KR20170138670A - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery, which comprises: an electrode assembly including an anode, a separator, and a cathode; an electrolyte comprising a lithium salt and a solvent comprising a linear carbonate and a cyclic carbonate in a volume ratio of 60:40 to 75:25; a battery case in which the electrode assembly and the electrolyte are embedded; and a swelling tape including a swelling layer containing an adhesive layer and polyurethane between the electrode assembly and the battery case. An object of the present invention is to provide the lithium secondary battery in which swelling tape positioned between the electrode assembly and the battery case has an excellent expansion ratio in a specific electrolyte and secures safety even in strong external impact and vibration.

Description

LITHIUM SECONDARY BATTERY [0002]

The present invention relates to a lithium secondary battery.

As technology development and demand for mobile devices are increasing, the demand for batteries as energy sources is rapidly increasing, and accordingly, a lot of researches on batteries capable of meeting various demands have been conducted. Typically, in view of the shape of the battery, there is a high demand for a prismatic secondary battery and a pouch-type secondary battery that can be applied to products such as mobile phones with a small thickness. In terms of materials, lithium ion batteries having high energy density, discharge voltage, There is a high demand for a lithium secondary battery such as a lithium ion polymer battery.

Also, the secondary battery is classified according to how the electrode assembly having the anode / separator / cathode structure is formed. Typically, the long battery-shaped anodes and cathodes are jelly- A stacked (stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes cut in units of a predetermined size are sequentially stacked with a separator interposed therebetween; A stack / folding type electrode assembly having a structure in which bicell or full cells stacked in an interposed state are wound. Among these, the jelly-roll type electrode assembly has advantages of easy manufacture and high energy density per weight.

In particular, in the case of a circular battery, for example, an electrode assembly can be housed in a can and an electrolyte can be injected. Generally, since the electrode assembly has a smaller size than the can, a gap is formed between the electrode assembly and the inner wall of the can. In this case, the electrode assembly housed in the can can flow inside the can due to external vibration or impact, or rotate to a certain degree. In this case, for example, the welding portion of the tab is broken and the internal circuit is broken And the like may occur due to the phenomenon of power failure.

Therefore, a gap existing between the two objects which are spaced apart needs to be filled, and two objects which are spaced apart from each other in a state in which the gap is formed need to be fixed by filling the gap.

For example, when a battery is manufactured by housing an electrode assembly in a circular can, a gap is usually formed between the electrode assembly and the inner wall of the can because the electrode assembly has a smaller size than the circular can. In this case, the electrode assembly housed in the can flows through the can due to external vibration or impact. Such an electrode assembly flow causes an increase in the internal resistance of the battery and damage of the electrode tab, It is necessary to fill the gap and fix the electrode assembly.

KR 2015-0102226 A

An object of the present invention is to provide a lithium rechargeable battery in which swelling tape located between an electrode assembly and a battery case has an excellent expansion ratio in a specific electrolyte and secures safety even in strong external impact and vibration.

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery in which safety is ensured while reducing the influence on the weight and size of a lithium secondary battery.

In order to solve the above problems, the present invention provides an electrode assembly comprising an anode, a separator, and a cathode; An electrolyte comprising a lithium salt and a solvent comprising a linear carbonate and a cyclic carbonate in a volume ratio of 60:40 to 75:25; A battery case in which the electrode assembly and the electrolyte are embedded; And a swelling tape including a swelling layer containing an adhesive layer and polyurethane between the electrode assembly and the battery case.

The lithium secondary battery of the present invention has an excellent expansion ratio when the swelling tape positioned between the electrode assembly and the battery case contacts with a specific electrolyte and can effectively protect the inner electrode assembly, The safety of the lithium secondary battery as the final product is secured.

In addition, since the lithium secondary battery of the present invention places not only the swelling layer but also the swelling tape including the pressure-sensitive adhesive layer that expands when it comes into contact with the electrolyte, between the electrode assembly and the battery case, The expansion rate of the swelling tape after the contact with the electrolyte is remarkably excellent, so that the inner electrode assembly can be more effectively protected.

Further, since the shape of the swelling tape of the lithium secondary battery of the present invention may be a frame shape having one void or a net shape having a large number of voids, the area that can be protected by the same weight and thickness is widened. This has the advantage of ensuring safety while reducing the influence on the weight and size of the lithium secondary battery.

1 shows a lithium secondary battery according to an embodiment of the present invention.
2 shows a swelling tape included in a lithium secondary battery according to an embodiment of the present invention.
FIGS. 3 to 5 show positions where the swelling tape is attached to the lithium secondary battery according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed in an ordinary or dictionary sense and the inventor can properly define the concept of the term to describe its invention in the best possible way It should be construed as meaning and concept consistent with the technical idea of the present invention.

1 is a view illustrating a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, a lithium secondary battery includes an electrode assembly 100, a battery case 200, an electrolyte (not shown), and a swelling tape 300 according to an embodiment of the present invention.

The electrode assembly 100 includes an anode, a cathode, and a separator.

