction or the width direction of the electrode assembly, and the application area of the adhesive is 6% compared to the area of the electrode assembly may be more than When the application area of the adhesive satisfies the above range, the area for fixing the electrode assembly becomes sufficient, so that the vibration amplitude of the electrode assembly in the battery case can be reduced when it is dropped. The application area ratio is respectively calculated as follows.

Height direction application area ratio = (adhesive application height) / (electrode assembly height)

Width direction application area ratio = (adhesive application width) / (width of electrode assembly)

Area ratio = (Area of adhesive) / (Area of electrode assembly)

A method of applying the adhesive to the outer surface of the electrode assembly in the form of a dot array is not particularly limited, and may be applied, for example, by a piezoelectric jetting method. The adhesive may be applied in a square form or in a zigzag form in which adjacent rows intersect. In addition, the adhesive may be applied in a triangular, quadrangular, pentagonal, hexagonal, polygonal, circular, or star-shaped shape with an empty space spaced apart from each other. The adhesive applied in the dot array form may overlap each other to form a line, and the line may be plural. For example, the adhesive may be applied to the outermost portion of the electrode assembly in the form of a dot array.

The adhesive constituting the adhesive layer includes α,β-unsaturated dicarboxylic acid-modified polyolefin. In one example, the α,β-unsaturated dicarboxylic acid is maleic acid, and the polyolefin is polypropylene. Since the polypropylene resin has low electrolyte solution absorbency, it is possible to suppress a phenomenon in which the resin is softened by the electrolyte solution and the release of adhesion between the adhesive and the metal. In particular, when the inner resin of the battery case is a polypropylene resin, when a maleic acid-modified polypropylene resin of the same material series is used as an adhesive, the adhesive force may be further improved.

The α,β-unsaturated dicarboxylic acid functional group forms a chemical bond such as a hydrogen bond with a thin oxide film on the surface of the metal foil, and serves to increase adhesion to the metal. The electrolyte may be present in the middle between the functional group and the metal foil to impair the adhesion, but by increasing the fluidity of the adhesive, it is possible to secure the adhesion by pushing the electrolyte when the adhesive and the metal foil are combined.

The α,β-unsaturated dicarboxylic acid-modified polyolefin satisfies at least one of the following formulas (I) and (II).

(I): a/b ≥ 0.2

In the above formula,

a is the absorption intensity of the α,β-unsaturated dicarboxylic acid (the difference in transmittance between the maximum peak near 1,715 cm ^-1 and the baseline),

b is the absorption intensity of α,β-unsaturated dicarboxylic acid anhydride (the difference in transmittance between the maximum peak near 1,780 cm ^-1 and the baseline),

The baseline is a line connecting the transmittances of 1,550 cm ^-1 and 1,950 cm ^-1 .

In the present invention, a/b may be 0.2 or more, for example, 0.2 to 8. When a/b satisfies the above-mentioned range, low electrolyte absorption and high adhesion of the adhesive resin, in particular, adhesion retention after standing at a high temperature may be further improved.

Specifically, when a/b is less than 0.2, the adhesive strength after standing at a high temperature may be inferior. α,β-unsaturated dicarboxylic acid exhibits high metal adhesion because it has more carboxylic acid structure than α,β-unsaturated dicarboxylic acid anhydride, but when left at high temperature, α,β-unsaturated dicarboxylic acid It undergoes a dehydration reaction and is transformed into an α,β-unsaturated dicarboxylic acid anhydride. Therefore, when the content of the α,β-unsaturated dicarboxylic acid structure is high, the adhesive strength after being left at a high temperature can be maintained well. On the other hand, when a/b exceeds 8, the amount of α,β-unsaturated dicarboxylic acid anhydride is insufficient, so that the hydroxyl group on the metal surface and the resin do not chemically react, so that adhesion may decrease.

(II): (a/1.8 + b)/c ≥ 0.05

In the above formula,

a and b are the same as defined in formula (I) above,

c is the absorption intensity of the polyolefin (the difference in transmittance between the maximum peak near 2,915 cm ^-1 and the baseline),

The baseline is a line connecting the transmittances of 2,400 cm ^-1 and 3,750 cm ^-1 .