The positive electrode may include a positive electrode collector and a positive electrode active material. Specific examples of the cathode current collector include aluminum, nickel, and alloys thereof. The cathode active material is a compound capable of reversibly intercalating and deintercalating lithium, and examples thereof include spheres, polyhedrons, fibers, platelets, and scales. Specific examples of the positive electrode active material include lithium cobalt oxide such as Li _x CoO ₂ (0.5 <x <1.3); Lithium nickel oxides such as Li _x NiO ₂ (0.5 < x &lt;1.3); Lithium manganese oxides such as Li _{1 + x} Mn _{2 - x} O ₄ (0 _{? X?} 0.33), LiMnO ₃ , LiMn ₂ O ₃ , or Li _x MnO ₂ (0.5 <x <1.3); Lithium copper oxide such as Li ₂ CuO ₂ ; Lithium iron oxides such as LiFe ₃ O ₄ ; Lithium nickel cobalt manganese oxide such as Li [Ni _x Co _y Mn _z ] O ₂ (x + y + z = 1, 0 <x <1, 0 <y <1, 0 <z <1); Lithium nickel cobalt aluminum oxide such as Li [Ni _x Co _y Al _z ] O ₂ (x + y + z = 1, 0 <x <1, 0 <y <1, 0 <z <1); Lithium vanadium compounds such as LiV ₃ O ₈ ; Nickel-type lithium nickel oxides such as LiNi _{1 - x} M _x O ₂ (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga and 0.01? _X? 0.3); Li ₂ Mn ₃ MO ₈ (M = Fe, Co, Ni, Cu, or Zn), or the like, LiMn _2-x M _x O ₂ (M = Co, Ni, Fe, Cr, Lithium manganese composite oxide; LiMn ₂ O _{4 in} which a part of lithium is substituted with an alkaline earth metal ion; Disulfide compounds; Vanadium oxides such as V ₂ O ₅ or Cu ₂ V ₂ O ₇ ; Or Fe ₂ (MoO ₄ ) ₃ .

The negative electrode may include a negative electrode collector and a negative electrode active material. Specific examples of the negative electrode current collector include copper, gold, nickel, and alloys thereof. Specific examples of the negative electrode active material include low crystalline carbon such as hard carbon or soft carbon; Natural graphite, kish graphite, pyrolytic carbon, mesophase pitches, mesophase pitch based carbon fiber, meso-carbon microbeads, petroleum-derived Highly crystalline carbons such as petroleum derived cokes or coal tar pitch derived cokes; Li _x Fe ₂ O ₃ (0 _{≤ x ≤} 1), Li _x WO ₂ (0 _{≤ x ≤} 1), Sn _x Me _{1 - x} Me _y O _z (Me = Mn, Fe, Pb or Ge; Me ' = Al, B, P, Si, Group 1, Group 2, Group 3 elements or halogens of the periodic table, and 0 <x <1> 1 <y>3; Lithium metal; Lithium alloy; Silicon alloy; Silicon oxides; Tin alloy; Metal oxides such as SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , GeO, GeO ₂ , Bi ₂ O ₃ , or Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Or lithium titanium oxide, and one or more of these compounds may be included.

The separation membrane prevents a short circuit between the positive electrode and the negative electrode, and provides a movement path of lithium ions. The separator may be an insulating thin film having high ion permeability and mechanical strength. Specific examples of the separation membrane include polyolefin-based polymer membranes such as polypropylene and polyethylene, or their multiple membranes, microporous films, woven fabrics, and nonwoven fabrics.

The shape of the electrode assembly 100 is not particularly limited, but may be a jelly-roll type electrode assembly having a structure in which a long sheet-like anode and a cathode are wound with a separator interposed therebetween, A stacked (stacked) electrode assembly in which a plurality of positive electrodes and negative electrodes are sequentially stacked with a separator interposed therebetween; a bicell or full cell stacked with a separator interposed between a predetermined unit of positive and negative electrodes; And a stack / folding type electrode assembly having a structure in which the electrodes are wound. Specifically, it may be a jelly-roll type electrode assembly which is easy to manufacture and has a high energy density per weight.

The electrolyte (not shown) comprises a lithium salt, a solvent comprising linear carbonate and cyclic carbonate.

Examples of the lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 _{^{-, (CF 3) 3 PF}} 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, _{(CF 3 SO 2) 2 N} -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , SCN ^- or (CF ₃ CF ₂ SO ₂ ) ₂ N ^- . These may be contained in the electrolyte either singly or in combination.

The volume ratio of the linear carbonate to the cyclic carbonate of the solvent may be 60:40 to 75:25, and specifically 65:35 to 70:30. When the above-mentioned volume ratio is satisfied, the expansion rate of the swelling layer 320 is improved when the polyurethane contained in the swelling layer 320 of the swelling tape 300 contacts the electrolyte. When the adhesive layer 310 of the swelling tape 300 includes a pressure sensitive adhesive that expands when the pressure sensitive adhesive layer 310 contacts the electrolyte, when the pressure sensitive adhesive layer 310 contacts the electrolyte containing the solvent having the above- The swelling rate of the adhesive layer 320 is similar to that of the swelling layer 320 to prevent separation of the adhesive layer and the swelling layer 320, and an excellent expansion ratio can be realized. Due to the excellent expansion ratio, safety of the lithium secondary battery as a final product is ensured even in the case of external impact and vibration, so that the resistance characteristic is less changed and the risk of ignition is reduced. If only the cyclic carbonate is included in the solvent of the electrolyte, not only the polyurethane contained in the swelling layer of the swelling tape but also the adhesive layer is not sufficiently expanded, and the electrode assembly can not be effectively protected.