In the present invention, (a/1.8 + b)/c may be 0.05 or more, for example, 0.05 to 0.20. When (a/1.8 + b)/c satisfies the above-mentioned range, the low electrolyte solution absorption and high adhesiveness of the adhesive resin, in particular, the adhesive force retention after standing at a high temperature may be further improved. Specifically, when (a/1.8 + b)/c is less than 0.05, the rate of denaturation by α,β-unsaturated dicarboxylic acid is low, and the effect of improving adhesion may be insufficient. On the other hand, when (a/1.8 + b)/c exceeds 0.20, the melting point of the resin may be lowered and heat resistance may be lowered, and the polarity of the molecule may increase to increase the amount of electrolyte absorption, thereby lowering the adhesive force and adhesion after standing at high temperature. have.

The α,β-unsaturated dicarboxylic acid-modified polyolefin may be prepared by copolymerizing a monomer having an α,β-unsaturated dicarboxylic acid structure with the polyolefin. The monomer of the α,β-unsaturated dicarboxylic acid structure serves to improve the metal adhesion of the polyolefin resin, and includes α,β-unsaturated dicarboxylic acid, α,β-unsaturated dicarboxylic acid anhydride, α, β-unsaturated dicarboxylic acid ester, α,β-unsaturated dicarboxylic acid diester, α,β-unsaturated dicarboxylic acid derivative having a functional group bonded to α,β-unsaturated dicarboxylic acid, α,β- Unsaturated dicarboxylates or mixtures thereof may be used.

For example, the monomer of the α,β-unsaturated dicarboxylic acid structure is a monomer of a maleic acid structure, and the monomer of the maleic acid structure includes maleic acid, maleic anhydride, maleic acid ester, maleic acid diester, and maleic acid derivatives in which a functional group is bonded to maleic acid. , maleate or a mixture thereof may be used. As the maleic acid derivative in which a functional group is bonded to maleic acid, 2,3-dimethylmaleic anhydride, phenylmaleic anhydride, or the like may be used.

For example, the α,β-unsaturated dicarboxylic acid-modified polyolefin may be prepared by copolymerizing the polyolefin with α,β-unsaturated dicarboxylic acid anhydride. When α,β-unsaturated dicarboxylic acid anhydride is used as the copolymerization monomer, side reactions can be effectively suppressed. In this case, the prepared α,β-unsaturated dicarboxylic acid-modified polyolefin is subjected to high-temperature and high-humidity treatment to hydrolyze a certain amount of α,β-unsaturated dicarboxylic acid anhydride to change to α,β-unsaturated dicarboxylic acid. , α,β-unsaturated dicarboxylic acid-modified polyolefin satisfying formulas (I) and (II) of the present invention can be prepared.

The form of the copolymer is not particularly limited, and may be a random copolymer or a graft copolymer, and may have a hyper branched or dendrimer shape.

The α,β-unsaturated dicarboxylic acid-modified polyolefin may be prepared by copolymerizing a metal adhesive co-monomer and/or other comonomer with a monomer having an α,β-unsaturated dicarboxylic acid structure in the polyolefin. can As the metal adhesive comonomer, an acrylic acid derivative such as acrylic acid or methacrylic acid, vinyl alcohol, an acrylic acid ester derivative containing a hydroxyalkyl group, an acrylic acid ester derivative containing a carboxyalkyl group, or a mixture thereof may be used. In addition, a hydroxyl group or a carboxyl group (including an anhydride structure) having metal adhesion, an acid component (sulfonic acid, phosphonic acid, etc.), a functional group that causes a reaction with a metal surface such as a silane coupling reaction group) containing a polymerizable compound or a mixture thereof may be used. As other comonomers, ethylene, styrene, or a mixture thereof may be used. When the other comonomer is included, the melting point of the adhesive resin may be lowered, and fluidity may be improved. In general, since the functional group has a polarity, it absorbs the electrolyte and swells, thereby reducing adhesion, and even in a dry state, there is viscosity, which may cause problems in processability. Therefore, as the comonomer, it is preferable to use a comonomer having a high adhesive strength and a small number of functional groups.