The linear carbonate may be one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, methyl isopropyl carbonate, ethyl methyl carbonate and ethyl propyl carbonate. Specifically, it may be dimethyl carbonate.

The cyclic carbonate may be one or more selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and vinylethylene carbonate. Specifically, it may be ethylene carbonate, propylene carbonate or a combination thereof.

The battery case 200 includes the electrode assembly 100 and an electrolyte (not shown). The battery case 200 is not particularly limited and may be circular, square, pouch or coin type, and may be circular in shape, in particular, capable of embedding a jelly-roll type electrode assembly .

The swelling tape 300 is disposed between the electrode assembly 100 and the battery case 200 and includes an adhesive layer 310 and a swelling layer 320 including polyurethane. When the polyurethane which is the swelling layer 320 of the swelling tape 300 contacts with the electrolyte containing the linear carbonate and the cyclic carbonate in the volume ratio of 60:40 to 75:25 as described above, . This effectively protects the electrode assembly 100 and secures the safety of the lithium secondary battery as a final product. Accordingly, even when an external impact or vibration is applied to the lithium secondary battery, which is the final product, the resistance characteristic is less changed and the risk of ignition is reduced.

Depending on the type of the adhesive contained in the adhesive layer 310, not only the swelling layer 320 but also the adhesive layer 310 may be expanded when the adhesive layer 310 contacts the electrolyte. As a result, the swelling tape 300 can exhibit a significantly higher expansion ratio than the conventional swelling tape, and can protect the electrode assembly 100 more effectively.

The adhesive layer 310 may include one or more selected from the group consisting of an acrylic pressure sensitive adhesive, a urethane pressure sensitive adhesive, an epoxy pressure sensitive adhesive, a silicone pressure sensitive adhesive, and a rubber pressure sensitive adhesive.

More specifically, the adhesive layer 310 may be adhered to the electrode assembly 100 or the battery case 200 before being contacted with the electrolyte, and may include an acrylic adhesive agent capable of expanding together with the swelling layer when contacted with the electrolyte, . &Lt; / RTI &gt; The acrylic pressure sensitive adhesive is expanded together with the swelling layer 320 to prevent the swelling layer 320 from separating from the pressure sensitive adhesive layer 310 and effectively protect the electrode assembly 100. Further, in order not to affect the volume change of the electrode assembly 100 that may occur in the charging / discharging process, the acrylic pressure-sensitive adhesive lowers the adhesive force when the electrolyte is in contact with the electrolyte, Or may be easily detached from the substrate 100.

Examples of the acrylic pressure-sensitive adhesive include polymers having a polymerization unit derived from a (meth) acrylic acid ester monomer, a monomer represented by the following formula (1), and a crosslinkable monomer containing a crosslinkable functional group.

&Lt; Formula 1 >

In Formula 1,

R ₁ is hydrogen or a C1 to C12 alkyl group,

R ₂ is an alkylene group having from ₁ to 6 carbon atoms,

R ₃ is hydrogen, a C1 to C12 alkyl group, a C6 to C24 aryl group, or a C6 to C48 arylalkyl group,

n is 0 or more.

The (meth) acrylic acid ester monomer may be an alkyl (meth) acrylate. Specifically, the (meth) acrylic acid ester monomer may be an alkyl (meth) acrylate of C1 to C14 in consideration of the cohesive force of the pressure sensitive adhesive, the glass transition temperature or tackiness. Specific examples of the C1 to C14 alkyl (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) (Meth) acrylate, 2-ethylhexyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate or tetradecyl (meth) acrylate.

On the other hand, "(meth) acrylate" means acrylate or methacrylate, and the term "(meth)" is also used.

The monomer represented by the formula (1) is a monomer having excellent affinity with an electrolyte. The reason is that the oxygen atom contained in the monomer represented by the formula (1) has a high electronegativity, so that the monomer represented by the formula (1) has a high polarity. Accordingly, the pressure-sensitive adhesive layer containing the monomer represented by the formula (1) has high affinity with polar electrolytes and can expand when contacted with the electrolyte.

The monomer represented by the formula (1) may be a monomer represented by the following formula (2).

(2)

In the formula (2)

The definitions of R ₁ and R ₃ are as defined in the above formula (1)

p + q is 1 or more,

p is from 0 to 100, and q is from 0 to 100.