The α,β-unsaturated dicarboxylic acid-modified polyolefin has a weight average molecular weight (Mw) of 10,000 or more, for example, 10,000 or more, 1,000,000 as measured by gel permeation chromatography (GPC) or size exclusion chromatography (SEC). may be below. When the weight average molecular weight of the α,β-unsaturated dicarboxylic acid-modified polyolefin is less than the above range, the cohesive force of the adhesive layer may be lowered and thus the adhesive strength may not be maintained. This is low, and the anchor effect is also small, so the adhesive force may not be improved.

The α,β-unsaturated dicarboxylic acid-modified polyolefin may have a melting point of 130° C. or less, for example, 100° C. or less, and in another example, 40 to 100° C. A lower melting point of the α,β-unsaturated dicarboxylic acid-modified polyolefin exhibits sufficient softening properties and lowers the processing temperature, which is preferable in view of the process. In particular, when the material of the separator is polyethylene, it is preferable to have a processing temperature that does not exceed the melting point (134° C.) of polyethylene. On the other hand, when the melting point is less than 40 ° C., the effect of pushing the electrolyte between the adhesive and the metal foil is reduced while the softening property is lowered, so that the adhesive force may not be sufficiently exhibited, and the heat resistance may be lowered. The melting point of the α,β-unsaturated dicarboxylic acid-modified polyolefin can be lowered by increasing the copolymerization amount of the α,β-unsaturated dicarboxylic acid component. The polarity of the resin is increased to increase the absorption of the electrolyte, and as a result, the adhesive strength may be reduced.

The copolymerization ratio of the comonomers (a, β-unsaturated dicarboxylic acid-structured monomers, metal adhesive comonomers and other comonomers) copolymerized to the polyolefin is not particularly limited as long as it does not affect the adhesive properties or thermal properties. does not As an example, the copolymerization ratio of the comonomer copolymerized to the polyolefin may be 50 mol% or less, for example 25 mol% or less, and in another example 10 mol% or less. That is, the content of the polyolefin in the α,β-unsaturated dicarboxylic acid-modified polyolefin may be 50 mol% or more, for example, 75 mol% or more, and in another example, 90 mol% or more.

The adhesive according to the present invention may further include additives commonly used in the art in addition to the aforementioned α,β-unsaturated dicarboxylic acid-modified polyolefin. Non-limiting examples of the additive include a tackifier, a crosslinking agent, a metal surface modifier (a silane coupling agent, an acid inducer such as a phosphoric acid compound, a metal acid compound such as zirconium, titanic acid, and a chromic acid derivative). The above additives may be used alone or in combination of two or more.

The adhesive according to the present invention may have an electrolyte absorption of 30% by weight or less, for example 15% by weight or less. The electrolyte absorption amount is the amount of electrolyte absorbed after the adhesive is completely immersed in the electrolyte and left at 80° C. for 1 hour, and is calculated by the following formula.

Electrolyte absorption amount (wt%) = (weight of adhesive layer after immersion in electrolyte - weight of adhesive layer before immersion in electrolyte)/(weight of adhesive layer before immersion in electrolyte)*100

When the absorption amount of the electrolyte solution exceeds the above-mentioned range, the electrolyte solution approaches the interface between the adhesive and the metal foil, and the action of releasing the adhesion may be strengthened. In addition, since the electrolyte functions as a plasticizer in the resin, the cohesive force of the adhesive may be lowered, thereby reducing the adhesive force.

electrolyte

In one embodiment of the present invention, the electrolyte may be a polymer electrolyte or a non-aqueous electrolyte, and may be in liquid, solid or gel phase. Even when the polymer electrolyte is used, it may further include a lithium salt and a non-aqueous electrolyte. The non-aqueous electrolyte is used for dissolving or dissociating lithium salt, and is not particularly limited as long as it is used as a solvent for a conventional electrolyte solution for a battery. The non-aqueous electrolyte may include an organic solvent and a lithium salt.

case

In one embodiment of the present invention, the case may be a pouch, or may be formed of a metal such as aluminum or an aluminum alloy. The battery according to the present invention may be a pouch-type battery, or a prismatic or circular battery.