Specific examples of the monomer represented by Formula 1 or Formula 2 include methoxyethyl (meth) acrylate, methoxyethoxyethyl (meth) acrylate, ethoxyethoxyethyl (meth) acrylate, ethoxy triethylene glycol (Meth) acrylate, polyethylene glycol (meth) acrylate, polyethylene glycol methyl ether (meth) acrylate, ethoxylated nonylphenol (meth) acrylate, propoxylated nonylphenol (Meth) acrylate, methoxyethoxyethyl (meth) acrylate, isopropoxyethyl (meth) acrylate and polypropylene glycol (Meth) acrylate, ethoxytriethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate, or polyethylene glycol And recoiled methyl ether (meth) acrylate.

The crosslinkable monomer containing the crosslinkable functional group can be copolymerized with the other monomer contained in the (meth) acrylic acid ester monomer or the polymer and, after copolymerization, provides a crosslinking point capable of reacting with the multifunctional crosslinking agent in the main chain of the polymer It is a monomer that can be made.

The crosslinkable functional group may be a hydroxyl group, a carboxyl group, an isocyanate group, a glycidyl group or an amide group, and in some cases, it may be a photo-crosslinkable functional group such as an acryloyl group or a methacryloyl group. In the case of a photocrosslinkable functional group, a compound having a photocrosslinkable functional group may be reacted with the crosslinkable functional group provided by the copolymerizable monomer.

Specific examples of the crosslinkable monomer containing a hydroxy group include hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxyhexyl (meth) Octyl (meth) acrylate, hydroxyethyleneglycol (meth) acrylate, glycerol (meth) acrylate or hydroxypropyleneglycol (meth) acrylate.

Specific examples of the carboxyl group-containing monomer include (meth) acrylic acid, carboxyethyl (meth) acrylate, carboxypentyl (meth) acrylate, itaconic acid, maleic acid, fumaric acid and crotonic acid.

Specific examples of the isocyanate group-containing crosslinkable monomer include 2-isocyanatoethyl (meth) acrylate, 1,1-bis (acryloyloxymethyl) ethyl isocyanate, (meth) acryloyloxyethyl isocyanate, Meta-isopropenyl-?,? - dimethylbenzyl isocyanate, methacryloyl isocyanate or allyl isocyanate; An acryloyl monoisocyanate compound obtained by reacting a diisocyanate compound or a polyisocyanate compound with 2-hydroxyethyl (meth) acrylate; A diisocyanate compound or a polyisocyanate compound, a polyol compound and an acryloyl monoisocyanate compound obtained by reacting 2-hydroxyethyl (meth) acrylate.

Specific examples of the glycidyl group-containing crosslinkable monomer include epoxycycloalkylalkyl (meth) acrylates such as glycidyl (meth) acrylate, epoxyalkyl (meth) acrylate or epoxycyclohexylmethyl (meth) And the like.

Specific examples of the amide group-containing monomer include (meth) acrylamide, diethylacrylamide, N-vinylpyrrolidone, N, N-dimethyl (meth) acrylamide, N, (Meth) acrylate, aminoethyl (meth) acrylate, N, N'-methylene bisacrylamide, N, N-dimethylaminopropylacrylamide, N, N-dimethylaminopropylmethacrylamide, -Dimethylaminoethyl (meth) acrylate or N, N-dimethylaminopropyl (meth) acrylate.

The polymer may be polymerized with 30 to 300 parts by weight of the monomer represented by the formula (1) and 0.1 to 10 parts by weight of the crosslinkable monomer, based on 100 parts by weight of the (meth) acrylic acid ester monomer. When the above-described range is satisfied, the adhesive layer 310 containing the polymer can be expanded enough to desorb from the electrode assembly 100 when the electrode assembly 100 contacts the electrolyte. And sufficient adhesive strength to the electrode assembly 100 or the battery case 200 can be achieved before the adhesive layer 310 containing the polymer contacts the electrolyte.

The polymer may be in the form of polymerizing other functional comonomers as necessary. Specific examples of the other functional comonomer include (meth) acrylamide, N-butoxymethyl (meth) acrylamide, N-methyl (meth) acrylamide, (meth) acrylonitrile, N-vinylpyrrolidone or N Nitrogen-containing monomers such as vinylcaprolactam, styrene-based monomers such as styrene or methylstyrene; Glycidyl (meth) acrylate; Caprolactone, and vinyl esters of carboxylic acids such as vinyl acetate.

The polymer may be included in the adhesive layer 310 in a crosslinked form by a polyfunctional crosslinking agent. Specific examples of the polyfunctional crosslinking agent include an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, a metal chelate crosslinking agent, and a photo crosslinking agent, and a suitable crosslinking agent may be selected depending on the kind of the crosslinkable functional group present in the polymer.

The polymer may be prepared by applying a mixture of the monomers to a polymerization process such as solution polymerization, photopolymerization, bulk polymerization, suspension polymerization or emulsion polymerization.

The polymer may have a weight average molecular weight of 300,000 g / mol to 2,500,000 g / mol.

The polyurethane contained in the swelling layer 320 may have a weight average molecular weight of 90,000 g / mol to 110,000 g / mol. When the above-mentioned range is satisfied, the electrolyte membrane can be expanded with excellent expansion rate in a short time upon contact with the electrolyte. In addition, the pressure-sensitive adhesive layer 310 may have an expansion ratio similar to that of the pressure-sensitive adhesive layer 310 including the pressure-sensitive adhesive layer 310, specifically, the acrylic pressure-sensitive adhesive that can expand when the pressure-sensitive adhesive layer 310 contacts the electrolyte, Separation of the swelling layer 320 and the adhesive layer 310 can be prevented when the pressure-sensitive adhesive layer 310 is expanded.

The swelling layer 320 may be expanded to 130 to 150% in area and thickness after contact with the electrolyte. The adhesive layer 310 may expand at the same rate as the swelling layer 320 after the adhesive layer 310 contacts the electrolyte, if the adhesive layer 310 includes a pressure-sensitive adhesive which expands when the pressure-sensitive adhesive layer 310 contacts the electrolyte.

The thickness ratio of the adhesive layer 310 and the swelling layer 320 may be 1: 1.6 to 1: 2.5 before the swelling tape 300 contacts the electrolyte. The thickness ratio of the adhesive layer 310 and the swelling layer 320 after contact with the electrolyte may be 1: 2.08 to 1: 3.75, if the adhesive layer 310 does not expand even after contact with the electrolyte. If the adhesive layer 310 is expanded after contact with the electrolyte, the thickness ratio of the adhesive layer 310 and the swelling layer 320 may be the same before and after the contact with the electrolyte.

The width and thickness of the swelling layer 320 and the pressure-sensitive adhesive layer 310 need to be expanded in the above-mentioned range to effectively protect the electrode assembly, thereby securing the safety of the lithium secondary battery as a final product. In addition, separation between the swelling layer 320 and the adhesive layer 310 can be prevented during the swelling of the swelling tape 300.

The swelling tape 300 may be in the form of a plate having no void, a frame having one cavity, and a net having a plurality of voids.

The swelling tape 300 having a frame shape may have a porosity of 20% by volume to 30% by volume as compared with a swelling tape having the same size, that is, the same width, length and thickness, The swelling tape 300 can protect the electrode assembly from external shock or vibration at the same level as the swelling tape having no gap due to the shape of the frame and the porosity and can reduce the influence of the weight and size of the lithium secondary battery . When the swelling tape 300 is expanded after contact with the electrolyte, the swelling tape 300 is overlapped to prevent the phenomenon that the thickness of only a part of the swelling tape 300 becomes thick. Further, since the swelling tape 300 is expanded after contact with the electrolyte, the volume of pores in the swelling tape 300 may be reduced or the pores themselves may disappear.

Fig. 2 shows a swelling tape 300 in the form of a net having a plurality of voids.

The net-like swelling tape 300 may have porosity of 30% to 50% by volume as compared with a swelling tape having the same size, that is, the same width, length, thickness, and no gap. The swelling tape 300 may have a larger area than conventional swelling tapes having the same weight and thickness because of the net shape and porosity. As a result, the electrode assembly can be protected from external shock or vibration at the same level as the swelling tape having no gap, and the influence on the weight and size of the lithium secondary battery, which is the final product, can be reduced. When the swelling tape 300 is expanded after contact with the electrolyte, the swelling tape 300 is overlapped to prevent the phenomenon that the thickness of only a part of the swelling tape 300 becomes thick. Further, since the swelling tape 300 is expanded after contact with the electrolyte, the volume of pores in the swelling tape 300 may be reduced or the pores themselves may disappear.

The swelling tape 300 may be positioned on the entire outer circumferential surface of the electrode assembly 100, as shown in FIG.

The swelling tape 300 may be located on a part of the outer circumferential surface of the electrode assembly 100, as shown in FIG. When the swelling tape 300 is located on a part of the outer circumferential surface of the electrode assembly 100, the swelling tape 300 may be wound around the electrode The left and right ends of the swelling tape 300 may be positioned apart from the upper and lower ends of the assembly 100. More specifically, the swelling tape 300 is positioned at a distance of 15% to 25% of the length of the swelling tape 300 from the upper and lower ends of the electrode assembly 100, 300 may be positioned so as to be separated by 15% to 25% of the width of the swelling tape 300. When a plurality of the swelling tapes 300 are located on a part of the outer circumferential surface of the electrode assembly 100, considering the swelling rate of the swelling tape 300 when the electrolyte contacts the electrolyte, The plurality of swelling tapes 300 may be positioned apart from the upper and lower ends of the electrode assembly 100. Specifically, the swelling tape 300 may be positioned at a distance of 15% to 25% of the length of the swelling tape 300 from the upper and lower ends of the electrode assembly 100. When a plurality of the swelling tapes 300 are arranged in a row, the interval between the swelling tapes 300 may be set to be 15% to 25% of the width of the swelling tape 300 . The spacing between the swelling tapes 300 may be such that the length of the swelling tape 300 is 15% to 25% of the length of the swelling tape 300 .

The swelling tape 300 may be positioned on the entire outer circumferential surface of the battery case 200 as shown in FIG.