Hereinafter, the present invention will be described in more detail through examples.

[Example 1]

A battery of Example 1 was prepared using the adhesive according to Table 1 below. A polymer battery in a pouch film (t=111 um) case was used as the battery, and an adhesive was applied to the surface of the jelly roll using a bar coater (adhesive application amount: 10 um (thickness after application and heat press)) . Physical properties were measured according to the following method, and the results are shown in Table 1 below.

[Comparative Example 1-6]

Each of the batteries of Comparative Examples 1-6 were prepared in the same manner as in Example 1, except that the adhesive according to Table 1 was used, and physical properties were measured, and the results are shown in Table 1 below.

adhesion

Adhesion was measured according to ISO 527-3 (180° peeling, specimen width 15 mm, chucking jig distance 50 mm, tensile speed 300 mm/min). The average value of the adhesive presence interval was calculated, and the average value of the adhesive force of 10 samples was described. For the adhesives used in each Example and Comparative Example, the adhesive strength (23 ° C, 50 %RH) before battery manufacturing, the adhesion in the battery, and high temperature storage (at a standard full charge voltage, 60 ° C and 90 %RH environment for 2 weeks) ) and then the adhesive force was measured, respectively.

Electrolyte absorption

The adhesive used in each Example and Comparative Example was completely immersed in the electrolyte, and left at 80° C. for 1 hour, and then the amount of absorption of the electrolyte was measured. The electrolyte absorption amount was calculated by the following formula.

Electrolyte absorption amount (wt%) = (weight of adhesive layer after immersion in electrolyte - weight of adhesive layer before immersion in electrolyte)/(weight of adhesive layer before immersion in electrolyte)*100

drop test

According to the method of IEC 62133 (1.5 m, 18 times per cycle, 4 cycles), a drop test (severe test) was performed on the batteries of Examples and Comparative Examples. In addition, a drop test was performed on the batteries of Examples and Comparative Examples in the same manner after standing at high temperature (stand for 2 weeks at 60° C. and 90% RH at standard full charge voltage). When smoke and ignition did not occur, OCV did not decrease, and it was 50 mV or less after 120 hours, it was judged as OK.

Modified polypropylene adhesive: maleic acid-modified polypropylene (addition amount of maleic anhydride derivative: 4.5 mol%, a/b of formula (I): 3.02, (a/1.5+b)/c of formula (II): 0.09, Mw: 64,000, melting point: 64 ℃)

Acrylic adhesive: Scotch-Weld DP8405NS (3M company)

Urethane adhesive: Scotch-Weld PBA2665 (3M company)

Epoxy adhesive: Scotch-Weld DP190 (3M company)

Silicone adhesive: Hybrid adhesive 760 (3M company)

Rubber adhesive: Industrial adhesive SG4693 (3M company)

Polypropylene: Homo polypropylene unstretched film (Mw: 300,000, melting point: 164 ° C.)

As shown in Table 1, in the case of the maleic acid-modified polypropylene adhesive according to the present invention, not only the initial adhesive strength but also the adhesive strength after standing at a high temperature was excellent. As a result, the battery of Example 1 to which the maleic acid-modified polypropylene according to the present invention was applied as an adhesive showed excellent resistance in the initial drop test and the drop test after standing at high temperature.

On the other hand, in the case of adhesives made of acrylic, urethane, epoxy, or silicone, the adhesive strength in the battery was significantly reduced compared to the adhesive strength under normal circumstances. In addition, the adhesive of the above material was found to absorb a large amount of electrolyte, and maintained some adhesive strength in the initial stage when the degree of absorption of the electrolyte was relatively small, but after leaving it at high temperature, the resin expansion due to absorption of the electrolyte increased and the adhesive strength was greatly reduced became As a result, the batteries of Comparative Examples 1-4 to which the adhesive was applied respectively showed poor resistance in the drop test. In addition, the rubber adhesive had a low electrolyte absorption rate and showed relatively good adhesion even after being left at a high temperature, but the battery of Comparative Example 5 to which it was applied showed poor resistance to the drop test.