5, the swelling tape 300 may be located on a part of the inner circumferential surface of the battery case 200. [ When the swelling tape 300 is positioned on a part of the inner circumferential surface of the battery case 200, the swelling tape 300 may be wound around the battery cell 200 in consideration of the expansion rate when the swelling tape 300 contacts the electrolyte. The swelling tape 300 may be positioned apart from the upper and lower ends of the case 200 so that the left and right ends thereof are spaced apart from each other. More specifically, the swelling tape 300 is positioned at a distance of 15% to 25% of the length of the swelling tape 300 from the upper and lower ends of the battery case 200, 300 may be positioned so as to be separated by 15% to 25% of the width of the swelling tape 300. When a plurality of the swelling tapes 300 are located on a part of the inner circumferential surface of the battery case 200, considering the swelling rate of the swelling tape 300 when the electrolyte contacts the electrolyte, The plurality of swelling tapes 300 may be positioned apart from the upper and lower ends of the battery case 200. Specifically, the swelling tape 300 may be positioned at a distance of 15% to 25% of the length of the swelling tape 300 from the upper and lower ends of the electrode assembly 100. When a plurality of the swelling tapes 300 are arranged in a row, the interval between the swelling tapes 300 may be set to be 15% to 25% of the width of the swelling tape 300 . The spacing between the swelling tapes 300 may be such that the length of the swelling tape 300 is 15% to 25% of the length of the swelling tape 300 .

The plurality of swelling tapes 300 may be positioned so as not to overlap with each other when the swelling tape 300 is inflated until the position and the interval described above are satisfied.

The lithium secondary battery according to another embodiment of the present invention can be used not only in a battery cell used as a power source for a small device but also as a unit cell in a middle or large battery module including a plurality of battery cells. Specific examples of the medium and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, or electric power storage systems.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the appended claims. Such variations and modifications are intended to be within the scope of the appended claims.

Example  1 to Example  5 and Comparative Example  One: The lithium secondary battery  Produce

&Lt; Preparation of composition 1 for forming pressure-sensitive adhesive layer &

Preparation of polymer

98 parts by weight of n-butyl acrylate (n-BA) and 100 parts by weight of hydroxybutylacrylate (HBA) were added to a 1000 cc reactor equipped with a cooling device for nitrogen gas refluxing and easy temperature control. And 0.02 part by weight of n-dodecanethiol as a chain transfer agent were put in a flask, and 150 parts by weight of ethyl acetate (Ethyl Acetate, EAc) was added as a solvent. Then, nitrogen gas was purged at 60 占 폚 for 60 minutes to remove oxygen, and then maintained at 60 占 폚. After the mixture was homogenized, 0.04 parts by weight of azobisisobutyronitrile (AIBN) was added as a reaction initiator. The mixture was reacted for 8 hours to prepare a polymer (A1) having a weight average molecular weight of 800,000 g / mol. In the above, parts by weight means wt%.

Adhesive layer  Preparation of composition 1 for forming

0.3 parts by weight of a toluene diisocyanate adduct of trimethylolpropane as a multifunctional isocyanate-based crosslinking agent to 100 parts by weight of the polymer was added to an ethyl acetate solution, and the mixture was uniformly mixed at a proper concentration in consideration of coating properties.

&Lt; Preparation of composition 2 for pressure-sensitive adhesive layer &

Preparation of polymer

58 parts by weight of n-butyl acrylate (n-BA), 50 parts by weight of Methoxy Ethyl Acrylate (MEA) were added to a 1000 cc reactor equipped with a cooling device for regulating the temperature of the nitrogen gas, And 2 parts by weight of hydroxybutylacrylate (HBA) and 0.02 part by weight of n-dodecanethiol as a chain transfer agent were charged in a reaction vessel, and ethyl acetate (Ethyl Acetate, EAc) were added. Then, nitrogen gas was purged at 60 占 폚 for 60 minutes to remove oxygen, and then maintained at 60 占 폚. After the mixture was homogenized, 0.04 parts by weight of azobisisobutyronitrile (AIBN) was added as a reaction initiator. The mixture was reacted for 8 hours to prepare a polymer (A1) having a weight average molecular weight of 800,000 g / mol. In the above, parts by weight means wt%.

Adhesive layer  Preparation of composition 2 for forming

0.3 parts by weight of a toluene diisocyanate adduct of trimethylolpropane as a multifunctional isocyanate-based crosslinking agent to 100 parts by weight of the polymer was added to an ethyl acetate solution, and the mixture was uniformly mixed at a proper concentration in consideration of coating properties.

&Lt; Preparation of swelling tape &

On one side of the swelling layer, a composition for forming an adhesive layer as shown in Table 1 below was coated and dried to form a uniform adhesive layer having a thickness of 12 占 퐉 to prepare a plate-like swelling tape having no voids. Here, the composition for forming an adhesive layer 1 was a material that did not swell even when brought into contact with an electrolyte, and the composition for forming an adhesive layer 2 was a material that swelled upon contact with an electrolyte.

Adhesive layer Swelling layer division Configuration thickness Configuration Weight average molecular weight thickness Swelling tape 1 Composition 1 for forming an adhesive layer 12 탆 Polyurethane 100,000 g / mol 20 탆 Swelling Tape 2 12 탆 30 탆 Swelling Tape 3 12 탆 40 탆 Swelling Tape 4 Composition 2 for Adhesive Layer 12 탆 20 탆

&Lt; Preparation of positive electrode &

200 g of a mixture of 92 wt% LiCoO ₂ as a positive electrode active material, 4 wt% of carbon black as a conductive material, and 4 wt% of polyvinylidene fluoride (PVdF) as a binder polymer was prepared, (NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was coated on an aluminum (Al) thin film of a positive electrode current collector having a thickness of 20 m, followed by drying and rolling to produce a positive electrode.

&Lt; Preparation of negative electrode &

200 g of artificial graphite was added with 220 ml of N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m, followed by drying and rolling to produce a negative electrode.

&Lt; Production of lithium secondary battery >

A polyethylene separator was sandwiched between the positive electrode and the negative electrode, and then wound to produce a jelly-roll type electrode assembly. A swelling tape described in Table 2 below was attached to the entire outer peripheral surface of the electrode assembly, and the electrode assembly was inserted into a battery case of a circular can. The electrolyte described in Table 2 was poured into the battery case and sealed to complete a lithium secondary battery.

division Swelling tape Electrolyte (1.4M) Lithium salt Solvent (volume ratio) Example 1 Swelling tape 1 LiPF ₆ Dimethyl carbonate (DMC): Ethylene carbonate (EC): Propylene carbonate (PC) = 65: 30: 5 Example 2 Swelling Tape 2 LiPF ₆ Dimethyl carbonate (DMC): Ethylene carbonate (EC): Propylene carbonate (PC) = 65: 30: 5 Example 3 Swelling Tape 3 LiPF ₆ Dimethyl carbonate (DMC): Ethylene carbonate (EC): Propylene carbonate (PC) = 65: 30: 5 Example 4 Swelling Tape 3 LiPF ₆ Dimethyl carbonate (DMC): Ethylene carbonate (EC) = 70: 30 Example 5 Swelling Tape 4 LiPF ₆ Dimethyl carbonate (DMC): Ethylene carbonate (EC) = 70: 30 Comparative Example 1 none LiPF ₆ Dimethyl carbonate (DMC): Ethylene carbonate (EC): Propylene carbonate (PC) = 65: 30: 5

Test Example  1: Drum safety evaluation

The lithium secondary batteries of Example 1 and Comparative Example 1 were placed in a drum and vibration (66 rpm) was applied for 100 minutes to evaluate the drum safety. These evaluations were repeated up to seven times, and the voltage and resistance values after one, two, and seven evaluations are shown in Table 3.

division Before evaluation 1 time Episode 2 7 times Voltage resistance Voltage resistance Voltage resistance Voltage resistance Example 1 3.671 24.0 3.672 24.4 3.669 24.0 3.669 24.1 Comparative Example 1 3.670 23.2 1.684 Not measurable Abort evaluation

Referring to Table 3, it can be seen that even when the lithium secondary battery of Example 1 was subjected to the drum evaluation seven times, the change in voltage and resistance was small and the safety was secured by the swelling layer. On the other hand, when the lithium secondary battery of Comparative Example 1 was subjected to the drum evaluation once, the voltage was about 64% lower than that before the experiment, and the resistance was too high to measure. As a result of this one-time evaluation, it was judged that Comparative Example 1 lost its function as a battery, and the evaluation was not further advanced.

Test Example  2: Vibration safety evaluation

The vibration stability evaluation was performed by moving the lithium ^secondary battery of Example 1 and Comparative Example 1 10 times in the x-axis and 10 times in the y-axis at a frequency of 10 Hz to 200 Hz, an amplitude of 3.0 mm and a velocity of 300 m / s ² , Sir. These evaluations were repeated up to 30 times, and the voltage and resistance values after the 10th and 30th evaluations are shown in Table 4.

Before experiment 10 times 30 times Voltage resistance Voltage resistance Voltage resistance Example 1 3.112 33.7 3.119 44.332 3.119 44.358 Comparative Example 1 3.097 32.7 3.112 44.419 Unmeasured Not measurable

Referring to Table 4, the lithium secondary battery of Example 1 and Comparative Example 1 exhibited similar voltage and resistance values after 10 cycles of vibration evaluation, but it was significantly different after 30 cycles of vibration evaluation. The results of the vibration evaluation of the lithium secondary battery of Example 4 were not significantly different from those of the vibration evaluation of 10 times. However, it was found that the lithium secondary battery of Comparative Example 1 lost its function as a battery because the resistance was too high after 30 cycles of vibration evaluation and measurement was impossible. The voltage of the lithium secondary battery of Comparative Example 1 was judged to have lost its function as a battery and was not measured.

Test Example  3: Evaluation of impact stability

A steel bar having a diameter of 15.8 mm, a length of 30 cm and a weight of 9.1 kg was placed on the lithium secondary battery of Example 1 and Comparative Example 1 which were SOC 50. Then, 9.1 kg of the shank was dropped 5 times from 61 cm above the bar, and whether or not it was ignited is shown in Table 3.