On the other hand, in the case of polypropylene homopolymer, since friction with cast polypropylene (CPP), which is the inner layer of the exterior material, is large, the battery of Comparative Example 6 to which it is applied showed excellent resistance in the drop test. However, after standing at a high temperature, the gas permeated between the polypropylene and the exterior material due to the influence of the generated gas, thereby reducing frictional force, and as a result, resistance to the drop test was reduced.

[Preparation Example 1-18: Adhesive Preparation]

Powdered polypropylene, tert-butylperoxy-2-ethylhexyl carbonate, and a comonomer according to Table 2 were added to 2,2,4-trimethyl-1,3-pentanediol diisobutylate and mixed, and the mixture was then stirred at 180 °C. It was copolymerized at a temperature of After completion of the reaction, the unreacted maleic acid component was removed using acetone, and then the obtained maleic acid-modified propylene was dried under reduced pressure by heating. The resulting maleic acid-modified propylene was subjected to high-temperature or high-temperature, high-humidity treatment to control the ratio of maleic anhydride and maleic acid. By varying the treatment temperature (40-80 ℃), humidity (80-90%) and time, the resin of Preparation Example 1-18 was prepared.

For each resin prepared above, using infrared spectroscopy (FT-IR) spectrum (ATR single reflection method, resolution: 4 cm ^-1 , integration number: 32 times, vertical axis of spectrum: transmittance), maleic acid derivatives, maleic anhydride derivatives and The abundance ratio of polypropylene was calculated, and the calculated values are shown in Table 2 below.

In addition, the weight average molecular weight and melting point of each resin were measured and shown in Table 2 below. The weight average molecular weight was measured using a solvent in which each resin was dissolved, and the calculated weight average molecular weight was used as the molecular weight. The melting point was measured by differential scanning calorimetry (DSC). Primary heating, cooling, and secondary heating were sequentially performed in a nitrogen atmosphere at a heating rate of 10 °C/min, and the endothermic peak value during secondary heating was defined as the melting point.

By adding a tackifier and an additive according to Table 2 to each of the prepared resins, the adhesive of Preparation Examples 1-18 was prepared.

(a): Incapable of calculation because the absorption sites between comonomers overlap. It is an estimate based on the addition amount and reaction conditions during polymerization.

[Example 2-18]

Each of the batteries of Examples 2-18 were prepared in the same manner as in Example 1, except that the adhesive according to Table 3 was used, and their physical properties were measured, and the results are shown in Table 3 below.

[Comparative Example 7]

A battery of Comparative Example 7 was prepared in the same manner as in Example 1, except that an adhesive according to Table 3 was used, and physical properties were measured, and the results are shown in Table 3 below.

As can be seen in Tables 2 and 3, the resin of Preparation Example 2-18 copolymerized with maleic anhydride has a low melting point, and the experimental results for the battery of Example 2-18 using the resin of Preparation Example 2-18 , showed excellent adhesion to metal and adhesion after high temperature exposure. In particular, as can be seen from the results of Examples 4 and 9, when the value of a/b was increased by increasing the degree of hydrolysis to maleic anhydride, the adhesion to the metal and the adhesion after standing at a high temperature were more excellent.

On the other hand, the resin of Preparation Example 1, which was not modified with maleic acid, had a high melting point, and as a result of the experiment on the battery of Comparative Example 1 using the resin of Preparation Example 1, the adhesive strength and the adhesive strength after standing at a high temperature were very poor.

In addition, the resin of Preparation Example 10-12, which further includes a metal adhesive comonomer, has further improved adhesion compared to the resin of Preparation Example 5-6 that does not further include a comonomer, and in particular, a phosphonic acid group The resin of Preparation Example 12 including the polymerizable compound exhibited more excellent adhesion.