A steel bar having a diameter of 15.8 mm, a length of 30 cm and a weight of 9.1 kg was placed on the lithium secondary battery of Example 1 and Comparative Example 1 which were SOC100. Then, 9.1 kg of a bundle of steel was dropped 10 times from 61 cm above the bar, and the ignitability is shown in Table 5.

Whether SOC50 is ignited Whether SOC100 is ignited Example 1 0/5 1/10 Comparative Example 1 1/5 4/10

Referring to Table 5, when the lithium secondary battery of Example 1 of SOC 50 was repeated five times, no ignition occurred at all, and when the lithium secondary battery of Example 1 with SOC 100 was repeatedly dropped 10 times, woke up. However, when the lithium secondary battery of Comparative Example 1 which is SOC 50 was repeatedly dropped five times, ignition occurred once, and when the lithium secondary battery of Comparative Example 1 which was SOC100 was repeatedly dropped 10 times, ignition occurred four times. As a result, it can be seen that the lithium secondary battery of Example 1 is excellent in safety due to impact.

Test Example  4: Evaluation of expansion rate

Table 6 shows the swelling rate of the swelling tape inserted into the lithium secondary battery after 1 hour from the production of the lithium secondary battery of Example 4 and opened.

division The swelling rate of the swelling layer The rate of expansion of the adhesive layer Example 4 130% 100%

Referring to Table 6, it was predicted that the expansion coefficient of the swelling tape inserted in the lithium secondary battery of Example 4 was 130%, so that it had an excellent expansion rate, thereby effectively protecting the lithium secondary battery.

100: electrode assembly 200: battery case
300: swelling tape 310: adhesive layer
320: swelling layer

Claims (17)

An electrode assembly including an anode, a separator, and a cathode;
An electrolyte comprising a lithium salt and a solvent comprising a linear carbonate and a cyclic carbonate in a volume ratio of 60:40 to 75:25;
A battery case in which the electrode assembly and the electrolyte are embedded; And
And a swelling tape including a swelling layer containing an adhesive layer and polyurethane between the electrode assembly and the battery case.
The method according to claim 1,
Wherein the solvent comprises the linear carbonate and the cyclic carbonate in a volume ratio of 65:35 to 70:30.
The method according to claim 1,
Wherein the linear carbonate is one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, methyl isopropyl carbonate, ethyl methyl carbonate and ethyl propyl carbonate. .
The method according to claim 1,
Wherein the cyclic carbonate is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, and vinylethylene carbonate.
The method according to claim 1,
Wherein the adhesive layer of the swelling tape comprises a polymer having a polymerization unit derived from a (meth) acrylic acid ester monomer, a monomer represented by the following formula (1), and a crosslinkable monomer containing a crosslinkable functional group battery:
&Lt; Formula 1 >

In Formula 1,
R ₁ is hydrogen or a C1 to C12 alkyl group,
R ₂ is an alkylene group having from ₁ to 6 carbon atoms,
R ₃ is hydrogen, a C1 to C12 alkyl group, a C6 to C24 aryl group, or a C6 to C48 arylalkyl group,
n is 0 or more.
The method of claim 5,
Wherein the monomer represented by the formula (1) is a monomer represented by the following formula (2).
(2)

In the formula (2)
The definitions of R ₁ and R ₃ are as defined in claim 5,
p + q is 1 or more,
p is from 0 to 100, and q is from 0 to 100.
The method of claim 5,
The polymer
Based on 100 parts by weight of the (meth) acrylic acid ester monomer,
30 parts by weight to 300 parts by weight of the monomer represented by Formula 1;
And 0.1 to 10 parts by weight of the crosslinkable monomer.
The method according to claim 1,
Wherein the weight average molecular weight of the polyurethane is 90,000 g / mol to 110,000 g / mol.
The method according to claim 1,
Wherein the swelling tape is at least one selected from the group consisting of a plate having no void, a frame having one void, and a net having a plurality of voids.
The method according to claim 1,
Wherein the first electrode and the second electrode are spaced apart from upper and lower ends of an outer circumferential surface of the electrode assembly.
The method of claim 10,
Wherein the electrode assembly is located at a distance of 15% to 25% of the length of the swelling tape from the upper and lower ends of the outer circumferential surface of the electrode assembly.
The method according to claim 1,
Wherein the swelling tape is spaced apart from upper and lower ends of an inner circumferential surface of the battery case.
The method according to claim 1,
Wherein the battery case is located at a distance of 15% to 25% of the length of the swelling tape from the upper and lower ends of the outer circumferential surface of the battery case.
The method according to claim 1,
Wherein a plurality of the swelling tapes are contained in the lithium secondary battery.
15. The method of claim 14,
Wherein the swelling tape is spaced apart by 15% to 25% of a width of the swelling tape.
The method according to claim 1,
Wherein the thickness ratio of the pressure-sensitive adhesive layer to the swelling layer before contact with the electrolyte is 1: 1.6 to 1: 2.5.
The method according to claim 1,
Wherein the thickness ratio of the pressure-sensitive adhesive layer to the swelling layer after the contact with the electrolyte is 1: 2.08 to 1: 3.75.

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