[Examples 19-27]

Each of the batteries of Examples 19-27 were prepared in the same manner as in Example 1, except that the adhesive was applied according to the method shown in Table 4, and their physical properties were measured, and the results are shown in Table 4 below. The application area ratio was calculated as follows, respectively.

Height direction application area ratio = (adhesive application height) / (electrode assembly height)

Width direction application area ratio = (adhesive application width) / (width of electrode assembly)

Area ratio = (Area of adhesive) / (Area of electrode assembly)

As shown in Table 4, when the adhesive is applied at 30% or more and 10% or more of area ratio in the height direction and the width direction, respectively, it can be confirmed that more excellent resistance to the drop test is exhibited.

What has been described above is only one embodiment for implementing the secondary battery according to the present invention, and the present invention is not limited to the above embodiment, and as claimed in the claims below, it departs from the gist of the present invention. Without this, anyone with ordinary knowledge in the field to which the invention pertains will say that the technical spirit of the present invention exists to the extent that various modifications can be made.

110: electrode assembly
120: case

Claims (12)

an electrode assembly including a first electrode plate, a second electrode plate having a polarity different from that of the first electrode plate, and a separator between the first electrode plate and the second electrode plate; electrolyte; a case accommodating the electrode assembly and the electrolyte; and an adhesive layer located on the outer surface of the electrode assembly or the corresponding inner surface of the case,
The adhesive comprises an α,β-unsaturated dicarboxylic acid modified polyolefin,
A secondary battery in which the α,β-unsaturated dicarboxylic acid-modified polyolefin satisfies at least one of the following formulas (I) and (II):
(I): a/b ≥ 0.2
In the above formula,
a is the absorption intensity of the α,β-unsaturated dicarboxylic acid (the difference in transmittance between the maximum peak near 1,715 cm ^-1 and the baseline),
b is the absorption intensity of the α,β-unsaturated dicarboxylic acid anhydride (the difference in transmittance between the maximum peak near 1,780 cm ^-1 and the baseline),
The baseline is a line connecting the transmittance of 1,550 cm ^-1 and 1,950 cm ^-1 ,
(II): (a/1.8 + b)/c ≥ 0.05
In the above formula,
a and b are the same as defined in formula (I) above,
c is the absorption intensity of the polyolefin (the difference in transmittance between the maximum peak near 2,915 cm ^-1 and the baseline),
The baseline is the predecessor of the transmittances of 2,400 cm ^-1 and 3,750 cm ^-1 . The method of claim 1,
wherein the α,β-unsaturated dicarboxylic acid is maleic acid, and the polyolefin is polypropylene. The method of claim 1,
A secondary battery wherein the α,β-unsaturated dicarboxylic acid-modified polyolefin has a weight average molecular weight (Mw) of 10,000 or more and a melting point of 130° C. or less. The method of claim 1,
A secondary battery having a polyolefin content of 50 mol% or more in the α,β-unsaturated dicarboxylic acid-modified polyolefin. The method of claim 1,
A secondary battery having an electrolyte absorption amount of the adhesive of 30% by weight or less. The method of claim 1,
The adhesive is a secondary battery applied to at least one side of the front side or the back side of the electrode assembly. 7. The method of claim 6,
The application area of the adhesive is 25% or more of the height direction or the width direction of the electrode assembly. 7. The method of claim 6,
The application area of the adhesive is 6% or more of the area of the electrode assembly. 7. The method of claim 6,
The adhesive is a secondary battery applied to the outermost positive electrode substrate surface portion of the electrode assembly. The method of claim 1,
The adhesive is a secondary battery applied to at least one side of the upper or lower portion of the electrode assembly. The method of claim 1,
The adhesive is applied to at least one side of the width of both sides of the electrode assembly. The method of claim 1,
The adhesive may include a polygonal, circular or oval planar figure; straight, diagonal, curved or zigzag linear; Or a secondary battery applied in the form of at least one of a dot array (dot array).

Images